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A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels
Abstract
The molecules in our breath can provide a wealth of information about the health and well-being of a person. The level of carbon dioxide (CO2) is not only a sign of life but also when combined with the level of exhaled oxygen provides valuable health information in the form of our metabolic rate. We report upon the development of a MEMS-based non-dispersive infrared CO2 sensor for inclusion in a hand held portable breath analyser. Our novel sensor system comprises a thermopile detector and low power MEMS silicon on insulator (SOI) wideband infrared (IR) emitter. A lock-in amplifier design permits a CO2 concentration of 50ppm to be detected on gas bench rig. Different IR path lengths were studied with gases in dry and humid (25% and 50% RH) in order to design a sensor suitable for detecting CO2 in breath with concentrations in the range of 4-5%. A breath analyser was constructed from acetal and in part 3D printed with a side-stream sampling mechanism and tested on a range of subjects with two data-sets presented here. The performance of the novel MEMS based sensor was validated using a reference commercial breath-by-breath sensor and produced comparable results and gave a response time of 1.3s. Further work involves the detection of other compounds on breath for further metabolic analysis and reducing the overall resolution of our MEMS sensor system from ca. 250ppm to 10ppm.
... Gas sensors utilizing NDIR technology are highly regarded on the market for their exceptional selectivity, rapid response time, precise accuracy, extended service life, and robust stability when compared to alternative sensor types [11,12]. A typical NDIR gas sensor system based on infrared absorption comprises an infrared (IR) emitter, optical gas chamber, IR detector, and signal-processing circuit, as shown in Figure 1 [13][14][15]. IR emitters include lasers, lamps, and MEMS IR-emitters, etc. [16]. ...
... To verify the repeatability of the gas sensor, the gas sensor was tested six times, and the experimental data of the measured NO2 are shown in Table 6. The repeatability was calculated using Equation (14). ...
... To verify the repeatability of the gas sensor, the gas sensor was tested six times, and the experimental data of the measured NO 2 are shown in Table 6. The repeatability was calculated using Equation (14). The long-term stability of the gas sensor was demonstrated inside the chamber. ...
Increasing concerns about air quality due to fossil fuel combustion, especially nitrogen oxides (NOx) from marine and diesel engines, necessitate advanced monitoring systems due to the significant health and environmental impacts of nitrogen dioxide (NO2). In this study, a gas detection system based on the principle of the non-dispersive infrared (NDIR) technique is proposed. Firstly, the pyroelectric detector was developed by employing an ultra-thin LiTaO3 (LT) layer as the sensitive element, integrated with nanoscale carbon material prepared by wafer-level graphics technology as the infrared absorption layer. Then, the sensor was hermetically sealed using inert gas through energy storage welding technology, exhibiting a high detectivity (D*) value of 4.19 × 108 cm·√Hz/W. Subsequently, a NO2 gas sensor was engineered based on the NDIR principle employing a Micro Electro Mechanical System (MEMS) infrared (IR) emitter, featuring a light path chamber length of 1.5 m, along with integrated signal processing and software calibration algorithms. This gas sensor was capable of detecting NO2 concentrations within the range of 0–500 ppm. Initial tests indicated that the gas sensor exhibited a full-scale relative error of less than 0.46%, a limit of 2.8 ppm, a linearity of −1.09%, a repeatability of 0.47% at a concentration of 500 ppm, and a stability of 2% at a concentration of 500 ppm. The developed gas sensor demonstrated significant potential for application in areas such as industrial monitoring and analytical instrumentation.
... In this case, the optical path length, l, is defined as the straight path from the source to the detector filled with CO 2 molecules. The sensitivity of the CO 2 measurement depends on l, an increase which results in increased exposure to CO 2 , therefore yielding a more sensitive measurement [53]. On the other hand, higher absorption due to the longer path length and increased exposure to CO 2 molecules, limits the maximum PCO 2 , which can be measured. ...
... A broad range of applications in the automotive industry [83], air quality monitoring [84], breath analysis, and capnography devices [24], [53] entail NDIR-based sensing for monitoring CO 2 levels. Recently, several research groups have proposed NDIR-based sensing for transcutaneous CO 2 monitoring [25], [26], [49], [82], [85], mainly to overcome the drawbacks of traditional electrochemical-based sensing discussed in Section.IV-A, such as the necessity of frequent calibration with a gas bottle for accurate and drift-free measurements and slow response time of the sensor. ...
... Aside from the gas bottle within the calibration unit, which hinders the miniaturization of electrochemical-based monitors, the existence of the heating element demanding power outputs in the range of several hundred milliwatts to achieve a skin temperature of 44 • C necessitates the incorporation of large, high-capacity batteries [23], [93]. NDIR-based monitors can achieve greater sensitivity by increasing the optical path between the IR source and the sensor [53]. Therefore, the sensor component of these monitors, which measure several centimeters, are typically larger than that of electrochemicalbased monitors. ...
Wearable smart health applications aim to continuously monitor critical physiological parameters without disrupting patients' daily activities, such as giving a blood sample for lab analysis. For example, the partial pressure of arterial carbon dioxide, the critical indicator of ventilation efficacy reflecting the respiratory and acid-base status of the human body, is measured invasively from the arteries. Therefore, it can momentarily be monitored in a clinical setting when the arterial blood sample is taken. Although a noninvasive surrogate method for estimating the partial pressure of arterial carbon dioxide exists (i.e., transcutaneous carbon dioxide monitoring), it is primarily limited to intensive care units and comes in the form of a large bedside device. Nevertheless, recent advancements in the luminescence sensing field have enabled a promising technology that can be incorporated into a wearable device for the continuous and remote monitoring of ventilation efficacy. In this review, we examine existing and nascent techniques for sensing transcutaneous carbon dioxide and highlight novel wearable transcutaneous carbon dioxide monitors by comparing their performance with the traditional bedside counterparts. We also discuss future directions of transcutaneous carbon dioxide monitoring in next-generation smart health applications.
... Because of high sensitivity and the characteristics of small volume, optical sensor is widely adopted in the form of gas sensor. Typical applications include hand-held respiratory monitoring sensor [6] and Capone5, which is monitoring equipment of pressure of end-tidal carbon dioxide (PetCO2) applied in the hospital [7]. These systems operate on the principle of non-dispersive infrared (NDIR) absorption, guiding the detected gas to a compact gas chamber device for detection [8,9]. ...
... The working wavelength of the light source (EP2004-0-DM-DX1-FM) is 2.004 μm. The micro-nano optical fiber is placed in a Nasal cavity tube，which is set near the human nasal cavity to directly sense the exhaled carbon dioxide gas, the influence of external air disturbance on the results can be avoided at the same time.The change of the concentration of carbon dioxide in the exhaled gas is characterized by the change of the detector (Thorlabs S401C) and optical power meter (Thorlabs PM100USB) which the periodic change of CO2 concentration is transferred to the periodic 6 change of optical power. Therefore, micro-nano optical fibers can be adopted to monitor CO2 concentration and characterize the respiration cycle process. ...
... When the micro-nano fiber diameter is 1.0 μm, the optical power attenuation is more prominent, and its sensitivity is higher from the above comparative experiments. In addition, the data showed four periodic changes in the optical power within 30 seconds of the monitoring time according to the experimental results of diameters of 1, 3.5, and 6.3 μm in Figure 9. Therefore, It can be calculated that the respiratory is 10-11 times/minute, and the result is consistent with the average human respiratory rate [6,20]. ...
In the field of clinical medicine, the real-time monitoring of carbon dioxide gas exhaled by the human body is of great significance. At present, the detection devices in the market are mainly detected by sucking a small amount of gas in the nasal cavity to the detection device, and there are some problems such as too long sampling tubes, easy blockage or distortion, and abnormal gas dispersion. In this paper, a micro-nano optical fiber sensor that can directly detect the concentration of end-tidal carbon dioxide is proposed. The measurement is achieved by using the principle of high evanescent field absorption, and the operating band is 2.004 μm. The sensor uses micro-nano optical fiber as the sensing area, and then detects the presence of carbon dioxide gas exhaled by human body through optical power attenuation. The function of micro-nano fiber is to realize the transmission of signal light and also serve as the absorption medium of the gas to be measured. In addition, the variation of light power also reflects the respiratory cycle of the human body. The sensor can realize rapid real-time response to carbon dioxide gas detection, with small size, low cost, and easy to replace. It has great application potential in clinical scenarios such as Gastrointestinal Endoscopes that require real-time monitoring of human respiration.
... NDIR sensors detect the CO2 in a gaseous environment by its characteristic absorption and the vital components are an infrared (IR) source, a light tube, an interference filter (wavelength) and an infrared detector [24]. The exhaled CO2 could be measured non-invasively through the manipulation of Lambert-Beer's Law (LBL) [25,26]. The equation of LBL is calculated from Eq. (1). ...
... In 1860 John Tyndall inaugurally measured expired CO 2 by utilizing spectrum absorption with infrared technology [24][25][26][27][28][29][30]. This revolutionized the study of expiratory CO2. ...
Capnography is the graphical study of carbon dioxide during expiration. Capnography has evolved and is more than merely a biomedical device that is used in the emergency department and intensive care unit (ICU). There are volume based and time-based capnographs. Although end tidal CO2 (EtCO2) is the most used parameter in clinical medicine, there are an abundance of other parameters from the capnometer. The capnographic parameters could originate from specific plot points of the time-or volume-based curves, the area under the curve or other mathematical and computationally transformed data of the CO2. Although research of capnometry since its inception has focused on the respiratory aspects of the CO2 signal with EtCO2, newer parameters could be used to monitor, diagnose and prognose certain circulatory and metabolic disorders. In short, capnography is inevitably one of the important vital signs of modern medicine. As physiologically challenging conditions such as deep-sea diving and the now rampant space travel are becoming more common, there might be a need for familiarization with capnogram usage. In this narrative review, we go through the physiologic, mathematical, physics and clinical aspects of capnography.
... [2][3][4] Now-a-days pollution is increasing drastically due to various hazardous gases as output of industrialization, smoke from vehicles etc. 5 IR emitters are the ready-made choice for use in non-dispersive infrared (NDIR) gas concentration measurement instruments. [6][7][8] Spectroscopic techniques based on non-dispersive NDIR detection have high accuracy even at lower concentrations of gases. [8][9][10][11][12] Gas sensing can be carried out by different techniques 13 but sensors based on IR sensing offer high sensitivity and stability 13 and also, they have long lifetimes as well as smaller response time. ...
A thick film-based infrared (IR) source was fabricated using multilayer low-temperature co-fired ceramic (LTCC) technology. The proposed emitter was developed using screen printing of platinum material on LTCC substrates. The highly-uniform meander-shaped structure was fabricated with the size of 3.5 x 3.5 mm. Electrical, optical, and thermal characterization of the fabricated device were carried out. Device temperature reaches 600°C at 6.5 V. Optical characterization of the developed device shows that spectral range in the mid-IR region with power consumption of ~ 3 W. An in-house indigenised package was developed using glass metal seal technique for packaging of the developed IR source. Different windows viz., quartz, LiF, and CaF2 were used for packaging. The developed IR source demonstrated the potential to meet the performance, size, and cost requirements for various applications. The developed LTCC based IR source has planar and simple structure with high-temperature-stable lead-free interconnects.
... They often utilize non-dispersive infrared (NDIR) sensors for accurate CO2 measurements. Portable gas analyzers are convenient for spot measurements and can be used for quick assessments of soil CO2 efflux at specific locations (Vincent and Gardner, 2016 Complimentary Copy CO2 efflux. These systems usually consist of multiple chambers that are sequentially deployed over different soil areas. ...
Soil respiration (Rs) plays a crucial role in the global carbon cycle and is a major contributor to the amount of carbon dioxide (CO2) released into the atmosphere. It is the process by which microorganisms in the soil break down organic matter and release carbon dioxide (CO2) into the atmosphere and it is an important factor governing climate change. The amount of carbon released from Rs is estimated to be between 60 and 80 billion tons annually, which is roughly ten times the amount of carbon released by human activities such as burning fossil fuels (coal, natural gas, and oil), solid wastes and other biological materials etc. In addition to its impact on the global carbon cycle, Rs is also important for the health and productivity of ecosystems. It is a key component of nutrient cycling, as it releases nutrients from decomposing organic matter into the soil, making them available to plants. It also influences soil pH, soil moisture, and soil structure, all of which affect plant growth and ecosystem functioning. Warmer climate can increase microbial activity and accelerate the rate of decomposition, leading to higher rates of soil respiration and greater CO2 emissions. Changes in precipitation patterns can also impact soil moisture levels, which can affect Rs rates. These rates may vary significantly depending on the type of land use. Land use changes can alter the amount and quality of organic matter inputs to the soil, which can affect the microbial activity and, in turn, Rs rates. Rs rates are typically higher in forests than in agricultural lands. This is because forests typically have a greater quantity and diversity of organic matter inputs, such as leaf litter and woody debris, which can support a larger and more diverse microbial community. In contrast, agricultural lands often have reduced organic matter inputs due to frequent soil disturbance and crop harvest, which leads to lower Rs rates. Similarly, Rs rates may also vary between different agricultural landscapes. Earlier studies showed that Rs rates are typically higher in grasslands than in croplands. This is because grasslands typically have more extensive root systems, which may support a larger microbial community and greater soil respiration rates. Vegetation types can have a significant impact on Rs rates because different plant species have varying effects on soil organic matter and microbial communities. Overall, land use changes and vegetation types can have significant impacts on Rs rates and, in turn, the amount of carbon dioxide released into the atmosphere. Understanding these variations may help management practices those promote healthy soils and mitigate the impacts of climate change. Therefore, understanding the role of Rs in climate change and its sensitivity to environmental factors is important for developing effective strategies to mitigate the impacts of climate change and maintain healthy and productive ecosystems. Management practices that promote healthy soils, such as reducing soil disturbance and increasing soil organic matter, can help in reducing the amount of CO2 released through Rs and help in soil carbon sequestration and climate change mitigation.
... NDIR technology is based on the Beer-Lambert law, which is employed to determine the concentration of chemical substances with light absorption capacity. Carbon dioxide absorbs infrared light at a wavelength of approximately 4.26 µm, resulting in the attenuation of infrared radiation passing through a gas sample containing CO 2 [289]. In a previous study [288], the authors introduced a compact prototype with the potential for use as a wearable transcutaneous CO 2 device in healthcare applications. ...
This article explores the importance of wearable and remote technologies in healthcare. The focus highlights its potential in continuous monitoring, examines the specificity of the issue, and offers a view of proactive healthcare. Our research describes a wide range of device types and scientific methodologies, starting from traditional chest belts to their modern alternatives and cutting-edge bioamplifiers that distinguish breathing from chest impedance variations. We also investigated innovative technologies such as the monitoring of thorax micromovements based on the principles of seismocardiography, ballistocardiography, remote camera recordings, deployment of integrated optical fibers, or extraction of respiration from cardiovascular variables. Our review is extended to include acoustic methods and breath and blood gas analysis, providing a comprehensive overview of different approaches to respiratory monitoring. The topic of monitoring respiration with wearable and remote electronics is currently the center of attention of researchers, which is also reflected by the growing number of publications. In our manuscript, we offer an overview of the most interesting ones.
... In 2012, Wong et al. successfully integrated a novel CO 2 sensor into optical fibers by using micro-electro-mechanical systems (MEMS) transmitters and detectors [12]. Vincent et al. introduced an NDIR CO 2 sensor designed for portable breath analyzers with an operational range spanning from 0.5 % to 4 % in 2016 [13]. Furthermore, Daniel Popa from the University of Cambridge in the UK designed an integrated infrared gas sensor with low cost and low power consumption using mid-infrared absorption spectroscopy and MEMS technology in 2019 [14]. ...
We present a compact non-dispersive infrared (NDIR) gas sensor that can be adopted in high-moisture and low temperature environments. The NDIR gas sensor was formed by a Micro-Electro-Mechanical Systems (MEMS) emitter working at 400℃ with a broadband radiation spectrum, a MEMS thermopile detector that integrated with an optical filter, a compact gas-cell with high optical coupling efficiency of ~ 48 %, and an imbedded miniature thermostat. The footprint of the sensor is 24 mm × 8 mm × 8 mm (length × width × height), making it just 30 % of the size of conventional NDIR gas sensors with equivalent detection resolution, and its heat capa�bility is around 7.29 J/K that promise a cost-effective thermoregulation. The sensor is capable of accurately
detecting gas, such as Carbon dioxide, within a concentration range spanning from 0.5 % to 20 % with a reading error of ± 0.1 % covering a working temperature from − 20 ℃ to 60 ℃. Because the sensor is equipped with a waterproof breathable film at the air hole, the sensor can operate in the humidity range from 0 to 100 %RH, and
the maximum detection reading error is 0.1 % ± 230 ppm. It is possible to be applied for both low temperature environments (e.g. food preservation cabinet, biological cabinet, etc) and high-moisture environments (e.g. greenhouse, humidity chambers, etc.).
... [6][7][8] Providing continuous health monitoring for rehabilitated patients during this process can help doctors to develop a reasonable rehabilitation training plan to restore their body movement as soon as possible. In recent years, the rapid progress in the miniaturization of exhaled CO 2 analyzers has made it possible to transfer end-tidal CO 2 analysis from hospitals and clinics to family life, [9][10][11][12] but the disadvantages of large size and high power consumption of CO 2 sensors have limited its further development. Since COVID- 19, there has been a subtle change in the lifestyle of people who have become accustomed to using masks in various public places to ensure personal safety. ...
Human physiological metabolic status can be obtained by monitoring exhaled CO2 concentration, but current CO2 sensors have disadvantages such as large size, high power consumption, and slow response time, which limit their application in wearable devices and portable instruments. In this article, we report a small size, good performance, and large range CO2 infrared gas sensor that integrates a high emissivity MEMS emitter chip, a high detectivity thermopile chip, and a high coupling efficiency optical chamber to achieve high efficiency optical-thermal-electrical conversion. Compared with typical commercial sensors, the size of the sensor can be reduced by approximately 80% to only 10 mm × 10 mm × 6.5 mm, with the advantages of low power consumption and fast response speed. Further, a monitoring system for end-tidal CO2 concentration installed on a mask was developed using this sensor, and good results were achieved.
... This sensor has low power consumption and heat dissipation, which makes it widely used in CO 2 soil respiration and air quality monitoring. As far, NDIR sensors have great potential for development and are widely used in gas detection and respiratory analysis because of their unique advantages (Vincent and Gardner 2016). Relevant researchers will also continue improving such sensors in many aspects, such as power consumption, cost, and structure, making them one of the most representative gas sensors. ...
The development and renewal of gas sensor technology have enabled more and more low-cost gas sensors to form a carbon monitoring network to meet the requirements of the city. In the context of China’s commitment to achieving the “double carbon” target by 2060, this paper reviews the principles of four standard gas sensors and the application of several low-cost sensors in urban carbon monitoring networks, with the aim of providing a practical reference for the future deployment of carbon monitoring networks in Chinese cities. Moreover, the types, prices, and deployment of the sensors used in each project are summarized. Based on this review, non-dispersive infrared sensors have the best performance among the sensors and are commonly used in many cities. Lots of urban climate networks in cities were summarized by many reviews in the literature, but only a few sensors were studied, and they did not consider carbon dioxide (CO2) sensors. This review focuses on the dense CO2 urban monitoring network, and some case studies are also discussed, such as Seoul and San Francisco. To address the issue of how to better ensure the balance between cost and accuracy in the deployment of sensor networks, this paper proposes a method of simultaneously deploying medium-precision and high-precision fixed sensors and mobile sensors to form an urban carbon monitoring network. Finally, the prospects and recommendations, such as different ways to mitigate CO2 and develop an entire carbon monitoring system for future urban carbon monitoring in China, are also presented.
Graphical abstract
... There are a variety of detection methods for gas concentration, among which CO 2 gas sensor based on non-dispersive infrared (NDIR) technology has been used in air pollution detection, industrial processes, refined agriculture, medical diagnosis, as well as indoor and outdoor air quality monitoring due to its advantages of good selectivity and stability, high sensitivity, wide measuring range, as well as high precision. [1][2][3][4][5] The NDIR gas sensor is made up of a light source, a gas chamber, a photodetector, and a signal processing module. 6 According to the position of the light source and the photodetector, the NDIR gas sensors are divided into two types: direct and reflective. ...
In order to accurately monitor CO2 concentration based on the non-dispersive infrared technique, a novel flat conical chamber CO2 gas sensor is proposed and investigated by simulation analysis and experimental verification. First, the optical design software and computational fluid dynamics method are utilized to theoretically investigate the relationship between the energy distribution, absorption efficiency of infrared radiation, and chamber size. The simulation results show that the chamber length has an optimal value of 8 cm when the cone angle is 5° and the diameter of the detection surface is 1 cm, which makes infrared absorption efficiency optimal. Then, the flat conical chamber CO2 gas sensor system is developed, calibrated, and tested. The experimental results indicate that the sensor can accurately detect CO2 gas concentrations in the range of 0-2000 ppm at 25 °C. It is found that the absolute error of calibration is within 10 ppm, and the maximum repeatability and stability errors are 5.5 and 3.5%, respectively. Finally, the genetic neural network algorithm is presented to compensate for the output concentration of the sensor to solve the problem of temperature drift. Experimental results demonstrate that the relative error of the compensated CO2 concentration is varied from -0.85 to 2.32%, which is significantly reduced. The study has reference significance for the structural optimization of the infrared CO2 gas sensor and the improvement of the measurement accuracy.
... Low-cost (300 €) chemical sensors are miniature devices that offer a real-time output reflecting the concentration of gases and chemical volatile substances in contact with the sensor. The conditioning electronics' small size, lightweight, low power requirements, and simplicity make them easy to integrate into fixed and portable measurement systems, such as those commonly used for industrial safety Rezende, Le Calvé, Brandner and Newport (2019), environmental monitoring Baron and Saffell (2017), food analysis Loutfi, Coradeschi, Mani, Shankar and Rayappan (2015), and biomedicine applications Vincent and Gardner (2016). ...
... Based on this technology, we developed an NDIR gas sensor system. NDIR gas sensors are widely used for measuring gas concentrations [28,29], IR breadth analysis [30,31] and environmental monitoring [32,33] via their molecular vibrations [34,35]. In this technology, an infrared beam passes through the sampling chamber, and each gas component in the sample absorbs infrared rays of a specific frequency, as shown in Figure 1. ...
This paper proposes to apply a newly developed Non-Dispersive Infrared Spectroscopy (NDIR) gas sensing system composed of pyroelectric infrared detectors to monitor the thermal runaway (TR) process of lithium-ion batteries in real time and achieve an early warning system for the battery TR process. The new Electrical Vehicle Safety—Global Technical Regulation (EVS-GTR) requires that a warning be provided to passengers at least five minutes before a serious incident. The experimental results indicate that carbon dioxide and methane gas were detected during the overcharge test of the automotive battery, and the target gas was detected 25 s in advance before the battery TR when the battery vent was closed. In order to further explore the battery TR mechanism, an experiment was carried out using the battery sample with the battery vent opened. The target gas was detected about 580 s before the battery temperature reached the common alarm temperature (60 °C) of the battery management system (BMS). In this study, the beneficial effects of NDIR gas sensors in the field of thermal runaway warnings for automotive batteries were demonstrated and showed great application prospects and commercial value.
... Secondly, the fast response time (dependent on flow rate) and the high amount of readings per second, with values reported up to 50 Hz, provide them with the ability to perform breath-by-breath measurements [99]. In the typical range of an exhaled breath (4-5%) NDIR CO 2 sensors exist with an accuracy of ±2.9%, which is ±145 ppm if the exhaled breath contained 50,000 ppm CO 2 [100]. Another strength lies in the extremely low power consumption, e.g., 3.5 mW at 3.3 V in the ExplorIR-M NDIR CO 2 Sensor by SST Sensing [101]. ...
Indirect calorimetry (IC) is considered the gold standard for measuring resting energy expenditure (REE). This review presents an overview of the different techniques to assess REE with special regard to the use of IC in critically ill patients on extracorporeal membrane oxygenation (ECMO), as well as to the sensors used in commercially available indirect calorimeters. The theoretical and technical aspects of IC in spontaneously breathing subjects and critically ill patients on mechanical ventilation and/or ECMO are covered and a critical review and comparison of the different techniques and sensors is provided. This review also aims to accurately present the physical quantities and mathematical concepts regarding IC to reduce errors and promote consistency in further research. By studying IC on ECMO from an engineering point of view rather than a medical point of view, new problem definitions come into play to further advance these techniques.
... Over the above, MEMS technology has been utilized widely in the development of gas and chemical sensors [28]. Moreover, MEMS devices have been used for gas detection including sulfur dioxide ( SO 2 ) [50], carbon dioxide ( CO 2 ) [51], nitrogen dioxide ( NO 2 ) [52], and a few more gases that are constantly released by industry into the environment in the industrialization era. There are various gas sensors utilized in MEMS technologies including capacitive sensing [53], piezoresistive sensing [54,55], optical sensing [56], and piezoelectric sensing methods [15]. ...
Piezoelectric microelectromechanical system (piezo-MEMS)-based mass sensors including the piezoelectric microcantilevers, surface acoustic waves (SAW), quartz crystal microbalance (QCM), piezoelectric micromachined ultrasonic transducer (PMUT), and film bulk acoustic wave resonators (FBAR) are highlighted as suitable candidates for highly sensitive gas detection application. This paper presents the piezo-MEMS gas sensors' characteristics such as their miniaturized structure, the capability of integration with readout circuit, and fabrication feasibility using multiuser technologies. The development of the piezoelectric MEMS gas sensors is investigated for the application of low-level concentration gas molecules detection. In this work, the various types of gas sensors based on piezoelectricity are investigated extensively including their operating principle, besides their material parameters as well as the critical design parameters, the device structures, and their sensing materials including the polymers, carbon, metal-organic framework, and graphene.
... At present, the major popular optical gas sensors are NDIR (nondispersive infrared) sensors based on the spectrum absorption principle, which characterize the gas concentration by detecting the attenuation of optical intensity. The traditional gas sensors frequently apply to air chambers and are disadvantaged due to taking up too much room, high cost, only being used for specified situations, and the difficulty for industrial manufacturing [4][5][6]. ...
Two optical waveguide sensors based on SOS (silicon-on-sapphire) for detecting CO2 are theoretically proposed. The operational wavelength is 4.23 μm, which is the maximum absorption line of CO2. The power confinement factor (η) value is over 40% and 50%, the propagation loss is 0.98 dB/cm and 2.99 dB/cm, respectively, in the slot waveguide and SWGS (subwavelength grating slot) waveguide. An inverted tapered structure is used for the transition from strip waveguide to slot waveguide and constitutes the sensing absorption region, with the coupling efficiency that can reach more than 90%. When the optimal absorption length of the slot waveguide and SWGS waveguide is 1.02 cm and 0.33 cm, respectively, the maximum sensitivity can reach 6.66 × 10−5 (ppm−1) and 2.60 × 10−5 (ppm−1). Furthermore, taking the slot waveguide as an example, spiral and meander structures enable the long-distance sensing path to integrate into a small area.
... However, such a large fluctuation in atmospheric pressure is not expected in ambient air testing in the field. Gas molecule diffusion within the detection chamber is affected by temperature, and the absorption peaks of water molecules overlapped with CO2, affecting detection accuracy [24,25]. Therefore, temperature and humidity are two major ambient parameters that influence CO2 gas measurement in applications [26,27]. ...
Increasing carbon dioxide (CO2) concentrations threaten human production and life. Currently the equipment used for CO2 monitoring is heavy and expensive, without a portable CO2 detector that is inexpensive and resistant to interference. Here we designed a portable CO2 detector based on no-dispersive infrared sensors to measure CO2 concentration. The detector, which has a mass of 1 kg, is powered by a lithium battery with dimensions of 200 mm (length) × 150 mm (width) × 100 mm (height). Considering the fact that field observations are susceptible to humidity, a series of experiments were carried out to reduce the humidity interference on sensor responses at a laboratory. The values of humidity and CO2 variation were used in a regression model analysis to determine a quadratic function with an R2 above 0.94. The detector was compared with a reference analyzer in ambient CO2 measurement during a 7-day field campaign in Hangzhou, China. After humidity correction, the data show better correlation with the reference data, with the R2 0.62–0.97 increasing from 0.62–0.97 compared to before the correction and the value deviation decreasing to less than 3%. Cluster analysis of sensors revealed a reduction in average relative deviation of up to 1.4% as the number of sensors increased.
... The measurement of CO 2 in the exhaled breath, the normal level of which is 4-5% [40], of endotracheally intubated patients can be used to indicate correct tracheal intubation and show a steady breathing rate [41]. Although infrared absorption spectroscopy is very good for monitoring CO 2 levels in breath, the equipment is expensive and bulky [8,37,42]. ...
Two different, commercial colourimetric CO2 indicators are made in the lab, namely one based on an indicator in solution for monitoring the level of dissolved CO2 in an aquarium, i.e., a drop check indicator, and another based on an ink, for monitoring the level of CO2 in breath (capnography), i.e., a correct tracheal placement indicator. The selected commercial indicators are limited currently in terms of the analytical information they provide (qualitative) as they are normally assessed by eye. Thus, in each case, for both the lab-made and commercial indicators, colour photography coupled with digital image analysis, i.e., digital colour analysis (DCA), is used to convert the colour data from the indicator into a quantitative measure of CO2 and so markedly improve the quality of the analytical information provided by original indicator. This is the first time either indicator has been studied as a quantitative analytical system. The CO2 sensitivity of each of the lab-made indicators is found to match well that of its commercial counterpart. A simple program is provided to help non-experts and experts alike to apply DCA in this way. The potential of DCA to enhance the performance of other commercial indicators is discussed briefly.
... The NDIR sensors can be implemented in various applications including heating, ventilation, and air conditioning (HVAC) [9], environmental diagnostics [10,11], medical diagnostics [12], breadth analysis [13,14], and trace gas sensing [15] owing to their robustness. The qualitative analysis of unknown mixtures faces certain limitations since the selectivity depends on the center wavelength and bandwidth of the OBPF. ...
This study presents a multi-gas analyzer based on tunable filter non-dispersive IR (TF-NDIR) sensors that operate with a wide dynamic range of wavelength and concentration. A pyroelectric sensor coupled with a microsized Fabry–Perot interferometer, namely a tunable filter, enables sensing within a narrowly selected wavelength band. Three detectors capable of tuning the bandpass wavelength with a range of 3.8–5.0 μm, 5.5–8.0 μm, and 8.0–10.5 μm are combined to encompass the entire mid-IR region. single-pass cell with an optical path length (OPL) of 5 cm and a multi-pass cell with an OPL of 10.5 m is selected to encompass a concentration range from ppmv to percent. The TF-NDIR sensors and gas cells can be reconfigured by manipulating the beam path. A homemade lock-in amplifier is used to enhance the signal-to-noise ratio 88 times greater than that of the bare signal. The performance of the gas analyzer is evaluated by measuring the SF6 and Novec-4710/CO2 mixture, which are the dielectric gas medium for a gas-insulated switch (GIS). The mixing ratio of the Novec-4710/CO2 mixture is measured within a range of 3–7% using premixes. The measurement precision is 0.72% for 0.5 s. Trace level measurements of Novec-4710, CO2, SF6, which are measurands for detecting gas leakage from the GIS, CO, and SO2 which are measurands for detecting product generated by the arc or thermal decomposition in the switching electrode, are conducted based on dynamic partial pressure adjustment using 1000 ppmv mother premixes in N2. The limit of detection is 54.7 ppmv for Novec-4710, 112.8 ppmv for CO, 118.1 ppmv for CO2, 69.5 ppmv for SO2, and 33.5 ppmv for SF6.
... MEMS thermopiles can convert infrared radiation into electrical signals and have been widely used in non-contact thermometers [1,2], uncooled infrared cameras [3,4], gas flow sensors [5][6][7], heat flow sensors [8][9][10], nondispersive infrared sensors [11][12][13][14][15], and vacuum gauges [16,17], etc. The performance of thermopiles can be evaluated by various parameters, including responsivity, detectivity, response time, etc. Herein, the response time is the time required by the device to detect the object and reach the stable state, which reflects the response speed of the device to external excitation [18,19]. ...
The response time is an important parameter for thermopiles sensors, which reflects the response speed of the device. The accurate measurement of response time is extremely important to evaluate device characteristics for using them in suitable scenarios. In this work, to accurately measure the response time of thermopile sensors, an Al microheater is integrated in a MEMS thermopile as an in—situ heat source. Compared with the traditional chopper measurement method for response time, this approach avoids mechanical delay induced by chopper blades. Accordingly, based on this approach, the response time of the device is measured to be 6.9 ms, while that is 12.7 ms when a chopping system is used, demonstrating that an error of at least 5.8 ms is avoided. Such an approach is quite simple to realize and provides a novel route to accurately measure the response time.
Gases in the environment can significantly affect our health and safety. As mobile devices gain popularity, we consider to explore a human-centered gas detection system that can be integrated into commercial mobile devices to realize ubiquitous gas detection. However, existing gas sensors either have too long response delays or are too cumbersome. This paper shows the feasibility of performing gas sensing by shining infrared (IR) signals emitted from our hands through the gas, allowing the system to rely on a single IR detector. The core opportunity arises from the fact that the human hand can provide stable, broadband, and omnidirectional IR radiation. Considering that IR signals experience distinct attenuation when passing through different gases or gases with different concentrations, we can integrate the human hand into the gas sensing system to enable extremely low-power and sustainable gas sensing. Yet, it is challenging to build up a robust system directly utilizing the hand's IR radiation. Practical issues include low IR radiation from the hand, unstable optical path, impact of environmental factors such as ambient temperature, etc. To tackle these issues, we on one hand modulate the IR radiation from the hand leveraging the controllability of the human hand, which improves the hand's IR radiation. On the other hand, we provide a dual-channel IR detector design to filter out the impact of environmental factors and gases in the environment. Extensive experiments show that our system can realize ethanol, gaseous water, and CO2 detection with 96.7%, 92.1% and 94.2%, respectively.
An optical sensing approach that balances portability with cost efficiency has been designed for the reliable monitoring of fugitive methane (CH4) emissions. Employing a LiTaO3-based pyroelectric detector integrated with micro-electro-mechanical systems and a broad infrared source, the developed gas sensor adeptly measured CH4 concentrations with a low limit of detection of about 5.6 ppmv and showed rapid response times with t90 consistently under 3 s. Notably, the novelty of our method lies in its precise control and reduction of CH4 levels, enhanced by wavelet denoising. This technique, optimized through meticulous grid search, effectively mitigated noise interference noticeable at CH4 levels below 10 ppmv. Postdenoising, nonlinear regression analyses based on the modified Beer–Lambert equation returned R² values of 0.985 and 0.982 for the training and validation sets, respectively. In conclusion, this gas sensor has been shown to be able to meet the requirements for early warning of CH4 leakage on the surface in various carbon capture, utilization, and storage projects such as enhanced oil or gas recovery projects using CO2 injection.
Fine‐tuning the sensing properties of carbon dioxide (CO2) colorimetric sensors is a challenging task. In this study, a short synthetic route is developed for CO2‐responsive nanoparticles with diverse sensitivity and detection range across a wide range of CO2 concentrations. This involves the addition of oily liquids as inter‐chain spacers, which changes the diffusivity of CO2 gas into the sensing matrices without other chemical modifications. R values and the limit of detection (LOD) are estimated from Euclidean distance (ED) curves, indicating a ten‐fold difference in sensitivity. Optical and physical analyses revealed that these results arise from intercalating inter‐chain spacers between polymeric chains and modifying the gas diffusivity. Furthermore, the sensitivity and detection range can be easily tuned by mixing two CO2‐responsive nanoparticles having different inter‐chain spacers, allowing the fabrication of the sensors with subtle differences in sensitivity and detection range. Based on these results, a CO2 level meter with a horizontal linear gauge that allows visible identification of the level of CO2 over the entire range of CO2 concentrations (from 0% to 100%) is developed. Consequently, the findings will be helpful in achieving a better understanding of gas information and finding an effective way to control the characteristics of colorimetric sensors.
The relationship between the transmittance and FWHM of a Fabry-Perot filter for a nondispersive carbon dioxide (CO2) sensor was investigated as a function of the number of distributed Bragg reflector (DBR) pairs consisting poly-Si and SiO¬2 thin films. Given the significant prior research on the fabrication of high-performance Fabry-Perot filters, this study is focused on the relationship between the transmittance and FWHM that can be achieved by controlling the reflectance of the DBR pairs. Each layer of the filter was simulated adequately as the poly-Si and SiO2-based DBR pairs, and poly-Si and SiO2 were deposited on the soda–lime substrate by radio frequency sputtering and low-pressure chemical vapor deposition based on the simulation results. The fabricated filter showed a transmittance of 43.7% and FWHM of 125 nm at 4.26 µm. The NDIR CO2 sensor with Fabry-Perot filter showed enhanced selectivity to CH4 and CO compared with normalized CO2 response.
In this study, we developed a novel isotope gas filter for a mid-infrared (IR) LED-based NDIR spectroscopy system. Our novel isotope gas filter contains high-purity CO2 gas (99.99% content), and the intrinsic absorption characteristic of contained gas works as an optical stopband filter. Our filter achieves a 25 dB attenuation performance in the region of 4190–4350 nm, and is a core component in distinguishing the signal from different carbon isotopes such as 12CO2 and 13CO2 for an NDIR carbon-13 (C-13) based breath test. Compared with dielectric filters normally used for C-13 breath tests, our filter can provide more useful and consistent performance than dielectric filters in the mid-IR region.
Microelectromechanical system (MEMS) thermopile infrared (IR) detectors excel in contactless, highly sensitive, non-invasive temperature measurements over a wide range, without cooling systems, making them ideal for precise intelligent sensing applications. In this study, we present a micromachined thermopile IR detector utilizing a radially distributed dual-layer thermopile that demonstrates fast response time and significantly improved responsivity and detectivity. A dual-layer thermocouple array is designed by applying the N/P-poly, which are radially distributed on a SiO2 supporting layer and suspended by dry etching the backside of a silicon substrate. The results of the study, which compared traditional four-ended beam structures with radially distributed structures that were modeled and simulated, indicate that the latter design enhances the output voltage and significantly improves responsivity and detectivity, with an increase of 40.5% and 43.8%, respectively. With a fast response time of 9.5 ms at room temperature, the detector exhibited a measured responsivity of 100.6 V/W and detectivity of 5.2×107 cm∙Hz1/2/W in an experimental system constructed to evaluate its performance.
Exhaled breath analysis is considered an effective tool for diagnosing the patient's metabolic status because of its non‐invasive nature. Gas chromatography‐mass spectrometry (GC‐MS) and other mass spectrometry techniques are widely used for exhaled breath analysis. Nevertheless, the requirement of a handheld device for real‐time analysis and rapid processing time of multiple samples leads to advancing infrared (IR) based breath gas sensing techniques. Herein, the IR gas sensing technologies are discussed with a focus on non‐dispersive infrared (NDIR), photoacoustic (PAS), and tunable diode laser absorption spectroscopy (TDLAS) gas sensing technologies because of their highly selective gas detection among compound gases (mixture of VOCs), as well as their corresponding sensing mechanisms and characteristics, for real‐time monitoring of exhaled biomarkers. Carbon dioxide, acetone, ammonia, nitric oxide, methane, and ethylene are the significant biomarkers elaborated in this work with their respective clinical applications and the significance of non‐invasive real‐time monitoring using IR detectors. Challenges in selectivity and clinical trials leads to focus on this review. Current market analysis, present status of different techniques to detect specific biomarkers and other challenges with their possible solutions discussed in this review aid in developing highly selective IR‐based handheld breath VOC analyzers for early diagnosis and screening.
The ocean is one of the most extensive ecosystems on Earth and can absorb large amounts of carbon dioxide. Changes in seawater carbon dioxide concentrations are one of the most important factors affecting marine ecosystems. Excess carbon dioxide can lead to ocean acidification, threatening the stability of marine ecosystems and species diversity. Dissolved carbon dioxide detection in seawater has great scientific significance. Conducting online monitoring of seawater carbon dioxide can help to understand the health status of marine ecosystems and to protect marine ecosystems. Current seawater detection equipment is large and costly. This study designed a low-cost infrared carbon dioxide detection system based on molecular theory. Using the HITRAN database, the absorption spectra and coefficients of carbon dioxide molecules under different conditions were calculated and derived, and a wavelength of 2361 cm−1 was selected as the measurement channel for carbon dioxide. In addition, considering the interference effect of direct light, an infrared post-splitting method was proposed to eliminate the interference of light and improve the detection accuracy of the system. The system was designed for the online monitoring of carbon dioxide in seawater, including a peristaltic pump to accelerate gas–liquid separation, an optical path structure, and carbon dioxide concentration inversion. The experimental results showed that the standard deviation of the gas test is 3.05, the standard deviation of the seawater test is 6.04, and the error range is within 20 ppm. The system can be flexibly deployed and has good stability and portability, which can meet the needs of the online monitoring of seawater carbon dioxide concentration.
Carbon capture, storage, and utilization have become familiar terms when discussing climate change mitigation actions. Such endeavors demand the availability of smart and inexpensive devices for CO2 monitoring. To date, CO2 detection relies on optical properties and there is a lack of devices based on solid-state gas sensors, which can be miniaturized and easily made compatible with Internet of Things platforms. With this purpose, we present an innovative semiconductor as a functional material for CO2 detection. A nanostructured In2O3 film, functionalized by Na, proves to enhance the surface reactivity of pristine oxide and promote the chemisorption of even rather an inert molecule as CO2. An advanced operando equipment based on surface-sensitive diffuse infrared Fourier transform is used to investigate its improved surface reactivity. The role of sodium is to increase the concentration of active sites such as oxygen vacancies and, in turn, to strengthen CO2 adsorption and reaction at the surface. It results in a change in film conductivity, i.e., in transduction of a concentration of CO2. The films exhibit excellent sensitivity and selectivity to CO2 over an extra-wide range of concentrations (250-5000 ppm), which covers most indoor and outdoor applications due to the marginal influence by environmental humidity.
Non-dispersive infrared (NDIR) sensors have been widely used in measuring gas concentration in process industry. However, the inhomogeneous gas diffusion in the gas chamber of NDIR sensor increases the response time and causes measurement error. In this case, the fast-and-accurate measurement of gas concentration is of great importance in avoiding accidents. This article focuses on constructing a novel gas diffusion model among normalization concentration (N-concentration), inlet flow velocity, and diffusion time. Firstly, the structure model of gas chamber is constructed based on Fluent 15.0 and the turbulence intensity is calculated based on dynamic viscosity, inlet flow velocity, concentration, temperature and pressure. The simulation model is constructed based on the assumption of simultaneous reaction and mass transfer. The initial result shows that the N-concentration along the optical path is mainly influenced by inlet flow velocity and diffusion time, while the temperature, pressure and inlet concentration have less influence on gas diffusion. According to the velocity distribution map, the critical zone of inlet flow velocity is defined to divide the gas diffusion state into different zones. Then, a novel Multi-interval exponential diffusion model is proposed to calculate the N-concentration and the real-time measurement of gas concentration can be achieved based on inlet flow velocity, diffusion time and the pre-defined critical zone of inlet flow velocity. The proposed model is suitable for the gas concentration correction of different gases. Finally, the validation indexes include the coefficient of determination (R
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>
), Mean Squared Error (MSE) and standard uncertainty shows the accuracy of the proposed model can be obviously increased.
In this article, after reviewing the different mathematical methods used in quantification by IR, the main advantages and drawbacks and applications with or without previous sample treatment are presented. The bases of the use of quantitative IR in food analysis such as lipids (measurement of unsaturation degrees and lipids determination), carbohydrates, and proteins (secondary structures and quantitative analysis); original examples of the use of IR spectroscopy combined with enzymes; and modern applications in the clinical field are presented in detail, followed by examples of Fourier transform infrared (FTIR) analysis coupled with other analytical methods in different fields such as pharmaceuticals, petroleum, paints, and other industrial products and in the fields of health, environment, and trace compounds analysis in order to think about the limitations and perspectives of IR spectroscopy for quantitative analysis. It appears that the most significant developments in the field of quantitative analysis will probably come through the progress in chemometrics and instrumentation. More recently, approaches combining infrared spectroscopy and deep learning (DL) have shown great potential.
With the rapid progression of global climate changes and air pollution in recent years, there has been growing interest in the sensing and monitoring of CO2 gas. In the present study, an inverse opal photonic gel (IOPG) colorimetric sensor is demonstrated that is capable of real-time monitoring of CO2 gas in an open system without the necessity of a power supply. The IOPGs are fabricated via the opal-templated photo-polymerization of monomer mixtures of hydroxyethyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA) or 2-(dimethylamino)propyl methacrylamide (DMAPMAm), followed by template removal. When the IOPG sensor is immersed in water with a steady flow of mixed CO2/N2 gas at various ratios, the CO2 molecules dissolve in the water and are converted to carbonate anions, which subsequently bind to the amino groups of pDMAEMA to build up osmotic pressure, thus leading to swelling of the IOPG. A comparison of the sensing and recovery capabilities of the two types of IOPG indicates that the pDMAEMA-containing IOPG exhibits a limit of detection below 1.2%, and 2.6 times faster CO2 desorption kinetics compared to the pDMAPMAm-containing IOPG. The swelling behavior of the CO2-responsive IOPG is rigorously investigated at various pH values, and temperatures by analyzing the reflectance spectra of the IOPG in the visible wavelength range. The usefulness of the pDMAEMA-IOPG as a real-time CO2 sensor was confirmed by applying it to various carbonated drinks.
As discussed in previous chapters, carbon dioxide (CO2) gas released by human body is a notable excretory product from cellular respiration of living organism in identifying several respiratory and pulmonary illness. Among many, asthma as the primary respiratory disease is one of the key diseases that can be diagnosed with the evaluation of parameters identified from CO2 released by a patient. Regarding that, Chapters 3–5 have detailed about capnography, a noninvasive device that uses sensing technology and measures human respiration CO2 from the expired gasses and an incessant plot of exhaled CO2 over time, known as a capnogram. Capnography detects CO2 from expired gas and extracts the featured CO2 parameters such as end-tidal CO2 (EtCO2), respiratory rate slope angles, and many more, which can be used to differentiate asthmatic and nonasthmatic conditions. For an effective capnography, a high-performance CO2 sensor is necessary. There are a variety of CO2 sensors developed and a huge effort is involved in improving the technology for highly sensitive CO2 sensors. The present chapter discusses the types of CO2 sensors and its contribution for diagnosing asthma, as well as in enhancing capnography.
To realize early fire identification in cotton harvesting operations, a mid-infrared carbon monoxide (CO) sensor system was developed. To match the broadband light source with a 15° divergence angle, a multipass gas cell (MPGC) with an effective path length of 180 cm was designed to improve sensor sensitivity, leading to a limit of detection (LoD) of 0.83 parts-per-million by volume (ppmv). A damping module with springs at the bottom and front/back sides was fabricated, which can effectively reduce the vibration intensity by >80%. The sensor system can operate normally from -40 °C to 85 °C by stabilizing the temperature of the optical module through heating or cooling as well as using automotive electronic components. An adaptive early fire identification algorithm based on a dual-parameter threshold alarming method was proposed to avoid false and missing alarms. Field deployments on a harvester verified the good practicability of the sensor system.
The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff's law prescribes that only good absorbers make good thermal emitters. Based on a designed plasmonic crystal and exploiting a slow-wave lattice resonance and spontaneous thermal plasmon emission, we engineer a tungsten-based thermal emitter, fabricated in an industrial CMOS process, and demonstrate its markedly improved practical use in a prototype non-dispersive infrared (NDIR) gas-sensing device. We show that the emission intensity of the thermal emitter at the CO2 absorption wavelength is enhanced almost 4-fold compared to a standard non-plasmonic emitter, which enables a proportionate increase in the signal-to-noise ratio of the CO2 gas sensor.
Background and aims: A personal indirect calorimeter allows everyone to assess resting and
non-resting energy expenditure, thus enabling accurate determination of a person’s total calorie need
for weight management and fitness. The aim of this study is to compare the performance of a new
personal metabolic rate tracker based on indirect calorimetry, Breezing®, with the Douglas bag method,
the gold standard method for energy expenditure (EE) measurement.
Methods: Energy expenditures (EE) at rest and during activities, and respiratory quotient (RQ)
were measured for 12 healthy subjects, including 7 males and 5 females under different living conditions.
A total of 314 measurements were performed with Breezing®, and the results were compared with those
by the Douglas bag method.
Results: R-squared correlation coefficients (R2) between the data obtained with Breezing® and the Douglas bag method were 0.9976, 0.9986, 0.9981, and 0.9980, for VO2, VCO2, EE, and RQ, respectively.
Conclusions: The EE and RQ values determined by Breezing® are in good agreement with those
by the Douglas bag method.
Obesity is a major risk factor for non-communicable diseases (NCDs), such as diabetes, cardiovascular di - seases, and cancers. The worldwide prevalence of obesity has almost doubled between 1980 and 2008. In some regions, such as Europe, the Eastern Mediterranean and the Americas, more than 50% of women are overweight. Tonga, Nauru and the Cook Islands show the highest prevalence of obesity worldwide, above 60% in men and in women. China and the United States are the countries that experienced the largest absolute increase in the number of overweight and obese people between 1980 and 2008, followed by Brazil and Mexico. The regions with the largest increase in the prevalence of female obesity were Central Latin America, Oceania and Sou - thern Latin America. Updated data provide evidence that the progression of the epidemic has effectively slowed for the past ten years in several countries. In low-income countries obesity is generally more prevalent among the better-off, while disadvantaged groups are increasingly affected as countries grow. Many studies have shown an overall socio-economic gradient in obesity in modern industrialized societies. Rates tend to decrease progressively with increasing socio-economic status. Children obesity rates in Spain are amongst the highest in the OECD. One in 3 children aged 13 to 14 are overweight. Overweight in infants and young children is observed in the upper middle-income countries. However, the fastest growth occurs in the group of lower middle-income countries. There is a growing body of evidence for an inverse association between SES and child obesity in developed countries. The prevalence of overweight and obesity is high in all age groups in many countries, but especially worrying in children and adolescents in developed countries and economies in transition.
Increasing evidence associates excess refined sugar intakes with obesity, Type 2 diabetes and heart disease. Worryingly, the estimated volume of sugary drinks purchased in the UK has more than doubled between 1975 and 2007, from 510ml to 1140ml per person per week. We aimed to estimate the potential impact of a duty on sugar sweetened beverages (SSBs) at a local level in England, hypothesising that a duty could reduce obesity and related diseases.
We modelled the potential impact of a 20% sugary drinks duty on local authorities in England between 2010 and 2030. We synthesised data obtained from the British National Diet and Nutrition Survey (NDNS), drinks manufacturers, Office for National Statistics, and from previous studies. This produced a modelled population of 41 million adults in 326 lower tier local authorities in England. This analysis suggests that a 20% SSB duty could result in approximately 2,400 fewer diabetes cases, 1,700 fewer stroke and coronary heart disease cases, 400 fewer cancer cases, and gain some 41,000 Quality Adjusted Life Years (QALYs) per year across England. The duty might have the biggest impact in urban areas with young populations.
This study adds to the growing body of evidence suggesting health benefits for a duty on sugary drinks. It might also usefully provide results at an area level to inform local price interventions in England.
In this letter, we present a fully complementary-metal-oxide-semiconductor (CMOS) compatible microelectromechanical system thermopile infrared (IR) detector employing vertically aligned multi-walled carbon nanotubes (CNT) as an advanced nano-engineered radiation absorbing material. The detector was fabricated using a commercial silicon-on-insulator (SOI) process with tungsten metallization, comprising a silicon thermopile and a tungsten resistive micro-heater, both embedded within a dielectric membrane formed by a deep-reactive ion etch following CMOS processing. In-situ CNT growth on the device was achieved by direct thermal chemical vapour deposition using the integrated micro-heater as a micro-reactor. The growth of the CNT absorption layer was verified through scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The functional effects of the nanostructured ad-layer were assessed by comparing CNT-coated thermopiles to uncoated thermopiles. Fourier transform IR spectroscopy showed that the radiation absorbing properties of the CNT adlayer significantly enhanced the absorptivity, compared with the uncoated thermopile, across the IR spectrum (3 μm–15.5 μm). This led to a four-fold amplification of the detected infrared signal (4.26 μm) in a CO2 non-dispersive-IR gas sensor system. The presence of the CNT layer was shown not to degrade the robustness of the uncoated devices, whilst the 50% modulation depth of the detector was only marginally reduced by 1.5 Hz. Moreover, we find that the 50% normalized absorption angular profile is subsequently more collimated by 8°. Our results demonstrate the viability of a CNT-based SOI CMOS IR sensor for low cost air quality monitoring.
In this letter, we present a fully complementary-metal-oxide-semiconductor (CMOS) compatible microelectromechanical system thermopile infrared (IR) detector employing vertically aligned multi-walled carbon nanotubes
(CNT) as an advanced nano-engineered radiation absorbing material. The detector was fabricated using a commercial silicon-on-insulator (SOI) process with tungsten metallization, comprising a silicon thermopile and a tungsten resistive micro-heater, both embedded within a dielectric membrane formed by a deep-reactive ion etch following CMOS processing. In-situ
CNT growth on the device was achieved by direct thermal chemical vapour deposition using the integrated micro-heater as a micro-reactor. The growth of the CNT absorption layer was verified through scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The functional effects of the nanostructured ad-layer were assessed by comparing CNT-coated thermopiles to uncoated thermopiles. Fourier transform IR spectroscopy showed that the radiation absorbing properties of the CNT adlayer significantly enhanced the absorptivity, compared with the uncoated thermopile, across the IR spectrum (3 μm–15.5 μm). This led to a four-fold amplification of the detected infrared signal (4.26 μm) in a CO2 non-dispersive-IR gas sensor system. The presence of the CNT layer was shown not to degrade the robustness of the uncoated devices, whilst the 50% modulation depth of the detector was only marginally reduced by 1.5 Hz. Moreover, we find that the 50% normalized absorption angular profile is subsequently more collimated by 8°. Our results demonstrate the viability of a CNT-based SOI CMOS IR sensor for low cost air quality monitoring.
Breath-by-breath levels of O2 and CO2 may be used to determine human metabolic rate which, in turn, is related to the problem of obesity. A sensor system has been designed to not only monitor O2 and CO2 in breath, but also temperature, relative humidity (RH), volumetric flow-rate, and trace levels of CO. Our system targets energy expenditure measurements to within a 1% tolerance. A data driven modelling approach has been adopted to characterise the gas sensors at gas concentrations found in inhaled air and exhaled breath. Data were collected for model fitting from experiments performed on an automated gas testing rig. Bi-exponential curves were fitted to the sensor data using partial least squares (PLS) regression. These fits show that the O2 sensor functions close to the target accuracy, with a 95% confidence interval, whereas the CO2 sensor performs less well (70%). Development of a microcontroller interface combined with work on new low-power CMOS sensors will eventually lead to a miniature low-cost system for mobile phone application.
Obesity is a major risk factor for non-communicable diseases (NCDs), such as diabetes, cardiovascular diseases, and cancers. The worldwide prevalence of obesity has almost doubled between 1980 and 2008. In some regions, such as Europe, the Eastern Mediterranean and the Americas, more than 50% of women are overweight. Tonga, Nauru and the Cook Islands show the highest prevalence of obesity worldwide, above 60% in men and in women. China and the United States are the countries that experienced the largest absolute increase in the number of overweight and obese people between 1980 and 2008, followed by Brazil and Mexico. The regions with the largest increase in the prevalence of female obesity were Central Latin America, Oceania and Southern Latin America. Updated data provide evidence that the progression of the epidemic has effectively slowed for the past ten years in several countries. In low-income countries obesity is generally more prevalent among the better-off, while disadvantaged groups are increasingly affected as countries grow. Many studies have shown an overall socio-economic gradient in obesity in modern industrialized societies. Rates tend to decrease progressively with increasing socio-economic status. Children obesity rates in Spain are amongst the highest in the OECD. One in 3 children aged 13 to 14 are overweight. Overweight in infants and young children is observed in the upper middle-income countries. However, the fastest growth occurs in the group of lower middle-income countries. There is a growing body of evidence for an inverse association between SES and child obesity in developed countries. The prevalence of overweight and obesity is high in all age groups in many countries, but especially worrying in children and adolescents in developed countries and economies in transition.
Breath analysis is a young field of research with great clinical potential. As a result of this interest, researchers have developed new analytical techniques that permit real-time analysis of exhaled breath with breath-to-breath resolution in addition to the conventional central laboratory methods using gas chromatography-mass spectrometry. Breath tests are based on endogenously produced volatiles, metabolites of ingested precursors, metabolites produced by bacteria in the gut or the airways, or volatiles appearing after environmental exposure. The composition of exhaled breath may contain valuable information for patients presenting with asthma, renal and liver diseases, lung cancer, chronic obstructive pulmonary disease, inflammatory lung disease, or metabolic disorders. In addition, oxidative stress status may be monitored via volatile products of lipid peroxidation. Measurement of enzyme activity provides phenotypic information important in personalized medicine, whereas breath measurements provide insight into perturbations of the human exposome and can be interpreted as preclinical signals of adverse outcome pathways.
The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.
A flexible design for a low-noise lock-in amplifier for low-level signal and low bandwidth sensors, such as infrared detectors, thermal sensors and strain gauges is presented. This paper attempts to bridge the gap between the use of a high performance commercially available lock-in amplifiers or the design of a dedicated high performance lock-in amplifier for a sensor application from scratch. The presented system is dedicated to low-level signal sensor applications, operating at modulation frequencies up to a few kHz. The input amplifier can be flexibly adapted to different input sensors and signals. A tunable low-pass filter allows easy control of the system bandwidth. Compensation techniques, such as DC filtering, phase compensation and differential signal adjustments have been implemented. The circuit can be placed near the sensor on a small printed circuit board and uses low-cost commercially available components. The input noise is typically‥ nV/Hz and the bandwidth‥ kHz at 80 dB overall gain.
Exhaled breath volatile organic compound (VOC) analysis for airway disease monitoring is promising. However, contrary to nitric oxide the method for exhaled breath collection has not yet been standardized and the effects of expiratory flow and breath-hold have not been sufficiently studied. These manoeuvres may also reveal the origin of exhaled compounds.
15 healthy volunteers (34 +/- 7 years) participated in the study. Subjects inhaled through their nose and exhaled immediately at two different flows (5 L/min and 10 L/min) into methylated polyethylene bags. In addition, the effect of a 20 s breath-hold following inhalation to total lung capacity was studied. The samples were analyzed for ethanol and acetone levels immediately using proton-transfer-reaction mass-spectrometer (PTR-MS, Logan Research, UK).
Ethanol levels were negatively affected by expiratory flow rate (232.70 +/- 33.50 ppb vs. 202.30 +/- 27.28 ppb at 5 L/min and 10 L/min, respectively, p < 0.05), but remained unchanged following the breath hold (242.50 +/- 34.53 vs. 237.90 +/- 35.86 ppb, without and with breath hold, respectively, p = 0.11). On the contrary, acetone levels were increased following breath hold (1.50 +/- 0.18 ppm) compared to the baseline levels (1.38 +/- 0.15 ppm), but were not affected by expiratory flow (1.40 +/- 0.14 ppm vs. 1.49 +/- 0.14 ppm, 5 L/min vs. 10 L/min, respectively, p = 0.14). The diet had no significant effects on the gasses levels which showed good inter and intra session reproducibility.
Exhalation parameters such as expiratory flow and breath-hold may affect VOC levels significantly; therefore standardisation of exhaled VOC measurements is mandatory. Our preliminary results suggest a different origin in the respiratory tract for these two gasses.
This paper describes development of a novel mid-infrared light emitting diode (LED) and photodiode (PD) light source/detector combination and use within a non-dispersive infrared (NDIR) carbon dioxide gas sensor. The LED/PD based NDIR sensor provides fast stabilisation time (time required to turn on the sensor from cold, warm up, take and report a measurement, and power down again ≈1 second), longevity (>15 years), low power consumption and low cost. Described performance is compatible with "fit and forget" wireless deployed sensors in applications such as indoor air quality monitoring/control & energy conservation in buildings, transport systems, horticultural greenhouses and portable deployment for safety, industrial and medical applications. Fast stabilisation time, low intrinsic power consumption and cycled operation offer typical energy consumption per measurement of mJ's, providing extended operation using battery and/or energy harvesting strategies (measurement interval of ≈ 2 minutes provides >10 years operation from one AA battery). Specific performance data is provided in relation to measurement accuracy and noise, temperature performance, cross sensitivity, measurement range (two pathlength variants are described covering ambient through to 100% gas concentration), comparison with NDIR utilizing thermal source/pyroelectric light source/detector combination and compatibility with energy harvesting. Semiconductor based LED/PD processing together with injection moulded reflective optics and simple assembly provide a route to low cost high volume manufacturing.
In this paper, we demonstrate a micro-inkjet printing technique as a reproducible post-process for the deposition of carbon nanoparticles and fullerene adlayers onto fully CMOS compatible micro-electro-mechanical silicon-on-insulator infrared (IR) light sources to enhance their infrared emission. We show experimentally a significant increase in the infrared emission efficiency of the coated emitters. We numerically validate these findings with models suggesting a dominant performance increase for wavelengths <5.5 lm. Here, the bimodal size distribution in the diameter of the carbon nanoparticles, relative to the fullerenes, is an effective mediator towards topologically enhanced emittance of our miniaturised emitters. A 90% improvement in IR emission power density has been shown which we have rationalised with an increase in the mean thickness of the deposited carbon nanoparticle adlayer. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4809546]
An indium nitride (InN) gas sensor of 10 nm in thickness has achieved detection limit of 0.4 ppm acetone. The sensor has a size of 1 mm by 2.5 mm, while its sensing area is 0.25 mm by 2 mm. Detection of such a low acetone concentration in exhaled breath could enable early diagnosis of diabetes for portable physiological applications. The ultrathin InN epilayer extensively enhances sensing sensitivity due to its strong electron accumulation on roughly 5-10 nm deep layers from the surface. Platinum as catalyst can increase output current signals by 2.5-fold (94 vs. 37.5 μA) as well as reduce response time by 8.4-fold (150 vs. 1,260 s) in comparison with bare InN. More, the effect of 3% oxygen consumption due to breath inhalation and exhalation on 2.4 ppm acetone gas detection was investigated, indicating that such an acetone concentration can be analyzed in air.
Technological innovations in the ICU have led to artificially prolonged life, with an associated cost. Chronic critical illness (CCI) occurs in patients with prolonged mechanical ventilation and allostatic overload, and is associated with a discrete and consistent metabolic syndrome. Metabolic interventions are extrapolated from clinical critical care research, scientific theory, and years of CCI patient care experience. Intensive metabolic support (IMS) is a multi-targeted approach consisting of tight glycemic control with intensive insulin therapy, early and adequate nutrition therapy, nutritional pharmacology, management of metabolic bone disease, and meticulous attention to other endocrine/metabolic derangements. Ideally, IMS should be under the supervision of a metabolic support consultative team. Further research specifically focused on the CCI population is needed to validate this current approach.
Miniaturized non-dispersive infrared (NDIR) gas sensing systems require as key components bright thermal infrared (IR) sources that can be modulated at reasonably high speed to allow high-sensitivity lock-in detection to be applied. In addition such sources should provide a stable emission <sup>n</sup>affected by both short-term environmental changes as well as long-term drift. As miniaturized light bulbs, widely used in commercial NDIR gas sensing systems, cannot fulfil these requirements we have developed miniaturized thermal IR emitters with built-in monitoring and self-test features
Alcolocks and alcohol screening devices are becoming commonplace, and their use is expected to grow rapidly with cost reduction and improved usability. A new breath analyzer prototype is demonstrated, with the prospects of eliminating the mouthpiece, reducing expiration time and volume, improving long-term stability, and reducing life cycle cost. Simultaneous CO<sub>2</sub> measurements compensate for the sample dilution and unsaturated expiration. Infrared transmission spectroscopy is used for both the alcohol and CO<sub>2</sub> measurement, yet the entire system is contained within a small handheld unit. Experimental results are reported on the device sensitivity, linearity, resolution, and influence from varying measuring distance. The correlation between early and full-time sampling was established in 60 subjects. Basic concept verification was obtained, whereas resolution and selectivity still needs to be improved. Further improvements are expected by system optimization and integration.
Hollow fibers can be used for compact infrared gas sensors. The guided light is absorbed by the gas introduced into the hollow core. High sensitivity and a very small sampling volume can be achieved depending on fiber parameters i.e. attenuation, flexibility, and gas exchange rates. Different types of infrared hollow fibers including photonic bandgap fibers were characterized using quantum cascade lasers and thermal radiation sources. Obtained data are compared with available product specifications. Measurements with a compact fiber based ethanol sensor are compared with a system simulation. First results on the detection of trace amounts of the explosive material TATP using hollow fibers and QCL will be shown .
Breath possesses unique advantages as a specimen for clinical chemical analyses, including the continuous equilibrium of gases and volatile substances between expired alveolar air and the pulmonary blood circulation. Substances amenable to analysis in breath include O2, CO2, CO, and other gases, volatile organic compounds, and many drugs with sufficiently high vapor pressures at physiological temperatures. Practical aspects of breath sampling and breath analysis are discussed, exemplified by breath alcohol analysis. The requirements for obtaining breath samples in equilibrium with the pulmonary blood circulation are delineated, and experimental data are presented for the significant breath sample characteristics bearing on design of breath collection and storage systems (end expiratory temperature, breath volumes).
A brief review of the uses of breath analysis in studies of environmental exposure to volatile organic compounds (VOCs) is provided. The U.S. Environmental Protection Agency's large-scale Total Exposure Assessment Methodology Studies have measured concentrations of 32 target VOCs in the exhaled breath of about 800 residents of various U.S. cities. Since the previous 12-hr integrated personal air exposures to the same chemicals were also measured, the relation between exposure and body burden is illuminated. Another major use of the breath measurements has been to detect unmeasured pathways of exposure; the major impact of active smoking on exposure to benzene and styrene was detected in this way. Following the earlier field studies, a series of chamber studies have provided estimates of several important physiological parameters. Among these are the fraction, f, of the inhaled chemical that is exhaled under steady-state conditions and the residence times. tau i in several body compartments, which may be associated with the blood (or liver), organs, muscle, and fat. Most of the targeted VOCs appear to have similar residence times of a few minutes, 30 min, several hours, and several days in the respective tissue groups. Knowledge of these parameters can be helpful in estimating body burden from exposure or vice versa and in planning environmental studies, particularly in setting times to monitor breath in studies of the variation with time of body burden. Improvements in breath methods have made it possible to study short-term peak exposure situations such as filling a gas tank or taking a shower in contaminated water.
This review provides clinicians with a comprehensive overview of indirect calorimetry including the principles, methodology, technologic advancements, benefits, and challenges. Clinical applications for indirect calorimetry and the potential limitations are specifically addressed for both the inpatient and outpatient setting. Measurement of energy expenditure is the most accurate method to assess energy needs. Indirect calorimetry remains a gold standard in measuring energy expenditure in the clinical settings. The benefits of providing optimal nutrition for recovery from illness and chronic health management are well documented. Indirect calorimetry offers a scientifically-based approach to customize a patient's energy needs and nutrient delivery to maximize the benefits of nutrition therapy. With recent advances in technology, indirect calorimeters are easier to operate, more portable, and affordable. Increased utilization of indirect calorimetry would facilitate individualized patient care and should lead to improved treatment outcomes.
In this paper, we present the design and characterization of a low-power low-cost infra-red emitter based on a tungsten micro-hotplate fabricated in a commercial 1-μm SOI-CMOS technology. The device has a 250-μm diameter resistive heater inside a 600-μm diameter thin dielectric membrane. We first present electro-thermal and optical device characterization, long term stability measurements, and then demonstrate its application as a gas sensor for a domestic boiler. The emitter has a dc power consumption of only 70 mW, a total emission of 0.8 mW across the 2.5–15-μm wavelength range, a 50% frequency modulation depth of 70 Hz, and excellent uniformity from device-to-device. We also compare two larger emitters (heater size of 600 and 1800 μm) made in the same technology that have a much higher infra-red emission, but at the detriment of higher power consumption. Finally, we demonstrate that carbon nanotubes can be used to significantly enhance the thermo-optical transduction efficiency of the emitter.
Due to scarcity of accurate information and available data of actual human breathing, this investigation focuses on characterizing the breathing dynamic process based on the measurement of healthy human subjects. The similarities and differences between one breathing thermal manikin and the human subjects, including geometry and breathing functions, were thoroughly studied. As expected, actual human breathing is more complicated than that of the manikin in terms of airflow fluctuations, individual differences and exhaled flow directions. The simplification of manikin mouth structure could result in overestimated exhaled velocity and contaminant concentration. Furthermore, actual human breathing appears to be relatively stable and reproducible for an individual person in several conditions and is also accompanied by some uncertainties simultaneously. The averaged values are used to analyze the overall characteristics of actual human breathing. There are different characteristics of the exhaled breath between male and female subjects with or without wearing a nose clip. The experimental results obtained from the measurement of human subjects may be helpful for manikin specification or validation and accuracy assessment of CFD simulations. This article is protected by copyright. All rights reserved.
Non-dispersive infra-red (NDIR) gas detection has enjoyed widespread uptake as a result of development of devices in the standard miniature format for gas sensors, consisting of a cylinder with external dimensions of 20 mm diameter x 16.5 mm height. We present a new design for such a sensor, making use of low-cost injection moulding technology. The design pays particular attention to the problem of maintaining a high optical throughput while providing an acceptable optical pathlength for gas detection. A detailed analysis of the design is presented, with the results of optical raytracing, showing a raytrace estimate for 4% of the total emitted radiation reaching each of two separated detector elements and a pathlength of 32 mm. Finally, we show experimental results obtained with as-manufactured devices, with a short-term limit of detection for carbon dioxide (CO2) estimated at 1 ppm or a noise equivalent absorption (NEA) of 3 x 10(-5) AU.
The influence of passive construction improvements of a NDIR ethylene gas detector on the signal intensity and the detection limits were examined. Rectangularly and conically shaped measurement chambers with and without low-cost Fresnel lenses were used. Also the influence of the choice of the applied broadband IR-sources was investigated and an equation for detection limit estimation is described. In addition three digital signal processing methods were compared with results provided by a lock-in amplifier. It was shown that the best signal intensity can be achieved using a combination of a conically shaped chamber and Fresnel lenses. The IR-radiation measurement efficiency was improved from 0.8% to 4.2% in the best case. The achieved detection limits were 34 ppmv without and 25 ppmv with the lock in amplifier, the noise equivalent values 6 ppmv and 4 ppmv respectively. These limits match roughly with the calculation results and are comparable with results obtained with white cell systems.
During the last few years, thermopiles have come increasingly under the spotlight of commercial infrared sensing. This growing interest has motivated us to write an overview of micromachined thermopiles. The first part deals with the Seebeck effect and discusses the most important physical parameters with their interactions. We also describe the main noise sources and give a derivation of the figures of merit and their relevance for thermopile detectors. In the second part, a number of material systems, techniques and micromachined structures are discussed on the basis of different examples. We explain the motivation behind miniaturized thermopile detectors and give a functional explanation of physical interrelations. Finally, different applications are presented and discussed in terms of their future potential.
An infrared alcohol testing system based on differential absorption is presented. The technique relies on the fact that the breath alcohol gas has a unique, well-defined absorption characteristic within the infrared region of electromagnetic spectrum. It is used to detect the present and concentration of alcohol gas. The non-dispersive infrared gas detection principle is introduced in detail. Experiments show that the testing system has high precision, good environment adaptability, and its indication error and repeatability reach the China National Standards.
Obesity has long been recognized as having significant effects on respiratory function. The topic has been studied for at least the last half century, and some clear patterns have emerged. Obese patients tend to have higher respiratory rates and lower tidal volumes. Total respiratory system compliance is reduced for a variety of reasons, which will be discussed. Lung volumes tend to be decreased, especially expiratory reserve volume. Spirometry, gas exchange and airway resistance all tend to be relatively well preserved when adjusted for lung volumes. Patients may be mildly hypoxaemic, possibly due to ventilation-perfusion mismatching at the base of the lungs, where microatelectasis is likely to occur. Weight loss leads to a reversal of these changes. For all of these changes, the distribution of fat, that is, upper versus lower body, may be more important than body mass index.
Acetone in the human breath is an important marker for noninvasive diagnosis of diabetes. Here, novel chemo-resistive detectors have been developed that allow rapid measurement of ultralow acetone concentrations (down to 20 ppb) with high signal-to-noise ratio in ideal (dry air) and realistic (up to 90% RH) conditions. The detector films consist of (highly sensitive) pure and Si-doped WO(3) nanoparticles (10-13 nm in diameter) made in the gas phase and directly deposited onto interdigitated electrodes. Their sensing properties (selectivity, limit of detection, response, and recovery times) have been investigated as a function of operating temperature (325-500 degrees C), relative humidity (RH), and interfering analyte (ethanol or water vapor) concentration. It was found that Si-doping increases and stabilizes the acetone-selective epsilon-WO(3) phase while increasing its thermal stability and, thus, results in superior sensing performance with an optimum at about 10 mol % Si content. Furthermore, increasing the operation temperature decreased the detector response to water vapor, and above 400 degrees C, it was (<or=0.7) always below the threshold (10.6) for fake diabetes detection in ideal conditions. At this temperature and at 90% RH, healthy humans (<or=900 ppb acetone) and diabetes patients (>or=1800 ppb) can be clearly distinguished by a remarkable gap (40%) in sensor response. As a result, these solid state detectors may offer a portable and cost-effective alternative to more bulky systems for noninvasive diabetes detection by human breath analysis.
Triathlon is a sport consisting of sequential swimming, cycling and running. The main diversity within the sport of triathlon resides in the varying event distances, which creates specific technical, physiological and nutritional considerations for athlete and practitioner alike. The purpose of this article is to review physiological as well as nutritional aspects of triathlon and to make recommendations on ways to enhance performance. Aside from progressive conditioning and training, areas that have shown potential to improve triathlon performance include drafting when possible during both the swim and cycle phase, wearing a wetsuit, and selecting a lower cadence (60-80 rpm) in the final stages of the cycle phase. Adoption of a more even racing pace during cycling may optimise cycling performance and induce a "metabolic reserve" necessary for elevated running performance in longer distance triathlon events. In contrast, drafting in swimming and cycling may result a better tactical approach to increase overall performance in elite Olympic distance triathlons. Daily energy intake should be modified to reflect daily training demands to assist triathletes in achieving body weight and body composition targets. Carbohydrate loading strategies and within exercise carbohydrate intake should reflect the specific requirements of the triathlon event contested. Development of an individualised fluid plan based on previous fluid balance observations may assist to avoid both dehydration and hyponatremia during prolonged triathlon racing.
Designing a high temperature resistant IR-gas sensor for CO<sub>2</sub> and water vapor one has to consider the differences in the specific absorbances, spacings between the heated parts and optics/electronics, emission spectrum of cost-saving radiators and high humidity in the measuring gas. Using HITRAN database a sensor model was developed. Water vapor can be measured selectively at 1.85 μm with a chamber length of 20 cm. So CO<sub>2</sub> has to be measured at low wavelengths too. In the range of 2.7 μm CO<sub>2</sub> absorbs sufficiently but a water absorption is to be considered. The model shows that the CO<sub>2</sub> absorption reaches a maximum in the range from 2.7 μm to 2.75 μm with a decreasing water absorption with increasing wavelengths. After finishing the sensor the model was checked with the actual filter curves. The results show a good analogy between model data and measurements and the benefit of modeling in the design of IR-gas sensors. The analyze of cross sensitivity shows strong overlapping bands and a multiplicative influence of water absorption to the CO<sub>2</sub> signal. After correction of the absorption signal of 2.7 μm-channel with the absorption signal of the 1.85 μm-channel the cross sensitivity to water vapor was limited to <3% of CO<sub>2</sub> measuring range.
A new high-precision spectroscopic gas sensor measuring carbon dioxide (CO<sub>2</sub>) for harsh environmental conditions of automotive applications is presented. The carbon dioxide concentration is the primary parameter for sensing in cabin air quality, as well as an important safety parameter when R744 (carbon dioxide) is used as the refrigerant in the air conditioning system. The automotive environment challenges the potential sensor principles because of the wide temperature range from -40degC to +85degC, the atmospheric pressure from 700 to 1050 mbar, and relative humidity from 0% to 95%. The presented sensor system is based on the nondispersive infrared principle with new features for reaching high precision criteria and for enhancing long-term stability. A second IR source is used for internal recalibration of the primary IR source, redundancy purposes, and software plausibility checks. The CO<sub>2</sub> sensor system achieves an accuracy of better than plusmn5.5% over the whole temperature, pressure, and humidity ranges, with a resolution below 15 ppm and a response time shorter than 5 s. The operating time of the sensor system is more than 6000 h over a corresponding lifetime of more than 15 years. Experimental results show outstanding results for the intended automotive applications
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