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An attenuation loss spectrum of hollow optical fiber with an inner cyclic olefin polymer (COP) film. The inner diameter of the fiber is 700 µm and the length is 120 cm.
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A real-time gas monitoring system based on optical absorption spectroscopy is proposed for localized carbon dioxide (CO2) measurement in respiratory tracts. In this system, a small gas cell is attached to the end of a hollow optical fiber that delivers mid-infrared light with small transmission loss. The diameters of the fiber and the gas cell are...
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Context 1
... a result, the transmission loss of the fiber is much lower than the one without a dielectric layer at the targeted wavelength region. Figure 3 shows a loss spectrum of the hollow optical fiber with a COP inner layer used in the CO 2 measurement system. The small peak at 4.2 µm is from CO 2 contained in the air core of the fiber, and some absorption peaks of COP appear in the 3.5 µm and 6.5 µm wavelength regions. ...
Citations
... A real-time measurement of CO 2 concentration in human breath in 1 min shows the concentration in the range of 12,000 to 35,000 ppm in optical fiber probe (Katagiri et al. 2018) and 12,200 to 36,000 ppm in this developed sensor prototype. These figures show that this novel colorimetric CO 2 detection and quantification method would be a more precise analysis method. ...
The concentration of carbon dioxide (CO 2 ) in unhealthy people differs greatly from healthy people. High-precision CO 2 detection with a quick response time is essential for many biomedical applications. A major focus of this research is on the detection of CO 2 , one of the most important health biomarkers. We investigated a low-cost, flexible, and reliable strategy by using dyes for colorimetric CO 2 sensing in this study. The impacts of temperature, pH, reaction time, reusability, concentration, and dye selectivity were studied thoroughly. This study described real-time CO 2 analysis. Using this multi-dye method, we got an average detection limit of 1.98 ppm for CO 2 , in the range of 50–120 ppm. A portable colorimetric instrument with a smartphone-assisted unit was constructed to determine the relative red/green/blue values for real-time and practical applications within 15 s of interaction and the readings are very similar to those of an optical fiber probe. Environmental and biological chemistry applications are likely to benefit greatly from this unique approach.
... Recently, it has been developed a small gas cell attached to the distal end of a thin optical fiber probe, that could be inserted into airways via a catheter or a bronchoscope [76]. The target gas penetrates the cell through small holes. ...
There is a growing need to measure respiratory rate (RR) in a variety of applications, including in clinical and occupational settings, as well as during physical exercises. Fiber optic sensors (FOSs) is an attractive solution for wearable RR monitoring because of their small size, multiplexing capability, chemical inertness, and immunity to electromagnetic fields. Here, we review recent advances in FOSs for breath monitoring. We presented the sensing mechanisms of state-of-the-art sensors and analyze their advantages and disadvantages. We classified recently reported FOSs based on sensing principles and then critically analyze the strengths and weaknesses of representative recent works. Finally, we summarized the challenges and future prospects of breath FOSs, with the aim of applying them to real applications.
... Quantum cascade laser-based absorption spectroscopy (QCLAS) thus uniquely combines several major advantages, such as high sensitivity, exceptional time-resolution, and the possibility to perform real-time in situ measurements. In recent years, QCLAS has proved to be an essential probe of CO 2 in, e.g., biomedical breath analysis [3][4][5][6][7], the investigation of plasma and combustion processes [8,9], or environmental and atmospheric gas sensing [10][11][12][13]. ...
A quantum cascade laser-based sensing technique is presented which allows for in situ high-precision temperature and/or CO2 concentration measurements of gases in the room temperature regime with sampling rates up to about 40 kHz. The method is based on Boltzmann-like thermally populated fundamental and hot-band rovibrational transitions of CO2 with opposite temperature dependence. Single absorption spectra at about 2350 to 2352 cm−1 are recorded by a nanosecond frequency down chirped IR pulse of a pulsed distributed feedback quantum cascade laser (intrapulse mode). The statistical uncertainty (1σ) in the temperature measurement within one laser pulse is about 1 K and can be further reduced down to about 0.1 K by time averaging over 100 ms. Online temperature and CO2 concentration measurements on a breath simulator controlled gas flow were performed to demonstrate response-time and sensitivity for an application-driven test system.
... Recently, it has been developed a small gas cell attached to the distal end of a thin optical fiber probe, that could be inserted into airways via a catheter or a bronchoscope [76]. The target gas penetrates the cell through small holes. ...
... The reaction and absorption spectra given by NiO/rGO coatings [116] yield similar results to spectroscopic sensors but with a faster response over the same concentration ranges. Another point of concern with cavity sensors [112,113,187,188] is that they need additional apparatus to deliver the gas sample into the cavities, either via vacuum or high pressure, which is not needed for reactive coatings, such as NiO/rGO [116] or FOM [123,189]. Furthermore, for industrial monitoring applications of control processes, all sensors operate over a wider range, and have relatively slow response times [114,115,117,122,123]. ...
At the present time, there are major concerns regarding global warming and the possible catastrophic influence of greenhouse gases on climate change has spurred the research community to investigate and develop new gas-sensing methods and devices for remote and continuous sensing. Furthermore, there are a myriad of workplaces, such as petrochemical and pharmacological industries, where reliable remote gas tests are needed so that operatives have a safe working environment. The authors have concentrated their efforts on optical fibre sensing of gases, as we became aware of their increasing range of applications. Optical fibre gas sensors are capable of remote sensing, working in various environments, and have the potential to outperform conventional metal oxide semiconductor (MOS) gas sensors. Researchers are studying a number of configurations and mechanisms to detect specific gases and ways to enhance their performances. Evidence is growing that optical fibre gas sensors are superior in a number of ways, and are likely to replace MOS gas sensors in some application areas. All sensors use a transducer to produce chemical selectivity by means of an overlay coating material that yields a binding reaction. A number of different structural designs have been, and are, under investigation. Examples include tilted Bragg gratings and long period gratings embedded in optical fibres, as well as surface plasmon resonance and intra-cavity absorption. The authors believe that a review of optical fibre gas sensing is now timely and appropriate, as it will assist current researchers and encourage research into new photonic methods and techniques.
... A real-time gas monitoring system based on FTIR spectroscopy was proposed for CO 2 measurement in the respiratory tract. 75 A small gas cell was attached to the end of a hollow optical fiber that delivers mid-infrared light with small transmission loss in this system. The fiber diameter was smaller than 1.2 mm, so it can be inserted into a bronchoscope working channel (Fig. 2.10). ...
... During routine FTIR-based quantification of carbon dioxide in breath, it is necessary to account for a nonlinear signal response to the analyte Figure 2.10 A fiber-optic probe system for localized gas analysis in a respiratory tract. 75 concentration and disturbance factors arising from the gas background matrix. These factors, as well as day-to-day fluctuation, should be corrected via calibration. ...
... Microphones, instead, which represent the most common acoustic sensors, allow the measurement of pressure changes caused by the air turbulences during the breathing acts [16][17][18][19][20]. Air temperature sensors (e.g., thermistors, thermocouples) exploit different physical phenomena to measure the temperature variations of the breathed air [21][22][23][24][25][26], whereas air humidity sensors (e.g., capacitive sensors, resistive sensors, nanocrystal and nanoparticle sensors) provide a measurement of the humidity difference in the inhaled and exhaled air, since the latter is richer in water vapor than the former [27][28][29][30][31][32][33][34]. Besides, air component sensors (e.g., end-tidal O 2 /CO 2 measurement) measure essentially the variations of oxygen and carbon dioxide concentrations in the air, which allow distinguishing the inhalation and exhalation phases [35][36][37][38]. Sensors based on chest wall movements, instead, are substantially sensitive to the deformations of the thorax (e.g., resistive sensors, capacitive sensors) [39][40][41][42][43][44][45][46][47] and to the movements of the chest and abdomen (e.g., accelerometers, gyroscopes) [48][49][50][51][52]. Electric impedance plethysmography measures the changes in transthoracic impedance caused by the variations of air volume in the lungs involved in the respiratory activity [53][54][55][56]. ...
In the last few decades, a number of wearable systems for respiration monitoring that help to significantly reduce patients’ discomfort and improve the reliability of measurements have been presented. A recent research trend in biosignal acquisition is focusing on the development of monolithic sensors for monitoring multiple vital signs, which could improve the simultaneous recording of different physiological data. This study presents a performance analysis of respiration monitoring performed via forcecardiography (FCG) sensors, as compared to ECG-derived respiration (EDR) and electroresistive respiration band (ERB), which was assumed as the reference. FCG is a novel technique that records the cardiac-induced vibrations of the chest wall via specific force sensors, which provide seismocardiogram-like information, along with a novel component that seems to be related to the ventricular volume variations. Simultaneous acquisitions were obtained from seven healthy subjects at rest, during both quiet breathing and forced respiration at higher and lower rates. The raw FCG sensor signals featured a large, low-frequency, respiratory component (R-FCG), in addition to the common FCG signal. Statistical analyses of R-FCG, EDR and ERB signals showed that FCG sensors ensure a more sensitive and precise detection of respiratory acts than EDR (sensitivity: 100% vs. 95.8%, positive predictive value: 98.9% vs. 92.5%), as well as a superior accuracy and precision in interbreath interval measurement (linear regression slopes and intercepts: 0.99, 0.026 s (R2 = 0.98) vs. 0.98, 0.11 s (R2 = 0.88), Bland–Altman limits of agreement: ±0.61 s vs. ±1.5 s). This study represents a first proof of concept for the simultaneous recording of respiration signals and forcecardiograms with a single, local, small, unobtrusive, cheap sensor. This would extend the scope of FCG to monitoring multiple vital signs, as well as to the analysis of cardiorespiratory interactions, also paving the way for the continuous, long-term monitoring of patients with heart and pulmonary diseases.
... Chemical sensors have also been used in this field to analyze breathing air components and obtain the RR from the results of analyses. Katagiri et al. [23] presented a sensor to measure carbon dioxide (CO 2 ) based on optical absorption spectroscopy. Other chemical approaches were discussed in the surveys by Imani et al. [24] and Güntner et al. [25]. ...
Respiratory rate is an important parameter for many health, home care, work, or sport applications. In this paper, a new wearable sensing system based on a piezoresistive FlexiForce sensor has been developed. The sensor can be attached to any common chest strap. A compact 3D casing has been designed and printed with a 3D printer. This casing integrates the sensor and all auxiliary elements of the system: microcontroller, battery, Bluetooth module, connections, battery charger, and acquisition circuit. To the best of our knowledge, this is the first study presenting a FlexiForce respiration sensor that includes all system elements in a single compact casing. The source files with the design of the casing have been published as supplementary material to be reused by any interested researcher. The sensing system was tested with twenty-one subjects for different breathing rates. Two different algorithms were developed to obtain the respiratory rate from the voltage signals recorded by the sensor. Statistical tests were performed to determine the optimal computation time window and algorithm. This approach is also novel in this field. Low error values were obtained for a time window of 27 s with an algorithm based on the calculation of time between zero-crossings (4.02%) and with an algorithm based on counting them (3.40%). To promote research transparency and reusability, the dataset with the recorded data and the source code of the algorithms and statistical tests have also been published. Therefore, an open, replicable, low-error, wearable, wireless, and compact sensing system to measure respiratory rate was developed and tested.
... V(CO 2 ) is the voltage output. The scheme of fiber-optic sensors is adapted from [148]. ...
... Flexible hollow optical fiber that shows low transmission loss for mid-infrared light has been used. Recently, it has been developed a small gas cell attached to the distal end of a thin optical fiber probe that could be inserted into airways via a catheter or a bronchoscope [148]. The target gas penetrates the cell through small holes. ...
... The measurement of the CO 2 is then obtained with Fourier-transform infrared spectroscopy. Measurement error of the mentioned system is ±0.3%, minimum threshold of 0.45% of CO 2 [148]. ...
There is an ever-growing demand for measuring respiratory variables during a variety of applications, including monitoring in clinical and occupational settings, and during sporting activities and exercise. Special attention is devoted to the monitoring of respiratory rate because it is a vital sign, which responds to a variety of stressors. There are different methods for measuring respiratory rate, which can be classed as contact-based or contactless. The present paper provides an overview of the currently available contact-based methods for measuring respiratory rate. For these methods, the sensing element (or part of the instrument containing it) is attached to the subject’s body. Methods based upon the recording of respiratory airflow, sounds, air temperature, air humidity, air components, chest wall movements, and modulation of the cardiac activity are presented. Working principles, metrological characteristics, and applications in the respiratory monitoring field are presented to explore potential development and applicability for each method.
