No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Abstract
In this study, a wearable thermoelectric generator (TEG) in the flexible fabric is proposed for converting human body heat energy to electrical energy. The wearable TEG is composed of a flexible fabric material, thermoelectric columns (Bi2Te3) and electrical connection based on conductive fabric component. The proposed TEG showed the flexibility and the wearability suitable to be applied to the human body. The TEG was fabricated dispenser printing, and the fabricated device converted applied contact heat into electrical energy (0.98 μV/K). When the TEG applied to the human body, the measured output power was 178 nW in ambient temperature of 5 °C.
... 78,[80][81][82]100,[328][329][330][331] Generally, there are several ways to fabricate thermoelectric fabrics. On the one hand, these fabrics can be used as flexible substrates for supporting inorganic thermoelectric bulks/ films 27,83,332 and thermoelectric yarns, 64 such as the case shown in Fig. 9(i). On the other hand, these fabrics can be directly modified to possess thermoelectric features, such as infiltration or depositing/coating thermoelectric materials on their surfaces. ...
... In terms of the F-TEG, Fig. 11(a) shows the concept views of a F-TEG based on dispenser-printed inorganic materials on the fabric. 332 The fabric acted as the substrate of the F-TEG, and the conductive thread linked the dispenser-printed n-p thermoelectric materials, both providing the flexibility. Fig. 11(b) shows optical images of a 20-couple F-TEG printed with n-p Bi 2 Te 3 100-mesh powder. ...
... Fig. 11(b) shows optical images of a 20-couple F-TEG printed with n-p Bi 2 Te 3 100-mesh powder. 332 The as-designed F-TEG can be worn on the human body, showing good flexibility. By a DT of 30 K, an output voltage of B25 mV and an output power of 42 mW could be realized. ...
With the growing demand for solid, portable, and wearable electronics, exploring recyclable and stable charging and cooling techniques is of significance. Fiber-based thermoelectrics, enabling sustainable power generation driven by the temperature difference or refrigeration without noise and freon, exhibit great potentials for applying in advanced electronics. In this work, we review significant advances in fiber-based thermoelectrics, including inorganic fibers, organic fibers, inorganic/organic hybrid fibers, and fiber-based fabrics and devices. Fundamentals, synthesis, characterizations, property evaluation, and applications of thermoelectric fibers are comprehensively discussed with carefully selected cases, and corresponding thermoelectric devices based on these advanced fibers are introduced for both power generation and refrigeration. Further, we point out the challenges and future directions toward developments of fiber-based thermoelectrics.
... On the other hand, there have been efforts to synthesize paste-type inorganic materials to make them flexible and screen-printable. 20,21 In this paper, we first review the recent development of wearable thermoelectric generators, and discuss potential applications of these TEGs such as healthcare monitoring. Then we review recent flexible thermoelectric materials and the physics behind the ZT enhancement in these materials with discussion on charge transport mechanisms. ...
... By rolling up such a long stripe with a large number of TE elements, a voltage higher than 0.8 V was achieved for a small temperature difference like 5 1C in the transverse direction. Kim et al. 20 printed paste-type thermoelectric materials within holes in a polymer fabric using the dispenser printing method, and used silver-plated conductive fibers as electrodes connecting TE elements to fabricate highly flexible wearable TEGs. This TEG generated 178 nW power at an ambient temperature of 5 1C when worn on a human chest at 32 1C. ...
... In addition, there have been efforts to synthesize inorganic materials as paste-type so they can be printed on a flexible substrate while maintaining their high power factors. Kim et al. 20 mixed the Bi 2 Te 3 -based powders in a ceramic binder to make both p-type and n-type TE material pastes and printed 500 mm thick and 10 mm diameter TE elements on a flexible polyethylene terephthalate (PET) substrate using the dispenser printing method. The B. J. Cho team synthesized both n-type Bi 2 Te 3 and p-type Sb 2 Te 3 pastes that are screen-printable on a glass fabric. ...
In this paper, we review recent advances in the development of flexible thermoelectric materials and devices for wearable human body-heat energy harvesting applications. We identify various emerging applications such as specialized medical sensors where wearable thermoelectric generators can have advantages over other energy sources. To meet the performance requirements for these applications, we provide detailed design guides regarding the material properties, device dimensions, and gap fillers by performing realistic device simulations with important parasitic losses taken into account. For this, we review recently emerging flexible thermoelectric materials suited for wearable applications, such as polymer-based materials and screen-printed paste-type inorganic materials. A few examples among these materials are selected for thermoelectric device simulations in order to find optimal design parameters for wearable applications. Finally we discuss the feasibility of scalable and cost-effective manufacturing of thermoelectric energy harvesting devices with desired dimensions.
... of thermoelectric fabric using dispenser printing [6] The fabrication of fabric based thermoelectric module significantly attracts interest by its flexibility durability. The final product of the fabrication is depicted inFigure 10 which shows the characteristic of the fabric and its design properties. ...
... By aiming thermoregulation process from human body, heat will be an incessant source of energy for thermoelectric energy harvester. From the research done by Kim's research team [6], a prototype of thermoelectric wearable device was produced. The device was produced and applied in fabric which is flexible and lightweight material. ...
... The device was produced and applied in fabric which is flexible and lightweight material. The fabrication of the thermoelectric fabric can be referred to Figure 9. [6] The fabrication of fabric based thermoelectric module significantly attracts interest by its flexibility durability. The final product of the fabrication is depicted in Figure 10which shows the characteristic of the fabric and its design properties. ...
Thermoelectric energy (or power) harvester is a kind of renewable energy approach that extracts waste heat from targeted device or object to generate electrical power. It is an advance technology widespread among researchers for decades. By having plenty of promising advantages, the thermo-electric power harvester is being developed in types of feasible interfaces. This review paper focused on research had been done relating to thermo-electric power harvester, in the macro scale and mainly in the micro scale of power harvester. Several designs of thermo-electric technologies will be further discussed in this paper. This paper reveals the viability of thermo-electric power harvester in sustaining electric supply for micro-electronics applications. Eventually, some add-on is being proposed at the last part of the paper.
... At a temperature difference of 19 K between human skin and the air, the W.E.H. generated a power of 2.1 μW. Fig. 9(h) illustrates the WTEH developed by Kim et al. [152] and is incorporated into a fabric. Silver-plated conductive fiber is used for the electric connections, and a polyester-based fabric is chosen. ...
... This sweat glucose sensor, can be powered using photovoltaic cell, allowing for real time data analyzation and display on screen. Toh et al. [145]; (b) WTEH schematic by Leonov et al. [146]; (c) watch-like WTEH provided a complete power to a pulse oximeter [109]; (d) flexible T.E.G. by Weber et al. [148]; (e) self-powered glucose sensing device by Kim et al. [149]; (f) WTEH created by Hoang et al. [150]; (g) WTEH proposed by Jo et al. [151]; (h) WTEH developed by Kim et al. [152]. ...
This paper provides a comprehensive review of the recent progress made in energy harvesting systems for wearable technology. An energy-harvesting system would be a useful strategy to address the issue of powering wearable electronic devices. This review presents different wearable energy harvesting methods based on the human body's heat and mechanical energy. To achieve continuous operation and high performance, reduce the requirement for external sources of energy, and enhance the lifespan of wearable devices, the invention of a sustainable and compatible power supply is required. In the human body, heat and mechanical motions are the two reliable and readily available energy sources. This study highlights the most recent research and advancements in energy harvesting from the human's mechanical motion and heat source. This article provides a detailed overview of the different wearable energy harvesters, their fabrication, working, and output results, which include piezoelectric, electrostatic, triboelectric, electromagnetic, thermoelectric, solar and hybrid wearable energy harvesters. The second part defines wearable energy harvesting using smart systems and artificial intelligence technology. Then the comparison of these energy harvesters is analyzed. Hybrid wearable energy harvesters provide the maximum power densities because they use two combined energy conversions. The advantages, limitations, and future perspectives of wearable energy harvesting technology are also discussed. Lastly, the wearable energy harvesters' market, and general developing and manufacturing cost of each wearable device is also presented functioning as a point of reference to comprehend the cost factors that are taken into account during the development and manufacturing processes.
... Electricity 2021, 2, FOR PEER REVIEW 19 Figure 15. TEG and TEC in applications [148][149][150][151][152][153][154][155][156][157]. ...
... In this section, a review of the researchers' challenges while researching is presented Figure 15. TEG and TEC in applications [148][149][150][151][152][153][154][155][156][157]. Figure 15 shows that after the mid-1990s, thermoelectricity has come with the flow of novel ideas. Furthermore, working on enhancing TEG is an ongoing process, which also continues for future expectations, where theoretical expectations recommended that TEG efficiency could be impressively improved due to the nanostructure engineering [152], besides the hope for designing a better TEG has always been a target that the scientists work on especially after the innovation of the nanometer scale. ...
Electricity plays a significant role in daily life and is the main component of countless applications. Thus, ongoing research is necessary to improve the existing approaches, or find new approaches, to enhancing power generation. The thermoelectric generator (TEG) is among the notable and widespread technologies used to produce electricity, and converts waste energy into electrical energy using the Seebeck effect. Due to the Seebeck effect, temperature change can be turned into electrical energy; hence, a TEG can be applied whenever there is a temperature difference. The present paper presents the theoretical background of the TEG, in addition to a comprehensive review of the TEG and its implementation in various fields. This paper also sheds light on the new technologies of the TEG and their related challenges. Notably, it was found that the TEG is efficient in hybrid heat recovery systems, such as the phase change material (PCM), heat pipe (HP), and proton exchange membrane (PEM), and the efficiency of the TEG has increased due to a set of improvements in the TEG’s materials. Moreover, results show that the TEG technology has been frequently applied in recent years, and all of the investigated papers agree that the TEG is a promising technology in power generation and heat recovery systems.
... Francioso et al. [123] developed a flexible and wearable micro thermoelectric generator, composed of an array of 100 thin film thermocouples of Sb 2 Te 3 and Bi 2 Te 3 , designed to power very low-consumption electronical ambient assisted living (AAL) applications. The best result obtained was 430 mV in open circuit, and an electrical output power up to 32 nW at 40 • C. Kim et al. [140] manufactured a flexible fabric-shaped TEG, with 3D printing technology, composed of 20 thermocouples and with a thickness of 0.5 mm, as shown in Figure 13a. The TEG, when applied to a human body, generated an electrical power of 25 mV at an ambient temperature of 5 • C. A new approach was presented by Suarez et al. [141], using standard bulk legs interconnected to a stretchable low-resistivity eutectic alloy of gallium and indium (EGaIn), all in a flexible elastomer package, as shown in Figure 13b. ...
... The best result obtained was 430 mV in open circuit, and an electrical output power up to 32 nW at 40 °C. Kim et al. [140] manufactured a flexible fabric-shaped TEG, with 3D printing technology, composed of 20 thermocouples and with a thickness of 0.5 mm, as shown in Figure 13a. The TEG, when applied to a human body, generated an electrical power of 25 mV at an ambient temperature of 5 °C. ...
... Francioso et al. [123] developed a flexible and wearable micro thermoelectric generator, composed of an array of 100 thin film thermocouples of Sb 2 Te 3 and Bi 2 Te 3 , designed to power very low-consumption electronical ambient assisted living (AAL) applications. The best result obtained was 430 mV in open circuit, and an electrical output power up to 32 nW at 40 • C. Kim et al. [140] manufactured a flexible fabric-shaped TEG, with 3D printing technology, composed of 20 thermocouples and with a thickness of 0.5 mm, as shown in Figure 13a. The TEG, when applied to a human body, generated an electrical power of 25 mV at an ambient temperature of 5 • C. A new approach was presented by Suarez et al. [141], using standard bulk legs interconnected to a stretchable low-resistivity eutectic alloy of gallium and indium (EGaIn), all in a flexible elastomer package, as shown in Figure 13b. ...
... The best result obtained was 430 mV in open circuit, and an electrical output power up to 32 nW at 40 °C. Kim et al. [140] manufactured a flexible fabric-shaped TEG, with 3D printing technology, composed of 20 thermocouples and with a thickness of 0.5 mm, as shown in Figure 13a. The TEG, when applied to a human body, generated an electrical power of 25 mV at an ambient temperature of 5 °C. ...
A thermoelectric effect is a physical phenomenon consisting of the direct conversion of heat into electrical energy (Seebeck effect) or inversely from electrical current into heat (Peltier effect) without moving mechanical parts. The low efficiency of thermoelectric devices has limited their applications to certain areas, such as refrigeration, heat recovery, power generation and renewable energy. However, for specific applications like space probes, laboratory equipment and medical applications, where cost and efficiency are not as important as availability, reliability and predictability, thermoelectricity offers noteworthy potential. The challenge of making thermoelectricity a future leader in waste heat recovery and renewable energy is intensified by the integration of nanotechnology. In this review, state-of-the-art thermoelectric generators, applications and recent progress are reported. Fundamental knowledge of the thermoelectric effect, basic laws, and parameters affecting the efficiency of conventional and new thermoelectric materials are discussed. The applications of thermoelectricity are grouped into three main domains. The first group deals with the use of heat emitted from a radioisotope to supply electricity to various devices. In this group, space exploration was the only application for which thermoelectricity was successful. In the second group, a natural heat source could prove useful for producing electricity, but as thermoelectricity is still at an initial phase because of low conversion efficiency, applications are still at laboratory level. The third group is progressing at a high speed, mainly because the investigations are funded by governments and/or car manufacturers, with the final aim of reducing vehicle fuel consumption and ultimately mitigating the effect of greenhouse gas emissions.
... Francioso et al. [123] developed a flexible and wearable micro thermoelectric generator, composed of an array of 100 thin film thermocouples of Sb 2 Te 3 and Bi 2 Te 3 , designed to power very low-consumption electronical ambient assisted living (AAL) applications. The best result obtained was 430 mV in open circuit, and an electrical output power up to 32 nW at 40 • C. Kim et al. [140] manufactured a flexible fabric-shaped TEG, with 3D printing technology, composed of 20 thermocouples and with a thickness of 0.5 mm, as shown in Figure 13a. The TEG, when applied to a human body, generated an electrical power of 25 mV at an ambient temperature of 5 • C. A new approach was presented by Suarez et al. [141], using standard bulk legs interconnected to a stretchable low-resistivity eutectic alloy of gallium and indium (EGaIn), all in a flexible elastomer package, as shown in Figure 13b. ...
... The best result obtained was 430 mV in open circuit, and an electrical output power up to 32 nW at 40 °C. Kim et al. [140] manufactured a flexible fabric-shaped TEG, with 3D printing technology, composed of 20 thermocouples and with a thickness of 0.5 mm, as shown in Figure 13a. The TEG, when applied to a human body, generated an electrical power of 25 mV at an ambient temperature of 5 °C. ...
A thermoelectric effect is a physical phenomenon consisting of the direct conversion of heat into electrical energy (Seebeck effect) or inversely from electrical current into heat (Peltier effect) without moving mechanical parts. The low efficiency of thermoelectric devices has limited their applications to certain areas, such as refrigeration, heat recovery, power generation and renewable energy. However, for specific applications like space probes, laboratory equipment and medical applications, where cost and efficiency are not as important as availability, reliability and predictability, thermoelectricity offers noteworthy potential. The challenge of making thermoelectricity a future leader in waste heat recovery and renewable energy is intensified by the integration of nanotechnology. In this review, state-of-the-art thermoelectric generators, applications and recent progress are reported. Fundamental knowledge of the thermoelectric effect, basic laws, and parameters affecting the efficiency of conventional and new thermoelectric materials are discussed. The applications of thermoelectricity are grouped into three main domains. The first group deals with the use of heat emitted from a radioisotope to supply electricity to various devices. In this group, space exploration was the only application for which thermoelectricity was successful. In the second group, a natural heat source could prove useful for producing electricity, but as thermoelectricity is still at an initial phase because of low conversion efficiency, applications are still at laboratory level. The third group is progressing at a high speed, mainly because the investigations are funded by governments and/or car manufacturers, with the final aim of reducing vehicle fuel consumption and ultimately mitigating the effect of greenhouse gas emissions.
... To directly acquire waste heat without the energy transformation, scientists since the last century used thermoelectric generator (TEG) to convert thermal energy into electrical energy based on Seebeck effect, and the research works were continuously thriving. Because of the fast growth on semiconductor industry recently, new applications on TEG, especially for the power supplies on wearable devices [1][2], were prospected. With thin film and miniature thermoelectric devices [3][4][5] which bundle the human body or the electronic packaging, body heat or waste heat in an electronic packaging/system can be recycled into electricity through a flexible and wearable device without environmental limitation. ...
... To provide a suitable and convenient Seebeck coefficient measurement methodology on thin film thermoelectric devices, a testing platform design was proposed in this study according to the following requirements: (1) Eliminating the metallization process for metal electrodes so that the conventional bulk materials measurement methodologies, such as probing, can be directly employed. (2) Eliminating the substrate effect on temperature distribution on the thin film samples, as mentioned previously. Accordingly, a thin film thermoelectric device Seebeck coefficient measurement system as shown in Figure 1 were designed and manufactured. ...
This paper developed a new methodology which is a sandwich-like platform to measure Seebeck coefficient for single layer thin-film thermoelectric devices which are flexible and wearable without environmental limitation. With our new apparatus, a stably controlled temperature gradient environment is created on thin-film test samples so that the commonly used and simple probing can be employed for Seebeck coefficient measurements. This paper finally verified the accuracy and availability of the new experimental design through Seebeck coefficient measurements on a typical organic conductive material (PEDOT)
... Regarding flexible and eco-friendly substrates, paper has been in focus for printed electronic applications, including toin the fabricatefabrication of TE sensors and generatorsdevices, due to its flexibility, abundance, and biodegradable nature [12,[17][18][19][20][21]. Meanwhile, fabrics have also been explored, with research being allocated to substrates like polyester [14,22,23], glassfiber fabric [24,25], or cotton [26,27] which has valuable properties for wearable and flexible applications, such as its breathability, foldability, and elastic recovery [28]. ...
Despite the undoubtable interest in energy conversion, thermoelectric materials can be approached from a temperature-sensitive perspective, as they can detect small thermal stimuli, such as a human touch or contact with cold/hot objects. This feature offers possibilities for different applications being one of them the integration with scalable and cost-effective, biocompatible, flexible, and lightweight thermal sensing solutions, exploring the combination of sustainable Seebeck coefficient-holding materials with printing techniques and flexible substrates.
In this work, ethyl cellulose and graphite flakes inks were optimized to be used as functional material for flexible thermal touch sensors produced by screen-printing. Graphite concentrations of 10, 20 and 30 wt% were tested, with 1, 2 and 3 printed layers on four different substrates - office paper, sticker label paper, standard cotton, and organic cotton. The conjugation of these variables was assessed in terms of printability, sheet resistance and thermoelectric response. The best electrical-thermoelectric output combination is achieved by printing 2 layers of the ink with 20 wt% of graphite on office paper substrate. Subsequently, thermal touch sensors with up to 48 thermoelectric elements were produced to increase the output voltage response (> 4.5 mV) promoted by a gloved finger touch. Fast and repeatable touch recognition was obtained in optimized devices with a signal-to-noise ratio up to 340 and rise times bellow 0.5 s. The results evidence that the screen-printed graphite-based inks are highly suitable for flexible thermoelectric sensing applications.
... Similarly, a F-TEG, composed of p-type nylon fibers coated by Ag 2 Te nanocrystals and n-type nylon fibers coated by PEDOT:PSS, shows a ω of 6 mW m − 2 at a ΔT of 20 K [574]. Other works also report directly printed inorganic nanomaterials on organic substrates, such as polyester fabrics printed by Bi 2 Te 3 [575], polymer fabrics printed by Bi 0.5 Sb 1.5 Te 3 [576], and silk fabric deposited by nanostructured Sb 2 Te 3 [577]. Sometimes more complicated hybrids were designed for F-TEDs, such as core-shell-heterostructure Bi 2 S 3 @Bi nanorods/ polyaniline hybrids [578]. ...
Owing to their capabilities of solid-state conversion between heat and electricity, zero-emission, and high flexibility, flexible thermoelectric devices (F-TEDs) have exhibited great application possibilities for both portable power generation and localized refrigeration. However, with the rapid development of thermoelectric science and technology, there is still a lack of comprehensive review on the rational design of F-TEDs from the fundamentals to structures, which critically determines the performance and conformality of F-TEDs. To address this issue, here, we timely overview the latest progress on the up-to-the-date F-TEDs with their unique designs. We carefully summarize the structure-related principles and factors that determine the performance of F-TEDs and the advanced strategies for improving their utilities. Besides, we focus on the timeliest designs for the inorganic-based devices, organic-based devices, and hybrid-based devices targeting both power generation and refrigeration. In the end, we point out the current challenges, controversies, and prospects of F-TEDs.
... Moreover, various types of miniaturized power supply or generation devices called ''power MEMS'' have recently been developed for driving MEMS devices, for example, by vibration (Feng et al. 2018). Thermal energy such as body temperature was also used as a source for generating electrical power (Kim et al. 2013). ...
We propose an easy-to-use energy-less respiration monitoring device for monitoring the breathing flow using a thermo-sensitive film. Thermo-sensitive film less than 0.01 mm thick with thermo-sensitive ink and a base film were wrapped over the aperture and partially produced in the tube for monitoring the breathing status. The aperture used as the respiration monitoring area, also worked as thermal isolation to shorten the response time and to decrease thermal capacity in the monitoring area. The response time was investigated using a response evaluation device (designed and produced using MEMS technology) to follow the temperature change with the breathing cycle of 0.3 Hz. The response time depended on the thickness of both the ink and the base film and decreased with the decrease of the thickness due to thermal capacity reduction. The obtained minimum response time was 373 ms when the ink thickness was 6.8 μm and the base film thickness was less than 5.0 μm. The color of the ink at the breathing monitoring area formed on the aperture successfully changed from blue to transparent according to the temperature change of the airflow.
... Polymer-based fabric and silk fabric, etc., can also be used as the substrates for flexible TEGs, due to their advantages, such as flexible, low-cost, and low-density. For example, a flexible TEG fabricated by dispenser printed the mixture of ceramic binder and Bi 2 Te 3 powder (p-type and ntype, respectively) into the windows of the fabric was reported, and a maximum power output for the TEG with 20 thermocouples was 2.08 W at T = 30 K. When the flexible TEG was attached to the human body (chest), a power output of 178 nW was obtained in ambient temperature of 5 • C [177]. Kim et al. [178] fabricated a wearable TEG by dispenser printing of p-type Bi 0.5 Sb 1.5 Te 3 and n-type Bi 2 Se 0.3 Te 2.7 printable ink in a polymerbased fabric. ...
Thermoelectric generators (TEGs) can directly convert waste heat into electrical power. In the last few decades, most research on thermoelectrics has focused on inorganic bulk thermoelectric materials and corresponding devices, and their thermoelectric properties have been significantly improved. An emerging topic is flexible devices, where the use of bulk inorganic materials is precluded by their inherent rigidity. The purpose of this paper is to review the research progress on flexible thermoelectric materials and generators, including theoretical principles for TEGs, conducting polymer TE materials, nanocomposites comprised of inorganic nanostructures in polymer matrices and fully inorganic flexible TE materials in nanostructured thin films. Approaches for flexible TEGs and components are reviewed, and remaining challenges discussed.
... Therefore, researchers have been trying to use different methods to treat the inorganic materials. Kim et al. [58] reported a method that converts the inorganic materials from powder-type to paste-type by mixing them with binders. Later, they use the dispenser-printing method to print them on a flexible polymer substrate. ...
Recent advances in flexible thermoelectric (TE) materials and devices are reviewed in this chapter. A background on TE energy conversion is first discussed followed by the progress in the field over the past few decades. Flexible TE materials based on conducting polymers as well as emerging TE materials based on carbon nanotubes and graphene are illustrated. Advances in the development of thermoelectric generators (TEGs) are discussed, and a recent transition from rigid, inorganic TE material based devices to flexible TEGs is reviewed. Various device architectures for realizing three‐dimensional TE devices from planar flexible TEGs to transverse‐type devices are introduced and compared. Finite element method (FEM) simulations for power generation of transverse TEGs are presented to assess their potential applications in wearable energy harvesting. Finally, the recent research in flexible TE sensors is briefly discussed.
A rapidly expanding global population and a sizeable portion of it that is aging are the main causes of the significant increase in healthcare costs. Healthcare in terms of monitoring systems is undergoing radical changes, making it possible to gauge or monitor the health conditions of people constantly, while also removing some minor possibilities of going to the hospital. The development of automated devices that are either attached to organs or the skin, continually monitoring human activity, has been made feasible by advancements in sensor technologies, embedded systems, wireless communication technologies, nanotechnologies, and miniaturization being ultra-thin, lightweight, highly flexible, and stretchable. Wearable sensors track physiological signs together with other symptoms such as respiration, pulse, and gait pattern, etc., to spot unusual or unexpected events. Help may therefore be provided when it is required. In this study, wearable sensor-based activity-monitoring systems for people are reviewed, along with the problems that need to be overcome. In this review, we have shown smart detecting and versatile wearable electrical sensing mediums in healthcare. We have compiled piezoelectric-, electrostatic-, and thermoelectric-based wearable sensors and their working mechanisms, along with their principles, while keeping in view the different medical and healthcare conditions and a discussion on the application of these biosensors in human health. A comparison is also made between the three types of wearable energy-harvesting sensors: piezoelectric-, electrostatic-, and thermoelectric-based on their output performance. Finally, we provide a future outlook on the current challenges and opportunities.
Most thermoelectric modules on the market follow a conventional configuration which is essentially in flat shape. The adaptation of these flat modules to a gas/liquid thermoelectric generation system involves complexity in the conception., unlike the tubular shape, which presents the most practical and simple configuration for its implementation with such medium.
In this paper, the design and fabrication of a new finned tubular thermoelectric generator prototype is presented. The objective is to develop a simple, robust and compact design that can be easily integrated into gas/liquid thermoelectric conversion system, leading to a more cost-effective installation. For this purpose, the design is based on three construction requirements: (i) the thermoelectric legs are quadratic and axially arranged, (ii) the module is assembled by resin making it in semi-rigid structure, (iii) the fins are annular and incorporated to the module.
A numerical model is established to evaluate the physical parameters of the module, such as contact resistance and resin properties. We also simulated the thermal performance of the heat exchanger in order to define the optimal dimensional values such as fin height and fin spacing that can be adapted to the module. The output power of 25 mW and 600 mV as open-circuit voltage was generated during the test process under a temperature gradient of 60 °C.
Wearable thermoelectric generator arrays have the potential to use waste body heat to power on-body sensors and create, for example, self-powered health monitoring systems. In this work, we demonstrate that a surface coating of a conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT-Cl), created on one face of a wool felt using a chemical vapor deposition method was able to manifest a Seebeck voltage when subjected to a temperature gradient. The wool felt devices can produce voltage outputs of up to 120 mV when measured on a human body. Herein, we present a strategy to create arrays of polymer-coated fabric thermopiles and to integrate such arrays into familiar garments that could become a part of a consumer’s daily wardrobe. Using wool felt as the substrate fabric onto which the conducting polymer coating is created allowed for a higher mass loading of the polymer on the fabric surface and shorter thermoelectric legs, as compared to our previous iteration. Six or eight of these PEDOT-Cl coated wool felt swatches were sewed onto a backing/support fabric and interconnected with silver threads to create a coupled array, which was then patched onto the collar of a commercial three-quarter zip jacket. The observed power output from a six-leg array while worn by a healthy person at room temperature (ΔT = 15 °C) was 2 µW, which is the highest value currently reported for a polymer thermoelectric device measured at room temperature.
Recently, we have witnessed a remarkable proliferation of wearables in various smart applications. These applications include smart healthcare, smart military, smart infotainment, and smart industries, to name a few. However, wearables suffer from significant energy limitations. To cope with this challenging issue, energy harvesting can be a viable solution. In this paper, various ambient sources like heat, vibration, radio waves, and solar energy are compared and critically analyzed based on size, voltage, frequency, power density, and power. Critical analysis of vibrational, solar, heat, radiofrequency, and hybrid show convincing output results, but a hybrid solar wearable energy harvester (SWEH) and thermoelectric wearable energy harvester (TWEH) give a maximum output power of 501 mW. However, piezoelectric clothes fabrication is growing and coming out to be a good competitor because of flexibility and comfort. Work has been done on the hybridization of wearable clothes to generate maximum power and is good enough for wearable applications. On the other side, solar individually is enough to power wearable devices but for a specific time. In the radiofrequency still, research is required because of very low power generation or a flexible array can be integrated into a dress or certain other technique maybe adapted for flexible yet more power generation capability. Overall sizes of the reported wearable energy harvesters are in the millimeter to centimeter scale, with resonant frequencies in the range of 1 to 1400 Hz, while rectenna wearable energy harvester (RWEH) exceeds the limit and is reported in the range of 1.8 to 3.2 GHz. A maximum energy conversion for a piezoelectric wearable energy harvester can potentially reach up to 29.7 μW/cm3 and 14.28 μW/cm2. The power produced by the reported hybrid energy harvesters (HEHs) is in the range of 0.00012 to 501 mW. Due to the combined solar‐thermoelectric energy conversion in HEHs, these systems are capable of producing the highest power densities.
The rapid pace of developments in science and technology provides consumers with a new and improved lifestyle. Textile is one of the important consumer products; it attracts the field of research not only to enhance its basic functionality but also to be smart. Hence, research in the field of smart textile grabs the attention globally, one such being the integration of micro/ nanoelectronics with textile structures. In this context, the concept of wearable thermoelectric generator (TEG) is found to be interesting as it can generate electricity by making the temperature difference between the human body and ambient air, which has been recognized as the Seebeck effect. The power generated by the TEG is proportional to the temperature gradient between the hot and cold junctions. In this work, a power generating fabric has been developed for converting the human body heat energy to electric energy. The power generating fabric is fabricated through weaving technique with copper and aluminum wires as weft and cotton yarn as warp. Copper and aluminum wires act as P-type and N-type semiconductor to form a thermoelectric column. It is found that the developed fabric generates voltage up to 2.4 mV for the temperature difference of 50º C. The developed fabric can be integrated into normal clothing and can be used to give power supply to devices like RFID tracker, hearing aid, etc.
Thin-film thermoelectric generators (TFTEGs) can provide energy for ultra-low power devices such as microscale heaters, cooling-units, and autonomous sensors and actuators. Of particular interest are micro- and nano-structured thermoelectric materials deposited on organic substrates, which allow fabrication of ultra-fast Peltier elements, mechanically flexible TFTEGs, and integration of TFTEGs in transparent microfluidic cells. In this study we report on an integration process of bismuth telluride based cross-plane TFTEGs on polyimide as a model material for organic substrates by adapting a well-established planar technology method. The main advantage of this approach is that the length of the thermopiles is independent on the thickness of the thermoelectric materials, which allows for fabrication of TFTEGs with high aspect ratio.
Due to the mutual conversion of heat and electricity, thermoelectric devices (TEDs) have an outstanding display in the field of wearable electronics and human body temperature regulation. However, their rigidity affects their wearing comfort. In this paper, combined with finite element analysis (FEA), we present a flexible TED, which uses porous PDMS with low thermal conductivity to replace organic elastomer to fill thermoelectric (TE) pillars connected with liquid metal. Our design provides a method to reduce the heat transfer through TEDs. The optimal power density of 2.33 μW cm-2 can be obtained under the natural convection. And with an applied ΔT of 8.8 K, a power density of 27.02 μW cm-2 can be achieved. Moreover, at applied current of 0.9 A, the cooling effect of the flexible TED can reach up to 7 K under natural convection and 2.8 K on human wrist under 1-sun (1 kW m-2) irradiation.
The rapid growth of the Internet of Things (IoT) has accelerated strong interests in the development of low-power wireless sensors. Today, wireless sensors are integrated within IoT systems to gather information in a reliable and practical manner to monitor processes and control activities in areas such as transportation, energy, civil infrastructure, smart buildings, environment monitoring, healthcare, defense, manufacturing, and production. The long-term and self-sustainable operation of these IoT devices must be considered early on when they are designed and implemented. Traditionally, wireless sensors have often been powered by batteries, which, despite allowing low overall system costs, can negatively impact the lifespan and the performance of the entire network they are used in. Energy Harvesting (EH) technology is a promising environment-friendly solution that extends the lifetime of these sensors, and, in some cases completely replaces the use of battery power. In addition, energy harvesting offers economic and practical advantages through the optimal use of energy, and the provisioning of lower network maintenance costs. We review recent advances in energy harvesting techniques for IoT. We demonstrate two energy harvesting techniques using case studies. Finally, we discuss some future research challenges that must be addressed to enable the large-scale deployment of energy harvesting solutions for IoT environments.
Thermoelectric (TE) devices can realize the conversion of heat energy and electrical power based on Seebeck effect and Peltier effect. Among them, flexible TE devices have received more attention recently due to their better attachment to various heat sources and aimed components with arbitrary shapes. To improve the performance of flexible TE devices for various application scenarios, large efforts have been made to design the leg patterns, the electrical and thermal contact issues, and the substrate and encapsulation materials for the decrease of heat loss. This paper is to review the advancements about the design of flexible inorganic TE devices over the last decade. Firstly, the design of flexible thin-film TE devices based on the direction of temperature gradient, including the patterns of TE legs, the fabrication methods, and the flexible substrate materials is summarized. Secondly, the design of wearable TE devices that contains common architecture of the module, the substrates and encapsulations, the electrical and thermal contact, and some thin-film based wearable devices with curving TE legs is demonstrated. Thirdly, the characterizations of the flexibility of TE devices and the current applications are outlined. Moreover, some views about the future development for TE devices are proposed.
Thermoelectrics, enabling direct converting between heat and electricity, have become one of the most promising techniques for the realization of energy-saving and environmental protection. As a key member of the thermoelectric family, fiber-based thermoelectrics possess significant potential in the area of charging wearable electronics, owing to their high performance, high flexibility, and high stability features. Based on the fast development of fiber-based thermoelectrics, this review aims to comprehensively summarize the state-of-the-art fiber-based thermoelectric materials and devices, including their unique designs, chemical engineering, advanced fabrication methods, outstanding thermoelectric properties, and wide applications. In the end, we point out the challenge and outlook for further improving thermoelectric performance, flexibility, and stability of fiber-based thermoelectrics.
At present, device engineering has been limited to the rectangular-shaped TE leg. Therefore, a trapezoidal-shaped leg has been proposed for the TE system and prototypes are developed in this work. Performance comparison has been investigated between rectangular and proposed trapezoidal-shaped leg based TE prototypes. The n-type (0.98Bi,0.02Sb)2(0.9Te,0.1Se)3 and p-type (0.25Bi,0.75Sb)2(0.95Te,0.05Se)3 are considered as base material with Durabond-950 binder material to manufacture TE legs by using a cost-effective dispenser printing technology. The current study includes analysis of SEM imaging, characterization of manufactured TE legs, various experimental tests on TE prototypes, comparison between analytical and experimental results, and cost analyses. For the given restricted volume envelope, the trapezoidal-shaped TE prototype generates 1.24 times more voltage and 1.5 times more power when compared to the rectangular-shaped prototype at 30 °C hot side temperature when the cold side is exposed to the surrounding. For a given constant temperature boundary conditions (i.e., ΔT = 10 °C), the rectangular-shaped TE prototype harvests 1.4 times more power than the trapezoidal-shaped one, while the power density for rectangular TE prototype (i.e., 0.37 W/m³) is almost the same as trapezoidal one (i.e., 0.36 W/m³). Furthermore, the proposed trapezoidal-shaped prototype uses 28.6% less material by mass than the rectangular prototype.
This meta-study explores some factors that can potentially affect the efficiency of a wearable thermoelectric generator. These include, but are not limited to; doping percentage, manufacturing technology, thermocouple length, area, use of heat spreaders, material, airflow and specific position on the human body. These specific designs and materials have been reviewed in this paper and specific variables have been proposed to ensure greater efficiency. In this meta- study, Bi0.5Sb1.5Te3 and Ag2Se are found to be the most effective materials, with PVD as the most effective manufacturing method. A broad temperature differential generates greater power output. Practically, a condition where there is a difference in temperature of more than 40K between the body and its environment in the application of wearable thermoelectric devices is unlikely. Despite this, a temperature difference below 40K, although small, is extremely feasible and would be able to enough power to keep intended wearable thermoelectric devices running at a constant. Keywords: Thermoelectric; Seebeck Effect; Peltier; TEG; ZT; Wearable
Wearable thermoelectric generators are a promising energy source for powering activity trackers and portable health monitors. However, known iterations of wearable generators have large form factors, contain expensive or toxic materials with low elemental abundance, and quickly reach thermal equilibrium with a human body, meaning that thermoelectric power can only be generated over a short period of wear. Here, an all‐fabric thermopile is created by vapor printing persistently p‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐Cl) onto commercial cotton and this thermopile is integrated into a specially designed, wearable band that generates thermovoltages >20 mV when worn on the hand. It is shown that the reactive vapor coating process creates mechanically rugged fabric thermopiles that yield notably high thermoelectric power factors at low temperature differentials, as compared to solution‐processed counterparts. Further, best practices for naturally integrating thermopiles into garments are described, which allow for significant temperature gradients to be maintained across the thermopile despite continuous wear.
Nearly 60% of energy produced in the United States is lost as waste heat, which can be directly converted into electricity using thermoelectric devices through Seebeck phenomena. These solid-state devices are a promising renewable energy technology for waste heat harvesting because they are quite compact and have no moving parts. They can be used for power generation by directly converting heat given off from sources such as power plants, factories, motor vehicles, computers, or even human bodies. As such, the field of thermoelectricity has grown significantly in the last few decades by a combination of developing new materials and advancing in engineering novel devices. This chapter provides a review of the fundamental physics of thermoelectricity and recent advances in materials and engineering devices.
The rapid development of smart electronics has enabled their applications into such fields as portable instruments, wearable electronic devices, implantable medical devices and even assistive biomedical devices. As a result, power requirements of these devices continuously increase to such a degree that currently used batteries can not meet. Recently the heat and mechanical energy available in human daily activities have received increasing attention by researchers as alternatives. This paper looks into the physical mechanisms, materials and devices involved in possible energy harvesting from human motion. Heat and mechanical energy available in human daily activities are summarized to give an overview of the potential of energy harvesting from human motion. In addition, different energy transducing principles are discussed. Moreover, various proposed or demonstrated energy harvesting prototypes related to human motion are reviewed and discussed with respect to their working principles, device structures, implementations and performances. Finally, trends, challenges, applications and future developments of energy harvesting from human motion are discussed.
Thermoelectric generator (TEG) is a sensor that utilizes thermal gradients between cold plate and hot plate of the sensor and convert it into electricity. By having a concise and non-moving structure, the sensor attracts interest in studies to implement an autonomous self sustain system. Power generation of TEG is directly proportional to temperature gradient. Therefore, the device is dismissed when the gradient source of heat is small. This limits the aim of autonomous self sustain system when it uses human temperature as source of conversion. This paper focused on the power conditioning system for a low powered thermoelectric generator. At the same time, it also determines the viability of TEG application in human portable device by adapting body temperature as source of energy conversion. This paper reveals the feasibility of signal conditioning method for a regular TEG module using charge pump.
In this paper, a manual dispenser printing-based fabrication technique has been developed to synthesize
a flexible thermoelectric generator (FTEG). Fabricated FTEGs, printed on polyester fiber clothe, convert
the thermal energy from the human body into electrical energy using the Seebeck effect. Two flexible
prototypes (prototype A and prototype B) were fabricated using a manual dispenser printing technique
with n-type (0.98Bi,0.02Sb)2(0.9Te,0.1Se)3 and p-type (0.25Bi,0.75Sb)2(0.95Te,0.05Se)3 thermoelectric
(TE) materials. The fabricated prototypes consisted of 12 pairs of n-type and p-type legs connected by
silver conductive threads. The experimental investigations were conducted to determine the characteristics
and the electrical outputs of the fabricated prototypes. The open circuit voltage and power
output of prototype A and prototype B were 22.1 mV and 2.21 nW, and 23.9 mV and 3.107 nW,
respectively, at 22.5 �C temperature difference. The fabricated prototypes were also tested on the human
body at different body conditions and were found to be very flexible, twistable, and durable with the
substrate as well as conforming well to the human body.
Energy harvesting has become of a growing interest recently due to its potential to be utilized in wide area of self powered systems. The concept of energy harvesting is to capture unused ambient energy and convert into usable electrical energy which is stored and used for performing sensing or actuation. The latest advancement is focusing on energy scavenging system to power small and autonomous electronic devices. The main advantages of energy harvesting concept lie on the portability, clean, reduce dependency on battery power and it also offers long-term solutions. This research focuses on the human heat energy harvesting which converts human waste heat to electricity. This paper focuses on extracting heat energy from five parts of human body heat such as human palm, top palm, wrist, top wrist and leg. Thermoelectric module is utilized to convert the human body heat to electricity. A booster circuit is developed to boost the weak voltage to higher voltage in order to power up an LED as output indicator. Based on experimental results, the maximum output voltage from thermoelectric module obtained is from the human palm part, which is 0.1 V. It is able to be boosted up to 2.9 V at the voltage booster output. The output voltage generated at load is 2.47 V and the power output is 24.7 mW.
In this work we proposed design, fabrication and functional characterization of a very low cost energy autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG), finalized to power very low consumption electronics Ambient Assisted Living (AAL) applications. The prototype, integrating an array of 100 thin films thermocouples of Sb2Te3 and Bi2Te3, generates, at 40°C, an open circuit output voltage of 430 mV and an electrical output power up to 32 nW with matched load. In real operation conditions of prototype, which are believed to be very close to a thermal gradient of 15°C, the device generates an open circuit output voltage of about 160 mV, with an electrical output power up to 4.18 nW. In this work we proposed design, fabrication and functional characterization of a very low cost energy autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG), finalized to power very low consumption electronics Ambient Assisted Living (AAL) applications. The prototype, integrating an array of 100 thin films thermocouples of Sb2Te3 and Bi2Te3, generates, at 40°C, an open circuit output voltage of 430 mV and an electrical output power up to 32 nW with matched load. In real operation conditions of prototype, which are believed to be very close to a thermal gradient of 15°C, the device generates an open circuit output voltage of about 160 mV, with an electrical output power up to 4.18 nW.
In this paper, we present our vision of what kind of wearable devices and how they can be powered by the heat of human beings and by using ambient light. The basic principles of designing body-powered devices and ways of their hybridizing with photovoltaic cells are discussed. The mechanisms of thermoregulation in humans and the laws of thermodynamics enable placing a distinct boarder between realistic targets and the science fiction. These allow prediction of application areas for wearable energy harvesters accounting for competitive batteries with long service life. The existing family of body-powered wearable devices and new technologies for thermopiles are discussed. The theory and practice point at the necessity of using microelectronic and microelectromechanical system technologies for the target application area. These technologies for thermopiles offer the possibility of reduced production cost. Therefore, autonomous systems powered thermoelectrically could be successfully marketed. The related aspects of design and fabrication are discussed.
The present work reports on the fabrication and characterization of a planar Peltier cooler on a flexible substrate. The device was fabricated on a 12 µm thick Kapton(c) polyimide substrate using Bi 2 Te 3 and Sb 2 Te 3 thermoelectric elements deposited by thermal co-evaporation. The cold area of the device is cooled with four thermoelectric junctions, connected in series using metal contacts. Plastic substrates add uncommon mechanical properties to the composite film–substrate and enable integration with novel types of flexible electronic devices. Films were deposited by co-evaporation of tellurium and bismuth or antimony to obtain Bi 2 Te 3 or Sb 2 Te 3 , respectively. Patterning of the thermoelectric materials using lift-off and wet-etching techniques was studied and compared. The performance of the Peltier microcooler was analysed by infrared image microscopy, on still-air and under vacuum conditions, and a maximum temperature difference of 5 • C was measured between the cold and the hot sides of the device.
This work presents advancements in dispenser-printed thick film thermoelectric materials for the fabrication of planar and printable thermoelectric energy generators. The thermoelectric properties of the printed thermoelectric materials were measured as a function of temperature. The maximum dimensionless figures of merit (ZTs) at 302 K for the n-type Bi2Te3-epoxy composite and the p-type Sb2Te3-epoxy composite are 0.18 and 0.19, respectively. A 50-couple prototype with 5 mm × 640 µm × 90 µm printed element dimensions was fabricated on a polyimide substrate with evaporated metal contacts. The prototype device produced a power output of 10.5 µW at 61.3 µA and 171.6 mV for a temperature difference of 20 K resulting in a device areal power density of 75 µW cm−2.
Energy harvesting has grown from long-established concepts into devices for powering ubiquitously deployed sensor networks and mobile electronics. Systems can scavenge power from human activity or derive limited energy from ambient heat, light, radio, or vibrations. Ongoing power management developments enable battery-powered electronics to live longer. Such advances include dynamic optimization of voltage and clock rate, hybrid analog-digital designs, and clever wake-up procedures that keep the electronics mostly inactive. Exploiting renewable energy resources in the device's environment, however, offers a power source limited by the device's physical survival rather than an adjunct energy store. Energy harvesting's true legacy dates to the water wheel and windmill, and credible approaches that scavenge energy from waste heat or vibration have been around for many decades. Nonetheless, the field has encountered renewed interest as low-power electronics, wireless standards, and miniaturization conspire to populate the world with sensor networks and mobile devices. This article presents a whirlwind survey through energy harvesting, spanning historic and current developments.
Thermoelectrics have long been recognized as a potentially transformative energy conversion technology due to their ability to convert heat directly into electricity. Despite this potential, thermoelectric devices are not in common use because of their low efficiency, and today they are only used in niche markets where reliability and simplicity are more important than performance. However, the ability to create nanostructured thermoelectric materials has led to remarkable progress in enhancing thermoelectric properties, making it plausible that thermoelectrics could start being used in new settings in the near future. Of the various types of nanostructured materials, bulk nanostructured materials have shown the most promise for commercial use because, unlike many other nanostructured materials, they can be fabricated in large quantities and in a form that is compatible with existing thermoelectric device configurations. The first generation of these materials is currently being developed for commercialization, but creating the second generation will require a fundamental understanding of carriertransport in these complex materials which is presently lacking. In this review we introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carriertransport and how current research is addressing these questions. Finally, we discuss several research directions which could lead to the next generation of bulk nanostructured materials.
A thermoelectric power generation system is developed with a flexible structure. Its micro fabrication has the advantage of miniaturization and integration. Thermoelectric materials are fabricated by using micro fabrication technology. The developed structure is composed of a polyimide sheet as a substrate, thermoelectric materials deposited on the substrate, a heat absorber sheet and a heat sink sheet. The flexibility of this structure depends on the wavy form of the substrate and slits in the substrate, and the heat absorber and heat sink sheets. Because of the characteristic evaluation, open-circuit voltage of 16 µV K-1 per thermocouple was obtained. In addition, the thermopile generator does not break till a bending radius of curvature of 9 mm is reached. A prospect for practical application of the thermoelectric power generator for a curved surface was confirmed.
A coiled-up thermoelectric micro power generator is presented using metal films sputtered on a thin polyimide foil. The principle of coiling-up yields higher voltages at a smaller generator area. Design optimizations were made for maximum long-term power output using the human body as heat source. It is shown that for low-power electronics like a wrist-watch even simple materials are sufficient and allow lowest-cost production, e.g. screen printing. Thermoelectrical screen-printing pastes were developed and results of first screen printed thermocouples are given.
In this work we proposed design, fabrication and functional characterization of a very low cost energy autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG), finalized to power very low consumption electronics ambient assisted living (AAL) applications. The prototype, integrating an array of 100 thin films thermocouples of Sb2Te3 and Bi2Te3, generates, at 40 °C, an open circuit output voltage of 430 mV and an electrical output power up to 32 nW with matched load. In real operation conditions of prototype, which are believed to be very close to a thermal gradient of 15 °C, the device generates an open circuit output voltage of about 160 mV, with an electrical output power up to 4.18 nW.In the first part of work, deposition investigation Sb2Te3 and Bi2Te3 thin films alloys on Kapton HN polyimide foil by RF magnetron co-sputtering technique is discussed. Deposition parameters have been optimized to gain perfect stoichiometric ratio and high thermoelectric power factor; fabricated thermogenerator has been tested at low gradient conditioned to evaluate applications like human skin wearable power generator for ambient assisted living applications.Research highlights▶ Present work shows design, fabrication and functional characterization of a very low cost energy autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG). ▶ The preliminary prototype integrates an array of 100 thin films thermocouples of Sb2Te3 and Bi2Te3. ▶ At real operation conditions (thermal gradient of 15 °C), device generates an open circuit output voltage of about 160 mV, electrical output power up to 4.18 nW. ▶ Deposition investigation of Sb2Te3 and Bi2Te3 thin films alloys on Kapton HN polyimide foil by RF magnetron co-sputtering technique is discussed. ▶ Deposition parameters have been optimized to gain perfect stoichiometric ratio and high thermoelectric power factor.
Flexible thermoelectric power generators fabricated by evaporating thin films on flexible fiber substrates are demonstrated to be feasible candidates for waste heat recovery. An open circuit voltage of 19.6 μV K per thermocouple junction is measured for Ni–Ag thin films, and a maximum power of 2 nW for 7 couples at ΔT = 6.6 K is measured. Heat transfer analysis is used to project performance for several other material systems, with a predicted power output of 1 μW per couple for Bi2Te3/Sb2Te3-based fiber coatings with a hot junction temperature of 100 °C. Considering the performance of woven thermoelectric cloths or fiber composites, relevant properties and dimensions of individual thermoelectric fibers are optimized.
We present a novel polymer based wafer level fabrication process for micro thermoelectric generators (μTEGs) for the application on non-planar surfaces. The generators are fabricated by subsequent electrochemical deposition (ECD) of Cu and Ni in a 190-μm thick flexible polymer mold formed by photolithographic (PL) patterning of SU-8. First generators were tested and characterized. The TEG generated a power of 12.0 ± 1.1 nW/cm2 for a ΔT of 0.12 K at the μTEG interface, which is equivalent to a thermoelectric efficiency factor of 0.83 μW K−2 cm−2. The experimental data is in good accordance with a model introduced for the optimization of vertical micro thermoelectric generators. It allows calculation of the optimal geometric design parameters for any given material and thermal interfaces. The analysis reveals that the thermocouple length should be in the range of 80–150 μm when the best thermoelectric bulk material (BiTe) is used and realistic interface condition are assumed.
CRC Handbook of Thermoelectrics
- D M Rowe
D.M. Rowe (Ed.), " CRC Handbook of Thermoelectrics ", CRC Press, New York, 1995.