Restriction lift date: 2028-12-31
Development of micro-thermoelectric generator (µ-TEG) for powering wearable devices
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Date
2024
Authors
Tanwar, Amit
Journal Title
Journal ISSN
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Publisher
University College Cork
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Abstract
Wearable biomedical devices are the way forward from the episodic to the continuous healthcare system. The incorporation of energy harvesting technologies into wearable biomedical devices represents a significant advancement in sustainable technology, offering the promise of self-powered and autonomous operation. Thermoelectric generator (TEG) energy harvesting technology has garnered significant attention in recent years as an uninterrupted power supply for the continuous operation of wearable devices. TEGs are solid-state devices employed to convert heat energy to electrical energy based on the Seebeck effect. It offers a wide range of advantages, such as the direct conversion of energy without an intermediate step, no-moving parts, high reliability and durability at a low cost. Energy harvesting from body heat using TEG is a promising approach to realize a self-powered wearable device that can run continuously without batteries.
This thesis explores the multifaceted domain of thermoelectric technology, from vision to material synthesis, device geometrical design optimization, fabrication of micro-thermoelectric generator, development of an application-based evaluation system and finally, integration of the TEG devices. Over the several years, researchers have made significant progress in using thermoelectric devices for practical applications through collaborative efforts. The performance and efficiency of a thermoelectric device mainly depend on two aspects: namely, the thermoelectric material efficiency and the design optimization of the device.
First, as part of materials development, the binary Sb2Te3 and ternary CuSbTe thin film thermoelectric material using the low-cost electrodeposition process has been developed. Amorphous CuSbTe ternary films of varied compositions are electrodeposited by adjusting the [Cu2+] concentration in the electrolytes. The as-deposited films are characterized using a combination of spectro-analytical techniques. The co-deposition of Cu with Sb2Te3 induced the phase transition, which created the anti-site defects and grain-boundaries in a disordered structure and ultimately enhanced the thermoelectric performance of the material. The as-deposited film containing 5.7 at% Cu shows a high Seebeck coefficient (-382 µV K-1) and an outstanding power factor of 2.8 mW m-1 K-2 near room temperature.
Furthermore, the developed binary and ternary thin films are thermally treated (annealed) for 1 hour at different temperatures ranging from 100-300 °C. Annealing reduces the defects and repairs the crystalline structure, which converts the films into p-type material. The Cu0.4SbTe films annealed at 200 °C show the highest power factor of 760 µW m-1 K-2 due to the highest Seebeck coefficient of 66.75 µV K-1 and good electrical conductivity of 1.70 x 105 S m-1.
Later a design optimization of the micro-thermoelectric device is carried out for power generation and efficiency calculation from a single-leg pair to a complete device using COMSOL Multiphysics simulation. The device’s geometrical optimization is conducted by varying different parameters such as shape, height, interconnect material thickness, choice of filler material and the cross-sectional area of the single-leg pair. The results obtained from this study will provide the design guidelines to improve the performance of a micro-thermoelectric generator.
In addition, this thesis presents the design, development, and implementation of a fully automated measurement system tailored for the characterization of micro-thermoelectric devices operating near room temperature based on the ASTM D5470-06 standard. The developed system is fully controlled by a LabVIEW program, which provides precise control on temperature gradient and pressure across the device, electrical measurement capabilities and data acquisition functionalities to evaluate both macro and micro-thermoelectric devices efficiently and accurately. At the end, the developed p-type CuSbTe material is integrated in a 3.5×4.5 mm2 silicon-based micro-thermoelectric generator (µ-TEG). A total of 7 photolithography masks are designed and implemented to fabricate the micro-TEG. The micro-devices are characterized by an automated measurement system. At a temperature gradient of 5 K and 10 K, the micro-TEG delivers a voltage output of 46 and 85 mV, respectively. A power density of 11.32 and 40.13 µW cm-2 is achieved for those two temperature gradients. Thereby, this work contributes to the development of micro-thermoelectric devices for low-temperature applications, particularly in the context of wearable medical devices.
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Keywords
Thermoelectric , Chalcogenides , Electrodeposition , Micro-thermoelectric generator , Energy harvesting
Citation
Tanwar, A. 2024. Development of micro-thermoelectric generator (µ-TEG) for powering wearable devices. PhD Thesis, University College Cork.