Calculated performance characteristics of micromachined thermopiles in wearable devices

Thermal properties of human beings have been measured in this work and used for design optimization of wearable thermoelectric energy harvesters. The theory of wearable thermoelectric generator is applied for designing miniature thermopiles that could be batch-fabricated in a microelectronic-like or a MEMS process. It is shown that low-cost film-based thermopiles with satisfactory performance characteristics are feasible for reaching market expectations of the cost of self-powered wearable devices. It is however shown, too, that thin, e.g., millimeter-thin thermoelectric generators cannot be effective. This result changes the basic design approaches for wearable thermoelectric generators. The comparison of performance characteristics of wearable thermoelectric and photovoltaic generators is performed. The results allow defining the application area and the target performance characteristics of wearable energy harvesters of the human body heat. This is done by using experimental results on power consumption of advanced wearable low-power wireless sensors. Current state of the art in development of optimized film-based thermopiles by using surface and bulk micromachining technique is discussed.