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WEARABLE & IMPLANTABLE ELECTRONICS Fig. 3: TI’s TPS82740A module in a classical configuration. skin cannot be effectively converted into electrical energy, even if a human being generates on average more than 100W. If we suppose a low conversion of about 1 to 2%, the amount of available power is sufficient to operate a low power wearable device. The thermal circuit of a TEG wearable placed in direct contact with the skin can be described by a thermal resistance of the body and that of the environment. These resistors are connected in series and represent the thermal resistance of the thermoelectric generator. We constantly produce heat as a side effect of our metabolism. However, only part of this heat is dissipated in the environment as a flow of heat and infrared radiation, the remainder being rejected in the form of water vapour. What’s more, only a small fraction of the heat flow can be collected and stored as energy. The magnitude of the voltage V generated between the two layers depends on the material and the temperature, following a linear relationship as a function of the Seebeck coefficient S. The energy optimization, as we have seen, necessarily brings with it the need for accurate choices, not only of the various components, but also of a power supply and an intelligent management system, capable of supplying power only when necessary. There are many aspects to consider when designing a low power system: power consumption, required cycles, voltage and total power consumed. All design scenarios will require careful planning. AUTORISIERTER DISTRIBUTOR UMT-H SMD fuse with high breaking capacity – High breaking capacity up to 1500 A – High rated voltages up to 277 VAC / 250 VDC – 24 rated currents from 160 mA to 30 A – Compact, square design: 5.3 x 16 mm umt-h.schurter.com RV-8063-C7 Real-Time Clock Module with SPI Bus Automotive qualified, according to AEC-Q200 Rev. C, Size: 3.2 x 1.5 x 0.80 mm, Temperature range: -40°C to + 85°C, 100% leadfree, RoHS-compliant www.microcrystal.com MICRO CRYSTAL SWITZERLAND Our authorised distributor WDI AG is pleased to assist you.  +49 4103 1800-0  microcrystal@wdi.ag  www.wdi.ag/microcrystal Fig. 4: Example of a block diagram for a pacemaker with thermal energy harvesting. www.electronics-eetimes.com Electronic Engineering Times Europe March 2017 43


EETE MAR 2017
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