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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.

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This paper presents a discussion on energy scavenging for wearable devices in conjunction with human body properties. Motivation, analysis of the relevant properties of the human body, and results of optimization of a thermopile and a thermoelectric generator for wearable and portable devices are presented. The theoretical limit for power generation on human beings is evaluated and confirmed by experimental results. The requirements for wearable thermopiles are summarized. The results allow certain conclusions to be drawn concerning directions for future development of body-powered devices.

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Hybrid wearable energy harvesters consisting of a thermoelectric generator (TEG) and photovoltaic (PV) cells are used in this work for powering two autonomous medical devices: an electroencephalography (EEG) system and an electrocardiography (ECG) system in a shirt. Two alternative solutions for powering the systems have been implemented. In the battery-free EEG diadem, PV cells cover the outer surface of radiators used in a TEG. In the ECG shirt, thermoelectric modules are the main power supply that constantly recharges a battery, while PV cells are used mainly to provide standby power, i.e., when the shirt is not worn. Both devices are maintenance free for their entire service life.

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