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Human passive power

Francesc Moll
There is an increasing demand for portable electronics which depend on batteries, and need to be recharged periodically. On the other hand, the power necessary to operate electronic devices goes down, and this trend opens a possibility to increase the autonomy of these devices by using the energy generated by the user in its normal activity. The possibility to harvest energy from the environment to power electronic circuits may be exploited in several low power systems, like wearable devices or sensor networks. Each application has its own energy harvesting options. At the High Performance Integrated Circuits Design Group of the Dept of Electronic Engineering we focus on energy harvesting for consumer electronics and we aim to calculate the energy that can be harvested from a person's activity. More specifically, we work towards passive power. Energy harvesting from human activity can be classified as active or passive. Active power means that the user is doing a specific work in order to generate the energy, while passive power uses the user’s everyday actions without conscious intervention, and therefore creates less discomfort to the user.

As we focus on the energy generated by the user, we consider two types of energy: kinetic and thermal. Under kinetic energy, we consider four types of transducers to convert it into electrical energy: piezoelectric, capacitive, inductive, and a more speculative one, based on triboelectricity generation. For the moment our work has been in the piezoelectric transducer, modeling its behaviour and studying the optimum mechanical structure. For each energy source we will also study optimum power conditioning circuits.
Our next objectives are the modeling of the human body as a thermal source, and a study of the kinetic energy during normal day activity in different parts of the body.

Alternate energy sources require the study of appropriate transducers and also the design of the necessary conditioning circuits to adapt the power obtained from mechanical (or other) transducer to the requirements of an electronic system. An important goal is to maximize the efficiency of the converter from the primary energy source to the electronic system power input.