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Having to depend on batteries to recharge low-energy devices could be avoided thanks to the energy generated by the body. Capturing this energy is known as “energy harvesting” or “energy scavenging”. The system also harvests ambient energy and is used in some devices to power certain mechanisms or sensors.

This was precisely the topic chosen by Loreto Mateu for her doctoral thesis, entitled Energy Harvesting from Human Passive Power. With degrees in Industrial Engineering and Advanced Electronic Engineering, Loreto Mateu decided to study different systems to capture energy, basically consisting of a transducer, a power converter and a rechargeable battery or capacitor to store the electric energy harvested. “The intention is to use the captured energy to supply electricity for low-energy power devices that measure a physical parameter of the user's environment”, explains Loreto Mateu, who currently works at the Power Efficient Systems Department of the Fraunhofer Institute for Integrated Circuits (Fraunhofer IIS) in Nuremberg, Germany.

Her thesis, which she defended last year at the School of Telecommunications Engineering of Barcelona, allowed her to conduct a study on how to improve systems for harvesting energy. In it, two systems were analyzed: a piezoelectric and inductive transducer that transforms the kinetic energy associated with the movement of the human body into electrical energy; and a thermogenerator that converts thermal energy from the human body and the surroundings into electrical energy.

In the past two or three years, commercial devices using harvested power sources have proliferated. In an intelligent building, for instance, where various parameters such as temperature or humidity in different rooms need to be monitored, hundreds of sensors are necessary. If these were not recharged using energy harvesting technology, their batteries would have to o be constantly recharged or replaced.

With regard to capturing human energy, experts refer to BAN (body area network), consisting of a network of sensors measuring an individual's vital signs and transmitting them wirelessly. Such actions as walking, running and going up or down stairs produce sufficient energy to recharge the different nodes that comprise this network. Thus, according to Loreto Mateu, “the mechanic energy generated by walking can be turned into electrical energy by placing a piezoelectric material of a polymer type on the foot”.

Today, however, devices using energy generated by the human body are not yet available on the market because this would involve combining the design of the energy harvesting device and its sensors with e-textile technology, which would integrate the electronics in fabrics.

“Moreover, adds Loreto Mateu, the power levels that can be harvested from the human body are lower than levels from ambient energy and this makes it more difficult to power devices exclusively through energy harvesting”.