Human body energy harvesting for activities recognition

Abstract

Nowadays, the research field of the energy harvesting from the human body is attracting great interest in the scientific community, with the objective of designing new ways of capturing energy sources to power wearable devices. Smart wearable devices are increasingly being used in different health-related application fields, thanks to the low cost and to the availability of miniaturized technology, and this makes it possible to capture variables associated with the health and safety status of the human being. Unfortunately, the battery size of these devices determines their operating time, thus limiting applicability for the long-term monitoring. Among all the technologies for harvesting the energy from the environmental sources, this PhD thesis deals with recovering the energy directly from devices placed onto the human body surface. In particular, the motion of the limbs during the daily physical activities and the continuously wasted heat are the recoverable energies that were specifically targeted in this PhD thesis. Therefore, the proposed thesis reviews both flexible technologies for biomechanical energy harvesting and miniaturized devices for recovering the thermal energy on the body surface, with a specific focus on those technologies able to minimize discomfort to the wearer. In the experimental sections, two commercial technologies, one piezoelectric and one based on the Seebeck effect, were tested for understanding the real possibility of harvesting the biomechanical and thermal energies, respectively. For both technologies, the range of the values of the power output is about 1 – 10 µW, by employing just a harvester for each test. In addition, measurements performed to evaluate the ability of such devices to the main phases of the gait cycle were made by using the piezoelectric transducer on the back side of the knee joint. The results show the feasibility to detect the phases of gait cycle by using a passive device. Therefore, these tests may help contribute to the route of innovation for developing self-powered monitoring systems.