Miniaturised Electromagnetic Generators for Portable Applications

Abstract

With the advent of wearable electronics, the demands on power sources for portable electronic equipment are ever-increasing. Requirements include increased functionality and decreased size, with power sources (e.g. batteries) providing at least the same lifetime as the device. In this project, the possibility of unobtrusively capturing some of the energy expended by a person while walking / running and converting it into electrical energy is investigated. The development of such alternative or complementary power sources would significantly reduce the demands on conventional power sources. Modelling and analysis of an electromagnetic generator designed for harvesting power produced during walking is presented. The generator is designed to be inconspicuous to the user by embedding it within the thickness of a normal shoe sole, and by applying a passive generation principle which requires minimal additional force over that normally exerted by the user during walking. In this way, a portion of the power used in walking is harvested for potential use in powering portable electronic devices. The main outcome of the work is specification and comparison of the power levels available from the electromagnetic generators designed for integration into shoes. Circuit models are applied to predict maximum voltage and power levels produced during walking. Analytical and Finite Element Analysis (FEA) models are applied to design the generator winding and core structures. Furthermore, analysis of different geometrical and material properties is applied to identify the conditions for optimised generator designs. The nature of the generator output necessitated the development of AC/DC conversion methods which are modelled to predict the maximum DC power available within the given structure. DC power levels of up to 10 mW are demonstrated within a volume of 15 × 15 × 100 mm^3 at a walking speed of 2 steps per second. At least two of these volumes can be easily accommodated within a standard shoe heel to provide up to 40 mW of DC power per user, with higher power levels achieved for faster walking or running speeds. A microprocessor/transceiver system integrated into the shoe is demonstrated to identify the possible commercial use of such generator designs.