Coupling Factor Between the Magnetic and Mechanical Energy Domains in Electromagnetic Power Harvesting Applications

Micro-power generation is an area developing to support autonomous and battery-free wireless sensor networks and miniature electronic devices. Electromagnetic power harvesting is one of the main techniques for micro-power generation and it uses the relative motion between wire coils and miniature magnets to convert mechanical energy to electricity according to Faraday´s law of induction. Crucial for the design and analysis of these power systems is the electromechanical coupling factor K , which describes the coupling between the mechanical and electromagnetic energy domains. In current literature K is defined as NBl : the product between the number of turns in the coil (N), the average magnetic induction field (B), and the length of a single coil turn (l) . This paper examines the validity of the current K definition and presents two case studies involving cylindrical permanent magnets and circular coil geometries to demonstrate its limitations. The case studies employ a numerical method for calculating K which uses the toroidal harmonics technique to determine the magnetic induction field in the vicinity of the cylindrical magnet.