Design and fabrication of LTCC electro-magnetic energy harvester for low rotary speed

Abstract

This study focuses on the design and fabrication of a planar rotary electromagnetic energy harvester with a low rotary speed for bicycle dynamos. The primary components of a dynamo system include planar multilayer and multipole coils, a soft magnet (iron) used to enhance magnetic efficiency, and a multipole Nd/Fe/B (neodymium, iron, and boron) permanent magnet. Finite element analysis and the Taguchi method were used to design this dynamo system. The optimal parameters of the magnet, coil, and soft magnet were determined by using the Taguchi method. Low temperature co-fired ceramics (LTCC) technology was applied to fabricate silver planar multilayer coils with 10 and 20 layers, respectively. Nd/Fe/B was sintered to obtain the desired characteristics of a permanent magnet. A 28-pole magnet Nd/Fe/B with an outer diameter of 50mm and a thickness of 2mm was also sintered and magnetized, creating a magnetic field of 1.4T. Simulation results show that a harvester with 20-layer and 22 poles coils, a linewidth of 200μm, an interspace of 100μm, and a layer thickness of 40μm can generate voltages of 1.796V at a rotary speeds of 300rpm. This harvester system was approximately 50mm×50mm×3mm in volume (including 20-layer micro-coils+magnet+spacing between the coil and magnet surface). The experimentally induced voltages of 20-layer coils were 1.539V. Measurements show a similar trend with finite element simulations. The power output was 0.788mW with an external resistance load of 737Ω. This harvester is capable of powering 200 LEDs (forward voltage (VF)<2.2V and 20mA) using a rotary speed of 250rpm, and could be used for bicycle dynamo lighting.