Modelling, microfabrication and performance evaluation of non-spiral planar microcoils for biomedical wireless power transfer systems

Abstract

Microfabrication, electrical characterization, and mathematical modelling of a non-spiral planar micro coil useful for wireless power transfer applications in biomedical devices are presented in this work. The fabrication method using the existing very-large-scale integration manufacturing process requires a single mask level, and a single metal level without any via enables direct integration with a complementary metal oxide semiconductor sensing circuitry. An analytical model of magnetic field distribution in a non-spiral micro coil is developed for the first time in this work, which satisfies the form of a Bessel function of the first kind. An electrical model of the non-spiral planar micro coil is also developed and compared with experimental results. Experimental results are in good agreement with the theoretical model. Based on the experimental results, using optimized coil geometry, a wireless power transfer link suitable for biomedical wireless power transfer applications is studied. The maximum possible value of coupling factor of the wireless link is found to be 60% for a small separation between the coil and the magnet whereas the minimum value of coupling factor is found to be below 10% for large separations. It is found that introducing Neodymium magnetic shield layer at the receiving coil enhances the coupling factor significantly.