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

Abstract

Microfabrication, electrical characterisation, and mathematical modelling of a non-spiral planar microcoil 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 microcoil 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 microcoil is also developed and compared with experimental results. Experimental results are in good agreement with the theoretical model. Based on the experimental results, using optimised 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.