Planar Microcoil Optimization of MEMS Electrodynamic Microspeakers

A method for optimizing the planar microcoil of MEMS electrodynamic microspeakers with the aim of maximizing the electroacoustic efficiency is presented. The proposed approach is based on a mixed-model using both analytical models and finite element method (FEM). FEM simulation was used for computing the spatial distribution of the magnetic field created by the permanent magnets, making thus possible to analyze any geometry of permanent magnets. Different configurations of magnets were considered, and for each the planar copper microcoil was optimized while taking into account the technological constraints due to the microfabrication process, the associated electronics and the targeted acoustic power emission. The results showed that the proposed method predicts the force factor in very good agreement with experimental measurements carried out on the micromachined device. Moreover, according to the electro-mechano-acoustic model, these results showed that the optimized microcoil associated to the best magnet configuration increases the electroacoustic efficiency by more than 200% compared to conventional microspeakers.