Nonlinear capacitance and distortion reduction in dual backplate condenser microphones

Dual backplate microphones have gained attention for their ability to improve sensitivity and dynamic range and suppress even-order harmonic distortion compared to traditional single backplate designs. This study investigates the nonlinear behavior of these microphones, focusing on the nonlinear capacitance changes that occur as the diaphragm moves between the two backplates. A theoretical model is developed to describe how asymmetries in the air gaps and parasitic capacities contribute to harmonic distortion. The results show that the second harmonic decreases significantly as the air gaps and the parasitic capacities become more symmetrical, confirming that the dual backplate structure can effectively cancel even-order harmonics. The model is then validated through acoustic measurements on a dual backplate micro-electro-mechanical systems microphone, from which the key model parameters are estimated. In addition, a signal-domain correction algorithm-originally designed for single backplate microphones-is adapted and shown to reduce distortion further when applied to dual backplate designs. These findings provide both a clearer understanding of nonlinear distortion mechanisms in dual backplate microphones and a practical means to improve their performance in high-demand acoustic applications.