Influence of backplate perforation distribution on squeeze-film damping in condenser microphones

This paper investigates the overlooked influence of backplate hole distribution on the performance of condenser microphones. While classical lumped-parameter models consider only the perforation ratio, hole size, and number, this study explicitly demonstrates and quantifies that the spatial distribution of these holes is a critical factor governing squeeze-film damping and the resulting frequency response. Finite element simulations and experimental measurements on 1/2-in. microphones with varied hole patterns reveal that distributing holes toward the backplate center dramatically reduces squeeze-film damping and consequently increases the system bandwidth. A new dimensionless hole distribution coefficient (ψ) is defined, and an empirical correction function ξ(ψ) is derived from the simulation data. This correction, integrated into the classical resistance model, improves its accuracy for non-uniformly perforated backplates. Furthermore, the core finding is validated through simulation on a 1-in. microphone, confirming the broader relevance of the mechanism. The findings provide a critical design guideline for optimizing high-performance condenser microphones by deliberately placing backplate perforations.