Prediction of the spatial response of a microphone capsule using scattering and lumped-element simulations

Abstract

When a microphone capsule is placed in an environment with surrounding structures, the electrical response of the capsule will be dictated by the capsule design and by acoustic scattering of the structures surrounding it. Lumped element models of the transducer are typically used in predicting the electrical response to the field, but when the transducer is operating at a frequency where the spatial variation of the field is significant, the simplifying assumptions used in these models no longer hold. In this work, a finite element-based scattering simulation provides blocked-port field quantities to drive a lumped element circuit model, predicting the electrical output as a function of the frequency and incident angle of an incoming plane wave. The scattering simulation allows for the inclusion of mechanical supporting structures and protective screens, and their influence on the field at the rear port of a gradient transducer. Simulated results are shown for the simplified capsule and compared to measurements of a real capsule in free field conditions as well as with surrounding structures.