Design, analysis and characterization of a miniature second-order directional microphone

Presented in this dissertation are the design and analysis of a first order directional comb finger microphone. The first order microphone diaphragm has a simple and very small mechanical structure so that the complexity of fabrication process can be reduced. An analytical model and a finite element model are developed to predict the characteristics of the diaphragm, such as natural frequencies, mode shapes and the acoustic response due to sound. Also, the comparison of the predicted and the measured results is presented in the dissertation.;Based on the first order directional comb finger microphone, a miniature second-order directional microphone diaphragm is developed, which consists of two first order microphone diaphragms. The design and analysis of the second order directional microphone diaphragm is presented in the dissertation. It involves the detailed analytical model and the finite element model of the diaphragm to predict the mode shapes, the natural frequencies and the responses of the diaphragm. The second order directional response of the diaphragm in the first mode has been achieved through carefully designing the mechanical structure of the diaphragm by optimizing its directivity index. In order to diminish the unwanted responses of the diaphragm in the third and second modes, which dominated in the total response and results in the omni-and first order directional response, the new designs of the microphone is introduced, in which the diaphragm is compliantly suspended over an enclosed air volume or a pair of separate air volumes. The analytical model is extended to account for the effects of air in the back volume that acts like a linear spring. From the extended model, the directivity of the microphone is predicted by using the numerical method. Due to the effects of air in the separate volumes, the second order directional pattern of the response of the diaphragm is achieved.