Effect of a protective enclosure on the acoustical response of a MEMS directional microphone

A novel differential microphone design has been proposed by Miles et al. based on the ears of the fly Ormia ochracea. An important aspect of the overall package design for this microphone is the design of a cover to protect the microphone diaphragm from the effects of dust and other foreign particles.;The cover is placed on top of the microphone chip. Screens are attached on top of the cover. Screens can have an effect on the acoustic response of the system and hence need to be accounted for. In the analysis presented, two cover and screen assemblies are used for the two halves of the differential microphone. The response of this assembly to sound is studied using an acoustical transfer matrix model. The response of the differential microphone with this protective enclosure is also measured and this is compared to the predictions. Another important part of this effort is to characterize the acoustical properties of the screen materials. To study the effect of the porous screen on sound transmission, it is necessary to characterize the material using two basic parameters: the complex acoustic propagation constant and the complex impedance. A setup is developed for the insertion loss measurement, which is then used to predict the impedance.;An optimized differential microphone design is also proposed. The stress due to the fabrication process induces out-of-plane displacement in the microphone diaphragm. This displacement can cause the diaphragm to hit into the back-plate. Hence design changes are introduced to ensure a relatively stress-free skin. Optimization routines are also run to minimize the mechanical-thermal noise of the microphone.