Beam structure for CMUT with desired frequency spectrum

Abstract

Capacitive Micro-machined Ultrasound Transducers (CMUTs) with beam structures independently control resonance frequency and fractional band width (FBW). We used a theoretical approach to calculate equivalent stiffness and mass with CMUT diaphragm with rectangular beams. We also investigated the relationship between a base diaphragm's thickness and width and those of beams in terms of resonance frequency, FBW and collapse voltage. We found that a CMUT's frequency spectrum can be controlled merely by controlling base diaphragm and beam thickness. To effectively change the frequency spectrum, the beam width is made as small as possible compared with the pitch of the beams. We examined a simple three-dimensional (3-D) model in which rectangular beams were placed on a uniform rectangular diaphragm aligned in one direction with constant pitch and compared its characteristics to those obtained with theoretical approach. The resonance frequency and collapse voltage calculated by the theoretical model showed good agreement with those obtained with the 3-D model. We concluded that beam structures are one means of enabling CMUTs to be designed more freely.