Bandwidth and sensitivity optimization in CMUTs for airborne applications

We previously proposed venting the cavities of CMUTs for using them in environments with extreme pressure variation. Such CMUTs have zero differential pressure across the plate at any ambient pressure, thus ensuring a stable operating point and preventing mechanical failure. The air in the cavity between the moving CMUT plate and the substrate forms a squeeze film which gives some stiffening and damping effect to the CMUT. The additional damping from the squeeze film helps to enhance the CMUT´s bandwidth significantly. By properly selecting the size, number, and location of the venting holes, the squeeze film effect can be controlled and the sensitivity and bandwidth of the CMUT can be optimized. We developed a finite element model for simulating such CMUTs with vented cavities. Using this model, we designed a variety of CMUTs with varying sensitivity and bandwidth. These CMUTs were fabricated and characterized. The measurements closely match our finite element model results.