Modeling and optimization of micromachined air-coupled capacitance transducers

A transmission line equivalent circuit network model has been developed to understand and control the high frequency performance of micromachined air-coupled capacitance transducers. The geometric size of the air cavities, the spacing between cavities, diaphragm thickness, air viscosity, bias voltage of the diaphragm and the compressibility of the air gap separating the film and the backplate are included. The performance of transducers was predicted before construction since the use of total dissipation resistance is avoided in our network model. The model has been validated using data from electrical admittance measurements and from published results of other transducer designs. This work is expected to allow optimization of air-coupled capacitance transducers for applications to production engineering and non destructive evaluation.