An accurate model for fluid loading on circular CMUTs

An accurate analytical model is presented for circular CMUT arrays operating in immersion. Our model emphasises the fluid loading and its effects on circular CMUTs performance when operated as an element of large array. The model can accurately predict the series and parallel resonance frequencies as well as the bandwidth of a CMUT array in immersion. CMUT acoustical impedance, in its exact closed form, augments the conventional CMUT equivalent circuit. CMUT material density is replaced with a frequency dependent equivalent density that accounts for the distributed fluid loading. Data fitting against an FEM model is used to determine the equivalent density dimensional dependence. A correction is also suggested for the equivalent circuit transformer ratio. Test cases are presented to illustrate the accuracy of the proposed model as well as its speed as compared to its FEM counterpart.