System modelling plays an important part in the design of transducer systems especially when designing active arrays for apodising or beam steering . Computational models have been developed within MATLAB to predict the acoustic field from transducers, taking into account device geometry and the transmission medium, although at present only relatively simple element geometries can be handled these models produce good agreement with experimental measurements for multi element arrays.

Modelling Micromachined Devices.

We have also been looking at modelling the mechanical characteristics of micromachined transducers. Unlike most other reported devices ours have an air filled cavity behind the membrane and the membrane itself is considerably larger (~1mm square). When modeling these devices, taking into account only the mechanical properties of the membrane is insufficient as it predicts a resonance in the region of around 60KHz, whereas experimentally we see a resonance of around 1MHz. This can be explained by combining the membrane model with that of a gas plane piston.

Plots of mechanical stiffness and resultant resonant frequency for varying size of memrane for a 1um air gap and 1um membrane thickness.
As can be seen from the graphs above for devices typical of those we use above 0.25mm square the piston model dominates, below this it is the membrane stiffness that determines the resonance.

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