An array of CMUT cells has a DC bias voltage coupled to the top electrodes of the cells to bias the electrode to a desired collapsed or partially collapsed state. In the event of a short circuit failure of a CMUT cell a protection circuit for the cell senses an over current condition and responds by opening the DC current path through the failed cell. The protection circuit further disables the transmit and receive circuitry of the cell. In another implementation a sense circuit senses an over current condition of the DC bias supply and responds by disabling all of the CMUT cells of the array then sequentially re enabling them except that an attempt to re enable a failed cell results in that cell remaining in a disabled state.
