An ultrasonic diagnostic imaging system comprises a CMUT transducer probe with an array (10′) of CMUT cells either of the same or variable diameters operated in a conventional mode during ultrasonic signal reception and a collapsed mode during ultrasonic signal transmission. The frequency response to the CMUT cells is tailored for different clinical applications or continuously varied during echo reception by decreasing the DC bias voltage for the CMUT cells for lower frequency clinical applications, increasing the DC bias voltage for higher frequency clinical applications, or continuously decreasing the DC bias voltage as echoes are received to track the information frequency composition of the returning echo signals.