Capacitive micromachined ultrasonic transducers

A method for ultrasonic harmonic imaging by use of a capacitive micromachined ultrasonic transducer cell comprising the steps of:

• applying an electrical drive signal to said cell which exhibits a nominal fundamental transmit frequency and which is predistorted in consideration of a nonlinear operating characteristic of said cell;
• and
• producing an acoustic wave from said cell in response to said electrical drive signal with low spectral content at a harmonic of said fundamental frequency.

A harmonic ultrasonic transducer comprising:

• an array of transducer elements, each element comprising a plurality of micromachined cells located on a substrate with each cell having a membrane which moves with a nonlinear electromechanical response in response to an ultrasonic drive signal applied to a membrane electrode;
• and
• a source of ultrasonic drive signals, coupled to membrane electrodes of cells of said array, said drive signals being predistorted in consideration of said nonlinear electromechanical response so as to transmit acoustic waves with reduced signal content at the harmonic of a fundamental transmit frequency.