Elevation beam profile control with bias polarity patterns applied to microfabricated ultrasound transducers

In contrast to PZT probes, capacitive microfabricated ultrasonic transducers (cMUTs) require a DC bias. We investigate elevation beam profile shaping by spatially varying this bias polarity. Such a scheme introduces a 180/spl deg/ phase shift in the device's impulse response. A Fresnel zone plate is realized which is capable of generating tight elevation foci using a large aperture. This paper presents measurements from a prototype Fresnel cMUT probe, and matching simulation results. The Fresnel probe is capable of improved slice thickness compared with both a conventionally lensed probe and a multi-row design. Also, combinations of bias polarity control and multiple firings can enable harmonic imaging without pre-distortion of the transmit signal. Multiple firing schemes further optimize slice thickness, and allow beam steering in elevation.