A 120+ 120- Element Crisscross CMUT Probe's with Real-Time Switchable Electronic and Fresnel Focusing Capabilities

Biplane modality is frequently used in medical ultrasound imaging applications. Crossed array configurations, in which two orthogonal 1-D arrays co-exist on the same area, are particularly suitable for biplane imaging. However, the imaging performance is limited by the absence of focusing capability in the arrays respective elevation directions. In this paper, we present a novel 120+120-element 7 MHz crisscross Capacitive Micromachined Ultrasonic Transducer (CMUT) probe in which the orthogonal arrays are both provided with Fresnel elevation focusing capability. The CMUT probe includes low-noise amplifiers and high-voltage switches, which allow fast switching (<;200 μs) of the CMUT bias voltage of each array element between 0 V and high voltages up to +300 V. The bias polarity selection enables the elevation aperture Fresnel focusing, while the switching capability allows to alternately apply the elevation bias pattern to the two orthogonal arrays in realtime during biplane scan. A crisscross CMUT array was fabricated, packed and electrically characterized. The focusing capabilities were tested by interfacing the probe to the ULA-OP 256 scanner. C-scans of radiated pressure fields were acquired at the focal depth, and side lobe levels were evaluated.