A 32x32 Integrated CMUT Array for Volumetric Ultrasound Imaging

Real-time 3D volumetric ultrasound imaging systems require transmit and receive circuitry to generate the ultrasound beam and process the received echo signals. Since a 2D array is required for 3D imaging, the complexity of building such a system is significantly higher, e. g., front-end electronics need to be interfaced to the transducer, a large number of elements need to be interfaced to the backend system and a large dataset needs to be processed. In this work, we present a 3D imaging system using capacitive micromachined ultrasonic transducer (CMUT) technology that addresses many of the challenges in building such a system. The transducer is a 5-MHz CMUT array with an 8 mm x 8 mm aperture size. The aperture consists of 1024 elements (32x32) with an element pitch of 250 m. An integrated circuit (IC) is integrated very close to the CMUT array. It consists of a transmit beamformer and receive circuitry to improve the noise performance of the overall system. Simultaneous multi-beam transmit is also incorporated in the IC to improve the imaging frame rate. The CMUT is flip-chip bonded to the IC and the final assembly measured 9.2 mm x 9.2 mm. The assembly was then interfaced with an FPGA and a backend system (comprising of a data acquisition system and PC). The FPGA provided the digital I/O signals for the IC and the backend system was used to process the received RF echo data (from the IC) and reconstruct the volume image using a phased array imaging approach. Imaging experiments were performed using wire phantoms. Real-time volumetric images were captured at 5 volumes per second and are presented in this paper.