A FPGA Based Front-end Circuit for Air-coupled CMUT Arrays: Preliminary Design

Air-coupled capacitive micromachined ultrasonic transducer (CMUT) arrays have good application prospects in ultrasonic ranging, ultrasound imaging and gesture recognition. However, the existing integrated CMUT systems are mostly designed for liquid-coupled CMUTs, which is not suitable for air-coupled CMUTs because of the different requirements in bandwidth and DC bias voltage. In order to realize an integrated system of air-coupled CMUTs based on FPGA, this paper reports a front-end circuit and subsequent experimental results. The front-end circuit we developed consists of four parts: a pulser, an AC-DC coupling circuit, a T/R switch and a transimpedance amplifier. The experimental result shows that the emission energy of our air-coupled CMUT can be significantly increased using bipolar square-wave burst excitation produced by our designed pulser instead of sin-wave burst excitation produced by our previous commercial equipment. Working with our 210 kHz 16×16 air-coupled CMUT array, the reported front-end circuit can perform 22 dB SNR in burst-echo testing. The preliminary design of the circuit and its experimental results demonstrate the feasibility of an integrated application system solution for air-coupled CMUT arrays.