PHASED SUBARRAY IMAGING FOR LOW-COST, WIDEBAND COHERENT ARRAY IMAGING

The front-end hardware complexity of conventional full phased array (FPA) imaging is proportional to the number of array elements. Phased subarray (PSA) imaging has been pro- posed as a method of reducing the hardware com- plexity—and therefore system cost and size—while achieving near-FPA image quality. A new method is presented for designing the subarray-dependent interpolation filters suitable for wideband PSA imaging. The method was tested experimentally using pulse-echo data of a wire target phantom acquired using a 3.2-cm, 128-element capacitive micromachined ultrasonic transducer (CMUT) array with 85% fractional bandwidth at 3 MHz. A specific PSA configuration using seven 32-element subarrays was compared to FPA imaging, repre- senting a 4-fold reduction in front-end hardware complexity and a 43% decrease in frame rate. For targets near the fixed transmit focal distance, the mean 6-dB lateral resolution was identical to that of FPA, the axial resolution improved by 4%, and the SNR decreased by 5 dB. Measurements were repeated for 10 different PSA configurations with subarray sizes ranging from 4 to 60. The lateral and axial resolutions did not vary significantly with subarray size; both the SNR and contrast-to- noise ratio (CNR) improved with increased subar- ray size. I. INTRODUCTION Conventional phased array imaging systems simul- taneously transmit on and receive from all transducer elements to form each beam of a sector image. We refer to this method as full phased array (FPA) imag- ing. This architecture requires that each element have a dedicated front-end electronic channel for pulse transmission, received signal amplification, filtering, time-gain compensation, and analog-to-digital con- version. The number of front-end channels—or front-