Subarray delta-sigma beamforming for low-cost underwater acoustic imaging

In real-time digital underwater acoustic imaging, the size, power consumption and cost of the front-end hardware are critical design issues especially for applications like UUV. The number of active array channels and sampling scheme directly affect these specifications. For low-cost front-end, we present a beamforming architecture based on subarray processing with nonuniform oversampling delta-sigma (/spl Delta//spl Sigma/) data conversion. We use a small-sized active subarray multiplexed over a large transducer array to acquire low-resolution beam lines, where the RF echo signal received at each subarray channel is digitized using 1-bit /spl Delta//spl Sigma/ modulator with nonuniform oversampling. In the nonuniform oversampling scheme, samples are taken in the time instants associated with the beamforming delays. The /spl Delta//spl Sigma/ coded partial beam outputs from the subarrays are first demodulated and then coherently summed to form a high-resolution image frame. By the way, the limited number of acquired beam lines are upsampled using beam space interpolation, thus allowing real-time processing in acquiring beams and also maintaining acceptable image quality. Our experimental results show that the proposed beamforming scheme provides high-resolution acoustic imaging while simplifying the front-end circuitry.