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We propose a new technique for acoustic imaging that employs a back-projection algorithm to process signals from a static ultrasonic microphone array. To obtain the projection data for a target, we integrate the time distribution of received signal powers gained by pulse compression with the Radon transform of a sound field in polar coordinates. The proposed method is expected to improve angular resolution. In this paper, we describe the principle of this algorithm, explaining how it improves the resolution and performs better than conventional methods. Deconvolution is used to improve the quality of the images obtained. We have conducted computer simulations to verify the performance of the proposed algorithm. From these simulations, the angular resolution of the images achieved by the proposed technique was shown to be double that obtained by a conventional beamforming method. In our future work, we plan to conduct experiments with real environments and investigate the theoretical aspects of the proposed method more deeply.

We have developed an ultrasonic sound processing system for 3D imaging with 128 microelectromechanical systems (MEMS) microphones and a highly configurable field programmable gate array (FPGA). The system consists of a sensor array board, analog-to-digital converter (ADC) modules, and a processing board. The ultrasonic MEMS sensors are precisely aligned on a printed circuit board (PCB) to form a 16 × 8 planar grid with 112 ° × 50° viewing angles for wide-band signals with the center frequency at 40 KHz.