UNDER WATER 3-D IMAGING SYSTEM USING ACOUSTICAL HOLOGRAPHY

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We have developed an underwater 3-D imaging system using acoustical holography, which utilizes the acoustical holography or synthetic aperture focusing technique. We have previously proposed a high-speed imaging system using Walsh-function-modulated transmission pulses. In this project, we have developed a low-cost imaging system base on the proposed method.Following results are obtained :1) We have proposed an image reconstruction method for targets moving relative to an array of a measurement system. Multiple cycles of transmission and reception of acoustical wavefront are required to reconstruct high-quality images, whereas our system is able to from one image for each cycle. In many practical situations, targets are in motion relative to the array of the system, and imaging must be performed considering these relative motions when repetitive data acquisition is employed. In order to expand the imaging system to relatively moving targets, a new algorithm for image reconstruction is developed.2) We have constructed a array transducer with piezoelectric rubber sheet and p (VDF-TrFE) copolymer film. We also developed a 64ch swiching amplifiers for the array. The amplifiers are directly controlled by logic signal. The output range is 2 Vpp to 100Vpp. The switching frequency range is 1KHz to 10MHz. Transduces are driven with binary waveforms, which are obtained with DELTASIGMA-modulation.3) We have installed the DSP co-processor board to low-cost PC system, and developed a high speed computing system. The computing system was connected with a data acquisition system.