UNDER WATER 3-D IMAGING SYSTEM USING ACOUSTICAL HOLOGRAPHY

我们研制了一种利用声全息或合成孔径聚焦技术的水下三维成像系统。我们先前已经提出了一个高速成像系统使用沃尔什函数调制的传输脉冲。在本课题中，我们研制了一套基于该方法的低成本成像系统，取得了以下成果：1）提出了一种目标相对于测量系统阵列运动的图像重建方法。重建高质量的图像需要多个声波阵面传输和接收周期，而我们的系统能够在每个周期生成一幅图像。在许多实际情况下，目标相对于系统的阵列是运动的，并且当采用重复数据采集时，必须考虑这些相对运动来执行成像。为了将成像系统扩展到相对运动的目标，提出了一种新的图像重建算法。2）利用压电橡胶片和p（VDF-TrFE）共聚物薄膜构建了阵列换能器。我们还研制了一个64通道开关放大器的阵列。放大器由逻辑信号直接控制。输出范围为2 Vpp至100 Vpp。开关频率范围为1 KHz ~ 10 MHz。3）在低成本PC机上安装DSP协处理器板，开发了高速运算系统。计算系统与数据采集系统连接。

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.