A new acoustical imaging by means of frequency-differential hologram matrix

一种基于频率微分全息图矩阵的新声学成像

• 批准号: 61550277
• 负责人: NAKAYAMA JUNICH
• 金额: $ 0.83万
• 依托单位: Kyoto Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1986
• 资助国家: 日本
• 起止时间: 1986 至 1987
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-61550277/
• 关键词: Acoutical imaging; Acoustical holography; Frequency modulatin; 周波数応答; 反射計

In the conventional multifrequency holography, a continuous carrier with frequency f is transmitted and the phase and amplitude of the received signal is measured to get the frequency response H(f) associated with transmitting and receiving transducer arrays. As a new scheme of CW sonar, however, we have introduced the concept of the FDHM ( frequency-differential hologram matrix) D(f). The scheme makes it possible to compensate the propagation loss, so that a weak signal from a far-region target can be enhanced.To measure the FDHM, we transmit a carrier frequency-modulated by a sinusoidal signal, and the received signal is first phase-detected and then product-detected using the sinusoidal modulation signal. Making up such transmitter and receiver, We constructed a computercontrolled system for measuring the FDHM. We then measured the FDHM at 256 different carrier frequency and the data was Fouriertransformed to get a one-dimensional image of a target. As a result, several merits of the method were experimentally proved, such as canceling of unwanted effect due to coupling between transmitter and receiver, improvement in signal to noise level by about 15 dB, compared with the result by the frequency response method, and the compensation of the propagation loss by which a weak signal from a target in the far region can be enhanced.Next, for designing a two-dimensional imaging system by means of the FDHM with respect to a linear array, a computer simulation has been carried out. It was shown that the FDHM measured with an array with 32 transducer elements and 32 carier frequencies gives a clear image of a target. We also propose to use the secon-order FDHM, because it gives an image of targets with uniform intensities.

在传统的多频全息术中，发射频率为f的连续载波，并测量接收信号的相位和幅度，以获得与发射和接收换能器阵列相关联的频率响应H（f）。作为连续波声纳的一种新方案，我们引入了频差全息矩阵D（f）的概念。该方案可以补偿传播损耗，从而增强来自远区目标的微弱信号。为了测量FDHM，我们发射一个由正弦信号调制的载波，接收信号首先进行相位检测，然后使用正弦调制信号进行乘积检测。我们利用这种发射机和接收机，构建了一个计算机控制的FDHM测量系统。然后，我们在256个不同的载波频率下测量FDHM，并将数据进行傅立叶变换以获得目标的一维图像。结果，实验证明了该方法的几个优点，例如，消除了由于发射机和接收机之间的耦合而产生的不希望的影响，与频率响应方法的结果相比，信噪比提高了约15 dB，并且补偿了传播损耗，通过该传播损耗，可以增强来自远区域中的目标的弱信号。为了利用FDHM设计二维成像系统，对线阵进行了计算机模拟。结果表明，用32个换能器阵元和32个载频组成的阵列测量的FDHM给出了清晰的目标图像。我们还建议使用二阶FDHM，因为它给出了具有均匀强度的目标的图像。