3-Dimensional Acoustic Imaging by Multifrequency Hologram Matrix

多频全息成像方法利用二维空间接收器(或发射机)阵列实现横向二维分辨率，利用频率阵实现距离分辨率，以获得真实的三维分辨率。首先，我们对三维多频全息成像进行了各种计算机模拟，证实了该方法具有理想的三维分辨率。也就是说，不仅横向分辨率，而且距离分辨率都约为频率阵列中心频率的3.7倍波长。我们设计并订购了二维声换能器阵列给日本电工株式会社。换能器正面尺寸为80 mm×80 mm。在由环氧树脂和金属粉末制成的衬垫块上粘结了质量良好的大型PZT板。用所谓的钻石刀具切割，我们制作了16×16(=256)个小孔径为1.0 mm×1.0 mm的接收器换能器元件，其中…更多的e间距为4.5 mm。PZT材料的其余部分也由许多换能器的小碎片组成。将它们电并联，制成80 mm×80 mm的大尺寸传声换能器。这种换能器结构保证了活塞的均匀振动，并将理想的平行平面波传输到物体上。谐振频率设计为600 kHz，多频全息图的频率孔径设计为450 kHz~550 kHz。因此，在该频率范围内的灵敏度或增益和相位特性是非常均匀的，并且相邻元件之间的相互耦合也非常小，即-60分贝。介绍了一种快速响应的直接频率合成器，对传统的全息测量控制电路进行了改进，使在短时间内测量多频全息图成为可能。即每帧32ms，由小型机的软件直接控制。这一速度对于活体医学成像是必不可少的。我们为每个接收元件设计并制作了多通道前置放大器，并为每个原始矩阵设计并同时数字化电路，以使测量速度尽可能快。较少

Multifrequency holographic imaging method uses a two-dimensional spatial receiver (or transmitter) array for lateral two-dimensional resolution and a frequency array for range resolution to get a true three-dimensional resolution.First, we made a variety of computer simulations of three dimensional multifrequency holographic imaging, and confirmed that this method gives us a desirable true three dimensional resolution of the reconstructed images. That is, not only lateral but also range resolutions are both about 3.7 times wavelength of the central frequency of the frequency array.We designed and ordered two-dimensional acoustic transducer array to Nippon Denpa Kogyo Company Limited. Front size of the transducer is 80 mm times 80 mm. A large PZT plate of a good quality is cemented on the backing block made of Epoxy resin and metallic powder. Cutting it by a so-called diamond cutter, we made 16 times 16 (=256) receiver transducer elements of a small aperture of 1.0 mm times 1.0 mm, whos … More e spacing is 4.5 mm. Rest part of the pzt material is also composed of many small fragments of transducers. Those were connected electrically parallel to make a big size of transmitting acoustic transducer of 80 mm times 80 mm. This type of transducer structure is guaranteed to make a uniform piston oscillation and to transmit an ideal parallel plane wave to the object. Resonance frequency was designed to 600 KHz, and the frequency aperture of multifrequency hologram is designed from 450 KHz to 550 KHz. Therefore, sensitivity or gain and phase characteristics over this frequency range is very uniform and also mutual coupling between the adjacent elements is very small, i. e. -60 dB. These characteristics are very important for multifrequency holographic imaging of synthetic aperture method.Introducing a direct frequency synthesizer of a fast response, we modified the conventional control circuit of holographic measurement, and made it possible to measure multifrequency hologram in a desirable short time. i. e. 32 ms per frame, being directly controlled by a software of a minicomputer. This speed is necessary for medical imaging of living body.We designed and fabricated multi-channel preamplifiers for every receiver elements and simultaneously digitizing circuits for each raw of the matrix to make the measurement as fast as possible. Less