CODING FOR ARRAY SIGNAL USING MULTIDIMENSIONAL OVERSAMPLING TECHNIQUES

本文提出了一种新的声换能器阵列数模转换技术。该技术利用阵列信号的多维带限特性。利用该技术，将大动态范围的波前转换为多个1比特波形，并在时间和空间上进行过采样，取得了以下成果：1.提出了一种基于二维DELTASIGMA调制的一维或二维换能器阵过采样技术。证实了二维一阶Δ ∑调制的稳定性。阐明了信噪比与二维Δ ∑调制参数如采样频率、阵列间隔等的关系。在空间或时间采样频率加倍的情况下，信噪比可提高9dB。我们研究了矩阵阵、圆形阵和环形阵的编码方法。该系统由64路数字方向图发生器和开关放大器阵列组成。放大器直接由数字模式信号控制。输出范围为2 Vpp至100 Vpp。开关频率范围为1 KHz ~ 10 MHz。3.将P（VDF-TrFE）共聚物薄膜与图形电极层压在印刷电路板上制成超声阵列换能器。搭建了机载动圈扬声器阵列。4.利用该系统产生了聚焦声束。指向性的最大误差为0.3%，焦点处观测波形的信噪比为80 dB（空间过采样比为16，时间过采样比为16）。利用环形阵列产生了球面波。

We have proposed a new digital to analog conversion technique for acoustical transducer array. This technique utilizes the multidimensional band-limited property of array signals. Using the technique, a large dynamic-range wavefront is converted to multiple 1-bit waveforms which are oversampled temporally and spatially.Following results are obtained :1.We have proposed an oversampling technique using two dimensional DELTASIGMA-modulation for 1-D or 2-D transducer arrays. The stability of 2-D first-order DELTASIGMA-modulation os confirmed. We have clarified the relation between the SN ratio and the parameters of the 2-D DELTASIGMA-modulation, such as sampling frequency and array intervals. The SN ratio increases 9dB for doubling the spatial or temporal sampling frequency.We have developed coding methods for matrix array, circular array and annular array.2.We have constructed a trial DA conversion system for acoustical transducer array. This system consists of 64ch digital pattern generator and array of switching amplifiers. The amplifiers are directly controlled by digital pattern signal. The output range is 2 Vpp to 100Vpp. The switching frequency range is lKHz to 10MHz.3.An ultrasonic array transducer was constructed by laminating P (VDF-TrFE) copolymer films with pattern electrode on a printed circuit board. The airborne dynamic-speaker array was also constructed.4.A focused acoustical beam was generated by the proposed system. The maximum error of the directivity was 0.3%, and the SN ratio of observed waveform at the focal point was 80dB (over-sampling ratio is 16 for space, 16 for time). The spherical wave was also generated using the annular array.