Gammell Paul M, Maruvada Subha, Harris Gerald R
Food and Drug Administration, Center for Devices and Radiological Health, Silver Spring, MD 20993, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2007 May;54(5):1036-44. doi: 10.1109/tuffc.2007.349.
Time-delay spectrometry (TDS) is a swept-frequency technique that has proven useful in several ultrasonic applications. Commercial TDS systems are available, but only in the audio frequency range. Several ultrasonic research TDS systems have been constructed, and they have been used effectively for substitution calibration of hydrophones and for measurement of attenuation and sound velocity in materials. Unfortunately these systems depend on features of commercial equipment no longer manufactured, so a new system has been designed using modern equipment and straightforward signal processing. This system requires a frequency source with a reasonably linear sweep of frequency versus time, audio frequency filters, a standard double-balanced mixer, a power splitter, a waveform digitizer capable of handling audio frequency signals, and a personal computer. An optional implementation that shifts the signal to a lower frequency for more convenient digitization and easier velocity measurements additionally requires an audio frequency oscillator and an audio-range analog multiplier. The processing steps are performed with standard signal processing software. To demonstrate the operation of the system, substitution calibration measurements of hydrophones as well as attenuation measurements on a tissue mimicking material were obtained and compared to a custom TDS system previously described by the authors. The data from these two TDS systems agree to within +/- 0.5 dB in the 1-10 MHz frequency range used. Higher frequency source transducers could be used to extend this range.
时延光谱法（TDS）是一种扫频技术，已在多种超声应用中证明是有用的。市面上有商用TDS系统，但仅适用于音频范围。已经构建了几个超声研究TDS系统，它们已有效地用于水听器的替代校准以及材料中衰减和声速的测量。不幸的是，这些系统依赖于不再生产的商用设备的特性，因此已使用现代设备和简单的信号处理设计了一种新系统。该系统需要一个频率与时间具有合理线性扫频的频率源、音频滤波器、一个标准的双平衡混频器、一个功率分配器、一个能够处理音频信号的波形数字化仪以及一台个人计算机。一种可选的实现方式是将信号移至较低频率以便更方便地进行数字化和更容易地进行速度测量，这还需要一个音频振荡器和一个音频范围的模拟乘法器。处理步骤使用标准信号处理软件执行。为了演示该系统的运行情况，获得了水听器的替代校准测量结果以及对一种仿组织材料的衰减测量结果，并与作者先前描述的定制TDS系统进行了比较。在使用的1 - 10 MHz频率范围内，这两个TDS系统的数据在±0.5 dB范围内一致。可以使用更高频率的源换能器来扩展这个范围。
