Round W H, Bates R H
Ultrason Imaging. 1987 Jan;9(1):18-28. doi: 10.1177/016173468700900102.
When an ultrasonic pulse is scattered off a particle, the spectrum of the scattered pulse differs from that which was transmitted. A mathematical analysis is presented to show that the center frequency of the backscattered pulse is greater than that of the transmitted pulse and that the bandwidth decreases slightly when the spectrum of the pulse is Gaussian in shape. The results of measurements designed to test the theory are presented. The magnitude of the shift in center frequency for pulses backscattered off subwavelength-diameter wires is found to be similar to that predicted by the analysis. It is shown that characteristics of the spectra of the backscattered pulses can differ from those predicted if the shape of the spectrum is not truly Gaussian (as is assumed in most published analyses, including that introduced here). In medical ultrasonic imaging, the pulses are modified by scattering and absorption. The analysis is extended to account for the effects of both interactions. This allows the bandwidth and center frequency of pulses backscattered from tissues and received by medical ultrasonic scanners to be predicted.
当一个超声脉冲从一个粒子上散射时，散射脉冲的频谱与发射的频谱不同。本文进行了数学分析，以表明背向散射脉冲的中心频率高于发射脉冲的中心频率，并且当脉冲频谱为高斯形状时，带宽会略有减小。文中给出了旨在验证该理论的测量结果。发现从亚波长直径的金属丝背向散射的脉冲的中心频率偏移量与分析预测的相似。结果表明，如果频谱形状不是真正的高斯形状（正如大多数已发表的分析中所假设的，包括本文介绍的分析），背向散射脉冲的频谱特性可能与预测的不同。在医学超声成像中，脉冲会因散射和吸收而发生改变。该分析扩展到考虑这两种相互作用的影响。这使得从组织背向散射并被医学超声扫描仪接收的脉冲的带宽和中心频率得以预测。
