Hunter Christopher, Sapozhnikov Oleg A, Maxwell Adam D, Khokhlova Vera A, Wang Yak-Nam, MacConaghy Brian, Kreider Wayne
CIMU, Applied Physics Laboratory, University of Washington, 1013 NE 40 Street, Seattle, WA 98105, USA.
Physics Faculty, Moscow State University, Leninskie Gory, Moscow 119991, Russia.
Phys Procedia. 2016;87:93-98. doi: 10.1016/j.phpro.2016.12.015.
In medical and industrial ultrasound, it is often necessary to measure the acoustic properties of a material. A specific medical application requires measurements of sound speed, attenuation, and nonlinearity to characterize livers being evaluated for transplantation. For this application, a transmission-mode caliper device is proposed in which both transmit and receive transducers are directly coupled to a test sample, the propagation distance is measured with an indicator gage, and receive waveforms are recorded for analysis. In this configuration, accurate measurements of nonlinearity present particular challenges: diffraction effects can be considerable while nonlinear distortions over short distances typically remain small. To enable simple estimates of the nonlinearity coefficient from a quasi-linear approximation to the lossless Burgers' equation, the calipers utilize a large transmitter and plane waves are measured at distances of 15-50 mm. Waves at 667 kHz and pressures between 0.1 and 1 MPa were generated and measured in water at different distances; the nonlinearity coefficient of water was estimated from these measurements with a variability of approximately 10%. Ongoing efforts seek to test caliper performance in other media and improve accuracy via additional transducer calibrations.
在医学和工业超声领域，常常需要测量材料的声学特性。特定的医学应用需要测量声速、衰减和非线性特性，以便对供移植评估的肝脏进行特征描述。针对此应用，提出了一种透射模式卡尺装置，其中发射换能器和接收换能器均直接与测试样品耦合，传播距离用指示计测量，并记录接收波形以供分析。在这种配置下，准确测量非线性特性存在特殊挑战：衍射效应可能相当显著，而短距离内的非线性失真通常较小。为了能从无损伯格斯方程的准线性近似中简单估计非线性系数，该卡尺使用了一个大型发射器，并在15至50毫米的距离处测量平面波。在水中不同距离处产生并测量了667千赫兹、压力在0.1至1兆帕之间的波；根据这些测量结果估计水的非线性系数，其变化率约为10%。正在进行的工作旨在测试该卡尺在其他介质中的性能，并通过额外的换能器校准提高精度。
