Bauer Adam Q, Marutyan Karen R, Holland Mark R, Miller James G
Department of Physics, Washington University in Saint Louis, Saint Louis, Missouri 63130, USA.
J Acoust Soc Am. 2007 Jul;122(1):222-8. doi: 10.1121/1.2735803.
Phase cancellation effects can compromise the integrity of ultrasonic measurements performed with phase sensitive receiving apertures. A lack of spatial coherence of the ultrasonic field incident on a phase sensitive receiving array can produce inaccuracies of the measured attenuation coefficient and phase velocity. The causal (Kramers-Kronig) link between these two quantities in the presence of phase distortion is investigated using two plastic polymer materials, Plexiglas and Lexan, that exhibit attenuation coefficients that increase linearly with frequency, in a fashion analogous to that of soft tissue. Flat and parallel plates were machined to have a step of a thickness corresponding to an integer number of half wavelengths within the bandwidth investigated, 3 to 7 MHz. Insonification of the stepped portion of each plate produces phase cancellation artifacts at the receiving aperture and, therefore, in the measured frequency dependent attenuation coefficient. Dispersion predictions using two different forms of the Kramers-Kronig relations were performed for the flat and the stepped regions of each plastic plate. Despite significant phase distortion and a detection system sensitive to these aberrations, the Kramers-Kronig link between the apparent attenuation coefficient and apparent phase velocity dispersion remains intact.
相位抵消效应可能会损害使用相敏接收孔径进行的超声测量的完整性。入射到相敏接收阵列上的超声场缺乏空间相干性，可能会导致测量的衰减系数和相速度不准确。使用两种塑料聚合物材料，即有机玻璃和聚碳酸酯，研究了在存在相位失真的情况下这两个量之间的因果（克拉默斯 - 克朗尼格）联系，这两种材料的衰减系数随频率线性增加，其方式类似于软组织。将平板加工成具有一个厚度阶跃，该厚度阶跃对应于所研究带宽（3至7兆赫兹）内的整数个半波长。对每个平板的阶梯部分进行超声照射会在接收孔径处产生相位抵消伪像，因此也会在测量的频率相关衰减系数中产生相位抵消伪像。对每个塑料平板的平坦区域和阶梯区域使用两种不同形式的克拉默斯 - 克朗尼格关系进行了色散预测。尽管存在明显的相位失真以及对这些像差敏感的检测系统，但表观衰减系数和表观相速度色散之间的克拉默斯 - 克朗尼格联系仍然成立。
