Aubry J F, Tanter M, Gerber J, Thomas J L, Fink M
Laboratoire Ondes et Acoustique, ESPCI, Université Paris VII, URA CNRS 1503, France.
J Acoust Soc Am. 2001 Jul;110(1):48-58. doi: 10.1121/1.1377052.
To focus ultrasonic waves in an unknown heterogeneous medium using a phased array, one has to calculate the optimal set of signals to be applied on the transducers of the array. (In most applications of ultrasound, medical imaging, medical therapy, nondestructive testing, the first step consists of focusing a broadband ultrasound beam deeply inside the medium to be investigated.) Focusing in a homogeneous medium simply requires to compensate for the varying focus-array elements geometrical distances. Nevertheless, heterogeneities in the medium, in terms of speed of sound, density, or absorption, may strongly degrade the focusing. Different techniques have been developed in order to correct such aberrations induced by heterogeneous media (time reversal, speckle brightness, for example). In the companion to this paper, a new broadband focusing technique was investigated: the spatio-temporal inverse filter. Experimental results obtained in various media, such as reverberating and absorbing media, are presented here. In particular, intraplate echoes suppression and high-quality focusing through a human skull, as well as hyper-resolution in a reverberating medium, will be shown. It is important to notice that all these experiments were performed with fully programmable multichannel electronics whose use is required to fully exploit the spatio-temporal technique.
为了使用相控阵在未知的非均匀介质中聚焦超声波，必须计算要施加在阵列换能器上的最佳信号集。（在超声的大多数应用中，如医学成像、医学治疗、无损检测，第一步是将宽带超声束聚焦到待研究介质的深处。）在均匀介质中聚焦只需补偿聚焦阵列元件的几何距离变化。然而，介质在声速、密度或吸收方面的非均匀性可能会严重降低聚焦效果。为了校正由非均匀介质引起的这种像差，已经开发了不同的技术（例如时间反转、散斑亮度）。在本文的配套文章中，研究了一种新的宽带聚焦技术：时空逆滤波器。这里展示了在各种介质（如混响介质和吸收介质）中获得的实验结果。特别地，将展示抑制板内回波以及通过人类头骨实现高质量聚焦，以及在混响介质中的超分辨率。需要注意的是，所有这些实验都是使用完全可编程的多通道电子设备进行的，充分利用时空技术需要使用这种设备。
