Walker S C, Roux Philippe, Kuperman W A
Marine Physical Laboratory of the Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0238, USA.
J Acoust Soc Am. 2009 Jun;125(6):3828-34. doi: 10.1121/1.3117374.
Time-reversing the transfer function between a time-reversal mirror (TRM) and a distant probe source location generates an acoustic spatio-temporal focus at the location. It is shown that a TR focus behaves as a "virtual" source (in the far-field limit) in the outbound direction with respect to the TRM. By extension, a collection of TRM-to-probe source transfer functions constitutes a virtual source array (VSA) that can serve as a remote platform for active imaging methods such as beam-steering and other coherent wavefront techniques. As a demonstration, a set of a-priori sampled TRM-to-VSA transfer functions are steered to coherently focus at a selected location beyond the VSA for which the transfer function is not known a-priori. In this case the VSA acts as a lens that refocuses the TRM field to the target location. Under proper conditions, the resolution is comparable to that of standard TR. While the specific application of active focusing is presented as a validation of the concept, the relationship between coherent focusing and the transfer function implies that the virtual array concept may find use in a range of imaging methods, both active and passive. Possible applications are discussed, and simulation and experimental results are presented.
对时间反转镜（TRM）与远处探测源位置之间的传递函数进行时间反转，会在该位置产生一个声学时空焦点。结果表明，在相对于TRM的出射方向上，TR焦点在远场极限下表现为一个“虚拟”源。由此推广，一组TRM到探测源的传递函数构成一个虚拟源阵列（VSA），它可以作为一个远程平台，用于诸如波束控制和其他相干波前技术等有源成像方法。作为一个演示，一组先验采样的TRM到VSA的传递函数被控制，以相干地聚焦在VSA之外的一个选定位置，而该位置的传递函数是先验未知的。在这种情况下，VSA起到一个透镜的作用，将TRM场重新聚焦到目标位置。在适当条件下，分辨率与标准TR相当。虽然有源聚焦的具体应用被作为该概念的验证提出，但相干聚焦与传递函数之间的关系意味着虚拟阵列概念可能在一系列有源和无源成像方法中得到应用。讨论了可能的应用，并给出了模拟和实验结果。
