Robert Jean-Luc, Fink Mathias
Philips Research North America, Briarcliff Manor, New York 10510, USA.
J Acoust Soc Am. 2008 Dec;124(6):3659-68. doi: 10.1121/1.3005560.
The decomposition of the time-reversal operator (DORT) is a detection and focusing technique using an array of transmit receive transducers. It can extract Green's functions of scatterers in a medium. A variant consists in transmitting focused beams (FDORT). It is shown here that the FDORT method can be interpreted as the decomposition of a time-reversal operator between an array of virtual transducers located at the transmit beams' foci and the physical array. The receive singular vectors correspond to scatterers' Green's functions expressed in the physical array while the transmit singular vectors correspond to Green's functions expressed in the virtual array. The position of the virtual array can be changed by varying the position of the foci, thus offering different points of view. Parameters and performance of some transmit schemes are discussed. Appropriately positioning the virtual transducers can simplify some problems. One application is measuring and correcting aberration in the case of a far-field phase screen model. Placing the virtual transducers near the phase screen transforms the problem in a simpler near-field phase screen problem.
时间反转算子分解（DORT）是一种利用发射-接收换能器阵列的检测和聚焦技术。它可以提取介质中散射体的格林函数。一种变体是发射聚焦波束（FDORT）。本文表明，FDORT方法可以解释为位于发射波束焦点处的虚拟换能器阵列与物理阵列之间的时间反转算子分解。接收奇异向量对应于在物理阵列中表示的散射体格林函数，而发射奇异向量对应于在虚拟阵列中表示的格林函数。通过改变焦点位置可以改变虚拟阵列的位置，从而提供不同的视角。讨论了一些发射方案的参数和性能。适当地放置虚拟换能器可以简化一些问题。一个应用是在远场相位屏模型的情况下测量和校正像差。将虚拟换能器放置在相位屏附近会将问题转化为一个更简单的近场相位屏问题。
