Cassereau D, Fink M
Lab. Ondes et Acoustique, Paris VII Univ.
IEEE Trans Ultrason Ferroelectr Freq Control. 1992;39(5):579-92. doi: 10.1109/58.156176.
For pt.II see ibid., vol.39, no.5, p.567-78 (1992). A theoretical model for time-reversal cavities to optimize focusing in homogeneous and inhomogeneous media is described. The concept of the cavity can be understood as the most realistic approximation to an exact three-dimensional (3-D) time-reversal of ultrasonic fields; it is also a generalization of the time-reversal mirrors realized experimentally in the laboratory. The proposed method is based on an approach in the transient regime that is more general than the monochromatic formalism used in optics to analyze the phase conjugation mirrors efficiency. This method uses impulse diffraction theory to obtain the impulse response of the cavity in any inhomogeneous medium. An original interpretation of the limitations due to diffraction observed in wave field propagation in terms of the different waves generated inside the cavity is also proposed. The time-reversal focusing process using a closed cavity in a weakly inhomogeneous medium is compared with more classical techniques to compensate wavefront distortions, thus illustrating the focusing improvement due to the time-reversal method.
第二部分见同刊第39卷，第5期，第567 - 578页（1992年）。本文描述了一种用于时间反转腔的理论模型，以优化在均匀和非均匀介质中的聚焦。腔的概念可理解为对超声场精确三维（3 - D）时间反转的最现实近似；它也是实验室中实验实现的时间反转镜的一种推广。所提出的方法基于瞬态 regime 中的一种方法，该方法比光学中用于分析相位共轭镜效率的单色形式主义更具一般性。此方法使用脉冲衍射理论来获得腔在任何非均匀介质中的脉冲响应。还提出了一种关于在波场传播中观察到的由于衍射导致的局限性的原始解释，该解释基于腔内产生的不同波。将在弱非均匀介质中使用封闭腔的时间反转聚焦过程与更经典的补偿波前畸变的技术进行了比较，从而说明了时间反转方法带来的聚焦改善。
