Time Reversal of Ultrasonic Fields-Part I : Basic Principles
Time Reversal of Ultrasonic Fields-Part I : Basic Principles
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发表时间：
2000
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通讯作者：
Mathias Fink
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作者：
Mathias Fink
超声场的时间反转是一种通过非均匀介质聚焦的方法。这可以通过由线性响应并允许对入射声压进行采样的发射-接收换能器阵列制成的时间反转镜（“M”）来完成。然后，压力场被时间反转并重新发射。该过程可用于通过非均匀介质聚焦在被声穿透后表现为声源的反射目标上。在讨论用于聚焦脉冲波通过非均匀介质的经典技术（自适应延时技术）时引入了时间反转方法。利用非均匀介质中的互易性，脉冲波时反聚焦实现了对基阵和目标之间非均匀传输传递函数的时空匹配滤波，是最优的。时间反转聚焦技术通过最大化目标位置处的压力来向换能器元件提供最佳输入。对时间反演波场的研究也导致了本文所描述的新概念的发展：时间反演腔，扩展了TRM的概念;迭代时间反演处理，用于根据目标的反射率和扩展目标的共振自动分选目标。在论文的最后一部分，TRM和相位共轭镜之间的根本区别进行了描述。
Time reversal of ultrasonic fields represents a way to focus through an inhomogeneous medium. This may be acomplished by a time-reversal mirror ("M) made from an array of transmit-receive transducers that respond linearly and allow the incident acoustic pressure to be sampled. The pressure field is then time-reversed and re-emitted. This process can be used to focus through inhomogeneous media on a reflective target that behaves as an acoustic source after being insonified. The time-reversal approach is introduced in a discussion of the classical techniques used for focusing pulsed waves through inhomogeneous media (adaptative time-delay techniques). Pulsed wave time-reversal focusing is shown using reciprocity valid in inhomogeneous medium to be optimal in the sense that it realizes the spatial-temporal matched filter to the inhomogeneous propagation transfer function between the array and the target. Time-reversal focusing technique provides the optimal inputs to the transducer elements by maximizing the pressure at the target location. The research on time-reversed wave fields has also led to the development of new concepts that are described in the paper: time-reversal cavity that extends the concept of the TRM; iterative time-reversal processing for automatic sorting of targets according to their reflectivity and resonating of extended targets. In the last part of the paper the fundamental differences between a TRM and a phase-conjugated mirror are described.