Water Tunnel Acoustic Measurements Using a Time Reversal Mirror

Abstract

Acoustic time reversal is a process in which acoustic energy received at an array is recorded, time-reversed, and then rebroadcast through the same or a collocated array. The result is that the original signal is “retrofocused” in time and space to the original source location without regard to the propagation paths or characteristics of the complex media between source and receiver. The array used for receive and rebroadcast, together with the data acquisition and processing system, is referred to as a time reversal mirror (TRM). Adaptation of time reversal mirrors to the problem of water tunnel acoustic measurements is examined. A concept demonstration test is planned for the Garfield Thomas Water Tunnel (GTWT) at the Pennsylvania State University Applied Research Laboratory, with the objective of demonstrating improved acoustic measurement capabilities compared to other conventional measurement techniques. An outline of the planned test is presented, as well as results from preliminary water tank testing of the arrays and instrumentation to be used in the GTWT experiment. A mathematical description of the time reversal mirror is developed, and preliminary conclusions regarding expected TRM performance in the water tunnel environment and limitations of the proposed measurement scheme are discussed.