Matched signals: The beginnings of time reversal.

Abstract

This paper discusses the original time reversal experiments as conducted by Antares Parvulescu and Clarence Clay. The idea of conducting the first time reversal experiment came about from measurements of the reproducibility of sound transmissions in the ocean in the late 1950's and early 1960's. Then it was believed by many that long range acoustic signal transmissions in the ocean were not reproducible or stable. During a coffee hour in 1960, Parvulescu proposed a simple experiment to create an acoustic matched signal through the use of time reversal, in their coffee room/lab area. This represents the first known record of a time reversal experiment. The paper will then discuss a series of experiments that were conducted underwater to communicate between two ships through the use of this matched signal technique. Details are in the theoretical - experimental monograph of Ivan Tolstoy and Clay [Ocean Acoustics (Mcgraw-Hill 1966 and Acoust. Soc. Am. 1987), Sections 7.4-7.7]. This paper calls attention to these early experiments and theory as the first demonstrations of the now popular technique termed time reversal.