Applying phase conjugate arrays to sonar

Abstract

A phase conjugate array (time reversal mirror) is a method of focusing acoustic energy spatially and temporally in a complex ocean propagation environment. Signals from a probe source are received on an array, time-reversed and re-transmitted. Multipath components are directed back along the paths over which they arrived, in the reverse order they were received. Numerical models have been developed to predict the focusing achievable with different array configurations in different types of environment. The effect of a time dependent rough surface has also been calculated. The models are described and examples of results obtained presented. An alternative focusing method based on inverse filters has been developed which may be an important enhancement to the basic reversal method. The relationship between the two methods and the advantages of each are explained. The models of focusing performance need validation using data taken in real environments. The type of experimental system required to provide this validation is described. The focusing techniques can be used in a number of ways to improve the performance of sonar and underwater communication systems. Examples of new types of sonar that exploit the focusing techniques to deliver improved performance are described.