Transducer to generate phase-encoded wavefields

Abstract

A transducer capable of generating a phase-encoded wavefield is described. The encoded phase is related to the angular co-ordinates of direction of transmission. By decoding the phase values of the received wavefield, a direction can be obtained. Therefore, in navigation applications this transmitter gives additional location information not available from a single received signal using traditional methods such as 'range-range' and 'hyperbolic' systems. In its simplest configuration, the new transducer comprises two transducers which can be individually controlled. In more complex constructions use of more than two transducers increases the controllability of the desired phase characteristics of the resulting wavefield. It has also been discovered that by using two different phase-encoded wavefields, direction finding of small reflectors can not only be accomplished, but small reflectors can be distinguished from large plane reflectors or else dispersive properties of the propagation medium can be characterized. The first wavefield takes the form of monotonic phase increments with direction as for example would be produced by the present invention, while the second wavefield simply reverses the sense of phase increments of the first. The second wavefield is easily obtained from a source that generates the first either by reprogramming the electronic driving signals for transducers or mechanically interchanging the components of the transducers.