Array Processing Using Bragg Diffracted Trace Wavelengths

When periodic discontinuities are embedded within a coating, such as a polyurethane, the periodic structures act as a means to scatter an incident acoustic trace wavelength, precisely into repeating smaller replicas of the trace wavelength. The well-known phenomena, Bragg diffraction, is independent of loading, occurring both in-air or in-water. The repeating replicas can then be sampled at a much finer scale, generating significant directivity gains. Processing these replicas, in an appropriate manner, may overcome a fundamental limit of every sonar system - the length of the acoustic aperture - by creating a means to generating shorter wavelength replicas of the original acoustic signal. The result is an increase in the ratio of measured wavelengths to the length of the fixed array aperture, which increases the array's directivity. The shorter replicas of the original signal are sampled at a finer scale, significantly improving directivity gains, by 10 dB or more, especially at lower sonar frequencies. Verification measurements using a prototype, US patented planar array, were conducted in December 2014 at an acoustic test facility. Initial results validated replicas of the incident trace wavelength.