An Analytical Evaluation of Turbulence-Induced Flexural Noise in Planar Arrays of Extended Sensors

Large-area, hull-mounted conformal sonar arrays typically employ extended sensors that are configured to detect acoustic signals by means of thickness strains that are induced by the incident pressure field. In most cases, extended sensors also have an appreciable sensitivity to strains in the lateral dimensions. Thus flexure of such a sensor would induce a signal that would not be differentiated from that of a target. Hull-mounted conformal arrays are evolving toward using lightweight, flexible sensors and support structures therefore, flexure-induced noise is an ever present concern. This paper presents an analytical approach and a general mathematical model for the noise arising from flexure of the array support plate coupled into the array via the lateral sensitivity of the sensor. The excitation that drives the flexure is assumed to be the turbulent boundary layer created by motion of the platform through the external fluid medium. An analytical expression is derived for the equivalent plane-wave spectral density for this noise source. The result is expressed in terms of the frequency response function of the plate, the wave-number-frequency spectral density of the excitation, and the spatial filtering characteristics of the array.