Adaptive array imaging in inhomogeneous media

In ultrasonic imaging of inhomogenous or anisotropic composites, the time delays of spherical wavefronts may not be proportional to path lengths. To overcome this effect, an adaptive algorithm has been formulated which compensates for random signal time shift variations. To demonstrate the performance of the algorithm, a laboratory prototype array has been developed. Point-source transmitters broadcast broad-directivity ultrasonic fields into the composite. Backscattering from features in the interior of the material is sensed by a 32-element array of broadband, wide-field-of-view receivers. Tests of the adaptive algorithm on simulated scattering data and on the experimental data gathered with the new array show an improved ability to detect scatterers in the composite over conventional delay and sum imaging.<>