Tomographic imaging of an ultrasonic field in a plane by use of a linear array: theory and experiment

Quantitative ultrasonic characterization of inhomogeneous and anisotropic materials is often difficult due to undesired phenomena such as beam steering and phase aberration of the insonifying field. We introduce a method based on tomographic reconstruction techniques for the visualization of an ultrasonic field using a linear array rotated in a plane. Tomographic reconstruction of the ultrasonic field is made possible through the phase-sensitive nature of the tall, narrow piezoelectric elements of a linear array that act as parallel line integrators of the pressure field. We validate the proposed imaging method through numerical simulations of propagated ultrasonic fields based upon the angular spectrum decomposition technique. We then demonstrate the technique with experimental measurements of two textile composites and a reference water path. We reconstruct images of the real and imaginary parts of a transmitted 2 MHz ultrasonic field that are then combined to reconstruct images of the power and unwrapped phase. We also construct images of the attenuation and phase shift for several regions of the composites. Our results demonstrate that tomographic imaging of an ultrasonic field in a plane using a rotated linear array can potentially improve ultrasonic characterization of complex materials.