3D simulations of a phased array based utrasonic polar scan system

The Ultrasonic Polar Scan (UPS) is a novel method to determine the viscoelastic properties of materials by insonifying a single material spot from various incidence angles ?(?,?) and analyzing the reflected or transmitted response. In order to create a portable UPS device, it is investigated whether a cylindrically focused transducer can be employed to activate many incident angles ?? at once, together with a Circular Phased Array (C-PA) to capture the reflected field. A numerical model which is based on the decomposition of harmonic ultrasonic fields into its plane wave components is used together with an analytical model treating the plane wave-plate interaction in 3D. Afterwards, the complete reflected field can be reconstructed from the various reflected plane wave components. The reflected field data captured by the C-PA have been used in a post-processing procedure based on Fourier Transforms to determine plane wave reflection coefficients. The incident field produced by the proposed setup has been simulated, as well as its interaction with a unidirectional Carbon/Epoxy plate, after which the acquired data has been post-processed. In general, the plane wave reflection coefficient were retrieved with a high accuracy for a broad range of incident angles ?? in a single measurement if the lateral width of the C-PA elements is large enough. However, for higher frequency ranges, aliasing effects disturb the result significantly. This problem can be circumvented using multiple emitters with a smaller angular coverage, properly treating the data related to these emitters separately, and subsequently merging the results of these individual emitters.