Towards a Phased Array Based Ultrasonic Polar Scan: Simulation Study and Comparison with Plane Wave Results

Abstract

Abstract:The ever-increasing use of composite materials in the industry has resulted in the need for new, intricate approaches to not only properly characterize their anisotropic mechanical properties (i.e., the visco-elastic tensor), but also to detect various types of internal flaws. Both goals can be achieved by the Ultrasonic Polar Scan (UPS). During an UPS experiment, a material spot is insonified at many oblique incidence angles Ψ(θ,φ), with θ the vertical incident angle and φ the inplane polar angle, after which the reflected or transmitted ultrasound signal is recorded. The resulting dataset provides an integral view of the angle-dependent reflection (R) and transmission (T) scatter coefficients, and can be employed to infer the material properties. Although the current UPS scanner provides highly accurate experimental data, it is impractical for in-situ measurements. In order to create a more compact and practical measuring device, we propose the use of a hemispherical phased array, consisting of small piezoelectric elements, to generate a broadband, quasi plane wave signal. It will be shown, based on simulations, that a circular phased array concept allows for the determination of the reflection coefficients in θ − f space, from which the dispersion curves can be immediately inferred. Comparison of these results with the plane wave theoretical results show an excellent agreement.