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

Jannes Daemen,Koen Van Den Abeele,Mathias Kersemans,Wim Van Paepegem,Steven Delrue,Erik Verboven,Arvid Martens

doi:10.3390/icem18-05327

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 in-plane 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.

Highlights

As contemporary industries need to innovate on a regular basis, there has been an increasing interest in the development and characterization of new types of materials
Polar plots of the amplitude or the Time-of-Flight (TOF) of these signals show characteristic contours which offer a local fingerprint of the stiffness parameters of the material, which can be extracted by means of an inversion algorithm [5,6,7]
The extrema in the polar plots correspond to the conditions for efficient Lamb wave stimulation, which offer a similar relation to the stiffness parameters

Summary

Introduction

As contemporary industries need to innovate on a regular basis, there has been an increasing interest in the development and characterization of new types of materials. Applying this harmonic UPS procedure for different frequencies (individually or at once using a spectroscopic analysis of a pulse) offers more information to be used in the inversion algorithm, leading to potentially better parameter estimations. By applying appropriate element-specific time delays and apodization weights, the beam can be tuned such that a quasi-plane wave can be created [10] and specific Lamb modes can be activated.

Results

Conclusion