A Review of Research Progress in Ultrasonic Nonlinearity Parameter Measurement Methods Over the Past Decade

Abstract

Nonlinear ultrasonic techniques offer significant advantages over conventional methods based on the linear properties of ultrasonic wave propagation by allowing evaluation of microstructural changes or degradation of materials at the early stage of damage. Key techniques include harmonic generation (HG), which uses the amplitude of second or higher harmonic components generated during wave propagation; nonlinear wave mixing (WM), which analyzes new frequencies generated by interacting waves; and nonlinear resonance (NR), which tracks changes in resonance frequency with wave amplitude. However, because the nonlinear characteristics of ultrasound are weak, it is important to measure them effectively and precisely. Most recent studies related to this issue have explored the use of various wave types (longitudinal, shear, Rayleigh, guided) and configurations (through-transmission vs. pulse-echo, collinear vs. non-collinear). This review summarizes related measurement methodologies developed in the past decade, including advances in signal processing, sensor technology, and experimental design to enhance measurement precision and sensitivity. This review also explores second- and third-order nonlinearity parameters (β and γ), typically measured as relative values due to challenges in measuring absolute values. An overview of recent trends in this field is expected to help both researchers and industry professionals utilizing nonlinear ultrasonic technology to understand the characteristics of each technology, while also providing new inspiration.