Characterizing excitability of Lamb waves generated by electromagnetic acoustic transducers with coupled frequency domain models.

Electromagnetic acoustic transducers (EMATs) are versatile non-contact ultrasonic transducers with relatively low transduction efficiency. A fundamental problem not answered completely yet is how the structure of an EMAT influences the generation of various Lamb wave modes. We tackle this problem with fully coupled frequency domain EMAT models where the underlying integro-differential equations are solved directly and the magnitudes of the phasors of the displacement components at a point in the middle plane of a plate are used to represent the strength of the S0 and A0 mode waves.

A multi-objective structural optimization of an omnidirectional electromagnetic acoustic transducer.

In this paper an axisymmetric model of an omnidirectional electromagnetic acoustic transducer (EMAT) used to generate Lamb waves in conductive plates is introduced. Based on the EMAT model, the structural parameters of the permanent magnet were used as the design variables while other parameters were fixed. The goal of the optimization was to strengthen the generation of the A0 mode and suppress the generation of the S0 mode.

Multi-Mode Electromagnetic Ultrasonic Lamb Wave Tomography Imaging for Variable-Depth Defects in Metal Plates.

This paper proposes a new cross-hole tomography imaging (CTI) method for variable-depth defects in metal plates based on multi-mode electromagnetic ultrasonic Lamb waves (LWs). The dispersion characteristics determine that different modes of LWs are sensitive to different thicknesses of metal plates. In this work, the sensitivities to thickness variation of A0- and S0-mode LWs are theoretically studied.

A new omni-directional EMAT for ultrasonic Lamb wave tomography imaging of metallic plate defects.

This paper proposes a new omni-directional electromagnetic acoustic transducer (EMAT) for the ultrasonic Lamb wave (ULW) tomography imaging (TI) of defects in metallic plates. The proposed EMAT is composed of a permanent magnet and a coil with a contra-flexure structure. This new EMAT coil structure is used for omni-directional ULW transmission and reception and ULW TI for the first time.

Simulation of Lamb wave's interactions with transverse internal defects in an elastic plate.

Lamb wave's interactions with transverse internal defects in an elastic plate are investigated in this paper to help practical inspection work with guided wave. A 2D frequency domain hybrid boundary element method approach previously mainly used to study Lamb wave's interactions with external defects in elastic plates is adopted in this work and extended to study the cases of internal defects. Simulation examples are presented to illustrate the reflection and transmission coefficients' variations with various parameters including defect's height, width, testing fd for internal symmetrical and non-symmetrical cracks, with symmetry defined with respect to the middle plane of the plate.