title: Multi-Mode Electromagnetic Ultrasonic Lamb Wave Tomography Imaging for Variable-Depth Defects in Metal Plates.
abstract: 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. The principles and procedures for the cooperation of A0- and S0-mode LW CTI are proposed. Moreover, the experimental LW imaging system on an aluminum plate with a variable-depth defect is set up, based on A0- and S0-mode EMAT (electromagnetic acoustic transducer) arrays. For comparison, the traditional single-mode LW CTI method is used in the same experimental platform. The imaging results show that the computed thickness distribution by the proposed multi-mode method more accurately reflects the actual thickness variation of the defect, while neither the S0 nor the A0 single-mode method was able to distinguish thickness variation in the defect region. Moreover, the quantification of the defect's thickness variation is more accurate with the multi-mode method. Therefore, theoretical and practical results prove that the variable-depth defect in metal plates can be successfully quantified and visualized by the proposed multi-mode electromagnetic ultrasonic LW CTI method.
authors.affiliation: State Key Lab of Power Systems, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China. huangsling@tsinghua.edu.cn.
authors.forename: Songling
authors.initials: S
authors.lastname: Huang
authors.affiliation: State Key Lab of Power Systems, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China. zhang-yu13@mails.tsinghua.edu.cn.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Lab of Power Systems, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China. wangshen@mail.tsinghua.edu.cn.
authors.forename: Shen
authors.initials: S
authors.lastname: Wang
authors.affiliation: State Key Lab of Power Systems, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China. zhaowei@mail.tsinghua.edu.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhao
keywords: cross-hole tomography imaging (CMI); electromagnetic acoustic transducers (EMATs); multi-mode Lamb waves (LWs); variable-depth defects