title: A new omni-directional EMAT for ultrasonic Lamb wave tomography imaging of metallic plate defects.
abstract: 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. The theoretical background and the working principles of this EMAT are presented and analyzed. The experimental results of its use on a 3 mm thick aluminum plate indicate that the EMAT with a contra-flexure coil (CFC) can transmit and receive a pure single A0 mode ULW with a high signal-to-noise ratio (SNR). Thus, the extraction of the projection data used for ULW TI may be performed accurately. The circumferential consistency of the projection data is only slightly influenced by the distortion of the eddy current field that is induced by the new CFC with an irregular shape. When the new EMAT array is used for ULW TI using the cross-hole method and SIRT arithmetic, a desirable imaging quality can be achieved, and the estimated size of an artificial corrosion defect agreed well with its actual value. The relation between the reconstruction resolution and the number of the new EMATs used is analyzed. More TI experiments are carried out when the aluminum plate defect is in two different locations relative to the EMAT array, for the further investigation of the performances of the new EMATs.
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. weizhengbj@163.com.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Wei
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
authors.affiliation: State Key Lab of Power Systems, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China. wangshen@tsinghua.org.cn.
authors.forename: Shen
authors.initials: S
authors.lastname: Wang