This paper reports simulations of the generation of Lamb wave modes in thin plates using a meander coil (meander line) EMAT, which works under the principle of Lorentz force mechanism in non-magnetic materials. The numerical simulations have been compared with measurements. The numerical work presented in this paper is divided into two parts. First, a 2D electromagnetic model is developed for calculating the Lorentz force density, which is the driving force for elastic wave generation within the plate. Second, the calculated force at each point in the metal is used as the driving force for generating elastic wave modes in the plate. These calculated Lamb wave modes are compared with those generated experimentally in a thin plate. Additionally, the measured wave modes are analyzed with the help of dispersion curves and a timefrequency analysis. Our numerical work is also extended to analyze the interaction of Lamb wave modes with defects. The simulations compare favorably with the measurements presented here. © 2010 Elsevier Ltd. All rights reserved.

Krishnan Balasubramaniam

Department of Mechanical Engineering

Dispersion curves

Lamb wave

Lamb waves

MEANDER COIL

Time frequency analysis

Computer simulation

Dispersion (waves)

Elastic waves

finite element method

Laser optics

Lorentz force

Magnetic materials

Plate metal

Plates (structural components)

Soil structure interactions

Ultrasonic waves

Magnetic field effects

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

NDT and E International

This study investigates the reflection behaviour of SH0 guided wave mode from a flat plate edge. SH0 is generated using Periodic Permanent Magnet - Electromagnetic Acoustic Transducers (PPM-EMAT) of constant wavelength (λ). Reflection characteristics of this mode are studied by varying the angle of incidence from 0° to 70°. The probes are positioned in such a way that incident and reflected angles are equal. The response of SH0 mode at the various angle of incidents is explored in terms of amplitude variation. 3D finite element model is developed to investigate reflection characteristics of SH0 mode further. The exact configuration of the PPM-EMAT has been simulated using a two-stage modelling approach. The spatially varying Lorentz force was calculated in the electrodynamic module and then applied to the elastodynamic module, and the resulting elastic disturbances are compared with experimental results. © 2019 Author(s).

AIP Conference Proceedings

Reflection study of SH0 mode with plate edge at different incident angles

Guided waves inspection is a well-established method for the long-range ultrasonic inspection of pipes. Guided waves, used in a pulse-echo arrangement, can inspect a large range of the pipe from a single point as the pipe structure carries the waves over a large distance due to the relatively low attenuation of the wave modes. However, the complexity of the dispersion characteristics of these pipe guided wave modes are well known, and can lead to diffculty interpreting the obtained results. The torsional family of guided wave modes are generally considered to have much simpler dispersion characteristics; especially the fundamental T(0,1) mode, which is nominally non-dispersive, making it particularly useful for guided wave inspection. Torsional waves have been generated by a circumferential ring of transducers to approximate an axi-symmetric load to excite this T(0, 1) mode. Presented here is a new design of Electromagnetic Acoustic Transducer (EMAT) that can generate a T(0, 1) as a single transducer, rather than a circumferential array of transducers that all need to be excited in order to generate an axisymmetric force. The EMAT consists of a periodic permanent magnet array and a single meander coil, meaning that the excitation of the torsional mode is greatly simplified. The design parameters of this new EMAT are explored, and the ability to detect notch defects on a pipe is demonstrated. © 2017 Author(s).

Fulltext

A new electromagnetic acoustic transducer design for generating torsional guided wave modes for pipe inspections

This paper reports the quantitative comparison of A-scans obtained from the simulations of fundamental guided wave modes in a plate by split-domain Finite Element Modeling approach with the more conventional single domain FEM method. Split Approach is the computationally efficient technique that has been developed for simulating long-range guided wave propagation in complex structures with limited computation resources. This Split Approach method involves sub-domain FE modeling which involves the splitting the larger FE model into smaller sub-domain models, solving them individually and finally transferring the wave from one sub-domain to the next sub-domain. In this paper, simulations of guided wave propagation were carried out in a plate using ABAQUS® Explicit FE package. The results thus obtained by split approach were compared with conventional full model approach. © 2015 AIP Publishing LLC.

Guided wave simulation in plates using split-domain FEM approach

Finite Element Analysis (FEA) is an important tool that has been extensively used in wave propagation models for NDE applications. With the increase and diversification of Non Destructive Evaluation (NDE) applications, the complexity and size of FE models increase considerably. Also for modeling wave propagation models, the size of the FE problem depends on the frequency that is used and velocity of sound in the material. High ultrasonic frequency applications and materials with lower ultrasonic velocity contribute immensely to the increase in the FE problem size. Additionally, the requirements for 3D models are also increasing. This calls for higher computation resources to be available at the hands of the researcher at significant costs. We have developed a new approach to model such extremely large FE problems that involves splitting the entire model to be analyzed into smaller sub-models and by solving each sub-models sequentially, while transferring the outputs at the boundaries between the sub-models. Thus, the entire "large" model now consists of a few "smaller" sub-models. The size of these smaller models can be decided upon by the researcher depending on the computing capacity available. While this approach may not provide significant improvements in the time of computation, it allows for the computation of large models possible with relatively less computational resources. The model was tested on a few case studies and validated with the results obtained from a full "large" model. © 2014 AIP Publishing LLC.

Split approach for FEA simulations of very large wave propagation models

This paper reports on a new means of generating higher-order mode clusters of guided waves (HOMC-GW) using a meander-coil (MC) electromagnetic acoustic transducer (EMAT) in plates at frequencies significantly higher than the lower-order plate modes. These wave modes are considerably less dispersive and they occur at much higher frequency¿thickness (f x d) products. Our studies cover the f x d range of 13 to 20 MHzmm. Experimental measurements were carried out on Al plate samples of different thicknesses using three different EMAT coil periods. To understand the generation and propagation characteristics of HOMC-GW with EMATs, several simulations were carried out using 2-D finite element models at different f x d products. These simulations captured all features observed in the experiments. The time¿frequency smoothed pseudo Wigner-Ville distribution (SPWVD) was used to analyze the HOMC-GW modes. Defect detection measurements using HOMC-GW generated using EMATs were made on Al plates with machined defects. © 2012 IEEE.

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Generation and detection of higher-order mode clusters of guided waves (HOMC-GW) using meander-coil EMATs

Journal of Xidian University

Analysis of LSE and MMSE Pilot Based Channel Estimation Techniques for MIMO-OFDM System Using MATLAB

Springer Series in Measurement Science and Technology

Electromagnetic Acoustic Transducers

Electromagnetic Modeling and Simulation

Antennas: Isotropic Radiators and Beam Forming/Beam Steering

Finite Element Analysis of Composite Materials using Abaqus™

Sealing Technology

COMSOL Multiphysics Version 4.0 released

A hybrid finite element model for simulation of electromagnetic acoustic transducer (EMAT) based plate waves

Journal	NDT and E International
ISSN	09638695
Open Access	No