Modellingof Electromagnetic Acoustic Transducers Operatingon Ferromagnetic Materials

Ribichini, R.; Cegla, Frederic; Nagy, Péter B.; Cawley, P.; Thompson, Donald O.; Chimenti, Dale E.

doi:10.1063/1.3362538

Cited by 14 publications

(24 citation statements)

References 2 publications

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“…A meander coil in conjunction with a normal magnetic field causes a series of alternating tractions parallel to the surface of the sample. As a result, guided waves, with a wavelength equal to double the spacing between the wires, are excited [2]. This configuration has very good mode selectivity due to its meander-coil design and tone-burst excitation.…”

Section: Introductionmentioning

confidence: 98%

Application of Synthetic Aperture Focusing Technique for inspection of plate-like structures using EMAT generated Lamb waves

2018

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Abstract. The main challenge for guided wave inspection is exact defect characterization and sizing. EMAT generated Lamb waves usually have low signal-to-noise ratio which reduces the defect detection, characterization and sizing capabilities. That's why in most cases the method is used only as a screening tool. The Synthetic Aperture Focusing Technique is a process that increases the signal-to-noise ratio by numerically focusing the acoustic fields. In this paper the application of SAFT is tested over EMAT generated Lamb waves. The improvement of lateral resolution and signal-to-noise ratio is evaluated. Results are presented as a comparison between standard B-scan and SAFT processed data.

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Section: Introductionmentioning

confidence: 98%

Application of Synthetic Aperture Focusing Technique for inspection of plate-like structures using EMAT generated Lamb waves

2018

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“…In [26], this model is experimentally validated and, given the similarity to the model proposed here, a realistic behaviour of the model is expected. In contrast to the work in [26], this paper additionally implements the bias magnetic field within the model, so that the geometric parameters of the magnet may participate in controlling the mode selectivity between the A0 and S0 modes. Figure 4(b) depicts the EMAT model as it is implemented in COMSOL.…”

Section: Model Overviewmentioning

confidence: 99%

“…In this region the mesh density is extremely high, in order to correctly approximate the electromagnetic-elastodynamic interaction. A convergence study on a single wire over a half space FE model using COMSOL has been conducted in [26] by comparing the numerical results to an analytical solution given in [28]. It is found that at least one element per length of skin depth is necessary for accurate approximation.…”

Section: Model Overviewmentioning

confidence: 99%

“…The model is numerically implemented using the FE software COMSOL [25] to model and simulate the EMAT under development. The modelling approach employed is adapted from [26], where the software COMSOL was used to model and simulate EMATs for shear wave applications. In [26], this model is experimentally validated and, given the similarity to the model proposed here, a realistic behaviour of the model is expected.…”

Section: Model Overviewmentioning

confidence: 99%

“…The modelling approach employed is adapted from [26], where the software COMSOL was used to model and simulate EMATs for shear wave applications. In [26], this model is experimentally validated and, given the similarity to the model proposed here, a realistic behaviour of the model is expected. In contrast to the work in [26], this paper additionally implements the bias magnetic field within the model, so that the geometric parameters of the magnet may participate in controlling the mode selectivity between the A0 and S0 modes.…”

Section: Model Overviewmentioning

confidence: 99%

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Model-Based Design of Low Frequency Lamb Wave EMATs for Mode Selectivity

et al. 2015

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A low-frequency, omni-directional A0 Lamb wave ElectroMagnetic Acoustic Transducer (EMAT) is developed for applications in guided wave tomography, operating at 50 kHz on a 10 mm thick steel plate. The key objective is to excite an acceptably pure A0 wave mode in relation to the S0 mode, which can also be present at this operating point and is desired to be suppressed by approximately 30 dB. For that, a parametric Finite Element (FE) model of the design concept is implemented in a commercially available FE software, where the bias magnetic field is calculated initially, then combined with the eddy current caused by the induction coil to produce a force. A numerical optimization process employing a genetic algorithm is set up and the EMAT design is optimized to yield an improved A0 mode selectivity. The parameters subjected to optimization are the magnet diameter and the magnet lift-off, which control the direction of the exciting force in the skin depth layer and therefore the mode selectivity. Although there are three possible electromagnetic acoustic interaction mechanisms, the optimisation considers only the Lorentz force, as its performance surface contains a clear optimum and from the optimised design a physical prototype is built. The FE model is validated against measurements on an aluminium plate for the Lorentz force excitation mechanism and on a steel plate for both the Lorentz and magnetisation force. For the steel plate, it is found that only considering the Lorentz force leads to a significant overestimation of the mode selectivity, as the S0 amplitude is underestimated by the Lorentz force, but the A0 amplitude remains mainly uninfluenced. Further, it has been found that additionally including the magnetisation force into the optimisation leads to a better mode selectivity, however, the optimisation drives the optimum to a minimum magnet diameter and therefore reduces the EMAT sensitivity. In a numerical study robustness is shown for fairly large variations of the magnet lift-off and the magnetic permeability. Based on the findings, a two-step model-based design approach is proposed whereby only the Lorentz force is used in the first step for the optimisation and then in a second step, a realistic estimate of the mode selectivity of the optimised design can be obtained by additionally considering the magnetisation force.

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Investigation of acoustic fields generated by eddy currents using an atomic force microscope

Nalladega¹,

Sathish²,

Blodgett³

2013

AIP Conference Proceedings

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Modellingof Electromagnetic Acoustic Transducers Operatingon Ferromagnetic Materials

Cited by 14 publications

References 2 publications

Application of Synthetic Aperture Focusing Technique for inspection of plate-like structures using EMAT generated Lamb waves

Application of Synthetic Aperture Focusing Technique for inspection of plate-like structures using EMAT generated Lamb waves

Model-Based Design of Low Frequency Lamb Wave EMATs for Mode Selectivity

Investigation of acoustic fields generated by eddy currents using an atomic force microscope

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