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Title: Calculation of ultrasonic fields radiated in a ferromagnetic medium by an EMAT of arbitrary bias field driven by a current of arbitrary intensity

ElectroMagnetic Acoustic Transducers (EMATs) are contactless transducers generating ultrasonic waves in conductive media, notably shear horizontal and torsional waves (in plates and pipes, respectively), possibly in hostile environments. In a ferromagnetic part, the elastic strain and the magnetic field couple through magnetostriction phenomena, so that a magnetostriction and magnetization forces add up to the Lorentz force created in any conductive medium. Here, a model is proposed to predict these forces for an arbitrary bias field due to the EMAT permanent magnet and whatever the current intensity in its electric circuit, whereas the usual assumption of high bias field and low intensity current leads to important model simplifications. To handle the nonlinear behavior of all the three forces when the usual assumption cannot be made, forces are expressed in the time domain. In particular, magnetostriction force generates waves at several harmonic frequencies of the driving current frequency. Forces are then transformed into equivalent surface stresses readily usable as source terms in existing models of ultrasonic radiation, under the assumption that ultrasonic wavelengths are much longer than force penetration depths, (which is generally true in NDT applications of EMATs). Force spectra computed in various EMAT configurations are compared for illustration.
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. CEA, LIST, Bât. 565, PC 120, F-91191 Gif-sur-Yvette Cedex, France and Université de Bordeaux, I2M, 351 cours de la Libération, F-33405 Talence Cedex (France)
  2. CEA, LIST, Bât. 565, PC 120, F-91191 Gif-sur-Yvette Cedex (France)
  3. Université de Bordeaux, I2M, 351 cours de la Libération, F-33405 Talence Cedex (France)
  4. CETIM, F-60300, Senlis (France)
Publication Date:
OSTI Identifier:
22263805
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1581; Journal Issue: 1; Conference: 40. annual review of progress in quantitative nondestructive evaluation, Baltimore, MD (United States), 21-26 Jul 2013, 10. international conference on Barkhausen noise and micromagnetic testing, Baltimore, MD (United States), 21-26 Jul 2013; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; LORENTZ FORCE; MAGNETIC FIELDS; MAGNETIZATION; MAGNETOSTRICTION; PENETRATION DEPTH; PERMANENT MAGNETS; SHEAR; SPECTRA; STRAINS; STRESSES; SURFACES; TRANSDUCERS; ULTRASONIC WAVES