ASTM E1774-96(2007)
(Guide)Standard Guide for Electromagnetic Acoustic Transducers (EMATs)
Standard Guide for Electromagnetic Acoustic Transducers (EMATs)
SCOPE
1.1 This guide is intended primarily for tutorial purposes. It provides an overview of the general principles governing the operation and use of electromagnetic acoustic transducers (EMATs) for ultrasonic examination.
1.2 This guide describes a non-contact technique for coupling ultrasonic energy into an electrically conductive or ferromagnetic material, or both, through the use of electromagnetic fields. This guide describes the theory of operation and basic design considerations as well as the advantages and limitations of the technique.
1.3 This guide is intended to serve as a general reference to assist in determining the usefulness of EMATs for a given application as well as provide fundamental information regarding their design and operation. This guide provides guidance for the generation of longitudinal, shear, Rayleigh, and Lamb wave modes using EMATs.
1.4 This guide does not contain detailed procedures for the use of EMATs in any specific applications; nor does it promote the use of EMATs without thorough testing prior to their use for examination purposes. Some applications in which EMATs have been applied successfully are outlined in Section 9.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E1774–96 (Reapproved 2007)
Standard Guide for
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Electromagnetic Acoustic Transducers (EMATs)
This standard is issued under the fixed designation E1774; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
General—The usefulness of ultrasonic techniques is well established in the literature of nonde-
structive examination. The generation of ultrasonic waves is achieved primarily by means of some
form of electromechanical conversion, usually the piezoelectric effect.This highly efficient method of
generating ultrasonic waves has a disadvantage in that a fluid is generally required for mechanical
coupling of the sound into the material being examined. The use of a couplant generally requires that
the material being examined be either immersed in a fluid or covered with a thin layer of fluid.
Principle—An electromagnetic acoustic transducer (EMAT) generates and receives ultrasonic
waves without the need to contact the material in which the acoustic waves are traveling. The use of
an EMAT requires that the material to be examined be electrically conductive or ferromagnetic, or
both.TheEMATasageneratorofultrasonicwavesisbasicallyacoilofwire,excitedbyanalternating
electric current, placed in a uniform magnetic field near the surface of an electrically conductive or
ferromagneticmaterial.Asurfacecurrentisinducedinthematerialbytransformeraction.Thissurface
current in the presence of a magnetic field experiences Lorentz forces that produce oscillating stress
waves. Upon reception of an ultrasonic wave, the surface of the conductor oscillates in the presence
of a magnetic field, thus inducing a voltage in the coil. The transduction process occurs within an
electromagnetic skin depth.An EMAT forms the basis for a very reproducible noncontact system for
generating and detecting ultrasonic waves.
1. Scope 1.4 This guide does not contain detailed procedures for the
use of EMATs in any specific applications; nor does it promote
1.1 This guide is intended primarily for tutorial purposes. It
the use of EMATs without thorough testing prior to their use
provides an overview of the general principles governing the
for examination purposes. Some applications in which EMATs
operation and use of electromagnetic acoustic transducers
have been applied successfully are outlined in Section 9.
(EMATs) for ultrasonic examination.
1.5 This standard does not purport to address all of the
1.2 This guide describes a non-contact technique for cou-
safety concerns, if any, associated with its use. It is the
pling ultrasonic energy into an electrically conductive or
responsibility of the user of this standard to establish appro-
ferromagneticmaterial,orboth,throughtheuseofelectromag-
priate safety and health practices and determine the applica-
netic fields. This guide describes the theory of operation and
bility of regulatory limitations prior to use.
basic design considerations as well as the advantages and
limitations of the technique.
2. Referenced Documents
1.3 This guide is intended to serve as a general reference to
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2.1 ASTM Standards:
assist in determining the usefulness of EMATs for a given
E127 Practice for Fabricating and Checking Aluminum
application as well as provide fundamental information regard-
Alloy Ultrasonic Standard Reference Blocks
ing their design and operation. This guide provides guidance
E428 Practice for Fabrication and Control of Metal, Other
for the generation of longitudinal, shear, Rayleigh, and Lamb
than Aluminum, Reference Blocks Used in Ultrasonic
wave modes using EMATs.
Testing
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This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-
tive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic
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Method. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedJuly1,2007.PublishedJuly2007.Originallyapproved contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
in 1995. Last previous edition approved in 2002 as E1774 - 96(2002). DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E1774-96R07. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E1774–96 (2007)
E1065 Guide for Evaluating Characteristics of Ultrasonic waves. (Note that in order to produce this wave mode by
Search Units conventional ultrasonic techniques, either an epoxy or a highly
E1316 Terminology for Nondestructive Examinations viscous couplant
...
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