ASTM E1774-17
(Guide)Standard Guide for Electromagnetic Acoustic Transducers (EMATs)
Standard Guide for Electromagnetic Acoustic Transducers (EMATs)
SIGNIFICANCE AND USE
4.1 General—Ultrasonic testing is a widely used nondestructive method for the examination of a material. The majority of ultrasonic examinations are performed using transducers that directly convert electrical energy into acoustic energy through the use of piezoelectric crystals. This guide describes an alternate technique in which electromagnetic energy is used to produce acoustic energy inside an electrically conductive or ferromagnetic material. EMATs have unique characteristics when compared to conventional piezoelectric ultrasonic search units, making them a significant tool for some ultrasonic examination applications.
4.2 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. There are two basic components of an EMAT system, a magnet and a coil. The magnet may be an electromagnet or a permanent magnet, which is used to produce a magnetic field in the material under test. The coil is driven using alternating current at the desired ultrasonic frequency. The coil and AC current also induce a surface magnetic field in the material under test. In the presence of the static magnetic field, the surface current experiences Lorentz forces that produce the desired ultrasonic 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. The EMAT forms the basis for a very reproducible noncontact system for generating and detecting ultrasonic waves.
4.3 Specific Advantages—Since an EMAT technique does not have to be in contact with the material under examination, no fluid couplant is required. Important consequences of this include applications to moving objects, in...
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.
1.5 Units—The values stated in inch-pound units are to be regarded as the standard. The SI values given in parentheses are for information only.
1.6 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.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: E1774 − 17
Standard Guide for
1
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.
1. Scope* 2. Referenced Documents
2
1.1 This guide is intended primarily for tutorial purposes. It 2.1 ASTM Standards:
provides an overview of the general principles governing the E127 Practice for Fabrication and Control of Aluminum
operation and use of electromagnetic acoustic transducers Alloy Ultrasonic Standard Reference Blocks
(EMATs) for ultrasonic examination. E428 Practice for Fabrication and Control of Metal, Other
than Aluminum, Reference Blocks Used in Ultrasonic
1.2 This guide describes a non-contact technique for cou-
Testing
pling ultrasonic energy into an electrically conductive or
E1065 Practice for Evaluating Characteristics of Ultrasonic
ferromagneticmaterial,orboth,throughtheuseofelectromag-
Search Units
netic fields. This guide describes the theory of operation and
E1316 Terminology for Nondestructive Examinations
basic design considerations as well as the advantages and
E543 Specification forAgencies Performing Nondestructive
limitations of the technique.
Testing
3
1.3 This guide is intended to serve as a general reference to
2.2 ASNT Documents:
assist in determining the usefulness of EMATs for a given
SNT-TC-1A Recommended Practice for Personnel Qualifi-
application as well as provide fundamental information regard-
cations and Certification in Nondestructive Testing
ing their design and operation. This guide provides guidance
ANSI/ASNT CP-189 Standard for Qualification and Certifi-
for the generation of longitudinal, shear, Rayleigh, and Lamb
cation for Nondestructive Testing Personnel
4
wave modes using EMATs.
2.3 Aerospace Industries Association Standard:
1.4 This guide does not contain detailed procedures for the NAS-410 Certification and Qualification of Nondestructive
Test Personnel
use of EMATs in any specific applications; nor does it promote
5
the use of EMATs without thorough testing prior to their use 2.4 ISO Standard:
ISO 9712 Non-Destructive Testing: Qualification and Certi-
for examination purposes. Some applications in which EMATs
fication of NDT Personnel
have been applied successfully are outlined in Section 9.
1.5 Units—The values stated in inch-pound units are to be
3. Terminology
regarded as the standard. The SI values given in parentheses
3.1 Definitions—Related terminology is defined in Termi-
are for information only.
nology E1316.
1.6 This standard does not purport to address all of the
3.2 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the
3.2.1 bulk wave—an ultrasonic wave, either longitudinal or
responsibility of the user of this standard to establish appro-
shear mode, used in nondestructive testing to interrogate the
priate safety and health practices and determine the applica-
volume of a material.
bility of regulatory limitations prior to use.
3.2.2 electromagnetic acoustic transducer (EMAT)—an
1.7 This international standard was developed in accor-
electromagnetic device for converting electrical energy into
dance with internationally recognized principles on standard-
acoustical energy in the presence of a magnetic field.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
mendations issued by the World Trade Organization Technical
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Barriers to Trade (TBT) Committee. Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3
AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
1
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc- 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
4
tive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Available fromAerospace IndustriesAssociation ofAmerica, Inc. (AIA), 1000
Method. WilsonBlvd.,Suite1700,Arlington,VA22209-3928,http://www.aia-aerospace.org.
5
Current edition approved June 1, 2017. Published June 2017. Originally Available from International Organization for Standardization (ISO), ISO
approved in 1995. Last previous edition approved in 2012 as E1774 - 12. DOI: Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
10.1520/E1774-17. Geneva, Switzerland, http://www.iso.org.
*A Summary of Changes section appears
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1774 − 12 E1774 − 17
Standard Guide for
1
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. The EMAT as a generator of ultrasonic waves is basically a coil of wire, excited by an alternating
electric current, placed in a uniform magnetic field near the surface of an electrically conductive or
ferromagnetic material. A surface current is induced in the material by transformer action. This surface
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*
1.1 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.
1.5 Units—The valuevalues stated in inch-pound units are to be regarded as the standard. The SI values given in parentheses
are for information only.
1.6 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.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
1
This guide is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Method.
Current edition approved June 15, 2012June 1, 2017. Published August 2012June 2017. Originally approved in 1995. Last previous edition approved in 20072012 as
E1774 - 96 (2007).E1774 - 12. DOI: 10.1520/E1774-12.10.1520/E1774-17.
*A Summary of Changes section appears at the end of this standard
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