ASTM E1774-12
(Guide)Standard Guide for Electromagnetic Acoustic Transducers (EMATs)
Standard Guide for Electromagnetic Acoustic Transducers (EMATs)
SIGNIFICANCE AND USE
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.
Specific Advantages—Since the EMAT technique is noncontacting, it requires no fluid couplant. Important consequences of this include applications to moving objects, in remote or hazardous locations, to objects at elevated temperatures, or to objects with rough surfaces. The technique is environmentally safe since it does not use potentially polluting or hazardous chemicals. The technique facilitates the rapid scanning of components having complex geometries. EMAT signals are highly reproducible as a consequence of the manner in which the acoustic waves are generated. EMATs can produce horizontally polarized shear (SH) waves without mode conversion and can accommodate scanning while using SH waves. (Note that in order to produce this wave mode by conventional ultrasonic techniques, either an epoxy or a highly viscous couplant is required. Thus, conventional ultrasonic techniques do not lend themselves easily to scanning when using SH wave modes.) Also, EMATs provide for the capability to steer shear waves electronically.
Specific Limitations—EMATs have very low efficiency. The insertion loss of EMATs can be as much as 40 dB or more when compared to conventional ultrasonic methods. The EMAT technique can be used only on materials that are electrical conductors or ferromagnetic. The design of EMAT probes is usually more complex than comparable piez...
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 value stated in inch-pound units are to be regarded as the standard. The 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.
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Designation: E1774 − 12
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.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 Units—The value stated in inch-pound units are to be
1.2 This guide describes a non-contact technique for cou-
regarded as the standard. The values given in parentheses are
pling ultrasonic energy into an electrically conductive or
for information only.
ferromagneticmaterial,orboth,throughtheuseofelectromag-
1.6 This standard does not purport to address all of the
netic fields. This guide describes the theory of operation and
safety concerns, if any, associated with its use. It is the
basic design considerations as well as the advantages and
responsibility of the user of this standard to establish appro-
limitations of the technique.
priate safety and health practices and determine the applica-
1.3 This guide is intended to serve as a general reference to
bility of regulatory limitations prior to use.
assist in determining the usefulness of EMATs for a given
application as well as provide fundamental information regard-
2. Referenced Documents
ing their design and operation. This guide provides guidance
2
2.1 ASTM Standards:
for the generation of longitudinal, shear, Rayleigh, and Lamb
E127 Practice for Fabricating and Checking Aluminum Al-
wave modes using EMATs.
loy Ultrasonic Standard Reference Blocks
1
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
2
Method. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 15, 2012. Published August 2012. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1995. Last previous edition approved in 2007 as E1774 - 96 (2007). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E1774-12. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E1774 − 12
E428 Practice for Fabrication and Control of Metal, Other 4.2 Specific Advantages—Since the EMAT technique is
than Aluminum, Reference Blocks Used in Ultrasonic noncontacting
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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:E1774–96 (Reapproved 2007) Designation:E1774–12
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.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*
1.1 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 value stated in inch-pound units are to be regarded as the standard. The 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
This guide is under the jurisdiction ofASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Method.
Current edition approved July 1, 2007. Published July 2007. Originally approved in 1995. Last previous edition approved in 2002 as E1774-96(2002). DOI:
10.1520/E1774-96R07.
Current edition approved June 15, 2012. Published August 2012. Originally approved in 1995. Last previous edition approved in 2007 as E1774 - 96 (2007). DOI:
10.1520/E1774-12.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
E1774–12
2. Referenced Documents
2
2.1 ASTM Standards:
E127 Practice for Fabricating and Ch
...
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