WO2004106913A1 - Transducteur acoustique electromagnetique d'ondes guidees - Google Patents

Transducteur acoustique electromagnetique d'ondes guidees Download PDF

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Publication number
WO2004106913A1
WO2004106913A1 PCT/US2003/014814 US0314814W WO2004106913A1 WO 2004106913 A1 WO2004106913 A1 WO 2004106913A1 US 0314814 W US0314814 W US 0314814W WO 2004106913 A1 WO2004106913 A1 WO 2004106913A1
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WO
WIPO (PCT)
Prior art keywords
emat
products
product
transducer
magnetic field
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Application number
PCT/US2003/014814
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English (en)
Inventor
Charles M. Fields
Daniel P. Grier
Original Assignee
Flova, John, H.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Flova, John, H. filed Critical Flova, John, H.
Priority to PCT/US2003/014814 priority Critical patent/WO2004106913A1/fr
Priority to AU2003239415A priority patent/AU2003239415A1/en
Publication of WO2004106913A1 publication Critical patent/WO2004106913A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G01N29/2412—Probes using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
    • G01N29/0609—Display arrangements, e.g. colour displays
    • G01N29/0645—Display representation or displayed parameters, e.g. A-, B- or C-Scan
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/11—Analysing solids by measuring attenuation of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0422—Shear waves, transverse waves, horizontally polarised waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0423—Surface waves, e.g. Rayleigh waves, Love waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0427—Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/044—Internal reflections (echoes), e.g. on walls or defects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/26—Scanned objects
    • G01N2291/262—Linear objects
    • G01N2291/2626—Wires, bars, rods
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/26—Scanned objects
    • G01N2291/263—Surfaces
    • G01N2291/2634—Surfaces cylindrical from outside

Definitions

  • the present invention relates to electromagnetic acoustic transducers in general and more specifically to an electromagnetic acoustic design which provides for the transmission and reception of guided acoustic waves in metallic rods, bars, wire and tubes for the purpose of detection of defects therein and for measuring certain properties of these metal products during and after their fabrication.
  • Electromagnetic Acoustic Transducers are electrical devices that can transmit and receive ultrasonic sound waves in an electrically conducting material without requiring contact of the probe with the material being inspected.
  • EMATs are typically composed of arrays of electrical conductors, commonly referred to as coils and magnets, which can either be permanent magnets or electromagnets.
  • coils and magnets When the electrical conductors comprising the arrays are energized by an alternating electrical current and placed in close proximity to an electrically conducting material, eddy currents are induced in the material.
  • Lorentz forces are applied to the transient electrons of the induced eddy currents.
  • a Lorentz force (F) at a point in the material is described mathematically by the cross product of the magnetic flux density (B), the induced eddy current density (J) and the relationship therebetween is shown in the following equation.
  • the sum of these Lorentz forces produce an acoustic stress wave having the same frequency with respect to time as the induced eddy currents.
  • the various types and modes of the waves which can be generated by EMATs are determined primarily by the configuration of the magnet, the configuration of the electrical conductors and their physical position with respect to each other.
  • Guided waves such as the well known Lamb wave modes are easily generated in metal plates and cylinders by EMATs. These guided waves are generated near the surface of a section of the plate which is in close proximity to the EMAT and are transmitted from the EMAT in at least on direction within the material.
  • Guided waves traveling under an EMAT are detected by the reverse process by causing the magnetic field under a conductor to change at the same frequency as the acoustic wave. As this alternating field is coupled to the electrical conductors of the EMAT coil, a signal voltage will be detected at the terminals of the coil as the acoustic wave travels under the EMAT.
  • EMATs offer several advantages when compared to piezoelectric transducers. EMATs do not require any fluid coupling for one and the acoustic waves that are generated are generated immediately below the surface of the material being tested unlike piezoelectric transducers in which the sound is produced in the probe and transferred to the material through a coupling medium such as oil or water. The latter characteristic provides substantially greater accuracy, reliability and repeatability for applications in which the test material is contaminated, rough, hot or moving at high speeds relative to the transducer. As EMAT fabrication can be very precise, components such as a sensor coil and/or a magnet or, even the entire EMAT, can be interchanged with little or no variation in acoustic beam shape and signal response to defects and/or to the material characteristics being detected or measured. Another advantage of the basic EMAT is its inherent simplicity of construction provides an almost unlimited variety of designs to implement shaping, steering and focusing acoustic beams to achieve the desired effect.
  • a further advantage of EMATs is their ability to generate guided waves in uniform metal components such as rods, plates and pipe.
  • Lamb waves are produced by the interaction of alternating magnetic fields with relatively constant magnetic fields at the surface of a metal component.
  • the horizontally polarized shear waves are usually generated in ferromagnetic materials such as carbon steel and steel alloys which have the property of magnetostriction but can be generated through the interaction of magnetic fields which alternate in space but are constant in time with magnetic fields which are constant in space but alternate in time.
  • the focus of this patent is the generation of Lamb waves in ferromagnetic and nonferromagnetic metal components which have a central axis symmetry.
  • TJ. S. Patent No. 6,443,011 discloses a device for detecting faults or measuring wall thicknesses of a continuously moving strip, section or tubes of plastic, using ultrasonic signals.
  • Latimer discloses, in J. S. Patent No. 5, 359,898, a method of checking for hydrogen damage in a boiler tube which includes a pair of electromagnetic acoustic coils which are mounted for movement to and away from one another but does not show segmented magnets and flexible coils.
  • Latimer is one of the inventors in TJ. S. Patent No. 5,085,082 which is used to detect flaws in welded pipes and the like.
  • EMATS are employed to generate ultrasonic acoustic surface and shear waves.
  • Camplin et al show, in TJ. S. Patent No. 5,866,820, a defect detection system for an EMAT inspection system to identify surface defects and sub-surface defects by using Lamb waves. The system does not show the features of the instant system and therefore could not be used in the same manner.
  • TJ. S. Patent No. 6,170,336 to Johnson shows an EMAT configuration for sensing vibrations in a cylindrical object and methods of using an EMAT to determine resonant frequencies and physical properties of cylindrical objects. This system is very different from the instant invention.
  • Cook, in TJ. S. Patent No. 5,907,100, shows a method for detecting defects in piping which employs an EMAT with sensors using a chirp coil and pulse sender. This system is incapable of performing like the instant invention .
  • the EMATs of the instant invention are designed to detect defects or to measure properties within metallic components such as rod, wire, bar and relatively small cylinders which are symmetric about the central axis of any of the components.
  • magnets are used to provide magnetic fields in the components are either symmetrical or asymmetrical about a central axis.
  • Coils of electrical conductors are wound or wrapped around said components and excited with an alternating current to provide magnetic fields which are symmetric with respect to the axis.
  • These magnetic and coil combinations generate Lamb wave modes which are either symmetric or asymmetric with respect to the central axis of the components.
  • These symmetric Lamb wave modes exhibit acoustic reflections of greater amplitude from defects on the central axis compared with reflections from defects which are located on the surface of said products.
  • This nondestructive test facilities the removal of defective portions of the copper rod prior to drawing and finishing of the wire. This not only assures a high quality finished wire but also can provide substantial cost savings in labor and energy by diverting defective rod from further processing. Furthermore, the detection of defects during fabrication of the rod can provide additional savings by reducing the number of failures and resultant production down time during subsequent wire drawing process
  • segmented magnets and flexible coils which retract from the center to provide a larger opening for passage of the leading end of a product as it exits from the production line at high speeds. After the leading end passes through the expanded opening the segmented EMAT will close around the product and inspection will commence. This closing prevents damage or destruction of the EMAT as well as minimizing the risk of stopping production or injury to production facility personnel.
  • a still further object of this invention is to provide for segmented magnets and flexible coils in an EMAT arrangement for measuring defects in metallic symmetrical objects, and
  • Yet another object of this invention is to provide an EMAT system for measuring for properties and defects in a high-speed rotating environment
  • Fig. 1 illustrates the essential elements of an EMAT for generation of Lamb waves in a rod or tube of electrically conducting material
  • Fig. 2 illustrates the essential elements of an EMAT for detection of Lamb waves in a rod or tube of electrically conducting material.
  • Fig. 3 is a diagram of an EMAT system being used for inspection of copper rods which illustrates a path traveled by the guided acoustic waves.
  • Fig. 4 shows a cross-section of an EMAT for generation and detection of symmetrical guided wave metal rods and shows a permanent magnet, a set of coils and the magnetic field induced in a rod by these components.
  • Fig. 5 illustrates the peak amplitude of the alternating stress distribution of the second order symmetrical Lamb wave mode.
  • Fig. 6 shows a cross-sectional view of an EMAT for generation and detection of asymmetrical guided waves in metal rods and shows a permanent magent, a set of coils and the magnetic fields induced thereby.
  • Fig. 7 illustrates the peak amplitude of the alternating stress distribution of the first order asymmetrical Lamb wave mode.
  • Fig. 8 shows a collapsible EMAT composed of segmental magnets and a flexible coil which can be opened during the start of an inspection for safe passage of the leading edge of a rod traveling at high speed.
  • Fig. 9 is an illustration of a flexible coil which is attached to the internal surfaces of the magnet sections of a collapsible EMAT.
  • Fig. 10 illustrates the assembly of two - side flexible printed circuit coils for use with a collapsible EMAT. Detailed Description of the Invention.
  • FIG. 1 illustrates the essential elements of the EMAT and the basic principles of the generation of Lamb waves in a rod or tubes of electrically conducting material.
  • the acoustic waves 1 and 2 are produced by Lorentz forces generated by the EMAT at a fraction of a millimeter under the surface of the rod.
  • the Lorentz forces 3 are generated by the interaction of a static magnetic field 4 from a magnetizing source such as a permanent magnet and eddy currents 5 induced by alternating currents 6 flowing through coils 7 of electrical conductors which encircle the rod.
  • the eddy currents are induced by exciting the coils with an alternating current having a temporal frequency within the range of 50 KHz to 5 MHz.
  • the excitation frequency is selected according to the desired acoustic wave mode, the acoustic properties of the rod or tube and the diameter of the rod or the wall thickness of the tube being inspected.
  • the eddy currents flow around the circumference of the rod at a location immediately under the windings of each encircling coil and in a direction parallel to the windings of the coil These eddy currents produce magnetic fields which either add or subtract to the magnetic bias field of the permanent magnet.
  • the radial Lorentz forces are increased.
  • the radial Lorentz forces are decreased. This variation in the Lorentz forces produces Lamb waves which propagate away from the coils and down the length of the rod in two directions.
  • the amplitude of the acoustic shear wave is increased substantially by the addition of encircling coils as they are excited by electrical currents of the same frequency.
  • Adjacent coils are wound in the opposite direction, i.e., one in the clockwise direction and the other in the counter clockwise direction.
  • the coils are separated at a distance equal to half of a wave length of the acoustic Lamb wave generated in the rod.
  • the frequency of the excitation current is adjusted electronically so that the radial Lorentz forces of adjacent coils are at maximum when the transmitted wave has traveled a distance along the rod equal to half a wavelength of the Lamb wave.
  • the acoustic wave transmission from each coil is increased in amplitude by the acoustic transmission from all of the other coils until a maximum amplitude occurs.
  • the amplitude of the acoustic wave is maintained at a maximum until the electrical excitation current is removed or caused to decrease to zero.
  • the acoustic wave decays to zero after the electrical excitation is removed in a manner which is similar to its ascent to maximum.
  • Detection of the Lamb waves is essentially the reverse process of transmission. Illustrated in Figure 2 is the detection of either the transmitted or reflected Lamb waves.
  • the Lamb waves 1 can be detected by either a separate set of EMAT coils 7 or by the coils which are used to transmit the Lamb wave. In both of these cases, the coils are subjected to the relatively static field from either a permanent magnet or electromagnet.
  • a Lamb wave 1 passes under the detector coils, the rod expands and contracts at the temporal frequency of the Lamb wave.
  • This vibration of the rod in the presence of the magnetic bias induces eddy currents 5 which flow in a direction that is parallel to the windings of the detector coils
  • the eddy currents in turn induce a voltage which can be detected or measured at terminals of each coil.
  • the coils are connected in series so that the induced voltages are added to provide a maximum signal voltage at the terminals 8 and 9 of the connected coils. This signal voltage can be detected by electronic amplifier.10 and transmitted to other system electronics for
  • FIG. 3 shows an EMAT having a guided wave configuration being used for inspection of a solid cylindrical rod. Shown are two EMATs, a transmitter EMAT 11 and a receiver EMAT 12, housing 17 and the rod 13 being pulled through each EMAT and coiled on the other side of the EMATs into a large spool 14. Guided waves 15 and 16 are generated by the transmitter EMAT 11. The guided wave 16 is detected by the receiver EMAT 12 and results in an electrical signal response 18 displayed by the EMAT instrumentation 9. The guided wave 16 then continues to propagate toward the defect 21. Part of the wave 20 reflects from the defect and propagates back toward the receiver 12 where it is detected and results in a signal response 22 displayed by the EMAT instrumentation.
  • FIG. 4 there is shown a cross-section of an EMAT, either a receiver or transmitter.
  • the EMAT is composed of a magnet 23, pole pieces 24 and 25, and sets of coils 26 which encircle the rod.
  • the coils for both the transmitter EMAT and the receiver EMAT are separated by equal distances between adjacent coils.
  • the coils are wound with alternating polarity, i.e., clockwise, then counter clockwise, then clockwise, etc. and then are electrically connected in series.
  • a static field 27 which is symmetrical with respect to the central axis of the EMAT and rod is induced by the magnet in the rod section which is closest to the bore of the magnet.
  • the pole pieces 24 and 25 are composed of a hardened, ferromagnetic material such as carbon steel to provide the dual function of guiding the magnetic field into the rod and protecting the set of coils from wear and damage.
  • the alternating currents produce alternating magnetic fields 28 around each coil. Interaction of these alternating magnetic fields with the static fields to produce Lamb waves 15 and 16 which propagate in both directions along the length of the rod.
  • the interaction of the symmetrical, static, magnetic field 27 with the induced alternating magnetic field 28 results in a Lamb wave which has a dynamic acoustic stress that is as a function of the radial distance from the center of the rod.
  • the peak amplitude in time of the alternating stress distribution of the second order symmetrical mode reaches a maximum acoustic stress 29 at the center of the rod and minimum stress 30 and 31 at the surface of the rod.
  • This symmetric wave mode produces relatively large amplitude acoustic reflections from defects located at or nearer the surface of the rod as compared to acoustic reflections from defects located near the surface of the rod.
  • Figure 6 illustrates an EMAT which produces guided waves asymmetrical about the central axis of a rod.
  • magnets 32 and 33 generate a static magnetic field 34 which is perpendicular to rod 3 and the central axis of a set of coils 35.
  • the end pieces 36 and 37 keep the rod 3 near the center of coils 35 and are composed of nonferromagnetic material to insure that the magnetic field 25 through the rod is maximized.
  • the asymmetric static magnetic field interacts with alternating fields 38 from the coils and eddy currents to thereby generate guided wave modes which are asymmetric with respect to the central axis.
  • the interaction of the asymmetrical, static magnetic field 34 with the induced alternating field 38 produces a Lamb wave which has a dynamic acoustic stress that is as a function of the radial distance from the center of the rod.
  • the peak amplitude in time of the alternating pressure distribution of the first order asymmetrical mode produces a minimum acoustic stress 39 at the center of the rod and a maximum stress 40 and 41 at the surface of the rod.
  • This asymmetrical wave mode produces a greater acoustic stress at the surface of the rod, thereby providing relatively large amplitude acoustic reflections from defects located at or near the surface of the rod as compared to defects located near the center of the rod.
  • the acoustic wave 16 which travels away from the spool 14 passes through a portion of the rod that is inside the receiver EMAT 12.
  • Signal response 18 can be observed on left hand portion of the A - Scan Display 19.
  • the reflection 20 of the transmitted guided wave from defect 21 in the rod have a similar effect on the receiver EMAT 12.
  • the amplitude of the reflected waves is smaller than the amplitude of the initial transmittedwave as indicated by the signal response 22 on the instrument display.
  • a gated data acquisition and signal processing instrumentation such as an oscilloscope orcomputer with an analog-to- digital converter.
  • a pulse repetition rate of, say 500 Hz, and gate widths of sufficiently long duration to acquire and process the reflection signals are employed.
  • commencement of a high-speed online inspection usually has the difficulty associated with it of threading the rod through the sensor without inflicting serious damage to the sensor and/or injury to personnel. If the attempt to pass the rod through the sensor is unsuccessful, substantial loss of production and revenue can result. This mechanical aspect is not affected by the acoustic waves and vice versa.
  • Figure 8 shows a collapsible EMAT composed of segmented magnets 42 and 43 and a flexible coil 44.
  • the magnet sections are connected by a hinge 45 in this case so t that they can be rotated about the hinge to provide an opening sufficiently wide to facilitate removal of the EMAT from the region through which the end of the rod will pass.
  • Theflexible coil is attached to the internal sufaces of magnet sections so that it conforms to the contour of the magnet sections.
  • Figure 9 shows a flexible coil which is attached to the interior of a magnet section. It is composed of electrical conductors 46 etched on a thin plate substrate 47 typical of the material used in the fabrication of printed circuits. The coil windings are covered with a thin sheet of the same material to insulate the electrical conductors and prevent electrical arcing or shorting to the rod.
  • the inside view of the flexible coil shown on the left hand side of Figure 9, shows the continuous current 48 path when a voltage is applied to the terminals with the indicated polarity. The current flows from the positive terminal 49 along the conductor and passes through the via or electrical connection to the outside surface illustrated on the right hand side of Figure 9 and then proceeds to flow from the via to the negative terminal 35.
  • Figure 10 shows a perspective view of the double-sided flexible printed circuit assembly.
  • EMAT electrical current 48 enters the positive terminal 49 and passes along the conductor 46 on the inside surface of flexible substrate 47 to via 50.
  • the electrical current then passes through the via to the conductors on the outside surface of substrate 47 where it flows along the conductors in the same direction as the current flowing in the adjacent conductors on the inside surface of the substrate and into the negative terminal.
  • the flexible coil is designed so that the portions of it which are wrapped closely around the rod have overlaying conductors on the inside and outside surfaces of the flexible substrate.
  • the induced magnetic field increases by approximately a factor of two compared to the field induced by a coil that has conductors only on one side the substrate. This results in a corresponding increase in the eddy current density induced in the rod under each part of the flexible coil which is in close proximity to the rod.
  • a similar, double sided receiver coil design provides approximately twice the signal voltage at the output terminal compared to a single sided coil design.

Abstract

L'invention concerne des transducteurs acoustiques électromagnétiques (11 et 12) en général et, plus précisément, une conception acoustique électromagnétique destinée à l'émission et à la réception d'ondes acoustiques guidées (15 et 16) dans des tiges, barres, fils et tubes métalliques, aux fins de détection de défauts dans ceux-ci et de mesure de certaines propriétés de ces produits métalliques pendant et après la fabrication.
PCT/US2003/014814 2003-05-06 2003-05-09 Transducteur acoustique electromagnetique d'ondes guidees WO2004106913A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/US2003/014814 WO2004106913A1 (fr) 2003-05-09 2003-05-09 Transducteur acoustique electromagnetique d'ondes guidees
AU2003239415A AU2003239415A1 (en) 2003-05-06 2003-05-09 Guided wave electromagnetic acoustic transducer

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2003/014814 WO2004106913A1 (fr) 2003-05-09 2003-05-09 Transducteur acoustique electromagnetique d'ondes guidees

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Cited By (8)

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WO2008086463A1 (fr) * 2007-01-11 2008-07-17 Baker Hughes Incorporated Système de mesure de contrainte dans des éléments tubulaires de fond
WO2010006041A2 (fr) * 2008-07-08 2010-01-14 Baker Hughes Incorporated Système pour mesurer la contrainte de cisaillement dans des dispositifs tubulaires de fond de trou
CN104155366A (zh) * 2014-08-06 2014-11-19 乌鲁木齐霞明创新电子科技有限公司 一种超声波无损检测管道装置
KR101729039B1 (ko) 2009-06-26 2017-04-21 티.디.더블유델라웨어인코포레이티드 이중 나선형 ｅｍａｔ 센서 어레이를 갖는 파이프라인 검사 도구
CN108426948A (zh) * 2018-05-14 2018-08-21 南京航空航天大学 一种激发单一模态Lamb波的电磁超声换能器及其工作方法
CN110672718A (zh) * 2019-07-08 2020-01-10 南昌航空大学 用于钢轨踏面检测的电磁超声点聚焦/发散表面波方法及其装置
CN113325087A (zh) * 2021-04-19 2021-08-31 中国石油天然气集团有限公司 一种用于板材非分层缺陷和表面缺陷的电磁超声检测方法
CN116026934A (zh) * 2023-01-04 2023-04-28 南通和禾声学科技有限公司 一种用于激发弯曲模态导波的交叉时延阵列换能器

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US5721379A (en) * 1993-11-13 1998-02-24 The University Of Warwick Electromagnetic acoustic transducers
US6109108A (en) * 1995-12-13 2000-08-29 Ebara Corporation Electromagnetic acoustic transducer EMAT and inspection system with EMAR
US5866820A (en) * 1996-09-20 1999-02-02 Camplin; Kenneth R. Coil volumetric and surface defect detection system
US5808202A (en) * 1997-04-04 1998-09-15 Passarelli, Jr.; Frank Electromagnetic acoustic transducer flaw detection apparatus
US5907100A (en) * 1997-06-30 1999-05-25 Gas Research Institute Method and system for detecting and displaying defects in piping
US6070467A (en) * 1997-10-17 2000-06-06 Gas Research Institute Electromagnetic acoustic transducer (EMAT) system and method for eliminating noise produced by static discharge
US6125703A (en) * 1998-06-26 2000-10-03 Mcdermott Technology, Inc. Detection of corrosion fatigue in boiler tubes using a spike EMAT pulser
US6164137A (en) * 1999-02-03 2000-12-26 Mcdermott Technology, Inc. Electromagnetic acoustic transducer (EMAT) inspection of tubes for surface defects
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