RU2656134C2 - Electromagnetic-acoustic transducer - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of nondestructive testing of articles. Electromagnetic-acoustic transducer (EMAT) comprises a housing in which a dielectric layer is placed, a constant magnetic field source and a coil assembly, the constant magnetic field source and the inductor unit are located in the housing with the possibility of interaction, and the inductor unit comprises a generator coil and at least one receiving coil. In this case, the inductors are made in the form of separate flat spiral coils of inductance, which are located on one side of the dielectric layer and whose turns have a common center.

EFFECT: technical result is an increase in the sensitivity of the EMAT and the possibility of making control measurements of products of small thickness at large working gaps.

6 cl, 5 dwg

Description

Technical field

The present invention relates to the field of non-destructive testing of products, and more particularly to an electromagnetic-acoustic transducer that can be used to measure the thickness of products from conductive materials and to identify defects in such products.

State of the art

Currently, as one of the main methods of non-destructive testing, the ultrasonic testing method is used. The basis of the ultrasonic control method is the generation of ultrasonic waves in the material of the controlled product with the subsequent reception of such waves reflected from the boundary of the media. The specified control method can be used to detect defects, such as cracks, voids, injection shells, in products from conductive materials, as well as to determine the linear dimensions of such products. The ultrasonic control method is carried out by an electromagnetic-acoustic transducer (EMAT). The EMAT design is based on a block of induction coils that generate ultrasonic waves in a controlled product and receive reflected waves. Various designs of induction coil units and EMAT with such coil units are known.

From the RF patent 2268517 for the invention (IPC class H01F 27/30), an EMAT inductor located on a dielectric board and an EMAT equipped with such a coil are known. The known coil can be made single-layer or multi-layer, contains one or more sections and is made in the form of two symmetrical petals. A disadvantage of the known coil is that it is used both in the generating coil mode and in the receiving coil mode, as a result of which the EMAT equipped with such a coil has a low sensitivity.

From the patent of the Russian Federation 2325638 for the invention (IPC class G01N 29/22) a block of coils for electromagnetic-acoustic transducers is known containing a group of inductors located one below the other with overlap and independently connected to its receiver, while the group of coils has an arbitrarily large common the length of the working area, and the coils in the group are located in several layers in the direction of the rectilinear, curvilinear, circumferential, depending on the purpose of ultrasonic testing, the shape and direction of movement of the object la. A disadvantage of the known design of the coil unit is the mutual overlap of adjacent coils and the presence of their electromagnetic coupling, which leads to a deterioration of the noise immunity and the ability to select ultrasonic signals among the interference from an EMAT equipped with such a coil unit.

An EMAT with a coil unit is known from the RF patent 2476949 for the invention (IPC index H01F 27/30), which contains a first group of inductors, in which the coils are located one below the other with overlap and are independently connected to their receiver, while the first group of coils has a large overall length of the working area is desired, and the coils in the group are located in several layers in a straight, curved, circumferential direction, depending on the purpose of the ultrasonic inspection, the shape and direction of movement of the test object. The known block of coils is also provided with a second group of inductors connected to their generators located above the first group of coils with full or partial overlap of the coils of the first group. A disadvantage of the known design of the coil unit is the multilayered structure, as a result of which EMAT equipped with such a coil unit has less sensitivity due to spurious inductive-capacitive coupling caused by mutual overlap of the coils, which negatively affects the accuracy of measurements performed by EMAT.

The closest in technical essence and the achieved technical result to the claimed invention is a coil unit and EMAT equipped with such a coil unit described in RF patent 2206888 for the invention (IPC indices G01N 29/04, H04R 9/00). Known EMAT contains a block of coils, consisting of at least two inductors located in layers by stacking one on the other with a shift in the direction of the winding and made in the form of separate sections, wound with one wire and laid close to each other, and the turns of sections of one inductance coil are located between the turns of the sections of another inductor, and the ends are bent and isolated from the ends of the sections of another inductor with an electrically insulating elastic material, both inductance coils and have terminals for connection to a high frequency generator and a receiver of electrical signals. A disadvantage of the known block of coils is the presence of bent ends that do not allow them to be placed as close to the surface of the magnetic field concentrators (round or rectangular plates made of special material), which is located between the permanent magnet and the coil, which increases the heterogeneity of the acoustic field created by the block of coils , and also contributes to the emission of an inclined wave, as a result of which an EMAT with a known block of coils has a lower sensitivity, a smaller value of the working charge the gap and the large dead zone of the acoustic tract, which makes it impossible to control products of small thickness.

Disclosure of invention

The problem to which the invention is directed, is to improve the design of the known EMAT in order to expand the range of its use.

This problem is solved by the proposed EMAT, which contains a housing in which a dielectric layer is placed, a source of a constant magnetic field and a block of inductors, the source of a constant magnetic field and a block of inductors located in the housing with the possibility of interaction, in which the block of inductors enters the region the action of the magnetic field of the source of a constant magnetic field, while the block of inductors contains a generator coil and at least one receiving coil, and eratornaya coil is adapted to connect to a generator of electric signals, and at least one receiver coil configured to connect to a receiver of electrical signals. The proposed EMAT is characterized in that the inductors are made in the form of separate flat spiral inductors, which are located on one side of the dielectric layer and whose turns have a common center.

The technical result to which the claimed invention is directed is to increase the sensitivity of the EMAT and to provide the ability to make control measurements of products of small thickness with large working gaps.

The working gap is the distance between the EMAT surface facing the control object and the surface of the control object. The increase in the working gap, in particular, is due to the fact that the measurement objects are often operated under conditions in which layers of non-metallic materials, for example rust, are formed on their surface, in addition, a paint layer can be applied to the measurement objects. Thus, there is a need to create an EMAT with a larger working gap, which avoids the need to clean the top layer of the controlled object or otherwise prepare it for inspection.

According to one embodiment of the proposed EMAT, the coil unit comprises one generating coil and one receiving coil, the generating coil being located around the receiving coil. This arrangement of the coil avoids unnecessary stray inductive-capacitive coupling between the coils, which, in turn, will increase the sensitivity of the EMAT.

According to another embodiment of the proposed EMAT, the coil unit further comprises a second receiving coil, which is located around the generator coil. The presence of an additional receiving coil allows you to increase the area of reception of reflected waves and further increase the sensitivity of EMAT.

According to another embodiment of the proposed EMAT, the inductors are made in the form of printed flat spiral inductors. The use of printed inductors makes it possible to simplify the manufacture of EMAT and reduce its overall dimensions.

According to another embodiment of the proposed EMAT, the source of the constant magnetic field is an electromagnet. Using an electromagnet allows you to control the magnetic field and to avoid magnetizing EMAT to the object of control.

According to another embodiment of the proposed EMAT, the source of the constant magnetic field is a permanent magnet. The use of a permanent magnet allows you to further simplify the design of EMAT and reduce energy consumption.

Brief Description of the Drawings

The following is a description of preferred embodiments of the proposed EMAT with reference to the drawings, in which:

FIG. 1 schematically shows a general view of an EMAT according to the present invention,

FIG. 2 shows one preferred embodiment of a coil unit according to the present invention;

FIG. 3 shows another preferred embodiment of a coil unit according to the present invention;

FIG. 4 illustrates the signals obtained when measuring on a control sample with a working gap of 4.5 mm between the coil of the proposed EMAT and the control sample;

FIG. 5 illustrates the signals obtained by measurement on a control sample with a working gap of 4.5 mm between the EMAT coil of the prior art and the control sample.

The implementation of the invention

In FIG. 1 schematically shows an example of the proposed electromagnetic-acoustic transducer (EMAT), which contains a housing 1, in which there is a layer 2 of a dielectric fixed to the wall of the housing 1 motionless, a block 3 of inductors located on the dielectric layer, and a source 4 of a constant magnetic field , which is located in the housing with the possibility of interaction with the block 3 coils, in which the block 3 coils is in the field of magnetic field of the source 4 of a constant magnetic field. The source 4 of a constant magnetic field is an electromagnet.

In FIG. 2 shows a preferred embodiment of a block 3 of inductors. Block 3 contains a generator inductor 7 and a receiving coil 8 inductance. These coils 7, 8 are made in the form of flat printed spiral coils, which allows to simplify the manufacture of EMAT and reduce its size. Coils 7, 8 are made on one side of the dielectric layer 2 and are located essentially in the same plane. As can be seen from FIG. 2, the generator coil 7 is located around the receiver coil 8, so that the spirals of the conductive lines forming the coils 7, 8 have a common center. Coils 7, 8 have terminals (not shown) that enable them to be connected respectively to an electric signal generator and an electric signal receiver (not shown).

The proposed EMAP works as follows.

EMAT set in the working position (control position) relative to the control object. Then, a constant magnetic field is applied to block 3 coils from the side of source 4. A coil 7, connected to an electric signal generator, is supplied with an alternating current electric pulse of frequency f (Hz) —a probing pulse. As a result, an alternating electromagnetic field arises around the coil 7. The Lorentz forces arising as a result of the interaction of the fields excite ultrasonic waves in the metal of the test object, causing vibrations of its individual layers in the metal. As a result of these oscillations, induction microcurrents arise, creating a magnetic field that interacts with a receiving coil (s) connected to an electrical signal receiver, which converts an electromagnetic pulse into an electric one. EMAT creates a transverse wave with circular and radial polarization, propagating in the object of control by two beams (converging beam to the center of the coil and diverging beam from the center of the coil) at small angles to the normal to the plane of the coil. The acoustic wave reflected from the bottom surface (or scattered on the defect) is concentrated on the internal receiving coil 8 (in the presence of an external receiving coil it also concentrates on it), providing almost complete reception of the radiated energy.

Separate use of coils 7, 8 allows for their optimal coordination with the generator and receiver independently of each other, increasing the sensitivity of the EMAT and, as a result, the overall noise immunity and reliability of ultrasonic testing. The peculiarity of such a topology of the block of 3 coils allows to reduce spurious inductive-capacitive coupling. An increase in the signal-to-noise ratio due to the optimal choice of coil topology and their matching allows monitoring at large working gaps.

Separate execution of coils 7, 8 on one side of the dielectric layer allows to reduce inductive capacitive coupling between coils 7, 8, which allows to reduce the dead zone of the EMAT acoustic path and to provide the ability to control products of small thickness.

In FIG. 3 shows another embodiment of the coil unit 3, which, in addition to the generator coil 7 and the receiver coil 8, comprises a second receiver coil 10, said coil 10 enclosing the coil 7 and thus being located around the generator coil 7, which, in turn, located around the receiving coil 8. The coil 10 also has terminals (not shown) for connecting to an electrical signal receiver to which the coil 8 is connected.

As a result of the implementation of the present invention, an EMAT was obtained, between the inductors of which the inductance-capacitive coupling is significantly reduced, the acoustic wave is emitted at a smaller angle to the normal, the coils are made with such an arrangement and connection in the unit, which ensures their independent operation from each other in different modes from different generators, different receivers. EMAT according to the invention has an increased value of the working gap and a reduced value of the minimum measured thickness.

In FIG. 4 and 5 are graphs illustrating the signals received on the control sample when measuring the thickness (nominal thickness of the control sample 14 mm) with a working gap of 4.5 mm, respectively, claimed EMAT and EMAT, known from the prior art. As seen in FIG. 4, during the measurement, a bottom echo signal was obtained, according to which the thickness of the control sample can be determined with a given accuracy (error not more than 0.1 mm). At the same time, in FIG. Figure 5 shows that, when measuring on a control sample, only noise signals were obtained whose amplitude does not allow one to isolate the bottom echo signal and, as a result, measure the thickness of the control sample with a given accuracy.

The above description of the embodiments of the claimed invention is not limiting, for example, the inductance coils of the coil unit can be obtained manually by winding with a wire, and not necessarily obtained by printing, the constant magnetic field source can be a permanent magnet, and the receiving coils can be connected to different receivers of electrical signals. Other modifications of the claimed invention are also possible, as a result of which it should be noted that the scope of the claimed claims is limited only by the following claims.

Claims (17)

1. An electromagnetic acoustic transducer comprising: the housing in which the dielectric layer is placed, constant magnetic field source and block of inductors moreover, the source of the constant magnetic field and the block of coils of inductance are located in the housing with the possibility of interaction, in which the block of coils of inductance is in the field of action of the magnetic field of the source of the constant magnetic field, wherein the block of inductors contains: generator coil and at least one receiving coil, and the generator coil is configured to be connected to an electric signal generator, and at least one receiving coil is configured to connect electrical signals to the receiver, characterized in that these inductors are made in the form of separate flat spiral inductors, which are located on one side of the dielectric layer and which have a common center. 2. The Converter according to claim 1, in which the coil unit comprises one generator coil and one receiver coil, the generator coil located around the receiver coil. 3. The Converter according to claim 2, in which the coil unit further comprises a second receiving coil, which is located around the generator coil. 4. The converter according to paragraphs. 1-3, in which the inductors are made in the form of a printed flat spiral inductor. 5. The Converter according to claim 1, in which the source of the constant magnetic field is an electromagnet. 6. The Converter according to claim 1, in which the source of the constant magnetic field is a permanent magnet.

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