JP2004333448A - Electromagnetic ultrasonic probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a flaw detection capability and a measurement capability by making a magnet structure stronger or smaller. <P>SOLUTION: The electromagnetic ultrasonic probe comprises one or more pairs of magnet arrangement units which periodically arrange many prism-shaped permanent magnets and apply a magnetic field to a member to be inspected, and a coil which generates or detects an eddy current in the member to be inspected. The magnet arrangement unit 30 comprises a periodic arrangement structure in which primary magnets 32a and auxiliary magnets 32b are combined with their height direction aligned, wherein the primary magnets 32a are magnetized in the height direction and are arranged so that their magnetization directions are alternatingly opposed, and the auxiliary magnets 32b are magnetized in the thickness direction and are placed between the primary magnets and at both the ends so that their magnetization directions are alternatingly reversed. The surface of the north pole side of the primary magnet which is in contact with the surface of the north pole side of the auxiliary magnet is set to be a magnet working surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electromagnetic ultrasonic probe used for non-contact and non-destructive inspection or measurement of a conductive inspection material such as a metal. More specifically, the present invention relates to an electromagnetic ultrasonic probe which is magnetized in a vertical direction (height direction). The present invention relates to an electromagnetic ultrasonic probe devised so that a high ultrasonic intensity can be obtained by combining a magnet and an auxiliary magnet magnetized in a lateral direction (thickness direction) to form a magnet arrangement unit.
[0002]
[Prior art]
[Patent Document 1]
Japanese Patent Application Laid-Open No. H10-282071
Various ultrasonic transducers are used in an ultrasonic flaw detector, and one of them is an electromagnetic ultrasonic probe. An electromagnetic ultrasonic probe sends a high-frequency current to a coil located near the surface of a test object having conductivity, thereby causing an eddy current induced in the test material and a permanent magnet provided on the probe. This device generates ultrasonic waves directly in the material to be inspected by the interaction with the magnetic field, thereby inspecting the defect and measuring the thickness of the material to be inspected. For example, as shown in FIG. 5, the electromagnetic ultrasonic probe 10 includes a magnet structure 12 that applies a magnetic field to a material to be inspected (not shown), and a transmission coil (or a material that generates an eddy current to the material to be inspected). A receiving coil (detection coil) 14 for detecting an eddy current of the inspection material is provided, and the coil lead wire 16 is connected to a high-frequency current source or a flaw detector (not shown).
[0004]
In such an electromagnetic ultrasonic probe, various modes of transmitting and receiving ultrasonic probes can be easily configured by appropriately combining the structure and arrangement of the permanent magnets and the coil structure for eddy current excitation. For this reason, application to high temperature environments and applications to fields such as nuclear power plants and railway flaw detection as non-contact and non-destructive inspection methods have been actively studied.
[0005]
As shown in FIG. 6, a conventional magnet array unit used for applying a magnetic field in an electromagnetic ultrasonic probe usually includes a large number of prism-shaped permanent magnets 20 magnetized in a height direction, and the adjacent magnets 20 In this structure, the magnetization directions are arranged in a line so that they are opposite to each other. One of the upper and lower surfaces of the magnet array unit 22 is a magnet working surface (a surface facing the material to be inspected). The arrow in the figure indicates the magnetization direction (the direction from the S pole to the N pole). Therefore, each magnet in the magnet arrangement unit is in a state of being alternately magnetized in the direction perpendicular to the magnet working surface in the opposite direction. Such a magnet arrangement unit 22 can constitute a magnet structure by only one set. Further, two magnet arrays 24 are obtained by arranging the same number of such magnet arrangement units 22 so that the magnets adjacent to each other in the groups have the magnetization directions opposite to each other (B in FIG. 6). reference). Further, the magnet array units may be increased according to a similar rule, so that a multi-row magnet structure is obtained.
[0006]
By using such a magnet structure and combining it with a coil for supplying an induced current (in the case of a transmitting probe) and / or a coil for detecting an eddy current (in the case of a receiving probe), the electromagnetic ultrasonic probe is used. The child will be composed.
[0007]
Incidentally, as another conventional example of the magnet arrangement unit, a configuration in which a nonmagnetic spacer is interposed between permanent magnets has also been proposed (see Patent Document 1). In this structure, the interposition of the spacer increases the magnetic resistance in the spacer and increases the strength of the magnetic field that can be applied to the material to be inspected, thereby improving the sensitivity.
[0008]
[Problems to be solved by the invention]
In any case, in such a conventional magnet structure, the upper and lower surfaces are magnetically symmetrical, and the magnetic characteristics are the same regardless of which of the upper and lower surfaces is the magnet working surface. Therefore, only half of the magnetic energy of the magnet can be used as an electromagnetic ultrasonic probe.
[0009]
Further, in a conventional magnet structure of an electromagnetic ultrasonic probe, a configuration having a large magnet height L (a configuration using a high prismatic permanent magnet) is employed. This is because if the magnet height L is small, the magnetic properties may be weakened. Therefore, the magnet height L is usually set to about two to three times the magnet arrangement cycle length or more. As a result, not only is the magnet large, but also heavy.
[0010]
An object of the present invention is to provide an electromagnetic ultrasonic probe capable of improving flaw detection capability and measurement capability. Another object of the present invention is to provide an electromagnetic ultrasonic probe that can be reduced in size and weight.
[0011]
[Means for Solving the Problems]
When the magnet magnetized in the thickness direction has a thin and flat shape, the effect of the demagnetizing field is large, and a decrease in magnet performance is expected. For this reason, it was common technical knowledge that the use of a flat magnet magnetized in the thickness direction for the magnet structure of the electromagnetic ultrasonic probe should be avoided as much as possible. However, as a result of repeated numerical analysis and experimental trial production, the present inventors have improved magnetic properties by properly combining a main magnet magnetized in the height direction and an auxiliary magnet magnetized in the thickness direction. And found that it enhances the ultrasonic performance. The present invention has been completed based on this knowledge.
[0012]
The present invention provides one or more sets of magnet arrangement units for periodically arranging a large number of prismatic permanent magnets and applying a magnetic field to a material to be inspected, and generating an eddy current in the material to be inspected or generating an eddy current in the material to be inspected. In the electromagnetic ultrasonic probe having the coil to be detected, the magnet array unit has a main magnet that is magnetized in the height direction and is arranged so that the magnetization directions are alternately opposite to each other, and in the thickness direction. An auxiliary magnet positioned between the main magnets and at both ends so as to be magnetized and the magnetization directions alternately opposite is formed in a periodic array structure in which the height directions are aligned, and the N pole of the auxiliary magnet is formed. An electromagnetic ultrasonic probe characterized in that the surface on the N pole side of the main magnet that is in contact with the surface on the side is a magnet working surface. Therefore, to further add, in this specification, the height direction means a direction perpendicular to the magnet working surface, and the thickness direction means a magnet arrangement direction.
[0013]
Here, it is preferable that the end auxiliary magnets located at both ends of the magnet arrangement unit have the magnet thickness dimension b ′ set to 0.25 to 1 times the magnet thickness dimension b of the other auxiliary magnets. Further, the magnet height L is preferably set to a dimension of 0.5 to 1.5 times the magnet arrangement cycle length T = 2 (a + b) (where a is the thickness of the main magnet). Further, it is desirable to make the magnet thickness dimension a of the main magnet equal to the magnet thickness dimension b of the auxiliary magnet. In these cases, the main magnet and the auxiliary magnet are made of the same magnetic material.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of a magnet arrangement unit and each magnet constituting a magnet structure used in the present invention. The magnet arrangement unit 30 has a structure in which a large number of square pillar-shaped (here, a rectangular cross-section is a columnar body having a rectangular cross section) periodic arrangement of permanent magnets. The magnets used are of two types: a main magnet 32a magnetized in the height direction (vertical direction in the drawing) and an auxiliary magnet 32b magnetized in the thickness direction (horizontal direction in the drawing). Are periodically arranged in consideration of the direction of magnetization. More specifically, the main magnets 32a are arranged so that the magnetization directions are alternately opposite to each other, and the auxiliary magnets are located between and at both ends of the main magnets 32a so that the magnetization directions are alternately opposite to each other. The magnets 32b are arranged in the same height direction. Then, the N pole side surface of the main magnet 32a that is in contact with the N pole side surface of the auxiliary magnet 32b is selected as the magnet working surface. Therefore, in FIG. 1, the lower surface of the magnet arrangement unit 30 is the magnet working surface, the height direction of the magnet is the direction perpendicular to the magnet working surface, and the thickness direction is the magnet arrangement direction. Incidentally, since the magnetic flux density is much lower on the upper surface of the magnet array unit 30 than on the lower surface (the magnetic characteristics are asymmetric on the upper surface and the lower surface), it is not used as a magnet working surface. Such a magnet arrangement unit 30 alone functions as a magnet structure of the electromagnetic ultrasonic probe.
[0015]
FIG. 1B shows this magnet arrangement state in two dimensions. As shown in the figure, an xy coordinate system is set in which the right hand direction is the x direction and the upward direction is the y direction. A main magnet 32a magnetized upward (y direction), an auxiliary magnet 32b magnetized rightward (x direction), a main magnet 32a magnetized downward (-y direction), and a left magnet (-x The magnet arrangement period T is constituted by the auxiliary magnet 32b magnetized in the (direction). Here, for the following description, the dimensions of the magnet are defined as follows.
L: Height of magnet a: Thickness of main magnet b: Thickness of auxiliary magnet b ': Thickness of end auxiliary magnet w: Width of magnet
The magnet structure to be incorporated in the electromagnetic ultrasonic probe needs to keep the magnetic flux density perpendicular to the magnet working surface as periodic as possible. Therefore, in the present invention, as described above, the structure is such that both ends of the magnet structure serve as auxiliary magnets. This is because if there are no auxiliary magnets at both ends, the uniform periodicity of the magnetic flux density distribution is impaired. In addition, the magnetization directions of the auxiliary magnets (end auxiliary magnets) arranged at both ends may be the same or opposite. When the main magnet and the auxiliary magnet are made of the same magnetic material, the thickness b 'of the end auxiliary magnet is 0.25 to 1 times the thickness b of the other auxiliary magnets. The electromagnetic ultrasonic probe exhibits high performance at a small lift-off distance (distance from the working surface), and the actual measurement lift-off distance is usually within about 1.5 mm. Therefore, the above range is appropriate. Here, the optimum value of the thickness dimension b 'of the end auxiliary magnet depends on the lift-off distance. If the lift-off distance is short, the dimension b' is adjusted to be smaller. That is, the uniformity of the magnetic flux density distribution can be improved by setting the dimension b 'according to the lift-off distance.
[0017]
Further, the magnet height L is preferably 0.5 to 1.5 times the magnet arrangement cycle length T = 2 (a + b). If the magnet height L is too small, the power will be insufficient. Conversely, if the magnet height L is too large, the magnet will become large and heavy, and if the magnet height L is increased to some extent, the magnetic properties will be saturated. Further, it is preferable that the ratio of the thickness dimension a of the main magnet to the thickness dimension b of the auxiliary magnet be in the range of 1: 1.5 to 1.5: 1, but it is preferable that the ratio be approximately equal (1: 1). Is optimal. At that time, the ultrasonic intensity can be maximized.
[0018]
In the magnet structure used in the present invention, there is no restriction on the material of the main magnet and the auxiliary magnet, and the magnet materials may be the same or different. If different, the optimal dimensional relationship between the main magnet and the auxiliary magnet is not always the same as above. However, in different combinations of the thickness a of the main magnet and the thickness b of the auxiliary magnet, only the ultrasonic intensity of the electromagnetic ultrasonic probe is different, and the function as the electromagnetic ultrasonic probe is not lost.
[0019]
FIG. 2 shows another example of the magnet structure used in the present invention. In this magnet structure 34, two sets of magnet arrangement units 30 as shown in FIG. 1 are adjacent to each other, and the magnetization directions of the adjacent main magnets 32a are opposite to each other, and the magnetization directions of the auxiliary magnets 32b are also mutually opposite. They are combined in the opposite way. Although illustration is omitted, by arranging three or more sets of magnet array units in parallel according to the same rule, a multi-row magnet structure can be formed.
[0020]
3 and 4 show a combination of a magnet structure and a coil. FIG. 3 shows a structure that is effective when the magnet structure is constituted by one set of magnet arrangement units 30 (see FIG. 1). The coil 40 has a structure in which a wire is wound a predetermined number of times around an axis substantially perpendicular to the xy plane from the upper surface to the lower surface (working surface) of the magnet structure. In particular, it is preferable to make the direction of the coil wire along the working surface parallel to the x direction. FIG. 4 shows a case where the magnet structure 34 is constituted by two sets of magnet arrangement units (see FIG. 2). A planar coil 42 is used and placed on the magnet working surface (here, the lower surface) of the magnet structure. One side in the coil width direction is provided immediately below one magnet array unit, and the other side is provided immediately below the other magnet array unit.
[0021]
Such an electromagnetic ultrasonic probe can be used for both transmission and reception. Further, by arranging the transmission coil and the reception coil in an overlapping manner (different number of turns are possible and different dimensions are possible), it is also possible to configure a transmission / reception electromagnetic ultrasonic probe. These can be performed by a conventionally known method as described in Patent Document 1, for example. By incorporating such a magnet structure and a coil into an electromagnetic ultrasonic probe, the size and performance of the electromagnetic ultrasonic probe can be reduced.
[0022]
【Example】
The analysis result of the magnet structure will be described below. FIG. 7 shows the lift-off distance dependency of the magnetic flux density in the y-direction (perpendicular to the working plane). The horizontal axis is the relative position of the magnet along the x-direction (parallel to the working plane), and the vertical axis is the y-direction. This is the magnetic flux density By. A is the analysis result of the product of the present invention, and B is the analysis result of the conventional product. In each case, the lift-off distance (the distance from the working surface) is changed in the range of 0.1 to 4.0 mm. In the present invention, the same magnet material is used for the main magnet and the auxiliary magnet, and the height L of the magnet is 7 mm, the thickness a of the main magnet is 1.25 mm, and the thickness b of the auxiliary magnet is 1.25 mm. In the conventional product, the height L of the magnet is 7 mm and the thickness of the magnet is 2.5 mm. From these results, both the present invention and the conventional product are the same in that the smaller the lift-off distance is, the stronger the magnetic flux density By in the y direction becomes. However, when comparing the two at the same lift-off distance, the product of the present invention has a higher magnetic flux density. It can be seen that By is much increased. That is, the product of the present invention has stronger magnetic properties than the conventional product.
[0023]
Although illustration is omitted, it is confirmed that when the end auxiliary magnets are not present, the magnetic flux density distribution at both ends is clearly lower, and the whole lacks uniformity. In FIG. 7A, when the lift-off distance is as short as about 0.1 mm or less, the magnetic flux density exhibits uniform periodicity. According to the analysis results, when the thickness of the end auxiliary magnet is b '= 3b / 4, the uniformity of the magnetic flux density at the lift-off distance of 0.5 mm is good, and the electromagnetic ultrasonic probe is measured at the lift-off distance of about 0.5 mm. When the thickness of the auxiliary magnet is b '= b / 2, the uniformity of the magnetic flux density at a lift-off distance of 1.0 mm is good, and the electromagnetic ultrasonic probe is measured at a lift-off distance of about 1.0 mm. It has been confirmed that it is suitable for children. In general, an electromagnetic ultrasonic probe exhibits high performance at a small lift-off distance, so for example, in the example shown here, in the case of an electromagnetic ultrasonic probe suitable for 700 to 900 kHz, the actual measurement lift-off distance is 1. It is considered to be within about 5 mm. From these facts, it is appropriate that the thickness b 'of the end auxiliary magnet is in the range of 0.25b to b.
[0024]
FIG. 8 shows the magnet thickness dimension dependence of the magnetic flux density By in the y direction in the center longitudinal section (m-m section in FIG. 1) of the magnet magnetized in the vertical direction (height direction), and the horizontal axis represents y. The relative position in the direction and the vertical axis are the magnetic flux density By in the y direction. Various combinations in which the sum of the thickness a of the main magnet and the thickness b of the auxiliary magnet (thickness b '= b of the end auxiliary magnet) is constant (a + b = 2.5 mm in this case) are analyzed. The vertical line at the center of the figure corresponds to the working surface, and the left area corresponds to the inside of the magnet and the right area corresponds to the outside of the magnet. Outside the magnet, the smaller the thickness a of the main magnet, the greater the magnetic flux density in the y direction near the magnet surface, but decreases as the lift-off distance increases, and the curves may intersect and reverse. In any case, the bottom of many magnetic flux density distribution curves corresponds to the structure of b = 0 (that is, the conventional product without the auxiliary magnet), and the magnetic flux density distribution of the conventional product is the weakest. Means that.
[0025]
FIG. 9 shows the magnet height dimension dependence of the magnetic flux density By in the y direction in the center longitudinal section (m-m section in FIG. 1) of the magnet magnetized in the longitudinal direction (height direction), The relative position in the y direction and the vertical axis indicate the magnetic flux density By in the y direction. The analysis is performed by changing the magnet height L within a range of 2 to 10 mm. The vertical line at the center of the figure corresponds to the working surface, and the left area corresponds to the inside of the magnet and the right area corresponds to the outside of the magnet.
[0026]
Within the magnet, the maximum magnetic flux density differs due to the influence of the magnet height L. However, outside the magnet, when L = 5, 7, and 10 mm, the three curves are almost overlapped, and begin to fall slightly from the curve when L = 3 mm, and when L = 2.5 mm and L = 2 mm, There is a clear power reduction. As a result, it was found that the y-direction magnetic flux density was not sensitive to the magnet height L. In other words, even if a magnet having a small height L is used, the magnet has almost the same magnetic characteristics as a magnet having a very large height L. It can be seen that miniaturization and weight reduction of the child can be easily achieved.
[0027]
In consideration of the performance variation due to the manufacture of the magnet, the performance deterioration of the surface processing layer, and the difficulty of assembling the magnet, the magnet height L is 0.5 times or more of the magnet arrangement period T = 2 (a + b) (that is, here L ≧ 2.5 mm) is desirable, and in consideration of weight reduction, if the height is too large, the weight becomes heavy. Therefore, the magnet height L is 1.5 times or less the magnet arrangement period T (that is, L ≦ 7.5 mm here). ) Is desirable.
[0028]
FIG. 10 shows the magnet height dimension dependence of the magnetic flux density By in the y direction in the center longitudinal section (m-m section in FIG. 1) of the magnet magnetized in the longitudinal direction (height direction), The relative position in the y direction and the vertical axis indicate the magnetic flux density By in the y direction. The analysis is performed by changing the magnet height L. The vertical line at the center of the figure corresponds to the working surface, and the left area corresponds to the inside of the magnet and the right area corresponds to the outside of the magnet. Here, distribution curves of the magnetic flux density By in the y direction are obtained for three types of magnet structures in which the magnet height L is changed to 5, 7, and 10 mm. This complements FIG. 9 and shows the magnetic flux density distribution on the magnet working surface side as well as on the opposite surface side.
[0029]
Two sets of curves are observed outside the magnet. The upper curve is the y-direction magnetic flux density distribution on the working surface side, and the lower curve is the y-direction magnetic flux density distribution on the opposite surface side of the working surface. Obviously, the magnetic properties on the side opposite to the working side are weaker. This weak magnetic property is a result of the appearance of strong magnetic properties on the working surface side. Therefore, in the present invention, it is necessary to appropriately select a working surface, and it can be seen that a stronger electromagnetic ultrasonic probe can be configured even with the same material and substantially the same amount of magnet material used.
[0030]
Next, the ultrasonic intensity characteristics of the electromagnetic ultrasonic probe according to the present invention will be described. The analysis conditions are: magnet arrangement cycle number 8 + one auxiliary magnet, frequency 700 kHz, magnet height L = 7 mm, magnet arrangement cycle length 2 (a + b) = 5 mm, and the propagation medium material is stainless steel (SUS304). FIG. 11 shows the ultrasonic intensity characteristics when the sum (a + b) of the thickness a of the main magnet and the thickness b of the auxiliary magnet is fixed and the combination of a and b is changed. Each combination of a and b shows similar ultrasonic distribution characteristics. This indicates that the ultrasonic distribution characteristic is not a function of the combination of a and b, but a function of the sum of a + b. When the combination of a and b is different, only the peak value of the ultrasonic intensity changes, and the directivity shape and the like hardly change. In the figure, one strong main lobe peak and seven weak side lobe peaks are observed, and the total number 8 coincides with the magnet arrangement period number. A strong main lobe peak means sharp ultrasonic directivity, and the peak value of the main lobe can be evaluated as ultrasonic intensity. The analysis was performed on the relative ultrasonic distribution characteristics, and the vertical and horizontal axes in the figure show relative values.
[0031]
FIG. 12 shows the result of rearranging the peak value of the ultrasonic intensity and the ultrasonic refraction angle as a function of the magnet thickness a based on the data of FIG. As the difference between a and b is larger, the peak value of the ultrasonic intensity is smaller, and the ratio of the thickness dimension a of the main magnet to the thickness dimension b of the auxiliary magnet is in the range of 1: 1.5 to 1.5: 1. Good ultrasonic intensity can be obtained. In particular, when both are the same (a = b = 1.25 mm), the strongest ultrasonic intensity is obtained. Therefore, it is understood that the output of the probe can be adjusted by changing the thickness a of the main magnet and the thickness b of the auxiliary magnet of the magnet arrangement structure used in the electromagnetic ultrasonic probe of the present invention. Note that, in the figure, the case of b = 0 corresponds to a conventional magnet structure. Comparing the peak values of both ultrasonic intensities, it was possible to achieve a 1.4-fold improvement in performance when a = b as compared to when b = 0. On the other hand, the change in the angle of refraction of the ultrasonic waves is slight (within a range of 0.3 °) regardless of the combination of a and b, and it can be seen that the directionality of the ultrasonic waves does not change much.
[0032]
From these analysis results, it has been clarified that the performance of the electromagnetic ultrasonic probe according to the present invention is dramatically improved with the improvement of the magnetic characteristics. This performance improvement is achieved in both weight reduction and power up.
[0033]
【The invention's effect】
As described above, the present invention employs a magnet array unit that appropriately combines a main magnet that is vertically magnetized and an auxiliary magnet that is horizontally magnetized. It is possible to achieve miniaturization and high performance (improvement of flaw detection capability and measurement capability). According to the present invention, in an inspection / measurement environment that requires a stronger electromagnetic ultrasonic probe or an inspection / measurement environment that requires a smaller electromagnetic ultrasonic probe, a nondestructive inspection using electromagnetic ultrasonic waves can be performed. The defect detectability is improved, the measurement accuracy of the non-destructive evaluation is improved, and the reliability of the non-destructive inspection and evaluation using electromagnetic ultrasonic waves is improved as a whole.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an example of a magnet structure used in the present invention.
FIG. 2 is an explanatory view showing another example of the magnet structure used in the present invention.
FIG. 3 is an explanatory view showing an example of a combination of a magnet structure and a coil.
FIG. 4 is an explanatory view showing another example of a combination of a magnet structure and a coil.
FIG. 5 is an explanatory view showing a structural example of an electromagnetic ultrasonic probe.
FIG. 6 is an explanatory view showing an example of a magnet structure used in a conventional electromagnetic ultrasonic probe.
FIG. 7 is a graph showing an example of a lift-off distance dependency of a y-direction magnetic flux density By.
FIG. 8 is a graph showing an example of the dependence of the magnetic flux density By in the y direction on the thickness of the magnet.
FIG. 9 is a graph showing an example of the magnet height dimension dependency of the y-direction magnetic flux density By.
FIG. 10 is a graph showing another example of the dependence of the magnetic flux density By in the y direction on the height of the magnet.
FIG. 11 is a graph showing ultrasonic intensity characteristics with respect to magnet dimensions.
FIG. 12 is a graph showing a relationship between a peak value of an ultrasonic intensity and a refraction angle of an ultrasonic wave with respect to a magnet size.
[Explanation of symbols]
30 Magnet array unit 32a Main magnet 32b Auxiliary magnet

Claims (4)

One or a plurality of magnet arrangement units for periodically arranging a large number of prism-shaped permanent magnets and applying a magnetic field to a material to be inspected, and a coil for generating an eddy current in the material to be inspected or detecting an eddy current of the material to be inspected. In the equipped electromagnetic ultrasonic probe,
The magnet arrangement unit has a main magnet that is magnetized in the height direction and arranged so that the magnetization directions are alternately opposite to each other, and the main magnets are magnetized in the thickness direction and the magnetization directions are alternately opposite to each other. The auxiliary magnets located between and at both ends of the main magnet have a periodic array structure in which the height direction is combined, and the N pole side surface of the main magnet that is in contact with the N pole side surface of the auxiliary magnet is magnet working. An electromagnetic ultrasonic probe having a surface. 2. The electromagnetic device according to claim 1, wherein the end auxiliary magnets located at both ends of the magnet array unit have a magnet thickness dimension b 'set to 0.25 to 1 times the magnet thickness dimension b of the other auxiliary magnets. Ultrasonic probe. 3. The electromagnetic ultrasonic probe according to claim 2, wherein the magnet height L is 0.5 to 1.5 times the magnet arrangement cycle length T = 2 (a + b) (where a is the thickness of the main magnet). Child. 4. The electromagnetic ultrasonic probe according to claim 3, wherein a magnet thickness dimension a of the main magnet is equal to a magnet thickness dimension b of the auxiliary magnet.

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