JP2006005508A - Electromagnetic ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform remote flaw detection on the surface of a metallic structure using an electromagnetic ultrasonic sensor with high sensitivity. <P>SOLUTION: An arcuate permanent magnet 1 having a centrally recessed arcuate pole surface facing the coil side of an electromagnetic ultrasonic sensor is employed, and magnetic flux generated from that arcuate permanent magnet 1 is converged to the surface of a metallic structure 3. When an AC current is supplied to a coil 2 located under the arcuate permanent magnet 1, an eddy current is generated in the metallic structure 3. A Rorentz force is generated at the intersection (becoming a sound source) of the eddy current and the magnetic flux and an ultrasonic wave generated by the Rorentz force propagates through the surface layer of the metallic structure 3. Since the magnetic flux is converged, the size of a sound souce becomes small and directivity for making the ultrasonic wave propagate in the horizontal direction parallel with the surface of the metallic structure 3 is improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique effective in increasing the sensitivity of an electromagnetic ultrasonic sensor.

  Piezoelectric vibration-type sensors can only introduce ultrasonic waves into an object to be inspected by transmitting ultrasonic waves generated in the sensor to the object to be inspected, whereas electromagnetic ultrasonic sensors are inspected by electromagnetic action. An ultrasonic wave can be directly generated in the body, and the ultrasonic wave in the body to be inspected can be received as an induced electromotive force in the coil by electromagnetic action. For this reason, the electromagnetic ultrasonic sensor has no restriction for transmission between the ultrasonic sensor and the object to be inspected, as compared with the piezoelectric vibration type sensor.

  As described above, since the electromagnetic ultrasonic sensor uses only an electromagnetic action for transmitting and receiving ultrasonic vibrations, flaw detection is performed when inspecting defects such as scratches on the object to be inspected using the piezoelectric vibration type sensor. It is unnecessary to apply a contact medium (ultrasonic transmission medium for transmitting and receiving ultrasonic waves between the sensor and the object to be inspected) and press the sensor. Therefore, the electromagnetic ultrasonic sensor can perform flaw detection with high quantitativeness, reproducibility, and operability.

  While the electromagnetic ultrasonic sensor has such advantages, the transmission / reception sensitivity of the electromagnetic ultrasonic sensor is two orders of magnitude lower than that of the piezoelectric vibration type sensor, and improvement of the transmission / reception sensitivity is a major issue. In order to improve the problem, a method of focusing an ultrasonic wave by devising a shape of a permanent magnet as a means for generating a magnetic flux and a coil for passing a current is known. The known contents are that a permanent magnet having a radius of curvature R is arranged in a fan shape so that the ultrasonic waves generated in the body to be inspected are directed from the sound source (the location where the ultrasonic waves are generated) to the focusing point at a distance R, and the spiral coil. This is an electromagnetic ultrasonic sensor having an arrangement structure in which the linear shape portion is directed to the focusing point. Thus, by contriving the shape and arrangement of the permanent magnet and the coil, it is possible to focus ultrasonic waves within the surface of the metal structure (see, for example, Patent Document 1).

JP 2000-88816 A

  The above-mentioned conventional technique can focus the ultrasonic wave generated in the metallic structure, which is the object to be inspected, by the electromagnetic ultrasonic sensor within the plane of the metallic structure. It is not possible to focus in a direction perpendicular to the surface facing the object to be inspected. Therefore, when a surface defect of a metal structure far away from the electromagnetic ultrasonic sensor is detected at a long distance, there is a problem that diffusion of ultrasonic waves in the thickness direction becomes large.

印はそれぞれ紙面に対して手前側と奥側に向かって流れるコイル２ａ内の電流の向きを表している。コイル２ａに接続した電源から図２（ａ）に示したような向きに交流電流をコイル２ａ内に流すと、送信用のコイル２ａに近接する被検査体である金属製構造物３内にコイル電流と逆向きの渦電流Ｉが生じる。送信用のコイル２ａの上には磁束の発生手段として永久磁石４ａが置かれており、金属製構造物３内には矢印の向きに磁束密度Ｂの磁場が形成される。 Here, the dimension of the electromagnetic ultrasonic sensor and the diffusion of the ultrasonic wave in the thickness direction will be described with reference to FIGS. Prior to that, the principle of ultrasonic transmission / reception of the electromagnetic ultrasonic sensor will be described as follows. That is, as shown in FIG. 2, it is displayed in the cross section of the transmission coil 2a, which is a constituent element of the transmission electromagnetic ultrasonic sensor 5a.

Each mark represents the direction of current in the coil 2a flowing toward the near side and the far side with respect to the paper surface. When an alternating current is passed through the coil 2a from the power source connected to the coil 2a in the direction shown in FIG. 2 (a), the coil is placed in the metal structure 3 which is an object to be inspected close to the transmission coil 2a. An eddy current I opposite to the current is generated. A permanent magnet 4a is placed on the transmission coil 2a as means for generating magnetic flux, and a magnetic field having a magnetic flux density B is formed in the metal structure 3 in the direction of the arrow.

  By this magnetic field and eddy current, a Lorentz force F (= I × B) is generated in the direction of the horizontal white arrow in the metal structure 3. The Lorentz force F causes mechanical distortion in the metal structure 3, and the distortion vibration propagates as ultrasonic waves. The reception of ultrasonic propagation vibrations uses an electromagnetic action as in the case of transmission. The reception principle is shown in FIG. When the ultrasonic vibration propagating through the metal structure 3 in FIG. 2B reaches below the electromagnetic ultrasonic sensor 5b on the receiving side, it is perpendicular to both the ultrasonic vibration direction and the magnetic field direction of the permanent magnet 4b. An eddy current is generated in the direction. When the magnetic flux generated by the eddy current interlinks with the receiving coil 2b, an induced electromotive force is generated in the receiving coil 2b, and the induced electromotive force is observed as an electric signal by a measuring device connected to the receiving coil 2b. Is done.

印はそれぞれ紙面に対して手前側と奥側に向かって生じるローレンツ力の向きを表している。このローレンツ力の発生する範囲を音源と呼ぶ。図２内に示した一般的な電磁超音波センサ５ａにおいて、渦電流Ｉは金属製構造物３の表面のコイル２ａの直下に流れる。すなわち、渦電流はコイル内の電流の向きとは逆であるが、渦電流の生じる範囲はコイル
２ａの寸法（コイル２ａと永久磁石４ａの下端磁極面との重なり合う範囲）と等しい。金属製構造物３の表面を透過する永久磁石の磁束の範囲も永久磁石の寸法とほぼ等しくなる。これは、永久磁石４ａが金属製構造物３の表面に近づけて配置されるためである。図４に永久磁石４の磁束分布の概念図を示す。点線で描かれたものが永久磁石４の磁束を表している。永久磁石４の磁束はＮ極からＳ極に向かってループを形成し、Ｎ極とＳ極の表面では磁極表面に垂直となる。これらのことから、永久磁石４の下全体にコイル２が敷詰められている場合、音源は永久磁石４の寸法に等しくなる。 Thus, based on the principle of ultrasonic transmission / reception of the electromagnetic ultrasonic sensor, ultrasonic vibration generated by the electromagnetic ultrasonic sensor is generated in a region where magnetic fields having an eddy current I by a coil and a magnetic flux density B by a permanent magnet overlap. An example is shown in FIG. In FIG.

Each mark represents the direction of Lorentz force generated toward the near side and the far side with respect to the paper surface. A range where the Lorentz force is generated is called a sound source. In the general electromagnetic ultrasonic sensor 5 a shown in FIG. 2, the eddy current I flows directly under the coil 2 a on the surface of the metal structure 3. That is, the eddy current is opposite to the direction of the current in the coil, but the range in which the eddy current is generated is equal to the dimension of the coil 2a (the overlapping range of the coil 2a and the bottom pole surface of the permanent magnet 4a). The range of the magnetic flux of the permanent magnet that passes through the surface of the metal structure 3 is also substantially equal to the size of the permanent magnet. This is because the permanent magnet 4 a is arranged close to the surface of the metal structure 3. FIG. 4 shows a conceptual diagram of the magnetic flux distribution of the permanent magnet 4. What is drawn with a dotted line represents the magnetic flux of the permanent magnet 4. The magnetic flux of the permanent magnet 4 forms a loop from the north pole to the south pole, and the surfaces of the north and south poles are perpendicular to the magnetic pole surface. From these facts, when the coil 2 is laid all over the permanent magnet 4, the sound source is equal to the size of the permanent magnet 4.

A general electromagnetic ultrasonic sensor has permanent magnets 4a and 4b arranged on coils 2a and 2b as shown in FIG. When the ultrasonic wave (surface SH wave) propagating in the horizontal direction is transmitted to the surface of the metal structure 3 by the electromagnetic ultrasonic sensor of FIG. 2, the length L of the permanent magnets 4a and 4b is 2 of the ultrasonic wavelength. It is known that a fraction of a length is good. For example, if the metal structure 3 is SUS 304 material and the ultrasonic frequency is 300 kHz, the permanent magnet 4a,
The length L of 4b is about 5.2 mm.

The length L of the permanent magnets 4a and 4b affects the directivity characteristics of ultrasonic waves. The directivity characteristic perpendicular to the magnetic pole surface of ultrasonic waves generally becomes sharper as the sound source is larger. That is, the amplitude of ultrasonic waves propagating in the thickness direction of the metal structure (direction perpendicular to the magnetic pole surface) increases. In the case of an electromagnetic ultrasonic sensor, the size of the sound source depends on the length L of the permanent magnets 4a and 4b as described above. In the above example, since the length L (= 5.2 mm) of the permanent magnet is large, the transmission wave of the electromagnetic ultrasonic sensor is likely to spread in the thickness direction of the metal structure 3. An example is shown in FIG. The dotted line represents the wavefront of the transmitted wave. When the transmission wave spreads in the thickness direction of the metal structure 3 as shown in FIG. 5, the reflected wave from the surface defect becomes small. Thus, the conventional electromagnetic ultrasonic sensor is not suitable for long-distance flaw detection because of the large diffusion of ultrasonic waves in the thickness direction of the metal structure. Therefore, there is a need for an electromagnetic ultrasonic sensor having a structure that can increase the amplitude of ultrasonic waves that propagate in a horizontal direction on the surface of a metal structure.

  The directivity of the reception sensitivity of the electromagnetic ultrasonic sensor for reception varies depending on the length L of the permanent magnet. The directivity is the same as that in the case of transmission. As the length L of the permanent magnet is larger, the reception sensitivity in the thickness direction of the metal structure is improved. That is, the conventional electromagnetic ultrasonic sensor is not suitable for detecting a surface defect of a metal structure over a long distance.

  Accordingly, an object of the present invention is to provide an electromagnetic ultrasonic sensor suitable for long-distance flaw detection of a surface defect of an inspection object.

  In a specific means for achieving the object of the present invention, the object is an electromagnetic ultrasonic sensor in which permanent magnets are arranged on a coil, wherein the bottom surface shape is constituted by an arcuate permanent magnet and a coil. Is achieved. The object is achieved by an electromagnetic ultrasonic sensor in which permanent magnets are arranged on a coil, comprising a permanent magnet, a pole piece having an arched bottom shape, and a coil. The object is achieved by an electromagnetic ultrasonic sensor in which permanent magnets are arranged on a coil, comprising a magnetic pole piece having a bottom surface area smaller than the magnetic pole surface area of the permanent magnet, a permanent magnet, and the coil.

  According to the present invention, an electromagnetic ultrasonic sensor having a structure capable of increasing the ultrasonic amplitude propagating in the horizontal direction on the surface of the object to be inspected can be provided. It is possible to perform long-range flaw detection of surface defects of the object to be inspected without adopting complicated magnet and coil arrangements.

Example 1
The configuration of the electromagnetic ultrasonic sensor 6 according to the first embodiment includes the following contents. That is, as shown in FIG. 1 (a), a plurality of arch-type permanent magnets 1 are provided with magnetic flux generating means such that different polarities are adjacent to each other in a metal case 20 represented by an aluminum case. As shown in FIG. The plurality of permanent magnets 1 are fixed in the case 20 by a resin 25 filled in the case 20. A coil 2 made of enameled wire, for example, is arranged directly below the arch-type permanent magnet 1. The coil 2 is wrapped and protected by a very thin protective film 21. The protective film 21 is fixed to the case 20 with a set screw 22. An extension of the enamel wire forming the coil 2 is connected to the connector 24 as a lead wire 23 of the coil 2. The connector 24 is installed in the case 20 and is used as an electrical connection means to an electromagnetic ultrasonic measurement device outside the case 20.

  In such an electromagnetic ultrasonic sensor 6 for transmission, as shown in FIGS. 1A and 1B, the shape of the bottom surface (magnetic curved surface close to the coil 2) of each arch-type permanent magnet 1 is the center. It is an arched shape with a curved surface. Each arch-type permanent magnet 1 is in close contact with each other by its magnetic force. The arch-type permanent magnets 1 arranged in two columns and four rows, that is, the array is set as one set, and a multi-turn coil 2 is arranged on the bottom side of the array as a common coil for each arch-type permanent magnet. .

  The electromagnetic ultrasonic sensor 14 for reception has the same configuration as the electromagnetic ultrasonic sensor 6 for transmission.

FIG. 6 is a configuration diagram of an electromagnetic ultrasonic measurement device electrically connected to each of the transmission / reception electromagnetic ultrasonic sensors 6 and 14. In FIG. 6, 6 is a transmission electromagnetic ultrasonic sensor. Reference numeral 7 denotes a transmission matching circuit, which can match a transmission circuit by combining commercially available impedance elements. 8 is a power amplifier, 9 is a pulser receiver, 10 is a computer, 11 is a monitor,
Reference numeral 12 denotes a reception signal amplifier, and all commercially available products can be used. Reference numeral 13 denotes a receiving matching circuit, which can be matched with a commercially available impedance element.
Reference numeral 14 denotes a receiving electromagnetic ultrasonic sensor. The transmission electromagnetic ultrasonic sensor 6 is connected to a pulsar receiver 9 via a transmission matching circuit 7 and a power amplifier 8. The reception electromagnetic ultrasonic sensor 14 is connected to the pulsar receiver 9 via the reception matching circuit 13 and the reception signal amplifier 12. The signal from the reception electromagnetic ultrasonic sensor 14 and the control signal from the pulser receiver 9 can be observed by the monitor 11 via the computer 10.

  Next, the operation of the electromagnetic ultrasonic measurement apparatus using the electromagnetic ultrasonic sensor 6 for transmission and the electromagnetic ultrasonic sensor 14 for reception according to the present invention will be described with reference to FIG. The pulsar receiver 9 generates an internal clock. The internal clock generates an alternating voltage in the pulser receiver 9. The AC voltage is amplified by the power amplifier 8. The AC voltage is applied to the transmission electromagnetic ultrasonic sensor 6 via the transmission matching circuit 7, and an AC current is generated in the coil 2 in the transmission electromagnetic ultrasonic sensor 6. As a result, ultrasonic vibration is excited in the vicinity of the inner surface layer of the metal structure as the object to be inspected.

  The ultrasonic vibration reaches under the electromagnetic ultrasonic sensor 14 for reception by reflection and scattering at the defect. When the ultrasonic vibration reaches the reception electromagnetic ultrasonic sensor 14, the ultrasonic vibration is converted into an AC voltage by the electromagnetic ultrasonic sensor 14. The AC voltage is sent to the reception signal amplifier 12 via the reception matching circuit 13. The reception signal amplifier 12 amplifies the AC voltage and transmits it to the pulser receiver 9. The pulsar receiver 9 digitally processes the AC voltage and sends it to the computer 10. The digitally processed AC voltage information is displayed on the monitor 11 as an image, and the received ultrasonic wave information is displayed.

  Next, directivity characteristics of the electromagnetic ultrasonic sensor 6 for transmission and the electromagnetic ultrasonic sensor 14 for reception will be described with reference to FIGS. Ultrasonic vibration generated by the electromagnetic ultrasonic sensor is generated in a region where magnetic fields having an eddy current I generated by the coil 2 and a magnetic flux density B generated by the permanent magnet 1 overlap. In the case of the electromagnetic ultrasonic sensor 6 for transmission, since the arch type permanent magnet 1 is used, the range of the magnetic flux which permeate | transmits the surface of the metal structure 3 changes according to the bottom face shape.

印を囲っている矩形の図形部分）は図８に示したようにアーチ型永久磁石の長さＬよりも短くなる。音源のサイズと超音波の指向特性の関係は、弾性波素子技術ハンドブック（日本学術振興会弾性波素子技術第１５０委員会編）Ｐ１３１より式１で表される。 An example of the magnetic flux distribution when the magnetic flux of the arch-type permanent magnet 1 is focused on the surface of the metal structure 3 is shown in FIG. The dotted line represents the magnetic flux. The magnetic flux of the arch-type permanent magnet 1 is perpendicular to the magnetic pole surfaces of the N pole and S pole, which are curved surfaces, and is focused on the surface of the metal structure 3. Therefore, the sound source (in FIG.

The rectangular graphic portion surrounding the mark is shorter than the length L of the arch-type permanent magnet as shown in FIG. The relationship between the size of the sound source and the directivity characteristics of the ultrasonic wave is expressed by Formula 1 from the elastic wave element technology handbook (edited by the 150th Committee of Elastic Wave Element Technology, JSPS) P131.

ここで、Ａ₀ は中心軸上の音圧（Ａ(０)）、θは中心軸からの角度、Ｌは音源のサイズ、λは超音波の波長である。

Here, A ₀ is the sound pressure (A (0)) on the central axis, θ is the angle from the central axis, L is the size of the sound source, and λ is the wavelength of the ultrasonic wave.

  That is, as the size L of the sound source in Equation 1 is smaller than the wavelength of the ultrasonic wave, the ultrasonic component propagating in the direction horizontal to the surface of the metal structure is relatively increased. For this reason, the wavefront of the transmission ultrasonic wave of the electromagnetic ultrasonic sensor 6 for transmission is as shown in FIG. The dotted line in FIG. 9 represents the wavefront of the transmission wave. Compared with the wavefront shown in FIG. 5, the wavefront of FIG. 9 has less ultrasonic components in the direction perpendicular to the surface of the metal structure 3. That is, as shown in FIG. 9, the transmission ultrasonic wave is difficult to spread in the thickness direction (vertical direction in FIG. 9) of the metal structure 3, so that the reflected wave of the ultrasonic wave from the surface defect is larger than that in FIG. 5. Become. The reception sensitivity of the electromagnetic ultrasonic sensor 14 for reception is also improved with respect to the component in the direction horizontal to the surface of the metal structure 3 for the above reason.

  Next, the effect of the electromagnetic ultrasonic measuring apparatus using the electromagnetic ultrasonic sensor 6 for transmission and the electromagnetic ultrasonic sensor 14 for reception will be described with reference to FIG. FIG. 10 (a) is a received waveform displayed on the monitor when the electromagnetic ultrasonic sensors 5a and 5b shown in FIG. 2 are used, and FIG. 10 (b) is shown in FIGS. 1 (a) and 1 (b). 6 is a received waveform when the electromagnetic ultrasonic sensors 6 and 14 employing the arch-type permanent magnet 1 are used. In the measurement, electromagnetic ultrasonic sensors for transmission and reception were arranged side by side on the metal structure 3. A transmission wave transmitted by the electromagnetic ultrasonic sensor for transmission propagated through the metal structure 3, and the intensity of the wave reflected by the surface defect was measured by the electromagnetic ultrasonic sensor for reception. FIGS. 10A and 10B show the received waveform of the reflected wave of the ultrasonic wave from the surface defect. As understood from the above description, the surface defect detection sensitivity is improved in the measurement (FIG. 9) by the electromagnetic ultrasonic measurement device using the electromagnetic ultrasonic sensor 6 for transmission and the electromagnetic ultrasonic sensor 14 for reception. However, the received signal intensity increases as compared with that in FIG. 10A, as in the ultrasonic intensity of the reflected wave shown in FIG. Thereby, the surface defect of the metal structure 3 can be detected with high sensitivity from a long distance.

  In the description so far, the metal structure 3 is an example to which the embodiment of the present invention can be applied. However, the present invention is applicable to all conductive objects.

(Example 2)
In the embodiment of Example 1, the electromagnetic wave using the electromagnetic ultrasonic sensor 6 for transmission and the electromagnetic ultrasonic sensor 14 for reception provided with the arch-type permanent magnet 1 whose magnetic pole surface facing the coil is an arch type. Although the ultrasonic measuring apparatus has been described, instead of molding the magnetic pole end face of the permanent magnet itself into an arch shape, as shown in FIG. 11, an arch type magnetic pole piece 15 having one end face that is flat and the other end face having an arch-shaped curved surface. May be prepared so that one end face of the arched pole piece 15 is magnetically attracted to the pole face near the coil 2 of the permanent magnet 4 having a flat pole face. The coil 2 is disposed under the permanent magnet 4 and the arched pole piece 15. The material of the arched pole piece 15 is made of a material having a higher magnetic permeability than that of the atmosphere around the arched pole piece 15. Other configurations and operations are the same as those in the first embodiment.

  As shown in FIG. 11, the permanent magnet 4 and the arched pole piece 15 are in close contact with each other by magnetic force. Therefore, the magnetic flux generated by the permanent magnet 4 passes through the arched pole piece 15 and is deflected so as to be focused on the surface layer portion of the object to be inspected when radiated from the arched curved surface of the arched pole piece 15. Thus, the same effects as those of the first embodiment are exhibited.

Example 3
Further, instead of the arched pole piece 15 of the second embodiment, the magnetic pole whose one end face is the same as the area of the magnetic pole face near the coil 2 of the permanent magnet 4 and whose other end face is smaller than the area of the magnetic pole face. A piece 16 is prepared, and one end surface of the magnetic pole piece 16 is provided to be magnetically attracted by facing the magnetic pole surface near the coil 2 of the permanent magnet 4 without excess or deficiency as shown in FIG. The coil 2 is disposed below the pole piece 16. The magnetic pole piece 16 is made of a material whose permeability is higher than that of the atmosphere around the magnetic pole piece. Other configurations are the same as those of the first embodiment.

  Also in such an embodiment, the magnetic flux generated from the permanent magnet 4 is focused in the magnetic pole piece 16 when passing through the magnetic pole piece 16, and the focused magnetic flux is coiled from the other end surface of the magnetic pole piece 16 having a small area. Since it is radiated to the surface and reaches the surface layer portion of the object to be inspected, the same effects as those of the first embodiment can be obtained.

  The present invention has application in a nondestructive inspection apparatus using an electromagnetic ultrasonic sensor as a sensor.

It is explanatory drawing of the electromagnetic ultrasonic sensor by Example 1 of this invention, (a) A figure is the longitudinal cross-sectional view of the sensor, (b) A figure is a perspective view which shows arrangement | positioning of the coil and permanent magnet of the sensor. . It is explanatory drawing showing the transmission-and-reception principle of the ultrasonic wave by an electromagnetic ultrasonic sensor, (a) A figure is a transmission principle, (b) A conceptual diagram showing a reception principle. It is a schematic diagram showing the Lorentz force generation | occurrence | production area | region in the metal structures by an electromagnetic ultrasonic sensor. It is a schematic diagram showing an example of the magnetic flux distribution by the permanent magnet of an electromagnetic ultrasonic sensor. It is a figure showing an example of the directivity of ultrasonic propagation using the electromagnetic ultrasonic sensor of FIG. It is a block diagram showing the structure of the electromagnetic ultrasonic measurement apparatus by Example 1 of this invention. It is a schematic diagram showing an example of magnetic flux distribution of the arch type permanent magnet employ | adopted for the electromagnetic ultrasonic sensor by Example 1 of this invention. It is a schematic diagram showing the Lorentz force generation | occurrence | production area | region in the metal structure of the electromagnetic ultrasonic sensor by Example 1 of this invention. It is a figure showing an example of the directivity of the ultrasonic propagation by the electromagnetic ultrasonic sensor by Example 1 of this invention. FIG. 5 is a view showing an example of a received waveform at the time of ultrasonic flaw detection with respect to a surface defect by an electromagnetic ultrasonic sensor, where (a) shows the case where the electromagnetic ultrasonic sensor shown in FIG. 2 is used, and (b) shows the present invention. The example at the time of using the electromagnetic ultrasonic sensor by Example 1 is represented. It is the arrangement figure showing arrangement relation of an arch type magnetic pole piece of an electromagnetic ultrasonic sensor by Example 2 of the present invention, a permanent magnet, and a coil. It is the arrangement figure showing arrangement relation of an arch type magnetic pole piece of an electromagnetic ultrasonic sensor by Example 3 of the present invention, a permanent magnet, and a coil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Arch type permanent magnet, 2, 2a, 2b ... Coil, 3 ... Metal structure, 4, 4a, 4b ... Permanent magnet, 5a, 5b, 6, 14 ... Electromagnetic ultrasonic sensor, 7 ... Matching circuit for transmission , 8 ... power amplifier, 9 ... pulser receiver, 10 ... computer, 11 ... monitor, 12 ... reception signal amplifier, 13 ... matching circuit for reception, 15 ... arch type pole piece, 16 ... pole piece.

Claims (4)

In an electromagnetic ultrasonic sensor comprising a magnetic flux generating means and a coil that is arranged to cross the magnetic flux and is energized,
An electromagnetic ultrasonic sensor characterized in that the magnetic flux generating means includes means for converging the magnetic flux.   2. The magnetic flux generating means according to claim 1, wherein said magnetic flux generating means is a permanent magnet, and said magnetic flux converging means is formed by molding a surface of said permanent magnet facing said coil into an arch shape recessed at a central portion of said permanent magnet. An electromagnetic ultrasonic sensor.   2. The magnetic flux generating means according to claim 1, wherein said magnetic flux generating means is a permanent magnet, and said magnetic flux converging means is an arch-shaped magnetic pole piece attached to a magnetic pole surface of said permanent magnet on said coil side and having a recessed central portion. An electromagnetic ultrasonic sensor. 2. The magnetic flux generating means according to claim 1, wherein the magnetic flux generating means is a permanent magnet, and the magnetic flux converging means is mounted on the coil side magnetic pole surface of the permanent magnet, and the coil side surface is narrower than the magnetic pole surface. An electromagnetic ultrasonic sensor characterized by being a formed magnetic pole piece.

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