JP4565093B2 - Movable FBG ultrasonic sensor - Google Patents

Description

  The present invention relates to the technical field of strain measurement using an optical fiber sensor and an ultrasonic / AE detection device, and in particular, when detecting an ultrasonic wave using an ultrasonic measurement device using an FBG as a sensor, The present invention relates to a movable FBG ultrasonic sensor for detecting an ultrasonic wave with high sensitivity by moving the surface of a subject.

  In recent years, it is expected to construct a soundness evaluation apparatus for the purpose of improving the reliability of a structure. When evaluating the soundness of a structure, it is very important to detect defects such as cracks and cracks. In the past, strain was often measured using a resistance strain gauge that utilizes the change in electrical resistance associated with metal deformation. As a technique for detecting defects such as cracks, detection of elastic wave emission (AE) accompanying the occurrence of defects and nondestructive inspection using ultrasonic waves are performed.

  For example, strain evaluation in structures such as bridges, transportation equipment, buildings, detection of elastic wave emission (AE) accompanying the occurrence of destruction of the structure, non-destructive inspection using ultrasonic waves on the structure, strain, super The present invention can be applied to a soundness evaluation monitoring apparatus for a structure that combines sound waves and AE measurement.

  In non-destructive inspection of structures using ultrasonic waves, the existence of cracks affects the propagation characteristics of ultrasonic waves. This is to check for the presence or absence. At that time, the higher the ultrasonic wave detection sensitivity, the higher the defect detection capability. For this reason, development of a sensor with high ultrasonic detection sensitivity is desired.

  So far, piezoelectric element sensors have been used as AE detection sensors and ultrasonic detection sensors in nondestructive inspection using ultrasonic waves. However, in the case of a piezoelectric element sensor, there are problems in practical use such as being affected by electromagnetic interference because it is an electric sensor, and requiring one cable for each sensor, resulting in complicated wiring. .

  In recent years, attention has been focused on ultrasonic detection using an FBG sensor which is a kind of optical fiber sensor that can improve these drawbacks of piezoelectric elements. FBG (fiber Bragg grating) is expected to be used as a strain and ultrasonic / AE detection sensor in structural soundness evaluation. The FBG ultrasonic sensor has features such as being free from electromagnetic interference and being capable of being attached to a plurality of sensors on a single optical fiber, and has many advantages in practical use.

  Ultrasonic / AE detection methods using an FBG ultrasonic sensor can be broadly classified into two types depending on the type of light source used. One is a type using a broadband light source, and the other is a type using a laser light source, that is, a single wavelength light source. In the Japanese Patent Application No. 2003-172321, an apparatus for detecting strain and ultrasonic waves / AE using a broadband light source is proposed in Japanese Patent Application No. 2003-172321, and in the Japanese Patent Application No. 2004-145880, an ultrasonic wave / AE detection apparatus using a laser light source is proposed. is suggesting.

  Several papers have been reported so far regarding ultrasonic measurement using a laser light source (see Non-Patent Document 1). In these studies, the oscillation wavelength of the tunable laser is set to a wavelength at which the reflectance of the FBG serving as the sensor is halved, and the reflected light intensity from the FBG ultrasonic sensor changes with the Bragg wavelength of the sensor. Experiments that detect ultrasound have been reported.

An experimental example in which ultrasonic waves have been measured using an FBG ultrasonic sensor has been reported so far (see, for example, Non-Patent Document 1), and further, the damage state of a material can be evaluated from ultrasonic measurement using an FBG ultrasonic sensor. It has been reported that this can be done (Non-Patent Document 2).
DC Betz et al., Smart Materials and Structures, 12 (2003) 122-128 H. Tsuda et al., Smart Materials and Structures, 13 (2004) 719-724

  In the soundness evaluation of a structure using ultrasonic waves, a damaged part may exist adjacent to the healthy part of the structure, and the FBG ultrasonic sensor is spot-fixed on the surface of the structure that is the subject. Even if measured, the damaged part may be overlooked. Therefore, in order to improve the accuracy of soundness evaluation, it is desirable that the FBG ultrasonic sensor be movable with respect to the surface of the subject.

  However, in order to make the FBG ultrasonic sensor movable, the grading attachment structure of the FBG ultrasonic sensor including the attachment for attaching the grading of the FBG ultrasonic sensor and moving the surface of the subject is important.

  The FBG ultrasonic sensor grading is attached to a fixture, and this fixture moves along the surface of the subject. However, depending on the material of this fixture, the soundness is evaluated without propagation of ultrasonic waves to the grading. Is impossible or the accuracy of soundness evaluation is extremely reduced. Furthermore, if the adhesive is applied to the grading to attach the grading of the FBG ultrasonic sensor to the fixture, there is a problem that the measurement accuracy of ultrasonic detection is lowered.

  The present invention solves such a problem, and realizes a movable FBG ultrasonic sensor that has high ultrasonic detection sensitivity and can perform soundness evaluation with high accuracy. In particular, pay attention to the influence on the ultrasonic detection sensitivity by attaching the grading of the FBG ultrasonic sensor to the fixture, and pay attention to the influence on the ultrasonic detection sensitivity by the material of the fixture, and grade the FBG ultrasonic sensor. The problem is to improve the ultrasonic detection sensitivity and improve the accuracy of soundness evaluation by devising the structure to be attached to the fixture (specifically, the adhesive structure) and the selection of the fixture material. is there.

  In order to solve the above-described problems, the present invention is configured such that the grating of the FBG ultrasonic sensor formed on the optical fiber is bonded to a fixture made of a material having a lower sound velocity than the subject, and the fixture is attached to the subject. Provided is a movable FBG ultrasonic sensor that is capable of ultrasonic detection by being moved on a surface.

  In order to solve the above-mentioned problems, the present invention is such that only the portions separated from both ends of the grating of the FBG ultrasonic sensor formed on the optical fiber are bonded to a fixture made of a material having a lower sound velocity than the subject. The movable FBG ultrasonic sensor is characterized in that ultrasonic detection can be performed by moving the fixture on the surface of the subject.

  In order to solve the above-described problems, the present invention provides a movable FBG ultrasonic sensor in which a grating of an FBG ultrasonic sensor formed on an optical fiber is covered with a hollow container, and the hollow container is more than a subject. It is made of a material having a low sound velocity, and both ends of the hollow container are shielded by both ends of the hollow container at positions away from both ends of the grating, and the hollow container moves on the surface of the subject. A movable FBG ultrasonic sensor is provided that enables ultrasonic detection.

  The grading is adhered along the flat surface of the fixture, and is used in contact with the subject so that the grading direction is the same as the ultrasonic displacement direction of the subject. It is characterized by being.

  The flat surface of the fixture is parallel to, perpendicular to, or inclined at a predetermined angle with respect to a surface where the fixture contacts the subject.

  The movable FBG ultrasonic sensor according to the present invention attaches the grating of the FBG ultrasonic sensor to the fixture, and the fixture is made of a material having a lower sound velocity than the subject, so that the fixture is not fixed to the subject. Ultrasonic detection of the FBG ultrasonic sensor can be performed, and the soundness evaluation of each part of the subject can be easily performed.

  In the movable FBG ultrasonic sensor according to the present invention, in particular, if the structure of attaching the grating of the FBG ultrasonic sensor to the fixture is configured to adhere only the portions away from both ends from both sides, the subject Even if it is not fixed, the ultrasonic detection sensitivity of the FBG ultrasonic sensor can be improved, and the accuracy of soundness evaluation can be further enhanced.

  The best mode for carrying out the movable FBG ultrasonic sensor according to the present invention will be described below with reference to the drawings and the like based on the embodiments.

  FIG. 1 is a diagram showing an overall configuration of an ultrasonic detection apparatus 1 in a state where a movable FBG ultrasonic sensor 5 according to the present invention is applied to measurement of a subject 9. The ultrasonic detection apparatus 1 includes a tunable laser light source 2, an optical circulator 4 connected to the tunable laser light source 2 through an optical fiber 3, a movable FBG ultrasonic sensor 5 connected to the optical circulator 4, and an optical circulator. 4 and a photoelectric converter 6 connected by an optical fiber 3.

  The output wavelength of the tunable laser light source 2 is set to a wavelength at which the change rate of the reflectance-wavelength relationship of the movable FBG ultrasonic sensor 5 is maximized, usually around the wavelength at which the reflectance is halved. The ultrasonic detection apparatus 1 includes a signal generator 14 for generating ultrasonic waves, and an ultrasonic oscillator 16 connected to the signal generator 14 via an electric wire 14 '.

  The ultrasonic oscillator 16 is placed on the subject 9 and the drive signal generated by the signal generator 14 is input to the ultrasonic oscillator 16 placed on the subject 9 via the electric wire 14 ′. Can be generated and transmitted to the subject.

  Although the overall configuration of the ultrasonic detection apparatus 1 is as described above, the present invention is characterized by the configuration of the movable FBG ultrasonic sensor 5 in which the grading 8 (Bragg grating) is attached to the fixture 11. .

  As a specific means for attaching the grating 8 to the fixture 11, in this embodiment, it is configured to be adhered (attached) to the fixture 11 with an adhesive. In this case, in the first embodiment, as shown in FIG. 1 and FIG. 2A, a structure in which only the portion separated from both ends of the grating 8 on both sides is adhered to the subject 9 with the adhesive 10 (this is referred to as “ Named “Bridge Adhesion”).

  As another means for attaching the grating 8 to the fixture 11, the entire grating 8 is directly bonded to the fixture 11 with an adhesive 10 as shown in FIG. 2B (this is named "complete adhesion"). It may be a structure.

  By the way, the ultrasonic wave propagating through the subject 9 needs to be transmitted to the movable FBG ultrasonic sensor 5. For this purpose, the fixture 11 to which the grating 8 is attached needs to use a material whose sound speed is lower than that of the subject 9 as a medium.

  In the first embodiment, for example, when the subject 9 is an aluminum plate, an acrylic plate 15 having a sound velocity lower than that of the aluminum plate is employed as the fixture 11, and the grating 8 is placed on the acrylic plate 15 as shown in FIG. As shown in a), the movable FBG ultrasonic sensor 5 was constructed by bonding with a bridge.

  The operation of this embodiment having the above configuration will be described with reference to FIG. FIG. 3 shows an example in which the ultrasonic oscillator 16 and the movable FBG ultrasonic sensor 5 are disposed on a subject and applied to ultrasonic damage detection.

  In use, the ultrasonic oscillator 16 is placed on the subject 9, and the drive signal generated by the pulse generator 14 is input to the ultrasonic oscillator 16 through the electric wire 14 ′ to generate ultrasonic waves, Tell the specimen.

  The laser beam from the wavelength tunable laser light source 2 is incident on the movable FBG ultrasonic sensor 5 via the optical circulator 4, and the reflected light from the movable FBG ultrasonic sensor 5 is converted into a photoelectric converter via the optical circulator 4. 6 where the light intensity is converted into a voltage signal.

  When inspecting, the ultrasonic oscillator 16 and the movable FBG ultrasonic sensor 5 are arranged on a straight line, the ultrasonic oscillator 16 is moved in the direction of the arrow, and the movable FBG ultrasonic wave corresponding to the movement. The sensor 5 moves simultaneously in the direction of the arrow so that the fixture 11 is traced against the surface of the subject 9. At this time, in order to increase the ultrasonic propagation efficiency between the ultrasonic oscillator 16 and the subject 9 and between the fixture 11 and the subject 9, a liquid such as water is added as a coupling agent. This is a well-known means as an ultrasonic detection technique). Thereby, it is possible to detect ultrasonic waves while moving the movable FBG ultrasonic sensor 5.

  In the FBG ultrasonic sensor 5 of the present embodiment, as described above, when the bridge bonding (the structure in which only the portions separated from both sides of the grating 8 on both sides are bonded to the fixture 11 with the adhesive 10) is adopted, the FBG is used. The ultrasonic detection sensitivity of the ultrasonic sensor can be improved. This point will be briefly described below.

  Conventionally, as shown in FIG. 4A, the FBG ultrasonic sensor 17 has been directly attached to the subject 9 for measurement. At that time, a structure in which the entire grating 8 is directly adhered to the subject 9 with the adhesive 10 (complete adhesion) was employed.

  On the other hand, as shown in FIG. 4B, the present inventor has an FBG having a structure in which only a portion separated from both ends of the grating 8 on both sides is bonded to the subject 9 with the adhesive 10 (bridge bonding). The ultrasonic sensor 18 has been invented and has been filed. The point that ultrasonic detection sensitivity is improved by such bridge bonding has already been described in detail in the above-mentioned other application with experimental data, so the explanation is omitted here, but its theoretical basis. Is considered as follows.

  That is, according to complete adhesion, the grating 8 has a large birefringence due to the influence of the residual stress, and the reflection wavelength range of the FBG ultrasonic sensor 17 is widened. As a result, the gradient of the reflectance-wavelength relationship is lowered. Sensitivity to ultrasound is reduced. On the other hand, in the case of bridge bonding, since the grating 8 is not bonded, there is no influence of birefringence. Therefore, it is considered that the gradient of the reflectance-wavelength relationship is not affected by birefringence and sensitivity to ultrasonic waves does not decrease.

  That is, the bridge bonding is an attachment structure that does not cause the influence of birefringence on the grating 8, and it is considered that the ultrasonic detection sensitivity can be increased by eliminating the birefringence generated in the grating 8 by the bonding. The movable FBG ultrasonic sensor 5 of the present invention can improve the ultrasonic detection sensitivity of the FBG ultrasonic sensor 18 by adopting such bridge bonding.

(Experimental example 1)
In order to confirm the effect of the first embodiment, an ultrasonic detection experiment was performed using the movable FBG ultrasonic sensor 5 of the first embodiment and an experimental system as shown in FIG. In this experimental example 1, the fixture 11 is an acrylic plate, and bridge bonding is performed on the acrylic plate with an adhesive 10 so that the grating 8 is sandwiched between them. 12 mm.

  In this experiment, the subject 9 is an aluminum plate, and an ultrasonic wave is applied to the subject 9 with an ultrasonic oscillator 16 similar to that shown in FIG. Then, the movable FBG ultrasonic sensor 5 was placed at a position away from the ultrasonic oscillator 16 in a straight line in the horizontal direction in FIG.

  For comparison, an ultrasonic response signal detection experiment was performed with a piezoelectric element that has been frequently used for ultrasonic detection.

  The result of this experiment is as shown in FIG. In FIG. 5, the transmission signal to the piezoelectric ultrasonic oscillator which generated the ultrasonic wave and the response signals of the movable FBG ultrasonic sensor and the piezoelectric sensor are shown. As a result of this experiment, it was confirmed that the response of the movable FBG ultrasonic sensor has a very high S / N ratio even through the acrylic plate moving tool as in Example 1.

(Experimental example 2)
An experimental example 2 performed to verify the effectiveness of the movable FBG ultrasonic sensor will be described. In Experimental Example 2, the effectiveness of damage detection using ultrasonic waves of the movable FBG ultrasonic sensor 5 of Example 1 was examined using an orthogonal laminated fiber reinforced composite material having impact damage as an object. FIG. 6 is a diagram for explaining the outline of the experiment.

  In Experimental Example 2, the orthogonal laminated fiber reinforced composite material plate 19 as the subject 9 has an impact damaged portion 20 centering on a location 60 mm away from the end of the test piece in the Y-axis direction. In the impact damaged portion 20, fiber axis direction cracking and delamination are observed, and damage of about 12 mm is spread in the Y axis direction. The reinforcing fibers of the test piece are arranged in the X and Y axis directions in the drawing.

  An ultrasonic wave is applied to the subject 9 with an ultrasonic oscillator 16 similar to the means shown in FIG. Then, the ultrasonic oscillator 16 and the movable FBG ultrasonic sensor 5 are placed on a straight line, and the movable FBG ultrasonic sensor 5 is moved in parallel with the ultrasonic oscillator 16 in the Y-axis direction. The ultrasonic response waveform detected by the type FBG ultrasonic sensor was recorded.

  FIG. 7 shows the relationship between the arrival time of the ultrasonic wave detected by the movable FBG ultrasonic sensor 5, that is, the response waveform start time and the Y-axis position. As shown in FIG. 7, the response start time is earlier than that of the healthy part at the place where the impact damaged part 20 exists. From theoretical considerations, it is conceivable that the ultrasonic wave passing through the impact damaged part 20 has a faster arrival time than the ultrasonic wave passing through the healthy part.

  The reason is as follows. The ultrasonic wave propagation speed in a material is expressed as a function of the stiffness (Young's modulus) and density of the material. When the density is constant, the ultrasonic wave propagation speed increases with Young's modulus. In the case of the subject, since the density does not depend on the position, the ultrasonic wave propagation speed is given as a function of Young's modulus. In the impact damaged portion 20, delamination occurs, and the reinforcing fiber layers in the X-axis direction and the Y-axis direction are separated.

  In the ultrasonic propagation direction, in this case, the Young's modulus in the X-axis direction is highest in the reinforcing fiber layer in the X-axis direction in the impact damaged portion 20, followed by the reinforcing fiber layer in the Y-axis direction in the healthy portion and the damaged impact scratched portion 20. Order. For this reason, the ultrasonic wave that has propagated through the reinforcing fiber layer in the X-axis direction in the region (damaged region) of the damaged impact scratch 20 becomes the highest speed. Therefore, it is considered that the response start time is earlier when the ultrasonic wave passes through the damaged part than through the healthy part.

  Since the position resolution of ultrasonic detection of the movable FBG ultrasonic sensor is the diameter (about 130 μm) of the grating portion of the sensor, it is higher than the piezoelectric element that has been widely used in the past (usually 6 mm or more in a commercial product). Since such a movable sensor enables measurement at an arbitrary place where an ultrasonic wave is to be measured, it is very convenient compared to a stationary sensor and has been widely used for ultrasonic detection in the past. It is expected to be used as an alternative sensor for piezoelectric elements.

  FIG. 8 is a diagram for explaining a second embodiment of the present invention. The movable FBG ultrasonic sensor 13 according to the second embodiment covers the grating 8 using a hollow container 21 as a fixture 11, and both ends of the hollow container 21 are shielded from the both ends of the grating 8 at both sides. This is a shielded structure.

  The hollow container 21 which is the fixture 11 of the second embodiment needs to use a material having a sound velocity lower than that of the subject 9 as a medium so as to transmit ultrasonic waves to the grating 8 as in the first embodiment. For example, when the subject 9 is an aluminum plate, a container made of an acrylic material whose sound speed is lower than that of the aluminum plate is employed.

  Since the movable FBG ultrasonic sensor 13 supports the optical fiber 7 on which the grating 8 is formed at a position away from both ends of the grating 8 and no adhesive is applied to the grating 8, as described above, the sensitivity of the ultrasonic wave is increased. There is no reduction.

  In use, as in the first embodiment, the ultrasonic wave is moved along with the ultrasonic oscillator so that the hollow container 21 of the movable FBG ultrasonic sensor 13 is traced along the surface of the subject 9. Can be measured to detect the damaged part of the subject.

  The movable FBG ultrasonic sensor 13 according to the second embodiment is configured such that the portion shielded by the shielding agent 12 is bridge-bonded in a state where the grating 8 is covered and protected by the hollow container 21. Therefore, if the length of the hollow container 21 is appropriately selected, the bridge interval can be easily set, and the movable FBG ultrasonic sensor 13 is protected from damage and the environment by surrounding the grating 8 with the hollow container 21. It will have.

  FIG. 9 is a diagram for explaining a third embodiment of the movable FBG ultrasonic sensor according to the present invention. The third embodiment has substantially the same structure as that of the first embodiment, but the characteristic configuration is that the ultrasonic wave is oscillated from the ultrasonic oscillator and propagated to the subject 9 and formed on the optical fiber 7. This is a point in which the direction of the graded grading 8 is made parallel.

  Here, “the direction of the grading 8” is the axial direction of the optical fiber constituting the grading 8. Since the grading 8 has a structure in which a core part that is a light guide for an optical fiber is provided with regions having different refractive indexes periodically in the fiber axis direction, the “direction of the grading 8” is, in other words, the fiber 7 It is also the major axis direction of the portion where the grading 8 is formed.

  With respect to the third embodiment, the grading 8 is bonded along the flat surface of the fixture 11 so that the direction of the grading 8 and the ultrasonic displacement direction of the subject 9 are the same. Thus, it is used in contact with the subject 9.

Then, there are the following three examples of the relationship between the surface of the fixture 11 on which the FBG is attached and the surface on which the fixture 11 contacts the subject 9.
(1) The surface to which the FBG is attached is parallel to the surface on which the fixture 11 contacts the subject 9 (see FIG. 9A).
(2) The surface to which the FBG is attached is perpendicular to the surface on which the fixture 11 contacts the subject 9 (see FIG. 9B).
(3) The surface to which the FBG is attached is inclined at a predetermined angle with respect to the surface on which the fixture 11 contacts the subject 9 (see FIG. 9C).

  The operational effects of having such a configuration in the third embodiment will be described. The ultrasonic wave has a displacement (vibration) direction. When the ultrasonic wave displacement direction and the direction of the grating of the FBG sensor are parallel, the ultrasonic detection sensitivity of the FBG sensor is maximized. In the case of being perpendicular to the surface of the fiber subject 9, there is an effect that the sensitivity does not change regardless of the direction in which the ultrasonic wave propagates.

  For example, as shown in FIG. 9A, for an ultrasonic wave having a displacement direction in the in-plane direction of the subject 9 (in the direction of the arrow in the figure), as shown in FIG. The ultrasonic detection sensitivity can be maximized by adopting the configuration of the movable FBG ultrasonic sensor 11 that is attached in the same direction as the ultrasonic displacement direction.

  9B shows the direction of the grading 8 perpendicular to the surface of the subject 9 with respect to the ultrasonic wave having the displacement direction in the out-of-plane direction (the arrow direction in the drawing) of the subject 9. The movable FBG ultrasonic sensor 11 is mounted in the same direction as the direction of the ultrasonic displacement direction.

  The present inventor has obtained the knowledge that the ultrasonic wave propagation direction has a great influence on the detection sensitivity in the ultrasonic detection of the FBG sensor. However, with the configuration shown in FIG. Even if it propagates from any direction of the subject, the sensitivity does not change, and the attachment method does not depend on the propagation direction, so that a very large effect is practically produced.

  Further, for an ultrasonic wave having a displacement direction of a certain angle θ, as shown in FIG. 9C, the direction of the grading 8 on the surface having the angle θ of the fixture 11 is the same as the direction of the ultrasonic displacement direction. By adopting the configuration of the FBG ultrasonic sensor 11 attached as described above, the ultrasonic detection sensitivity can be maximized.

  The best mode for carrying out the invention of the movable FBG ultrasonic sensor according to the present invention has been described above by taking only ultrasonic detection as an example, but acoustic wave emission (acoustic emission: AE) is also ultrasonic. Needless to say, the present invention is also applicable to AE detection.

  Since the movable FBG ultrasonic sensor according to the present invention has high ultrasonic detection sensitivity and is movable, ultrasonic detection is possible at an arbitrary position of the subject. It becomes a sensor with utility value. In addition, the realization of the movable sensor form in this way makes it easy to handle the same piezoelectric sensor that has been conventionally used as an ultrasonic detection sensor.

It is a figure which shows the whole structure of the ultrasonic detection apparatus which attaches and measures the movable FBG ultrasonic sensor which makes the premise of this invention to a subject. It is a figure explaining the attachment structure of an FBG ultrasonic sensor, (a) is bridge | bridging adhesion | attachment, (b) has each shown complete adhesion | attachment. It is a figure explaining the usage example of Example 1 of the movable FBG ultrasonic sensor of this invention, and Experimental example 1 using Example 1. FIG. It is a figure explaining complete adhesion and bridge adhesion, and both are related with a prior art example and prior art. It is a figure which shows the result of the experiment example of Example 1 of the movable FBG ultrasonic sensor of this invention. It is a figure explaining the outline | summary of Experimental example 2 of the movable FBG ultrasonic sensor of this invention. It is a figure explaining the experimental result of Experimental example 2 of this invention. It is a figure explaining Example 2 of the movable FBG ultrasonic sensor of this invention. It is a figure explaining Example 3 of the movable FBG ultrasonic sensor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic detection apparatus 2 Wavelength variable laser light source 3 Optical fiber 4 Optical circulator 5 Movable FBG ultrasonic sensor 6 Photoelectric converter 7 Optical fiber of FBG ultrasonic sensor 8 Grating 9 Subject 10 Adhesive 11 Attachment 12 Shielding agent 13 FBG ultrasonic sensor 14 Signal generator 14 'Electric wire 15 Acrylic plate 16 Ultrasonic oscillator 17 FBG ultrasonic sensor 18 FBG ultrasonic sensor 19 Orthogonal laminated fiber reinforced composite material 20 Impact damage part 21 Hollow container

Claims (5)

A movable FBG ultrasonic sensor used for structural soundness evaluation ,
The grating of the FBG ultrasonic sensor formed on the optical fiber is bonded to a fixture made of a material having a lower sound velocity than the subject, and ultrasonic detection is possible by moving the fixture on the surface of the subject. A movable FBG ultrasonic sensor characterized by the above. A movable FBG ultrasonic sensor used for structural soundness evaluation ,
Only the portions that are separated from both ends of the grating of the FBG ultrasonic sensor formed on the optical fiber are bonded to a fixture made of a material having a lower sound velocity than the subject, and the fixture is attached to the surface of the subject. A movable FBG ultrasonic sensor that is capable of detecting ultrasonic waves by being moved up. A movable FBG ultrasonic sensor used for structural soundness evaluation ,
Grating covered with a hollow container formed of the FBG ultrasonic sensor formed in the optical fiber is,
The hollow container is formed of a material having a lower sound velocity than the subject, and both ends of the hollow container are shielded at both ends of the hollow container at locations away from both ends of the grating,
A movable FBG ultrasonic sensor characterized in that ultrasonic detection is possible by moving the hollow container on the surface of a subject.   The grating is bonded along the flat surface of the fixture, and is used in contact with the subject so that the orientation of the grating is the same as the direction of ultrasonic displacement of the subject. The movable FBG ultrasonic sensor according to claim 1 or 2, wherein the ultrasonic sensor is a movable FBG ultrasonic sensor.   5. The flat surface of the fixture is parallel to, perpendicular to, or inclined at a predetermined angle with respect to a surface on which the fixture contacts the subject. Movable FBG ultrasonic sensor.