JP2011149828A - Vibration detection system, device using the system, and vibration detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems wherein, even though a vibration detection device for an ultrasonic wave, AE, or the like, that uses a fiber Bragg grating (FBG) is used for elastic wave detection at a material impact time or for ultrasonic flaw detection, in an environment receiving temperature change or strain change, ultrasonic detection is impossible or performance is lowered, and to attain miniaturization or weight reduction. <P>SOLUTION: In a system, wide-band light including an FBG reflection wavelength region is allowed to enter the FBG by using a wide band light source; the reflected light intensity from the FBG is converted into an electrical signal; a signal processing for extracting a response signal based on vibration received by the FBG is performed, relative to the electric signal, to thereby detect vibration; and thereby the vibrations of the ultrasonic waves, or the like, are detected without using an optical filter. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a system for detecting vibration from an audible range to an ultrasonic range using a fiber Bragg grating using broadband light, an apparatus using the system, and a vibration detection method. For example, the present invention relates to a system useful for an ultrasonic flaw detection apparatus, an acoustic emission (AE) sensor, and a material (including a structure) soundness evaluation apparatus.

  When propagating through a material, an ultrasonic wave has a characteristic that the ultrasonic wave is greatly dispersed and attenuated at a defective portion, so that the propagation state differs depending on whether or not there is a defect. A material defect detection method using this property is ultrasonic flaw detection. Conventionally, piezoelectric elements have been frequently used as ultrasonic sensors. In addition, when a microscopic breakdown occurs in the material, acoustic emission (AE) is released. Therefore, the microscopic breakdown state of the material can be monitored by detecting the AE. Since AE is an elastic wave in the ultrasonic range, piezoelectric elements are frequently used in the AE sensor as in the ultrasonic sensor.

  However, the piezoelectric element which is an electric sensor has problems such as being damaged by electromagnetic waves and not being usable in a flammable atmosphere. In recent years, fiber Bragg grating (hereinafter also referred to as “FBG”), which is a kind of optical fiber sensor, is expected as an ultrasonic wave / AE sensor that can solve these problems.

  Ultrasonic or AE detection systems using an FBG as a sensor are roughly classified into two types using a laser or broadband light as a light source. In the case of using a laser, an FBG reflected light intensity synchronized with an ultrasonic wave or AE vibration received by the FBG can be obtained by entering a laser that oscillates at a wavelength with a large reflectance change in the FBG reflection spectrum. FIG. 24 shows a case where a broadband light source is used. When the broadband light source 2 is used, broadband light including the FBG reflection wavelength region is incident on the FBG 4 via the optical circulator 3, and the optical filter 5 whose transmission or reflection characteristics change sharply in the FBG reflection wavelength region is applied to the FBG. By making the reflected light incident, it is possible to obtain optical filter transmission or reflected light intensity synchronized with the ultrasonic wave / AE vibration. The light transmitted through the optical filter is input to the photoelectric converter 6 where it is converted into an electrical output corresponding to the light intensity. The waveform recorder 7 displays the electrical output from the photoelectric converter 6 on the display unit as AE / ultrasound detected by the FBG 4 or records it in the recording device. The same function can be obtained even if the optical filter 5 shown in FIG. 24 is installed between the broadband light source 2 and the optical circulator 3. Non-Patent Document 1 by the inventor shows an experiment in which ultrasonic detection and ultrasonic flaw detection are performed by FBG using each light source. Moreover, there exist patent documents 1 thru | or 5 by inventors as a prior art.

The fiber Bragg grating (FBG) has a structure in which the refractive index of a core, which is a light guide for an optical fiber, periodically changes in the fiber axis direction, and is centered on a Bragg wavelength λ _B represented by the equation (1). Reflects narrowband light.

n represents a refractive index, and Λ represents a periodic interval (grating interval) of refractive index change. When the FBG receives a change in temperature or strain, the refractive index n and the grating interval Λ change, and the Bragg wavelength λ _B changes accordingly (see equation (1)). The amount of change in Bragg wavelength caused by strain and temperature change is 1.2 pm / micro strain and 14 pm / ° C., respectively, in an FBG having a Bragg wavelength in the 1.55 μm band that is widely used in the communication field. Elastic waves such as ultrasonic waves and AE cause weak vibrations of at most several microstrains, so when the FBG receives ultrasonic waves or AEs, its Bragg wavelength changes only at most about several pm. In general, many FBGs used for evaluating the soundness of structures have a grating length of 1 to 20 mm, and the total width of the reflection spectrum is about 1 to 2 nm at most. For this reason, when the FBG undergoes a large temperature or strain change, the Bragg wavelength changes greatly, and in a system using a laser light source, the laser wavelength may deviate from the reflection wavelength region of the FBG. Even in a system using a broadband light source, the FBG reflection spectrum and the wavelength region where the transmission or reflection characteristics of the optical filter change sharply do not intersect. In such a case, the ultrasonic waves and AE received by the FBG cannot be detected.

  Therefore, it is conceivable to use a wavelength tunable laser or a tunable filter to control the laser wavelength or the wavelength at which the optical characteristics of the optical filter change according to the Bragg wavelength change of the FBG. However, when the Bragg wavelength of the FBG fluctuates at high speed, these controls cannot follow the Bragg wavelength change, and ultrasonic waves and AE cannot be detected. In particular, AE is a phenomenon associated with an instantaneous strain change that occurs when a material breaks down. Therefore, high-speed Bragg wavelength fluctuation occurs when AE occurs. For this reason, it is considered difficult to detect AE in a measurement system using a wavelength tunable laser or a tunable filter.

  In order to solve this problem, a technique for detecting an ultrasonic wave or AE that propagates through a subject without attaching an FBG to the subject is disclosed in “Material Soundness Evaluation Device” of Patent Document 3 by the inventor. In conventional ultrasonic detection and FAE detection using FBG, the FBG is attached to the subject. In this technique, a portion other than the FBG of the optical fiber in which the FBG is written is brought into contact with the subject. Ultrasound or AE propagating through the subject flows into the optical fiber via the contact point of the optical fiber, and propagates through the optical fiber, causing the FBG to undergo ultrasonic / AE vibration. Since the FBG is not attached to the subject, the Bragg wavelength of the FBG is independent of the strain experienced by the subject. However, the Bragg wavelength change of the FBG accompanying the temperature change cannot be eliminated, and there remains a problem in ultrasonic detection and AE detection in an environment where the temperature change occurs.

  In addition, in the “AE / ultrasonic detection system, and the material monitoring apparatus and non-destructive inspection apparatus including the same” disclosed in Patent Document 4 by the inventor, an ultra-independent of the Bragg wavelength of the FBG using two Fabry-Perot filters. A sound wave / AE detection technique is disclosed. This prior art is characterized in that broadband light is incident on the FBG and FBG reflected light is incident on two Fabry-Perot filters. The two Fabry-Perot filters have an FSR (Free Spectral Range: interval of transmittance peak wavelengths of a Fabry-Perot filter having periodic transmission characteristics) that is substantially equal to the full width of the reflection spectrum of the FBG. Only FSR / 4 is different. In this prior art, regardless of the Bragg wavelength of the FBG, the transmitted light intensity of at least one Fabry-Perot filter fluctuates in synchronization with the ultrasonic wave or AE vibration received by the FBG, and the ultrasonic wave does not depend on the Bragg wavelength change. Or AE detection is possible.

JP 2005-326326 A JP 2005-009937 A JP 2007-240447 A JP 2008-046036 A JP 2006-132952 A

Hiroshi Tsuda, “Ultrasound and Damage Detection in CFRP using Fiber Bragg Grating Sensors”, Composites Science and Technology, Vol. 66, p. 676-683 (2006) J. et al. R. Lee, H.C. Tsuda, “Acousto-ultrasonic sensing using capsule fiber Bragg gratings for temperature compensation”, Meas. Sci. Technol. 17 (2006) 2920-2926

  In an environment subject to temperature changes and strain changes, the Bragg wavelength changes greatly, and in a system using a laser light source, there is a problem that the laser wavelength deviates from the reflection wavelength region of the FBG. desired. However, when a broadband light source is used, an optical filter whose transmission or reflection characteristics change sharply in the FBG reflection wavelength region is required. In addition, the conventional technology has a problem that the Bragg wavelength change of the FBG accompanying the temperature change cannot be eliminated.

  In the ultrasonic / AE detection system described in Patent Document 4, first, two Fabry-Perot filters having FSR substantially equal to the full width of the reflection spectrum of the FBG are arranged, and second, two Fabry-Perot filters are arranged. It is necessary to shift the transmittance peak wavelength by FSR / 4. However, precise control of the FBG reflection spectrum full width and the Fabry-Perot filter FSR, which are the first requirement, is difficult in the manufacture of these, and causes the system components to be expensive. In order to shift the transmittance peak wavelength of the two Fabry-Perot filters, which are the second requirement, by FSR / 4, a temperature controller for controlling the transmittance peak wavelength is attached to the Fabry-Perot filter, or a number of Fabry-Perot filters. It is necessary to prepare a Perot filter and select two Fabry-Perot filters with transmittance peak wavelengths shifted by FSR / 4. As described above, the technique of Patent Document 4 has a problem that the system components are expensive and the number of system components increases.

  Furthermore, a soundness evaluation system mounted on a transport aircraft, particularly a transport aircraft used in the aerospace field, is required to satisfy strict weight restrictions, power restrictions, and dimensional restrictions.

  The present invention solves these problems, and detects ultrasonic waves or AE under strain and temperature fluctuation conditions that eliminates the need for an optical filter of a conventional ultrasonic / AE detection system using broadband light as a light source. The purpose is to realize a highly reliable detection system. Another object of the present invention is to improve the detection ability of ultrasonic waves and AE. It is another object of the present invention to realize a system that has a small number of components, is free of expensive elements, can be assembled in a small size, is light, and is inexpensive.

  In order to solve the above problems, the present invention makes broadband light incident on an FBG, and without using an optical filter for detecting a Bragg wavelength change, the reflected light from the FBG is incident on a photoelectric converter and reflected light. The response signal corresponding to the ultrasonic wave / AE received by the FBG is obtained by converting the intensity into an electric signal and performing appropriate signal processing such as averaging processing or frequency filter processing on the electric signal. .

  In the present invention, the FBG sensor is provided with a resonance structure by attaching a part of the FBG of the optical fiber in which the FBG sensor is written, or a portion other than the FBG to a subject. After converting the reflected light intensity from the FBG sensor having the resonance structure into an electric signal, by performing appropriate signal processing on the electric signal, the ultrasonic wave / AE detection ability can be further improved.

  The present invention has the following features in order to achieve the above object.

  The apparatus of the present invention is a vibration detection system, and detects vibrations in an audible range to an ultrasonic range. The vibration is typically ultrasonic or acoustic emission. The vibration detection system of the present invention includes a broadband light source, a fiber Bragg grating (FBG), a photoelectric conversion unit, and a signal processing unit. The broadband light source emits broadband light including an FBG reflection wavelength region. When broadband light including an FBG reflection wavelength region is incident on the FBG, a wavelength component called a Bragg wavelength is reflected by the FBG, and the remaining components are transmitted. The Bragg wavelength shift is caused by ultrasonic vibration or AE, whereby the FBG reflected light intensity changes. The signal processing unit performs signal processing for extracting a response signal based on vibration received by the FBG, with respect to the electrical signal obtained by converting the FBG reflected light intensity. The signal processing is one or more of an averaging process and a frequency filter process. The frequency filter process is a low-pass filter process or a band-pass filter process. The vibration detection system of the present invention is characterized by not using an optical filter for Bragg wavelength change detection.

  The vibration detection system of the present invention is characterized in that the FBG sensor has resonance characteristics. It is preferable that a part of the FBG of the optical fiber in which the FBG is written or a part other than the FBG is brought into contact with the subject so that the FBG sensor has resonance characteristics. The vibration is caused to flow into the optical fiber through a contact portion with the subject. In addition, when performing the frequency filter processing, it is desirable that the band pass filter processing is in the vicinity of the resonance frequency band based on the resonance characteristics. The frequency filtering process in the vibration detection system of the present invention is a resonance determined based on the length of the optical fiber resonance part, which is the distance between the contact point with the subject in the optical fiber in which the FBG is written and the free end. The process is characterized by passing the frequency. The resonance frequency can be controlled by adjusting the length of the optical fiber resonance portion.

  The vibration detection system of the present invention can be configured to be movable. When a non-resonant type structure is adopted, the FBG is brought into contact with a medium having a lower ultrasonic propagation speed than the subject or a medium of 1 mm or less to form a movable FBG sensor, and the movable FBG sensor is attached to the subject. It is good to contact. When taking a resonance type structure, by contacting a part of the FBG of the optical fiber in which the FBG is written, or a place other than the FBG with a medium having a lower ultrasonic propagation velocity than the subject or a medium of 1 mm or less, A movable FBG sensor having resonance characteristics may be used, and the movable FBG sensor may be brought into contact with the subject.

  The vibration detection system of the present invention can perform multipoint measurement by providing a plurality of FBG sensors. Using the vibration detection system of the present invention, by detecting the state of ultrasonic propagation, a material soundness evaluation apparatus for evaluating the soundness of a subject, an ultrasonic flaw detection apparatus, or acoustic emission generated at the time of material destruction is detected. Providing equipment.

  The method of the present invention is a vibration detection method, in which broadband light including an FBG reflection wavelength region is incident on the FBG, the reflected light intensity from the FBG is converted into an electric signal, and the electric signal is Signal processing for extracting a response signal based on the vibration received by the FBG is performed.

  According to the present invention, ultrasonic waves and AE can be detected using FBG even in a situation where strain and temperature fluctuate. In addition, according to the present invention, in the ultrasonic / AE detection system using broadband light as a light source, an optical filter that has been conventionally required is unnecessary, so the number of system components is small, and the system is reduced in size and weight.・ Price reduction and high reliability can be improved. Further, according to the present invention, the ultrasonic wave / AE response can be detected by converting the FBG reflected light intensity into an electric signal and performing signal processing such as averaging and frequency filtering. Moreover, the detection capability of an ultrasonic wave or AE can be improved by making a FBG sensor into a structure with a resonance characteristic.

  According to the present invention, it is possible to detect vibrations in a range from the audible range to the ultrasonic range. Since it is possible to detect only a single ultrasonic pulse, it is possible to accurately detect acoustic emission (AE) emitted when material destruction occurs. In addition, when obtaining a response signal using periodic ultrasonic vibration, an FBG sensor having a resonance structure shows a response having a high component intensity at a resonance frequency close to the frequency of the received ultrasonic wave. By performing the frequency filter process, the detection ability of ultrasonic waves and AE can be further improved.

  Further, according to the present invention, by making the FBG sensor movable, it is possible to provide a device that is convenient for examining a subject.

The figure showing the system used for the ultrasonic measurement experiment corresponding to the 1st Embodiment of this invention. The figure showing the system used for the ultrasonic measurement experiment corresponding to the 2nd Embodiment of this invention. (A) is a response waveform without an averaging process when a laser is used as a light source, (b) is a response waveform without an averaging process, and (c) with respect to a spike wave excitation ultrasonic wave of an FBG sensor having a non-resonant structure. FIG. 6 is a diagram showing a response waveform after an averaging process. (A) (b) (c) is a figure which shows the frequency characteristic of the response waveform shown to Fig.3 (a) (b) (c), respectively. (A) is a response waveform without averaging processing when a laser is used as a light source, (b) is a response waveform without averaging processing, and (c) is for a spike wave excitation ultrasonic wave with an optical fiber resonator length of 291 mm. The figure which shows the response waveform which performed the averaging process. (A) (b) (c) is a figure which shows the frequency characteristic of the response waveform shown to Fig.5 (a) (b) (c), respectively. Obtained from an FBG sensor having a resonance structure with an optical fiber resonance part length of 291 mm with respect to spike wave excitation ultrasonic waves, (a) is a response waveform that is bandpass filtered without averaging, and (b) is unfiltered. The figure which shows the response waveform averaged in FIG. Obtained from an FBG sensor having a resonant structure with an optical fiber resonance part length of 50.5 mm with respect to spike wave excitation ultrasonic waves, (a) is a response waveform averaged without filtering, and (b) is unfiltered. The response waveform without a process and an averaging process, (c) is a figure which shows the response waveform by which the low pass filter process was carried out without the averaging process. (A) (b) is a figure which shows the frequency characteristic of the response waveform shown to Fig.8 (a) (b), respectively. An FBG sensor response waveform having a resonance structure of an optical fiber resonance part length of 50.5 mm with respect to a three-cycle sinusoidal excitation ultrasonic wave having a changed frequency, where the frequency of the sine wave is 100 kHz, (b) is 200 kHz, ( The figure which shows a response waveform when c) is 300 kHz and (d) is 400 kHz. (A) (b) (c) (d) is a figure which shows the frequency characteristic of the response waveform shown to Fig.10 (a) (b) (c) (d), respectively. The figure showing the system of 5th Embodiment. (A) is a response waveform for an ultrasonic wave that has passed only through a healthy part, and (b) is a diagram showing a response waveform for an ultrasonic wave that has passed through an impact damage part, obtained in a flaw detection experiment. (A) and (b) are the figures which show the frequency characteristic of the response waveform shown to Fig.13 (a) (b), respectively. The figure showing the system of 6th and 7th embodiment. Obtained from the FBG sensor having a resonance structure with respect to the ultrasonic wave propagating through the subject, (a) is a low-pass filter processed and averaged response waveform, and (b) is low-pass filtered without averaging. (C) is a diagram showing a response waveform that has been bandpass filtered without averaging. (A) (b) is a figure which shows the frequency characteristic of the response waveform shown to Fig.16 (a) (b), respectively. Obtained from the FBG sensor having a non-resonant structure with respect to the ultrasonic wave propagating through the subject, (a) is a response signal subjected to low-pass filter processing and averaging processing, and (b) is low-pass filtering processing without averaging processing. FIG. (A) and (b) are the figures which show the frequency characteristic of the response signal shown to Fig.18 (a) (b), respectively. The figure showing the apparatus which made the sensor part of 9th Embodiment movable. The figure showing the multipoint measuring device of 10th Embodiment. The figure showing the simultaneous multipoint measuring device of 10th Embodiment. The figure showing the simultaneous multipoint measuring apparatus using the wavelength separation technique of 10th Embodiment. The figure showing a prior art example.

  The present invention relates to a system for detecting vibrations from an audible range to an ultrasonic range, and as the vibrations, a sound wave having an audible frequency of about 30 Hz to 20 kHz and higher, that is, an ultrasonic wave, or in a broad sense, directly in a human ear. It is a system for detecting sound waves that are not intended to be heard, ie, ultrasonic waves. Further, it can be applied to AE detection, ultrasonic flaw detectors, acoustic emission (AE) sensors, and material (structure) soundness evaluation devices that use these detections as in the case of ultrasonic detection. Embodiments of the present invention will be described below.

(First embodiment)
The first embodiment is a basic form of ultrasonic response using an FBG sensor. The ultrasonic detection system of the present embodiment is characterized by detecting the ultrasonic wave received by the FBG without using an optical filter that is an essential component in a detection system using a conventional broadband light source. Is. The ultrasonic detection system of this embodiment includes a broadband light source, an optical circulator, an FBG, a photoelectric converter, and a waveform recorder. In the ultrasonic detection system of the present embodiment, the broadband light source and the optical circulator are connected by an optical fiber, and the optical circulator and the photoelectric converter are connected by an optical fiber. The broadband light from the broadband light source is incident on the optical fiber on which the FBG is written via the optical circulator, the reflected light from the FBG is incident on the photoelectric converter via the optical circulator, and the reflected light intensity from the FBG is And converted into an electric signal by a photoelectric converter. This electric signal is amplified and filtered as necessary, and then recorded in a waveform recorder. In this embodiment, the electrical signal from the photoelectric converter is averaged to detect the ultrasonic wave received by the FBG and display it on the display unit of the waveform recorder or record it on the recording device. As shown in the following experiment, the averaging process is obtained by averaging the response signal waveforms for a single pulsed ultrasonic wave a plurality of times. For example, the averaging signal may be added and averaged using the excitation signal of the spike excitation ultrasonic oscillator as a trigger. Further, the waveform recorder may have an averaging processing function.

  1 and 2 are schematic diagrams of a system used in an ultrasonic measurement experiment for explaining the vibration detection system of the present invention, and are diagrams for understanding the first and second embodiments. The ultrasonic measurement experiment system of FIG. 1 includes a broadband light source 12, an optical circulator 13, an FBG 14, an ultrasonic oscillator 11, a photoelectric converter 15, an amplifier 16, a filter 17, and a waveform recorder 18. Is bonded to the ultrasonic oscillator 11. The ultrasonic measurement experimental system in FIG. 2 includes a broadband light source 22, an optical circulator 23, an FBG 24, an ultrasonic oscillator 21, a photoelectric converter 25, an amplifier 26, a filter 27, and a waveform recorder 28. Is bonded to the ultrasonic oscillator 21.

  This will be described below with reference to FIG. In the ultrasonic measurement experiment system of FIG. 1, the broadband light source 12 and the optical circulator 13 are connected by an optical fiber, and the optical circulator 13 and the photoelectric converter 15 are connected by an optical fiber. Broadband light from the broadband light source 12 is incident on the optical fiber in which the FBG 14 is written via the optical circulator 13, and reflected light from the FBG 14 is incident on the photoelectric converter 15 via the optical circulator 13 and reflected from the FBG 14. The light intensity is converted into an electric signal by the photoelectric converter 15. This electrical signal is amplified and filtered as necessary, and then recorded in the waveform recorder 18. The system shown in FIGS. 1 and 2 is characterized in that it does not include the optical filter 5 that is an essential component in the detection system using the conventional broadband light source shown in FIG.

  In order to propagate the ultrasonic wave to the optical fiber in which the FBG is written, a part of the optical fiber is bonded to the ultrasonic oscillator as shown in FIG. 1 or FIG. The ultrasonic oscillator vibrates ultrasonically when an excitation signal is input, and the ultrasonic wave flows through the optical fiber through the bonded portion. In FIG. 1, the FBG is attached to the ultrasonic oscillator. In FIG. 2, a part of an optical fiber having an FBG is bonded to an ultrasonic oscillator, and an optical fiber including an FBG (also referred to as an FBG sensor) reciprocates between the optical fiber bonding point and the optical fiber free end. Since a sound wave is detected, the response shows resonance characteristics. Therefore, in the present invention, the length of the optical fiber from the optical fiber bonding point to the free end is defined as “optical fiber resonance portion length”. FIG. 2 illustrates the optical fiber resonator length L.

  As a comparative example, an ultrasonic response signal obtained using a laser as a light source was recorded. At that time, the optical filter 5 shown in FIG. 24 was removed, the broadband light source was replaced with a tunable laser, and the laser wavelength was set to a wavelength at which the reflectance of the FBG was reduced by half.

  The grating length of the FBG used in this embodiment is 10 mm, and in the other embodiments, the FBG having a length of 10 mm is used in an example in which the grating length of the FBG is not particularly described.

  As the FBG sensor, an optical fiber resonance part length is 0 mm, that is, an FBG sensor having a non-resonant structure in which the entire length of the FBG is attached to the ultrasonic oscillator, and an ultrasonic oscillator having a center frequency of 250 kHz is excited by a spike wave, Response waveforms were recorded using two different systems. FIG. 3 shows the response waveform. FIG. 3A shows a response waveform obtained when a single spike wave is input to the ultrasonic oscillator using a laser as a light source. Hereinafter, a response signal to an ultrasonic wave oscillated by a single excitation signal input is referred to as “response signal without averaging process”. A large ultrasonic response appears at time zero, but the response amplitude decays rapidly with time.

  FIG. 3B is a “response waveform without averaging processing” obtained from the system using the broadband light source shown in FIG. 1 for spike wave excitation ultrasonic waves. Noisy and no ultrasonic response can be identified from the waveform. FIG. 3C shows a waveform obtained by averaging 512 responses to spike wave excitation ultrasonic waves using the same system as FIG. 3B. The laser shown in FIG. 3A is used as a light source. A waveform similar to the response waveform obtained from the system was obtained. It can be seen that ultrasonic detection is possible by averaging the response waveform obtained from the sensor having a non-resonant structure using the system shown in FIG. 1 that does not use an optical filter.

  In conventional ultrasonic detection using a system using a broadband light source, a tunable filter capable of shifting the wavelength of optical characteristics in accordance with a change in the Bragg wavelength of the FBG is used, or the reflection total width of the FBG is almost the same as in Patent Document 4. It was necessary to use a Fabry-Perot filter with equal FSR. That is, the Bragg wavelength change of the FBG caused by the ultrasonic vibration is changed to the light intensity through the optical filter whose optical characteristics depend on the wavelength. On the other hand, in the ultrasonic detection system of the present embodiment, the ultrasonic waves received by the FBG are detected without using an optical filter whose optical characteristics depend on the wavelength. Since no optical filter depending on the wavelength is used in the detection unit, ultrasonic detection is possible regardless of the Bragg wavelength of the FBG. That is, it is possible to detect ultrasonic waves that are not related to the strain or temperature experienced by the FBG.

  FIG. 4 shows frequency characteristics of the response signals shown in FIG. The frequency characteristics shown in FIGS. 4 (a) and 4 (c) have a wideband characteristic centered on the center frequency of the ultrasonic oscillator of 250 kHz. On the other hand, in FIG. 4B, a high component intensity appears at random in the entire frequency band. Filtering can be considered as a means for obtaining an ultrasonic response from a signal buried in noise, but the filter conditions for extracting the response signal cannot be set from the frequency characteristics of the “response signal without averaging”. Extraction of ultrasonic response by filtering is impossible.

  From the above, in this embodiment, the response signal based on the ultrasonic wave received by the FBG can be detected by averaging the electrical signal from the photoelectric converter.

(Second Embodiment)
The second embodiment is a case of an ultrasonic response of an FBG sensor having a resonance structure. In the vibration detection system of the present embodiment, a part of the FBG of the optical fiber in which the FBG is written, or a part other than the FBG is brought into contact with the subject to give the FBG sensor resonance characteristics. Ultrasonic vibration is caused to flow into the optical fiber through the contact point with the subject. And the response signal based on the ultrasonic wave which FBG receives can be detected by frequency-filtering the electrical signal from a photoelectric converter by a band pass filter. Similar to the first embodiment, the ultrasonic detection system of the second embodiment includes a broadband light source, an optical circulator, an FBG, a photoelectric converter, and a waveform recorder.

  In order to describe the second embodiment, an ultrasonic measurement experiment similar to that of FIG. 1 except for the structure of the FBG sensor will be described with reference to FIG. FIG. 5 shows the result of an ultrasonic detection experiment similar to that shown in FIG. 1 using an FBG sensor having a resonant structure with an optical fiber resonator length of 291 mm. FIG. 5A shows a response waveform without an averaging process when a laser is used as the light source. The first ultrasonic response appeared at time zero and the second response was detected after 0.11 ms. These first two responses are that the ultrasonic wave generated from the ultrasonic oscillator propagates through the optical fiber, passes through the FBG at time zero, and then reflects at the free end of the optical fiber to 0.11 ms from the first FBG passage. This corresponds to the phenomenon of passing through the FBG again later. After that, the ultrasonic wave reciprocated between the optical fiber adhesion point on the ultrasonic oscillator and the optical fiber free end, and a response with a large amplitude was detected every time the ultrasonic wave passed through the FBG. Thus, a configuration or structure in which a response with a large amplitude is detected by reciprocating ultrasonic waves is referred to as a “configuration having resonance characteristics” or a “resonance structure”.

  FIG. 5B shows a response waveform without averaging processing when broadband light is incident on the FBG. In this case, the ultrasonic response cannot be recognized due to large noise. Accordingly, FIG. 5C shows a response waveform that has been averaged 512 times. By performing the averaging process, a response waveform (FIG. 5C) similar to the waveform obtained from the system using the laser as the light source (FIG. 5A) is obtained. Also in the FBG sensor having a resonance structure, ultrasonic waves can be detected by performing an averaging process in the same manner as in the case of having a non-resonance structure.

  FIG. 6 shows frequency characteristics of the response signals shown in FIG. 6A, 6B, and 6C, resonance characteristics having discretely high component strengths appeared. In the response waveform obtained from the laser system, the maximum component intensity appeared at 248 kHz which is in good agreement with the center frequency of the ultrasonic oscillator of 250 kHz (see FIG. 6A). The frequency interval at which the high component intensity appears was 8.7 kHz.

  FIGS. 6B and 6C show frequency characteristics of “response signal without averaging process” and “response signal subjected to averaging process” obtained in the broadband optical system, respectively. Both have similar frequency characteristics in which the maximum component intensity appears at 282 kHz, and the frequency interval at which the high component intensity appears is 8.7 kHz, the same as in FIG. Further, the frequency characteristic of the “response signal without averaging process” has a component intensity that cannot be ignored even in a high frequency range of 400 kHz or higher, and it is considered that the ultrasonic response could not be identified due to these high frequency noises ( (Refer FIG.5 (b)).

The operation principle of the resonance of the FBG sensor having a resonance structure with the optical fiber resonance part length having a predetermined value will be considered. When the FBG sensor is attached as shown in FIG. 2, this FBG sensor exhibits the same resonance characteristics as a cantilever beam having the length of the optical fiber resonance portion as the beam length, and the resonance frequency _{fr, n} is _expressed by the formula ( 2).

Here, v and L represent the ultrasonic wave propagation speed and the optical fiber resonance part length in the optical fiber, respectively. From equation (2), the frequency interval Delta] f _r where high component strength appears, is given by Equation (3).

In the present embodiment, Δf _r = 8.7 kHz and the optical fiber resonator length L = 291 mm. The ultrasonic wave propagation velocity v in the optical fiber obtained by substituting these values into Equation (3) is 5,060 m / s, and the ultrasonic wave having a frequency of 200 kHz that propagates in the optical fiber described in Non-Patent Document 2. It agrees very well with the speed of 5,110 m / s.

  The frequency characteristics of the response waveform obtained from the broadband optical system shown in FIGS. 6B and 6C show the maximum component intensity at 282 kHz regardless of the presence or absence of the averaging process. It is considered that an ultrasonic response can be obtained by performing a nearby band pass filter process. FIG. 7A shows a waveform recorded without averaging processing with the filter of FIG. 2 set to a band pass of 280 kHz to 290 kHz. Further, for reference, a response signal that has not been filtered and is averaged 512 times is shown in FIG. 7B (same as FIG. 5C). A waveform having a large amplitude at the same time as the response waveform subjected to the averaging process could be obtained by the band pass filter process in the vicinity of the frequency band where the maximum component intensity appears even without the averaging process.

  From the above, in the second embodiment, it is possible to detect ultrasonic waves by using an FBG sensor having a resonance structure in which the length of the optical fiber resonance part is a predetermined value. Specifically, broadband light from a broadband light source is incident on an FBG sensor having a resonance structure having a predetermined optical fiber resonance length via an optical circulator, and reflected light from the FBG is transmitted via an optical circulator. The light is incident on the photoelectric converter and the reflected light intensity from the FBG is converted into an electric signal by the photoelectric converter. This electric signal is amplified as necessary, frequency-filtered, and recorded in a waveform recorder. The frequency filter process is preferably a bandpass filter process in the vicinity of the frequency band where the maximum component intensity appears. The electrical signal does not need to be averaged, but by performing the averaging process, the detection capability becomes higher.

(Third embodiment)
The third embodiment relates to a case where the length of the optical fiber resonance part is adjusted for the ultrasonic response of the FBG sensor having a resonance structure. The ultrasonic detection system of this embodiment includes a broadband light source, an optical circulator, an FBG, a photoelectric converter, and a waveform recorder. In the present embodiment, as in the second embodiment, a part of the FBG of the optical fiber in which the FBG is written or a portion other than the FBG is brought into contact with the subject so that the FBG sensor has resonance characteristics. . Ultrasonic vibration is caused to flow into the optical fiber through the contact point with the subject. And the response signal based on the ultrasonic wave which FBG receives can be detected by carrying out the frequency filter process by the low-pass filter etc. about the electrical signal from a photoelectric converter.

  In order to understand the third embodiment, an ultrasonic measurement experiment similar to that of the second embodiment will be described except for the optical fiber resonance structure. FIG. 8 shows a response waveform to the spike wave excitation ultrasonic wave when the length of the optical fiber resonance part is set to 50.5 mm using the ultrasonic measurement experiment apparatus shown in FIG. FIG. 8A shows a response waveform that has been averaged 512 times. In FIG. 8A, a continuous response appears instead of the intermittent response (see FIG. 5C) exhibited by the FBG sensor having an optical fiber resonance portion length of 291 mm. This is a continuous response signal because the optical fiber resonance portion is shortened and the ultrasonic waves reciprocate through the FBG in a short time. The response waveform without the averaging process is shown in FIG. 8B, but it is buried in noise and the ultrasonic response cannot be identified.

FIGS. 9A and 9B are frequency characteristics of the response waveforms in FIGS. 8A and 8B, respectively. The maximum component intensity of both response waveforms appeared at 270 kHz. In both response waveforms, a relatively large component intensity appears even at 320 kHz. In the frequency characteristic of the response signal subjected to the averaging process, component intensities other than the resonance frequency having high component intensities indicated by arrows in FIG. 9A are extremely low. Further, from FIG. 9A, the resonance frequency interval is 51 kHz. The value of this resonance frequency interval is calculated by the following equation (3): the ultrasonic wave propagation velocity v = 5,060 m / s in the optical fiber evaluated from the second embodiment, and the length of the optical fiber resonance portion in this embodiment. This is in good agreement with Δf _r = 50 kHz calculated by substituting the length L = 50.5 mm.

  As shown in FIGS. 9A and 9B, since the response signal has a large component intensity at a frequency of 320 kHz or less regardless of whether or not the averaging process is performed, in order to obtain an ultrasonic response without the averaging process. It is considered that a low-pass filter process using a frequency slightly higher than the resonance frequency as a cutoff frequency is effective. Therefore, the filter shown in FIG. 2 was set as a low-pass filter having a cutoff frequency of 350 kHz, and recorded without averaging. The recorded waveform is shown in FIG. As with the averaging process, a response having a large amplitude appears at time zero.

  As can be seen from the above experiment, the resonance frequency and the frequency interval of the FBG sensor having a resonance structure can be controlled by the length of the optical fiber resonance portion.

  In this embodiment, an electrical signal from the photoelectric converter is subjected to filter processing. A low-pass filter is preferably used as the filter. As the low-pass filter, based on a predetermined resonance frequency and frequency interval corresponding to the length of the optical fiber resonance part of the FBG sensor having a resonance structure, a frequency slightly higher than the resonance frequency may be set as a cutoff frequency. In addition, when performing the filtering process, it is not necessary to perform the averaging process, but the averaging process may be performed.

  In the present embodiment, in the ultrasonic detection system of the FBG sensor having a resonance structure, the filter condition for obtaining the ultrasonic response can be controlled by adjusting the length of the optical fiber resonance portion.

(Fourth embodiment)
The fourth embodiment relates to a case where periodic ultrasonic waves are used. The effect of the ultrasonic frequency on the ultrasonic response of the FBG sensor having a resonance structure is utilized. The ultrasonic detection system of the fourth embodiment includes a broadband light source, an optical circulator, an FBG, a photoelectric converter, and a waveform recorder. In this embodiment, as in the second embodiment, a part of the FBG on which the FBG is written or a portion other than the FBG is brought into contact with the subject so that the FBG sensor has resonance characteristics. . Ultrasonic vibration is caused to flow into the optical fiber through the contact point with the subject. And the response signal based on the ultrasonic wave which FBG receives can be detected by frequency-filtering the electric signal from a photoelectric converter by a low pass filter or a band pass filter.

  In order to understand the fourth embodiment, an ultrasonic measurement experiment similar to that shown in the second embodiment except for the optical fiber resonance structure and ultrasonic waves will be described.

  When a periodic sine wave is used as the excitation signal input to the ultrasonic oscillator, the frequency of the oscillated ultrasonic wave matches the frequency of the sine wave. That is, the frequency of the oscillated ultrasonic wave can be controlled. Here, in order to evaluate the influence of the ultrasonic frequency on the response signal of the resonance type FBG sensor, a response signal to the ultrasonic wave excited by a three-cycle sine wave of 100 kHz to 400 kHz was recorded. The length of the optical fiber resonance part in the present embodiment is 50.5 mm.

  10A to 10D, the frequency of the ultrasonic excitation sine wave signal is set to 100 kHz, 200 kHz, 300 kHz, and 400 kHz, and the averaging process is performed 512 times without filtering using the system of FIG. The recorded response waveform is shown. Moreover, the frequency characteristics of each response waveform are shown in FIGS.

  In this experiment, the resonance frequency of the order n from 1 to 8 is calculated from Equation (2) as 75.1 kHz, 125 kHz, 175 kHz, 225 kHz, 276 kHz, 326 kHz, 376 kHz, and 426 kHz. The frequencies having high component intensity appearing in FIGS. 11A to 11D correspond to these resonance frequencies, and the maximum component intensity appears at the resonance frequency close to the ultrasonic frequency. That is, the FBG sensor having a resonance structure shows a response having a high component intensity at a resonance frequency close to the frequency of the received ultrasonic wave.

  From the above, in the present embodiment, the ultrasonic wave in the second and third embodiments is set to a predetermined frequency as the ultrasonic wave, so that the FBG sensor having a resonance structure receives the ultrasonic wave. It shows a response with a high component intensity at a resonance frequency close to that frequency. Using this response characteristic, filtering is performed using a filter suitable for the response. When a low-pass filter is used as the filter, a frequency slightly higher than the resonance frequency close to the frequency of the received ultrasonic wave may be set as the cutoff frequency. The cut-off frequency may be appropriately set based on the resonance frequency and the frequency interval.

  When a response signal is obtained by using periodic ultrasonic vibration as in the present embodiment, the FBG sensor having a resonance structure has a high component intensity at a resonance frequency close to the frequency of the received ultrasonic wave. If the frequency filter processing such as the low-pass filter and the band-pass filter is used, it is possible to further improve the detection ability of ultrasonic waves and AE.

(Fifth embodiment)
The fifth embodiment is an apparatus in which the ultrasonic detection system described in the first to fourth embodiments is applied to ultrasonic flaw detection. FIG. 12 shows an example in which ultrasonic flaw detection is performed on carbon fiber reinforced plastic (CFRP) having impact damage using the ultrasonic detection system of the present invention. The ultrasonic flaw detector shown in FIG. 12 includes a broadband light source 32, an optical circulator 33, an FBG 34, an ultrasonic oscillator 31, a photoelectric converter 35, an amplifier 36, a filter 37, and a waveform recorder 38. Contact is made at a contact point 39. The subject 40 is a 300 × 150 mm ² orthogonally laminated CFRP plate, and there is an elliptical impact damage 41 having a major axis and a minor axis of 30 mm and 20 mm, respectively, in the center of the subject 40. In FIG. 12, the impact damage 41 is schematically indicated by an ellipse, and the optical fiber contact point is schematically indicated by a circle as a contact location 39. The distance between the ultrasonic oscillator 31 and the optical fiber contact point was set to 150 mm, and the ultrasonic oscillator 31 having a center frequency of 250 kHz was excited with a spike wave. Responses to the ultrasonic wave that passed only the healthy part of the subject 40 and the ultrasonic wave that passed the minor axis direction of the impact damage 41 were recorded. In this example, the length of the optical fiber resonance part is 52 mm, and in signal recording, a low-pass filter process with a cut-off frequency of 1 MHz and an averaging process are performed 512 times.

  FIGS. 13 (a) and 13 (b) show response waveforms for ultrasonic waves that have passed through only the healthy part and ultrasonic waves that have passed through the damaged part, respectively. When both response waveforms are compared, it can be seen that the response level to the ultrasonic wave that has passed through the damaged portion is extremely lowered.

  FIGS. 14A and 14B show the frequency characteristics of the two response waveforms shown in FIGS. 13A and 13B, respectively. A large component intensity appeared in both response waveforms around 250 kHz, which is the center frequency of the ultrasonic oscillator. As shown in FIG. 14 (a), when the ultrasonic wave passed only through the healthy part, the component intensity of 250 kHz or higher was extremely low, and in the frequency band lower than that, a frequency range having a high component intensity appeared discretely. On the other hand, as shown in FIG. 14B, the response waveform to the ultrasonic wave that passed through the damaged portion showed a maximum component intensity at 72.5 kHz corresponding to 1/4 of the oscillator center frequency. Also, a relatively high component intensity appeared at 500 kHz corresponding to twice the ultrasonic frequency.

  In this way, ultrasonic flaw detection can be performed by utilizing the fact that the intensity change of the response waveform appears depending on the presence or absence of damage in the ultrasonic propagation path, or in addition, the characteristic that the frequency characteristic changes. In the present embodiment, ultrasonic flaw detection can be detected with high accuracy by performing frequency filter processing and averaging processing using a low-pass filter and a band-pass filter.

(Sixth embodiment)
In the sixth embodiment, an example in which the ultrasonic detection system described in the first to third embodiments is applied to AE detection will be described. The ultrasonic detection system of this embodiment includes a broadband light source, an optical circulator, an FBG, a photoelectric converter, and a waveform recorder.

  AE is a sudden elastic wave emission accompanying microscopic destruction of a material, and propagates through the material as an elastic wave in the ultrasonic band. That is, AE can be said to be a single pulsed ultrasonic wave. For this reason, AE cannot be detected unless the measurement system can detect ultrasonic waves propagating in the material without averaging. In the second embodiment and the third embodiment, it has been shown that ultrasonic waves can be detected without performing an averaging process (see FIGS. 7A and 8C). In these examples, it is considered that strong ultrasonic waves propagated in the optical fiber because ultrasonic waves were caused to flow from the ultrasonic oscillator into the optical fiber in which the FBG was written.

  In order to verify whether ultrasonic waves propagating in the material can be detected without averaging, an experimental apparatus shown in FIG. 15 was assembled. The AE detection experiment system of FIG. 15 includes a broadband light source 52, an optical circulator 53, an FBG 54, a photoelectric converter 55, an amplifier 56, a filter 57, and a waveform recorder 58. The subject 60 uses an aluminum plate having a thickness of 1 mm. In FIG. 15, the optical fiber contact points are schematically shown as circles as contact points 59. The distance between the contact point of the ultrasonic oscillator 51 and the optical fiber was 150 mm, and an ultrasonic oscillator having a center frequency of 250 kHz was spiked to propagate the ultrasonic wave to the subject 60. In this example, an FBG having a grating length of 20 mm is used, and the length of the optical fiber resonance portion is 22 mm. In some cases, the FBG location in the optical fiber cannot be specified, and in the experiment, a part of the FBG may be adhered to the subject. However, whether or not the FBG is contained in the adhesion location 59 is detected. Has no effect.

  FIG. 16A shows a response signal subjected to low-pass filter processing with a cutoff frequency of 500 kHz and averaging processing 512 times. By averaging the response to the ultrasonic wave that has passed through the subject 60, the ultrasonic wave can be clearly detected. FIG. 16B shows a response waveform that has been subjected to 500 kHz low-pass filter processing without averaging processing. The ultrasonic response cannot be identified by the low-pass filter process without the averaging process.

  FIGS. 17A and 17B show the frequency characteristics of both response waveforms shown in FIGS. 16A and 16B, respectively. FIG. 17A shows a case where low-pass filter processing with a cutoff frequency of 500 kHz and 512 averaging processing are performed, and FIG. 17B shows a case where 500 kHz low-pass filter processing is performed without averaging processing. . 17A and 17B, the maximum component intensity appears in both response signals at 173 kHz. On the other hand, the resonance frequency of the FBG sensor used in this embodiment is calculated by substituting the optical fiber resonance portion length L = 22 mm and the ultrasonic wave propagation velocity v = 5,060 m / s in the optical fiber into the equation (2). Are calculated as 57.5 kHz, 172.5 kHz, 287.5 kHz, and 402.5 kHz in order from the order 0 to the higher order. Therefore, the maximum component intensity appears at the primary resonance frequency, and it is considered that the bandpass filter processing near this resonance frequency is effective for extracting the ultrasonic response buried in the noise.

  Therefore, in FIG. 15, the electrical signal from the photoelectric converter is recorded by the waveform recorder 58 after performing bandpass filter processing with a center frequency of 170 kHz without averaging processing. FIG. 16C shows the recorded response waveform. The amplifier 56 may be appropriately provided as necessary for amplification. According to FIG. 16C, an ultrasonic response with a large amplitude can be confirmed at time zero. From this result, it is understood that it is possible to detect the ultrasonic wave propagating through the subject by performing an appropriate filtering process without the averaging process, and in particular, it is possible to detect the AE based on the present invention. .

  As shown in the fourth embodiment, it is known that an FBG sensor having a resonance structure shows a response having a high component intensity at a resonance frequency close to the frequency of the ultrasonic wave received by the FBG. In FIGS. 17 (a) and 17 (b), a response having a high component intensity appears at the primary resonance frequency. However, when an ultrasonic wave having a lower frequency than this example is received, a high component intensity at the zeroth resonance frequency is obtained. When a high frequency ultrasonic wave is received, it is considered that a response having a high component intensity appears at a secondary or higher resonance frequency.

  From the above, in the apparatus for detecting AE according to the present embodiment, AE generation is performed by performing band pass filter processing of a band centering around a plurality of resonance frequencies of the resonance type FBG sensor on the response signal. It can be detected without omission. As the bandpass filter, for example, a bandpass filter centering on a plurality of resonance frequencies such as 0th order, 1st order, and 2nd order may be used.

(Seventh embodiment)
In the seventh embodiment, a case where an FBG sensor having a non-resonant structure is used is shown.

  The sixth embodiment has already shown that the ultrasonic wave propagating through the subject can be detected without averaging processing using the FBG sensor having a resonance structure, that is, AE detection is possible. In order to demonstrate that the resonance structure of the FBG sensor greatly contributes to the ultrasonic wave and AE detection of the present invention, in the apparatus shown in FIG. 15, the entire FBG is adhered to the subject to form a non-resonance structure. The same experiment as that shown in the sixth embodiment was performed. FIGS. 18A and 18B show a response waveform that has been averaged 512 times after low-pass filter processing with a cutoff frequency of 500 kHz, and a response waveform that has been recorded without averaging after the same filter processing. Even if the FBG sensor has a non-resonant structure, ultrasonic detection is possible by averaging the response signal, but without the averaging process, the ultrasonic response is buried in noise and cannot be identified.

  FIGS. 19A and 19B show the frequency characteristics of the response waveforms shown in FIGS. 18A and 18B, respectively. The frequency characteristic (FIG. 19A) of the response waveform obtained by averaging the non-resonant structure FBG sensor has a wide band and is large at 300 kHz or less as compared with the case of having a resonance structure (FIG. 17A). Ingredient strength appeared. In addition, the frequency characteristic of the response signal without the averaging process (FIG. 19B) is a frequency characteristic having a large component intensity even in a high frequency region exceeding 300 kHz. Had greatly different characteristics. For this reason, in an FBG sensor having a non-resonant structure, it is difficult to find an appropriate filter condition for extracting an ultrasonic response, and it is extremely difficult to detect ultrasonic waves without averaging processing, and is applicable to AE detection. It is considered impossible. An averaging process is effective for vibration detection other than AE.

  From the above, it has been shown that the ultrasonic detection performance is improved by using the FBG sensor as a resonance structure (second to sixth embodiments). On the other hand, in the case of the present embodiment using a non-resonant structure, the ultrasonic response can be extracted only by the averaging process, or by the low-pass filter process and the averaging process.

(Eighth embodiment)
The signal processing for ultrasonic detection shown in the above embodiments can take the following forms. In each embodiment, in order to take out the ultrasonic wave and AE response buried in noise, frequency filter processing is performed before signal recording by the waveform recorder. -The AE response may be taken out. In addition to frequency filter processing for sensor output, spectral subtraction processing for removing background noise components is an effective means for ultrasonic / AE detection and can be provided.

  The FBG sensor having a resonance structure outputs a response signal having a large component intensity at the resonance frequency when receiving ultrasonic waves or AE. Therefore, when recording an ultrasonic wave or AE response using a resonance type FBG sensor, the resonance frequency of the sensor may be set to the measurement signal frequency of the lock-in amplifier, and the lock-in amplifier output may be used as a recording trigger.

  Regardless of whether the structure of the FBG sensor is non-resonant or resonant, the averaging process is an effective means for extracting an ultrasonic response, and can be appropriately combined with the filter process shown in each embodiment.

(Ninth embodiment)
In the ninth embodiment, a case where ultrasonic waves are detected while moving an ultrasonic wave transmission / reception point is shown. In the embodiment already shown, the case where the optical fiber on which the FBG is written is attached to the subject has been shown. However, in many ultrasonic flaw detection, it is more practical and convenient to make both the ultrasonic oscillator and the FBG sensor movable because the defect position is identified while moving the ultrasonic transmission / reception point. A technique for making the FBG sensor movable is disclosed in Patent Document 5, but the sensor unit of the ultrasonic detection system according to the present invention also has a movable part structure similar to that of Patent Document 5 described above, and FBG The sensor can also be movable.

  FIG. 20 shows an apparatus in which the ultrasonic detection system shown in the above embodiment is movable. As shown in FIG. 20, a part of the optical fiber in which the FBG 74 is written is attached to the movable jig 71, and the ultrasonic wave transmitted through the subject 70 is transmitted to the optical fiber via the movable jig 71. For example, a part of the FBG 74 of the optical fiber in which the FBG is written, or a part other than the FBG is bonded to a medium having a low ultrasonic propagation speed or a thin medium having a thickness of 1 mm or less (corresponding to the movable jig 71) at an adhesion point 79. It is preferable that the movable FBG sensor has a resonance characteristic by contacting. An ultrasonic wave or AE propagating through the subject is detected by bringing the movable FBG sensor into contact with the subject 70.

  FIG. 20 illustrates an example of a resonant FBG sensor, but a non-resonant FBG sensor can be attached to a movable jig to form a movable vibration detection system. Specifically, the FBG is brought into contact with a medium having a slower ultrasonic propagation speed than the subject or a thin medium having a thickness of 1 mm or less to form a movable FBG sensor, and the movable FBG sensor is brought into contact with the subject. Thus, the ultrasonic wave or AE propagating through the subject is detected.

  By making the FBG sensor movable, ultrasonic detection and ultrasonic flaw detection can be easily performed.

(Tenth embodiment)
In this embodiment, a case where the above-described embodiment is applied to a system having a plurality of FBGs will be described.

  An apparatus for multipoint measurement using the ultrasonic detection system of the present invention is shown in FIG. 21 includes a broadband light source 82, an optical circulator 83, a plurality of FBGs (1, 2,... N), a photoelectric converter 85, a waveform recorder 88, and an optical switch 89. The amplifier 86 and the filter 87 are provided as necessary. The FBG (1, 2,..., N) on which the broadband light is incident is selected using the optical switch 89.

  An apparatus for simultaneous multipoint measurement using the ultrasonic detection system of the present invention is shown in FIG. 22 includes a broadband light source 92, a plurality of optical circulators 93, a plurality of FBGs (1, 2,... N), a photoelectric converter 95, a waveform recorder 98, and 1 ×. N coupler 99, and amplifier 96 and filter 97 are provided as necessary. Using 1 × N coupler 99, broadband light is simultaneously incident on a plurality of FBGs, the reflected light intensity from each FBG is measured, and the plurality of FBG reflection intensities are simultaneously measured.

An apparatus for simultaneous multipoint measurement using the ultrasonic detection system of the present invention is shown in FIG. 23 includes a broadband light source 102, an optical circulator, a plurality of FBGs (1, 2,... N), a photoelectric converter 105, a waveform recorder 108, and an optical demultiplexer 109. The amplifier 106 and the filter 107 are provided as necessary. The simultaneous multipoint measurement apparatus of FIG. 23 passes reflected light from a plurality of FBGs having different Bragg wavelengths through optical demultiplexers 109 having different output lines depending on the wavelengths, and sets the reflected light intensity from each FBG to different lines (λ ₁ , λ ₂ ,... Λ _n ), and the reflected light intensity from each FBG is measured, thereby simultaneously measuring a plurality of FBG reflection intensities.

  In the above embodiment, an example in the case of an ultrasonic band exceeding 20 kHz has been shown, but an audible range vibration of 20 kHz or less can be similarly detected. In the case of a resonance type FBG sensor, the resonance frequency can be given to an audible range of 20 kHz or less by adjusting the length of the optical fiber resonance part. The ultrasonic detection system of the present invention can be applied to devices such as defect detection by ultrasonic flaw detection, damage occurrence detection by AE detection, and machine abnormality detection by vibration detection shown in the embodiments.

  In the present invention, the signal processing shown in each embodiment can be implemented in appropriate combination. In addition, the example shown by the said embodiment etc. was described in order to make invention easy to understand, and is not limited to this form.

  The present invention is useful for defect detection by ultrasonic flaw detection, damage occurrence detection by AE detection, machine abnormality occurrence detection by vibration detection, and the like.

2, 12, 22, 32, 52, 72, 82, 92, 102 Broadband light source 3, 13, 23, 33, 53, 73, 83, 93 Optical circulator 4, 14, 24, 34, 54, 74 FBG
5 Optical filter 6, 15, 25, 35, 55, 75, 85, 95, 105 Photoelectric converter 7, 18, 28, 38, 58, 88, 98, 108 Waveform recorder 11, 21, 31, 51 Ultrasound Oscillator 16, 26, 36, 56, 86, 96, 106 Amplifier 17, 27, 37, 57, 87, 97, 107 Filter 19, 29, 39, 59, 79 Bonded point 40, 60, 70 Subject 41 Impact Damage 42 Ultrasound 62 Ultrasound or AE
71 Moving jig 89 Optical switch 99 1 × N coupler 109 Optical demultiplexer

Claims (17)

A system for detecting vibration in the ultrasonic range from the audible range,
A broadband light source;
A fiber Bragg grating (hereinafter referred to as FBG) on which broadband light from the broadband light source is incident;
A photoelectric conversion unit that converts the intensity of reflected light from the FBG into an electrical signal;
A signal processing unit that performs signal processing on the electrical signal to extract a response signal based on vibration received by the FBG;
A vibration detection system comprising:   The vibration detection system according to claim 1, wherein the signal processing is at least one of averaging processing and frequency filtering processing.   In the vibration detection system, a part of the FBG of the optical fiber in which the FBG is written or a part other than the FBG is brought into contact with the subject, the FBG sensor has resonance characteristics, and the vibration is brought into contact with the subject. 3. The vibration detection system according to claim 1, wherein the vibration detection system is caused to flow into the optical fiber.   The vibration detection system according to claim 3, wherein the frequency filter process is a band-pass filter process in the vicinity of a resonance frequency band based on the resonance characteristics.   The vibration detection system according to claim 2, wherein the frequency filter process is a low-pass filter process.   The vibration detection system according to claim 2, wherein the frequency filter process is a band-pass filter process.   The frequency filtering process is a process of passing a resonance frequency determined based on the length of the optical fiber resonance part between the contact point with the subject and the free end in the optical fiber in which the FBG is written. The vibration detection system according to claim 2.   The vibration detection system according to claim 7, wherein the resonance frequency is controlled by adjusting a length of the optical fiber resonance unit.   The vibration detection system according to claim 1, wherein multipoint measurement is performed by providing a plurality of the FBGs.   The movable FBG sensor is brought into contact with the subject by contacting the FBG with a medium having an ultrasonic wave propagation speed slower than that of the subject or a medium of 1 mm or less, and the movable FBG sensor is brought into contact with the subject. The vibration detection system of any one of thru | or 9.   A movable FBG sensor having a resonance characteristic by bringing a part of the FBG of the optical fiber in which the FBG is written, or a part other than the FBG into contact with a medium having an ultrasonic wave propagation speed slower than the subject or a medium of 1 mm or less. The vibration detection system according to any one of claims 2 to 9, wherein the movable FBG sensor is brought into contact with a subject.   The vibration detection system according to claim 1, wherein the vibration is an ultrasonic wave or an acoustic emission.   2. The vibration detection system according to claim 1, wherein an optical filter for detecting a Bragg wavelength change is not used.   An ultrasonic flaw detector comprising the vibration detection system according to claim 1.   A material soundness evaluation apparatus for evaluating the soundness of a subject by measuring an ultrasonic wave propagation state using the vibration detection system according to any one of claims 1 to 13.   A material soundness evaluation apparatus for detecting acoustic emission generated at the time of material destruction by using the vibration detection system according to any one of claims 1 to 13, and evaluating the soundness of an object. .   Broadband light including an FBG reflection wavelength region is incident on the FBG, the reflected light intensity from the FBG is converted into an electric signal, and a response signal based on vibrations received by the FBG is extracted from the electric signal. A vibration detection method characterized by detecting vibration by performing processing.

Images