JP2010112867A - Vibration or elastic wave detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a vibration or elastic wave detector for improving a signal noise ratio of AE, ultrasonic response or response signals for vibration by having a simple structure. <P>SOLUTION: The vibration or elastic wave detector for making wide band light including a reflective wavelength region of a receiving part FBG1 and a filter part FBG2 incident on the receiving part FBG1 and the filter part FBG2 and measuring vibration or elastic waves received with the receiving part FBG1 from intensity change of transmission light or reflection light of the receiving part FBG1 and the filter part FBG2 attaches the receiving part FBG1 and the filter part FBG2 to a specimen 7 so that reflection light distribution of the receiving part FBG1 and the filter part FBG2 is always intersected even when the receiving part FBG1 receives temperature change or strain. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vibration or elastic wave detection device.

  The present invention relates to a vibration or elastic wave detection device that detects vibration, strain, acoustic emission (AE), and ultrasonic waves using a fiber Bragg grating (FBG), and is applied to structural soundness evaluation, etc. Related to the technology that can be.

  Conventionally, strain gages and piezoelectric elements have been widely used for detecting vibrations and elastic waves, respectively. However, since strain gauges and piezoelectric elements are subject to electromagnetic interference, vibration and elastic wave measurement cannot be performed in an electromagnetic wave atmosphere. In addition, since the piezoelectric element has a narrow response frequency characteristic, there is a drawback that it is necessary to change the type of the piezoelectric element in accordance with the vibration or elastic wave frequency band to be detected.

  In recent years, a vibration or elastic wave measurement technique using an FBG, which is a kind of optical fiber sensor, has been attracting attention in order to solve the above-described problem of vibration or elastic wave measurement using a strain gauge or a piezoelectric element. The FBG has a structure in which the refractive index is slightly changed periodically in the fiber axis direction of the core, which is a light guide path of the optical fiber, and narrow band light centered on the Bragg wavelength λB given by the following equation (1). It has a reflective feature.

λB = 2nΛ (1)
Here, n and Λ represent the refractive index of the core and the periodic interval of the refractive index change.

  It is known that when an FBG is subjected to strain or temperature change, its Bragg wavelength changes in proportion to strain or temperature. Therefore, when the FBG receives an elastic wave (AE or ultrasonic wave) that causes minute and high-speed strain vibration, the Bragg wavelength of the FBG vibrates in synchronization with the elastic wave.

  FIG. 1 shows a vibration or elastic wave detection system using broadband light used as a light source and FBG as a sensor. Broadband light including the reflection wavelength region of the FBG sensor is incident on the FBG sensor via the optical circulator 4, and reflected light from the FBG sensor is incident on the optical filter via the optical circulator 4.

  The light transmitted through the optical filter or the reflected light is incident on the photoelectric converter 5 and the light intensity is converted into an electric signal. The fluctuation of the Bragg wavelength of the FBG due to the elastic wave reception is a minute level of 1 pm (picometer, minus 10 to the power of 12) or less. In order to detect the vibration of this minute Bragg wavelength with high sensitivity, the optical filter needs to have a steep characteristic change in the vicinity of the Bragg wavelength of the FBG and in a narrow wavelength range of several pm to several tens of pm.

  An FBG having a Bragg wavelength of 1550 nm under room temperature and unstrained conditions changes the Bragg wavelength by about 14 pm per 1 ° C. and about 1.2 pm per micro strain. Therefore, when the wavelength at which the optical characteristics of the optical filter change is fixed in the system shown in FIG. 1, when the FBG sensor is subjected to a temperature change of 10 ° C. or more, or a strain change exceeding 100 microstrain, the Bragg of the FBG sensor The wavelength deviates from the narrow band characteristic change wavelength region of the optical filter, and the elastic wave cannot be detected.

  Therefore, it is necessary to use a wavelength tunable filter as the optical filter, and to control the characteristic change wavelength range of the optical filter in accordance with the fluctuation of the Bragg wavelength accompanying the temperature and strain change of the FBG sensor. However, it takes at least about 1 second to evaluate the Bragg wavelength using a commercially available measuring instrument and to control the tunable filter based on the result.

  For this reason, it is impossible to detect an elastic wave by a system using a wavelength tunable filter in a member that receives a vibration that gives a continuous strain change. Another disadvantage of this system is that the tunable filter is expensive.

  The inventor of the present invention uses a Fabry-Perot filter having a periodic transmission band for each wavelength FSR as an optical filter in Japanese Patent Application Laid-Open No. 2008-046036. The FBG sensor undergoes large distortion or temperature change, and the Bragg wavelength greatly fluctuates. However, an invention that can always detect elastic waves has been proposed (see Patent Document 1).

  In the present invention, a temperature controller is used to set the transmission ranges of two Fabry-Perot filters having an FSR equivalent to the reflection wavelength width of the FBG so as to differ by FSR / 4. By arranging two Fabry-Perot filters satisfying the above specifications in parallel in FIG. 1 as an optical filter, even if the FBG sensor is subjected to distortion or temperature change, the Bragg wavelength fluctuates. The transmission region of either Fabry-Perot filter always exists in the wavelength region where the reflection characteristic changes monotonously, and the elastic wave can always be detected.

JP2008-046036

  The invention described in Patent Document 1 requires a Fabry-Perot filter and a temperature controller for controlling the transmission region thereof, so that the apparatus itself is expensive. In the elastic wave measurement system using the above-described wavelength tunable filter and Fabry-Perot filter, it is necessary to arrange these devices for each channel. Therefore, it becomes a very expensive device when performing elastic wave measurement with multiple channels.

  The present invention aims to solve the above-mentioned conventional problems, and realizes a vibration or elastic wave detection device that has a simple configuration and can improve the signal-to-noise ratio of the response signal to the elastic wave response and vibration. The task is to do.

  In order to solve the above-described problem, the present invention makes broadband light including the reflection wavelength range of the reception unit FBG and the filter unit FBG incident on the reception unit FBG and the filter unit FBG, or the transmitted light of the reception unit FBG and the filter unit FBG or In the vibration or elastic wave detection device that measures the vibration or elastic wave received by the receiving unit FBG from the intensity change of the reflected light, the reflected light distribution of the receiving unit FBG and the filter unit FBG remains even if the receiving unit FBG is subjected to distortion or temperature change. Provided is a vibration or elastic wave detection device in which a reception unit FBG and a filter unit FBG are attached to a subject so as to always intersect.

  In order to solve the above-described problem, the present invention makes broadband light including the reflection wavelength range of the reception unit FBG and the filter unit FBG incident on the reception unit FBG and the filter unit FBG, or the transmitted light of the reception unit FBG and the filter unit FBG or In a vibration or elastic wave detection device that measures vibration and distortion received by the receiving unit FBG from intensity change of reflected light, the vibration or elasticity that causes the FBG that is a filter to receive the temperature change received by the receiving unit FBG equally. A wave detection device is provided.

  A configuration may be adopted in which one FBG has two functions of the receiving unit FBG and the filter unit FBG by introducing local distortion into one FBG to have two peaks in reflection characteristics.

  The vibration or elastic wave detection device of the present invention is used to detect vibration or elastic waves at an arbitrary location.

  According to the present invention, it is possible to obtain a vibration or elastic wave detection device that has a simple configuration and that can improve the signal-to-noise ratio of the response signal to the elastic wave response and vibration.

  DESCRIPTION OF EMBODIMENTS Embodiments of an elastic wave measuring apparatus and a measuring method according to the present invention will be described below with reference to the drawings based on examples.

  FIG. 2 is a diagram illustrating the overall configuration of the present invention. As shown in FIG. 2, in the present invention, a receiving unit 1 made of FBG (hereinafter referred to as “receiving unit FBG”) and a filter unit 2 made of FBG (hereinafter referred to as “filter unit FBG”) are provided. ing. In FIG. 2, even if the order of the receiving unit FBG1 and the filter unit FBG2 is reversed, the function of detecting vibrations or elastic waves described below does not change.

  Broadband light including the reflection wavelength range of the receiving unit FBG1 and the filter unit FBG2 is incident on the receiving unit FBG1 and the filter unit FBG2 via the optical circulator 4 from the broadband light source 3, and reflected light from the receiving unit FBG1 and the filter unit FBG2 Is incident on a photoelectric converter 5 that converts light intensity into an electric signal via an optical circulator 4 and is connected to a device (signal recording / display device) 6 that records the electric signal and displays it as necessary. .

  When the receiving unit FBG1 and the filter unit FBG2 are arranged in series as shown in FIG. 2, the reflected light intensity from the receiving unit FBG1 and the filter unit FBG2 incident on the photoelectric converter 5 in FIG. And the area surrounded by the reflected light intensity distribution curve of the filter unit FBG2.

  In a non-distorted state at a certain temperature of the subject, the reflected light distribution of the receiving unit FBG1 and the filter unit FBG2 is represented by FIG.

  Consider a case where an elastic wave arrives at the receiving unit FBG1 and a strain change in which minute tension and compression alternately appear in the receiving unit FBG1. When the receiving unit FBG1 is pulled, as shown in FIG. 3B, the Bragg wavelength of the receiving unit FBG1 is shifted to the long wavelength side, the area where both reflected light distribution curves intersect is reduced, and both reflected light is reflected. Since the area surrounded by the distribution curve increases, the output of the photoelectric converter 5 increases.

  On the contrary, when the receiving unit FBG1 is compressed, as shown in FIG. 3C, the area surrounded by the both reflected light distribution curves decreases, and thus the output of the photoelectric converter 5 decreases. As described above, when the reflected light distributions of the reception unit FBG1 and the filter unit FBG2 always intersect, an elastic wave can be detected based on the principle described above.

  However, if the reflected light distribution curves of the receiving unit FBG1 and the filter unit FBG2 are subjected to a large distortion or temperature change so as to be completely separated, the reflected light distribution curves do not intersect, so that even if the receiving unit FBG1 receives an elastic wave, No change appears in the converter 5 output. Strain and temperature change (Reference: FBG reflected light distribution is not only thermal strain caused by thermal expansion due to temperature change, but also the photoelastic constant, which is the optical characteristic of optical fiber, depends on temperature. Regardless of the change in the elastic constant, the Bragg wavelength fluctuates.) Regardless of whether the Bragg wavelength fluctuates, the following two methods are conceivable as means for constantly intersecting the reflected light distributions of the receiving unit FBG1 and the filter unit FBG2 as shown in FIG.

  The first means allows a strain to remain in a part of the FBG by fixing a part of the FBG to the surface of the subject with an adhesive or by embedding and fixing the FBG inside the subject. That is, as shown in FIG. 26, a part of one FBG is bonded or embedded in a subject to form a receiving unit FBG1, and the remaining non-bonded or non-embedded unit is used as a filter unit FBG2. In this configuration, the receiving unit FBG1 and the filter unit FBG2 are continuous in the optical fiber axial direction, and the bonding or embedding interface is the interface between the receiving unit FBG1 and the filter unit FBG2.

  Thus, by giving a residual strain to a part of the FBG, two different strain states exist in the FBG. Therefore, reflected light distributions of two different Bragg wavelengths appear, and the two reflected light distributions can be crossed by controlling the residual strain. Residual strain applied to the FBG can be controlled by adjusting the bonding force of the FBG, or the pressing force at the time of embedding, and the tensile or compressive force in the optical fiber axial direction.

  As shown in FIG. 27, the second means uses two FBGs as the receiving unit FBG1 and the filter unit FBG2, respectively, and attaches both FBGs on the surface of the subject or inside so that the reflected light distributions of both FBGs intersect each other. .

  Here, an example of a structure for attaching the receiving unit FBG1 and the filter unit FBG2 to a specific subject will be described below.

Structural example 1:
In FIG. 4A, the two individual FBGs are used as the receiving unit FBG1 and the filter unit FBG2 so that the reflected light distributions of the two FBGs intersect as shown in FIG. 7 is attached inside.

  Even if the subject 7 is subjected to temperature and strain changes, it is attached to a location where there is no difference in the temperature and strain received by the receiving unit FBG1 and the filter unit FBG2 so that both reflected light distributions intersect. In addition, when the distortion and temperature change received by the receiving unit FBG1 are very small and the conditions where the two reflected light distributions cross each other are not destroyed, an attachment structure in which the filter unit is not bonded is also possible.

Structural example 2:
As shown in FIG. 4B, a plate (referred to as a waveguide plate) for guiding an elastic wave propagating through the subject 7 without transmitting the strain received by the subject 7 is attached to the subject 7, and the waveguide plate The two individual FBGs are bonded as the receiving unit FBG1 and the filter unit FBG2 so that the reflected light distributions of the two FBGs intersect as shown in FIG.

  In addition, by using a member having the same thermal expansion coefficient as that of the optical fiber for the waveguide plate 8, even if the filter unit FBG2 is not bonded to the waveguide plate 8, the reception unit FBG1 and the filter unit FBG2 are the same due to temperature changes. It will be subject to Bragg wavelength change. For this reason, even if a temperature change occurs, the condition where the reflected light distributions of the reception unit FBG1 and the filter unit FBG2 intersect is not broken.

Structure example 3:
As shown in FIG. 4C, this attachment structure is attached so that the part adhered to the waveguide plate 8 attached to the subject 7 becomes the receiving part FBG1, and the non-adhesive part becomes the filter part FBG2. By giving local residual distortion to the receiving unit FBG1, two peaks as shown in FIG. 3 exist, and an FBG having reflection characteristics in which both reflected light distributions intersect can be configured. In FIG. 4C, the function does not change even if the bonded receiver FBG 1 is coupled to the optical circulator 4 or the non-adhered filter unit FBG 2 is coupled to the optical circulator 4.

  At this time, when a member having a coefficient of thermal expansion different from that of the optical fiber is used for the waveguide plate 8, the Bragg wavelength change received by the receiving unit FBG1 and the filter unit FBG2 differs depending on the temperature change. For this reason, there is a possibility that the condition where the reflected light distributions of the reception unit FBG1 and the filter unit FBG2 that are necessary for elastic wave detection intersect is broken. When a member having the same coefficient of thermal expansion as that of the optical fiber is used for the waveguide plate 8, the Bragg wavelength change that both undergo with the temperature change is the same, and the elastic wave detection sensitivity can be maintained.

  As described above, when the receiving unit FBG1 and the filter unit FBG2 are attached to the waveguide plate 8, the distortion change received by the subject 7 does not affect the Bragg wavelengths of the receiving unit and the filter unit FBG2 at all. Even if the temperature changes, by using a member having the same coefficient of thermal expansion as that of the optical fiber for the waveguide plate 8, the Bragg wavelengths of the receiving unit and the filter unit FBG2 are similarly changed. That is, the condition for detecting the elastic wave can be maintained without breaking the condition in which the two reflected light distributions necessary for the elastic wave detection intersect regardless of the temperature or strain change received by the subject 7.

  Further, when the distortion or temperature change received by the receiving unit FBG1 is very small and the conditions where the two reflected light distributions intersect do not break, the receiving unit FBG1 is bonded without using the waveguide plate 8 as shown in FIG. It may be configured to be directly attached to the subject 7 together with the filter unit FBG2 in a state in which local residual strain is given by being fixed to the subject 7 with an agent.

Structural example 4:
When a material having a sound velocity lower than that of the subject 7 is brought into contact with the surface of the subject 7 via a coupling agent such as water, it functions as an acoustic wave waveguide plate 8 (Japanese Patent Laid-Open No. 2006-132952). Further, the wave guide plate 8 functions as the plate thickness is reduced regardless of the speed of sound with the subject 7.

  For example, as shown in FIG. 4 (d), two individual FBGs are provided on the waveguide plate 8 as a receiving unit FBG1 and a filter unit FBG2, so that the reflected light distributions of the two FBGs intersect as shown in FIG. Adhere to. The waveguide plate 8 to which the receiving unit FBG1 is attached can be attached to an arbitrary portion of the subject 7 and functions as a movable elastic wave detection unit.

  When a member having the same coefficient of thermal expansion as that of the optical fiber that does not break the condition that the reflected light distributions of the receiving unit FBG1 and the filter unit FBG2 intersect even when the temperature is changed is used as the waveguide plate 8, the filter An attachment structure in which the portion FBG2 is not bonded to the waveguide plate 8 is also possible.

  The waveguide plate 8 in which the reception unit FBG1 and the filter unit FBG2 that have crossed reflected light distributions by giving local residual strain are pasted as shown in FIG. 29 has a minute temperature change and the reflected light distributions intersect. If the conditions to be used are not broken, or a member having the same coefficient of thermal expansion as that of the optical fiber is used for the waveguide plate 8, it functions as a movable elastic wave detector.

  When the receiving unit FBG1 and the filter unit FBG2 are attached to the subject 7 or the waveguide plate 8, broadband light is incident on the receiving unit FBG1 and the filter unit FBG2, and is received from the receiving unit FBG1 and the filter unit FBG2 using an optical spectrum analyzer. It is preferable to work while confirming the intersection of the reflected light distributions.

Structural example 5:
By attaching the receiving unit FBG1 and the filter unit FBG2 to the subject 7 so as to receive the same temperature, it is possible to measure distortion of the subject 7 due to audible vibration and deformation. As a structural example for giving the same temperature change to the filter unit FBG2 as the receiving unit FBG1 and transmitting the strain received by the subject 7 to the receiving unit FBG1, two points of the subject 7 as shown in FIGS. Are connected by a member having the same coefficient of thermal expansion as that of the optical fiber, only the FBG receiving unit is adhered to the connecting member, and the filter unit FBG2 is installed in a range that receives the same temperature as the receiving unit.

  In FIG. 5A, the receiving unit FBG1 and the filter unit FBG2 are each configured by an individual FBG. FIG. 5B shows a detection unit in which the reception unit FBG1 and the filter unit FBG2 are configured by a single FBG by introducing local residual strain into the reception unit FBG1, and the single FBG has two functions. Represents.

  If the temperature change can be ignored, vibration and strain can be measured by attaching the receiving unit FBG1 to the surface of or inside the subject 7 as shown in FIG. It is.

Structural example 6:
As shown in FIG. 5C, it is possible to directly attach the receiving unit FBG1 and the filter unit FBG2 without using the waveguide plate 8 as the vibration / strain detecting unit. The receiving unit FBG1 and the filter unit FBG2 are attached to different portions of the subject 7. At this time, both FBGs are installed to receive the same temperature. It is possible to measure the difference in strain at the location where the receiving unit FBG1 and the filter unit FBG2 are attached. 4 and 5 show a common structure, FIG. 4 is a sensor structure for elastic wave measurement, and FIG. 5 is a sensor structure for strain / vibration measurement.

  When two FBGs are used for the reception unit and the filter unit, the grating length of the filter unit FBG2 is made shorter than that of the reception unit FBG1, or by using a chirp FBG for the filter, as shown in FIG. In comparison, the filter section FBG2 can have reflection characteristics in a wide wavelength range.

  As shown in FIG. 6, when the filter unit FBG2 has a reflection characteristic in a wider wavelength range than the reflection characteristic of the reception unit, the reflected light intensity from the reception unit FBG1 and the filter unit FBG2 is the Bragg wavelength of the reception unit FBG1. This is proportional to the height of the reflectance of the filter unit FBG2.

  Therefore, since the Bragg wavelength change accompanying the distortion change of the receiving unit FBG1 can be detected as the reflected light intensity from the receiving unit FBG1 and the filter unit FBG2, the combination of two FBGs having optical characteristics as shown in FIG.・ It will function as a strain detection sensor. In such a sensor, by combining FBGs having different reflection characteristics, a strain range in which vibration / strain measurement is possible can be controlled.

  A part of the FBG is attached to the subject 7 with an adhesive, and a local residual strain is introduced into the FBG so that the reflection characteristic has two peaks. An experiment that has two functions and detects an elastic wave propagating through the subject 7 will be described below as a first embodiment.

  FIG. 7 shows the vibration or elastic wave detection device of the first embodiment. In the first embodiment, an aluminum plate is used as the subject 7 for propagating the elastic wave, and a half-length portion of the FBG is fixed to the subject 7 with an adhesive material to form the receiving unit FBG1, and the remaining non-adhered FBG. Was defined as a filter unit FBG2. An ultrasonic excitation signal is sent from the signal generator 10 to the ultrasonic oscillator 9, and the ultrasonic wave is propagated from the ultrasonic oscillator 9 to the subject 7.

  On the other hand, the broadband light from the broadband light source 3 is incident on the receiving unit FBG1 and the filter unit FBG2 through the optical circulator 4, and the reflected light from the receiving unit FBG1 and the filter unit FBG2 is sent to the photoelectric converter 5 through the optical circulator 4, Therefore, the reflected light intensity is converted into an electric signal. The output of the photoelectric converter 5 is sent to the signal recording / display device 6 through the signal amplifier 11 and the electric signal filter 12.

  The ultrasonic wave propagating through the subject 7 passes through the receiving unit FBG1 bonded to the subject 7, and the reflected light distribution of the receiving unit FBG1 vibrates in synchronization with the ultrasonic vibration. On the other hand, since the reflected light distribution of the filter unit FBG2 is fixed without being affected by the ultrasonic wave, the output of the photoelectric converter 5 changes in synchronization with the ultrasonic vibration as described with reference to FIG. Become.

  In the first embodiment, the receiving unit FBG1 is distorted by distorting the aluminum plate which is the subject 7 so that the ultrasonic detection sensitivity is maximized, and the ultrasonic wave detection sensitivity is maximized. The reflection characteristics of FBG1 were controlled.

  FIG. 8 shows the reflection characteristics of the receiving part FBG1 before bonding to the subject 7 and the receiving part and the filter part when the ultrasonic detection sensitivity is maximized by bonding a part of the FBG as in the first embodiment. The FBG reflection characteristics having two functions are shown in comparison. There was one reflected light peak in the reflected light distribution before adhering to the subject 7. When a part of the FBG is bonded to the subject 7, two reflection peaks appear from the receiving unit FBG1 that is the bonded unit and the filter unit FBG2 that is the non-bonded unit by applying distortion to the bonded unit (FIG. 8).

  When the reflected light distributions of the receiving unit FBG1 and the filter unit FBG2 are schematically shown, they can be expressed as shown in FIG. The high reflectance, that is, the reflected light intensity is different because the grating lengths of the receiving unit and the filter unit are different.

  FIG. 10 shows a response signal in which the ultrasonic wave propagated through the subject 7 is detected by a vibration or elastic wave detection device as shown in FIG. In addition, in the ultrasonic response waveform recording, the averaging process was performed 512 times. The response waveform when the filter processing is not performed is shown at the bottom of FIG. A signal appearing after the test time of 0 ms is a response to the ultrasonic wave.

  FIG. 11 shows the result of examining the frequency component intensity of the unfiltered signal. In this case, a high frequency component intensity appeared below 400 kHz. Therefore, low-frequency pass processing was performed using an electric signal filter. The top five response waveforms after the low-frequency pass processing from 100 to 500 kHz are shown in FIG. By performing the filtering process using the electric signal filter as described above, it becomes possible to detect the ultrasonic response more clearly using the vibration or elastic wave detection device.

  For the purpose of simulating the detection of AE that occurs due to the destruction of the material, an experiment in which AE that occurs when the mechanical pencil core is crushed will be described as Example 2. The vibration or elastic wave detector used in FIG. 7 performed a mechanical pencil core collapse on the subject 7 instead of the ultrasonic oscillator, and propagated the pseudo AE to the subject 7.

  Other than that, the same vibration or ultrasonic detection device as in FIG. 7 is used. However, since AE signal detection accompanying accidental material destruction is simulated, averaging processing is not performed in response waveform recording.

  FIG. 12 shows a pseudo AE response waveform at the time of mechanical pencil crushing. The bottom of FIG. 12 is a response waveform when the filtering process by the electric signal filter 12 is not performed. It is not possible to identify whether the pseudo AE has been detected due to noise.

  FIG. 13 shows the frequency component intensity of this unfiltered waveform. This response waveform not subjected to the averaging process contains a lot of noise components, and a wide frequency characteristic appears. However, in general, the AE associated with the occurrence of destruction is sufficient for detecting the destruction if a band of several hundred kHz or less is measured. Therefore, the response signal at the time of the pencil core folding was subjected to low-frequency pass filter processing using 50 kHz, 100 kHz, and 200 kHz as cutoff frequencies.

  The results are shown in the upper three graphs of FIG. By performing the low-frequency pass filter processing in this way, it becomes possible to detect the pseudo AE signal buried in the high-frequency noise using the main vibration or elastic wave detection device.

  In the vibration or elastic wave detection device described in the first and second embodiments, the reflected light distributions of the reception unit and the filter unit FBG2 that can detect elastic waves intersect each other by applying local residual strain to one FBG. The reflected light distribution is given as follows.

  Since the reflection characteristics having such characteristics can be realized by the FBG mounting structures shown as the structural examples 1 to 4 above, the elastic waves can be similarly detected by these mounting structures.

  An experiment in which vibration is measured by attaching an FBG with a local residual strain introduced to the subject 7 will be described as Example 3. As shown in FIG. 14, the vibration or elastic wave detection apparatus used has a length of about half of the FBG 13 attached to the surface of the subject 7 with the adhesive 14, and the rest is distorted without being adhered to the subject 7. There was no state.

  Since the FBG of the bonded portion receives the same strain as the subject 7, it functions as the receiving portion FBG 1, and the FBG of the non-bonded portion converts the fluctuation of the Bragg wavelength accompanying the strain of the bonded portion FBG into a reflected light intensity. It will play the role of FBG2.

  The broadband light is incident on the receiving unit FBG1 and the filter unit FBG2 through the optical circulator 4, and the reflected light from the receiving unit FBG1 and the filter unit FBG2 is incident on the photoelectric converter 5 through the optical circulator 4, and the light intensity. Is converted into an electrical signal and stored in the signal recording / display device 6.

  The output of the photoelectric converter 5 was recorded when the subject 7 was cantilevered as shown in FIG. 14 and subjected to free vibration by applying a bending load to the free end. For reference, a strain gauge was attached next to the receiving unit FBG1 (bonding unit 14), and strain was recorded at the same time.

  FIG. 15 shows the strain measured from the output of the photoelectric converter 5 and the strain gauge during free vibration of the cantilever. With the increase in tensile strain when a bending load at the start of the test was applied, the output rate of the photoelectric converter 5 decreased after exceeding a certain strain, and the maximum output was shown at the maximum tensile strain.

  Thereafter, with respect to the strain change in which tension-compression appears periodically due to free vibration, the output of the photoelectric converter 5 up to a test time of about 5 seconds showed a response behavior that was not synchronized with the periodic strain change. However, after that, periodic photoelectric converter 5 output consistent with the strain change was observed.

  The response when the output of the photoelectric converter 5 that does not synchronize with the periodic strain change appears is shown in an enlarged manner in FIG. The maximum point of the photoelectric converter 5 output corresponds to the maximum or the minimum point of distortion. The minimum point of the photoelectric converter 5 output is when it receives a compressive strain of about 30 microstrain.

  From such a photoelectric converter 5 output-distortion relationship, the reflected light distribution change of the receiving unit FBG1 and the filter unit FBG2 due to the distortion is considered as follows. As described with reference to FIG. 3, the intensity of reflected light from the receiving unit FBG1 and the filter unit FBG2 is proportional to the area surrounded by the respective reflected light distribution curves.

  In the undistorted state, as shown in FIG. 18C, the Bragg wavelength of the receiving unit FBG1 is longer than that of the filter unit FBG2, and the reflected light distributions of both of them intersect. When subjected to compression, the Bragg wavelength of the receiving unit FBG1 shifted to the low frequency side as shown in FIG.

  At this time, since the area surrounded by the both reflected light distribution curves was reduced as compared with the case of 18 (c), the reflected light intensity was lowered. When subjected to compression of about 30 microstrain, the reflected light distribution from the reception unit FBG1 and the filter unit FBG2 shifts to the reflection distribution of FIG. 18 (e), and the reflected light intensity is minimized.

  When further compressed, the Bragg wavelength of the receiving unit FBG1 is shifted to a lower wavelength side than that of the filter unit as shown in FIG. 18 (f), and the reflected light intensity increases because the area where the reflected light distribution overlaps increases. . After that, when the compressive strain changed to the tensile strain, the two reflected light distributions changed from FIG. 18 (f) to FIG. 18 (b). As in the case of compression, the reflected light intensity reached a maximum at the maximum point of tensile strain.

  Both response behaviors when the strain and the output of the photoelectric converter 5 show a periodic change in synchronization are enlarged and shown in FIG. It is considered that the positional relationship between the reflected light distributions of the receiving unit FBG1 and the filter unit FBG2 in this vibration has changed in the range from FIG. 18 (b) to FIG. 18 (d).

  The reason why the output increase rate of the photoelectric converter 5 decreased when the strain increased linearly around the test time of 2 seconds when the tensile strain due to bending was first applied is as follows. When the receiving unit FBG1 is subjected to a large tensile strain, ideally the reflected light distributions from the receiving unit FBG1 and the filter unit FBG2 should be separated as shown in FIG.

  However, in the third embodiment, half of one FBG is the receiving unit FBG1, and the rest is the filter unit FBG2. In such a configuration, the reflected light distribution actually obtained when the receiving unit FBG1 is subjected to a large tensile strain is the receiving unit FBG1 like the reflected light distribution when the 300 micro tensile strain in FIG. Although the reflection peaks of the filter unit FBG2 are far apart, both distributions intersect without being separated in a region where the reflection intensity is low.

  And in the 400 micro tensile strain given a larger strain, there is a large reflected light distribution corresponding to the receiving unit FBG1 and the filter unit FBG2 on the long wavelength side and the short wavelength side, but there is a small reflection peak in the middle. Appears. In this way, when the receiving unit FBG1 and the filter unit FBG2 are configured by one FBG, when receiving a large strain, the reflected light distribution is not completely separated, and the region where the reflected light intensity is low spreads. Become.

  Thus, in the region of a large tensile strain that causes the region of low reflected light intensity to expand, the output of the photoelectric converter 5 increases while decreasing the increase rate as the strain increases. When the receiving unit FBG1 and the filter unit FBG2 are configured by individual FBGs, it is considered that the reflected light distribution is completely separated and the output of the photoelectric converter 5 is saturated when subjected to a large strain.

  From these experimental results, the following can be said. Consider a case where the receiving unit FBG1 and the filter unit FBG2 are configured by individual FBGs, and the Bragg wavelength of the receiving unit FBG1 is on the longer wavelength side than that of the filter unit FBG2. When the receiving unit FBG1 is compressed and shifted to a lower wavelength side than the Bragg wavelength of the filter unit FBG2, the phase of the response to vibration is inverted.

  Conversely, when the receiving unit FBG1 is pulled and the Bragg wavelength of the receiving unit FBG1 shifts to the long wavelength side, and the reflected light distributions of the receiving unit FBG1 and the filter unit FBG2 are completely separated, the output of the photoelectric converter 5 Is saturated. Here, the case where the Bragg wavelength of the receiving unit FBG1 is on the longer wavelength side than that of the filter unit FBG2 has been described, but the same applies to the reverse relationship.

  When it is desired to determine whether or not the distortion exceeds a certain value, the Bragg wavelength shift amount of the receiving unit FBG1 resulting from the distortion is set to the Bragg wavelength difference between the receiving unit FBG1 and the filter unit FBG2 in the undistorted state, or the receiving unit FBG1. And the reflected light distribution of the filter unit FBG2 are set to be completely separated.

  By controlling the residual strain applied to the receiving unit FBG1 when the receiving unit FBG1 and the filter unit FBG2 are attached to the strain measurement object (subject 7), and using the receiving unit FBG1 and the filter unit FBG2 having different reflection characteristics. The Bragg wavelength difference between the receiving unit FBG1 and the filter unit FBG2 and the wavelength difference for separating the reflected light distribution can be easily controlled.

  By using the FBG having such a reflection characteristic, the output of the photoelectric converter 5 synchronized with the strain caused by the vibration can be obtained below the strain serving as the threshold. And when distortion more than a threshold value arises, a phase inversion behavior (refer FIG. 16) and saturation will appear in the output of the photoelectric converter 5, and it can identify that the overstrain was added.

  In strain and vibration measurement by the vibration or elastic wave detection device of the third embodiment, a local residual strain is given to one FBG to give a reflected light distribution having two peaks. Since the reflection characteristics having such characteristics can also be realized by the FBG mounting structure described in Structural Example 5 and Structural Example 6 for solving the problems, the strain and vibration can be similarly measured by these mounting methods. .

  When the AE, ultrasonic detection, or strain / vibration measurement described here is performed at multiple points, the AE, ultrasonic wave, strain / vibration received by the receiving unit FBG1 by the system shown in FIGS. It is considered possible to measure.

  The broadband light is branched by a 1 × N coupler, the branched broadband light is incident on the receiving unit FBG1 and the filter unit FBG2, and the reflected light or transmitted light intensity is converted into an electrical signal by the photoelectric converter 5, This is a system for outputting to the signal recording / display device 6.

  Since the changes in the transmitted light intensity and the reflected light intensity of the receiving unit FBG1 and the filter unit FBG2 are in a phase inversion relationship, even when the transmitted light intensity of the FBG as shown in FIG. It can be considered that detection similar to that in FIG.

  As in the systems shown in FIGS. 22 and 23, the FBG to be subjected to AE, ultrasonic wave, and vibration measurement can be selected by selecting the incidence of broadband light to the receiving unit and the filter unit FBG2 by the optical switch.

  Since the changes in the intensity of the transmitted light and the reflected light from the receiving unit FBG1 and the filter unit FBG2 are in a phase inversion relationship, both the transmitted light and the reflected light from the receiving unit FBG1 and the filter unit FBG2 are photoelectrically converted as shown in FIG. The signal-to-noise ratio of the response signal to the elastic wave response or vibration can be improved by entering the converter 5 and inverting and synthesizing the phase of one of the photoelectric converters 5. Furthermore, strain can be quantitatively evaluated using the method described in the reference (Tsuda et al., Composites Science and Technology 2007 Vol. 67 p.1353-1361).

  As shown in FIG. 25, a plurality of receiving units having different reflection wavelength ranges and a filter unit FBG2 are provided on a single optical fiber, and broadband light covering these reflection wavelength ranges is incident, and the reflected light is divided into optical components. By inputting only the reflected light from each FBG into the photoelectric converter 5 using a waver, AE / ultrasonic detection or strain / vibration measurement can be performed simultaneously at multiple points.

  As described above, the best mode of the vibration or elastic wave detection device according to the present invention has been described based on the embodiments. However, the present invention is not limited to such embodiments, and the technical scope described in the claims is not limited thereto. It goes without saying that there are various embodiments within the scope of the matter.

  Since the vibration or elastic wave detection device according to the present invention is as described above, it is possible to determine whether the structure is placed in an abnormal operating state by measuring vibration and strain that the structure receives during operation. Judgment can be made. Further, since acoustic emission (AE) occurs when the material breaks down, it is possible to detect damage to the structure by detecting AE. In addition, the damage state of the material / structure can be inspected nondestructively using ultrasonic waves.

It is a block diagram of the conventional FBG sensor elastic wave detection system using broadband light. It is a block diagram of the FBG sensor elastic wave detection system based on this invention using broadband light. It is a figure showing the reflective characteristic of receiving part FBG and filter part FBG when receiving part FBG receives distortion based on the present invention. It is the figure which showed the structural example of the receiving part FBG and the filter part FBG for the elastic wave detection based on this invention. It is the figure which showed the structural example of the receiving part FBG and the filter part FBG for the vibration and distortion detection based on this invention. It is a reflection characteristic schematic diagram at the time of combining receiving part FBG and filter part FBG which have different reflection characteristics. It is drawing which showed the system configuration | structure in the experiment and Example 1 which comprised the receiving part FBG and the filter part FBG from single FBG, and detected the ultrasonic wave based on this invention. It is the figure which showed the change of the reflection spectrum by having constituted the receiving part FBG and the filter part FBG by adhering a part of single FBG to the subject. It is the figure which showed typically the reflective characteristic of the receiving part FBG and the filter part FBG. It is the figure which showed the ultrasonic response waveform in Example 1. FIG. It is the figure which showed the frequency analysis result of the unfiltered waveform recorded in Example 1. FIG. It is the figure which showed the pseudo | simulation AE detection waveform in Example 2. FIG. It is the figure which showed the frequency analysis result of the unfiltered waveform recorded in Example 2. FIG. FIG. 6 is a configuration diagram of an experimental system used in Example 3. It is the figure which showed the photoelectric converter output at the time of cantilever free vibration in Example 3, and a strain gauge output. It is the figure which expanded the response at the time of the photoelectric converter output which does not synchronize with a periodic distortion change in Example 3. FIG. It is the figure which expanded the response at the time of the photoelectric converter output which synchronized with the periodic distortion change in Example 3. FIG. It is the figure which showed the reflective characteristic change of the receiving part FBG and the filter part FBG accompanying the distortion change in Example 3. FIG. It is the figure which showed the reflective characteristic change at the time of continuing applying a tensile strain in the receiving part FBG and filter part FBG which consist of single FBG. It is the figure which showed the system configuration example (the 1) for performing AE and ultrasonic detection or distortion and vibration measurement simultaneously at multiple points. It is the figure which showed the system configuration example (the 2) for performing AE and ultrasonic detection or distortion and vibration measurement simultaneously at multiple points. It is the figure which showed the system configuration example (the 1) for selecting the FBG sensor attached to multiple points, and performing AE and ultrasonic detection, and vibration and distortion measurement. It is the figure which showed the system configuration example (the 2) for selecting the FBG sensor attached to multiple points, and performing AE and ultrasonic detection, and vibration and distortion measurement. It is a system block diagram for combining the reflected light and transmitted light of the FBG in order to improve the signal-to-noise ratio of the response signal. It is a figure which shows the example of a system structure for arrange | positioning several FBG on one optical fiber, and performing AE and ultrasonic detection or distortion and vibration measurement simultaneously at multiple points. It is a figure explaining the 1st means of Example 1. FIG. It is a figure explaining the 2nd means of Example 1. FIG. FIG. 6 is a diagram for explaining a structural example 3 of the first embodiment. FIG. 6 is a diagram for explaining a structural example 4 of the first embodiment. FIG. 6 is a diagram for explaining a structural example 5 of the first embodiment.

Explanation of symbols

1 Receiver FBG
2 Filter section FBG
DESCRIPTION OF SYMBOLS 3 Broadband light source 4 Optical circulator 5 Photoelectric converter 6 Signal recording and display apparatus 7 Test object 8 Waveguide plate 9 Ultrasonic oscillator 10 Signal generator 11 Signal amplifier 12 Electric signal filter 13 FBG
14 Adhesive

Claims (4)

Broadband light including the reflection wavelength range of the reception unit FBG and the filter unit FBG is incident on the reception unit FBG and the filter unit FBG, and the reception unit FBG receives the intensity change of transmitted light or reflected light of the reception unit FBG and the filter unit FBG. In a vibration or elastic wave detector for measuring vibration or elastic wave,
Vibration or elastic wave, characterized in that the receiving unit FBG and the filter unit FBG are attached to the subject so that the reflected light distributions of the receiving unit FBG and the filter unit FBG always intersect even if the receiving unit FBG receives distortion or temperature change. Detection device. Broadband light including the reflection wavelength range of the reception unit FBG and the filter unit FBG is incident on the reception unit FBG and the filter unit FBG, and the reception unit FBG receives the intensity change of transmitted light or reflected light of the reception unit FBG and the filter unit FBG. In a vibration or elastic wave detector for measuring vibration and strain,
A vibration or elastic wave detection device characterized in that a temperature change received by the receiving unit FBG is also received equally by the FBG as a filter.   2. A single FBG is provided with two functions of a receiving unit FBG and a filter unit FBG by introducing local distortion into one FBG and having two peaks in reflection characteristics. Or the vibration or elastic wave detection apparatus of 2.   The vibration or elastic wave detection device according to claim 1 is used for detecting vibration or elastic wave at an arbitrary place.