JP2012037480A - Ae measuring method and equipment by optical fiber sensor using wide band light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately measure an AE signal even by using a wide band light source whose noise is large.SOLUTION: AE measuring equipment includes: an optical fiber 22 configured to include an FBG sensor part 21, and arranged in a cantilever beam or twin beam state; a wide band light source 2 including the Bragg wavelength of the FBG sensor part 21; an optical circulator 3 for separating the rays of light reflected from the FBG sensor part 21; Fabry-Perot filters 5, 6 to which reflected rays of light are made incident; photoelectric converters 7, 8 for converting the rays of light into an electric signal; a signal recording device 23 for recording light intensity change to be output from the photoelectric converters 7, 8; a signal processor 24 for processing a voltage signal recorded by the signal recording device 23 by successive wavelet transformation; and a signal determination device 25 for extracting a signal which is equivalent to a specific frequency from the signal processed by the successive wavelet transformation, and for setting a threshold, and for determining whether or not the signal is an AE signal.

Description

  The present invention relates to an AE measurement method using an optical fiber sensor using broadband light and an apparatus therefor.

  2. Description of the Related Art In recent years, an AE measurement method using detection of elastic wave emission (AE: acoustic emission) accompanying strain generation exists as a technique for detecting strain for an inspection object such as a structure.

  In the AE measurement method, it is considered that an FBG (Fiber Bragg Grating) sensor, which is a kind of optical fiber sensor, is used instead of a piezoelectric element that receives electromagnetic interference.

  Such an AE measuring apparatus will be described. As shown in FIG. 6, the AE measuring apparatus includes a broadband light source 2 including the Bragg wavelength of the FBG sensor 1, an optical circulator 3 positioned between the broadband light source 2 and the FBG sensor 1, An optical coupler 4 that branches light from the optical circulator 3, a first Fabry-Perot filter (FFP) 5 that transmits one of the lights branched by the optical coupler 4, and the other branched by the optical coupler 4 A second Fabry-Perot filter (FFP) 6 that transmits the first light, a first photoelectric converter 7 that converts the light transmitted through the first Fabry-Perot filter 5 into an electrical signal, and a second A second photoelectric converter 8 for converting the light transmitted through the Fabry-Perot filter 6 into an electrical signal, and an AE measuring instrument 9 for processing signals from the first photoelectric converter 7 and the second photoelectric converter 8. And a data recorder 10 (see, for example, Patent Document 1).

  The broadband light source 2 continuously outputs broadband light, and a first optical fiber 11 is disposed between the broadband light source 2 and the optical circulator 3 to guide incident light to the optical circulator 3. Further, a second optical fiber 12 is disposed between the optical circulator 3 and the FBG sensor 1 to guide incident light to the FBG sensor 1.

  The FBG sensor 1 is a sensor that forms a diffraction grating at a constant interval along the optical axis direction in the core portion of the optical fiber. When light enters the FBG sensor 1, the wavelength component of the Bragg wavelength is changed to the FBG sensor 1. So that the remaining components are transmitted. In addition, the shift amount of the Bragg wavelength changes depending on the strain to be inspected. Further, the FBG sensor 1 is disposed by being adhered to a measurement target.

  The optical circulator 3 guides the incident light from the broadband light source 2 to the second optical fiber 12 and controls the reflected light from the FBG sensor 1 so as to control the direction of the guided light by the incident light or the reflected light. The light is guided to the optical coupler 4 through the three optical fibers 13.

  The optical coupler 4 includes a fourth optical fiber 14 and is connected to the first Fabry-Perot filter 5, and a fifth optical fiber 15 is disposed and connected to the second Fabry-Perot filter 6. Therefore, the reflected light is split into 50:50 and is incident on the first Fabry-Perot filter 5 and the second Fabry-Perot filter 6.

  The first Fabry-Perot filter 5 and the second Fabry-Perot filter 6 are optical characteristics in which the transmittance of the filter periodically changes at a constant wavelength interval (FSR: Free Spectral Range). , 6 and the wavelength with which the reflected light spectrum of the FBG sensor 1 overlaps are transmitted. The first Fabry-Perot filter 5 guides the transmitted light to the first photoelectric converter 7 through the sixth optical fiber 16, and the second Fabry-Perot filter 6 transmits the transmitted light through the seventh optical fiber 17. The light is guided to the second photoelectric converter 8.

  The first photoelectric converter 7 converts the transmitted light from the first Fabry-Perot filter 5 into an electrical signal, and sends the electrical signal to the AE measuring instrument 9 and the data recorder 10 through the first connection line 18. I have to. Similarly to the first photoelectric converter 7, the second photoelectric converter 8 converts the transmitted light from the second Fabry-Perot filter 6 into an electric signal, and the electric signal is AEed by the second connection line 19. Are sent to the measuring instrument 9 and the data recorder 10.

  The AE measuring instrument 9 and the data recorder 10 measure the high frequency component of the change in light intensity, and acquire and record the AE. Here, the AE measuring device 9 and the data recording device 10 may be configured separately or may be configured by one device.

  When measuring AE, the reflected light from the FBG sensor 1 is split 50:50 by the optical coupler 4 and is incident on the first Fabry-Perot filter 5 and the second Fabry-Perot filter 6. Next, in the first Fabry-Perot filter 5 and the second Fabry-Perot filter 6, the first photoelectric converter is made to transmit the overlapping wavelength of the transmission wavelength of the Fabry-Perot filters 5 and 6 and the reflected light spectrum of the FBG sensor 1. 7 and the second photoelectric converter 8, and the first photoelectric converter 7 and the second photoelectric converter 8 convert the intensity of transmitted light into electric signals, respectively. The AE measuring instrument 9 and the data recorder 10 measure the high frequency component of the light intensity change, respectively, and acquire the AE.

JP 2008-46036 A

  However, the high-frequency component of the photoelectrically converted signal has a problem that noise is large due to fluctuations in the light intensity emitted from the broadband light source 2 and fluctuations in the transmittance of the Fabry-Perot filters 5 and 6.

  Further, the transmittance of the Fabry-Perot filters 5 and 6 periodically changes at a constant wavelength interval (FSR). At this time, the light intensity transmitted through the Fabry-Perot filters 5 and 6 also increases, and the noise level of the high frequency component also changes accordingly. Therefore, a constant threshold (trigger level) is set for the voltage signal of the high frequency component during AE measurement. Even if an attempt is made, the noise level increases when the Bragg wavelength is at the maximum transmittance wavelength of the Fabry-Perot filters 5 and 6, and conversely, when the Bragg wavelength is at the minimum transmittance wavelength of the Fabry-Perot filters 5 and 6, the noise level is increased. There is a problem that it becomes small and it is difficult to make the threshold value constant.

  For these two problems, it has been studied to use a wavelength tunable laser beam as a light source as disclosed in JP-A-2005-326326. However, when a wavelength tunable laser is used, one FBG sensor 1 is used. On the other hand, since one tunable laser is required, there is a problem that the optical system becomes complicated. Moreover, the wavelength tunable laser light source having a narrow wavelength width that can be used for the half-value width of the reflected light of the FBG sensor 1 is expensive and large in size, and constitutes a multipoint measurement system or a variable measuring device. There was a problem that it was difficult to configure.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to appropriately measure an AE signal even when a broadband light source having a large noise is used.

In the AE measurement method using an optical fiber sensor using broadband light according to the present invention, the FBG sensor unit is not bonded to the measurement target, but is bonded to the measurement target and includes the FBG sensor unit. An optical fiber arranged in a state, a broadband light source including the Bragg wavelength of the FBG sensor unit, and the light emitted from the broadband light source is transmitted and incident on the FBG sensor unit of the optical fiber and reflected from the FBG sensor unit An optical circulator for separating light, a Fabry-Perot filter on which reflected light separated by the optical circulator is incident, and a photoelectric converter for converting light transmitted through the Fabry-Perot filter into an electrical signal,
An AE measurement method using an optical fiber sensor using broadband light, which detects a longitudinal elastic wave corresponding to the resonance frequency of the optical fiber arranged in a cantilevered or double-ended state,
The light intensity change output from the photoelectric converter is acquired, the acquired voltage signal is processed by continuous wavelet transform, a signal corresponding to a specific frequency is extracted from the signal subjected to continuous wavelet transform, and a threshold is provided. It is discriminate | determined whether it is an AE signal.

  In the AE measurement method using the optical fiber sensor using broadband light according to the present invention, when acquiring the light intensity change output from the photoelectric converter, the voltage signal corresponding to the light intensity change is continuously acquired over time. It is preferable to do.

  In the AE measurement method using an optical fiber sensor using broadband light according to the present invention, the threshold value is set to the signal strength of the elastic wave detected by the FBG sensor unit using a signal in a state where no AE signal is generated, When a signal corresponding to a specific frequency is extracted from a signal subjected to continuous wavelet transform, it is preferable to identify a signal exceeding the threshold as an AE signal.

The AE measuring apparatus using the optical fiber sensor using the broadband light according to the present invention has a configuration in which the FBG sensor unit is not bonded to the measurement target but is bonded to the measurement target and includes the FBG sensor unit. An optical fiber arranged in a state;
A broadband light source including the Bragg wavelength of the FBG sensor unit;
An optical circulator disposed between the broadband light source and an optical fiber including the FBG sensor unit, which transmits the light irradiated from the broadband light source, enters the FBG sensor unit, and separates the light reflected from the FBG sensor unit; ,
A Fabry-Perot filter on which the reflected light separated by the optical circulator is incident;
A photoelectric converter that converts the light transmitted through the Fabry-Perot filter into an electrical signal;
A signal acquisition device for acquiring a change in light intensity output from the photoelectric converter;
A signal processing device for processing the voltage signal acquired by the signal acquisition device by continuous wavelet transform;
A signal discriminating device for extracting a signal corresponding to a specific frequency from a signal subjected to continuous wavelet transform and determining whether it is an AE signal by providing a threshold;
It is equipped with.

  In the AE measuring apparatus using an optical fiber sensor using broadband light according to the present invention, the signal acquisition device is preferably configured to continuously acquire a voltage signal corresponding to a change in light intensity in terms of time.

  In the AE measuring apparatus using an optical fiber sensor using broadband light according to the present invention, the signal discriminating apparatus uses a signal in a state where no AE signal is generated, and sets a threshold value for the signal intensity of the elastic wave detected by the FBG sensor unit. Is set, and when a signal corresponding to a specific frequency is extracted from a signal subjected to continuous wavelet transform, a signal exceeding the threshold is preferably identified as an AE signal.

  According to the present invention, a change in light intensity output from a photoelectric converter is acquired, the acquired voltage signal is processed by continuous wavelet transform, and a signal corresponding to a specific frequency is extracted from the signal subjected to continuous wavelet transform. In addition, since the threshold is set to determine whether the signal is an AE signal, even if the noise level is high due to fluctuations in the light intensity emitted from the broadband light source or fluctuations in the transmittance of the Fabry-Perot filter, the AE signal and the noise are discriminated. Thus, the AE signal can be appropriately measured. Even if the noise level changes due to the configuration of the FBG sensor unit and the Fabry-Perot filter and a constant threshold value cannot be set for the voltage signal, the voltage signal is continuously wavelet transformed to convert the AE signal and noise. This makes it possible to determine the AE signal. Further, since a broadband light source is used and the voltage signal is processed by continuous wavelet transform, a complicated optical system that requires one wavelength tunable laser for one FBG sensor unit can be eliminated. In addition, since the AE signal is measured without using an expensive wavelength tunable laser, the cost can be reduced, and the configuration of a multipoint measurement system and the configuration of a variable measurement device can be made. An excellent effect of being able to measure can be achieved.

It is a block diagram which shows the example of embodiment of this invention. This is data indicating the voltage signal, the amplitude after continuous wavelet processing, and the frequency when the AE signal and noise can be discriminated only by the voltage signal. This is data indicating a voltage signal, amplitude after continuous wavelet processing, and frequency when only a noise signal is present. This is data indicating the voltage signal, the amplitude after the continuous wavelet processing, and the frequency when the AE signal and noise cannot be identified only by the voltage signal, and the AE signal and noise can be identified by the continuous wavelet processing. It is a graph which shows the AE signal acquired from the raw data of a voltage, and the AE signal acquired from the data to which continuous wavelet processing is applied when distortion is generated in the measuring object. It is a block diagram which shows the conventional AE measuring device.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an AE measurement method and apparatus using an optical fiber sensor using broadband light according to the present invention will be described below with reference to FIGS. In the figure, the same reference numerals as those in FIG. 6 denote the same parts.

  The embodiment includes an optical fiber 22 including an FBG sensor unit 21, a broadband light source 2 including the Bragg wavelength of the FBG sensor unit 21, an optical circulator 3 positioned between the broadband light source 2 and the FBG sensor unit 21, An optical coupler 4 that branches the light from the circulator 3, a first Fabry-Perot filter (FFP) 5 that transmits one light branched by the optical coupler 4, and the other branched by the optical coupler 4 A second Fabry-Perot filter (FFP) 6 that transmits light, a first photoelectric converter 7 that converts light transmitted through the first Fabry-Perot filter 5 into an electrical signal, and a second A second photoelectric converter 8 that converts light that has passed through the Fabry-Perot filter 6 into an electrical signal, and a signal acquisition that acquires changes in light intensity output from the first photoelectric converter 7 and the second photoelectric converter 8. The apparatus 23 includes a signal processing device 24 that processes a signal acquired by the signal acquisition device, and a signal determination device 25 that determines a signal from the signal processing device 24. Here, the broadband light source 2, the optical circulator 3, the Fabry-Perot filters 5 and 6, and the photoelectric converters 7 and 8 are the same as those in FIG. In the embodiment, two lines are formed which are branched by the optical coupler 4 and pass through the Fabry-Perot filters 5 and 6 and the photoelectric converters 7 and 8, but may be one line. Alternatively, it may be a plurality of other lines.

  The optical fiber 22 including the FBG sensor unit 21 does not adhere the FBG sensor unit 21 to the measurement target S, but a part of the optical fiber 22 is adhered to the measurement target S by an adhesive means 26 such as an adhesive. When the elastic wave is generated in the measuring object S, the elastic wave is applied to the optical fiber 22 from the bonded portion of the optical fiber 22. The longitudinal elastic wave is guided to the FBG sensor unit 21. Here, the optical fiber sensor means the optical fiber 22 including the FBG sensor unit 21. Further, the optical fiber 22 and the FBG sensor unit 21 attached as a cantilever or a double-sided tension have a structure having high sensitivity to the resonance frequency of the longitudinal vibration of the tension.

  The signal acquisition device 23 is configured to continuously acquire a voltage signal of the light intensity change with respect to the light intensity change output from the photoelectric converters 7 and 8, and the voltage signal is transmitted via the first connection line 27. To the signal processing device 24. Here, the continuous acquisition time may be all the time during measurement or may be a certain period.

  The signal processing device 24 has a configuration for processing the voltage signal acquired by the signal acquisition device 23 by continuous wavelet transformation, and sends the signal subjected to continuous wavelet transformation to the signal discrimination device 25 via the second connection line 28. ing. Here, the processing such as continuous wavelet transform may be performed simultaneously with the continuous acquisition of the signal acquisition device 23 or after the continuous acquisition.

  The signal discriminating device 25 is configured to extract a signal corresponding to a specific frequency from the signal subjected to continuous wavelet transform by the signal processing device 24 and discriminate whether the signal is an AE signal by setting a threshold value in advance. Moreover, the specific frequency said here is corresponded to the frequency corresponded to the resonant frequency of the cantilever of the optical fiber 22 containing the FBG sensor part 21, or both ends. Further, the signal discriminating device 25 may process the process of extracting a signal corresponding to a specific frequency and the process of discriminating whether or not it is an AE signal with separate components. Furthermore, the signal acquisition device 23, the signal processing device 24, and the signal discrimination device 25 may be configured by one device, or other devices may be used.

  Hereinafter, the operation of the embodiment implemented by the AE measurement method and apparatus using the optical fiber sensor using the broadband light according to the present invention will be described.

  When measuring the AE signal, the light emitted from the broadband light source 2 passes through the optical circulator 3 and enters the FBG sensor unit 21 of the optical fiber 22, and the light reflected from the FBG sensor unit 21 is the optical circulator 3. Separated by Then, the reflected light separated by the optical circulator 3 enters the respective Fabry-Perot filters 5 and 6 through the optical coupler 4 and is converted into electric signals by the photoelectric converters 7 and 8, and the electric signals are converted into the signal acquisition device 23. Recorded continuously in time.

  At this time, when an external load is applied to the measuring object S and the strain exceeds a certain level, a damage signal is generated. The damage signal propagates in the measurement target S as an elastic wave, and the optical fiber 22 including the FBG sensor unit 21 that is in a cantilevered or double-supported state from the portion of the optical fiber 22 bonded to the measurement target S (FIG. 1). Then it propagates to the cantilevered state. Then, a reflected light intensity change from the FBG sensor unit 21 corresponding to the longitudinal longitudinal resonance frequency of the optical fiber 22 including the FBG sensor unit 21 occurs, and the optical fiber 22 is traced back from the optical circulator 3 through the optical coupler 4. The optical signal passes through the Fabry-Perot filters 5 and 6 and is converted into an electric signal by the photoelectric converters 7 and 8, and the damage state of the measuring object S is monitored using the signal acquisition device 23, the signal processing device 24, the signal discrimination device 25, and the like. Will be.

Ψはマザーウェーブレットであり、ａがスケール、ｂがシフトを表す。￣は複素共役を示す。χ（ｔ）は時間ｔに対する連続信号である。また上式は信号χ（ｔ）とウェーブレット基底Ψ（（ｔーｂ）／ａ）を時間軸上でコンボリューション（たたみ込み積分）を行うことを示す。更にスケールａは周波数に相当し、シフトｂは時間に相当する。Ｗ_Ψχはスケールａシフトｂの時の信号強度を表す。
ここでマザーウェーブレットΨは次式に示すガボールウェーブレットを適用している。

また連続ウェーブレット変換は任意のマザーウェーブレットを適用しても良いが、ガボールウェーブレットは周波数局在性が強く、特定の周波数の信号を抽出することに適している。 The signal processing device 24 processes the voltage signal from the signal acquisition device 23 by continuous wavelet transform. Continuous wavelet transform is signal processing consisting of time-frequency-signal intensity for an original time series signal, and a specific frequency component is obtained by a wavelet function without losing time domain information in a wide frequency domain. It can be done. Further, in the present embodiment, the frequency at which the FBG sensor unit 21 attached as a cantilever or a double-sided splinter varies depending on the object to be measured, and the frequency slightly changes depending on the length of the stretch. For the conversion, continuous wavelet processing capable of analyzing an arbitrary frequency is the optimum processing. Hereinafter, the definition of the continuous wavelet transform will be specifically described as follows.

Ψ is a mother wavelet, where a represents a scale and b represents a shift.示 す indicates a complex conjugate. χ (t) is a continuous signal with respect to time t. The above equation indicates that the signal χ (t) and the wavelet basis Ψ ((tb) / a) are convolved (convolution integration) on the time axis. Furthermore, the scale a corresponds to the frequency, and the shift b corresponds to the time. W _Ψ χ represents the signal intensity at the scale a shift b.
Here, the Gabor wavelet shown in the following equation is applied to the mother wavelet Ψ.

An arbitrary mother wavelet may be applied to the continuous wavelet transform, but the Gabor wavelet has a strong frequency localization and is suitable for extracting a signal of a specific frequency.

  Next, the signal discriminating device 25 extracts a signal corresponding to a specific frequency from the signal subjected to the continuous wavelet transform, discriminates whether or not it is an AE signal based on a threshold value, and detects the AE signal. Here, the threshold is set using a noise signal in a state where no AE signal is generated, and the state where the AE signal is not generated may be a condition before the state change of the measurement target S occurs. It may be in a state of other preparation stage.

[Test 1]
In the following, the conventional comparative example and the embodiment are tested, and the AE signal and noise can be identified only when the voltage signal alone can identify the AE signal and noise, and the voltage signal alone. First, an AE signal and a case where noise can be identified by continuous wavelet processing are acquired, and the data and results are shown.

  First, a conventional comparative example is tested, and the voltage signal, amplitude after continuous wavelet processing, and frequency when the AE signal and noise can be distinguished only by the voltage signal are shown in FIG. In the voltage signal of FIG. 2A, the voltage value increases from a predetermined position, and it can be determined that the AE signal is generated. Further, in the amplitude of FIG. 2B when this signal is subjected to continuous wavelet processing, the amplitude value corresponding to the AE signal is large, and the AE signal is clear at the frequency of FIG. Such signals do not require continuous wavelet transform or continuous recording of signals.

  Next, FIG. 3 shows voltage signals, amplitudes after continuous wavelet processing, and frequencies when only noise signals are present. In the voltage signal of FIG. 3A, the voltage value is within a certain range, and the amplitude of FIG. 3B and the frequency of FIG. 3C when the signal is continuously wavelet processed are also in a certain range. There is no change. Here, the case where only the noise signal of FIG. 3 exists may be set as the threshold value. In FIG. 3B, the amplitude value (0.00014) at which the noise peak does not reach is set as the threshold value.

  FIG. 4 shows the voltage signal, the amplitude after the continuous wavelet processing, and the frequency when the AE signal and the noise cannot be distinguished from the voltage signal alone and the AE signal and the noise can be identified by the continuous wavelet processing. In the voltage signal of FIG. 4A, the voltage width is within a certain range, and the AE signal and noise cannot be clearly distinguished as shown in FIG. In the amplitude of FIG. 4B when this signal is subjected to continuous wavelet processing, the amplitude value corresponding to the signal of the frequency corresponding to the resonance frequency of the FBG sensor unit 21 attached in the cantilever state is large. The AE signal is clear at a frequency of 4 (c). Even when the AE signal and noise cannot be identified only from the voltage signal, it is possible to identify the AE signal and noise by continuous wavelet processing from FIGS. 4B and 4C. Thus, it is clear that an AE signal having a small amplitude is identified even when a broadband light source having a large noise level is used.

[Test 2]
Next, when distortion is generated in the measurement object S, an AE signal identified from only a voltage signal (voltage raw data) and an AE signal identified from data to which continuous wavelet processing is applied are shown.

  In the test conditions, a load is applied to the measurement target S and strain is gradually applied, and the strain and AE of the measurement target are measured simultaneously. In addition, strain gauges are used for strain measurement. Furthermore, in the test, the AE signal identified from only the voltage signal and the one identified from the data to which the continuous wavelet processing is applied are recorded by the signal (AE Hits / sec) identified as the AE signal per unit time. did. It should be noted that the portion where the strain increases rapidly after 900 seconds indicates that the strain gauge resistance wire is broken because the generated strain is large.

  As a result, as shown in FIG. 5, only a few points (one point in FIG. 5) can be detected by identifying the AE signal only from the voltage signal, and many have identified the AE signal from the data to which continuous wavelet processing is applied. The point was detected. In particular, many AE signals are measured immediately before and just before the time when the distortion changes discontinuously between 600 and 900 seconds, indicating that the state change of the measurement target has been captured. Indicates that the measurement is valid.

  As described above, according to the embodiment, the light intensity change output from the photoelectric converters 7 and 8 is acquired, the acquired voltage signal is processed by the continuous wavelet transform, and specified from the signal subjected to the continuous wavelet transform. Since a signal corresponding to the frequency of λ is extracted and a threshold value is provided to determine whether the signal is an AE signal, the noise level is caused by fluctuations in the light intensity emitted from the broadband light source 2 and fluctuations in the transmittance of the Fabry-Perot filters 5 and 6. Even if it is large, the AE signal and the noise can be discriminated and the AE signal can be appropriately measured. Further, even when the noise level changes due to the configuration of the FBG sensor unit 21 and the Fabry-Perot filters 5 and 6 and a constant threshold value cannot be set for the voltage signal, the voltage signal is continuously wavelet transformed, It becomes possible to distinguish between the AE signal and noise, and thus the AE signal can be appropriately measured. Further, since the broadband light source 2 and the like are used and the voltage signal is processed by continuous wavelet conversion, a complicated optical system that requires one wavelength variable laser for one FBG sensor unit 21 is made unnecessary. Can do. In addition, since the AE signal is measured without using an expensive wavelength tunable laser, the cost can be reduced, and the configuration of a multipoint measurement system and the configuration of a variable measurement device can be made. It can be measured.

  In the embodiment, when the light intensity change output from the photoelectric converters 7 and 8 is acquired, the voltage signal corresponding to the light intensity change is continuously acquired in time. Continuous wavelet processing can be applied to the signal, and threshold setting and AE signal discrimination can be performed appropriately.

  In the embodiment, the threshold is set to the signal strength of the elastic wave detected by the FBG sensor unit 21 using a signal in a state where no AE signal is generated, and a specific frequency is obtained from the signal subjected to continuous wavelet transform. When the signal corresponding to is extracted, the signal exceeding the threshold is identified as the AE signal, so that the AE signal can be appropriately measured. In addition, focusing on only a specific frequency among the signals subjected to continuous wavelet transform and setting criteria (evaluation criteria) from the amplitude value of the specific frequency, it is possible to easily distinguish the AE signal from noise.

  Of course, the AE measurement method and apparatus using the optical fiber sensor using the broadband light of the present invention can be variously modified without departing from the gist of the present invention.

2 Broadband light source 3 Optical circulator 5 Fabry-Perot filter 6 Fabry-Perot filter 7 Photoelectric converter 8 Photoelectric converter 21 FBG sensor unit 22 Optical fiber 23 Signal acquisition device 24 Signal processing device 25 Signal discrimination device

Claims (6)

An optical fiber that is bonded to a measurement target without being bonded to the measurement target and includes the FBG sensor unit and arranged in a cantilevered or double-ended state, and includes the Bragg wavelength of the FBG sensor unit A broadband light source, an optical circulator that transmits the light emitted from the broadband light source, enters the FBG sensor unit of the optical fiber, and separates the light reflected from the FBG sensor unit, and the reflected light separated by the optical circulator includes An incident Fabry-Perot filter; and a photoelectric converter that converts light transmitted through the Fabry-Perot filter into an electrical signal;
An AE measurement method using an optical fiber sensor using broadband light, which detects a longitudinal elastic wave corresponding to the resonance frequency of the optical fiber arranged in a cantilevered or double-ended state,
The light intensity change output from the photoelectric converter is acquired, the acquired voltage signal is processed by continuous wavelet transform, a signal corresponding to a specific frequency is extracted from the signal subjected to continuous wavelet transform, and a threshold is provided. An AE measurement method characterized by determining whether an AE signal or not.   2. The light using broadband light according to claim 1, wherein when acquiring a light intensity change output from the photoelectric converter, a voltage signal corresponding to the light intensity change is continuously acquired over time. AE measurement method using fiber sensor. The threshold is set to the signal strength of the elastic wave detected by the FBG sensor unit using a signal in a state where no AE signal is generated,
The broadband light according to claim 1 or 2, wherein when a signal corresponding to a specific frequency is extracted from a signal subjected to continuous wavelet transform, a signal exceeding the threshold is identified as an AE signal. AE measurement method using an optical fiber sensor. An optical fiber that is bonded to the measurement target without being bonded to the measurement target and is arranged in a cantilevered or double-ended state in a configuration including the FBG sensor unit;
A broadband light source including the Bragg wavelength of the FBG sensor unit;
An optical circulator disposed between the broadband light source and an optical fiber including the FBG sensor unit, which transmits the light irradiated from the broadband light source, enters the FBG sensor unit, and separates the light reflected from the FBG sensor unit; ,
A Fabry-Perot filter on which the reflected light separated by the optical circulator is incident;
A photoelectric converter that converts the light transmitted through the Fabry-Perot filter into an electrical signal;
A signal acquisition device for acquiring a change in light intensity output from the photoelectric converter;
A signal processing device for processing the voltage signal acquired by the signal acquisition device by continuous wavelet transform;
A signal discriminating device for extracting a signal corresponding to a specific frequency from a signal subjected to continuous wavelet transform and determining whether it is an AE signal by providing a threshold;
An AE measuring apparatus using an optical fiber sensor using broadband light.   5. The AE measurement apparatus using an optical fiber sensor using broadband light according to claim 4, wherein the signal acquisition device is configured to continuously acquire voltage signals corresponding to changes in light intensity in terms of time.   The signal discriminating device sets a threshold value for the signal strength of the elastic wave detected by the FBG sensor unit using the signal in a state where no AE signal is generated, and a signal corresponding to a specific frequency from the signal subjected to continuous wavelet transform 6. The AE measuring apparatus using an optical fiber sensor using broadband light according to claim 4, wherein a signal exceeding the threshold value is identified as an AE signal when the signal is extracted.

Images