CN112197886A

CN112197886A - Fiber Bragg grating demodulator and demodulation method

Info

Publication number: CN112197886A
Application number: CN202010645016.3A
Authority: CN
Inventors: 廖旺才; 刘木清
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-07-06
Filing date: 2020-07-06
Publication date: 2021-01-08
Anticipated expiration: 2040-07-06
Also published as: CN112197886B

Abstract

The present invention relates to a demodulator and a demodulation method of a fiber bragg grating, and a computer-readable storage medium. The demodulator is suitable for being connected with a target sensor arranged at a position to be monitored. The target sensor comprises a fiber bragg grating. The demodulator comprises a spectrum light source, a reference sensor, a photodiode, a piezoelectric actuator and a controller. The spectral light source is used to provide a continuous spectrum. The reference sensor comprises a fiber Bragg grating, the optical coupler is connected with the target sensor and is suitable for being matched with the target sensor to obtain an optical signal indicating the difference value of the central wavelengths of the reference sensor and the target sensor. The photodiode is used to convert an optical signal into an electrical signal. The piezoelectric actuator is used to provide a deforming force to the reference sensor. The controller is configured to: gradually varying the driving voltage to gradually vary the deformation force, thereby gradually varying the center wavelength of the reference sensor; monitoring the electric signal output by the photodiode in real time; and determining structural change and/or temperature change of the position to be monitored according to the valley driving voltage corresponding to the valley of the electric signal.

Description

Fiber Bragg grating demodulator and demodulation method

Technical Field

The present invention relates to sensing detection technologies, and in particular, to a demodulator and a method for demodulating a Fiber Bragg Grating (FBG).

Background

The fiber bragg grating sensor is a fiber optic sensor with a wide application range. Compared with the traditional electric signal sensor, the fiber Bragg grating sensor has excellent anti-electromagnetic interference capability and capability of adapting to a severe measuring environment, is suitable for distributed application, and has the advantages of compact structure and the like.

The center Wavelength (Central Wavelength) of the fiber bragg grating sensor changes with a measured parameter (e.g., temperature or strain caused by deformation). Therefore, by measuring the deviation of the central Wavelength of the fiber Bragg grating relative to the Bragg Wavelength (Bragg Wavelength), the size or temperature of the deformation corresponding to the applied tension can be calculated.

In the field of sensing and detecting, a fiber bragg grating demodulator is generally adopted to convert a wavelength signal output by a fiber bragg grating sensor into an electrical signal, so as to digitally measure an output quantity of the fiber bragg grating sensor. Conventional FBG demodulators are mostly implemented by Tunable filters (Tunable filters) of mechanical type. Most of the traditional FBG demodulators are large in size and low in sampling frequency, and cannot meet the monitoring requirements of large objects to be detected such as buildings.

In order to overcome the above defects in the prior art, there is an urgent need in the art for a demodulation technique for fiber bragg gratings, which is used to extend the dynamic measurement range to be measured and improve the central wavelength resolution and sampling frequency of the fiber bragg gratings, thereby satisfying the monitoring requirements for various objects to be measured, such as large building structures, human joint motions, and the like.

Disclosure of Invention

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In order to overcome the defects in the prior art, the invention provides a fiber bragg grating demodulator, a fiber bragg grating demodulation method and a computer readable storage medium, wherein the dynamic measurement range to be measured is expanded by utilizing a piezoelectric actuator, and the central wavelength resolution and sampling frequency of the fiber bragg grating are improved, so that the monitoring requirements on large objects to be measured such as buildings and the like are met.

The fiber Bragg grating demodulator provided by the invention is suitable for being connected with a target sensor arranged at a position to be monitored. The target sensor includes a fiber bragg grating. The fiber Bragg grating demodulator comprises a spectrum light source, a reference sensor, a photodiode, a piezoelectric actuator and a controller. The spectral light source is configured to provide a continuous spectrum covering a range of variations of a center wavelength of the target sensor. The reference sensor comprises a fiber Bragg grating, is optically coupled with the target sensor and is suitable for being matched with the target sensor to obtain an optical signal indicating the difference value of the central wavelengths of the reference sensor and the target sensor. The photodiode is used for converting the optical signal into an electrical signal. The piezoelectric actuator is used for providing a deformation force to the reference sensor. The controller is communicatively coupled to the photodiode and the piezoelectric actuator and configured to: gradually varying a drive voltage supplied to the piezoelectric actuator to gradually vary the deformation force, thereby gradually varying a center wavelength of a reference sensor; monitoring the electric signal output by the photodiode in real time; and determining the structural change and/or the temperature change of the position to be monitored according to the valley driving voltage corresponding to the valley of the electric signal.

Optionally, in some embodiments of the present invention, the fiber bragg grating demodulator may further include an optical coupler splitter. The optical coupler separator may be respectively connected to the spectrum light source, the target sensor, and the reference sensor, and is adapted to input the continuous spectrum provided by the spectrum light source to the target sensor, and separate an optical signal reflected by the target sensor to the reference sensor, so as to obtain an optical signal indicating the difference. Alternatively, the optical coupler-splitter may be connected to the target sensor, the reference sensor, and the photodiode, respectively, and adapted to input an optical signal transmitted through the reference sensor to the target sensor, and split an optical signal indicating the difference reflected by the target sensor to the photodiode.

Preferably, in some embodiments of the present invention, the piezoelectric actuator may comprise a piezoelectric crystal. The controller may be further configured to: determining the maximum value and the minimum value of the driving voltage according to the central wavelength resolution of the target sensor and the central wavelength variation range of the target sensor; and gradually increasing the driving voltage from the minimum value to the maximum value or gradually decreasing from the maximum value to the minimum value in units of the minimum value to determine the valley driving voltage.

Preferably, in some embodiments of the present invention, the controller may be further configured to: determining a center wavelength of the reference sensor from the valley drive voltage, the center wavelength of the reference sensor being equal to a center wavelength of the target sensor; and determining structural change and/or temperature change of the position to be monitored according to the central wavelength of the target sensor.

Optionally, in some embodiments of the present invention, the controller may be further configured to: recording its corresponding valley drive voltage in response to the electrical signal reaching a valley; determining the change direction of the valley driving voltage according to the change trends of the plurality of recorded valley driving voltages; and gradually changing the driving voltage according to the change direction from the last recorded valley driving voltage to determine the valley driving voltage corresponding to the valley of the current electric signal.

Preferably, in some embodiments of the present invention, the demodulator may be connected to a plurality of the target sensors. A plurality of the target sensors may have different bragg wavelengths, the spectral light source providing a continuous spectrum covering a total range of variation of the center wavelength of each of the target sensors. A plurality of the target sensors may be connected in series to the same optical fiber. The reference sensor is adapted to acquire, in cooperation with the plurality of target sensors, superimposed optical signals indicative of differences in center wavelengths of the respective sensors. The photodiode is adapted to convert the superimposed optical signal into a superimposed electrical signal.

Preferably, in some embodiments of the present invention, the controller may be further configured to: determining the maximum value and the minimum value of the driving voltage according to the central wavelength resolution and the total variation range of each target sensor; gradually changing the driving voltage according to the maximum value and the minimum value to determine a plurality of valley driving voltages corresponding to a plurality of valleys of the superimposed electrical signal; and determining structural changes and/or temperature changes of the plurality of places to be monitored according to the plurality of valley driving voltages.

Preferably, in some embodiments of the present invention, the controller may be further configured to: gradually changing the driving voltage according to the maximum value and the minimum value to determine a corresponding relation curve of the superimposed electrical signal and the driving voltage, wherein the value of the superimposed electrical signal indicates the intensity of the superimposed optical signal, and the value of the driving voltage indicates the central wavelength of the reference sensor; according to the driving voltage, the central wavelength of the reference sensor is adjusted to the Bragg wavelength of each target sensor so as to obtain a corresponding superposed electrical signal; determining the difference value between the current central wavelength of the corresponding target sensor and the Bragg wavelength thereof according to the corresponding superposed electrical signal and the corresponding relation curve; and determining the structural change and/or the temperature change of the corresponding position to be monitored according to the difference value of the current central wavelength of the target sensor and the Bragg wavelength thereof.

According to another aspect of the present invention, there is also provided a demodulation method of a fiber bragg grating.

The demodulation method of the fiber bragg grating provided by the present invention may be configured to execute the configuration of the controller of the fiber bragg grating demodulator provided in any one of the embodiments, so as to control the fiber bragg grating demodulator to demodulate the optical signal provided by the target sensor.

According to another aspect of the present invention, a computer-readable storage medium is also provided herein.

The present invention provides the above computer readable storage medium having stored thereon computer instructions. The computer instructions, when executed by a processor, may implement the demodulation method for fiber bragg gratings provided by the above embodiments.

Drawings

The above features and advantages of the present disclosure will be better understood upon reading the detailed description of embodiments of the disclosure in conjunction with the following drawings. In the drawings, components are not necessarily drawn to scale, and components having similar relative characteristics or features may have the same or similar reference numerals.

Fig. 1 illustrates an architectural schematic of a monitoring device provided in accordance with some embodiments of the present invention.

Fig. 2A illustrates a schematic diagram of a continuous spectrum provided according to some embodiments of the invention.

FIG. 2B illustrates a schematic diagram of a reflectance spectrum provided in accordance with some embodiments of the present invention.

Fig. 2C shows a schematic of a transmission spectrum provided according to some embodiments of the present invention.

Fig. 3 illustrates a flow diagram of a method of controlling a monitoring device provided in accordance with some embodiments of the present invention.

FIG. 4 illustrates a schematic diagram of variations in center wavelength of a reference sensor provided in accordance with some embodiments of the present invention.

Fig. 5 illustrates a plot of signal strength versus center wavelength difference for photodiodes provided in accordance with some embodiments of the present invention.

Fig. 6 illustrates a plot of signal strength versus center wavelength difference for photodiodes provided in accordance with some embodiments of the present invention.

Fig. 7 illustrates a waveform diagram of a driving voltage of a piezoelectric actuator provided according to some embodiments of the present invention.

Fig. 8 is a schematic diagram illustrating an architecture of a monitoring device according to another embodiment of the present invention.

Detailed Description

The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure. While the invention will be described in connection with the preferred embodiments, there is no intent to limit its features to those embodiments. On the contrary, the invention is described in connection with the embodiments for the purpose of covering alternatives or modifications that may be extended based on the claims of the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be practiced without these particulars. Moreover, some of the specific details have been left out of the description in order to avoid obscuring or obscuring the focus of the present invention.

As described above, the conventional fiber bragg grating demodulator is mostly implemented by a mechanical tunable filter. Most of the traditional fiber Bragg grating demodulators are large in size and low in sampling frequency, and cannot meet the monitoring requirements of large objects to be detected such as buildings.

In order to overcome the defects in the prior art, the invention provides a fiber bragg grating demodulator, a fiber bragg grating demodulation method, a computer readable storage medium, a structure health monitoring device and a structure health monitoring method.

Referring to fig. 1, fig. 1 is a schematic diagram illustrating an architecture of a monitoring device according to some embodiments of the present invention.

As shown in fig. 1, in some embodiments of the present invention, a structural health monitoring device may include a target sensor 11 and a fiber bragg grating demodulator 12. The target sensor 11 may be a Fiber Bragg Grating (FBG) sensor, which includes one or more FBGs 1-FBGn. That is, the target sensor 11 can be regarded as a sensor assembly composed of one or more fiber Bragg grating sensors FBG1 FBGn. The fiber bragg grating demodulator 12 may include a spectral light source 121, an optical coupler splitter 122, a reference sensor FBG0, a photodiode 123, a piezoelectric actuator 124, and a controller 125.

When the target sensor 11 is in a zero-strain state (i.e. without any deformation), the center wavelengths λ of the fiber Bragg gratings FBG1 FBGn_cAt its Bragg wavelength λ_B. When the target sensor 11 is subjected to strain caused by deformation or temperature change, the center wavelengths λ of the fiber Bragg gratings FBG 1-FBGn_cChanges to deviate from its Bragg wavelength lambda_B. In some embodiments, the target sensor 11 may be disposed at a site to be monitored of a large building structure to monitor whether the building structure is deformed and whether the temperature is changed. The large building structure comprises but is not limited to bridges, buildings, dams, ships, blades of wind driven generators and other objects to be detected, wherein whether the structure is healthy or not needs to be monitored. In some preferred embodiments, the structural health monitoring device may output an alarm signal in response to the structural deformation or the temperature change of the object to be measured exceeding a preset threshold value, so as to prompt a maintenance person to perform maintenance.

In some embodiments for monitoring building structures, the target sensor 11 may be disposed on a load-bearing structure such as a building foundation and a beam column, and is used for monitoring whether the building foundation and the beam column structure deform. In other embodiments, the target sensors 11 may be disposed around the building to monitor the building for settlement and determine whether the settlement is uniform.

In some embodiments of monitoring a bridge structure, the target sensor 11 may be disposed on a bearing structure of a bridge, such as a bridge pier, a cable, or a rivet, and configured to monitor whether the bearing structure of the bridge is deformed. In other embodiments, the target sensors 11 may be uniformly arranged on the whole bridge deck of the bridge for monitoring the deformation of the whole bridge deck of the bridge to evaluate the safety of vehicle traffic.

It will be appreciated by those skilled in the art that the buildings and bridges described above are but some non-limiting examples provided by the present invention, which are intended to illustrate the main concepts of the invention and to provide specific solutions for the implementation by the public, and are not intended to limit the scope of the invention. In other embodiments, the target sensor 11 can be disposed on other building structures by those skilled in the art according to the concept of the present invention to achieve the effect of monitoring the corresponding building structures.

Referring to fig. 2A, fig. 2A is a schematic diagram illustrating a continuous spectrum provided according to some embodiments of the present invention.

As shown in fig. 2A, in some embodiments of the present invention, the spectral Light Source 121 may be a Broadband Light Source (Broadband Light Source) such as a broad-spectrum LED, which is used to provide a continuous spectrum for the target sensor 11 and the reference sensor FBG0 to monitor the building structure. The spectral range of the continuous spectrum may cover the center wavelength λ of the target sensor 11_cSo that the object sensor 11 completely converts the incident light spectrum to the wavelength λ located at the center thereof_cThe narrow spectrum optical signal is reflected to the optocoupler separator 122.

The optical coupler separator 122 may be respectively connected to the spectral light source 121, the target sensor 11 and the reference sensor FBG0 through optical fibers, and is adapted to transmit the incident spectrum provided by the spectral light source 121 to the target sensor 11 for the first spectral filtering, and then separate the narrow-spectrum optical signal reflected by the target sensor 11 to the reference sensor FBG0 for the second spectral filtering.

Referring to fig. 2B and 2C in combination, fig. 2B shows a schematic diagram of a reflection spectrum provided according to some embodiments of the present invention, and fig. 2C shows a schematic diagram of a transmission spectrum provided according to some embodiments of the present invention.

As shown in fig. 2B and 2C, in response to the continuous spectrum inputted by the optical coupler splitter 122, the fiber bragg grating FBG1 of the target sensor 11 may first perform a first optical processing on the continuous spectrum, and the incident spectrum is located at the center wavelength λ thereof_c1Reflects the narrow spectrum optical signal back to the optocoupler 122 while transmitting the remainder of the incident spectrum to the back end. In some embodiments, the center wavelength λ of the fiber Bragg grating FBG1 is when the target sensor 11 is in a zero-strain state (i.e., no deformation occurs)_c1At its Bragg wavelength λ_B1Thus, the incident light spectrum can be located at its Bragg wavelength λ_B1Reflects the narrow spectrum optical signal back to the optocoupler 122 while transmitting the remainder of the incident spectrum to the back end.

In some embodiments of the present invention, the FBG0 of the reference sensor shown in fig. 1 may also be a fiber bragg grating sensor, which may include a fiber bragg grating. The reference sensor FBG0 may be arranged in the fiber bragg grating demodulator 12, connected to the photodiode 122 via an optical fiber, and connected to the target sensor 11 via the optical coupler splitter 125, and adapted to perform a second spectral filtering of the narrow-spectrum optical signal reflected by the target sensor 11, and further reflect the central wavelength λ of the reference sensor FBG0 therein_c0Thereby passing the remaining spectral components of the narrow spectrum optical signal to the photodiode 122. In some preferred embodiments, the fiber bragg grating demodulator 12 may be provided with a thermostatic chamber. The reference sensor FBG0 may preferably be provided in the thermostatic chamber to prevent variations in ambient temperature to the center wavelength λ of the reference sensor FBG0_c0An influence is produced.

Referring to FIGS. 2B and 2C, it can be seen that when the center wavelength λ of the sensor FBG0 is referenced_c0With the central wavelength λ of the fiber Bragg grating FBG1_c1At the same time, the narrow spectrum optical signal reflected by the target sensor 11 will be totally reflected by the reference sensor FBG 0. At this time, the remaining spectral components transferred to the photodiode 122 are minimized to reach the valley of the frequency domain range.

The photodiode 123 is a photoelectric device that converts a received optical signal into an electrical signal, and has the advantages of small size and low cost. In response to the remaining spectral components of the reference sensor FBG0 passing through the optical fiber, the photodiode 123 will generate a total Light Intensity (Light Intensity,I) the photocurrent of (c). In some embodiments, the photodiode 123 may be connected in series with a sampling resistor. The controller 125 can determine the light intensity of the remaining spectral components by measuring the voltage across the sampling resistor, thereby further determining the center wavelength λ of the target sensor FBG1_c1With the central wavelength λ of the reference sensor FBG0_c0The difference of (a). That is, the spectral components remaining after the two light processes of the target and reference sensors FBGs 1 and 0 may indicate the difference in the center wavelengths of the target and reference sensors FBG1 and 0.

In some embodiments of the present invention, the piezoelectric actuator 124 shown in FIG. 1 and described above may comprise a piezoelectric crystal. The piezoelectric crystal may be glued to the reference sensor FBG0, adapted to deform correspondingly according to the magnitude of the driving voltage, so as to provide a corresponding deforming force to the reference sensor FBG0 to change the central wavelength λ of the reference sensor FBG0_c0。

The aforementioned controller 125 may be communicatively connected to the piezoelectric actuator 124 and adapted to adjust the driving voltage stepwise to vary the deformation of its piezoelectric crystal stepwise, so as to realize a center wavelength λ of the reference sensor FBG0_c0Scanning of (2). In addition, the controller 125 can be communicatively connected to the photodiode 123, and is adapted to obtain electrical signals thereof to calculate the difference between the central wavelengths of the target sensor FBG1 and the reference sensor FBG0, so as to monitor whether the building structure is deformed or not and whether the temperature is changed or not.

The operation of the monitoring device will be described below in connection with some control methods of the controller 125. For the public understanding, the control method will be described only by the cooperation of the target sensor FBG1 and the reference sensor FBG0, and the partial control schemes of the target sensors FBG2 to FBGn are omitted as appropriate. It will be appreciated by those skilled in the art that these control methods are but a few non-limiting examples, which are intended to clearly demonstrate the broad concepts of the invention and to provide a number of specific details for the convenience of the public without limiting the scope of the invention.

Referring to fig. 3, fig. 3 is a flow chart illustrating a control method of a monitoring device according to some embodiments of the invention.

As shown in fig. 3, the control method provided in this embodiment may include step 301: the drive voltage supplied to the piezoelectric actuator is changed stepwise to change stepwise the deformation force supplied to the reference sensor.

As mentioned above, when the target sensor 11 is subjected to strain caused by deformation or temperature variation, the center wavelength λ of the fiber Bragg grating FBG1_c1Will vary away from its bragg wavelength lambda_B1. At this time, the center wavelength λ of the sensor FBG0 is referenced_c0With the central wavelength λ of the fiber Bragg grating FBG1_c1Instead, the photodiode 122 will receive more of the remaining spectral components, and the total light intensity of the spectral components at each wavelength will be greater, thereby generating a larger photocurrent.

As shown in fig. 1, in some embodiments of the present invention, the controller 125 may be connected to the piezoelectric actuator 124 through a Digital-to-analog conversion (DAC) and a driving module 126, and is adapted to provide a step-up step wave or a step-down step wave to the DAC module 126 to drive the piezoelectric actuator 124. The digital-to-analog conversion module 126 is adapted to convert the digital signal indicative of the magnitude of the step wave into an analog quantity of a driving voltage adapted to drive the piezoelectric actuator 124 to gradually change the deformation quantity of the piezoelectric crystal, thereby gradually changing the magnitude and direction of the deformation force provided to the reference sensor FBG 0.

Referring to fig. 4, fig. 4 is a schematic diagram illustrating a variation of a center wavelength of a reference sensor according to some embodiments of the invention.

As shown in FIG. 4, in some embodiments, the center wavelength λ of the reference sensor FBG0 is stepped up with the driving voltage_c0Will be from its lower limit value λ_c0To its upper limit value λ_c0"stepwise change. Variation range λ 'of center wavelength of reference sensor FBG 0'_c0～λ_c0"can cover the central wavelength λ of the target sensor FBG1_c1To achieve a central wavelength λ of the target sensor FBG1_c1Scanning of (2).

In some embodiments of the invention, controllingThe controller 125 can be based on the center wavelength resolution and the center wavelength λ of the target sensor FBG1_c1The maximum value and the minimum value of the driving voltage are determined. In particular, assume the center wavelength λ of the target sensor FBG1 to be measured_c1Has a resolution of 0.1pm and a central wavelength lambda_c1The variation range of (2) is 0.1 nm. Then it means the center wavelength lambda_c1There are 1000 possible values. Therefore, it is necessary to ensure that the excitation voltage of the piezoelectric crystal has 1000 possible values enough to characterize the central wavelength λ_c1Each value of (a). In some embodiments, a piezoelectric crystal with a maximum excitation voltage of 10.0V may be selected, and the minimum value and unit variation of the driving voltage are determined to be 10.0mV, thereby ensuring a center wavelength λ_c1Each value of (a) is characterized by a corresponding value of the drive voltage.

After determining the maximum and minimum values of the driving voltage, the controller 125 may gradually increase the driving voltage from the minimum value to the maximum value (or gradually decrease the driving voltage from the maximum value to the minimum value) as a unit variation of the adjusted driving voltage, so as to scan the central wavelength λ of the target sensor FBG1_c1。

As shown in fig. 3, the control method provided in this embodiment may further include step 302: and monitoring the electric signal output by the photodiode in real time.

In some embodiments of the present invention, the controller 125 shown in fig. 1 may be connected to the photodiode 123 and the sampling resistor connected in series through an Analog-to-digital conversion (ADC) module 127. The analog-to-digital conversion module 127 is adapted to convert the analog voltage across the sampling resistor into a corresponding digital signal. The controller 125 is adapted to monitor the digital signal provided by the analog-to-digital conversion module 127 in real time and calculate the voltage across the sampling resistor based on the digital signal, thereby determining the total light intensity of the remaining spectral components.

Referring to fig. 5, fig. 5 is a graph illustrating the relationship between the signal intensity and the central wavelength difference of a photodiode according to some embodiments of the present invention.

As shown in FIG. 5, the center wavelength λ of the reference sensor FBG0_c0Will gradually change with the change of the driving voltage. When the center wavelength λ of the reference sensor FBG0_c0Near the center wavelength λ of the target sensor FBG1_c1In time, the voltage across the sampling resistor will gradually decrease. When the center wavelength λ of the reference sensor FBG0_c0With the central wavelength λ of the fiber Bragg grating FBG1_c1At the same time, the center wavelength λ of the reference sensor FBG0_c0With the central wavelength λ of the fiber Bragg grating FBG1_c1The difference of (c) is zero. At this time, the remaining spectral components transferred to the photodiode 122 are minimized to reach the valley of the electric signal in the frequency domain. When the center wavelength λ of the reference sensor FBG0_c0Away from the center wavelength λ of the target sensor FBG1_c1The voltage across the sampling resistor will rise again. The controller 125 may record the driving voltage at which the electrical signal is at the valley as the valley driving voltage of the frequency domain.

As shown in fig. 3, the control method provided in this embodiment may further include step 303: and determining the structural change and/or the temperature change of the position to be monitored of the building structure according to the valley driving voltage corresponding to the valley of the electric signal.

As described above, the center wavelength of the fiber bragg grating sensor changes with strain caused by deformation, and the amount of deformation of the piezoelectric crystal is positively correlated to the driving voltage to which it is subjected. When the driving voltage is zero, the piezoelectric crystal is not deformed and the reference sensor FBG0 is not affected by any tension, its central wavelength λ_c0At its Bragg wavelength λ_B0To (3). In some embodiments of the invention, the reference sensor FBG0 may be pre-tested to determine the drive voltage and center wavelength λ_c0The corresponding relationship curve of (2).

In monitoring the building structure, the controller 125 can substitute the recorded valley drive voltage into the drive voltage and the center wavelength λ_c0To determine the central wavelength lambda corresponding to the valley driving voltage_c0. Since now the center wavelength λ of the reference sensor FBG0_c0Center wavelength λ of the target sensor FBG1_c1Is zero, the controller 125 may be further based on the centerWavelength lambda_c0Determining the center wavelength λ of the target sensor FBG1_c1. The controller 125 can then determine the center wavelength λ of the target sensor FBG1_c1Relative to its Bragg wavelength λ_B1Determines the tension to which the target sensor FBG1 is subjected, and thus further determines the structural changes and temperature changes at the site of the building structure to be monitored. The method for determining the structural change and the temperature change of the position to be monitored according to the tension applied to the fiber bragg grating sensor belongs to the prior art in the field, and is not described herein again.

In the above monitoring apparatus provided in the present invention, the controller 125 may cyclically scan the central wavelength λ of the target sensor 11_cTo monitor the deformation and/or temperature changes of the building structure over time. The sampling frequency of the monitoring device is related to the number of fiber bragg gratings FBG 1-FBGn in the target sensor 11. In some embodiments, the fiber bragg grating demodulator 12 may select a piezoelectric crystal with a maximum response frequency of 1.0MHz to cyclically adjust the deformation force applied to the reference sensor FBG 0. When the target sensor 11 comprises only one fiber bragg grating FBG1, the center wavelength λ is taken into account_c1With 1000 possible values, the sampling frequency of the monitoring device can reach 1.0 MHz/1000-1.0 kHz, which is sufficient for most applications.

In some preferred embodiments, the center wavelength λ of the fiber Bragg grating FBG1 is substantially continuous due to the generally continuous tension experienced by the fiber Bragg grating FBG1 and the very short interval between scans_c1Only slight deviations will generally occur. Therefore, the controller 125 may record the corresponding valley driving voltage in response to the voltage across the sampling resistor reaching the valley value, and predict the change direction after the valley driving voltage according to the previously recorded change trends of the plurality of valley driving voltages. Thereafter, the controller 125 may gradually change the driving voltage in the changing direction from the last recorded valley driving voltage to determine the valley driving voltage corresponding to the next sampled voltage valley.

By recording and counting the history data of the valley driving voltage, the change range and the change direction of the tension in the next scanning period can be roughly calculated. Thus, scanning can be performed in a smaller range, thereby further increasing the sampling frequency of the monitoring device. In general, the valley of the sampling voltage can be reached again only by scanning the driving voltage of less than 500 piezoelectric crystals on average. That is, the preferred embodiment can increase the sampling frequency of the monitoring device by more than one time.

As described above, in some embodiments of the present invention, the target sensor 11 may include a plurality of fiber Bragg gratings FBGs 1 FBGn. The plurality of fiber Bragg gratings FBG 1-FBGn can be connected in series with the same optical fiber and distributed on a plurality of load-bearing structures to be monitored of the building structure, and are used for respectively monitoring the deformation condition and the temperature change condition of each load-bearing structure. The plurality of fiber Bragg gratings FBG 1-FBGn may have different Bragg wavelengths λ_BSo that the controller 125 can identify the fiber bragg gratings FBG 1-FBGn. In some preferred embodiments, the Bragg wavelength λ of each of the fiber Bragg gratings FBG 1-FBGn_BMay be distributed over different wavelength frequency domains. At this time, the center wavelengths λ of the fiber Bragg gratings FBG 1-FBGn_cDoes not cover the Bragg wavelength λ of any of the remaining fiber Bragg gratings_BThus avoiding interference to the optical signals output by the other fiber Bragg gratings. The continuous spectrum provided by the broad-spectrum LED light source can cover the central wavelength lambda of each fiber Bragg grating FBG 1-FBGn_cSo that the monitoring device completes the central wavelength lambda of each fiber Bragg grating FBG 1-FBGn_cScanning of (2).

In the above embodiment, the optical signal received by the photodiode 123 is a superimposed spectrum signal processed by the fiber bragg gratings FBG 1-FBGn and the reference sensor FBG0, and indicates the central wavelength λ of the reference sensor FBG0_c0With the central wavelength λ of each of the fiber Bragg gratings FBG 1-FBGn_c1～λ_cnThe difference of (a). The photodiode 123 is adapted to convert the superimposed spectral signal into a corresponding superimposed photocurrent. The sampling resistor is adapted to convert the superimposed photocurrent to a corresponding superimposed voltage. In general, theThe superimposed voltage exhibits a peak of nV 0. When the center wavelength λ of the reference sensor FBG0_c0Near the center wavelength λ of any one of the fiber Bragg gratings FBG 1-FBGn_c1～λ_cnThe superimposed voltage is reduced. When the center wavelength λ of the reference sensor FBG0_c0With the central wavelength λ of any one of the fiber Bragg gratings FBG 1-FBGn_c1～λ_cnAt the same time, the superimposed voltage reaches its valley (n-1) V0 in the frequency domain.

In some embodiments, the controller 125 may determine the respective central wavelengths λ according to the central wavelength resolution of the respective target sensors FBG 1-FBGn_c1～λ_cnDetermines the maximum and minimum values of the driving voltage. For example: assume that the center wavelength resolution of each of the target sensors FBG 1-FBGn to be measured is 0.1pm, and the center wavelength λ_c1～λ_cnIs 1nm, then means the central wavelength λ_c1～λ_cnThere are 10000 possible values. Therefore, it is necessary to ensure that the excitation voltage of the piezoelectric crystal has 10000 possible values to completely characterize the central wavelength λ_c1～λ_cnEach value of (a). Therefore, a piezoelectric crystal having a maximum excitation voltage of 10.0V can be selected and the minimum value of the drive voltage is determined to be 1.0mV, thereby ensuring the center wavelength λ_c1～λ_cnEach value of (a) is characterized by a corresponding value of the drive voltage.

After determining the maximum and minimum values of the driving voltage, the controller 125 may gradually increase the driving voltage from the minimum value to the maximum value (or gradually decrease the driving voltage from the maximum value to the minimum value) using the minimum value as a unit variation for adjusting the driving voltage, so as to scan the central wavelengths λ of the target sensors FBG 1-FBGn_c1～λ_cn. In a complete scanning period, each time the reference sensor FBG0 and any one of the target sensor FBGs 1 FBGn have the center wavelength λ_c1～λ_cnSimilarly, the superimposed voltage will reach its valley (n-1) V0 in the frequency domain. The controller 125 may be based on each center wavelength λ_c1～λ_cnIdentifies the corresponding target sensors FBG 1-FBGn, and respectivelyThe valley drive voltages of the target sensors FBG1 to FBGn are recorded. Then, the controller 125 can determine the structural change and the temperature change of each load-bearing structure one by one from the valley driving voltages of the target sensors FBG1 to FBGn.

As described above, the sampling frequency of the monitoring device is related to the number of fiber Bragg gratings FBG1 FBGn in the target sensor 11. Considering the central wavelength λ of each fiber Bragg grating FBG 1-FBGn_cHas 1000 possible values, and the sampling frequency of the monitoring device is 1.0MHz/1000n DEG

When monitoring large buildings such as cross-river bridges and skyscrapers, when the target sensor 11 includes 1000 fiber bragg gratings FBG 1-FBG 1000, the sampling frequency of the monitoring device can only reach 1 Hz. At this time, it is difficult for the monitoring device to quickly feed back the abnormality of the building.

In response to the above-mentioned need for monitoring large buildings, in some preferred embodiments, the controller 125 may also perform the above-mentioned center wavelength λ_c1～λ_cnDuring scanning, determining a corresponding relation curve of the superposed voltage and the driving voltage. Since the value of the superimposed electrical signal indicates the intensity of the superimposed optical signal, the value of the driving voltage indicates the central wavelength λ of the reference sensor FBG0_c0The corresponding relation curve can also indicate the total light intensity received by the photodiode and each central wavelength lambda_c1～λ_cnThe corresponding relation of the difference values.

Referring to fig. 6, fig. 6 is a graph illustrating a relationship between signal intensity and a central wavelength difference of a photodiode according to some embodiments of the present invention.

As shown in fig. 6, in general, the superimposed voltage across the sampling resistor is stably maintained at the high level nV 0. Whenever the center wavelength λ of the reference sensor FBG0_c0Near the center wavelength λ of a fiber Bragg grating FBGn_cnIn time, the superimposed voltage across the sampling resistor will gradually decrease. When the center wavelength λ of the reference sensor FBG0_c0With the central wavelength lambda of the fiber Bragg grating FBGn_cnAt the same time, the superimposed voltage reaches its valley (n-1) V0 in the frequency domain. When the center of the reference sensor FBG0Wavelength lambda_c0Again away from the central wavelength lambda of the fiber bragg grating FBGn_cnThe superimposed voltage across the sampling resistor will rise again.

After determining the corresponding relationship curve of the superimposed voltage and the driving voltage, the controller 125 may extract a quasi-linear section (i.e., a non-saturation region in a rectangular box in fig. 6) therein. In the embodiment shown in fig. 6, the left rectangle indicates the tension in the reverse direction, and the right rectangle indicates the tension in the forward direction. In general, the center wavelengths λ of the target sensors FBG 1-FBGn_c1～λ_cnDoes not vary beyond its Bragg wavelength λ_B1～λ_BnThe quasi-linear interval of (a).

For applications that do not require consideration of the direction of the tension, the controller 125 can individually tune the center wavelength λ of the reference sensor FBG0_c0Bragg wavelength λ adjusted to each of the target sensors FBG 1-FBGn_B1～λ_BnAnd according to the reading of the signal of the photoelectric tube and the linear relation between the signal of the photoelectric tube and the difference value of the central wavelength, the central wavelength lambda of each target sensor FBG 1-FBGn is quickly determined_c1～λ_cnWith a central wavelength λ_c0The difference of (a).

As shown in FIG. 6, in some embodiments, in response to a photocell signal reading of 37, the controller 125 can quickly determine the center wavelength λ of the reference sensor FBG0 directly from the linear relationship of the superimposed voltage to the drive voltage_c0Center wavelength λ of target sensor FBGn_cnThe difference in (c) is 40 pm. That is, the center wavelength λ of the target sensor FBGn_cnDeviating from its Bragg wavelength lambda_BnHas a value of 40 pm. Thereafter, the controller 125 may determine the center wavelength λ of the target sensor FBGn_cnRelative to its Bragg wavelength λ_BnThe tension to which the target sensor FBGn is subjected is determined, thereby further determining the structural change and the temperature change of the building structure where it is to be monitored.

By adopting the above preferred scheme, even if the target sensor 11 comprises 1000 fiber bragg gratings FBG 1-FBG 1000, the monitoring device only needs to scan 1000 specified wavelengths (i.e. λ_B1～λ_B1000) The signal of the photoelectric tube can determine the structural change and the temperature change of the building structure to be monitored. In this case, the sampling frequency of the monitoring device can be increased to 1.0MHz/1000 ═ 1.0kHz, which greatly increases the sampling rate of the plurality of target sensors FBG 1-FBGn, thereby realizing real-time monitoring of large buildings.

Referring to fig. 7, fig. 7 shows an example of a waveform of a driving voltage of the piezoelectric actuator. As shown in FIG. 7, the measurement values of each of the target sensors FBG1 FBGn can be obtained in one sweep from the minimum driving voltage to the maximum driving voltage. Repeating the above scanning can achieve continuous measurement of the parameters of each of the target sensors FBG 1-FBGn.

It will be appreciated by those skilled in the art that the architecture of the monitoring device shown in fig. 1 is only a non-limiting example, intended to clearly illustrate the main concepts of the present invention and to provide a concrete solution for the implementation by the public, and not intended to limit the scope of protection of the present invention.

Alternatively, in other embodiments, a person skilled in the art may also make appropriate modifications to the architecture of the monitoring device based on the concept of fig. 1 to achieve the same technical effect.

Referring to fig. 8, fig. 8 is a schematic diagram illustrating an architecture of a monitoring device according to another embodiment of the present invention.

In other embodiments of the present invention, as shown in fig. 8, the reference sensor FBG0 in the fiber bragg grating demodulator 82 may also be disposed between the spectral light source 821 and the optical coupler splitter 822, and adapted to perform a first spectral filtering of the continuous spectrum provided by the spectral light source 821, reflecting its center wavelength λ_c0And the remaining part of the spectral components is transferred to the rear-end photocoupler 822. The optocoupler splitter 822 is adapted to pass the spectral signal transmitted through the reference sensor FBG0 to the target sensor 81 for a second spectral filtering.

In response to the spectral signal provided by the optocoupler 822, each of the fiber Bragg gratings FBG 1-FBGn in the target sensor 81 is adapted to have a respective center wavelength λ therein_c1～λ_cnThe nearby narrow spectrum optical signal is reflected back to the optocoupler 822. The optocoupler splitter 822 is adapted to split the remaining spectral signal reflected by the target sensor 81 to the photodiode 823 to generate a corresponding photocurrent.

In the embodiment shown in fig. 8, the operation principles of the piezoelectric actuator 824, the controller 825, the digital-to-analog conversion and driving module 826, and the signal amplification and analog-to-digital conversion module 827 are similar to those of the embodiment shown in fig. 1, and are not described herein again.

According to another aspect of the present invention, there is also provided a demodulation method of a fiber bragg grating. The demodulation method may implement the configuration of the

controller

125 or 825 of the fiber bragg grating demodulator provided in any one of the above embodiments to control the fiber bragg grating demodulator to demodulate the optical signal provided by the target sensor.

According to another aspect of the present invention, a structural health monitoring method is also provided herein. The structural health monitoring method is to determine structural change and/or temperature change of a large building structure to be monitored by using the structural health monitoring device provided by any one of the above embodiments. Specifically, the structural health monitoring method provided by the invention can comprise the steps of opening the monitoring device and monitoring the building structure by using the control method. Therefore, the structural health monitoring method provided by the invention can also expand the dynamic measurement range to be measured and improve the resolution and sampling frequency of the central wavelength of the fiber Bragg grating, thereby meeting the monitoring requirements on large objects to be measured such as buildings.

While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more embodiments, occur in different orders and/or concurrently with other acts from that shown and described herein or not shown and described herein, as would be understood by one skilled in the art.

According to another aspect of the present invention, a computer-readable storage medium is also provided herein. The computer readable storage medium has stored thereon computer instructions. The computer instructions, when executed by the processor, may implement the demodulation method of the fiber bragg grating provided by the above embodiments. The processor includes, but is not limited to, the

controllers

125 and 825 of the fiber bragg grating demodulator provided in any of the above embodiments.

Although the above embodiments describe the

controllers

125 and 825 as being implemented by a combination of software and hardware. It is understood that the

controllers

125 and 825 may be implemented solely in software or hardware. For a hardware implementation, the

controllers

125 and 825 may be implemented on one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), digital signal processing devices (DAPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic devices adapted to perform the functions described herein, or a selected combination thereof. For software implementations, the

controllers

125 and 825 may be implemented by separate software modules running on a common chip, such as program modules (processes) and function modules (functions), each of which may perform one or more of the functions and operations described herein.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fiber bragg grating demodulator adapted to be connected to a target sensor disposed at a location to be monitored, the target sensor including a fiber bragg grating, the demodulator comprising:

a spectral light source for providing a continuous spectrum covering a range of variations of a center wavelength of the target sensor;

the reference sensor comprises a fiber Bragg grating, is optically coupled with the target sensor and is suitable for being matched with the target sensor to obtain an optical signal indicating the difference value of the central wavelengths of the reference sensor and the target sensor;

a photodiode for converting the optical signal into an electrical signal;

a piezoelectric actuator for providing a deformation force to the reference sensor; and

a controller communicatively coupled to the photodiode and the piezoelectric actuator and configured to:

gradually varying a drive voltage supplied to the piezoelectric actuator to gradually vary the deformation force, thereby gradually varying a center wavelength of a reference sensor;

monitoring the electric signal output by the photodiode in real time; and

and determining the structural change and/or the temperature change of the position to be monitored according to the valley driving voltage corresponding to the valley of the electric signal.

2. The demodulator of claim 1, further comprising an optical coupler splitter, wherein,

the optical coupler separator is respectively connected with the spectrum light source, the target sensor and the reference sensor, and is suitable for inputting the continuous spectrum provided by the spectrum light source to the target sensor and separating the optical signal reflected by the target sensor to the reference sensor so as to obtain the optical signal indicating the difference value, or

The optical coupler separator is respectively connected with the target sensor, the reference sensor and the photodiode, and is suitable for inputting an optical signal transmitted by the reference sensor to the target sensor and separating an optical signal which is reflected by the target sensor and indicates the difference value to the photodiode.

3. The demodulator of claim 1, wherein the piezoelectric actuator comprises a piezoelectric crystal, the controller further configured to:

determining the maximum value and the minimum value of the driving voltage according to the central wavelength resolution of the target sensor and the central wavelength variation range of the target sensor; and

and gradually increasing the driving voltage from the minimum value to the maximum value or gradually decreasing from the maximum value to the minimum value by taking the minimum value as a unit so as to determine the valley driving voltage.

4. The demodulator of claim 3, wherein the controller is further configured to:

determining a center wavelength of the reference sensor from the valley drive voltage, the center wavelength of the reference sensor being equal to a center wavelength of the target sensor; and

and determining the structural change and/or the temperature change of the position to be monitored according to the central wavelength of the target sensor.

5. The demodulator of claim 3, wherein the controller is further configured to:

recording its corresponding valley drive voltage in response to the electrical signal reaching a valley;

determining the change direction of the valley driving voltage according to the change trends of the plurality of recorded valley driving voltages; and

and gradually changing the driving voltage according to the change direction from the last recorded valley driving voltage to determine the valley driving voltage corresponding to the valley of the current electric signal.

6. A demodulator, as in claim 3, adapted to interface with a plurality of said target sensors,

a plurality of said target sensors having different Bragg wavelengths, said spectral light source providing a continuous spectrum covering a total range of variation of a center wavelength of each said target sensor,

a plurality of the target sensors are connected in series to the same optical fiber, the reference sensor is adapted to cooperate with the plurality of target sensors to acquire superimposed optical signals indicative of differences in center wavelengths of the sensors,

the photodiode is adapted to convert the superimposed optical signal into a superimposed electrical signal.

7. The demodulator of claim 6, wherein the controller is further configured to:

determining the maximum value and the minimum value of the driving voltage according to the central wavelength resolution and the total variation range of each target sensor;

gradually changing the driving voltage according to the maximum value and the minimum value to determine a plurality of valley driving voltages corresponding to a plurality of valleys of the superimposed electrical signal; and

and determining structural change and/or temperature change of a plurality of positions to be monitored according to the plurality of valley driving voltages.

8. The demodulator of claim 7, wherein the controller is further configured to:

gradually changing the driving voltage according to the maximum value and the minimum value to determine a corresponding relation curve of the superimposed electrical signal and the driving voltage, wherein the value of the superimposed electrical signal indicates the intensity of the superimposed optical signal, and the value of the driving voltage indicates the central wavelength of the reference sensor;

according to the driving voltage, the central wavelength of the reference sensor is adjusted to the Bragg wavelength of each target sensor so as to obtain a corresponding superposed electrical signal;

determining the difference value between the current central wavelength of the corresponding target sensor and the Bragg wavelength thereof according to the corresponding superposed electrical signal and the corresponding relation curve; and

and determining the structural change and/or the temperature change of the corresponding position to be monitored according to the difference value of the current central wavelength of the corresponding target sensor and the Bragg wavelength thereof.

9. A demodulation method of a fiber bragg grating, characterized in that the configuration of the controller of the fiber bragg grating demodulator according to any one of claims 1 to 8 is performed to control the fiber bragg grating demodulator to demodulate an optical signal provided by a target sensor.

10. A computer readable storage medium having stored thereon computer instructions, which when executed by a processor, implement the method for demodulating a fiber bragg grating as claimed in claim 9.