KR101529610B1

KR101529610B1 - Apparatus and Sensing System for Fiber Bragg Grating Probes Having Controlled Sensitivity and Method for Sensing and Manufacturing thereof

Info

Publication number: KR101529610B1
Application number: KR1020140083613A
Authority: KR
Inventors: 권일범; 김미현
Original assignee: 한국표준과학연구원
Priority date: 2014-07-04
Filing date: 2014-07-04
Publication date: 2015-06-30

Abstract

The present invention relates to an FBG probe capable of easily controlling sensitivity with respect to deformation and sensitivity with respect to a temperature by applying a sensitivity control probe with a low thermal expansion coefficient to a package of a fiber Bragg grating. According to an embodiment of the present invention, the FBG probe with controlled sensitivity comprises: a first fiber Bragg grating to reflect light of a first Bragg wavelength and to allow first light to pass; a second fiber Bragg grating to reflect light of a second Bragg wavelength which is at least part among the first light and to allow second light to pass; a sensitivity control element consisting of a material whose thermal expansion coefficient is lower than a predetermined first value, to adjust sensitivity of at least one between the first fiber Bragg grating and the second fiber Bragg grating, and attached to the first fiber Bragg grating and the second fiber Bragg grating between the optical fibers; and a packaging unit formed to surround the sensitivity control element, to bind the first fiber Bragg grating and the second fiber Bragg grating, and located in a measured object. At least one between the first Bragg wavelength and the second Bragg wavelength is changed according to a deformation variable related to the measured object. The deformation variable is at least one between a temperature change of the measured object and a deformation degree of the measured object. The sensitivity is a rate of change in at least one between the first Bragg wavelength and the second Bragg wavelength according to the deformation variable.

Description

FIELD OF THE INVENTION [0001] The present invention relates to an FBG sensor, a FBG sensor, a sensing method, and a sensing method,

More particularly, the present invention relates to an FBG sensor having a sensitivity to temperature and a sensitivity to strain by simply applying a sensitivity control device having a low thermal expansion coefficient to the packaging of an optical fiber Bragg grating. It is about the probe.

In the case of large structures such as bridges and buildings, it is necessary to monitor the structures and to inspect the structures.

Electronic strain gauges (such as strain gauges) are used extensively to measure the load or deformation of buildings. Electronic strain gauges are very sensitive and highly reliable because they have been used for a long time. However, this sensor is very vulnerable to electromagnetic waves. For example, an electronic strain gauge installed on the Hangang Bridge can be said to have all of these disadvantages caused by lightning strikes.

In order to overcome the disadvantages of such electromagnetic waves, there are many attempts to use a fiber Bragg Grating (FBG) sensor which is not affected by electromagnetic waves. Fig. 1 shows the general structure of such an optical fiber.

As shown in FIG. 1, the optical fiber generally comprises a core portion which is the center of the optical fiber, a cladding portion which protects the center, and a cover portion. The main component of the core and the cladding is made of glass, and the cladding surface is coated with a polymer or an acrylate to protect the core and the cladding which are the main constituents.

In the optical fiber core, a germanium (Ge) material is usually added to increase the refractive index of the cladding, which may cause structural defects in the process of placing the material on the silica glass. In this case, when the optical fiber core is irradiated with strong ultraviolet rays, the refractive index of the optical fiber is changed while the bonding structure of Ge is deformed.

The fiber Bragg grating refers to a periodic change in the refractive index of the optical fiber core using this phenomenon. This grating reflects only the wavelengths satisfying the Bragg condition and transmits the other wavelengths as they are.

When the ambient temperature of the grating is changed or an axial load is applied to the grating, the refractive index or the length of the optical fiber changes, so that the wavelength of the reflected light changes. Therefore, by measuring the wavelength of the light reflected from the fiber Bragg grating, temperature, tensile, pressure or bending can be detected, and the sensor can be applied.

The fiber Bragg grating sensor is a fiber optic device that periodically modulates the refractive index of the core according to the energy distribution of the interference fringe and reflects light of a specific wavelength (Bragg wavelength).

FIG. 2 is a schematic view of a configuration of a conventional optical fiber Bragg grating sensor and a lattice portion of a probe, and FIGS. 3A through 3C schematically show a signal input to a fiber Bragg grating sensor, a passed signal, and a reflected signal.

The fiber Bragg grating has the structure and operating characteristics as shown in Fig. The periodic change in refractive index of the core serves as a Bragg grating.

When a broadband light is incident on the Bragg grating, the light of a wavelength corresponding to the Bragg condition as shown in the following Equation 1 causes a constructive interference to be reflected at the Bragg grating portion, and the light of the remaining wavelength is transmitted.

here,

Is the Bragg wavelength,

Is a core effective reffractive index, which represents the average refractive index when light travels in one cycle of the Bragg grating,

Represents the period of the Bragg grating engraved in the core.

As can be seen from the above equation (1), the Bragg wavelength of light reflected from the lattice

) Is the effective refractive index (

) And the grating period (

) &Lt; / RTI > Since the effective refractive index and the period of the grating are a function of the temperature and the strain, the Bragg wavelength is changed when disturbance such as temperature or strain is applied to the fiber Bragg grating.

The following equation (2) can be obtained by taking an entire differential value of Bragg wavelength in the Bragg condition, and then substituting the equation of temperature, strain, lattice spacing, and effective refractive index.

here,

Is the thermal expansion coefficient of the optical fiber,

Is a thermodynamic number indicating the refractive index change of the optical fiber due to temperature,

Is a photoelastic constant and has a value of approximately 0.22.

If the changed Bragg wavelength is precisely measured, the temperature or strain applied to the optical fiber grating can be calculated through Equation (2). This is the principle that a fiber Bragg grating can be used as a sensor.

Assuming that there is no change in the temperature applied to the sensor in Equation (2)

), Equation (2) can be simply expressed as Equation (3) below.

Using Equation (3), FGB can be used as a strain sensor. As shown in Equation (3), this strain can be obtained by accurately measuring the amount of change in wavelength.

The FBG sensor is suitable for long-term measurement because it is easy to multiplex the sensor regardless of electromagnetic interference, and has excellent corrosion resistance. Recently, it has been applied to various fields such as structural integrity monitoring, slope monitoring, and hull stress monitoring of civil structures such as bridges and tunnels.

Specifically, the conventional FGB transducer system 10 comprises a light source 12, a connecting means 14 and a wavelength detector 16, as shown in Fig. 2, which are connected by optical fibers.

As can be seen from the enlarged drawing, the Bragg grating sensor portion of the optical fiber is engraved with a Bragg grating by a predetermined length. The Bragg wavelength of the reflected light reflected by the Bragg grating among the light irradiated through the optical fiber in the light source 12 is measured and the degree of deformation of the measured object (for example, a large structure such as a bridge or a building) based on the change of the Bragg wavelength .

Since the optical fiber Bragg grating sensor is fabricated by using the ultraviolet (UV) laser with a strong optical power and the phase mask after removing the coating polymer of the communication optical fiber, it is about 1/10 of the standard optical fiber having the tensile break strength of about 6000 Mpa It decreases. This uncoated FBG is vulnerable to impact and long term durability and is difficult to install. Therefore, it is important to package FBGs that are easy to install and maintain the original spectrum.

Thus, an epoxy packaging sensor has been developed considering the ease of installation of the user while controlling the strain and temperature sensitivity of the FBG sensor probe.

However, in the case of epoxy packaging, the temperature sensitivity of the FBG transducer is changed by about 40 pm with respect to the change of 1 ° C due to thermal deformation due to temperature, and the like.

Such a large temperature sensitivity has a disadvantage that it is difficult to apply in the field requiring precise measurement and greatly limits the utilization of the fiber Bragg grating sensor.

Therefore, it is required to develop a packaging technique for accurately measuring the deformation of the measured object by lowering the temperature sensitivity.

Korean Patent No. 10-1288493 Korean Patent No. 10-1280922 Korea Patent No. 10-0943710

SUMMARY OF THE INVENTION The present invention has been conceived to overcome the above-mentioned problems, and it is an object of the present invention to provide a FBG sensor capable of easily controlling the sensitivity to temperature and the sensitivity to strain by applying a sensitivity control device having a low thermal expansion coefficient to packaging of an optical fiber Bragg grating. The purpose is to provide the transducer to the user.

In addition, the present invention provides a FBG transducer to a user that can greatly improve the precision of measurement by measuring the deformation of the measured object at the same position using a pair of optical fiber Bragg gratings having different degrees of strain and temperature sensitivity, .

It is another object of the present invention to provide a FBG probe to a user by packaging such a pair of optical fiber Bragg gratings with a plastic material such as an epoxy resin, thereby improving installation easiness and ease of use.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. It can be understood.

In order to achieve the above object, there is provided an FBG sensor having sensitivity controlled according to an example of the present invention, including: an optical fiber in which light propagates; A first optical fiber Bragg grating (FBG) disposed in the optical fiber for reflecting light of a first Bragg wavelength, which is at least a part of the light, and passing the first light; A second optical fiber Bragg grating (FBG) disposed in the optical fiber spaced apart from the first optical fiber Bragg grating to reflect light of a second Bragg wavelength, which is at least a part of the first light, ; Wherein the first optical fiber Bragg grating and the second optical fiber Bragg grating are formed of a material having a thermal expansion coefficient lower than a predetermined first value to adjust the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating, A sensitivity control element attached to the grating; And a packaging portion formed to surround the sensitivity control element and bundling the first optical fiber Bragg grating and the second optical fiber Bragg grating and positioned in the measured object, wherein the first light is the first And the second light is light that does not correspond to the second Bragg wavelength of the first light, and the first Bragg wavelength and the second Bragg wavelength At least one of the Bragg wavelengths is changed and the deformation parameter is at least one of a temperature change of the object to be measured and a degree of deformation of the object to be measured and the sensitivity is at least one of the first Bragg wavelength and the second Bragg wavelength / RTI >

A first sensitivity control element, which is a part of the plurality of sensitivity control elements, is attached to an upper surface and a lower surface of the first fiber Bragg grating, and the second sensitivity control element is a part of the plurality of sensitivity control elements. The device may be attached to the upper surface and the lower surface of the second fiber Bragg grating.

In addition, the thermal expansion coefficient of the first sensitivity control element and the thermal expansion coefficient of the second sensitivity control element may be different from each other.

The first value is a thermal expansion coefficient of the optical fiber.

In addition, the sensitivity can be adjusted corresponding to the stiffness of the sensitivity control element.

In addition, the rigidity of the sensitivity control element may be smaller than the rigidity of the packaging portion.

The packaging unit may be manufactured using an epoxy resin and a curing agent.

In addition, the sensitivity may include a temperature sensitivity, which is a rate of change of the Bragg wavelength depending on a temperature change of the measured object, and a strain sensitivity, which is a rate of change of the Bragg wavelength depending on a degree of deformation of the measured object.

In addition, the temperature sensitivity may be set lower than a preset reference value.

In addition, the strain sensitivity may be set within a predetermined reference range.

Also, as at least one of the first Bragg wavelength and the second Bragg wavelength is changed, the wavelength of light reflected from at least one of the first optical fiber Bragg grating and the second optical fiber Bragg grating may be changed.

In addition, the sensitivity control element may be carbon fiber reinforced plastics (CFRP).

In order to achieve the above-mentioned object, an FBG sensor system with sensitivity control according to an embodiment of the present invention includes: a light source for emitting light in a broadband wavelength band; An optical fiber through which the light travels; A first optical fiber Bragg grating (FBG) disposed in the optical fiber for reflecting light of a first Bragg wavelength, which is at least a part of the light, and passing the first light; A second optical fiber Bragg grating (FBG) disposed in the optical fiber spaced apart from the first optical fiber Bragg grating to reflect light of a second Bragg wavelength, which is at least a part of the first light, ; Wherein the first optical fiber Bragg grating and the second optical fiber Bragg grating are formed of a material having a thermal expansion coefficient lower than a predetermined first value to adjust the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating, A sensitivity control element attached to the grating; And a packaging portion formed to surround the sensitivity control element and bundling the first optical fiber Bragg grating and the second optical fiber Bragg grating and positioned in the measured object; An optical fiber coupler connected to the FBG probe and receiving the reflected first Bragg wavelength light and the second Bragg wavelength light to output an optical signal; And an optical spectrum analyzer connected to the optical fiber coupler and receiving the optical signal, wherein the first light is light that does not correspond to the first Bragg wavelength of the light, Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a deformation parameter related to the object to be measured so that the first optical fiber Bragg grating and the second Bragg grating The wavelength of light reflected from at least one of the fiber Bragg gratings is changed and the deformation parameter is at least one of a temperature change of the object to be measured and a degree of deformation of the object to be measured, And the second Bragg wavelength, and the optical spectrum analyzer calculates the difference between the first and second Bragg wavelengths Recognition using the wavelength variation of the reflected light, and can be used to measure the deformation to be measured water level corresponding to the wavelength variation of the reflected light.

The first value may be a thermal expansion coefficient of the optical fiber.

According to another aspect of the present invention, there is provided a sensing method for an FBG sensor, the sensing method comprising the steps of: irradiating light of a broadband wavelength range from a light source; Advancing the light into the optical fiber; The first optical fiber Bragg grating (FBG) disposed in the optical fiber reflects light of a first Bragg wavelength, which is at least a part of the light, and passes through the first optical fiber Bragg grating (FBG); A second Bragg wavelength of at least a part of the first light is reflected by a second optical fiber Bragg grating (FBG) disposed on the optical fiber, the second Bragg wavelength being separated from the first optical fiber Bragg grating, ; The optical fiber coupler receiving the reflected first Bragg wavelength light and the second Bragg wavelength light and transmitting the optical signal to the optical spectrum analyzer; The optical spectrum analyzer recognizing the wavelength change of the reflected light using the received optical signal; And a step of measuring a degree of deformation of the object to be measured corresponding to a change in the wavelength of the reflected light, wherein a portion of the optical fiber, on which the first optical fiber Bragg grating and the second optical fiber Bragg grating are disposed, And the sensitivity control element is made of a material having a thermal expansion coefficient lower than a predetermined first value to control the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating, Wherein the first optical fiber Bragg grating and the second optical fiber Bragg grating are bundled together and positioned in a measured object, the first light is light that does not correspond to the first Bragg wavelength of the light, 2 light is light that does not correspond to the second Bragg wavelength of the first light, and the deformation associated with the measured object Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a variable and the deformation parameter is at least one of a temperature change of the measured object and a deformation degree of the measured object, Of the first Bragg wavelength and the second Bragg wavelength of the second Bragg wavelength.

The first value may be a thermal expansion coefficient of the optical fiber.

In order to achieve the above-mentioned object, a manufacturing method of an FBG sensor having sensitivity controlled according to an example of the present invention includes a first optical fiber Bragg grating (FBG) for reflecting light of a first Bragg wavelength to an optical fiber, Disposing a second optical fiber Bragg grating (FBG) that reflects light of a second Bragg wavelength; Attaching a first sensitivity control element, which is a part of a plurality of sensitivity control elements made of a material having a thermal expansion coefficient lower than a predetermined first value, to upper and lower surfaces of the first fiber Bragg grating, Attaching a sensitivity control element to upper and lower surfaces of the second fiber Bragg grating; Injecting a plastic material into the transducer mold surrounding the plurality of sensitivity control elements to thermally cure the transducer mold; And forming a packaging portion from the thermosetting transducer mold, wherein the plurality of sensitivity control elements adjust the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating, Wherein the optical fiber Bragg grating passes a first light of light traveling into the optical fiber and the second optical fiber Bragg grating passes a second light of the first light and the first light passes through the first Bragg And the second light is light that does not correspond to the second Bragg wavelength of the first light, and the packaging unit is formed to surround the plurality of sensitivity control elements, and the first optical fiber Bragg grating And a second optical fiber bragg grating, which is located in the object to be measured, and which, according to a deformation parameter associated with the object to be measured, Wherein at least one of the wavelength and the second Bragg wavelength is changed and the deformation parameter is at least one of a temperature change of the object to be measured and a degree of deformation of the object to be measured, And at least one of the second Bragg wavelengths.

On the other hand, in a recording medium on which a program of instructions executable by the digital processing apparatus to implement the sensing method of the sensitivity-controlled FBG transducer is tangibly embodied and can be read by the digital processing apparatus, A method of sensing an FBG transducer in which the sensitivity of the recording medium is controlled according to an embodiment of the present invention for realizing the task includes the steps of: irradiating light of a broadband wavelength band from a light source; Advancing the light into the optical fiber; The first optical fiber Bragg grating (FBG) disposed in the optical fiber reflects light of a first Bragg wavelength, which is at least a part of the light, and passes through the first optical fiber Bragg grating (FBG); A second Bragg wavelength of at least a part of the first light is reflected by a second optical fiber Bragg grating (FBG) disposed on the optical fiber, the second Bragg wavelength being separated from the first optical fiber Bragg grating, ; The optical fiber coupler receiving the reflected first Bragg wavelength light and the second Bragg wavelength light and transmitting the optical signal to the optical spectrum analyzer; The optical spectrum analyzer recognizing the wavelength change of the reflected light using the received optical signal; And a step of measuring a degree of deformation of the object to be measured corresponding to a change in the wavelength of the reflected light, wherein a portion of the optical fiber, on which the first optical fiber Bragg grating and the second optical fiber Bragg grating are disposed, And the sensitivity control element is made of a material having a thermal expansion coefficient lower than a predetermined first value to control the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating, Wherein the first optical fiber Bragg grating and the second optical fiber Bragg grating are bundled together and positioned in a measured object, the first light is light that does not correspond to the first Bragg wavelength of the light, 2 light is light that does not correspond to the second Bragg wavelength of the first light, and the deformation associated with the measured object Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a variable and the deformation parameter is at least one of a temperature change of the measured object and a deformation degree of the measured object, Of the first Bragg wavelength and the second Bragg wavelength of the second Bragg wavelength.

The present invention can provide a user with an FBG transducer which can easily control the sensitivity to temperature and the sensitivity to strain by applying a sensitivity control element having a low thermal expansion coefficient to the packaging of an optical fiber Bragg grating.

In addition, the present invention can provide a user with an FBG transducer capable of greatly improving the precision of measurement by measuring deformation of the object at the same position by using a pair of optical fiber Bragg gratings having different degrees of strain and temperature sensitivity.

In addition, the present invention can provide a FBG transducer to a user, which can package the optical fiber Bragg grating with a plastic material such as an epoxy resin, thereby improving installation easiness and ease of use.

It should be understood, however, that the effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those skilled in the art to which the present invention belongs It will be possible.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a preferred embodiment of the invention and, together with the description, serve to provide a further understanding of the technical idea of the invention, It should not be construed as limited.
1 shows a general structure of an optical fiber according to the present invention.
2 is a diagram schematically showing a configuration of a conventional optical fiber Bragg grating sensor and a lattice portion of a probe.
FIGS. 3A to 3C schematically show a signal input to a fiber Bragg grating sensor, a passed signal, and a reflected signal.
4 schematically illustrates an embodiment of an optical fiber Bragg grating probe sensing system of the present invention.
5 shows a configuration of an optical fiber Bragg grating sensor applicable to the present invention.
6 is a flow chart associated with one example of a method for fabricating an optical fiber Bragg grating probe of the present invention.
7A to 7D schematically illustrate an example of a method of manufacturing the optical fiber Bragg grating probe of the present invention.
8 is a flowchart related to an example of a method of measuring a strain of a measured object using the optical fiber Bragg grating probe of the present invention.
9 shows a configuration of a fiber Bragg grating probe for testing the sensitivity change according to the present invention.
Figure 10 shows a temperature chamber for applying heat to a fiber Bragg grating probe for testing the sensitivity change according to the present invention.
11 shows the temperature sensitivity according to the stiffness of the sensitivity control element attached to the optical fiber Bragg grating.
FIG. 12 shows strain sensitivity according to the stiffness of a sensitivity control element attached to an optical fiber Bragg grating.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In addition, the embodiment described below does not unduly limit the contents of the present invention described in the claims, and the entire configuration described in this embodiment is not necessarily essential as the solution means of the present invention.

Conventionally, a photosensor bragg grating sensor has been widely used to measure the deformation of a building or a structure, and a photosensor bragg grating has been packaged and used so that it can be easily attached to an object to be measured.

However, these photosensor Bragg grating sensors are sensitive to both physical and thermal properties, and have difficulty in precise measurement in use in environments exposed to temperature and deformation. Especially, the photosensor bragg grating packaged with epoxy resin has a temperature sensitivity of about 40 pm / ° C, which is larger than the temperature sensitivity (about 11 pm / ° C) when not packaged. It became a disorder.

In the present invention, a method of controlling the sensitivity of the optical sensor Bragg grating sensor to provide accurate measurement of the object to be measured is proposed.

<Sensitivity controlled optical fiber Bragg Configuration of Sensor using Grid>

Hereinafter, the structure of the optical fiber Bragg grating with sensitivity controlled according to the present invention will be described in detail with reference to FIGS. 4 and 5. FIG.

4 schematically illustrates an embodiment of an optical fiber Bragg grating probe sensing system of the present invention. 4, the FBG transducer sensing system 100 may include a light source 110, an optical fiber coupler 120, an optical spectrum analyzer 130, an FBG transducer 200, and the like . However, the components shown in FIG. 4 are not essential, so that the FBG probe sensing system 100 having more or fewer components may be implemented.

The light source 110 may use a light emitting diode, or a light emitting device such as a laser diode (LD), an organic EL device, an inorganic EL device, a multi-wavelength lamp, or the like may be used. The light emitted from the light source 110 is totally reflected in the optical fiber 210.

The optical fiber coupler 120 connects the light source 110 and the FBG probe 200 so that the light emitted from the light source 110 travels toward the FBG probe 200. The FBG probe 200, which is at least a part of the light emitted from the light source 110, And receives light reflected from the light source 200. The optical fiber coupler 120 outputs the optical signal corresponding to the input reflected light to the optical spectrum analyzer 130. As the optical fiber coupler 120, an optical circulator, an optical coupler, or the like can be used.

The optical spectrum analyzer 130 receives the optical signal output from the optical fiber coupler 120 and can recognize the wavelength change of the reflected light using the optical signal and measure the degree of deformation of the measured object. That is, the optical spectrum analyzer 130 calculates the strain based on the temperature and the load of the measured object. Thus, there is no separate light sensing means such as a photodiode.

A specific configuration of the FBG transducer 200 applicable to the FBG transducer sensing system 100 of the present invention will be described with reference to FIG. 5 shows a configuration of an optical fiber Bragg grating sensor applicable to the present invention.

5, the FBG probe 200 applicable to the present invention includes a first optical fiber Bragg grating 220, a second optical fiber Bragg grating 230, a sensitivity control element 240, a packaging portion 250, And the like. However, the components shown in FIG. 5 are not essential, so that the FBG probe 200 having more or fewer components may be implemented.

The first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 are disposed at predetermined positions of the optical fiber 210, respectively. The first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 are spaced apart from each other by a predetermined distance. Light emitted from the optical fiber 210 passes through the first optical fiber Bragg grating 220, And passes through the optical fiber Bragg grating 230.

The first optical fiber Bragg grating 220 reflects light of a first Bragg wavelength and passes the remaining light (first light). The second fiber Bragg grating 230 reflects the second Bragg wavelength of the first light and passes the remaining light (the second light).

The sensitivity control element 240 is attached to a portion of the optical fiber 210 in which the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 are disposed as an element whose thermal expansion coefficient is lower than the thermal expansion coefficient of the optical fiber 210 . The sensitivity control element 240 may adjust the sensitivity of the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230.

Here, the sensitivity represents the rate of change of at least one of the first Bragg wavelength and the second Bragg wavelength depending on the temperature change of the measured object and the degree of deformation of the measured object. These sensitivities include temperature sensitivity, which is the rate of change of the Bragg wavelength depending on the temperature change of the measured object, and strain sensitivity, which is the rate of change of Bragg wavelength depending on the degree of deformation of the measured object.

If the temperature sensitivity is too high, the Bragg wavelength will vary greatly due to the temperature change associated with the object, making it difficult to accurately measure the deformation of the object. Therefore, the temperature sensitivity should be set lower than the reference value, preferably less than 10 pm / ° C, or more preferably less than 5 pm / ° C.

In addition, it is preferable that the strain sensitivity is set to a range suitable for the measurement object (for example, 0.2 pm / micro-strain to 0.8 pm / micro-strain). When the strain sensitivity becomes too small, It becomes disadvantageous because the range becomes narrow.

The sensitivity can be adjusted according to the stiffness of the sensitivity control element 240. Preferably, the rigidity of the sensitivity control element 240 should be selected to be less than the rigidity of the packaging portion 250.

The sensitivity control element 240 may use carbon fiber reinforced plastics (CFRP) prepreg as an example. A plurality of sensitivity control elements may be applied to the FBG probe 200 of the present invention. The first sensitivity control element 242, which is a part of the plurality of sensitivity control elements, is attached to the upper and lower surfaces of the first fiber Bragg grating 220, and the second sensitivity control element 244, which is a part of the plurality of sensitivity control elements, And is attached to the upper and lower surfaces of the optical fiber bragg grating 230.

The thermal expansion coefficient of the sensitivity control element 240 should preferably be smaller than the thermal expansion coefficient of the optical fiber 210 and the first sensitivity control element 242 and the second sensitivity control element 244 may have different thermal expansion coefficients .

The packaging unit 250 is configured to enclose the sensitivity control device 240 to package the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 so that the ease of installation can be secured. Since the packaging unit 250 is located in the object to be measured, the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 in the packaging unit 250 can sense deformation of the measured object.

<Sensitivity controlled optical fiber Bragg Manufacturing Method of Grid>

Hereinafter, a method for fabricating an optical fiber Bragg grating with sensitivity controlled according to the present invention will be described in detail with reference to FIG. 6 and FIGS. 7A to 7D.

Fig. 6 is a flowchart related to an example of a method of manufacturing an optical fiber Bragg grating probe of the present invention, and Figs. 7a to 7d schematically illustrate an example of a method of manufacturing an optical fiber Bragg grating probe of the present invention.

First, a first optical fiber Bragg grating 220 for reflecting light of a first Bragg wavelength and a second optical fiber Bragg grating 230 for reflecting light of a second Bragg wavelength are disposed on the optical fiber 210 (S100).

The first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 are manufactured to periodically change the refractive index of the optical fiber 210 core to reflect light of a specific Bragg wavelength, 220, and 230 are disposed to be spaced apart from each other by a predetermined distance.

Then, a sensitivity control element 240 made of a material having a thermal expansion coefficient lower than a preset value is attached to the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 (S110). The thermal expansion coefficient of the first optical fiber Bragg grating 220 and the thermal expansion coefficient of the second optical fiber Bragg grating 230 are different from each other, can be different.

As the sensitivity control element 240, a carbon composite material (CFRP) prepreg may be used. Carbon composite material (CFRP) prepreg having a coefficient of thermal expansion of about -0.5 to 0.5 microns and having a plurality of sheets formed thereon and then adhering to the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 do.

7A, a first sensitivity control element 242, which is a part of a plurality of sensitivity control elements, is attached to the upper and lower surfaces of the first fiber Bragg grating 220, and has a second sensitivity The control element 244 is attached to the upper and lower surfaces of the second fiber Bragg grating 230. The sensitivity of the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 may be changed according to the first sensitivity control element 242 and the second sensitivity control element 244 to be attached.

Next, as shown in FIG. 7B, the transducer mold 254 is positioned near the sensitivity control element 240 and a plastic material is injected (S120). As an example of the plastic material, an epoxy resin 252 and a curing agent may be used. The epoxy resin may be YD-128, and the curing agent may be prepared by using IPDA in a ratio of 100: 23.

7C, the transducer mold 254 is thermally cured (S130), and the thermosetting transducer mold 254 is removed as shown in FIG. 7D to remove the packaging portion 250 (S140).

<Sensitivity controlled optical fiber Bragg Lattice Sensing method >

Hereinafter, a method for detecting deformation of an object to be measured using the optical fiber Bragg grating whose sensitivity is to be proposed by the present invention will be described with reference to FIG. 8 is a flowchart related to an example of a method of measuring a strain of a measured object using the optical fiber Bragg grating probe of the present invention.

First, light of a broadband wavelength range is irradiated from the light source 110, and the irradiated light proceeds along the optical fiber 210 connected to the light source 110 (S200). The total reflection occurs in the core due to the difference in refractive index inside the optical fiber 210,

Then, light of a first Bragg wavelength, which is at least a part of the light irradiated to the optical fiber 210, is reflected by the first fiber Bragg grating 220 disposed on the optical fiber 210, and the remaining first light is transmitted (S210 ).

Also, light of a second Bragg wavelength, which is at least a part of the first light, is reflected by the second optical fiber Bragg grating 230 disposed apart from the first optical fiber Bragg grating 220, and the remaining second light is transmitted (S220).

Then, the reflected first Bragg wavelength light and the second Bragg wavelength light are received by the optical fiber coupler 120, and the optical fiber coupler 120 transmits the optical signal corresponding to the reflected light to the optical spectrum analyzer 130 (S230).

Then, the optical spectrum analyzer 130 receives the optical signal output from the optical fiber coupler 120, recognizes the wavelength change of the reflected light using the received optical signal, The degree of deformation of the measured object is measured (S240).

The change of the Bragg wavelength of the optical fiber Bragg gratings 220 and 230 of the FBG probe 200 according to the present invention may be expressed by Equation (4) below.

here,

Is the strain sensing coefficient of the first optical fiber Bragg grating 220,

Is a thermal sensing coefficient of the first optical fiber Bragg grating 220,

Is a strain sensing coefficient of the second optical fiber Bragg grating 230,

Is the thermal sensing coefficient of the second fiber Bragg grating 230. [

Equation (4) can be expressed as Equation (5) as follows.

The temperature and strain of the object to be measured can be measured using Equation (5).

To control the elasticity and the thermal expansion coefficient of the FBG, the FBG sensor is fabricated with different thermal expansion coefficient to control the temperature and strain of the FBG sensor. It also serves to reduce the range. If the FBG sensor probe is fabricated and its response characteristics are obtained, the wavelength range of the FBG sensor system can be effectively used within a suitable range for measuring temperature and strain using a pair of sensitivity controlled FBG transducers.

<Sensitivity controlled optical fiber Bragg Effect according to grid>

Hereinafter, the sensitivity performance evaluation of the sensitivity-controlled optical fiber Bragg grating of the present invention will be described quantitatively with reference to FIGS. 9 to 12. FIG. FIG. 9 shows a configuration of an optical fiber Bragg grating probe for testing sensitivity changes according to the present invention, FIG. 10 shows a temperature chamber for applying heat to an optical fiber Bragg grating probe for testing a sensitivity change according to the present invention, 12 shows the sensitivity of strain according to the stiffness of the sensitivity control device attached to the optical fiber Bragg grating. FIG. 12 shows the temperature sensitivity according to the stiffness of the sensitivity control device attached to the optical fiber Bragg grating.

In order to minimize the wavelength use range, a number of FBG transducers 200 were fabricated as shown in FIG. 9 to see how much a sensitivity control device with a low thermal expansion coefficient should be attached on the FBG. The elastic modulus of the epoxy resin 252 for packaging is 141.8 Gpa. The same material as the packaging epoxy resin 252 was used for bonding to the blade. The curing of the packaging and the adhesive took 3 hours at room temperature curing and the curing time of 1 hour at about 80 ° c to ensure reliable performance. The epoxy used was YD-128, and the curing agent was IPDA in a ratio of 100: 23.

In order to test the performance of a pair of FBG transducers 200 of the present invention finally developed using the two FBGs 220 and 230, the FBG transducer 200 is attached to an aluminum plate to measure a temperature-dependent strain Temperature and strain.

A number of transducers were fabricated and tested to examine the change in sensitivity by varying the stiffness of the carbon composite material. That is, only the FBG transducer 200 and the FBGs 220 and 230, in which the FBGs 220 and 230 each having a total of 2, 4, and 8 CFRPs as sensitivity control devices are packaged with the epoxy resin 252, An FBG transducer 200 packaged with a resin 252 was produced as shown in Fig. 10 is a temperature chamber prepared for examining the performance of a pair of sensitivity-controlled FBG transducers.

As shown in the right photograph of FIG. 9, a pair of sensitivity-controlled FBG transducers were bonded onto an aluminum plate. On the aluminum plate, an electric resistance type strain gauge is attached to read the strain change due to the thermal expansion of aluminum.

The temperature rise test was carried out at room temperature for at least 30 minutes at each temperature while increasing the temperature from about 24 ° C to 36 ° C, 56 ° C and 76 ° C. After reading the wavelength change value of the FBG sensor interrogator, . The data obtained from such experiments are shown in Table 1 below.

Temperature from 24 ℃
(° C) Bared FBG
(pm) FBG with
0.25 mm CFRP
(pm) FBG with
0.5 mm CFRP
(pm) FBG with
1 mm CFRP
(pm) Strain from
ESG
(micro-strain) 36 417 341 233 157 137 56 1860 1051 546 447 367 79 3810 1645 1006 774 570

In general, FBG transducers not packaged have a strain sensitivity of 1.13 pm / micro - strain and a temperature sensitivity of 11 pm / ℃.

FBG transducer integrated with 0.25 mm CFRP, FBG transducer integrated with 0.5 CFRP with 4 CFRPs integrated, and FBG transducer with 1 mm thickness integrated with CFRP 8 are all made of epoxy resin The temperature and strain sensitivity changes of the probe packaged to about 2.5 mm were investigated using the results of Table 1 above.

Assuming that the strain sensitivity of FBG transducers with sensitivity control is equal to the value of general FBG transducer by applying CFRP, the strain of the transducer is calculated to be equal to the thermal expansion strain of aluminum, and the strain sensitivity of FBG transducer And the sensitivity is calculated by dividing the wavelength change by the temperature, the result shown in FIG. 11 can be obtained. As can be seen from FIG. 11, the sensitivity-controlled FBG transducer 200 of the present invention has a temperature sensitivity of 2.39 pm / ° C. when the CFRP thickness is 1 mm.

In order to examine the change of the strain sensitivity, the wavelength change value of the FBG transducer was calculated using the temperature change value and the temperature sensitivity of the FBG probe from the results of Table 1, There is only a wavelength change amount due to a pure strain change. Dividing this value by the strain gives a strain sensitivity which is shown in FIG.

As can be seen from FIG. 12, it can be seen that the strain sensitivity is 0.35 pm / micro-strain, which is the least when the CFRP thickness is 1 mm. From these results, it can be seen that it is possible to develop FBG transducers with much lower strain and temperature sensitivity than the sensitivity of general FBG transducers.

It can be seen from the experimental results of FIGS. 11 and 12 that the number of CFRPs attached to the first optical fiber Bragg grating 220 and the second optical fiber Bragg grating 230 is optimized when each is eight. That is, when the thickness of the carbon composite prepreg is about 1 mm, the temperature sensitivity is minimized and the strain sensitivity is 0.35 pm / micro-strain, which is a suitable range for measurement on the object to be measured and corresponds to the rigidity of CFRP 8 It is considered that the use of the sensitivity control element 240 is optimized.

According to the FBG transducer described above, the temperature sensitivity of the FBG transducer can be greatly reduced by attaching the sensitivity control device having a low thermal expansion coefficient to the optical fiber Bragg grating and packaging, and the strain sensitivity with a desired range value can be controlled. In addition, the FBG sensor can be used as a sensor that can operate more efficiently and stably, and the manufacturing method thereof is not so complicated, so that there is an advantage that the strain of the measured object can be measured more accurately at low cost.

The present invention can also be embodied as computer-readable codes on a computer-readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission via the Internet) . The computer readable recording medium may also be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the present invention can be easily inferred by programmers of the technical field to which the present invention belongs.

It should be understood that the above-described apparatus and method are not limited to the configuration and method of the embodiments described above, but the embodiments may be modified so that all or some of the embodiments are selectively combined .

100: FBG probe system
110: Light source
120: Fiber optic connector
130: Optical spectrum analyzer
200: FBG probe
210: Optical fiber
220: first optical fiber Bragg grating
230: second fiber Bragg grating
240: Sensitivity control element
242: first sensitivity control element
244: second sensitivity control element
250:
252: Epoxy resin
254: Transducer mold

Claims

An optical fiber through which light propagates;
A first optical fiber Bragg grating (FBG) disposed in the optical fiber for reflecting light of a first Bragg wavelength, which is at least a part of the light, and passing the first light;
A second optical fiber Bragg grating (FBG) disposed in the optical fiber spaced apart from the first optical fiber Bragg grating to reflect light of a second Bragg wavelength, which is at least a part of the first light, ;
Wherein the first optical fiber Bragg grating and the second optical fiber Bragg grating are formed of a material having a thermal expansion coefficient lower than a predetermined first value to adjust the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating, A sensitivity control element attached to the grating; And
And a packaging portion formed to surround the sensitivity control element and bundling the first optical fiber Bragg grating and the second optical fiber Bragg grating and positioned in the measured object,
Wherein the first light is light that does not correspond to the first Bragg wavelength of the light and the second light is light that does not correspond to the second Bragg wavelength of the first light,
Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a deformation parameter associated with the object to be measured and the deformation parameter is at least one of a temperature change of the object to be measured and a degree of deformation of the object to be measured,
Wherein the sensitivity is a rate of change of at least one of the first Bragg wavelength and the second Bragg wavelength according to the deformation parameter.

The method according to claim 1,
Wherein the sensitivity control element is plural,
Wherein a first sensitivity control element that is a part of the plurality of sensitivity control elements is attached to upper and lower surfaces of the first fiber Bragg grating,
And a second sensitivity control element, which is a part of the plurality of sensitivity control elements, is attached to upper and lower surfaces of the second fiber Bragg grating.

3. The method of claim 2,
Wherein a thermal expansion coefficient of the first sensitivity control element and a thermal expansion coefficient of the second sensitivity control element are different from each other.

The method according to claim 1,
Wherein the first value is a thermal expansion coefficient of the optical fiber.

The method according to claim 1,
Wherein the sensitivity is controlled in response to stiffness of the sensitivity control element.

The method according to claim 1,
And the stiffness of the sensitivity control element is smaller than the stiffness of the packaging portion.

The method according to claim 1,
Wherein the packaging portion is fabricated using an epoxy resin and a curing agent.

The method according to claim 1,
The sensitivity,
And a strain sensitivity which is a rate of change of the Bragg wavelength depending on a temperature sensitivity which is a rate of change of the Bragg wavelength according to a temperature change of the measured object and a degree of deformation of the measured object.

9. The method of claim 8,
And the temperature sensitivity is set to be lower than a preset reference value.

9. The method of claim 8,
Wherein the strain sensitivity is set within a predetermined reference range.

The method according to claim 1,
Wherein a wavelength of light reflected from at least one of the first optical fiber Bragg grating and the second optical fiber Bragg grating is changed as at least one of the first Bragg wavelength and the second Bragg wavelength is changed. FBG transducer.

The method according to claim 1,
Wherein the sensitivity control element is CFRP (Carbon Fiber Reinforced Plastics).

A light source for irradiating light of a broadband wavelength band;
An optical fiber through which the light travels; A first optical fiber Bragg grating (FBG) disposed in the optical fiber for reflecting light of a first Bragg wavelength, which is at least a part of the light, and passing the first light; A second optical fiber Bragg grating (FBG) disposed in the optical fiber spaced apart from the first optical fiber Bragg grating to reflect light of a second Bragg wavelength, which is at least a part of the first light, ; Wherein the first optical fiber Bragg grating and the second optical fiber Bragg grating are formed of a material having a thermal expansion coefficient lower than a predetermined first value to adjust the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating, A sensitivity control element attached to the grating; And a packaging portion formed to surround the sensitivity control element and bundling the first optical fiber Bragg grating and the second optical fiber Bragg grating and positioned in the measured object;
An optical fiber coupler connected to the FBG probe and receiving the reflected first Bragg wavelength light and the second Bragg wavelength light to output an optical signal; And
And an optical spectrum analyzer connected to the optical fiber coupler and receiving the optical signal,
Wherein the first light is light that does not correspond to the first Bragg wavelength of the light and the second light is light that does not correspond to the second Bragg wavelength of the first light,
Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a deformation parameter associated with the object to be measured so that a wavelength of light reflected from at least one of the first optical fiber Bragg grating and the second optical fiber Bragg grating Changed,
Wherein the deformation parameter is at least one of a temperature change of the measured object and a degree of deformation of the measured object,
Wherein the sensitivity is a rate of change of at least one of the first Bragg wavelength and the second Bragg wavelength according to the deformation parameter,
Wherein the optical spectrum analyzer recognizes the wavelength variation of the reflected light using the received optical signal and measures the degree of deformation of the measured object corresponding to the wavelength change of the reflected light. FBG transducer sensing system.

14. The method of claim 13,
Wherein the first value is a thermal expansion coefficient of the optical fiber.

14. The method of claim 13,
Wherein the sensitivity is controlled in response to stiffness of the sensitivity control element.

Irradiating light of a broadband wavelength band from a light source;
Advancing the light into the optical fiber;
The first optical fiber Bragg grating (FBG) disposed in the optical fiber reflects light of a first Bragg wavelength, which is at least a part of the light, and passes through the first optical fiber Bragg grating (FBG);
A second Bragg wavelength of at least a part of the first light is reflected by a second optical fiber Bragg grating (FBG) disposed on the optical fiber, the second Bragg wavelength being separated from the first optical fiber Bragg grating, ;
The optical fiber coupler receiving the reflected first Bragg wavelength light and the second Bragg wavelength light and transmitting the optical signal to the optical spectrum analyzer;
The optical spectrum analyzer recognizing the wavelength change of the reflected light using the received optical signal; And
And measuring a degree of deformation of the object to be measured corresponding to a change in the wavelength of the reflected light,
Wherein a sensitivity control element is attached to a portion of the optical fiber where the first optical fiber Bragg grating and the second optical fiber Bragg grating are disposed and the sensitivity control element is made of a material having a thermal expansion coefficient lower than a predetermined first value, Bragg gratings and the second fiber Bragg gratings,
The packaging section is formed so as to surround the sensitivity control element and binds the first optical fiber Bragg grating and the second optical fiber Bragg grating,
Wherein the first light is light that does not correspond to the first Bragg wavelength of the light and the second light is light that does not correspond to the second Bragg wavelength of the first light,
Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a deformation parameter associated with the object to be measured and the deformation parameter is at least one of a temperature change of the object to be measured and a degree of deformation of the object to be measured,
Wherein the sensitivity is a rate of change of at least one of the first Bragg wavelength and the second Bragg wavelength according to the deformation parameter.

17. The method of claim 16,
Wherein the first value is a thermal expansion coefficient of the optical fiber.

17. The method of claim 16,
Wherein the sensitivity is controlled corresponding to the stiffness of the sensitivity control element.

Disposing a first optical fiber Bragg grating (FBG) for reflecting light of a first Bragg wavelength on the optical fiber and a second optical fiber Bragg grating (FBG) for reflecting light of a second Bragg wavelength;
Attaching a first sensitivity control element, which is a part of a plurality of sensitivity control elements made of a material having a thermal expansion coefficient lower than a predetermined first value, to upper and lower surfaces of the first fiber Bragg grating, Attaching a sensitivity control element to upper and lower surfaces of the second fiber Bragg grating;
Injecting a plastic material into the transducer mold surrounding the plurality of sensitivity control elements to thermally cure the transducer mold; And
And forming a packaging portion from the thermosetting probe mold,
Wherein the plurality of sensitivity control elements adjust the sensitivity of at least one of the first fiber Bragg grating and the second fiber Bragg grating,
Wherein the first optical fiber Bragg grating passes a first light of light traveling into the optical fiber and the second optical fiber Bragg grating passes a second light of the first light,
Wherein the first light is light that does not correspond to the first Bragg wavelength of the light and the second light is light that does not correspond to the second Bragg wavelength of the first light,
Wherein the packaging portion is formed to surround the plurality of sensitivity control elements to bundle the first optical fiber Bragg grating and the second optical fiber Bragg grating,
Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a deformation parameter associated with the object to be measured and the deformation parameter is at least one of a temperature change of the object to be measured and a degree of deformation of the object to be measured,
Wherein the sensitivity is a rate of change of at least one of the first Bragg wavelength and the second Bragg wavelength according to the deformation parameter.

A recording medium on which a program of instructions executable by a digital processing apparatus to implement a sensing method of a sensitivity-controlled FBG transducer is tangibly embodied and which can be read by the digital processing apparatus,
The sensing method of the FBG transducer,
Irradiating light of a broadband wavelength band from a light source;
Advancing the light into the optical fiber;
The first optical fiber Bragg grating (FBG) disposed in the optical fiber reflects light of a first Bragg wavelength, which is at least a part of the light, and passes through the first optical fiber Bragg grating (FBG);
A second Bragg wavelength of at least a part of the first light is reflected by a second optical fiber Bragg grating (FBG) disposed on the optical fiber, the second Bragg wavelength being separated from the first optical fiber Bragg grating, ;
The optical fiber coupler receiving the reflected first Bragg wavelength light and the second Bragg wavelength light and transmitting the optical signal to the optical spectrum analyzer;
The optical spectrum analyzer recognizing the wavelength change of the reflected light using the received optical signal; And
And measuring a degree of deformation of the object to be measured corresponding to a change in the wavelength of the reflected light,
Wherein a sensitivity control element is attached to a portion of the optical fiber where the first optical fiber Bragg grating and the second optical fiber Bragg grating are disposed and the sensitivity control element is made of a material having a thermal expansion coefficient lower than a predetermined first value, Bragg gratings and the second fiber Bragg gratings,
The packaging section is formed so as to surround the sensitivity control element and binds the first optical fiber Bragg grating and the second optical fiber Bragg grating,
Wherein the first light is light that does not correspond to the first Bragg wavelength of the light and the second light is light that does not correspond to the second Bragg wavelength of the first light,
Wherein at least one of the first Bragg wavelength and the second Bragg wavelength is changed according to a deformation parameter associated with the object to be measured and the deformation parameter is at least one of a temperature change of the object to be measured and a degree of deformation of the object to be measured,
Wherein the sensitivity is a rate of change of at least one of the first Bragg wavelength and the second Bragg wavelength according to the deformation parameter.