TWI246589B - Lateral superstructure fiber grating pressure and temperature sensor - Google Patents

Abstract

Previous publications of fiber pressure sensors using a uniform fiber Bragg grating is based on the center-wavelength shift of the grating toward the shorter wavelength side due to the pressure directly to pressurize the fiber. Therefore the slope of the center-wavelength shift to the pressure is negative. Recently, the fiber sensors based on a SFBG have been developed to simultaneously measure multi-parameters for improving the function of a sensor system. The fabrication of a SFBG is generally utilized by exposing UV light going through a periodic low-spatial-frequency amplitude mask and a phase mask into the fiber. Thus a SFG includes the characteristics both of a FBG and a LPG, which can be used for measuring pressure and temperature simultaneously. We propose a high-sensitivity fiber sensor with the function of simultaneously measuring temperature and pressure, which based on a superstructure fiber grating (SFG) encapsulated in a polymer-half-filled metal cylinder with its end bonded to the central of a round plate attached to the surface of polymer. The cylinder has two openings on opposite side of the wall at the polymer part. In this way, the polymer can be pressurized along one radial direction only, and responds an axial force acting on the round plate, producing an axial strain on the SFG. The pressure sensitivity of our proposed sensors is greatly improved for comparing with that of a bare SFG. The scheme of this sensor is the combination of the structure of our previous lateral pressure sensor and the characteristics of a SFG for simultaneously measuring pressure and temperature. This sensor should be applied potentially for the measurement of the pressure and temperature of a boiler, and the underwater depth or the axial strain.

Description

-1246589 IX. Description of the Invention: [Technical Field] The present invention relates to a side-pressure type super-structured fiber grating pressure temperature sensor, in particular to a single super-structured fiber grating combined with lateral pressure type pressure The sensor structure achieves a high-sensitivity fiber grating sensor with simultaneous measurement of temperature and pressure, enabling the wide application in pressure and temperature measurement or oil and gas exploration in underwater and hot steel furnaces. [Prior Art] In recent years, due to the vigorous development of optoelectronic technology, the optoelectronic industry has become the new darling of this century. The demand and the increase in the quality and quantity of communication have made the optical fiber play a very important role in communication. Because of its light weight, small size, easy to be corroded and undisturbed, and its low loss and high efficiency transmission capability, it has been widely used in various communication networks, using fiber gratings to complete the sensor. For more than a decade, it has become one of the theories that have been valued in the field of sensors. Compared with traditional electromechanical sensors, fiber optic sensors are light and slender, easy to use, and the fiber optic components used as sensors are not affected by external environmental factors. The potential is due to the invention of the fiber and the use of copper wire as a transmission tool and electronic components as a sensory change. In the large-scale machine in the Minsheng industry, such as the factory sales, transportation tools, aircraft, and the monitoring system required for the boat, the number of sensors used accounts for the high proportion. In addition, since the sensor is fully utilized, the flow rate and temperature of the gas, liquid, etc. can also be measured. Therefore, the research on fiber Bragg grating sensors is a major focus of the practical application of the 1246589 system. By the literature [1 ] Μ · G · Xu, Η · Ge i ge r, and J. P. Dakin, ''Fiber grating pressure sensor with enhanced sensitivity using a glass -bubble housing, 〃 Electron, Lett·, Vol.32 , pp.128-129, (1996), [2] Y. Liu, Z. Guo, Y. Zhang, KS Chiang, and X. Dong , ''Simul t aneous pres sure and temperature measurement with po1yme r-coa t ed fiber Bragg grating, Electron, Lett., Vol. 36, pp. 564-566 (2000), literature [3] Y· Zhang, DFeng, Z. Liu, Z. Guo, X. Dong, KS Chiang, and Beatrice CB Chu, x'High-sensitivity pressure sensor using a shielded po1yme r-coa t ed fiber grating, "Photon. Techno 1· Lett., Vol·13, pp.618-619, (2001), it is known that Many scholars are working on the sensor with fiber grating as the backbone. When using fiber grating to sense the object to be tested, the temperature and strain change of the object to be tested often occur, so if you want to use a single grating. Separating the changes in temperature and strain from two variables is quite easy, in just a few years. It has started there are a number of approaches have been proposed to solve this problem. For example, the combination of Bragg grating and long-period grating method, the Bragg cavity sensor method 'Double-wavelength Bragg grating method, etc., but most of the above methods use the reflection wavelength offset of two different gratings to change the temperature and The physical quantities of the strain changes are separated, but each has its shortcomings. For example, the fusion loss between the fibers, the center wavelength difference between the two sets of gratings is too large, and it is necessary to use two sets of light sources of different bandwidths, which cannot effectively save costs and is in production. More complicated and complicated. This is in some literature [4] Bai -〇u Guan et al, 1246589 "Simultaneous Strain and Temperature Measurement Using a Superstructure Fiber Bragg Gratings, , 5 IEEE Photon. Technol. Lett, Vol.l2, No. 6, pp In .675-677, 2000, a concept was proposed in which the superstructure fiber grating has the characteristics of simultaneously measuring the temperature and strain of the object to be tested, and it is no longer necessary to use a multi-segment grating for sensing. The cumbersome production process simplifies the complexity of the sensor and saves a lot of unnecessary resources in terms of cost; only the above technology can simultaneously measure the stress and temperature, but the measurement is Lateral stress, not pressure, and its sensitivity is due to bare fiber, so its sensitivity still has room for improvement. It can be seen that the above-mentioned conventional techniques still have many shortcomings and shortcomings, which is not a good designer, but needs to be improved. In view of the shortcomings and shortcomings derived from the above sensing technology, the inventor of the present invention has improved and innovated, and after years of painstaking research, he finally succeeded in researching. The present invention aims to provide a side-pressure type super-structured fiber grating pressure and temperature sensor, which is a superstructure type (Superstructure). The fiber grating combined with an innovative side-pressure fiber grating pressure sensor is a new type of pressure temperature sensor, which can be used to measure the temperature and pressure simultaneously. Another object of the present invention is to provide - The lateral pressure type super-structured fiber grating pressure temperature sensor shows that the super-structured fiber grating side pressure type pressure and temperature sensor is effective and simultaneously performs the functions of pressure and temperature measurement, and Its high pressure and temperature sensing sensitivity' has a high potential in the simultaneous measurement of pressure and temperature in high temperature boilers, in addition to the considerable measurement capability of the 1246589 application for simultaneous measurement of water level and water temperature. A lateral pressure type super-structured fiber grating pressure temperature sensor capable of achieving the above object of the invention is a cylindrical hollow metal The internal structure of the crucible contains a superstructure fiber grating. The superstructure fiber grating will be completely coated in a polymer with appropriate elasticity. The pressure temperature sensor has a medium I and superstructure on the top of the polymer. One end of the fiber-optic grating has a circular opening on each side of the circular hard casing. The inside of the fiber-optic grating is filled with the external pressure, and the super-structured fiber grating passes through the small hole in the center of the bottom of the metal casing. Connected to the outside. Among them, the superstructure fiber grating is the effect of temperature and pressure, using the central wavelength, reflectivity = force: temperature relationship, when the side pressure type side pressure type super-structure fiber grating pressure When the temperature sensor is subjected to temperature or pressure changes, the center wavelength of a single channel and the single-channel reflectance A are smaller than the total offset Δλ, AR, and the obtained super-structured fiber grating is subjected to temperature. Or pressure, temperature, pressure coefficient. Then you can know the amount of change in temperature and pressure. The temperature and pressure are determined by the characteristics that the pressure or temperature changes the center wavelength and reflectance. The characteristics of the super-structured fiber grating can be changed as needed to achieve the measurement range size and the sensitivity adjustment of the reflectivity. The polymer, on the other hand, has a large characteristic of the modulus of the property, so that the sensitivity to pressure sensing can be greatly increased, and the melted polymer is poured into the cylindrical aluminum sensor mold during use. Naturally harden, so that the entire super-structured fiber 3 grating can be completely fixed in the polymer, and the strain generated by the external pressure on the polymer can drive the central wavelength of the super-structured fiber grating to shift. Measure the sense of pressure change. 1246589 [Embodiment] Please refer to FIG. 1 , which is a super-structured fiber grating structure diagram of a side-pressure type super-structured fiber grating pressure and temperature sensor according to the present invention. It can be seen from the figure that it is written on the optical fiber by using UV light. A section of a structure with no Bragg gratings spaced apart from each other, and this section has a period of no period; about a distance of tens to hundreds of micrometers (# m ), a superstructured fiber grating (SFBG) can be regarded as Combining the synthesis of Bragg Fiber Bragg Grating (FBG) and Long-Period Fiber Bragg Grating (LpG), the strong or weak reflectivity is determined by the coupling coefficient of the Bragg grating (proportional to the refractive index modifier), while the superstructure fiber grating reflection The distance between the channels can be determined by the period of the long-period fiber grating, so the period and strength of the super-structured fiber grating can be designed as needed. Simultaneously measuring the two parameters of temperature and strain by using the multi-channel characteristics of the 光纤- and Ό-structured fiber gratings, and separating the fluctuations of the two parameters of temperature and strain, when the super-structured fiber grating is subjected to the effect of temperature or strain, The optical spectrum not only has a wavelength that varies with temperature or strain. The reflectance also varies with temperature or strain. Therefore, as long as the superstructure fiber grating is buried in a building such as a bridge or a dam, The offset between the wavelength and the reflectance is measured by the instrument, so that the temperature and strain applied to the bridge or the dam at that time can be known, which also completes the sensing element that can simultaneously measure the temperature and strain. Although the application of superstructure fiber gratings is very wide, if combined with different research fields, it will be more unique to the super-structured fiber optical thumb. "Monthly referring to Fig. 1(a) to Fig. 2(c), is a top cross-sectional view, a side cross-sectional view and a side view of the side view of the super-structured fiber grating Glue temperature sensor of the present invention, It can be seen that the (four) type fiber grating temperature sensor i is a cylindrical hollow metal shell n, 1246589 ^ superstructure fiber grating 12, and half full and as a super structure fiber grating 12 outer lining The polymer 13 can completely coat the super-structured fiber precursor 12 to the elastically appropriate polymer, and has a round hard plate at the top of the polymer 13 and a central end of the super-structured fiber grating 12 The metal casing U has a circular opening 1U on each side, and the polymer 13 filled therein receives the external pressure, and the super-structured fiber grating 丨2 passes through the small hole in the center of the bottom of the metal casing, with the optical fiber and External connection. (1) The relationship between the center wavelength and the pressure of the side-pressure super-structured fiber grating pressure and temperature sensor········································ Located in the center of the polymer. First consider the case where the polymer is in the three-dimensional space, the direction (y direction) of the polymer is subjected to pressure or stress, as shown in Figure 3. When there is only pressure in the y direction in the environment, and the pressure is p, ^ and E are the buzon ratio and the elastic modulus of the polymer, respectively.

£y=P £Z = That is, when the pressure p in the y direction is generated, the strain of the heart, f ^ & will be generated in the X, y ' z direction, respectively. Now, if a fiber grating with a modulus of elasticity of 5^ and a cross-sectional area α is embedded in the central axis of the polymer along the z-axis, and one end of the fiber grating is the same as the cross-sectional area of the polymer, and is flat. Attached to the center point of a circular hard 1246589 plate on the top surface of the polymer, the other end is fixed to the center point of the polymer bottom surface, as shown in Figure 4. When p is generated in the y direction, a force in the Z direction and a size of pR is generated on the top circular hard plate of the polymer, and this force acts on the fiber grating and the polymer, that is, FR=Ffiber+FpQiymer, Fmef ' And hehe.丨ymerdw x(j a α)χ Heart coffee. When the sensor is pressed, the polymer has the same axial strain as the fiber grating (FBG), that is, the heart = ^ coffee, so there is

ζ ΙΛα A ten-J so

-vPA aEfiber+(Aa)Epolymer If the polymer is present in an aluminum casing, as shown in Figure 5, the strain in the y and Z directions will not occur except for the coating of the casing in the X direction. for\. Therefore, the relationship between the center wavelength and the pressure of the light-pressure type of the lateral pressure type super-structured fiber grating is as follows: vi j±

中心β V (2) side-pressure super-structured fiber grating pressure temperature sensor central wavelength and temperature relationship: When adding temperature to the super-structured fiber grating, the equivalent refractive index of the grating and the grating period will follow The temperature changes, so the reflection ~ wavelength will also change with temperature, the mathematical formula can mean:

AZBJ=2/^neffTA + 2neff£zTA where the first term represents the factor that causes the equivalent refractive index change of the Bragg fiber grating due to temperature, and the second term indicates that the strain effect is caused by the temperature, causing the fiber grating period to change. Factor, εζτ Table 12 1246589 shows the magnitude of the strain due to temperature change Δ T . The thermo-optic effect causes the temperature change to cause a change in the refractive index of the fiber' and the thermal expansion effect causes the fiber grating to strain, and the strain also causes a change in the equivalent refractive index. In the formula, Δη", can mean:

Aneff, T -^-(pnszJ -(Pn ^ Ρη)ν^ζ,τ) ^U1 J p 2 In the formula, the refractive index of the core changes when the unit temperature changes V U± J p

The size ' ε ζ, τ represents the magnitude of the axial strain due to the temperature change Δ T . The formula can be rewritten as: ΔΑ

BJ and β dn \dTj -^^ΐ2-ν(Ρη+Ρι2)) €ζ,Τ

AT

AT 疋 A A is a thermo- op tic coefficient, and B 疋 is a thermal expansion coefficient (therm 〇 expansion coefficient ′) and typical parameters of a general erbium-doped quartz (germansiHcate) single-mode fiber are shown in the following table.

Parameter thermal-optical coefficient rc; 6.8 X 10~6 Thermal expansion coefficient rc; 0.55 X 10 Busson ratio 0.17 Pn 0.121 Pl2 0.27 Refractive index 1.448 (3) Side-pressure superstructure fiber grating pressure and temperature sensor experiment 13 1246589 The following results are available:

Please refer to Figure 6(a) and Figure 6(b) for the pressure versus wavelength and reflectivity of the lateral pressure type super-structured fiber grating pressure and temperature sensor. Figure 6(a) shows the pressure respectively. The temperature sensor is subjected to the pressure of OMpa and 0.16Mpa, and the shift of the center wavelength and the reflectance change is as shown in Fig. 6(b). The reflection center wavelength of the fiber grating is shifted from the original 1536 · 6nm to 1 543.8 Nm, the principle of this fiber grating pressure and temperature sensor will be linearly shifted upward by 4.5μ increments for each O.IMpa pressure increase, in other words, its sensitivity to pressure measurement is 2.97\1〇. 21^&. The reflectivity is increased from the original 9dB to 13.5dB, which increases linearly with an increase of 2.8dB for each additional pressure of 〇 · i_a.

Please refer to Figure 7(a) and Figure 7(b) for the temperature versus wavelength and reflectivity of the lateral pressure type super-structured fiber grating pressure and temperature sensor. Figure 7 (a) represents this pressure. The temperature sensor is subjected to a temperature of 20 ° C and 80 ° C, and its center wavelength and reflectance change are shifted. As shown in Fig. 7 (b), the reflection center wavelength of the fiber grating is shifted from the original 1536.6 nm to At 1538 nm, the function of this fiber grating pressure and temperature sensor will be linearly offset upward by an increase of 0 · 23 nm for each additional temperature. Its reflectivity increased from the original 9dB to 18.6dB, with an increase of 1〇 each. The temperature increases linearly with an increase of 1.6 dB. (4) The central wavelength of the side-pressure super-structured fiber grating pressure temperature sensor, the relationship between reflectivity and pressure and temperature: the relationship between the center wavelength, reflectivity and pressure and temperature of the fiber grating pressure and temperature sensor of this structure Can be expressed as if not·· Αλ = ΑΑΡ + ΒΑΤ

AR = CAP + DAT 14 1246589 In the above formula, △ and Δ r are the reflections of the center wavelength of a single channel and the single channel when the pressure-temperature sensor of the side-pressure superstructure fiber grating is subjected to temperature or pressure. The total offset of the rate, and A, B, C, and D are the temperature and pressure coefficients of the super-structured fiber grating when subjected to temperature or pressure. Then you can use the above formula to know the changes in temperature and pressure. Due to the limited sensitivity of the bare Bragg fiber grating to pressure sensing, it is a practical purpose, and the fiber grating can be specially packaged to increase the sensitivity of the pressure sensing, and the package can be made by the fiber grating to generate the axial image tension. Achieving a more sensitive pressure sensing effect 'in the use of the sensor, different requirements and the use of space size limit' thus derived a different structure of the side-pressure fiber grating pressure structure sensor. Due to the different structure of the sensor, the sensitivity is also different. Depending on the needs of the sensor structure, there is still a disadvantage in that it cannot compensate for the temperature. Therefore, a super-structured fiber grating is combined so that temperature and pressure can be measured at the same time. The experimental results also show that the fiber grating side pressure type pressure sensor structure and the super structure type fiber grating combine to effectively perform the functions of simultaneous pressure and temperature measurement, and the high sensitivity of pressure and temperature sensing. In addition to the application of the measurement of the water level and the water temperature at the same time, it can exert considerable measurement of the monthly b force. In addition, the pressure and temperature of the south temperature steel furnace are simultaneously measured and the temperature deformation of the structure is monitored. Has potential and practical value. ' (5) ciadciing mode effect: Please refer to Figure 8 (a) ~ Figure 8 (e) for the side-pressure super-structured fiber grating pressure and temperature sensor at different temperatures From the results of the modal effects between the nucleus and the nucleus, another new phenomenon can be found from the results of the test. When the temperature or pressure changes, the center wavelength will be shifted, and the reflectivity will be Changed, among them, we also found that there is a fiber-shell mode, the fiber-shell mode will change due to the increase of temperature, and the spacing between the fiber-shell mode and the fiber-core mode is also There will be changes, resulting in the above various changes, because the super-structured fiber grating combines the effects of long-period fiber gratings and Bragg fiber gratings, causing a transition between modes. Then, by using these changes in physical phenomena, a single grating can be used to separate the changes of multiple environmental variables independently, and the function of measuring multiple environmental variables at the same time can be achieved, not only limited to measuring pressure and temperature. The two physical quantities can also be measured in other ways: ^%% of the environment variables, such as humidity, and this is a new structure that can simultaneously measure multiple environmental variables and improve sensing sensitivity; provide a reference for practical applications. The detailed description of the preferred embodiments of the present invention is intended to be limited to the scope of the invention, and is not intended to limit the scope of the invention. The patent scope of this case. / Not mentioned, this case is not only innovative in terms of technical thinking, but also enhances the above-mentioned multiple functions. It should be fully in line with the novel 'Li Jin: the statutory invention patent requirements of sex, and apply in accordance with the law. : ::Yuebei Bureau approved this invention patent application, invented to 16 1246589 [Simplified illustration] Figure 1 is a super-structured fiber grating of a side-pressure superstructure fiber grating pressure and temperature sensor Figure 1 (a) is a top cross-sectional view of the lateral pressure type super-structured fiber grating pressure and temperature sensor; Figure 1 (b) is the side of the side-pressure super-structured fiber grating pressure and temperature sensor Figure 1 (c) is a side view of the side pressure type super-structured fiber grating pressure temperature sensor; Figure 1 is the side-pressure type super-structure fiber grating pressure temperature sensor internal polymer shaft Schematic diagram of the strain generation; Figure 4 is a schematic diagram of the axial displacement of the circular flat plate of the lateral pressure type super-structured fiber grating pressure temperature sensor; Figure 5 is the pressure-temperature sense of the lateral pressure type super-structured fiber grating Diagram of pressure under pressure; Figure /, (a) and Figure 6 (b) are the relationship between pressure, wavelength and reflectivity of the lateral pressure type super-structure optical fiber optical pressure sensor. Figure 7 (a) and Figure 7 (b) is the relationship between the temperature and the wavelength and the reflectance of the lateral pressure type super-structured fiber grating pressure temperature sensor. FIG. 8(a) to FIG. 8(e) show the pressure temperature of the lateral pressure type super-structure type fiber grating. The coupled modal effect diagram of the sensor between the shell and the core at different temperatures. 17 1246589 [Description of main component symbols] 1 side pressure type fiber grating pressure temperature sensor 11 outer casing 111 round opening 12 super structure type fiber grating 13 polymer

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Claims (1)

1246589 X. Patent application scope: 1. A side-pressure super-structured fiber grating pressure and temperature sensor, which is made of cylindrical hollow metal and contains a super-structured fiber grating inside. The super-structured fiber grating will be completely Wrapped in a suitably elastic polymer, the pressure temperature sensor has a round hard plate with a center and a superstructure fiber grating at the top of the polymer, and a circular opening on each side of the metal casing. The polymer filled inside is subjected to external pressure here. The super-structured fiber grating is connected to the outside through a small hole in the center of the bottom of the metal casing. 2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ A structure in which gratings are spaced apart from each other. 3 The lateral pressure type super-structure type fiber grating pressure temperature sensor according to claim 1, wherein the super-structure type fiber grating 'can be regarded as a combination of a Bragg fiber grating and a long-period fiber grating, and the reflectance thereof The strength or weakness is determined by the blending coefficient of the Bragg grating (proportional to the refractive index modifier), and the distance between the reflection channels of the superstructured fiber grating can be determined by the period of the long period fiber grating, so the superstructure fiber grating The cycle and intensity can be designed as needed. 4) The lateral pressure type super-structure type fiber grating pressure temperature sensor according to claim 1, wherein the polymer has a large elastic modulus characteristic, so that the sensitivity to pressure sensing can be greatly increased. When used, the molten polymer is poured into the cylindrical shape and sensed as "naturally hardened" in the mold, so that the entire superstructured fiber grating can be completely fixed in the polymer by external pressure of 1246589 The strain generated by the polymer can drive the shift of the central wavelength of the super-structured fiber grating to measure the pressure change. 5 The lateral pressure type super-structured fiber grating pressure temperature sensor according to claim 1, wherein the side pressure type super-structure type fiber grating pressure temperature sensor has a central wavelength, a reflectance and a pressure and a temperature The relationship can be expressed as follows: ΑΛ = ΑΑΡ + ΒΑΤ ^r = cap+dat In the above formula, Δ λ and △ R are the total offsets of the central wavelength of a single channel and the reflectance of a single channel when the pressure-type sensor of the lateral pressure type super-structured fiber grating pressure temperature sensor is subjected to temperature or pressure. A, B, c, and D are the temperature and pressure coefficients of the super-structured fiber grating when subjected to temperature or pressure. 20