CN118050033B - F-P cascade optical fiber sensing structure for measuring seawater temperature and salt and preparation method thereof - Google Patents
F-P cascade optical fiber sensing structure for measuring seawater temperature and salt and preparation method thereof Download PDFInfo
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Abstract
The invention relates to an F-P cascade optical fiber sensing structure for measuring seawater temperature and salt and a preparation method thereof, comprising the following steps: a capillary quartz tube body; the single-mode fiber is arranged at the first end of the interior of the capillary quartz tube body; the temperature sensitive material is arranged at the second end of the interior of the capillary quartz tube body and is connected with the inner wall of the capillary quartz tube body; the temperature sensing cavity is arranged between the single-mode fiber and the temperature sensitive material; the quartz diaphragm is arranged at the end part of the temperature sensitive material and is connected with the second end inside the capillary quartz tube body; the metal sleeve component is sleeved outside the capillary quartz tube body; the salinity sensing cavity is arranged between the metal sleeve component and the quartz diaphragm and is connected with the metal sleeve component and the quartz diaphragm. According to the invention, the quartz membrane is welded on one side of the capillary quartz tube body close to the temperature-sensitive material, the temperature-sensitive material is isolated from seawater, the metal sleeve component is used for preventing seawater corrosion, the strength of the optical fiber sensor is enhanced, and the optical fiber sensor is deep in ocean exploration, and has the advantages of low cost, simple structure, good repeatability and high precision.
Description
Technical Field
The invention relates to the technical field of optical fiber sensors, in particular to an F-P cascade optical fiber sensing structure for measuring seawater temperature and salt and a preparation method thereof.
Background
The salinity of the seawater is an important reference for researching the trend of ocean currents and promoting the treatment of marine environments. The measurement of the salinity of seawater plays an irreplaceable role in the fields of marine scientific investigation, resource exploration, ecological protection and the like. Currently, researchers commonly derive the seawater salinity by measuring the refractive index of seawater, and the temperature and the salinity are important factors influencing the seawater refractive index, and in recent years, an optical fiber sensor for realizing high-precision integrated measurement of the temperature and the salinity through temperature compensation has rapidly developed. Wherein, the fabry-perot temperature sensor shows excellent temperature measurement performance due to its higher sensitivity and accuracy. Therefore, the fabry-perot temperature sensor is developed very rapidly and applied very widely.
Chinese patent CN115597658a discloses an F-P cascade optical fiber sensor for measuring seawater temperature and salt, which simply bonds glass tubes together by using glue, and the bonding part has low structural strength, so that it is difficult to cope with complex marine environment. In addition, the method for coating the temperature-sensitive material on one side of the capillary glass tube is only used when the temperature-sensitive material is filled, the method cannot control the filling volume and the filling position of the temperature-sensitive material in the capillary glass tube, the temperature-sensitive material is directly exposed to seawater, the service life of the temperature-sensitive material is reduced, and a large amount of raw materials are consumed for filling the temperature-sensitive material.
Therefore, in order to solve the technical problems in the prior art, it is necessary to provide an F-P cascade optical fiber sensing structure for measuring seawater temperature and salt and a preparation method thereof.
Disclosure of Invention
First, the technical problem to be solved
In view of the defects and shortcomings of the prior art, the invention provides an F-P cascade optical fiber sensing structure for measuring seawater temperature salt and a preparation method thereof, which solve the problems that in the prior art, the service life of a temperature sensitive material of an optical fiber sensor is low, the structural strength of a bonding part is low, the filling position and volume of the temperature sensitive material in a capillary glass tube cannot be controlled, and a large amount of temperature sensitive material is wasted in the manufacturing process.
(II) technical scheme
In order to achieve the above purpose, the main technical scheme adopted by the invention comprises the following steps:
the first aspect of the invention provides a manufacturing method of an F-P cascade optical fiber sensing structure for measuring sea water temperature and salt, comprising the following steps of:
S1: heating and tapering the hollow optical fiber to obtain a tapered hollow optical fiber, taking a syringe needle, inserting the hollow optical fiber into the syringe needle, sealing with epoxy resin glue, and standing for 24 hours to obtain a filling structure;
S2: the filling structure is connected into a first syringe, the front end of the first syringe connected with the filling structure is immersed into the temperature-sensitive material which is well placed, the temperature-sensitive material is extracted from a zero scale line by the first syringe according to the calculation result of the extraction total amount formula of the temperature-sensitive material, 5cm-10cm is extracted from the first syringe, the filling structure filled with the temperature-sensitive material is placed for 30min-60min, the filling structure filled with the temperature-sensitive material is removed from the first syringe, and then the filling structure filled with the temperature-sensitive material is connected into a second syringe;
wherein the extraction total amount formula is:
；
Wherein: q is the flow rate passing through the section of the pipeline, and the unit is 3/s; t is extraction time, and the unit is s; p 1 is the atmospheric pressure, and the unit is KPa; p 2 is the pressure in the first syringe after the first syringe is extracted, and the unit is KPa; η is the viscosity coefficient of the liquid in Pa.s; r 1 is the inner diameter of the hollow fiber before tapering, and the unit is μm; r 2 is the inner diameter of the hollow fiber after tapering, and the unit is μm; l is the total length of the hollow fiber after tapering, and the unit is mu m; k is a ratio coefficient of the difference between the inner diameters of the hollow optical fiber before and after tapering and the difference between the lengths of the hollow optical fiber before and after tapering;
s3: fixing a filling structure filled with temperature sensitive materials and a second needle cylinder in an actuating mechanism of the injection pump, connecting the actuating mechanism of the injection pump with a controller of the injection pump, and placing hollow optical fibers at the tail end of the filling structure on a clamping mechanism at one side of a six-dimensional adjusting frame;
S4: welding the capillary quartz tube body and the capillary quartz rod by using an arc welding machine, grinding the capillary quartz rod to ensure that the thickness of the capillary quartz rod is 10-20 mu m to obtain a quartz diaphragm, and placing the capillary quartz tube body welded with the quartz diaphragm on a clamping mechanism at the other side of the six-dimensional adjusting frame;
S5: on a six-dimensional adjusting frame, aligning the hollow optical fiber with a capillary quartz tube body welded with a quartz diaphragm, sending the hollow optical fiber into the capillary quartz tube body welded with the quartz diaphragm, and filling a temperature sensitive material into the capillary quartz tube body welded with the quartz diaphragm by controlling a syringe pump controller;
S6: welding the capillary quartz tube body filled with the temperature sensitive material and welded with the quartz membrane and the single-mode fiber together by using an arc welding machine, wherein a cavity formed between the single-mode fiber and the temperature sensitive material, namely a temperature sensing cavity, is formed, and then the optical fiber sensing structure with the temperature sensing cavity is obtained;
S7: the fiber sensing structure with the temperature sensing cavity is sleeved into the metal sleeve component, and a cavity formed between the metal sleeve component and the quartz diaphragm, namely the salinity sensing cavity, is used for completing the preparation of the F-P cascade fiber sensing structure for measuring the seawater temperature and the salt.
Alternatively, the quartz diaphragm has a thickness of 10 μm to 20 μm.
Optionally, the temperature sensitive material is polydimethylsiloxane.
Embodiments of the second aspect of the present invention provide an F-P cascade fiber optic sensing structure for measuring seawater temperature salts, comprising: a capillary quartz tube body; the single mode fiber is arranged at the first end of the interior of the capillary quartz tube body and is connected with the inner wall of the capillary quartz tube body; the temperature sensitive material is arranged at the second end of the inner part of the capillary quartz tube body and is connected with the inner wall of the capillary quartz tube body; the temperature sensing cavity is arranged in the capillary quartz tube body and between the single-mode fiber and the temperature sensitive material; the quartz diaphragm is arranged at the end part of the temperature sensitive material and is connected with the second end inside the capillary quartz tube body; the metal sleeve component is sleeved outside the capillary quartz tube body and is connected with the capillary quartz tube body; the salinity sensing cavity is arranged between the metal sleeve component and the quartz diaphragm and is connected with the metal sleeve component and the quartz diaphragm.
Optionally, the metal sleeve assembly comprises: the sleeve piece is sleeved outside the tube body of the capillary quartz tube and is connected with the capillary quartz tube; the tail part is arranged at the end part of the salinity sensing cavity, which is far away from the quartz membrane, and is connected with the salinity sensing cavity; the connecting piece is arranged between the tail part and the sleeve part and is connected with the salinity sensing cavity.
(III) beneficial effects
According to the manufacturing method of the F-P cascade optical fiber sensing structure for measuring seawater temperature and salt, provided by the first aspect, the thickness of the quartz diaphragm is controlled, so that the quartz diaphragm is prevented from interfering with the normal operation of an optical fiber sensor while isolating seawater, and the process of arc welding and filling temperature-sensitive materials is changed by improving the filling method of the temperature-sensitive materials, so that the manufacturing difficulty of the optical fiber sensing structure is reduced.
According to the F-P cascade optical fiber sensing structure for measuring the seawater temperature and salt, provided by the second aspect of the invention, the temperature sensing cavity and the salinity sensing cavity are arranged, so that the temperature and the salinity of the seawater can be measured, and the temperature sensitive material is isolated from the seawater due to the arrangement of the quartz membrane, so that on one hand, the corrosion of the seawater to the temperature sensitive material is avoided, on the other hand, salt particles are prevented from adhering to the surface of the temperature sensitive material, and the accurate perception of the temperature sensitive material on the temperature change is ensured. By the arrangement, the durability and the stability of the temperature-sensitive material can be ensured, the service life of the temperature-sensitive material is greatly prolonged, the service life of the optical fiber sensor in a complex marine environment is further prolonged, the sensitivity of the optical fiber sensor to temperature change can be prevented from being influenced, and the accurate monitoring of the temperature change is further maintained.
Drawings
FIG. 1 is a schematic diagram of the overall structure of an optical fiber sensing structure according to the present invention;
FIG. 2 is a flow chart of a manufacturing process of an optical fiber sensing structure according to the present invention;
FIG. 3 is a second flowchart of the optical fiber sensing structure of the present invention;
FIG. 4 is a schematic view of the front end of the filling structure of the present invention;
FIG. 5 is a third flowchart of the optical fiber sensing structure of the present invention;
FIG. 6 is a flowchart of a manufacturing process of the optical fiber sensing structure of the present invention;
FIG. 7 is a fifth flowchart of the optical fiber sensing structure of the present invention;
FIG. 8 is an optical path diagram of a fiber optic sensing structure of the present invention;
FIG. 9 is an interference spectrum of a fiber optic sensing structure incorporating the fiber optic sensing structure of the present invention;
FIG. 10 is a graph of a spatial spectrum of an optical fiber sensor having an optical fiber sensing structure according to the present invention after a fast Fourier transform;
FIG. 11 is a schematic diagram of the use of the fiber optic sensing structure of the present invention in combination with a fiber optic grating demodulator, an upper computer, a constant temperature oil tank and a high precision thermometer for temperature measurement;
FIG. 12 is a response plot of the spectrum of the temperature cavity of a fiber optic sensor incorporating the fiber optic sensing structure of the present invention at elevated temperatures;
FIG. 13 is a graph showing the response of a fiber optic sensor incorporating the fiber optic sensing structure of the present invention to a temperature cavity spectrum when the temperature is increased from 268.15K to 278.15K;
FIG. 14 is a plot of the sensitivity of a fiber optic sensor incorporating the fiber optic sensing structure of the present invention when the temperature is increased from 268.15K to 278.15K;
FIG. 15 is a schematic diagram of the use of the fiber sensing structure of the present invention in combination with a fiber grating demodulator, an upper computer, a high-precision thermometer and standard seawater for salinity measurement;
FIG. 16 is a response plot of the salinity chamber spectra of an optical fiber sensor incorporating the optical fiber sensing structure of the present invention as salinity increases;
FIG. 17 is a plot of sensitivity of a fiber sensor having a fiber sensing structure according to the present invention at salinity of 4 to 20%.
[ Reference numerals description ]
1: A single mode optical fiber; 2: a capillary quartz tube body; 3: solid temperature sensitive material; 4: quartz membrane; 5: a metal sleeve assembly; 6: a temperature sensing chamber; 7: a sleeve member; 8: a salinity sensing chamber; 9: a connecting piece; 10: a tail member; 11: a syringe needle; 12: hollow fiber; 13: filling the structure; 14: a first syringe; 15: a liquid temperature sensitive material; 16: a second cylinder; 17: an upper computer; 18: a syringe pump controller; 19: an injection pump actuator; 20: a six-dimensional adjusting frame; 21: an arc welding machine; 22: a fiber grating demodulator; 23: a high-precision thermometer; 24: a constant temperature oil tank; 25: standard saline.
Detailed Description
The invention will be better explained by the following detailed description of the embodiments with reference to the drawings.
In order that the above-described aspects may be better understood, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The embodiment provides a manufacturing method of an F-P cascade optical fiber sensing structure for measuring seawater temperature and salt, as shown in fig. 1 to 7, the manufacturing method comprises the following steps:
S1: heating and tapering the hollow optical fiber 12 to obtain a tapered hollow optical fiber, taking a syringe needle 11, inserting the hollow optical fiber 12 with the outer diameter of 106 mu m into the syringe needle 11, sealing with epoxy resin glue, and standing for 24 hours to form a filling structure 13;
A stable and reliable filling structure 13 is constructed through the operation of the step S1, and the epoxy resin adhesive has excellent chemical corrosion resistance and mechanical strength, so that the junction of the hollow optical fiber 12 and the needle head can be effectively sealed, the temperature-sensitive material is prevented from leaking, and the effect of saving the temperature-sensitive material is achieved.
S2: the filling structure 13 is connected into the first syringe 14, the front end of the filling structure is immersed into the liquid temperature-sensitive material 15 which is well placed, the first syringe 14 is extracted for 5cm from the zero scale mark, a tool (such as a battery and the like) can be found to clamp the injector for fixing the distance, meanwhile, a large enough pressure difference can be manufactured between the inside and the outside of the first syringe 14, the filling structure 13 is placed for a period of time according to the required filling times, and after the filling structure is placed, the filling structure 13 is taken down and connected into the second syringe 16 of 1 ml;
in step S2, the extraction amount of the temperature sensitive material is controlled by calculating the extraction total amount formula and controlling the extraction distance of the first syringe 14 and the standing period after the extraction, specifically as follows:
As shown in fig. 4, which is a schematic diagram of the hollow fiber 12 at the front end of the filling structure 13, the hollow fiber 12 after tapering is a circular truncated cone type pipeline, and further by using poise She Gongshi to analyze the flow condition in the pipeline,
Poise She Gongshi is denoted as:
；
Wherein Q is the flow rate passing through the section of the pipeline, and the unit is 3/s; eta is the viscosity coefficient unit of the liquid and is Pa.s; l is the length of a circular tube and the unit is mu m; r is the inner diameter of a circular tube, and the unit is mu m; p 1 is the pressure intensity of the upper end face of the circular tube, and the unit is Kpa; p 2 is the pressure of the lower end face of the circular tube, and the unit is KPa.
As shown in fig. 4, the hollow-core optical fiber 12 at the front end of the filling structure 13 of the present embodiment is different from the classical poise She Gongshi in that the cross-sectional area of the hollow-core optical fiber 12 at the front end of the filling structure 13 of the present embodiment is varied depending on the position, in which case the flow rate of the fluid at each cross-section is expressed as:
；
wherein A is the cross-sectional area of the cross section, and the unit is mu m 2; v is the flow rate of the liquid in μm/s over this section.
Given a known cross-sectional radius r, further expressed as:
；
Wherein r is the radius of the section, and the unit is mu m; the poiseuille law is applied to each small section of the hollow-core fiber 12, with:
；
where the cross-sectional radius r=r (x), x is the coordinate axis along the direction of the hollow-core optical fiber 12, and since the hollow-core optical fiber 12 is regarded as a truncated cone, R (x) is further expressed as:
；
Wherein r 2 is the inner diameter of the hollow fiber 12 after tapering, and the unit is μm; k is a ratio coefficient of a difference between inner diameters of the hollow fiber 12 before and after tapering and a difference between lengths of the hollow fiber 12 before and after tapering.
Where, when x takes 0, R (x) =r 1, and when x takes L, R (x) =r 2, there is:
；
Wherein r 1 is the inner diameter of the hollow fiber 12 before tapering, and the unit is μm; r 2 is the inner diameter of the hollow fiber 12 after tapering, and the unit is μm; l is the total length of the hollow fiber after tapering, and the unit is mu m; k is a ratio coefficient of a difference between inner diameters of the hollow fiber 12 before and after tapering and a difference between lengths of the hollow fiber 12 before and after tapering.
Thus, the total flow to the whole pipeline is:
；
substituting the R (x) formula into the arrangement to obtain the flow Q passing through the pipeline section:
；
Wherein eta is the viscosity coefficient of the liquid and the unit is Pa.s; r 1 is the inner diameter of the hollow fiber 12 before tapering, in μm; r 2 is the inner diameter of the hollow fiber 12 after tapering, and the unit is μm; q is the flow through the section of the pipeline, the unit is mu m 3/s;P1 is the atmospheric pressure, and the unit is KPa; p 2 is the pressure in the first syringe 14 after the first syringe 14 is withdrawn, and the unit is KPa; v 1 is the original gas volume in mL inside the first syringe 14; v 2 is the volume of air in the first syringe 14 in mL after the first syringe 14 is withdrawn a certain distance; l is the total length of the hollow fiber 12 after tapering, and the unit is mu m; k is a ratio coefficient of a difference between inner diameters of the hollow fiber 12 before and after tapering and a difference between lengths of the hollow fiber 12 before and after tapering.
P 1、P2 is calculated according to the following formula:
；
In the above formula, P 1 is the atmospheric pressure, and the unit is KPa; p 2 is the pressure in the first syringe 14 after the first syringe 14 is withdrawn, and the unit is KPa; v 1 is the original gas volume in mL inside the first syringe 14; v 2 is the volume of air in mL inside the first syringe 14 after the first syringe 14 is withdrawn a distance.
Therefore, the extraction total amount is expressed as:
；
Wherein Q is the flow rate passing through the section of the pipeline, and the unit is 3/s; t is extraction time, and the unit is s; p 1 is the atmospheric pressure, and the unit is KPa; p 2 is the pressure in the first syringe after the first syringe is extracted, and the unit is KPa; η is the viscosity coefficient of the liquid in Pa.s; r 2 is the inner diameter of the hollow fiber after tapering, and the unit is μm; l is the total length of the hollow fiber 12 after tapering, and the unit is mu m; k is a ratio coefficient of a difference between inner diameters of the hollow fiber 12 before and after tapering and a difference between lengths of the hollow fiber 12 before and after tapering.
Since the liquid is extracted as the temperature-sensitive material in the actual operation process, the use amount of the temperature-sensitive material is very small, the weight of the temperature-sensitive material is ignored, the pressure at one end of the hollow fiber 12 with the inner diameter of r 2 after the tapering operation is regarded as the atmospheric pressure P 1, and the negative pressure environment is formed in the P 1>P2, namely the first needle tube, so that the temperature-sensitive material is extracted into the filling structure 13. The temperature sensitive material may be polydimethylsiloxane.
Illustratively, in the step S2, a total of 20 capillary quartz tube bodies 2 are filled with polydimethylsiloxane, the length of the polydimethylsiloxane filled in each capillary quartz tube body 2 is 400 μm, the inner diameter of the capillary quartz tube body 2 is 125 μm, that is, the volume of the polydimethylsiloxane required for the inside of each capillary quartz tube body 2 is about 4.9×10 6μm3, and a total of 9.8×10 7μm3 of the polydimethylsiloxane is required for 20 capillary quartz tube bodies 2. The viscosity coefficient of the polydimethylsiloxane at 25℃was 600 Pa.s, the volume of the first syringe 14 before withdrawal was 0.5mL, the volume of the first syringe 14 after withdrawal was 20mL, the inner diameter of the hollow-core optical fiber 12 before tapering was 106. Mu.m, the inner diameter after tapering was 40. Mu.m, and the length was 1cm. Substituting the above values into the flow Q formula of the cross section of the pipeline, calculating the obtained flow q=2.6x 4μm3/s, wherein the extraction time is t=3769 s, and the total extraction amount v=9.8x 7μm3 of the temperature-sensitive material, namely about to stand for 1h, so that the filling requirement of 20 capillary quartz tube bodies 2 can be met. Through the calculation of the total extraction amount formula of the temperature-sensitive materials, and by limiting the extraction distance and the standing time of the first needle cylinder 14, the waste of the temperature-sensitive materials caused by excessive extraction is avoided, the leakage of the temperature-sensitive materials is effectively prevented, the leakage of the temperature-sensitive materials is further avoided, the six-dimensional adjusting frame 20 is further prevented from being polluted, and the service life of the six-dimensional adjusting frame 20 is prolonged.
S3: fixing 1ml of a second needle cylinder 16 and a filling structure 13 in a syringe pump actuating mechanism 19, connecting the syringe pump actuating mechanism 19 and a syringe pump controller 18 together, and placing a hollow fiber 12 at the tail end of the filling structure 13 on a clamping mechanism at one side of a six-dimensional adjusting frame 20;
In step S3, the syringe pump actuator 19 is used instead of a human hand, ensuring the stability and accuracy of the injection process. The syringe pump actuator 19 is used as a driving device, and can provide stable and controllable injection speed and pressure, so that the temperature sensitive material in the filling structure 13 can be ensured to be uniformly and continuously injected into the capillary quartz tube body 2, and the operation is helpful for reducing errors in the operation process and improving the precision of the syringe. Secondly, the injection pump controller 18 can adjust the action of the injection pump executing mechanism 19 according to preset parameters or real-time feedback signals, so that the accurate regulation and control of key parameters such as injection speed, pressure, injection quantity and the like are realized, and the injection mode not only improves the automation degree of operation, but also enables the injection process to be more flexible and controllable.
S4: welding the capillary quartz tube body 2 and the capillary quartz rod by using an arc welding machine 21, grinding the capillary quartz rod to ensure that the thickness of the capillary quartz rod is 10-20 mu m to form a quartz diaphragm 4, and placing the capillary quartz tube body 2 welded with the quartz diaphragm 4 on a clamping mechanism at the other side of the six-dimensional adjusting frame 20;
The arc welding technology utilizes high temperature to melt the contact surfaces of two materials and then cool and solidify to form firm connection. The connecting mode not only ensures the strength and the sealing performance of the connecting part, but also avoids uncertain factors caused by using glue or other adhesives; the quartz diaphragm 4 with the thickness of 10-20 mu m has good optical performance and mechanical performance, and can ensure the normal operation of the optical fiber sensor while ensuring the structural strength of the sensor.
S5: on a six-dimensional adjusting frame 20, aligning the hollow optical fiber 12 with the capillary quartz tube body 2 welded with the quartz membrane 4, feeding the hollow optical fiber 12 into the capillary quartz tube body 2 welded with the quartz membrane 4, filling the liquid temperature-sensitive material 15 into the capillary quartz tube body 2 welded with the quartz membrane 4 by controlling a syringe pump controller 18, and heating the liquid temperature-sensitive material 15 in an oven at a temperature of 100 ℃ for one hour after filling is finished, so that the liquid temperature-sensitive material 15 is solidified to form a solid temperature-sensitive material 3;
s6: the capillary quartz tube body 2 filled with the temperature sensitive material and welded with the quartz membrane 4 is welded with the single-mode fiber 1 by an arc welding machine 21, and a cavity formed between the single-mode fiber 1 and the temperature sensitive material, namely a temperature sensing cavity 6, is formed, so that an optical fiber sensing structure with only the temperature sensing cavity 6 is obtained;
S7: the optical fiber sensing structure with the temperature sensing cavity 6 is sleeved into the metal sleeve assembly 5, and a cavity formed between the metal sleeve assembly 5 and the quartz diaphragm 4, namely the salinity sensing cavity 8, is finally manufactured to complete the F-P cascade optical fiber sensor.
Illustratively, the temperature sensing chamber 6 is fabricated by: the capillary quartz tube body 2 and the capillary quartz rod are welded by an arc welding machine 21, the capillary quartz rod is ground to have the thickness of about 10 mu m to 20 mu m to form a quartz diaphragm 4, and the capillary quartz tube body 2 with the welded capillary quartz rod is placed on a clamping mechanism at one side of a six-dimensional adjusting frame 20. The hollow optical fiber 12 is inserted into a syringe, the syringe is extracted to form a negative pressure environment, the syringe is immersed into the prepared polydimethylsiloxane solution, and the syringe is placed on a clamping mechanism on the other side of the six-dimensional adjusting frame 20 after standing is completed. The injection speed of the syringe was adjusted, the prepared polydimethylsiloxane solution was filled in the rear end of the capillary quartz tube body 2 with the quartz membrane 4, the polydimethylsiloxane was cured by heating at 100 ℃ for 1 hour in an incubator, and then the single-mode optical fiber 1 and the capillary quartz tube body 2 with the quartz membrane 4 and filled with polydimethylsiloxane were welded together by an arc welding technique using an optical fiber welder, thereby manufacturing the temperature sensing chamber 6.
Illustratively, the salinity sensing chamber 8 is fabricated by: the manufactured temperature sensing structure is sleeved into the metal sleeve assembly 5, and then the salinity sensing cavity 8 is manufactured.
According to the manufacturing method of the F-P cascade optical fiber sensing structure for measuring sea water temperature and salt, through controlling the thickness of the quartz diaphragm 4, smooth passing of optical signals is ensured while isolation effect is ensured, and further, the quartz diaphragm 4 is ensured not to interfere with normal operation of an optical fiber sensor while isolating sea water, meanwhile, through improving the filling method of temperature sensitive materials, under general conditions, due to limitation of a microscope field of view and uncertainty of human hand operation, the temperature sensitive materials need to be filled into the capillary quartz tube body 2 when the temperature sensing structure is manufactured, and then the quartz diaphragm 4 is welded at one end, close to the temperature sensitive materials, of the capillary quartz tube body 2 through an arc welding technology, and due to the fact that a large amount of heat is emitted at the moment of arc welding, deterioration of the temperature sensitive materials is easy to be caused, high requirements are brought to the operation level of operators. The improved method comprises the steps of firstly welding the quartz diaphragm 4 at one end of the capillary quartz tube body 2 through an arc welding technology, introducing the injection pump controller 18 and the injection pump actuating mechanism 19, avoiding uncertainty of manual operation, improving filling precision and a fillable range in the capillary quartz tube body 2, reducing manufacturing difficulty of an F-P cascade optical fiber sensor structure for measuring seawater temperature and salt, and ensuring that the temperature sensitive material quantity extracted each time is accurately calculated by limiting the extraction distance and the standing time of the first needle cylinder 14, avoiding waste caused by excessive extraction, and further saving the temperature sensitive material.
In one possible embodiment, the first syringe 14 is withdrawn a distance of 5cm to 10cm.
This distance is used, for example, to fix the distance by clamping the injector with a tool (such as a battery, etc.), and to create a sufficient pressure difference between the inside and the outside of the first syringe 14, thereby creating a negative pressure environment inside and outside the syringe, and using the pressure difference between the inside and the outside of the syringe to suck the liquid temperature-sensitive material 15 into the filling structure 13.
In one possible embodiment, the first syringe 14 may be left to rest for a period of time ranging from 30 minutes to 60 minutes after withdrawal.
This extraction time can ensure that, for example, sufficient liquid temperature-sensitive material 15 is sucked into the filling structure 13, ensuring that the subsequent step S5 is performed to fill the liquid temperature-sensitive material 15 into the capillary tube body 2.
In one possible embodiment, the syringe has an injection rate of 10. Mu.L/s to 20. Mu.L/s.
Illustratively, the F-P cascading optical fiber sensor in the embodiment is provided with a metal sleeve assembly 5 on the outer side of the capillary quartz tube body 2, the metal sleeve assembly 5 is an important component part of the salinity sensing cavity 8, and the optical fiber sensor with the structure of the metal sleeve assembly 5 has better stability under a complex marine environment.
In one possible embodiment, the quartz membrane 4 has a thickness of 10 μm-20 μm.
Illustratively, if the quartz diaphragm 4 is too thin to be less than or equal to 10 μm, in a complex marine environment, the seawater pressure can directly crush the quartz diaphragm 4, resulting in damage to the optical fiber sensing structure, and if the quartz diaphragm 4 is too thick to be more than or equal to 20 μm, resulting in too low contrast of the spectrum of the salinity sensing chamber 8, which is detrimental to sampling of the salinity data by the salinity sensing chamber 8, and processing of the salinity data.
In one possible embodiment, the temperature sensitive material is polydimethylsiloxane.
Illustratively, the polydimethylsiloxane has high thermal expansion and thermo-optic effects, as well as good stability over a wide temperature range, enabling the F-P cascade fiber sensor in this embodiment to have high temperature sensitivity and a large measurement range, and to be able to resolve smaller temperature variations.
The embodiment of the invention provides an F-P cascade optical fiber sensing structure for measuring seawater temperature and salt, as shown in fig. 1, comprising: a capillary quartz tube body 2; the single-mode optical fiber 1 is arranged at the first end of the interior of the capillary quartz tube body 2 and is connected with the inner wall of the capillary quartz tube body 2; the temperature sensitive material is arranged at the second end of the interior of the capillary quartz tube body 2 and is connected with the inner wall of the capillary quartz tube body 2; the temperature sensing cavity 6 is arranged in the capillary quartz tube body 2 and is arranged between the single-mode fiber 1 and the temperature sensitive material; the quartz diaphragm 4 is arranged at the end part of the temperature sensitive material and is connected with the second end inside the capillary quartz tube body 2; the metal sleeve component 5 is sleeved outside the capillary quartz tube body 2 and is connected with the tube body of the capillary quartz tube; the salinity sensing cavity 8 is arranged between the metal sleeve component 5 and the quartz diaphragm 4 and is connected with the metal sleeve component 5 and the quartz diaphragm 4.
According to the F-P cascade optical fiber sensing structure for measuring the seawater temperature and salt, provided by the embodiment of the invention, the temperature sensing cavity 6 and the salinity sensing cavity 8 are arranged, so that the temperature and the salinity of seawater can be measured, and the quartz membrane 4 is welded at one side, close to the temperature sensitive material, of the capillary quartz tube body 2, so that the quartz membrane 4 is high in physical strength and good in chemical stability, and can effectively resist direct contact between the seawater and the temperature sensitive material, so that the temperature sensitive material is isolated from the seawater, on one hand, corrosion of the seawater to the temperature sensitive material is avoided, on the other hand, salt particles are prevented from adhering to the surface of the temperature sensitive material, and accurate sensing of temperature change by the temperature sensitive material is ensured. By the arrangement, the durability and the stability of the temperature-sensitive material can be ensured, the service life of the temperature-sensitive material is greatly prolonged, the service life of the optical fiber sensing structure in a complex marine environment is further prolonged, the sensitivity of the optical fiber sensing structure to temperature change can be prevented from being influenced, and the accurate monitoring of the temperature change is further maintained.
In one possible embodiment, as shown in fig. 1, the metal sleeve assembly 5 comprises: the sleeve piece 7 is sleeved outside the capillary quartz tube body 2 and is connected with the capillary quartz tube body 2; the tail part 10 is arranged at the end part of the salinity sensing cavity 8 far away from the quartz membrane 4 and is connected with the salinity sensing cavity 8; and the connecting piece 9 is arranged between the tail part 10 and the sleeve part 7 and is connected with the salinity sensing cavity 8.
Illustratively, the metal sleeve assembly 5 is 316L stainless steel. The 316L stainless steel has smooth surface and excellent corrosion resistance, and can well protect the structure of the optical fiber sensor.
Illustratively, the metal sleeve assembly 5 is 2507 stainless steel. 2507 stainless steel has high chromium and molybdenum contents, excellent resistance to pitting corrosion, crevice corrosion and uniform corrosion, and the dual-phase microstructure ensures that the steel has high resistance to stress corrosion cracking and high mechanical strength.
As shown in fig. 8, an optical path diagram of an F-P cascade optical fiber sensing structure in the embodiment of the present invention is shown, by reasonably designing the length of each cavity, at most 10 peaks can be found on a spatial spectrum formed by FFT conversion of an interference spectrum, and each peak is subjected to bandpass filtering processing to obtain an interference spectrum of a corresponding cavity, so as to find out the spectrum of a temperature sensing cavity 6, the spectrum of a salinity sensing cavity 8, and the center wavelength of a specific resonance peak corresponding to each spectrum, calculate the movement amounts of the center wavelengths of the specific resonance peaks corresponding to the spectrum of the temperature sensing cavity 6 and the spectrum of the salinity sensing cavity 8 under different temperatures and salinity, and then reversely deduce the temperature and the salinity of sea water by using a dual-wavelength matrix method; the shift amount is the difference value of the center wavelength of the specific resonance peak corresponding to the spectrum of the temperature sensing cavity 6 and the spectrum of the salinity sensing cavity 8.
As shown in fig. 9, a spectrum diagram formed by an F-P cascade optical fiber sensor with the optical fiber sensing structure of the present invention is shown, and after the interference spectrum is subjected to FFT transformation, a spatial spectrum shown in fig. 10 is formed, and the two diagrams together show how to extract information related to different cavities from an original spectrum, through which information we can accurately locate and extract interference information of each cavity, so that the interference spectrum of different cavities can be obtained by measuring and searching characteristic peaks of different frequencies while temperature and salinity are simultaneously measured.
Example 1
The F-P cascade fiber sensing structure of the present embodiment is used to perform temperature measurement by combining with a fiber grating demodulator 22, an upper computer 17, a constant temperature oil tank 24 and a high-precision thermometer 23, as shown in fig. 11, and specifically includes the following contents:
the optical fiber sensing structure to be subjected to temperature measurement and the probe of the high-precision thermometer 23 are tied together and immersed in the constant-temperature oil groove 24, and the positions of the oil in the oil groove and the optical fiber sensing structure are adjusted so that the oil can be uniformly heated; the power supply of the constant temperature oil groove 24 is turned on, the constant temperature oil groove 24 is sealed, heating is started after a start key is pressed, and data can be recorded when the set temperature value is reached and the numerical value of the high-precision thermometer 23 is unchanged for a long time.
The fiber grating demodulator 22 scans and emits wide-spectrum light, and the light is coupled into the fiber sensing structure through the fiber; the optical fiber sensing structure is internally provided with five reflecting surfaces of a single-mode optical fiber 1-air end surface, an air-temperature sensitive material end surface, a temperature sensitive material-quartz membrane 4 end surface, a quartz membrane 4-seawater end surface and a seawater-metal end surface, broad spectrum light is reflected by the five reflecting surfaces and then transmitted to the optical fiber grating demodulator 22 through an optical fiber to form an interference spectrum signal; then, the interference spectrum signal is transmitted to an upper computer 17, after bandpass filtering processing is carried out in the upper computer 17, the center wavelength of a specific resonance peak corresponding to the spectrum of the temperature sensing cavity 6 is obtained, the center wavelength movement amount of the specific resonance peak corresponding to the spectrum of the temperature sensing cavity 6 in different temperature environments is calculated, and the sea water temperature is reversely deduced; the shift amount is the difference of the center wavelengths of the specific resonance peaks corresponding to the spectra of the temperature sensing cavity 6.
As shown in fig. 12, the spectral response curve of the temperature sensing cavity 6 of the optical fiber sensor of the present embodiment increases with an increase in temperature. When the temperature rises, the temperature sensitive material is heated and expands, the cavity length of the temperature sensing cavity 6 is reduced, and the peak of the interference spectrum of the temperature sensing cavity 6 moves towards the direction of reducing the wavelength. In the embodiment, polydimethylsiloxane is selected as a temperature-sensitive material, and is a material with a high linear thermal expansion coefficient, and the polydimethylsiloxane is characterized in that the fiber sensor has higher sensitivity to temperature and can distinguish more tiny temperature change.
As shown in fig. 13, the response of the temperature cavity spectrum is that of the temperature rise from 268.15K to 278.15K. By recording the movement amount of the peak of the interference spectrum when the temperature changes, as shown in fig. 14, the sensitivity of the optical fiber sensor of the embodiment to the temperature can be obtained, the peak of the interference spectrum when the temperature changes is 268.15K-278.15K is recorded, the wavelength of the peak is 1606.21nm,1593.07nm,1579.91nm,1567.8nm,1552.61nm,1538.86nm,1524.87nm,1510.44nm,1496.21nm,1481.46nm,1467.27nm,, the wavelength of the peak is regarded as a function of the temperature, and the relationship between the wavelength of the peak and the temperature is y= -13.94636x+5347.49559, wherein y is the wavelength of the peak, x is the temperature, the movement amount of the peak of the optical fiber sensor of the embodiment reaches 13.94636nm/°c, that is, when the temperature is increased by 1 ℃, the movement amount of the peak reaches 13.94636nm, which indicates that the optical fiber sensor of the embodiment has higher sensitivity to the temperature.
As shown in fig. 14, in the sensitivity curve of the temperature cavity when the temperature is raised from 268.15K to 278.15K, because the optical fiber sensing structure in this embodiment has a structure that the end of the temperature sensitive material is blocked by the quartz membrane 4, the temperature sensitive material is in a unidirectional expansion structure, and under the condition that the expansion volume is the same, compared with the condition that the temperature sensitive material is expanded in two directions without the blocking of the quartz membrane 4, the temperature sensitive material in this embodiment expands only in one direction, thereby greatly improving the sensitivity of the optical fiber sensor in this embodiment to the temperature, the sensitivity of the F-P cascade optical fiber sensor in this embodiment to the temperature reaches 13.9nm/°c, the resolution reaches 0.07 ℃, and the linearity is as high as 0.99953, compared with the resolution of the optical fiber temperature sensor in current market, such as the preferential photoreceptor HG-T02:0.1 ℃, germany femtoseconds: as can be seen from comparison of 0.1 c, etc., the optical fiber sensing structure in this embodiment can distinguish a more minute temperature change.
Example 2
The F-P cascade fiber sensor of this embodiment is used in combination with a fiber grating demodulator 22, an upper computer 17, a high-precision thermometer 23 and standard seawater to measure salinity, as shown in fig. 15, and specifically includes the following:
The optical fiber sensing structure to be subjected to salinity measurement and the probe of the high-precision thermometer 23 are bound together and immersed into standard seawater, the liquid level of the standard seawater and the position of the optical fiber sensing structure are adjusted, so that the optical fiber sensing structure and the high-precision thermometer 23 can be completely immersed, and data recording is started after the reading of the high-precision thermometer 23 is stable for a period of time.
The fiber grating demodulator 22 scans and emits wide-spectrum light, and the light is coupled into the fiber sensing structure through the fiber; the optical fiber sensing structure is internally provided with five reflecting surfaces of a single-mode optical fiber 1-air end surface, an air-temperature sensitive material end surface, a temperature sensitive material-quartz membrane 4 end surface, a quartz membrane 4-seawater end surface and a seawater-metal end surface, broad spectrum light is reflected by the five reflecting surfaces and then transmitted to the optical fiber grating demodulator 22 through an optical fiber to form an interference spectrum signal; then transmitting the interference spectrum signals to an upper computer 17, carrying out band-pass filtering treatment in the upper computer 17 to obtain the spectrum of the temperature sensing cavity 6 and the spectrum of the salinity sensing cavity 8 and the center wavelength of a specific resonance peak corresponding to each spectrum, calculating the center wavelength movement amount of the specific resonance peak corresponding to the spectrum of the temperature sensing cavity 6 and the spectrum of the salinity sensing cavity 8 in different temperature and salinity environments, and reversely deducing the temperature and the salinity of the sea water by utilizing a double-wavelength matrix method; the shift amount is the difference between the center wavelengths of the specific resonance peaks corresponding to the spectrum of the temperature sensing cavity 6 and the spectrum of the salinity sensing cavity 8.
As shown in fig. 16, is the spectral response curve of the salinity chamber as the salinity increases. When the temperature is increased, the peak of the interference spectrum of the salinity cavity moves towards the direction of wavelength increase, wavelength data of adjacent peaks are read, and when the salinity is moved from 4 permillage to 20 permillage, the wavelengths of corresponding peaks are 1521.47nm,1526.89nm,1532.3nm,1537.68nm,1543.19nm,1548.56nm,1553.94nm,1559.23nm and 1564.61nm respectively, and the relationship between the wavelength of the obtained peak and the salinity can be expressed as: y=2.69783x+1510.72267, and the sensitivity of the optical fiber sensing structure in this embodiment to salinity is 2.69 nm/mill, i.e. when salinity is not increased by 1 mill, the wavelength of the peak is shifted by 2.69nm in the direction of wavelength increase.
As shown in fig. 17, the sensitivity curve of the salinity chamber is shown when the salinity is increased from 4 to 20%. The sensitivity of the F-P cascade optical fiber sensor in the embodiment to salinity reaches 2.69 nm/mill, the resolution reaches 0.37 mill, compared with the resolution of the common salinity meter adopting an optical structure in the current market, if the power of the substitution is 1%o, the power of the staring is 1%o, the power of the Yuxing HT211ATC is 1%o, and the comparison shows that the optical fiber sensor in the embodiment can distinguish more tiny salinity change.
In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium; may be a communication between two elements or an interaction between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
In the present invention, unless expressly stated or limited otherwise, a first feature is "on" or "under" a second feature, which may be in direct contact with the first and second features, or in indirect contact with the first and second features via an intervening medium. Moreover, a first feature "above," "over" and "on" a second feature may be a first feature directly above or obliquely above the second feature, or simply indicate that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is level lower than the second feature.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that alterations, modifications, substitutions and variations may be made in the above embodiments by those skilled in the art within the scope of the invention.
Claims (5)
1. The manufacturing method of the F-P cascade optical fiber sensing structure for measuring the sea water temperature and salt is characterized by comprising the following steps of:
S1: heating and tapering the hollow optical fiber to obtain a tapered hollow optical fiber, taking a syringe needle, inserting the tapered hollow optical fiber into the syringe needle, sealing with epoxy resin glue, and standing for 24 hours to obtain a filling structure;
S2: the filling structure is connected into a first syringe, the front end of the first syringe connected with the filling structure is immersed into the temperature-sensitive material which is well placed, the temperature-sensitive material is extracted by the first syringe according to the calculation result of the extraction total amount formula of the temperature-sensitive material, 5cm-10cm is extracted by the first syringe, then the filling structure filled with the temperature-sensitive material is placed for 30min-60min, the filling structure filled with the temperature-sensitive material is removed from the first syringe, and then the filling structure filled with the temperature-sensitive material is connected into a second syringe;
wherein the extraction total amount formula is as follows:
；
Wherein: q is the flow rate passing through the section of the pipeline, and the unit is 3/s; t is extraction time, and the unit is s; p 1 is the atmospheric pressure, and the unit is KPa; p 2 is the pressure in the first syringe after the first syringe is extracted, and the unit is KPa; η is the viscosity coefficient of the liquid in Pa.s; r 2 is the inner diameter of the hollow fiber after tapering, and the unit is μm; l is the total length of the hollow fiber after tapering, and the unit is mu m; k is a ratio coefficient of the difference between the inner diameters of the hollow optical fiber before and after tapering and the difference between the lengths of the hollow optical fiber before and after tapering;
s3: fixing a filling structure filled with temperature sensitive materials and a second needle cylinder in an actuating mechanism of the injection pump, connecting the actuating mechanism of the injection pump with a controller of the injection pump, and placing hollow optical fibers at the tail end of the filling structure on a clamping mechanism at one side of a six-dimensional adjusting frame;
S4: welding the capillary quartz tube body and the capillary quartz rod by using an arc welding machine, grinding the capillary quartz rod to obtain a quartz diaphragm, and placing the capillary quartz tube body welded with the quartz diaphragm on a clamping mechanism at the other side of the six-dimensional adjusting frame;
S5: on a six-dimensional adjusting frame, aligning the hollow optical fiber with a capillary quartz tube body welded with a quartz diaphragm, sending the hollow optical fiber into the capillary quartz tube body welded with the quartz diaphragm, and filling a temperature sensitive material into the capillary quartz tube body welded with the quartz diaphragm by controlling a syringe pump controller;
S6: welding the capillary quartz tube body filled with the temperature sensitive material and welded with the quartz membrane and the single-mode fiber together by using an arc welding machine, and forming a temperature sensing cavity between the single-mode fiber and the temperature sensitive material, thereby obtaining an optical fiber sensing structure only provided with the temperature sensing cavity;
S7: the optical fiber sensing structure with the temperature sensing cavity is sleeved into the metal sleeve assembly, a salinity sensing cavity is formed between the metal sleeve assembly and the quartz diaphragm, and finally the manufacturing of the optical fiber sensing structure is completed.
2. The method for manufacturing an F-P cascade optical fiber sensing structure for measuring seawater temperature and salt according to claim 1, wherein the thickness of the quartz diaphragm is 10 μm-20 μm.
3. The method for manufacturing the F-P cascade optical fiber sensing structure for measuring seawater temperature and salt according to claim 1, wherein the temperature sensitive material is polydimethylsiloxane.
4. An F-P cascade fiber optic sensing structure for measuring seawater temperature salt manufactured by the manufacturing method of claim 1, comprising:
A capillary quartz tube body;
the single-mode fiber is arranged at the first end of the interior of the capillary quartz tube body and is connected with the inner wall of the capillary quartz tube body;
the temperature sensitive material is arranged at the second end of the interior of the capillary quartz tube body and is connected with the inner wall of the capillary quartz tube body;
The temperature sensing cavity is arranged in the capillary quartz tube body and between the single-mode fiber and the temperature sensitive material;
the quartz membrane is arranged at the end part of the temperature sensitive material and is connected with the second end inside the capillary quartz tube body;
The metal sleeve component is sleeved outside the capillary quartz tube body and is connected with the capillary quartz tube body;
The salinity sensing cavity is arranged between the metal sleeve component and the quartz diaphragm and is connected with the metal sleeve component and the quartz diaphragm.
5. The F-P cascading fiber-optic sensing structure for measuring seawater temperature salt of claim 4, wherein the metal sleeve assembly comprises:
the sleeve piece is sleeved outside the tube body of the capillary quartz tube and is connected with the capillary quartz tube;
The tail part is arranged at the end part of the salinity sensing cavity, which is far away from the quartz membrane, and is connected with the salinity sensing cavity;
The connecting piece is arranged between the tail piece and the sleeve piece and is connected with the salinity sensing cavity.
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| WO2010142004A2 (en) * | 2009-06-10 | 2010-12-16 | Katholieke Universifeit Leuven | Controlled biosecure aquatic farming system in a confined environment |
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| CN115597658A (en) * | 2022-09-08 | 2023-01-13 | 东北大学（Cn） | F-P cascade optical fiber sensor and method for measuring temperature and salt of seawater |
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| US20180149537A1 (en) * | 2016-11-30 | 2018-05-31 | Fiber Optic Sensor Systems Technology Corporation | Dual acoustic pressure and hydrophone sensor array system |
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| WO2010142004A2 (en) * | 2009-06-10 | 2010-12-16 | Katholieke Universifeit Leuven | Controlled biosecure aquatic farming system in a confined environment |
| CN109974789A (en) * | 2019-04-25 | 2019-07-05 | 天津工业大学 | A kind of high integration mini optical fibre seawater thermohaline depth sensor based on MEMS technology and membrane material |
| CN115597658A (en) * | 2022-09-08 | 2023-01-13 | 东北大学（Cn） | F-P cascade optical fiber sensor and method for measuring temperature and salt of seawater |
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