CN112881952A

CN112881952A - Magnetic field sensor and preparation method thereof

Info

Publication number: CN112881952A
Application number: CN202011586451.XA
Authority: CN
Inventors: 王�华; 刘云启; 于阳东; 姜晨; 孙欣; 李路明; 吕康康; 牟成博; 祝远锋; 肖子洋
Original assignee: Jiangxi Normal University; Information and Telecommunication Branch of State Grid Jiangxi Electric Power Co Ltd; University of Shanghai for Science and Technology; State Grid Corp of China SGCC
Current assignee: Jiangxi Normal University; Information and Telecommunication Branch of State Grid Jiangxi Electric Power Co Ltd; University of Shanghai for Science and Technology; State Grid Corp of China SGCC
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-06-01

Abstract

The invention provides a magnetic field sensor and a preparation method thereof. The magnetic field sensor comprises an incident single-mode optical fiber, an outgoing single-mode optical fiber, a boron-germanium co-doped optical fiber and a capillary tube. In between, the laser directly writes the long-period fiber grating near the inflection point of dispersion on the boron-germanium co-doped fiber. The long-period fiber grating is encapsulated in a capillary, and the capillary is filled with magnetic fluid material, and the port of the capillary is sealed by UV curing glue. According to the magnetic field sensor provided by the present invention, when the external magnetic field changes, the refractive index of the magnetic fluid will change accordingly, and the two troughs on the spectrum will drift. It has the advantages of high sensitivity and good stability.

Description

Magnetic field sensor and preparation method thereof

Technical Field

The invention relates to the field of magnetic field and current detection, in particular to a magnetic field sensor and a preparation method thereof.

Background

In the development of the power industry, detection of electromagnetism or magnetic leakage in a smart grid system becomes indispensable, with the continuous miniaturization and intelligentization development of sensing technology, a magnetic field sensor which utilizes electric signals for sensing exposes the defects of large size, complex structure, low adaptability and the like, and the fiber bragg grating magnetic field sensor has the advantages of electromagnetic interference resistance, high sensitivity, small size, suitability for severe environment and the like, so that the fiber bragg grating magnetic field sensor has important application in the future development process of the smart grid.

At present, the fiber bragg grating magnetic field sensor is mainly based on a Faraday effect, a magnetostrictive material and a magnetofluid magnetic field sensor. The magnetic field sensor based on the faraday effect is an optical fiber except for part of optical devices in the whole system, but because the verdet constant of silicon dioxide is too low, the optical fiber needs to be wound by a plurality of turns to increase the polarization rotation angle, when the number of the winding turns is too large, the birefringence of the optical fiber can influence the measurement result, errors are easy to generate in experiments, and the requirement on the length of the optical fiber is high. The magnetic field sensor based on the magnetostrictive material is usually formed by directly sticking the fiber grating on a giant magnetostrictive rod, and the length of the giant magnetostrictive rod is usually small, so that the problems of low sensitivity and poor stability exist.

Disclosure of Invention

Based on the above, the invention aims to provide a magnetic field sensor and a preparation method thereof, so as to solve the problems of low sensitivity and poor stability of the existing fiber grating magnetic field sensor.

The invention provides a magnetic field sensor which comprises an incident single-mode fiber, an emergent single-mode fiber, a boron-germanium co-doped fiber and a capillary, wherein the input end and the output end of the boron-germanium co-doped fiber are respectively connected with one end of the incident single-mode fiber and one end of the emergent single-mode fiber, the other end of the incident single-mode fiber and the other end of the emergent single mode are respectively connected with a tunable laser and an optical power detection instrument, a long-period fiber grating close to a dispersion inflection point is arranged on the boron-germanium co-doped fiber, the long-period fiber grating is arranged in the capillary, a magnetic fluid is further arranged in the capillary, the capillary is arranged between magnetic field generators, and the magnetic field generators are connected with a.

The magnetic field sensor provided by the invention utilizes the tunability of the magnetic fluid under the action of the magnetic field, when the external magnetic field changes, the refractive index of the magnetic fluid changes along with the change of the magnetic fluid, the deviation is generated in the valley of the spectrum displayed by the optical power detection instrument, the measurement of the magnetic field can be realized by measuring the deviation, and the sensitivity of the fiber bragg grating sensor is greatly improved.

Furthermore, the cladding diameter range of the boron-germanium co-doped fiber is 120-130 microns, and the core diameter of the boron-germanium co-doped fiber is 6-7 microns.

Further, a magnetometer is arranged in the magnetic field generator.

Further, the period range of the long-period light grating is 100-2000 microns.

Further, the operating wavelength range of the long-period fiber grating is 600-2400 nm.

Further, the magnetic fluid is a water-based magnetic fluid.

The invention also provides a preparation method of the magnetic field sensor, which comprises the following steps:

writing a long-period fiber grating close to a dispersion inflection point: welding a boron-germanium co-doped fiber with a preset length between an incident single-mode fiber and an emergent single-mode fiber, and writing a long-period fiber grating close to a dispersion inflection point on the boron-germanium co-doped fiber through a laser;

the long-period fiber grating is arranged in a capillary, one end of the capillary is packaged by ultraviolet curing glue, after the ultraviolet curing glue is cured, magnetic fluid is guided into the capillary by an injector, axial pressure is applied to keep the long-period fiber grating in a straight state, and the other end of the capillary is sealed by the ultraviolet curing glue.

According to the preparation method of the magnetic field sensor, the laser machine is used for carrying out exposure treatment on the boron-germanium co-doped optical fiber, the long-period fiber grating close to the dispersion inflection point is engraved, the long-period fiber grating close to the dispersion inflection point has two wave troughs on a spectrum, the measurement of a magnetic field can be realized by measuring the wavelength difference corresponding to the two wave troughs after deviation, the design is flexible, the insertion loss of the long-period fiber grating is small, the processing is easy, and the stability is high.

Further, the preset length of the boron-germanium co-doped optical fiber is 3 cm.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

Fig. 1 is a schematic structural diagram of a magnetic field sensor according to a first embodiment of the present invention;

fig. 2 is a schematic structural diagram of a magnetic field detection system according to a first embodiment of the present invention;

FIG. 3 is a graph of the transmission spectrum of the long-period fiber grating of FIG. 1 before packaging;

FIG. 4 is a transmission spectrum of the long-period fiber grating of FIG. 1 after being encapsulated;

FIG. 5 is a diagram showing the dual-valley variation law of the long-period fiber grating in FIG. 1 in different magnetic fields;

FIG. 6 is a standard curve graph of the duplex wave valley variation law of FIG. 5.

Description of the main element symbols:

sensor with a sensor element	10	Wide band light source	11
				Incident single mode optical fiber	101	Spectrometer	12
Outgoing single mode optical fiber	102	Magnetic field generator	13
				Boron-germanium co-doped optical fiber	103	Stable power supply	15
Capillary tube	104	Magnetometer	14
				Long period optical fiber grating	1031	Ultraviolet curing adhesive	1042
Magnetic fluid	1041

The following detailed description will further illustrate the invention in conjunction with the above-described figures.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments presented herein without making any creative effort, shall fall within the protection scope of the present application.

It is obvious that the drawings in the following description are only examples or embodiments of the present application, and that it is also possible for a person skilled in the art to apply the present application to other similar contexts on the basis of these drawings without inventive effort. Moreover, it should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another.

Reference in the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the specification. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of ordinary skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments without conflict.

Unless defined otherwise, technical or scientific terms referred to herein shall have the ordinary meaning as understood by those of ordinary skill in the art to which this application belongs. Reference to "a," "an," "the," and similar words throughout this application are not to be construed as limiting in number, and may refer to the singular or the plural. The present application is directed to the use of the terms "including," "comprising," "having," and any variations thereof, which are intended to cover non-exclusive inclusions; for example, a process, method, system, article, or apparatus that comprises a list of steps or modules (elements) is not limited to the listed steps or elements, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus. Reference to "connected," "coupled," and the like in this application is not intended to be limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The term "plurality" as referred to herein means two or more. "and/or" describes an association relationship of associated objects, meaning that three relationships may exist, for example, "A and/or B" may mean: a exists alone, A and B exist simultaneously, and B exists alone. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. Reference herein to the terms "first," "second," "third," and the like, are merely to distinguish similar objects and do not denote a particular ordering for the objects.

Referring to fig. 1, a magnetic field sensor 10 according to a first embodiment of the present invention includes an incident single-mode fiber 101, an exit single-mode fiber 102, a boron-germanium co-doped fiber 103, and a capillary 104.

Specifically, the transmission end and the output end of the boron-germanium co-doped fiber 103 are respectively connected with one end of the incident single-mode fiber 101 and one end of the exit single-mode fiber 102, a long-period fiber grating 1031 close to a dispersion inflection point is arranged on the boron-germanium co-doped fiber 103, the long-period fiber grating 1031 is arranged in the capillary 104, and a magnetic fluid 1041 is further arranged in the capillary 104.

According to the magnetic field sensor 10 provided by the first embodiment of the invention, the magnetic fluid 1041 has tunability under the action of a magnetic field, when the external magnetic field changes, the refractive index of the magnetic fluid 1041 changes accordingly, at the moment, the deviation is generated when the optical power detection instrument detects the valley of the spectrum, the measurement of the magnetic field can be realized by measuring the deviation, and the sensitivity of the fiber bragg grating sensor is greatly improved.

Further, in the embodiment of the present invention, the magnetic fluid 1041 is a water-based magnetic fluid, the water-based magnetic fluid has both solid magnetism and fluidity of a liquid material, the refractive index of the magnetic fluid 1041 has a tunable characteristic, and when an external magnetic field changes, the refractive index changes, and the sensitivity to the magnetic field change is high.

In addition, in the present embodiment, the period range of the long-period fiber grating is 100-2000 μm, which makes the long-period grating mode be the high-order cladding mode LP12, and the higher the mode order of the long-period fiber grating 1031, the higher the ambient refractive index sensitivity.

Further, the cladding diameter range of the boron-germanium co-doped fiber 103 is 120-130 microns, the core diameter of the boron-germanium co-doped fiber 103 is 6-7 microns, and the smaller the cladding diameter of the fiber is, the higher the ambient refractive index sensitivity is.

It can be understood that the working wavelength range of the long-period fiber grating 1031 is 600-2400 nm, the working range is wide, the applicability is strong, and the higher the working wavelength is, the higher the environmental refractive index sensitivity is.

Referring to fig. 2, in the magnetic field detection system based on the magnetic field sensor, the other ends of the incident single-mode fiber 101 and the emergent single-mode fiber 102 are respectively connected to the broadband light source 11 and the spectrometer 12, the capillary 104 is disposed in the magnetic field generator 13, the magnetic field generator 13 is further provided with the magnetometer 14, and the magnetic field generator 13 is connected to the stable power supply 15.

The magnetic field generator 13 can be driven by the stabilized power supply 15, the magnetic field intensity can be changed by adjusting the power supply voltage, and the magnetometer 14 is used for detecting the magnetic field at the position of the long-period fiber grating 1031.

Further, the magnetic field sensor 10 is placed in the center of the magnetic field generator 13, the stabilized voltage power supply is rotated, the magnetic field at the position of the sensor is measured by the Tesla magnetometer 14, and the change rule of LPFG resonance wavelength under different magnetic field strengths is obtained, as shown in FIGS. 5 and 6, the result shows that the refractive index of the magnetic fluid 1041 is increased along with the increase of the magnetic field, the double-peak spacing of the long-period fiber grating 1031 is increased, the wave trough A drifts towards short wave, and the wave trough B drifts towards long wave; when the magnetic field intensity is 20.5mT, the wavelength offset of the two wave troughs is the largest, the wave trough A drifts from 1597.5nm to 1583.4nm, the drift amount is 14.9nm, the wave trough B drifts from 1895.3nm to 1917nm, and the drift amount is 21.6 nm; when the magnetic field intensity reaches 25mT, the offset of the two wave troughs is reduced, the superposition of the drift amounts of the wave trough A and the wave trough B is the wavelength variation of the magnetic field sensor 10, so that the magnetic field detection sensitivity is greatly improved, meanwhile, in order to ensure that the sensor reaches the highest magnetic field sensitivity, the magnetic field intensity is selected to be between 0 mT and 20.5mT, and then the long-period fiber grating 1031 is subjected to magnetic field detection.

The invention also provides a preparation method of the magnetic field sensor 10, which specifically comprises the following steps:

writing a long-period fiber grating 1031 close to a dispersion inflection point: welding a boron-germanium co-doped fiber 103 with a preset length between an incident single-mode fiber 101 and an emergent single-mode fiber 102, and writing a long-period fiber grating 1031 close to a dispersion inflection point on the boron-germanium co-doped fiber 103 through a laser;

the long-period fiber grating 1031 is arranged in the capillary 104, one end of the capillary 104 is packaged by using the ultraviolet curing glue 1042, after the ultraviolet curing glue 1042 is cured, the magnetic fluid 1041 is guided into the capillary 104 by using the injector, axial pressure is applied to keep the long-period fiber grating 1031 in a straight state, and the other end of the capillary 104 is sealed by using the ultraviolet curing glue 1042.

By adopting the preparation method, the long-period fiber grating 1031 close to the dispersion inflection point is engraved, the long-period fiber grating 1031 close to the dispersion inflection point has two wave troughs on the spectrum, the measurement of the magnetic field can be realized by measuring the wavelength difference corresponding to the two wave troughs after the deviation, the design is flexible, and the long-period fiber grating 1031 has the advantages of small insertion loss, easy processing and high stability.

Specifically, a carbon dioxide laser and a three-dimensional adjusting platform are used for constructing a long-period fiber grating 1031 preparation platform, and the optical path of the preparation platform is adjusted, so that the fiber core of the optical fiber can obtain the strongest exposure effect. Before preparing the long-period fiber grating 1031, a PS1250 optical fiber with the length of 3cm is stripped of a coating layer and is welded in the middle of a single-mode optical fiber, the optical fiber is clamped by a clamp of a three-dimensional adjusting platform, and two ends of the optical fiber are respectively connected with a broadband light source 11 and a spectrometer 12 to monitor the grating spectrum. In order to introduce periodic refractive index modulation, the working energy of the carbon dioxide laser is controlled, the exposure frequency of the laser is kept unchanged, the boron-germanium co-doped fiber 103 is subjected to high-energy exposure treatment until the contrast of the resonance wavelength of the long-period fiber grating 1031 reaches saturation, so that the long-period fiber grating 1031 close to the dispersion inflection point is prepared, the transmission spectrogram of the prepared long-period fiber grating 1031 is detected by the spectrometer 12, and as shown in fig. 3, the long-period fiber grating 1031 only has one trough according to the diagram.

It can be understood that the prepared long-period fiber grating 1031 is horizontally placed in the middle of the quartz capillary 104, one end of the capillary 104 is packaged by the ultraviolet curing glue 1042, after the long-period fiber grating 1031 is cured, the magnetic fluid 1041 is guided into the capillary 104 by the injector until the capillary 104 is filled up, axial tension is applied to keep the grating in a straight state, the other end of the capillary 104 is sealed, and at this time, a packaged LPFG transmission spectrogram can be obtained by detecting through the spectrometer 12, as shown in fig. 4, it is obtained according to the diagram that, along with the increase of the refractive index of the external environment, the long-period fiber grating 1031 is divided into double wave troughs from the original single wave trough, and the.

By comparing the spectrogram before and after the long-period fiber grating 1031 is packaged, the transmission spectrum packaged after the magnetic fluid 1041 is filled is changed into double wave troughs, and the change of the magnetic field is reflected by the superposition of the drift amounts of the two wave troughs, so that the sensitivity of magnetic field detection is greatly improved.

The invention provides a technical scheme that a carbon dioxide laser is used for writing a long-period fiber grating 1031 close to a dispersion inflection point on a boron-germanium co-doped fiber 103, so that the prepared long-period fiber grating 1031 at the dispersion inflection point can display two wave troughs on a transmission spectrogram, when an external magnetic field changes, the refractive index of a magnetic fluid 1041 can change accordingly, the two wave troughs on the spectrum can drift, the measurement of a magnetic field can be realized by measuring the wavelength difference of the two shifted wave troughs, and the magnetic field detection sensitivity is greatly improved.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. a magnetic field sensor, is characterized in that, comprises incident single-mode fiber, exit single-mode fiber, boron-germanium co-doped fiber and capillary, the incoming end and output end of described boron-germanium co-doped fiber are respectively the same as the incident single-mode fiber. The mode optical fiber is connected to one end of the outgoing single-mode optical fiber, the incident single-mode optical fiber and the other end of the outgoing single-mode optical fiber are respectively connected to a tunable laser and an optical power detection instrument, and the boron-germanium co-doped optical fiber is provided with a near-dispersion optical fiber. The long-period fiber grating of the inflection point, the long-period fiber grating is arranged in a capillary tube, and a magnetic fluid is also arranged in the capillary tube, and the capillary tube is arranged between the magnetic field generators, and the magnetic field generator is connected with a stable power supply.

2 . The magnetic field sensor according to claim 1 , wherein the diameter of the cladding of the boron-germanium co-doped optical fiber is 120-130 microns, and the core diameter of the boron-germanium co-doped optical fiber is 6-7 microns. 3 .

3 . The magnetic field sensor according to claim 1 , wherein a magnetometer is provided in the magnetic field generator. 4 .

4 . The magnetic field sensor according to claim 1 , wherein the period range of the long-period light grating is 100-2000 μm. 5 .

5 . The magnetic field sensor according to claim 1 , wherein the operating wavelength range of the long-period fiber grating is 600-2400 nanometers. 6 .

6. The magnetic field sensor according to claim 1, wherein the magnetic fluid is a water-based magnetic fluid.

7. The method for preparing a magnetic field sensor according to any one of claims 1-6, wherein the method comprises:

Writing a long-period fiber grating close to the dispersion inflection point: splicing a preset length of boron-germanium co-doped fiber between the incident single-mode fiber and the outgoing single-mode fiber, and writing the long-period fiber grating close to the dispersion inflection point on the boron-germanium co-doped fiber by a laser. Periodic fiber grating;

The long-period fiber grating is placed in the capillary tube, and one end of the capillary tube is encapsulated by ultraviolet curing glue. After the ultraviolet curing glue is cured, the magnetic fluid is introduced into the capillary tube by using a syringe, and axial pressure is applied to keep the long-period fiber grating in the capillary tube. In a straight state, the other end of the capillary is sealed with UV-curable glue.

8 . The method for preparing a magnetic field sensor according to claim 7 , wherein the preset length of the boron-germanium co-doped fiber is 3 cm. 9 .