Coaxial resonant cavity sensor for measuring micro water in insulating oil

Abstract

The utility model provides a coaxial resonant cavity sensor for measuring micro water in insulating oil, which is characterized by comprising a first grounding plane and a second grounding plane which are both L-shaped structures and are arranged in bilateral symmetry, the third grounding plane, the radiation plane, the winding line and the feeder line are arranged on the inner sides of the first grounding plane and the second grounding plane, the first PIN diode is connected with one end of the third grounding plane and the top end of the first grounding plane, and the second PIN diode is connected with the other end of the third grounding plane and the top end of the second grounding plane. The first PIN diode and the second PIN diode are arranged on the upper side of the winding line, the radiation plane is arranged on the lower side of the winding line, and the feeder line is arranged on the lower side of the radiation plane; the winding line is a bending structure of the CRLH transmission line; and SMA interfaces are welded at the bottoms of the feeder line and the grounding plane. According to the utility model, the problems of poor anti-interference capability, low precision, high cost, low efficiency and the like in detection of the micro-water content in the insulating oil are solved.

Description

Technical Field

[0001] The utility model relates to the field of microwave technology, in particular to a coaxial resonant cavity sensor used for measuring micro-water in insulating oil. Background Art

[0002] The safe and healthy operation of the power system is an important guarantee for national production and life. The reliable operation of the power transmission and transformation equipment in the power system is the most powerful guarantee for the safety of the power grid. In particular, as the core equipment in the field of high-voltage power transmission, the operating conditions of large oil-immersed power transformers and the degree of aging of internal insulation materials will be directly related to the safety of power transmission. At present, the average operating life of oil-immersed transformers manufactured and used in all countries around the world is about 30 years, and the length of service life also depends on the specific operating environment. Therefore, for oil-immersed transformers, especially transformers that have been in operation for more than 20 years, it is very important to monitor their insulation performance in real time, which is related to their operating stability and economy, and determines whether the transformer is retired.

[0003] Water is the most likely impurity to appear in insulating oil. If the water content is too high, it will increase the dielectric loss of the insulating oil and reduce the breakdown voltage of the insulating oil. If the water content exceeds the threshold specified by the industry, the water and organic matter in the oil will react under the catalysis of the operating environment. The change in the composition of the insulating oil will cause the insulation performance to drop drastically. If it is not replaced in time, it may even lose its arc extinguishing ability, which is the primary cause of transformer breakdown and burning failure.

[0004] The moisture content inside the transformer is not constant. As the operation time increases, the moisture content tends to increase gradually. Therefore, the transformer must be dried and dehydrated regularly after it is put into operation so that the micro-water content in the insulating medium can be strictly controlled. At present, the measurement of the micro-water content of insulating oil generally uses titration, which is a means of sampling and offline analysis. The entire titration analysis process not only requires special reagents, but also requires high rigor in the operation of the experimenter. The air humidity of the experimental environment will also affect the results. Therefore, the early fault hidden dangers inside the equipment cannot be discovered in time and accurately. With the increase in the transmission and transformation voltage of the power grid and the large-scale operation of oil-immersed transformers, the problem of transformer insulation aging has received more and more attention from many research institutions and scholars at home and abroad.

[0005] Prior art 1:

[0006] In 1935, Karl Fischer invented a Karl Fischer titration (KFT), which is still the most accurate and widely used chemical method for detecting moisture. Later, the coulometric method was derived from it. The moisture titration method now refers to Karl Fischer volumetric titration (KFVT) and coulometric titration (KFCT); the chemical principles based on Karl Fischer volumetric titration (KFVT) and coulometric titration (KFCT) are KFT reactions, which rely on a special chemical reagent containing four substances: I2, SO2, C5H5N, and CH3OH. The specific operation is to dissolve the oil sample to be tested in the reagent. If there is moisture in the oil, I2, SO2 and moisture undergo a reduction reaction, and HI compounds and methyl sulfide are generated under the specific catalytic conditions of C5H5N and CH3OH. The end of the reaction proves that the water in the oil is completely exhausted, and the detection display will show the reaction end point feedback from the platinum electrode. However, there are disadvantages:

[0007] The Coulomb law calculates the water content by recording the amount of electricity consumed by the oil sample. The biggest advantage of the Karl Fischer method is that the test results are accurate and the operation speed is fast, but the disadvantage is that when there are too many impurities in the oil reagent, a series of side reactions will occur, so many factors must be considered when testing aged insulating oil. In addition, when using the KFT method to test moisture, it is necessary to calculate the amount of reagent to avoid the occurrence of false titration endpoints during the titration process.

[0008] Prior art 2:

[0009] The distillation method is the international standard method for measuring trace water. The principle of the distillation method is based on the boiling point of two liquids with very low solubility or immiscible liquids, which are higher than the azeotropic point of the mixed solution. According to this principle, a reagent that is immiscible with water is selected and added to the oil sample containing water to be tested, and the solution is heated to an azeotropic state until the water is completely distilled out and the heating is stopped. The weight of the distilled water can be analyzed to calculate the water content of the oil sample. However, there are disadvantages:

[0010] The reason why the distillation method is widely used is that it does not require specific reagents and the principle is very simple, but it takes too long and the ambient humidity has a great impact on its results. At the same time, water droplets on the inner wall of the condenser will cause the measurement results to be low. Kopyltsova et al. found that the collector capacity and the water content of the distillation solvent will also affect the accuracy of the distillation method. Due to the difference in readability of water volume and the presence of oil-in-water emulsion in the container, the measurement accuracy of the distillation method for low-water-content oil is not satisfactory.

[0011] Existing technology three:

[0012] The burst test is a short-term on-site detection method; after the on-site operator puts on goggles, he drops the oil sample directly into the concave part of the clean aluminum foil, and heats the aluminum foil with an open flame at the bottom. When the oil contains less water, it will make a hissing sound when heated, and when the oil contains more water, it will produce an audible popping sound, which can be used to judge the degree of oil aging. However, there are disadvantages in the above method: the burst test method is only a qualitative detection method, which can only be judged by experience and cannot give specific parameters.

[0013] Prior art four:

[0014] Gas chromatography: The principle of micro-water measurement by gas chromatography is to put the oil sample into the gasification reaction chamber, and the water in the oil is vaporized in the gasification chamber to form water vapor. Using inert gas such as nitrogen or argon as carrier gas, the water vapor is carried into the polymer microsphere fixed box for separation, and then detected by corresponding detection methods such as thermal conductivity detectors. There are disadvantages in the above content: gas chromatography requires a long time to wait for the instrument to stabilize during the detection period, and the measurement repeatability is poor.

[0015] Prior art five:

[0016] Radio frequency attenuation method: The measurement principle of the radio frequency attenuation method is based on the radio frequency impedance theory, that is, the dielectric constant and conductivity of different media are different, and the attenuation characteristics of electromagnetic waves passing through different media are different. The attenuation characteristics of the radio frequency signal passing through the insulating oil are analyzed to determine its dielectric constant, and then the moisture content is calculated through the change in the dielectric constant. There are shortcomings in the above content: the radio frequency attenuation method can only be applied to the measurement of water content above 2%, and is basically used to measure the water content in crude oil, and is not suitable for measuring the micro-water content of insulating oil.

[0017] Prior art six:

[0018] Infrared spectroscopy detection method; the detection principle of this method is: when infrared rays pass through the measured micro-water insulating oil, it will absorb infrared light of a specific frequency, and the absorption intensity will change with the micro-water content of the insulating oil. Its law can refer to the Lambert-Beer law to calculate the micro-water content in the oil. There are disadvantages in the above content: it is not suitable for analyzing water-containing samples because the hydroxyl peak in water interferes with the determination, and the spectrum analysis mainly relies on experience.

[0019] Prior art seven:

[0020] PI film humidity sensor method; The principle of the PI film humidity sensor method is to place a capacitive humidity sensor composed of polyimide PI film into the oil sample to be tested. The water molecules in the oil will migrate between the PI film and the oil and finally form a dynamic balance. The increase in the water content in the oil will cause the PI film to adsorb more water molecules, thereby causing the PI film to change in the dielectric constant. The capacitance of the two plates of the humidity sensor increases with the change in the dielectric constant. The capacitance is converted into a measurable electrical signal, so that the electrical signal can be analyzed to detect the micro-water content in the oil. There are disadvantages in the above content: in the field detection, since the PI film and the oil need to achieve a dynamic balance of moisture, the detection time must be guaranteed for at least 5 to 10 minutes during the process, and the polyimide film is easy to deteriorate, which has a significant impact on the measurement accuracy. In addition, the primary and secondary circuits of the sensor are often affected by the capacitance and environment, making it difficult to achieve high-precision detection. Utility Model Content

[0021] In order to overcome the shortcomings of the prior art, the purpose of the utility model is to provide a coaxial resonant cavity sensor for measuring micro-water content in insulating oil. The utility model solves the problems of poor anti-interference ability, low precision, high cost and low efficiency in the prior art detection of micro-water content in insulating oil.

[0022] To achieve the above purpose, the utility model provides the following solutions:

[0023] A coaxial resonant cavity sensor for measuring micro-water in insulating oil, comprising:

[0024] A copper plate and a first PIN diode, a second PIN diode, a first ground plane, a second ground plane, a third ground plane, a radiation plane, a meandering line and a feeding line arranged on the copper plate;

[0025] The first ground plane and the second ground plane are both L-shaped structures, the first ground plane and the second ground plane are arranged symmetrically, the third ground plane, the radiation plane, the meander line and the feeder are all arranged inside the first ground plane and the second ground plane, the first PIN diode is respectively connected to one end of the third ground plane and the top of the first ground plane, the second PIN diode is respectively connected to the other end of the third ground plane and the top of the second ground plane, the first PIN diode and the second PIN diode are both arranged on the upper side of the meander line, the radiation plane is arranged on the lower side of the meander line, and the feeder is arranged on the lower side of the radiation plane;

[0026] The meander line is a bent structure of a CRLH transmission line;

[0027] The feed line and the bottom of the ground plane are welded with SMA interfaces.

[0028] Preferably, the diode is of model SMP1322.

[0029] A method for using a coaxial resonant cavity sensor for measuring trace water in insulating oil, comprising:

[0030] According to the Maxwell-Wagner inhomogeneous dielectric model, the equivalent complex dielectric constant expression of oil-water emulsion is determined;

[0031] Using HFSS software, the Fruquncy-S of oil-water emulsions with different water volume fractions were measured. 11 curve;

[0032] According to the Fruquncy-S 11 The curve determines the set of zero-order resonance points;

[0033] Fitting the zero-order resonance point set to obtain a medium relationship;

[0034] Determine the target medium value according to the medium relationship formula;

[0035] Based on the expression of the equivalent complex dielectric constant of the oil-water emulsion, the complex dielectric constant is obtained according to the target medium value.

[0036] Preferably, the equivalent complex dielectric constant of the oil-water emulsion is expressed as:

[0037]

[0038] in, represents the continuous phase medium, represents the discrete phase medium, Represents mixed media, is the volume fraction of the discrete phase.

[0039] According to the specific embodiments provided by the utility model, the utility model discloses the following technical effects:

[0040] The utility model provides a coaxial resonant cavity sensor for measuring micro-water in insulating oil. The utility model realizes the detection of micro-water content in insulating oil based on microwave coaxial resonant cavity technology. The microwave measurement method has strong anti-interference ability, high precision, good reliability, can realize fast on-site and online detection, and is simple and safe to operate. The participation of microwave sensors can simplify the production process and reduce production costs, and the sensors made using microwave antenna technology have the advantages of small size, wide bandwidth, low cost, high gain, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0042] Figure 1 A schematic diagram of the structure of a coaxial resonant cavity sensor for measuring trace water in insulating oil provided by an embodiment of the utility model;

[0043] Figure 2 An equivalent circuit diagram of a T-type composite left-handed and right-handed transmission line unit provided by an embodiment of the utility model;

[0044] Figure 3 A schematic diagram of the structure of a T-shaped composite left-handed and right-handed transmission line unit provided by an embodiment of the utility model;

[0045] Figure 4 A three-dimensional diagram of a coaxial resonant cavity sensor for measuring micro-water in insulating oil provided by an embodiment of the utility model;

[0046] Figure 5 An equivalent circuit diagram of a coaxial resonant cavity sensor for measuring trace water in insulating oil provided by an embodiment of the utility model;

[0047] Figure 6 The coaxial resonant cavity sensor for measuring micro-water in insulating oil provided by the embodiment of the utility model simulates the S 11 Graphs;

[0048] Figure 7 The internal electric field distribution diagram of the coaxial resonant cavity sensor for measuring micro-water in insulating oil provided by the embodiment of the utility model;

[0049] Figure 8 A diagram showing the internal magnetic field distribution of a coaxial resonant cavity sensor for measuring trace water in insulating oil provided by an embodiment of the utility model;

[0050] Fig. 9 A simulation f0=g(ε) fitting curve diagram of a coaxial resonant cavity sensor for measuring micro-water in insulating oil provided by an embodiment of the utility model;

[0051] Fig.10 A flow chart of a method for using a coaxial resonant cavity sensor for measuring trace water in insulating oil provided in an embodiment of the utility model.

[0052] Description of reference numerals:

[0053] (1) - first PIN diode, (2) - first ground plane, (3) - radiation plane, (4) - meander line, (5) - feed line, (6) - second PIN diode, (7) - third ground plane, (8) - second ground plane. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0055] The purpose of the utility model is to provide a coaxial resonant cavity sensor for measuring micro-water content in insulating oil. The utility model solves the problems of poor anti-interference ability, low precision, high cost and low efficiency in the detection of micro-water content in insulating oil in the prior art.

[0056] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0057] like Figure 1 As shown, the utility model provides a coaxial resonant cavity sensor for measuring micro-water in insulating oil, comprising:

[0058] A copper plate and a first PIN diode (1), a second PIN diode (6), a first ground plane (2), a second ground plane (8), a third ground plane (7), a radiation plane (3), a meandering line (4) and a feed line (5) arranged on the copper plate;

[0059] The first ground plane (2) and the second ground plane (8) are both L-shaped structures. The first ground plane (2) and the second ground plane (8) are arranged symmetrically on the left and right. The third ground plane (7), the radiation plane (3), the meandering line (4) and the feeder line (5) are all arranged inside the first ground plane (2) and the second ground plane (8). The first PIN diode (1) is respectively connected to one end of the third ground plane (7) and the top of the first ground plane (2). The second PIN diode (6) is respectively connected to the other end of the third ground plane (7) and the top of the second ground plane (8). The first PIN diode (1) and the second PIN diode (6) are both arranged on the upper side of the meandering line (4). The radiation plane (3) is arranged on the lower side of the meandering line (4). The feeder line (5) is arranged on the lower side of the radiation plane (3).

[0060] The meander line (4) is a bent structure of a CRLH transmission line;

[0061] The feed line (5) and the bottom of the ground plane are welded with an SMA interface.

[0062] Specifically, the first ground plane (2), the second ground plane (8), the third ground plane (7), the radiation plane (3), the meander line (4), and the feed line (5) are attached to a 12 mm×21 mm×1.6 mm copper plate in the form of patches, while the first PIN diode (1) and the second PIN diode (6) are welded on the copper plate. The positional relationship of the different structures on the copper plate is as follows: Figure 1 ;

[0063] SMA interfaces are welded on the feeder (5) and the ground plane, and the three-dimensional structure is simulated using Proe software, as shown in the figure. Figure 4 ;

[0064] The meander line (4) realizes the classic meander line structure of the CRLH transmission line to provide the right-hand capacitance C R and the left-hand inductor L L , the gap between the patch and the fold line provides the left-hand capacitor C L , the patch provides the right-hand inductor L R , forming the equivalent circuit diagram of the T-type composite left-handed and right-handed transmission line unit, as shown in Figure 2 , including: 2 first capacitors C L , 2 first inductors L R , 1 second inductor L L and a second capacitor C R ; Among them, the first first inductor, the first first capacitor, the second first inductor and the second first inductor are connected in series in sequence, the second capacitor and the second inductor are connected in parallel, and the parallel circuit is connected to the connection point of the first first capacitor and the second first inductor.

[0065] The first PIN diode (1) and the second PIN diode (6) correspond to different inductance and capacitance values ​​when they are turned on or off. In the device, the diode is equivalent to being in an off state in the circuit.

[0066] Specifically, the inner and outer conductors of the miniaturized antenna coaxial resonant cavity of the composite left-right-handed transmission line form a bent structure to form a coaxial line with short circuits at both ends, and there is a gap structure between the inner and outer conductors in the axial direction. It is usually designed as a composite left-right-handed transmission line structure, so it is called a coaxial resonant cavity sensor based on a composite left-right transmission line; the design of the sensor is based on a T-type composite left-right-handed transmission line unit structure, and adopts a classic bent line structure to realize a CRLH transmission line (composite left-right-handed transmission line) to provide a right-handed capacitor C R and the left-hand inductor L L, the gap between the patch and the fold line provides the left-hand capacitor C L , the patch provides the right-hand inductor L R .

[0067] Further, such as Figure 2 Figure 3 The designed unit structure realizes the characteristics of T-type composite left-handed transmission line and produces a zero-order resonance point. The SMA interface is welded between the feed line (5) and the bottom of the ground plane patch, and the coaxial line is connected to apply the structure to the sensor. According to the transmission line theory, ω se and ω sh They are the series resonant frequency and the parallel resonant frequency respectively, and their formulas can be expressed as follows:

[0068]

[0069]

[0070] Left hand capacitor C L and the right-hand inductor L R The change of will affect the series resonant frequency f se Change, similarly, the right hand capacitor C R and the left-hand inductor L L The change of the parallel resonant frequency f sh change.

[0071] According to C = εS / 4πkd, it can be concluded that the dielectric constant and the capacitance value are proportional. When ε increases, the left-hand capacitance increases, and the series resonant frequency decreases. Therefore, by simulating the Fruquncy-S 11 The change curve of , and find the zero-order resonance point. Fit f = g(ε), and then get the function pass Fig. 9 The data in the table show that the formula has a good fit.

[0072] Figure 1 The coaxial resonant cavity sensor structure based on the designed composite left and right transmission lines. The three-dimensional structure is as follows Figure 4 The antenna is placed on a 12mm×21mm×1.6mm FR4 substrate. The equivalent circuits of the antenna when the PIN diode is on and off are shown below. The diode model is SMP 1322. Voltage is applied to the diode to control its on or off. When the diode is on or off, different inductance and capacitance values ​​are corresponding. Figure 5 The diode in the figure is replaced by the parameter values ​​of its equivalent circuit.

[0073] The equivalent circuit diagram of the coaxial resonant cavity sensor for measuring micro-water in insulating oil is designed as shown below. Figure 5As shown, the model of the diode is SMP 1322, and the various parameter values ​​of its equivalent circuit are used to replace it. As shown, the model of the diode is SMP 1322. Voltage is applied to the diode to control its on or off, and different inductance and capacitance values ​​correspond to the on or off of the diode. Since the PIN diode is an active device, the simulation of passive devices is generally performed in HFSS software. The design of the sensor will be combined with HFSS software and ADS software for joint simulation. The transmission line structure of the T-type CRLH transmission line antenna is designed in HFSS software.

[0074] like Fig.10 As shown, this embodiment also provides a method for using a coaxial resonant cavity sensor for measuring trace water in insulating oil, including:

[0075] Step 100: Determine an equivalent complex dielectric constant expression of the oil-water emulsion according to the Maxwell-Wagner inhomogeneous dielectric model;

[0076] Step 200: Using HFSS software, measure the Fruquncy-S of oil-water emulsions with different water volume fractions. 11 curve;

[0077] Step 300: According to the Fruquncy-S 11 The curve determines the set of zero-order resonance points;

[0078] Step 400: fitting the zero-order resonance point set to obtain a medium relationship;

[0079] Step 500: Determine the target medium value according to the medium relationship formula;

[0080] Step 600: Based on the equivalent complex dielectric constant expression of the oil-water emulsion and according to the target medium value, the complex dielectric constant is obtained.

[0081] Specifically, the equivalent complex dielectric constant expression of the oil-water emulsion is derived according to the dielectric properties of the oil-water emulsion; the Maxwell-Wagner inhomogeneous dielectric equation (the equivalent complex dielectric constant expression of the oil-water emulsion) is:

[0082]

[0083] in, represents the continuous phase medium, represents the discrete phase medium, Represents mixed media, is the volume fraction of the discrete phase. The above formula can be simplified to:

[0084]

[0085] Furthermore, in order to verify the feasibility of the measurement method, a simulation of the measurement of the micro-water content in insulating oil was carried out:

[0086] The Fruquncy-S of oil-water emulsions with different water volume fractions were measured. 11 curve, record the zero-order resonance point f0, deduce f = g(ε), and then calculate the dielectric constant ε of the emulsion and the volume fraction of water Functional relationship.

[0087] Specifically, the experiment uses HFSS software simulation software; HFSS software simulation is used to simulate the mixing of pure oil with a dielectric constant of 2.3 with different contents of water, so that the dielectric constant changes by 0.1, and the corresponding Fruquncy-S 11 Curves, such as Figure 6 .

[0088] Simulate the mixing of pure oil with a dielectric constant of 5 into different amounts of water, and simulate the corresponding Fruquncy-S 11 The curve is used to find the zero-order resonance point, and the formula f = g(ε) is fitted. Then, the equivalent complex dielectric constant expression of the oil-water emulsion is introduced to obtain

[0089] Specifically, when pure oil with a dielectric constant of 5 is input into the coaxial resonant cavity sensor based on the composite left and right transmission lines, the electric field and magnetic field distribution inside the sensor are as follows: Figure 7 Figure 8 . Find the lowest resonance point of the curve under different dielectric constants and mark it, draw the curve and fit it, such as Fig. 9 . The formula can be fitted:

[0090] f0=-0.89519ε+6.9926

[0091] By analyzing the fitting equation, we can find that the sum of squares of the residuals at each point is 9.86741E-4, and the R square is 0.99659, and the fitting effect is good.

[0092] Take ε o =2,ε α =80,ε=ε m Substituting the equivalent complex dielectric constant expression of oil-water emulsion and taking the real number of the complex dielectric constant, we can get:

[0093]

[0094] The beneficial effects of the utility model are as follows:

[0095] The sensor made by microwave antenna technology has the advantages of small size, wide bandwidth, low cost, high gain, and high measurement accuracy. When the water volume fraction is less than 5%, the resonant frequency f increases by MHZ for every 0.1% increase in volume fraction, ensuring sensitivity.

[0096] In addition, the utility model realizes the detection of micro-water content in insulating oil based on microwave coaxial resonant cavity technology. The microwave measurement method has strong anti-interference ability, high precision, good reliability, and can realize fast on-site and online detection. The operation is simple and safe. The participation of microwave sensors can simplify the production process and reduce production costs. Sensors made using microwave antenna technology have the advantages of small size, wide bandwidth, low cost, and high gain.

[0097] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0098] This article uses specific examples to illustrate the principles and implementation methods of the utility model. The above examples are only used to help understand the method and core ideas of the utility model. At the same time, for those skilled in the art, according to the ideas of the utility model, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the utility model.

Claims

1. A coaxial resonant cavity sensor for measuring micro-water in insulating oil, characterized in that: include: A copper plate and a first PIN diode, a second PIN diode, a first ground plane, a second ground plane, a third ground plane, a radiation plane, a meandering line and a feeding line arranged on the copper plate; The first ground plane and the second ground plane are both L-shaped structures, the first ground plane and the second ground plane are arranged symmetrically, the third ground plane, the radiation plane, the meander line and the feeder are all arranged inside the first ground plane and the second ground plane, the first PIN diode is respectively connected to one end of the third ground plane and the top of the first ground plane, the second PIN diode is respectively connected to the other end of the third ground plane and the top of the second ground plane, the first PIN diode and the second PIN diode are both arranged on the upper side of the meander line, the radiation plane is arranged on the lower side of the meander line, and the feeder is arranged on the lower side of the radiation plane; The meander line is a bent structure of a CRLH transmission line; The feed line and the bottom of the ground plane are welded with SMA interfaces.

2. A coaxial resonant cavity sensor for measuring micro-water in insulating oil according to claim 1, characterized in that: The diode model is SMP 1322.

Images