A current detection device based on inverted microstrip antenna and detection method thereof

Abstract

The present invention belongs to the field of measurement and antenna technology, and relates to a current detection device based on an inverted microstrip antenna and a detection method thereof; the device includes a permanent magnet, an inverted microstrip antenna, a package and an upper end cover, wherein the inverted microstrip antenna is composed of a metal ground plate, an antenna patch, a feed device wavelength impedance converter, a microstrip line, a support body and a dielectric substrate, and the method is mainly used for the inverted microstrip antenna to wirelessly detect and wirelessly transmit current. The permanent magnet on the upper surface of the beam is subjected to magnetic force in the magnetic field around the wire, and the force is transmitted to the metal beam to deform it, changing the thickness of the air cavity between the beam and the antenna patch, so that the resonant frequency of the inverted microstrip antenna will shift accordingly. The current detection device based on the inverted microstrip antenna can realize current detection and wireless transmission of signals. Compared with traditional microstrip antennas, the inverted microstrip antenna eliminates the error in strain transmission and the error caused by stress fatigue of the antenna patch, and has a longer service life.

Description

Technical Field

[0001] The invention belongs to the technical field of measurement and antenna, and relates to a current detection device based on an inverted microstrip antenna and a detection method thereof. Background Art

[0002] With the country's great investment in popularizing electricity, the length of various lines erected has reached millions of kilometers. Electrical equipment is of various types and large in number, and widely distributed in various complex geographical environments. It is very difficult to achieve real-time and effective monitoring of the status of all lines and electrical equipment. Therefore, it is of great significance to propose an efficient and intelligent means of power grid monitoring.

[0003] The Internet of Things (IoT) technology is a combination of various advanced sensor perception technologies, Internet cloud technologies, artificial intelligence algorithms and automation technologies. It is the main direction of future breakthroughs in information technology and contains a huge space for theoretical and technological innovation. It provides a new solution and means for some urgent social, industrial and agricultural problems [4]. Based on the IoT technology, a large number of wireless sensor monitoring nodes are embedded and implanted into the objects of the system, which can draw a comprehensive operating status view for various systems, greatly improving the monitoring coverage and the accuracy of fault location. Therefore, it is particularly important to develop a current detection device that can detect current and transmit signals at the same time for real-time and effective monitoring of the power grid.

[0004] The current detection devices in the prior art mainly include capacitive current sensors, cantilever beam resonant current sensors, Hall current sensors, all-optical fiber current sensors, fluxgate current sensors, Rogowski coil current sensors, giant magnetoresistance current sensors, etc., which have the problems of complex structure, difficult processing, high cost, etc., and cannot realize wireless transmission of signals, which makes the entire current monitoring system complicated.

[0005] Since the emergence of practical microstrip antennas, the rapid development of this printed circuit antenna has been remarkable. Microstrip antennas are composed of patch antennas, dielectric substrates and ground planes. They have a simple structure and unique advantages that conventional antennas do not have, such as thin profile, small size, light weight and low cost. In recent years, microstrip antennas have been widely used. They have been widely used in a wide frequency range of about 100MHz to 100GHz, including satellite communications, radar, remote sensing, missile telemetry and remote control, environmental monitoring, biomedicine, portable radio equipment, etc. Microstrip antennas have great research potential in the fields of sensing and signal transmission. However, traditional microstrip antennas are attached to the surface of objects, follow the deformation of the objects, and obtain information from the offset of the resonant frequency. This method used in sensing not only has errors caused by strain transmission, but also errors caused by stress fatigue of the antenna patch, which reduces the service life of the microstrip antenna. Summary of the invention

[0006] In order to overcome the above problems, the present invention provides a current detection device based on an inverted microstrip antenna and a detection method thereof; there is an air cavity between the ground plate of the inverted microstrip antenna and the antenna patch, and the method is mainly used for the wireless detection and wireless transmission of current by the inverted microstrip antenna. The permanent magnet on the upper surface of the beam is subjected to magnetic force in the magnetic field around the conductor, and the force is transmitted to the metal beam to deform it, changing the thickness of the air cavity between the beam and the antenna patch, so that the resonant frequency of the inverted microstrip antenna will shift accordingly. The current detection device based on the inverted microstrip antenna can realize current detection and wireless transmission of signals. Compared with traditional microstrip antennas, the inverted microstrip antenna eliminates the error in strain transmission and the error caused by stress fatigue of the antenna patch, and has a longer service life.

[0007] A current detection device based on an inverted microstrip antenna comprises a permanent magnet 1, an inverted microstrip antenna, a package 8 and an upper end cover 9, wherein the inverted microstrip antenna is composed of a metal ground plate 2, an antenna patch 3, a feed device wavelength impedance converter 4, a microstrip line 5, two support bodies 6 and a dielectric substrate 7, and the upper end cover 9 is fixedly connected to the top of the package 8, the package 8 is covered, and the package semi-cylindrical groove 802 on the top of the package 8 is buckled with the upper end cover semi-cylindrical groove 901 at the bottom of the upper end cover 9 to form a complete cylindrical groove A square hole 801 is opened in the package 8, a dielectric substrate 7 is fixed at the bottom of the square hole 801, the antenna patch 3, the feeding device wavelength impedance converter 4 and the microstrip line 5 are deposited or attached to the rear end of the top surface of the dielectric substrate 7 from front to back, the front and rear ends of the bottom of the metal ground plate 2 are respectively connected to the dielectric substrate 7 through a support body 6, and the antenna patch 3, the feeding device wavelength impedance converter 4 and the microstrip line 5 are located between the metal ground plate 2 and the dielectric substrate 7, and a permanent magnet 1 is fixed to the upper surface of the metal ground plate 2.

[0008] The antenna patch 3 , the feeding device wavelength impedance converter 4 and the microstrip line 5 are integrated into one body and made of the same material, and the antenna patch 3 corresponds to the center position of the metal ground plate 2 .

[0009] An air cavity is formed between the lower surface of the metal ground plate 2 and the antenna patch 3 .

[0010] The shape of the antenna patch 3 is rectangular, circular, trapezoidal or regular polygonal.

[0011] The metal ground plate 2, the antenna patch 3, the feeding device wavelength impedance converter 4 and the microstrip line 5 are all made of good metal conductors, including copper, silver or gold.

[0012] The dielectric substrate 7 is made of insulating material.

[0013] The upper end cover 9 is positioned by means of the positioning posts 902 thereon and the positioning holes 803 on the package 8 .

[0014] A current detection method based on an inverted microstrip antenna comprises the following steps:

[0015] Step 1, fixing the current detection device on the cable to be tested through the cylindrical groove;

[0016] Step 2: The magnetic field generated by the current in the tested cable causes the permanent magnet 1 to bend, and the metal ground plate 2 bends accordingly, causing the thickness of the air cavity between the lower surface of the metal ground plate 2 and the antenna patch 3 to change; when the thickness of the air cavity changes within a certain range, the resonant frequency of the inverted microstrip antenna will shift monotonically, and a function model of the air cavity thickness and the resonant frequency of the inverted microstrip antenna is established, and the model is as follows:

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023] ΔL=h(ξ1ξ3ξ5 / ξ4)

[0024]

[0025]

[0026]

[0027] ξ4=1+0.0377tan -1 [0.067(w / h) 1.456 ]×{6-5exp(0.036(1-∈ r ))}

[0028] ξ5=1-0.218exp(-7.5w / h)

[0029]

[0030] Where: f rrepresents the resonant frequency of the inverted microstrip antenna; c represents the speed of light; L represents the length of the patch antenna 3; w represents the width of the patch antenna 3; ΔL represents the length compensation value of the inverted microstrip antenna; h represents the thickness of the air cavity; h2 represents the total thickness of the inverted microstrip antenna; ∈ eff represents the effective dielectric constant of the inverted microstrip antenna; ∈ r1 Represents the relative dielectric constant of air; ∈ r2 represents the effective dielectric constant of the dielectric substrate 7; q1 represents the spatial proportion of the air cavity in the entire radiation space obtained by conformal mapping; q2 represents the spatial proportion of the dielectric substrate 7 in the entire radiation space obtained by conformal mapping; w ef represents the effective width of the antenna patch 7; v ∈ The thickness of the dielectric substrate after conformal mapping; ξ1, ξ2, ξ3, ξ4 and ξ5 are dimensionless intermediate variables; ∈ r represents the relative dielectric constant of the dielectric substrate 7 in the inverted microstrip antenna;

[0031] The function model of the air cavity thickness and the resonant frequency of the inverted microstrip antenna established above is recorded as:

[0032] f r =f(h)

[0033] Step 3: When the permanent magnet 1 is subjected to force, the metal ground plate 2 and the antenna patch 3 are no longer parallel. The deflection at each point along the length direction of the metal ground plate 2 is not exactly the same. The deflection at the midpoint of the length direction of the metal ground plate 2 is brought into the function model f of the change in air cavity thickness and the shift in the resonant frequency of the inverted microstrip antenna. r =f(h), that is, let h = ν, and establish a functional model of the deflection at the midpoint of the length direction of the metal ground plate 2 and the resonant frequency offset of the inverted microstrip antenna:

[0034] f r =f(ν)

[0035] In the above formula, v represents the deflection at the midpoint of the length direction of the metal ground plate 2;

[0036] Step 4: Analyze the distribution of the induced magnetic field intensity and magnetic field gradient of the long straight wire in space according to the Biot-Savart law, use the infinitesimal method to study the force on the permanent magnet 1 in the magnetic field, and establish a function model of the measured current in the measured cable and the force on the permanent magnet 1: Among them B r is the residual magnetic flux of permanent magnet 1, V is the volume of permanent magnet 1, μ0 is the vacuum permeability, i iis the current of the i-th core inside the measured cable, x and z are the coordinates of any point in the coordinate system established with the straight line passing through the centroid of permanent magnet 1 and perpendicular to the upper surface of permanent magnet 1 as the z-axis and the straight line passing through the centroid of permanent magnet 1, perpendicular to the z-axis and orthogonal to the measured cable as the x-axis, x i 、z i is the coordinate of the i-th core inside the tested cable in the above coordinate system;

[0037] Then, the permanent magnet 1 and the metal grounding plate 2 are treated as a whole for force analysis, and a function model of the deflection at the midpoint of the length direction of the metal grounding plate 2 and the force of the permanent magnet 1 is established as follows:

[0038]

[0039] Wherein ν is the deflection at the midpoint of the length direction of the metal grounding plate 2; E is the elastic modulus of the metal grounding plate 2; I is the moment of inertia of the cross section of the metal grounding plate 2 about the bending neutral axis; l is the length of the metal grounding plate 2;

[0040] Step 5, let ν = ki0, establish a function model of the deflection at the midpoint of the length direction of the metal ground plate 2 and the resonant frequency offset of the inverted microstrip antenna to calculate the magnitude of the measured current, the model is as follows:

[0041] f r =f(ki0)

[0042] in:

[0043]

[0044] In a DC two-core cable: i1 = -i2; |i1| = |i2| = |i0|;

[0045] Beneficial effects of the present invention:

[0046] (1) Long service life: Traditional microstrip antennas are used as sensors by attaching to the surface of an object, following the deformation of the object, and obtaining information from the shift in the resonant frequency. However, the inverted microstrip antenna in the present invention uses the deformation of the metal ground plate to change the thickness of the air cavity between the metal ground plate and the antenna patch, thereby causing the antenna's resonant frequency to shift for sensing. The mechanical properties of the metal ground plate are better than those of the antenna patch deposited on the dielectric substrate, so the present invention can avoid errors caused by stress fatigue in the antenna patch and increase the service life of the microstrip antenna.

[0047] (2) Wireless signal transmission: The current detection devices in the prior art, such as the Hall current sensor, cannot realize wireless signal transmission, which makes the entire current monitoring system very complicated. The present invention is a current monitoring device based on an inverted microstrip antenna, which can not only detect current, but also transmit signals wirelessly, saving the lines used for signal transmission in the current monitoring system, bringing great convenience to the construction of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is an axonometric diagram of a current detection device based on an inverted microstrip antenna according to the present invention;

[0049] Figure 2 A partially cutaway front view of the overall structure of an embodiment of the present invention;

[0050] Figure 3 It is a cross-sectional view of the overall structure of an embodiment of the present invention along the AA plane;

[0051] Figure 4 An axonometric diagram of a detection unit structure according to an embodiment of the present invention;

[0052] Figure 5 is an exploded schematic diagram of a detection unit structure according to an embodiment of the present invention;

[0053] Figure 6 The schematic diagram of the present invention for detecting the current of a double-core cable;

[0054] Figure 7 The return loss S11 curve diagram of the inverted microstrip antenna resonant frequency shifting with the change of air cavity thickness in the present invention. DETAILED DESCRIPTION

[0055] The present invention will be further described below in conjunction with the accompanying drawings.

[0056] Example 1

[0057] like Figures 1 to 5As shown, a current detection device based on an inverted microstrip antenna includes a permanent magnet 1, an inverted microstrip antenna, a package 8 and an upper end cover 9, wherein the inverted microstrip antenna is composed of a metal ground plate 2, an antenna patch 3, a feed device wavelength impedance converter 4, a microstrip line 5, two support bodies 6 and a dielectric substrate 7, and the upper end cover 9 is fixedly connected to the top of the package 8 by screws 10, and the package 8 is covered, and the package semi-cylindrical groove 802 on the top of the package 8 is buckled with the upper end cover semi-cylindrical groove 901 at the bottom of the upper end cover 9 to form a complete cylindrical groove , to achieve the positioning and clamping of the measured wire, a square hole 801 is opened in the package 8, a dielectric substrate 7 is fixed at the bottom of the square hole 801, the antenna patch 3, the feeding device wavelength impedance converter 4 and the microstrip line 5 are deposited or attached to the rear end of the top surface of the dielectric substrate 7 from front to back, the front and rear ends of the bottom of the metal ground plate 2 are respectively connected to the dielectric substrate 7 through the support body 6, and the antenna patch 3, the feeding device wavelength impedance converter 4 and the microstrip line 5 are located between the metal ground plate 2 and the dielectric substrate 7, and a permanent magnet 1 is fixed to the upper surface of the metal ground plate 2.

[0058] Specifically, the lower surface of the dielectric substrate 7 of the inverted microstrip antenna is fixedly connected to the lower surface of the square hole 801, the antenna patch 3, the feeding device wavelength impedance converter 4 and the microstrip line 5 of the inverted microstrip antenna are deposited or attached on the dielectric substrate 7, the two ends of the metal ground plate 2 are fixed on two support bodies 6, and the other ends of the two support bodies 6 are connected to the dielectric substrate 7, and the upper surface of the metal ground plate 2 is fixed with a permanent magnet 1, so that an air cavity is formed between the lower surface of the metal ground plate 2 and the antenna patch 3.

[0059] The antenna patch 3 , the feeding device wavelength impedance converter 4 and the microstrip line 5 are integrated into one body and made of the same material, and the antenna patch 3 corresponds to the center position of the metal ground plate 2 .

[0060] An air cavity is formed between the lower surface of the metal ground plate 2 and the antenna patch 3 .

[0061] The shape of the antenna patch 3 is rectangular, circular, trapezoidal or regular polygonal.

[0062] The metal ground plate 2, the antenna patch 3, the feeding device wavelength impedance converter 4 and the microstrip line 5 are all made of good metal conductors, including copper, silver or gold.

[0063] The dielectric substrate 7 is made of insulating material.

[0064] The upper end cover 9 is positioned by means of the positioning posts 902 thereon and the positioning holes 803 on the package 8 .

[0065] A current detection method based on an inverted microstrip antenna comprises the following steps:

[0066] Step 1: fix the current detection device on the cable to be tested through the cylindrical groove; that is, the cable to be tested is placed and clamped in the cylindrical groove to achieve positioning and clamping of the wire to be tested;

[0067] Step 2, such as Figure 6 As shown, the magnetic field generated by the current in the tested cable causes the permanent magnet 1 to be stressed, and the metal ground plate 2 bends accordingly, causing the thickness of the air cavity between the lower surface of the metal ground plate 2 and the antenna patch 3 to change; when the thickness of the air cavity changes within a certain range, the resonant frequency of the inverted microstrip antenna will shift monotonically accordingly. The inherent relationship between the change of the air cavity thickness and the shift of the resonant frequency of the inverted microstrip antenna is studied, and a function model of the air cavity thickness and the resonant frequency of the inverted microstrip antenna is established. The model establishment process is as follows:

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074] ΔL=h(ξ1ξ3ξ5 / ξ4)

[0075]

[0076]

[0077]

[0078] ξ4=1+0.0377tan -1 [0.067(w / h) 1.456 ]×{6-5exp(0.036(1-∈ r ))}

[0079] ξ5=1-0.218exp(-7.5w / h)

[0080]

[0081] Where: f rrepresents the resonant frequency of the inverted microstrip antenna; c represents the speed of light; L represents the length of the patch antenna 3; w represents the width of the patch antenna 3; ΔL represents the length compensation value of the inverted microstrip antenna; h represents the thickness of the air cavity; h2 represents the total thickness of the inverted microstrip antenna (the distance between the upper surface of the metal ground plate 2 and the lower surface of the dielectric substrate 7); ∈ eff represents the effective dielectric constant of the inverted microstrip antenna; ∈ r1 Represents the relative dielectric constant of air (calculated by the above formula); ∈ r2 represents the effective dielectric constant of the dielectric substrate 7; q1 represents the spatial proportion of the air cavity in the entire radiation space obtained by conformal mapping; q2 represents the spatial proportion of the dielectric substrate 7 in the entire radiation space obtained by conformal mapping; w ef represents the effective width of the antenna patch 7; v ∈ The thickness of the dielectric substrate after conformal mapping; ξ1, ξ2, ξ3, ξ4 and ξ5 are dimensionless intermediate variables; ∈ r represents the relative dielectric constant of the dielectric substrate 7 in the inverted microstrip antenna (material-specific property, obtained by consulting the manual);

[0082] The function model of the air cavity thickness and the resonant frequency of the inverted microstrip antenna established above is recorded as:

[0083] f r =f(h)

[0084] Step 3: When the permanent magnet 1 is subjected to force, the metal ground plate 2 and the antenna patch 3 are no longer parallel. The deflections at various points along the length direction of the metal ground plate 2 are not completely the same. The center part of the metal ground plate 2 corresponds to the part directly above the antenna patch 3. The curvature of the center part of the metal ground plate 2 is small during the deformation process. Therefore, this part is approximated as a plane, and the deflection at the midpoint of the length direction of the metal ground plate 2 is brought into the function model f of the change in air cavity thickness and the shift in the resonant frequency of the inverted microstrip antenna r =f(h), that is, let h = v, and establish a functional model of the deflection at the midpoint of the length direction of the metal ground plate 2 and the resonant frequency offset of the inverted microstrip antenna:

[0085] f r =f(ν)

[0086] In the above formula, ν represents the deflection at the midpoint of the length direction of the metal ground plate 2; (the equation of f(ν) is the same as f(h) in step 2, only the independent variable is changed)

[0087] Step 4: Analyze the distribution of the induced magnetic field intensity and magnetic field gradient of the long straight wire in space according to the Biot-Savart law, use the infinitesimal method to study the force on the permanent magnet 1 in the magnetic field, and establish a function model of the measured current in the measured cable and the force on the permanent magnet 1: Among them Br is the residual magnetic flux of permanent magnet 1, V is the volume of permanent magnet 1, μ0 is the vacuum permeability, i i is the current of the i-th core inside the measured cable, x and z are the coordinates of any point in the coordinate system established with the straight line passing through the centroid of permanent magnet 1 and perpendicular to the upper surface of permanent magnet 1 as the z-axis and the straight line passing through the centroid of permanent magnet 1, perpendicular to the z-axis and orthogonal to the measured cable as the x-axis, x i 、z i is the coordinate of the i-th core inside the tested cable in the above coordinate system;

[0088] Then, the permanent magnet 1 and the metal grounding plate 2 are treated as a whole for force analysis, and a function model of the deflection at the midpoint of the length direction of the metal grounding plate 2 and the force of the permanent magnet 1 is established. The model establishment process is as follows:

[0089] The two-core cable under test has a live wire and a neutral wire inside, and their current directions are opposite, such as Figure 6 shown.

[0090] The magnetic field strength H0 around a single conductor is as follows: (referring to a single conductor in the cable on the side)

[0091]

[0092] The component H of the magnetic field strength around a single wire in the z-axis direction z0 for:

[0093]

[0094] The synthetic magnetic field strength H of the double-core cable in the z-axis direction z :

[0095]

[0096] The neutral line current i1 = -I0 inside the double-core cable, and the live line current i2 = I0.

[0097] Where μ0 is the magnetic permeability of vacuum, r is the radial distance from any point in space to a single conductor, i0 is the current of the measured cable, i i is the current of the i-th core inside the measured cable, x and z are the coordinates of any point in the coordinate system established with the straight line passing through the centroid of permanent magnet 1 and perpendicular to the upper surface of permanent magnet 1 as the z-axis and the straight line passing through the centroid of permanent magnet 1, perpendicular to the z-axis and orthogonal to the measured cable as the x-axis, x i 、z i is the coordinate of the i-th core inside the tested cable in the above coordinate system, i0 is the current in the tested cable;

[0098] The magnetic field gradient of a single wire in the z-axis direction is:

[0099]

[0100] The synthetic magnetic field gradient of the twin-core cable in the z-axis direction is:

[0101]

[0102] The magnetic field force F in the z-axis direction generated by the double-core cable on the permanent magnet 1 z for:

[0103]

[0104] By calculating F z From the optimal solution, it can be seen that for a two-core cable, when the z axis is the symmetric axis of the neutral line and the live line, the synthetic magnetic field force F on the permanent magnet 1 is z There is a maximum value, such as Figure 6 In order to improve the sensitivity, the present invention establishes an electromagnetic field model when the z-axis is the symmetric axis of the zero line and the live line. This position can be calibrated by making the measured cable and the device rotate relative to each other to reach the position where the output current is the largest.

[0105] At this time, the coordinates of the center of the cross section of the zero line in the coordinate system are x1 = -r0, z1 = a;

[0106] At this time, the coordinates of the cross-section center of the firing line in the coordinate system are x2=r0, z1=a;

[0107] Where r0 is the radius of each core in the measured cable, a is the vertical distance between the center of mass of the permanent magnet 1 and the contact surface between the package 8 and the upper end cover 9, B r is the residual magnetic flux of permanent magnet 1, V is the volume of permanent magnet 1;

[0108] The function of the deflection at the midpoint of the length direction of the metal ground plate 2 and the force on the permanent magnet 1 is as follows:

[0109]

[0110] Wherein ν is the deflection at the midpoint of the length direction of the metal grounding plate 2; E is the elastic modulus of the metal grounding plate 2; I is the moment of inertia of the cross section of the metal grounding plate 2 about the bending neutral axis; l is the length of the metal grounding plate 2;

[0111] Step 5: According to the function model of the deflection at the midpoint of the length direction of the metal ground plate 2 and the inverted microstrip antenna resonant frequency offset, the function model of the measured current in the cable and the force on the permanent magnet 1, and the function model of the deflection at the midpoint of the length direction of the metal ground plate 2 and the force on the permanent magnet 1, a function model of the measured current in the cable and the inverted microstrip antenna resonant frequency offset is established to calculate the measured current; that is, let ν = ki0, and establish a function model of the deflection at the midpoint of the length direction of the metal ground plate 2 and the inverted microstrip antenna resonant frequency offset to calculate the measured current, and the model is as follows:

[0112] f r =f(ki0)

[0113] in:

[0114]

[0115] In a DC two-core cable:

[0116] i1=-i2

[0117] |i1|=|i2|=|i0|

[0118] Then the deflection at the midpoint of the length direction of the metal ground plane 2 and the function model of the inverted microstrip antenna resonant frequency offset are r =f(ν)

[0119] f r =f(ki0)

[0120]

[0121] (The equation for f(ν) is the same as f(h) in step 2, only the independent variable is changed)

[0122] In the present invention, the relative position of the measured cable and the sensor is adjusted to meet the Figure 6 The detection principle diagram shown in the figure, then k is:

[0123]

[0124] Where i0 is the current in the cable under test.

[0125] The magnitude of the measured current in the cable is then obtained by inverting the shift in the resonant frequency of the microstrip antenna.

[0126] Example 2

[0127] In the current detection device based on an inverted microstrip antenna described in this embodiment, the dielectric substrate 7 of the detection unit is made of Rogers RT / duroid 6006 material with a size of 57.8mm×12mm×1.6mm (length×width×thickness), the antenna patch 3 is made of copper with a size of 9.7mm×6.4mm×0.05mm (length×width×thickness), the metal ground plate 2 is made of copper with a size of 57.8mm×12mm×0.2mm (length×width×thickness), and 1 / 4 wavelength feeding is adopted. The wavelength impedance converter 4 of the feeding device has a size of 4.85mm×1.20mm×0.05mm, the microstrip line 5 has a size of 19.2mm×2.98mm×0.05mm, the antenna patch 3 is photoetched on the dielectric substrate 7, and the metal ground plate 2, the support body 6 and the dielectric substrate 7 are bonded by strong glue. The entire sensor is connected to a vector network analyzer through an SMA interface and a coaxial cable. The sensor's resonant frequency is extracted from the backscattered signal by sending a microwave frequency modulation signal to the sensor and receiving the backscattered signal reflected from the sensor. Figure 7 The graph shows the return loss S11 curve of the inverted microstrip antenna resonant frequency shifting with the change of air cavity thickness. The resonant frequency of the inverted microstrip antenna shifts monotonically with the change of air cavity thickness. According to the function model of the measured current in the cable and the inverted microstrip antenna resonant frequency shift, the magnitude of the measured current in the cable is obtained through the shift of the inverted microstrip antenna resonant frequency.

Claims

1. A current detection device based on an inverted microstrip antenna, characterized in that The invention comprises a permanent magnet (1), an inverted microstrip antenna, a package (8) and an upper end cover (9), wherein the inverted microstrip antenna comprises a metal ground plate (2), an antenna patch (3), a feed device wavelength impedance converter (4), a microstrip line (5), two support bodies (6) and a dielectric substrate (7); the upper end cover (9) is fixedly connected to the top of the package (8), the package (8) is covered, and a package semi-cylindrical groove (802) at the top of the package (8) and an upper end cover semi-cylindrical groove (901) at the bottom of the upper end cover (9) are buckled to form a complete cylindrical groove; a square groove is opened in the package (8) A hole (801) is provided, a dielectric substrate (7) is fixed at the bottom of the square hole (801), an antenna patch (3), a feeding device wavelength impedance converter (4) and a microstrip line (5) are sequentially deposited or attached to the rear end of the top surface of the dielectric substrate (7) from front to back, the front and rear ends of the bottom of the metal ground plate (2) are respectively connected to the dielectric substrate (7) through a support body (6), and the antenna patch (3), the feeding device wavelength impedance converter (4) and the microstrip line (5) are located between the metal ground plate (2) and the dielectric substrate (7), and a permanent magnet (1) is fixed on the upper surface of the metal ground plate (2).

2. A current detection device based on an inverted microstrip antenna according to claim 1, characterized in that The antenna patch (3), the feeding device wavelength impedance converter (4) and the microstrip line (5) are an integral whole and made of the same material, and the antenna patch (3) corresponds to the center position of the metal ground plate (2).

3. A current detection device based on an inverted microstrip antenna according to claim 2, characterized in that An air cavity is formed between the lower surface of the metal ground plate (2) and the antenna patch (3).

4. A current detection device based on an inverted microstrip antenna according to claim 3, characterized in that The shape of the antenna patch (3) is rectangular, circular, trapezoidal or regular polygonal.

5. A current detection device based on an inverted microstrip antenna according to claim 4, characterized in that The metal ground plate (2), antenna patch (3), feeding device wavelength impedance converter (4) and microstrip line (5) are all made of good metal conductors, including copper, silver or gold.

6. A current detection device based on an inverted microstrip antenna according to claim 5, characterized in that The dielectric substrate (7) is made of insulating material.

7. A current detection device based on an inverted microstrip antenna according to claim 6, characterized in that The upper end cover (9) is positioned by means of the positioning posts (902) thereon and the positioning holes (803) on the package (8).

8. A current detection method based on an inverted microstrip antenna, characterized in that The following steps are involved: Step 1, fixing the current detection device on the cable to be tested through the cylindrical groove; Step 2: The magnetic field generated by the current in the measured cable causes the permanent magnet (1) to be stressed, and the metal ground plate (2) is bent accordingly, so that the thickness of the air cavity between the lower surface of the metal ground plate (2) and the antenna patch (3) changes; when the thickness of the air cavity changes within a certain range, the resonant frequency of the inverted microstrip antenna will shift monotonically accordingly, and a function model of the air cavity thickness and the resonant frequency of the inverted microstrip antenna is established, and the model is as follows: ΔL=h(ξ1ξ3ξ5 / ξ4) ξ4=1+0.0377tan -1 [0.067(w / h) 1.456 ]×{6-5exp(0.036(1-∈ r ))} ξ5=1-0.218exp(-7.5w / h) Where: f r represents the resonant frequency of the inverted microstrip antenna; c represents the speed of light; L represents the length of the patch antenna (3); w represents the width of the patch antenna (3); ΔL represents the length compensation value of the inverted microstrip antenna; h represents the thickness of the air cavity; h2 represents the total thickness of the inverted microstrip antenna; ∈ eff represents the effective dielectric constant of the inverted microstrip antenna; ∈ r1 Represents the relative dielectric constant of air; ∈ r2 represents the effective dielectric constant of the dielectric substrate (7); q1 represents the spatial proportion of the air cavity in the entire radiation space obtained by conformal mapping; q2 represents the spatial proportion of the dielectric substrate (7) in the entire radiation space obtained by conformal mapping; W ef represents the effective width of the antenna patch (7); v ∈ The thickness of the dielectric substrate after conformal mapping; ξ1, ξ2, ξ3, ξ4 and ξ5 are dimensionless intermediate variables; ∈ r represents the relative dielectric constant of the dielectric substrate (7) in the inverted microstrip antenna; The function model of the air cavity thickness and the resonant frequency of the inverted microstrip antenna established above is recorded as: f r =f(h) Step 3: When the permanent magnet (1) is subjected to force, the metal ground plate (2) and the antenna patch (3) are no longer parallel. The deflection at each point along the length direction of the metal ground plate (2) is not exactly the same. The deflection at the midpoint of the length direction of the metal ground plate (2) is incorporated into the function model f of the change in air cavity thickness and the shift in the resonant frequency of the inverted microstrip antenna. r =f(h), that is, let h = ν, and establish the function model of the deflection at the midpoint of the length direction of the metal ground plate (2) and the resonant frequency offset of the inverted microstrip antenna: F r =f(v) In the above formula, ν represents the deflection at the midpoint of the length direction of the metal ground plate (2); Step 4: Analyze the distribution of the induced magnetic field intensity and magnetic field gradient of the long straight wire in space according to the Biot-Savart law, use the infinitesimal method to study the force on the permanent magnet (1) in the magnetic field, and establish a function model of the measured current in the measured cable and the force on the permanent magnet (1): Among them B r is the residual magnetic flux of the permanent magnet (1), V is the volume of the permanent magnet (1), μ0 is the vacuum permeability, i i is the current of the i-th core inside the measured cable, x and z are the coordinates of any point in a coordinate system established with a straight line passing through the centroid of the permanent magnet (1) and perpendicular to the upper surface of the permanent magnet (1) as the z-axis and a straight line passing through the centroid of the permanent magnet (1), perpendicular to the z-axis and orthogonal to the measured cable as the x-axis, x i 、z i is the coordinate of the i-th core inside the tested cable in the above coordinate system; Then, the permanent magnet (1) and the metal grounding plate (2) are treated as a whole for force analysis, and a function model of the deflection at the midpoint of the length direction of the metal grounding plate (2) and the force of the permanent magnet (1) is established as follows: Wherein ν is the deflection at the midpoint of the length direction of the metal grounding plate (2); E is the elastic modulus of the metal grounding plate (2); I is the moment of inertia of the cross section of the metal grounding plate (2) about the bending neutral axis; l is the length of the metal grounding plate (2); Step 5, let v = ki0, establish a function model of the deflection at the midpoint of the length direction of the metal ground plate (2) and the resonant frequency offset of the inverted microstrip antenna to calculate the magnitude of the measured current, the model is: r =f(ki0) in: In a DC two-core cable: i1 = -i2; |i1| = |i2| = |i0|;

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