Microwave resonator, microwave sensor and solution detection method

Abstract

The invention belongs to the technical field of microwave liquid detection, and relates to a microwave resonator, a microwave sensor and a solution detection method. The coupling double-antenna structure is arranged on the dielectric substrate, comprises a first antenna and a second antenna which are the same in polarization direction, and is used for changing a coupling coefficient between the first antenna and the second antenna when the dielectric constant of the microwave transmission medium is changed, so that the transmission characteristic of a microwave input signal is changed; therefore, the coupling coefficient phase zero point characteristic frequency of the microwave output signal is changed; and the metal plate is arranged below the dielectric substrate, and forms a resonant cavity structure with the dielectric substrate and the coupled double-antenna structure. The microwave resonator provided by the scheme can capture changes caused by tiny differences of dielectric constants, and has high sensitivity and resolution, so that solutions can be accurately classified.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave liquid detection, and in particular to a microwave resonator, a microwave sensor and a solution detection method. Background Art

[0002] A microwave resonator is a device that can generate a resonance phenomenon at a specific microwave frequency. It mainly includes a dielectric substrate, an antenna disposed on the dielectric substrate, and a metal plate placed under the dielectric substrate. A microwave resonance cavity structure is formed by the metal plate, the dielectric substrate and the antenna, so as to generate a resonance phenomenon when transmitting a microwave signal. Based on the microwave resonator, a microwave signal source, a vector network analyzer and a liquid container, a microwave sensor as shown in Figure 1 can be obtained. In the figure, 10 represents the antenna, 20 represents the metal plate, and 30 represents the liquid container. The solution can be detected by using this microwave sensor.

[0003] When classifying a solution to be measured by using a microwave sensor, first connect the microwave resonator to a microwave signal source and a vector network analyzer, and then place the solution to be measured in the action area of the microwave resonator, such as above or around the antenna. Turn on the microwave signal source and obtain the phase curve of the reflection coefficient output by the vector network analyzer (that is, the curve of the phase of the reflection coefficient S11 changing with frequency). Since the dielectric constants of different solutions are different, when different solutions are in the action area of the microwave resonator, they will cause different effects on its magnetic field distribution and propagation characteristics, and then change the resonance frequency of the microwave resonator. This change in the resonance frequency corresponds to the changes in the resonance peak frequency position, amplitude and curve shape on the S11 curve. Therefore, by analyzing the S11 curve of the solution to be measured, the dielectric constant of the solution to be measured can be preliminarily judged, so as to judge the type of the solution to be measured. However, in the actual detection process, the dielectric constants of similar types of solutions are often relatively close, and the sensitivity of the microwave transmission characteristics of the existing microwave resonator is relatively low, making it difficult to capture the changes brought about by the subtle differences in the dielectric constants. The transmission characteristics exhibited by solutions with similar dielectric constants are similar, resulting in the characteristic points of the output S11 curve being very close, that is, the amplitude change, curve shape and resonance peak frequency position of the S11 curve are all very close, so that similar solutions cannot be accurately classified.

[0004] In summary, the existing microwave resonator has insufficient sensitivity and is difficult to capture the changes brought about by the subtle differences in the dielectric constants, resulting in a low resolution when classifying solutions based on the resonance phenomenon of the microwave resonator. It can only classify solutions with large dielectric constant differences and cannot accurately classify similar solutions. Summary of the Invention

[0005] To this end, the technical problem to be solved by the present invention is to overcome the problem that the microwave resonator in the prior art has insufficient sensitivity and is difficult to capture the changes brought about by the subtle differences in the dielectric constant, resulting in low resolution when classifying solutions based on the resonance phenomenon of the microwave resonator, and can only classify solutions with large dielectric constant differences, and cannot accurately classify similar solutions.

[0006] To solve the above technical problems, the present invention provides a microwave resonator, comprising: A dielectric substrate; A coupled dual-antenna structure disposed on the dielectric substrate, including a first antenna and a second antenna with the same polarization direction, for when the dielectric constant of the microwave transmission medium changes, the coupling coefficient between the first antenna and the second antenna changes, causing the transmission characteristics of the microwave input signal to change, and thus causing the characteristic frequency of the phase zero point of the coupling coefficient of the microwave output signal to change; A metal plate disposed below the dielectric substrate, and together with the dielectric substrate and the coupled dual-antenna structure, forms a resonant cavity structure.

[0007] Preferably, the extending directions of the first antenna and the second antenna on the dielectric substrate are the same, and the axes of the first antenna and the second antenna are parallel; The first end of the first antenna and the first end of the second antenna are located on a first straight line, and the second end of the second antenna and the second end of the second antenna are located on a second straight line; Wherein, the first straight line and the second straight line are parallel to each other and are both perpendicular to the axes of the first antenna and the second antenna.

[0008] Preferably, the perpendicular distance between the first antenna and the second antenna is 5 mm to 12.5 mm.

[0009] Preferably, the lengths of both the first antenna and the second antenna are 5 mm to 13 mm.

[0010] Preferably, the distance between the metal plate and the dielectric substrate is 1 / 4 to 1 / 2 of the electromagnetic wave wavelength.

[0011] Preferably, the coupling coefficient between the first antenna and the second antenna is expressed as: , , , Wherein, represents the coupling coefficient; represents the imaginary unit; represents the space wave impedance; represents the microwave signal propagation constant related to the dielectric constant, , represents the dielectric constant of the microwave transmission medium, represents the permittivity of free space, represents the relationship function between the microwave signal propagation constant and the dielectric constant; represents half of the length of the first antenna; represents half of the length of the second antenna; represents any point on the first antenna; represents any point on the second antenna; represents the partial derivative with respect to the z coordinate; represents the coupled Green's function; represents the distance between different positions of the first antenna and the second antenna; represents the perpendicular distance between the first antenna and the second antenna.

[0012] The present invention also provides a microwave sensor, comprising: the above-mentioned microwave resonator; a liquid container, arranged above the coupled dual-antenna structure in the microwave resonator, for containing the solution to be measured; a microwave signal source, connected to the input end of the microwave resonator, for generating a microwave input signal and transmitting it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal; a vector network analyzer, connected to the output end of the microwave resonator, for receiving the microwave output signal, outputting a coupling coefficient phase curve, and obtaining the coupling coefficient phase zero characteristic frequency based on the coupling coefficient phase curve, so as to classify the solution to be measured based on the coupling coefficient phase zero characteristic frequency.

[0013] Preferably, the distance between the liquid container and the coupled dual-antenna structure is 0 to 1 electromagnetic wave wavelength.

[0014] The present invention also provides a solution detection method, which is applied to the above-mentioned microwave sensor, comprising: placing the solution to be measured in the liquid container; using the microwave signal source to generate a microwave input signal and transmit it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal; using the vector network analyzer to receive the microwave output signal, output a coupling coefficient phase curve, and obtain the coupling coefficient phase zero characteristic frequency based on the coupling coefficient phase curve; obtaining the dielectric constant of the solution to be measured based on the coupling coefficient phase zero characteristic frequency, so as to determine the type of the solution.

[0015] Preferably, obtaining the dielectric constant of the solution to be measured based on the coupling coefficient phase zero characteristic frequency includes: Obtain standard solutions with different dielectric constants, and use a microwave sensor to obtain the characteristic frequency of the phase zero point of the coupling coefficient of each standard solution; Fit the dielectric constants and the characteristic frequencies of the phase zero points of the coupling coefficients of multiple standard solutions to obtain a relationship model between the dielectric constant and the characteristic frequency of the phase zero point of the coupling coefficient; Input the characteristic frequency of the phase zero point of the coupling coefficient of the solution to be measured into the relationship model between the dielectric constant and the characteristic frequency of the phase zero point of the coupling coefficient, and output the dielectric constant of the solution to be measured.

[0016] The above technical solutions provided by this application have the following advantages compared with the prior art: 1. In this application, by setting the first antenna and the second antenna with the same polarization direction on the dielectric substrate, a coupled dual-antenna structure is designed. In the coupled dual-antenna structure, when one antenna emits a microwave signal, the electromagnetic field generated by it will propagate in the surrounding space and be coupled into the other antenna. At this time, the coupled dual-antenna structure can be approximated as a transmission line model with mutual inductance. Based on the relationship between the transfer function of the transmission line model and the coupling coefficient, it can be known that when specific frequency conditions are met, the phase of the coupling coefficient will appear at zero, so that the microwave output signal of the microwave resonator contains the characteristic point of the characteristic frequency of the phase zero point of the coupling coefficient; further, when the microwave transmission medium changes, its dielectric constant changes, and this change will directly affect the coupling electromagnetic field strength and phase relationship between the first antenna and the second antenna, and then cause the coupling coefficient between the first antenna and the second antenna to change. According to the relationship between the transfer function of the transmission line model and the coupling coefficient, it can be known that when the coupling coefficient changes, the characteristic frequency of the phase zero point of the coupling coefficient will shift significantly. Through a large number of experiments in this application, it is found that this shift is more obvious than the amplitude change, the resonance peak frequency position change, and the curve shape change of the reflection coefficient phase curve output by the existing single-antenna structure microwave resonator. Even if there are only slight differences in the dielectric constants, the finally obtained characteristic frequencies of the phase zero points of the coupling coefficients also have obvious differences. Therefore, the microwave resonator provided by this application can capture the changes brought about by slight differences in the dielectric constant, has high sensitivity and resolution, and thus can accurately classify solutions; 2. By changing the placement positions and size parameters of the first antenna and the second antenna, the coupling degree and distribution of the electromagnetic field can be changed, and at the same time, the resonance characteristics of the antenna can be changed, amplifying the influence of the dielectric constant change on the coupling coefficient, so that the characteristic frequency of the phase zero point of the coupling coefficient is more obvious with respect to the change in the dielectric constant, and further improving the capture ability of the microwave resonator for slight differences in the dielectric constant, and improving the sensitivity and resolution; 3. The microwave sensor designed in this application no longer relies on the amplitude, shape, and resonant peak frequency position changes of the reflection coefficient phase curve. Instead, it introduces a new characteristic point, the characteristic frequency of the coupling coefficient phase zero point. Compared with the offset of the characteristic point of the single-antenna structure due to the change in the dielectric constant, the offset of this characteristic point of the dual-antenna structure will be greatly improved, thus having the non-contact and high-sensitivity recognition performance for solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the accompanying drawings, where: Figure 1 Schematic diagram of the microwave sensor structure in the prior art provided by this application; Figure 2 Schematic diagram of the microwave sensor structure provided by this application; Figure 3 Schematic diagram of the coupling principle of the coupled dual antennas provided by this application; Figure 4 Flowchart of the solution detection method provided by this application; Figure 5 Schematic diagram of the change curve of the sensitivity of the microwave sensor provided in the embodiment of this application with the size parameters of the coupled dual-antenna structure; where Figure 5 (a) in is the schematic diagram of the change curve of the sensitivity with the distance between the antennas in the coupled dual-antenna structure, Figure 5 and (b) in is the schematic diagram of the change curve of the sensitivity with the antenna length in the coupled dual-antenna structure; Figure 6 Schematic diagram of the coupling coefficient phase curves of different solutions output by the microwave sensor provided in Embodiment 3 of this application; Figure 7 Schematic diagram of the reflection coefficient phase curves of different solutions output by the microwave sensor provided in the comparative example of this application; Figure 8 Schematic diagram of the change curves of the dielectric constant and resonant points of the microwave sensors provided in Embodiment 3 and the comparative example of this application; Explanation of the reference numerals in the drawings of the specification: 10, antenna; 20, metal plate; 30, liquid container; 1, dielectric substrate; 11, coupled dual-antenna structure; 111, first antenna; 112, second antenna; 2, metal plate; 3, liquid container; 4, microwave signal source; 5, vector network analyzer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The following further illustrates the present invention in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited do not limit the present invention.

[0019] Regarding the problem that the microwave resonator in the prior art has insufficient sensitivity to the change of the dielectric constant of the microwave transmission medium, this application considers whether the coupling effect between multiple antennas can increase the characteristic points of the microwave output signal, and further determines whether the new characteristic points generated by the coupling effect are more sensitive to the change of the dielectric constant than the characteristic points of a single antenna, so as to design a microwave resonator based on the coupling effect to improve the capture ability of the microwave resonator for subtle differences in the dielectric constant, and then improve the solution detection accuracy.

[0020] First, this application constructs a microwave resonator based on a coupled dual-antenna structure and a microwave resonator based on a coupled multi-antenna structure. The microwave resonator of the coupled multi-antenna structure includes at least three antennas. By changing the microwave transmission medium placed on the above microwave resonator, the amplitude curve and phase curve of the coupling coefficient of the microwave output signal are obtained.

[0021] By comparing the amplitude curve and phase curve of the coupling coefficient of different microwave resonators, this application finds that when the number of antennas is greater than or equal to 3, even if there is a coupling effect between the antennas, it is difficult to find characteristic points that shift significantly with the change of the dielectric constant on either the amplitude curve or the phase curve of the coupling coefficient; when the number of antennas is 2, no characteristic points that shift significantly with the change of the dielectric constant are found on the amplitude curve of the coupling coefficient, but on the phase curve of the coupling coefficient, the microwave signal frequency value corresponding to the zero coupling coefficient phase will shift significantly with the change of the dielectric constant, and under the same change amount of the dielectric constant, the shift amount of this characteristic point is significantly greater than the shift amount of the characteristic point on the reflection coefficient phase curve output by the existing single-antenna structure microwave resonator.

[0022] Based on the above research findings, this application provides a microwave resonator based on a coupled dual-antenna structure, as Figure 2 shown. The microwave resonator includes a dielectric substrate 1, a coupled dual-antenna structure 11, and a metal plate 2.

[0023] The coupled dual-antenna structure 11 is arranged on the dielectric substrate 1 and includes a first antenna 111 and a second antenna 112 with the same polarization direction, which is used to change the coupling coefficient between the first antenna and the second antenna when the dielectric constant of the microwave transmission medium changes, so that the transmission characteristics of the microwave input signal change, and thus the characteristic frequency of the zero point of the coupling coefficient of the microwave output signal changes.

[0024] Optionally, the coupled dual-antenna structure 11 can be arranged on the surface of the dielectric substrate 1 or embedded in the dielectric substrate 1.

[0025] The metal plate 2 is arranged below the dielectric substrate 1 and forms a resonant cavity structure together with the dielectric substrate 1 and the coupled dual-antenna structure 11.

[0026] Further, in some embodiments of the present application, the extending directions of the first antenna 111 and the second antenna 112 on the dielectric substrate 1 are the same, and the axes of the first antenna 111 and the second antenna 112 are parallel; The first end of the first antenna 111 and the first end of the second antenna 112 are located on a first straight line, and the second end of the first antenna 111 and the second end of the second antenna 112 are located on a second straight line; Wherein, the first straight line and the second straight line are parallel to each other and are both perpendicular to the axes of the first antenna 111 and the second antenna 112.

[0027] By arranging the first antenna 111 and the second antenna 112 in parallel on the dielectric substrate 1, the magnetic field line cross-linking degree between the first antenna 111 and the second antenna 112 is higher, and at the same time, the distribution of the electric field between the two antennas is more uniform and the interaction area is increased, thereby enhancing the electrical coupling effect between the antennas. In addition, when the microwave transmission medium changes, the intensity, direction, and distribution range of the electric field and magnetic field in the dielectric substrate will change. Due to the strong electric field and magnetic field interaction between the two antennas placed in parallel, the changes in the distribution of the electric field and magnetic field will directly affect the coupled electric field and coupled magnetic field between the two antennas, so that the coupling coefficient is more sensitive to the change of the dielectric constant, that is, the characteristic frequency of the coupling coefficient phase zero point changes more significantly with the change of the dielectric constant.

[0028] Further, the perpendicular distance between the first antenna 111 and the second antenna 112 is 5 mm to 12.5 mm. For example, the perpendicular distance between the first antenna 111 and the second antenna 112 can be 5 mm, 7.5 mm, 10 mm, 12.5 mm.

[0029] Further, the lengths of both the first antenna 111 and the second antenna 112 are 5 mm to 13 mm. For example, the lengths of the first antenna 111 and the second antenna 112 can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm.

[0030] Further, the distance between the metal plate 2 and the dielectric substrate 1 is 1 / 4 to 1 / 2 of the electromagnetic wave wavelength. For example, the distance between the metal plate 2 and the dielectric substrate 1 can be 1 / 4 of the electromagnetic wave wavelength, 1 / 3 of the electromagnetic wave wavelength, 1 / 2 of the electromagnetic wave wavelength.

[0031] Specifically, by changing the size parameters of the coupled dual-antenna structure 11 and the distance parameters between the metal plate 2 and the dielectric substrate 1, the transmission characteristics of the microwave resonator can also be made more sensitive to the change of the dielectric constant, and its sensitivity and resolution can be improved.

[0032] As shown Figure 3 in the schematic diagram of the coupling principle of the coupled dual-antenna structure 11 provided by this application, the first antenna 111 and the second antenna 112 are z-direction parallel dipoles, and the center position of the first antenna 111 is , and the center position of the second antenna 112 is , is the half-length of the first antenna 111, is the half-length of the second antenna 112, is the radius of the first antenna 111, is the radius of the second antenna 112, , are respectively the distance from point to the observation point and the distance from point to the observation point , are the dipole currents caused by the voltage generator and the interaction, is the vertical distance between the first antenna 111 and the second antenna 112.

[0033] The coupling coefficient between the first antenna 111 and the second antenna 112 can be expressed as: , , , wherein, represents the coupling coefficient; represents the imaginary unit; represents the space wave impedance; represents the microwave signal propagation constant related to the dielectric constant, , represents the dielectric constant of the microwave transmission medium, represents the vacuum dielectric constant, represents the relationship function between the microwave signal propagation constant and the dielectric constant; represents half of the length of the first antenna; represents half of the length of the second antenna; represents any point on the first antenna; represents any point on the second antenna; represents the partial derivative with respect to the z coordinate; represents the coupling Green's function; represents the distance between different positions of the first antenna and the second antenna; represents the perpendicular distance between the first antenna and the second antenna.

[0034] When the microwave transmission medium changes, its dielectric constant changes, and the propagation constant of the microwave signal also changes accordingly, thereby affecting the amplitude and phase of the coupling coefficient. The characteristic frequency of the zero point of the coupling coefficient phase satisfies: , wherein, represents the phase; represents the characteristic frequency corresponding to the zero point of the coupling coefficient phase.

[0035] The sensitivity of the microwave resonator is expressed as: , It can be seen from the above coupling coefficient expression and sensitivity expression that when the size parameters of the coupled dual-antenna structure 11 change, the sensitivity of the microwave resonator also changes.

[0036] In this application, a first antenna and a second antenna with the same polarization direction are arranged on a dielectric substrate, so as to design a coupled dual-antenna structure. In the coupled dual-antenna structure, when one antenna emits a microwave signal, the electromagnetic field generated by it will propagate in the surrounding space and be coupled into the other antenna. At this time, the coupled dual-antenna structure can be approximated as a transmission line model with mutual inductance. Based on the relationship between the transfer function of the transmission line model and the coupling coefficient, it can be known that when specific frequency conditions are met, the phase of the coupling coefficient will have a zero point, so that the microwave output signal of the microwave resonator contains this characteristic point of the characteristic frequency of the zero point of the coupling coefficient phase; further, when the microwave transmission medium changes, its dielectric constant changes, and this change will directly affect the intensity and phase relationship of the coupled electromagnetic field between the first antenna and the second antenna, and further cause the coupling coefficient between the first antenna and the second antenna to change. According to the relationship between the transfer function of the transmission line model and the coupling coefficient, it can be known that when the coupling coefficient changes, the characteristic frequency of the zero point of the coupling coefficient phase will shift significantly. Through a large number of experiments in this application, it is found that this shift is more obvious than the amplitude change, resonance peak frequency position change, and curve shape change of the reflection coefficient phase curve output by the existing single-antenna structure microwave resonator. Even if there is only a slight difference in the dielectric constant, the finally obtained characteristic frequency of the zero point of the coupling coefficient phase also has an obvious difference. Therefore, the microwave resonator provided by this application can capture the changes brought about by the slight difference in the dielectric constant, has high sensitivity and resolution, and can thus accurately classify solutions.

[0037] Furthermore, by changing the placement positions and size parameters of the first antenna and the second antenna, the coupling degree and distribution of the electromagnetic field can be changed, and at the same time, the resonance characteristics of the antenna can be changed, amplifying the influence of the change in the dielectric constant on the coupling coefficient, so that the characteristic frequency of the phase zero point of the coupling coefficient becomes more obvious with respect to the change in the dielectric constant, thereby improving the ability of the microwave resonator to capture subtle differences in the dielectric constant and enhancing the sensitivity and resolution.

[0038] Based on the microwave resonator provided in the above embodiments, an embodiment of the present application also provides a microwave sensor, as Figure 2 shown. The microwave sensor includes the above microwave resonator, a liquid container 3, a microwave signal source 4, and a vector network analyzer 5.

[0039] The liquid container 3 is arranged above the coupled dual-antenna structure 11 in the microwave resonator for containing the solution to be measured. Specifically, the liquid container 3 is made of PET material.

[0040] The microwave signal source 4 is connected to the input end of the microwave resonator for generating a microwave input signal and transmitting it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal.

[0041] The vector network analyzer 5 is connected to the output end of the microwave resonator for receiving the microwave output signal, outputting a coupling coefficient phase curve, and obtaining the characteristic frequency of the phase zero point of the coupling coefficient based on the coupling coefficient phase curve, so as to classify the solution to be measured based on the characteristic frequency of the phase zero point of the coupling coefficient.

[0042] Furthermore, the distance between the liquid container 3 and the coupled dual-antenna structure 11 is 0 to 1 electromagnetic wave wavelength. For example, the distance between the liquid container 3 and the coupled dual-antenna structure 11 can be 0.2 electromagnetic wave wavelengths, 0.4 electromagnetic wave wavelengths, 0.6 electromagnetic wave wavelengths, 0.8 electromagnetic wave wavelengths, or 1 electromagnetic wave wavelength.

[0043] Based on the microwave sensor provided in the above embodiments, an embodiment of the present application also provides a solution detection method, as Figure 4 shown. The method specifically includes: S10: Place the solution to be measured in the liquid container.

[0044] S20: Use the microwave signal source to generate a microwave input signal and transmit it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal.

[0045] S30: Use the vector network analyzer to receive the microwave output signal, output a coupling coefficient phase curve, and obtain the characteristic frequency of the phase zero point of the coupling coefficient based on the coupling coefficient phase curve.

[0046] S40: Obtain the dielectric constant of the solution to be measured based on the characteristic frequency of the phase zero point of the coupling coefficient, so as to determine the type of the solution.

[0047] Further, in some embodiments of the present application, obtaining the dielectric constant of the solution to be measured based on the characteristic frequency of the phase zero point of the coupling coefficient includes: S400: Obtain a variety of standard solutions with different dielectric constants, and use a microwave sensor to obtain the characteristic frequency of the phase zero point of the coupling coefficient of each standard solution.

[0048] S401: Fit the dielectric constants and the characteristic frequencies of the phase zero points of the coupling coefficients of the multiple standard solutions to obtain a relationship model between the dielectric constant and the characteristic frequency of the phase zero point of the coupling coefficient.

[0049] S402: Input the characteristic frequency of the phase zero point of the coupling coefficient of the solution to be measured into the relationship model between the dielectric constant and the characteristic frequency of the phase zero point of the coupling coefficient, and output the dielectric constant of the solution to be measured.

[0050] Optionally, the dielectric constants of the multiple standard solutions and the characteristic frequencies of the phase zero points of the coupling coefficients of each standard solution can be fitted by using the non - linear least - squares method. Specifically, considering that the relationship between the characteristic frequency of the phase zero point of the coupling coefficient and the dielectric constant is non - linear, in a specific example of the present application, a polynomial equation is used to fit the relationship between the two, and a cubic polynomial equation of the dielectric constant and the characteristic frequency of the phase zero point of the coupling coefficient is obtained: , where represents the fitting coefficient of the cubic term, represents the fitting coefficient of the quadratic term, represents the fitting coefficient of the linear term, represents the constant term.

[0051] The microwave sensor designed in the present application no longer depends on the amplitude, shape, and resonant peak frequency position changes of the reflection coefficient phase curve, but introduces a new characteristic point, that is, the characteristic frequency of the phase zero point of the coupling coefficient. Compared with the offset of the characteristic point of the single - antenna structure due to the change of the dielectric constant, the offset of this characteristic point of the dual - antenna structure will be greatly improved, so as to have the non - contact and high - sensitivity identification performance for the solution. Therefore, when detecting the solution based on this microwave sensor, it also has higher resolution and detection accuracy.

[0052] The technical solution of the present application will be described in more detail below in combination with multiple embodiments and comparative examples. However, it should be understood that the following embodiments and comparative examples are only for explaining and illustrating the technical solution, and do not limit the scope of the present application.

[0053] Embodiment 1 of the present application provides a microwave sensor, which specifically includes a microwave resonator, a liquid container, a microwave signal source, and a vector network analyzer.

[0054] The microwave resonator includes a dielectric substrate, a coupled dual-antenna structure, and a metal plate.

[0055] The coupled dual-antenna structure is disposed on the dielectric substrate and includes a first antenna and a second antenna with the same polarization direction. When the dielectric constant of the microwave transmission medium changes, the coupling coefficient between the first antenna and the second antenna changes, causing the transmission characteristics of the microwave input signal to change, and thus causing the characteristic frequency of the phase zero point of the coupling coefficient of the microwave output signal to change.

[0056] The first antenna and the second antenna are placed in parallel on the dielectric substrate, and the perpendicular distance between them is 5 mm. The lengths of both the first antenna and the second antenna are 5 mm.

[0057] The metal plate is disposed at a distance of 1 / 4 of the electromagnetic wave wavelength below the dielectric substrate, and together with the dielectric substrate and the coupled dual-antenna structure, forms a resonant cavity structure.

[0058] The liquid container is disposed at a distance of 0.2 of the electromagnetic wave wavelength above the coupled dual-antenna structure in the microwave resonator for containing the solution to be measured.

[0059] The microwave signal source is connected to the input end of the microwave resonator for generating a microwave input signal and transmitting it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal.

[0060] The vector network analyzer is connected to the output end of the microwave resonator for receiving the microwave output signal, outputting the coupling coefficient phase curve, and obtaining the characteristic frequency of the phase zero point of the coupling coefficient based on the coupling coefficient phase curve, thereby classifying the solution to be measured based on the characteristic frequency of the phase zero point of the coupling coefficient.

[0061] Embodiment 2 of the present application provides a microwave sensor, specifically including a microwave resonator, a liquid container, a microwave signal source, and a vector network analyzer.

[0062] The microwave resonator includes a dielectric substrate, a coupled dual-antenna structure, and a metal plate.

[0063] The coupled dual-antenna structure is disposed on the dielectric substrate and includes a first antenna and a second antenna with the same polarization direction. When the dielectric constant of the microwave transmission medium changes, the coupling coefficient between the first antenna and the second antenna changes, causing the transmission characteristics of the microwave input signal to change, and thus causing the characteristic frequency of the phase zero point of the coupling coefficient of the microwave output signal to change.

[0064] The first antenna and the second antenna are placed in parallel on the dielectric substrate, and the perpendicular distance between them is 9 mm. The lengths of both the first antenna and the second antenna are 10.3 mm.

[0065] The metal plate is arranged at a position 1 / 3 of the electromagnetic wave wavelength below the dielectric substrate, and together with the dielectric substrate and the coupled dual-antenna structure, it forms a resonant cavity structure.

[0066] The liquid container is arranged at a position 0.6 of the electromagnetic wave wavelength above the coupled dual-antenna structure in the microwave resonator, and is used to hold the solution to be measured.

[0067] The microwave signal source is connected to the input end of the microwave resonator, and is used to generate a microwave input signal and transmit it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal.

[0068] The vector network analyzer is connected to the output end of the microwave resonator, and is used to receive the microwave output signal, output the coupling coefficient phase curve, and obtain the coupling coefficient phase zero characteristic frequency based on the coupling coefficient phase curve, so as to classify the solution to be measured based on the coupling coefficient phase zero characteristic frequency.

[0069] Embodiment 3 of the present application provides a microwave sensor, which specifically includes a microwave resonator, a liquid container, a microwave signal source and a vector network analyzer.

[0070] The microwave resonator includes a dielectric substrate, a coupled dual-antenna structure and a metal plate.

[0071] The coupled dual-antenna structure is arranged on the dielectric substrate, and includes a first antenna and a second antenna with the same polarization direction. When the dielectric constant of the microwave transmission medium changes, the coupling coefficient between the first antenna and the second antenna changes, so that the transmission characteristics of the microwave input signal change, and thus the coupling coefficient phase zero characteristic frequency of the microwave output signal changes.

[0072] The first antenna and the second antenna are placed in parallel on the dielectric substrate, and the perpendicular distance between them is 12.5 mm. The lengths of the first antenna and the second antenna are both 13 mm.

[0073] The metal plate is arranged at a position 1 / 2 of the electromagnetic wave wavelength below the dielectric substrate, and together with the dielectric substrate and the coupled dual-antenna structure, it forms a resonant cavity structure.

[0074] The liquid container is arranged at a position 1 of the electromagnetic wave wavelength above the coupled dual-antenna structure in the microwave resonator, and is used to hold the solution to be measured.

[0075] The microwave signal source is connected to the input end of the microwave resonator, and is used to generate a microwave input signal and transmit it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal.

[0076] A vector network analyzer is connected to the output end of the microwave resonator, used to receive the microwave output signal, output the coupling coefficient phase curve, and obtain the characteristic frequency of the coupling coefficient phase zero point based on the coupling coefficient phase curve, so as to classify the solution to be measured based on the characteristic frequency of the coupling coefficient phase zero point.

[0077] The comparative example of this application provides Figure 1 The microwave sensor shown, specifically including a microwave resonator, a liquid container, a microwave signal source, and a vector network analyzer.

[0078] The microwave resonator includes a dielectric substrate, a single antenna structure, and a metal plate.

[0079] The single antenna structure is arranged on the dielectric substrate and includes an antenna with a length of 13 mm, which is used to transmit the microwave input signal with different reflection coefficients under the action of microwave transmission media with different dielectric constants, so that the microwave resonator outputs different microwave output signals.

[0080] The metal plate is arranged at a position of 1 / 2 electromagnetic wave wavelength below the dielectric substrate, and forms a resonant cavity structure with the dielectric substrate and the single antenna structure.

[0081] The liquid container is arranged at a position of 1 electromagnetic wave wavelength above the single antenna structure in the microwave resonator, and is used to hold the solution to be measured.

[0082] The microwave signal source is connected to the input end of the microwave resonator, used to generate a microwave input signal and transmit it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured and obtains a microwave output signal.

[0083] The vector network analyzer is connected to the output end of the microwave resonator, used to receive the microwave output signal, output the reflection coefficient phase curve, and classify the solution to be measured based on the reflection coefficient phase curve.

[0084] As Figure 5 Shown is a schematic diagram of the change curve of the sensitivity of the microwave sensor provided by the embodiment of this application with respect to the size parameters of the coupled dual-antenna structure; among them, Figure 5 in (a) is a schematic diagram of the change curve of the sensitivity with respect to the distance between the antennas in the coupled dual-antenna structure, Figure 5 in (b) is a schematic diagram of the change curve of the sensitivity with respect to the antenna length in the coupled dual-antenna structure.

[0085] From Figure 5It can be seen that the sensitivity of the microwave sensor first increases and then decreases with the change of the distance between the two antennas in the coupled dual-antenna structure. Similarly, it also first increases and then decreases with the change of the antenna length. From the data in the figure, it can be seen that the microwave sensor provided in Embodiment 2 has the highest sensitivity, and the sensitivity of the microwave sensor provided in Embodiment 3 is higher than that of the microwave sensor provided in Embodiment 1.

[0086] As Figure 6 shown in the schematic diagram of the coupling coefficient phase curves of different solutions output by the microwave sensor provided in Embodiment 3 of the present application; Figure 7 shown in the schematic diagram of the reflection coefficient phase curves of different solutions output by the microwave sensor provided in the comparative example of the present application.

[0087] Comparing Figure 6 and Figure 7 it can be seen that the curve output by the microwave sensor with the coupled dual-antenna structure form has two characteristic points. The left characteristic point is the characteristic point generated by the coupling of the two antennas, that is, the characteristic frequency of the coupling coefficient phase zero point, which has a relatively obvious response to the change of the dielectric constant and a high sensitivity. The right characteristic point is the single-antenna characteristic point, which has a lower response to the change of the dielectric constant. Therefore, the microwave sensor designed based on the coupled dual-antenna structure in the present application has higher sensitivity and resolution compared with the microwave sensor with a single-antenna structure in the prior art, and can capture the subtle differences in the dielectric constant, thereby improving the accuracy of the solution detection result.

[0088] Figure 8 shown in the schematic diagram of the change curves of the dielectric constant and the resonance point of the microwave sensors provided in Embodiment 3 and the comparative example of the present application. It can be seen that as the dielectric constant of the solution to be measured increases, the resonance frequency point shifts towards the low-frequency direction. At the same time, the sensitivity of the microwave sensor based on the coupled dual-antenna structure provided in Embodiment 3 is much higher than that of the microwave sensor based on the single-antenna structure provided in the comparative example. Therefore, the microwave sensor provided in the present application has great advantages in detecting solutions.

[0089] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A microwave resonator, characterized in that, Comprising: A dielectric substrate; A coupled dual-antenna structure disposed on the dielectric substrate, including a first antenna and a second antenna with the same polarization direction, for when the dielectric constant of the microwave transmission medium changes, the coupling coefficient between the first antenna and the second antenna changes, causing the transmission characteristics of the microwave input signal to change, so that the characteristic frequency of the phase zero point of the coupling coefficient of the microwave output signal changes; A metal plate disposed below the dielectric substrate, forming a resonant cavity structure together with the dielectric substrate and the coupled dual-antenna structure.

2. The microwave resonator according to claim 1, wherein: The extending directions of the first antenna and the second antenna on the dielectric substrate are the same, and the axes of the first antenna and the second antenna are parallel; The first end of the first antenna and the first end of the second antenna are located on a first straight line, and the second end of the second antenna and the second end of the second antenna are located on a second straight line; Wherein, the first straight line and the second straight line are parallel to each other and are both perpendicular to the axes of the first antenna and the second antenna.

3. The microwave resonator according to claim 2, wherein: The perpendicular distance between the first antenna and the second antenna is 5 mm to 12.5 mm.

4. The microwave resonator according to claim 2, wherein: The lengths of both the first antenna and the second antenna are 5 mm to 13 mm.

5. The microwave resonator according to claim 1, wherein: The distance between the metal plate and the dielectric substrate is 1 / 4 to 1 / 2 of the electromagnetic wave wavelength.

6. The microwave resonator according to claim 1, characterized in that, The coupling coefficient between the first antenna and the second antenna is expressed as: ， ， ， Among them, represents the coupling coefficient; represents the imaginary unit; represents the space wave impedance; represents the microwave signal propagation constant related to the dielectric constant, , represents the dielectric constant of the microwave transmission medium, represents the vacuum permittivity, represents the relationship function between the microwave signal propagation constant and the dielectric constant; represents half of the length of the first antenna; represents half of the length of the second antenna; represents an arbitrary point on the first antenna; represents an arbitrary point on the second antenna; represents the partial derivative with respect to the z coordinate; represents the coupling Green's function; represents the distance between different positions of the first antenna and the second antenna; represents the perpendicular distance between the first antenna and the second antenna.

7. A microwave sensor, characterized in that, Comprising: The microwave resonator according to any one of claims 1 to 6; A liquid container disposed above the coupled dual-antenna structure in the microwave resonator for containing the solution to be measured; A microwave signal source connected to the input end of the microwave resonator for generating a microwave input signal and transmitting it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal; A vector network analyzer connected to the output end of the microwave resonator for receiving the microwave output signal, outputting a coupling coefficient phase curve, and obtaining the characteristic frequency of the phase zero point of the coupling coefficient based on the coupling coefficient phase curve, so as to classify the solution to be measured based on the characteristic frequency of the phase zero point of the coupling coefficient.

8. The microwave sensor according to claim 7, wherein: The distance between the liquid container and the coupled dual-antenna structure is 0 to 1 of the electromagnetic wave wavelength.

9. A solution detection method, characterized in that, The solution detection method is applied to the microwave sensor according to any one of claims 7 to 8, and is characterized by including: Placing the solution to be measured in the liquid container; Using the microwave signal source to generate a microwave input signal and transmit it to the microwave resonator, so that the microwave resonator transmits the microwave input signal under the action of the solution to be measured to obtain a microwave output signal; Using the vector network analyzer to receive the microwave output signal, output a coupling coefficient phase curve, and obtaining the characteristic frequency of the phase zero point of the coupling coefficient based on the coupling coefficient phase curve; Obtaining the dielectric constant of the solution to be measured based on the characteristic frequency of the phase zero point of the coupling coefficient, so as to determine the type of the solution.

10. The solution detection method according to claim 9, wherein Obtaining the dielectric constant of the solution to be measured based on the characteristic frequency of the phase zero point of the coupling coefficient includes: Obtain standard solutions with different dielectric constants, and use a microwave sensor to obtain the characteristic frequency of the coupling coefficient phase zero point for each standard solution; Fit the dielectric constants and the characteristic frequencies of the coupling coefficient phase zero points of multiple standard solutions to obtain a relationship model between the dielectric constant and the characteristic frequency of the coupling coefficient phase zero point; Input the characteristic frequency of the coupling coefficient phase zero point of the solution to be measured into the relationship model between the dielectric constant and the characteristic frequency of the coupling coefficient phase zero point, and output the dielectric constant of the solution to be measured.

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