Grain electromagnetic parameter measuring device and method

Abstract

The invention relates to the technical field of grain detection, discloses a grain electromagnetic parameter measuring device and method, and aims at solving the problem that an existing electromagnetic parameter detecting method is poor in accuracy, and the scheme mainly comprises a temperature sensor, a coaxial transmission line structure, a vector network analyzer and a control module. The coaxial transmission line structure comprises a cylindrical inner conductor and a cylindrical outer conductor, the inner conductor is located on the central axis of the outer conductor, and a hollow structure is formed between the inner conductor and the outer conductor; the hollow structure is used for filling grain, the temperature sensor is used for detecting grain temperature, the vector network analyzer is used for calculating electromagnetic parameters of the grain according to amplitudes and phases of output electromagnetic wave signals and input electromagnetic wave signals, and the control module is used for constructing a mapping relation between the grain temperature and the electromagnetic parameters. The mapping relation is used for grain pile temperature detection; the radiuses of the inner conductor and the outer conductor satisfy impedance matching conditions. The accuracy of grain electromagnetic parameter measurement is improved, and the method is suitable for various grains.

Description

Technical Field

[0001] The present invention relates to the technical field of grain detection, and particularly relates to a device and method for measuring electromagnetic parameters of grains. Background Art

[0002] Electromagnetic parameters can reflect the internal state of grains, such as moisture content, mildew condition or impurities. For example, grains with high moisture content may have a higher dielectric constant. By detecting the electromagnetic parameters of grains, it can be quickly determined whether they meet the standards to avoid mildew during storage. At the same time, the electromagnetic characteristics of different quality grains are different, and the quality of grains can be classified by electromagnetic parameters. In addition, during the processing process, the process can be optimized through electromagnetic parameters, such as drying or microwave treatment.

[0003] The existing detection methods for electromagnetic parameters mainly include the capacitance sensor method and the microwave resonance method. Among them, the capacitance sensor method mainly fills the medium evenly between the sensor electrodes, then uses an LCR meter or an impedance analyzer to measure the capacitance and loss factor, and finally inverses the dielectric constant through an equivalent circuit model or an empirical formula. However, due to the uneven distribution of grain particles or the difference in bulk density, when applying the capacitance sensor method to the detection of grain electromagnetic parameters, it will cause deviation in the measurement of the dielectric constant. In addition, both the moisture content of grains and the environmental humidity will affect the dielectric characteristics, making it difficult to distinguish the influence of moisture content and other factors on the capacitance. The microwave resonance method mainly inverses its electromagnetic parameters by analyzing the resonance characteristics of microwave signals in grains through a vector network analyzer. However, since grains are a complex medium with non-uniformity, porous structure and fluctuating moisture content, and the electromagnetic parameters of different varieties of grains vary significantly, when applying the microwave resonance method to the detection of grain electromagnetic parameters, the microwave energy is likely to be reflected at the container-grain interface. Excessive reflectivity will cause the microwave signal to be unable to penetrate the grains, and will reduce the effective field strength of the grains, weakening the detection sensitivity of the dielectric parameters. At the same time, impurities or moisture gradients may be mixed in the grains, resulting in local fluctuations in the dielectric constant, and the field distribution will shift towards the container wall, resulting in insufficient field strength in the central area of the grains, thereby affecting the accuracy of the detection results. In addition, the existing technology does not realize the influence of grain temperature on electromagnetic parameters, resulting in poor accuracy in the detection of grain electromagnetic parameters. Summary of the Invention

[0004] The present invention aims to solve the problem of poor accuracy existing in the existing detection methods for electromagnetic parameters, and proposes a device and method for measuring electromagnetic parameters of grains.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: In a first aspect, the present invention provides a measuring device for the electromagnetic parameters of grains. The measuring device includes a temperature sensor, a coaxial transmission line structure, a vector network analyzer, and a control module. The coaxial transmission line structure includes a cylindrical inner conductor and an outer conductor. The inner conductor is located on the central axis of the outer conductor, and a hollow structure is formed between the inner conductor and the outer conductor. The electromagnetic wave signal output port of the vector network analyzer is connected to one end of the coaxial transmission line structure, and the other end of the coaxial transmission line structure is connected to the electromagnetic wave signal input port of the vector network analyzer; The hollow structure is used to fill grains. The temperature sensor is used to detect the temperature of the grains. The vector network analyzer is used to calculate the electromagnetic parameters of the grains according to the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal. The control module is used to construct a mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used for detecting the temperature of the grain pile; The radii of the inner conductor and the outer conductor satisfy the following conditions: ; Wherein, represents the target characteristic impedance, represents the relative permittivity, represents the radius of the outer conductor, represents the radius of the inner conductor.

[0006] Further, the radii of the inner conductor and the outer conductor also satisfy the following conditions: ; Wherein, represents the target maximum available frequency, represents the speed of light in vacuum.

[0007] Further, the target characteristic impedance is 50 Ω, the radius of the outer conductor is 50 mm, and the radius of the inner conductor is 21.74 mm.

[0008] Further, the coaxial transmission line structure further includes a bakelite push plate, and the bakelite push plate is installed at the end of the outer conductor of the coaxial transmission line structure and can slide axially along the outer conductor.

[0009] Further, the materials of the inner conductor and the outer conductor are aluminum.

[0010] Further, the vector network analyzer is specifically used for: Determine the scattering parameters of the electromagnetic wave signal in the grains according to the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, solve the reflection coefficient and transmission factor of the electromagnetic wave according to the scattering parameters, calculate the propagation constant according to the transmission factor, and calculate the electromagnetic parameters of the grains according to the propagation constant and the reflection coefficient.

[0011] Furthermore, the mapping relationship is used for detecting the temperature of the grain heap, and its implementation method includes: Install a sensor matrix in the grain heap, and each sensor in the sensor matrix includes a temperature probe, an electromagnetic wave transmitting module, and an electromagnetic wave receiving module respectively; Obtain the temperature of the point where each sensor's temperature probe is located, and control each sensor to transmit and receive electromagnetic wave signals. The frequency of the electromagnetic wave signal transmitted by each sensor corresponds to the temperature of the point where it is located; Construct an electromagnetic wave propagation equation between any two sensors in the grain heap to generate an electromagnetic wave propagation equation set; Based on the frequency of the electromagnetic wave signal transmitted by each sensor, the amplitude and phase of the received electromagnetic wave signal, and the electromagnetic wave propagation equation set, generate an electromagnetic wave distribution field for representing the electromagnetic parameter distribution; Based on the electromagnetic wave distribution field and the mapping relationship between temperature and electromagnetic parameters, generate a temperature distribution field for representing the temperature distribution, and determine the temperature of any point in the grain heap according to the temperature distribution field.

[0012] Furthermore, the electromagnetic parameters are permittivity, permeability, or conductivity.

[0013] Furthermore, the electromagnetic wave propagation equation between any two sensors is as follows: ; ; ; ; ; Among them, represents the phase delay when the electromagnetic wave of the th sensor propagates to the th sensor, represents the propagation path of the electromagnetic wave of the th sensor propagating to the th sensor, represents the arc length parameter of the propagation path, which is used to describe the position on the propagation path, represents the position at which the phase constant is located, represents the integration variable, represents the amplitude attenuation when the electromagnetic wave of the th sensor propagates to the th sensor, represents the natural exponential function, represents the position at which the attenuation coefficient is located, represents the position The real part of the dielectric constant at represents the angular frequency of the electromagnetic wave signal, represents pi, represents the frequency of the electromagnetic wave signal.

[0014] In a second aspect, the present invention provides a method for measuring the electromagnetic parameters of grains, which is applied to the measuring device for the electromagnetic parameters of grains as described in the first aspect. The method includes: Loading a grain sample into the hollow structure of a coaxial transmission line structure; The temperature sensor detects the grain temperature and sends it to the control module; The electromagnetic wave signal output port of the vector network analyzer outputs an electromagnetic wave signal. After the electromagnetic wave signal penetrates the grains through the coaxial transmission line structure, it returns to the electromagnetic wave signal input port of the vector network analyzer. The vector network analyzer calculates the electromagnetic parameters of the grains based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal; The control module constructs a mapping relationship between the grain temperature and the electromagnetic parameters based on the received grain temperature and electromagnetic parameters. The mapping relationship is used for detecting the temperature of the grain pile.

[0015] The beneficial effects of the present invention are as follows: The measuring device and method for the electromagnetic parameters of grains provided by the present invention use a vector network analyzer to detect the electromagnetic parameters of grains based on the electromagnetic wave signals before and after penetrating the grains. By optimizing the coaxial transmission line structure to match its characteristic impedance with the impedance of the vector network analyzer, signal reflection of electromagnetic waves in the complex grain medium is reduced, the energy utilization rate and the accuracy of electromagnetic parameter measurement are improved. Moreover, when there are impurities and moisture gradients in the grains, impedance matching can maintain the uniform distribution of the grain electromagnetic field and avoid electromagnetic field distortion, so as to accurately reflect the dielectric characteristics of the whole grain, further improving the accuracy of grain electromagnetic parameter measurement. In addition, the present invention measures the electromagnetic parameters of grains at different temperatures respectively, constructs a mapping relationship between the temperature and the electromagnetic parameters of grains. Based on this mapping relationship, the propagation characteristics of electromagnetic wave signals are dynamically correlated with the temperature field, and thus the temperature of the grain pile can be inversely calculated by using the electromagnetic parameters. Determining the temperature by inverting the electromagnetic parameters is more in line with the real physical process. When the temperature gradient of the grain pile changes steeply due to uneven ventilation, electromagnetic inversion can accurately reflect the mutation boundary, further improving the accuracy of temperature detection. Description of the Drawings

[0016] Figure 1 is a schematic structural diagram of the measuring device for the electromagnetic parameters of grains provided in the embodiment; Figure 2 is a schematic structural diagram of the coaxial transmission line structure provided in the embodiment; Figure 3Flow schematic diagram of the method for measuring the electromagnetic parameters of grains provided in the embodiment; Figure 4 Schematic diagram of the installation structure of the sensor matrix provided in the embodiment; Figure 5 Schematic diagram of the transmission of electromagnetic wave signals provided in the embodiment. Detailed implementation manners

[0017] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution in this embodiment will be clearly and completely described below in conjunction with the accompanying drawings in this embodiment.

[0018] The technical solution of the present invention is applicable to application scenarios where the electromagnetic parameters of grains need to be measured, such as the measurement of the electromagnetic parameters of rice, wheat, corn, etc.

[0019] Since grains themselves are complex media with non-uniformity, porous structure, and fluctuating moisture content, when using the microwave resonance method to detect electromagnetic parameters, uneven distribution of grain particles or moisture content differences will cause local impedance mutations, triggering microwave signal reflection. Excessive reflectivity will cause the microwave signal to be unable to penetrate the grains, and will reduce the effective field strength of the grains, weakening the detection sensitivity of the dielectric parameters. At the same time, there may be impurities or moisture gradients in the grains, which will cause local dielectric constant fluctuations. In addition, the prior art has not realized the influence of grain temperature on electromagnetic parameters, resulting in poor detection accuracy of grain electromagnetic parameters.

[0020] In order to improve the detection accuracy of grain electromagnetic parameters, the technical solution of the present invention is proposed. In the present invention, the device for measuring grain electromagnetic parameters includes a temperature sensor, a coaxial transmission line structure, a vector network analyzer, and a control module. The coaxial transmission line structure includes a cylindrical inner conductor and an outer conductor. The inner conductor is located on the central axis of the outer conductor, and a hollow structure is formed between the inner conductor and the outer conductor. The electromagnetic wave signal output port of the vector network analyzer is connected to one end of the coaxial transmission line structure, and the other end of the coaxial transmission line structure is connected to the electromagnetic wave signal input port of the vector network analyzer; the hollow structure is used to fill grains, the temperature sensor is used to detect the grain temperature, the vector network analyzer is used to calculate the electromagnetic parameters of the grains according to the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, the control module is used to construct a mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used for detecting the grain pile temperature; the radii of the inner conductor and the outer conductor satisfy the following conditions: ; where represents the target characteristic impedance, represents the relative dielectric constant, represents the radius of the outer conductor, represents the radius of the inner conductor.

[0021] Specifically, the present invention uses a vector network analyzer to detect the electromagnetic parameters of grains based on the electromagnetic wave signals before and after penetrating the grains. By optimizing the coaxial transmission line structure to match its characteristic impedance with the impedance of the vector network analyzer, the reflection loss can be reduced, the signal penetration depth can be enhanced, the inversion accuracy of the dielectric constant and loss factor can be improved, thereby increasing the energy utilization rate and the accuracy of electromagnetic parameter measurement. Moreover, when there are impurities and moisture gradients in the grains, impedance matching can suppress the formation of standing waves, maintain the integrity of the signal waveform, maintain the uniform distribution of the grain electromagnetic field, and avoid electromagnetic field distortion, thus accurately reflecting the overall dielectric properties of the grains and further improving the accuracy of grain electromagnetic parameter measurement. In addition, by dynamically correlating the electromagnetic parameters with the temperature, the present invention can realize the inversion of the grain pile temperature using the electromagnetic parameters. Determining the temperature by inverting the electromagnetic parameters is more in line with the real physical process. When the temperature gradient in the grain pile changes sharply due to uneven ventilation, electromagnetic inversion can accurately reflect the mutation boundary, further improving the accuracy of temperature detection.

[0022] The technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0023] Figure 1 The structural schematic diagram of a measuring device for grain electromagnetic parameters is shown. Please refer to Figure 1 The measuring device includes a temperature sensor, a coaxial transmission line structure, a vector network analyzer, and a control module. The electromagnetic wave signal output port of the vector network analyzer is connected to one end of the coaxial transmission line structure, and the other end of the coaxial transmission line structure is connected to the electromagnetic wave signal input port of the vector network analyzer. The data output ports of the vector network analyzer and the temperature sensor are respectively connected to the data input port of the control module.

[0024] Please refer to Figure 2 The coaxial transmission line structure includes a cylindrical inner conductor and an outer conductor. The inner conductor is located on the central axis of the outer conductor, and a hollow structure is formed between the inner conductor and the outer conductor. The hollow structure is used to fill grains.

[0025] In this embodiment, the radii of the inner conductor and the outer conductor satisfy the following conditions: ; Where represents the target characteristic impedance, with the unit of ohm, represents the relative dielectric constant, dimensionless, represents the radius of the outer conductor, with the unit of millimeter, represents the radius of the inner conductor in millimeters. 138 represents a constant, dimensionless, originating from the wave impedance in electromagnetic field theory and the unit conversion process. Its essence is an approximate value obtained through coefficient adjustment when converting the natural logarithm to the base-10 logarithm.

[0026] In this embodiment, the radii of the inner conductor and the outer conductor further satisfy the following conditions: ; where, represents the target maximum available frequency in hertz, represents the speed of light in vacuum, taking m / s.

[0027] It can be understood that the coaxial transmission line only supports the main mode (TEM mode) transmission below the cut-off frequency. When the frequency exceeds the cut-off frequency, higher-order modes will be generated. The higher-order modes will cause signal energy dispersion and phase distortion, significantly reducing the measurement accuracy of electromagnetic parameters (such as dielectric constant, loss factor). At the same time, insufficient cut-off frequency will cause signal reflection and dispersion effects, resulting in amplitude and phase distortion of the transmitted signal. To further improve the measurement accuracy of electromagnetic parameters, in this embodiment, the coaxial transmission line structure is optimized through the above conditions, so that the cut-off frequency of the coaxial transmission line covers the target frequency band, ensuring that the test system meets the sensitivity requirements within the effective bandwidth.

[0028] In this embodiment, the target maximum available frequency is Hz. The materials of the inner conductor and the outer conductor are aluminum, and the coaxial transmission line structure is set according to a 50Ω air coaxial line, that is, the target characteristic impedance is 50Ω, and its higher-order modes are suppressed. Through comprehensive design, a coaxial transmission line structure with an outer conductor radius of 50mm and an inner conductor radius of 21.74mm is obtained, that is: First, set = 50Ω, = 50mm, = 1 (air) and substitute them into the above formula to get = 21.74mm; Then calculate the cut-off frequency: Hz, that is, the maximum available frequency of this coaxial transmission line is Hz, meeting the requirement that frequencies below the target maximum available frequency Hz are available.

[0029] By optimizing the coaxial transmission line structure, the characteristic impedance of the coaxial transmission line structure is matched with the impedance of the vector network analyzer, thereby reducing the signal reflection of electromagnetic waves in complex grain media, improving the energy utilization rate and the accuracy of electromagnetic parameter measurement. Moreover, when there are impurities and moisture gradients in the grain, impedance matching can maintain the uniform distribution of the grain electromagnetic field, avoid electromagnetic field distortion, and thus accurately reflect the dielectric properties of the whole grain, further improving the accuracy of grain electromagnetic parameter measurement. In addition, the cut-off frequency of the coaxial transmission line structure can cover the target frequency band, which can avoid the influence of multimode propagation on the measurement results, ensure that the measurement device meets the sensitivity requirements within the effective bandwidth, and further improve the reliability and data validity of the measurement device.

[0030] In this embodiment, the hollow structure is used to fill the grain, the temperature sensor is used to detect the grain temperature, the vector network analyzer is used to calculate the electromagnetic parameters of the grain according to the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, the control module is used to construct the mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used for detecting the temperature of the grain pile.

[0031] In this embodiment, the coaxial transmission line structure further includes a bakelite push plate, which is installed at the end of the outer conductor of the coaxial transmission line structure and can slide axially along the outer conductor, used to press the grain, and there is a scale outside the outer conductor to judge the pressing degree of the grain.

[0032] Please refer to Figure 3 , based on the above measurement device, the method for measuring the electromagnetic parameters of grain provided in this embodiment includes the following steps: Step 1: Fill the grain sample into the hollow structure of the coaxial transmission line structure; Step 2: The temperature sensor detects the grain temperature and sends it to the control module; Step 3: The electromagnetic wave signal output port of the vector network analyzer outputs an electromagnetic wave signal. After the electromagnetic wave signal penetrates the grain through the coaxial transmission line structure, it returns to the electromagnetic wave signal input port of the vector network analyzer. The vector network analyzer calculates the electromagnetic parameters of the grain according to the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal; Step 4: The control module constructs the mapping relationship between the grain temperature and the electromagnetic parameters according to the received grain temperature and electromagnetic parameters, and the mapping relationship is used for detecting the temperature of the grain pile.

[0033] In practical applications, a food sample is loaded into the hollow structure of a coaxial transmission line structure and compacted, and then the measuring device is started. After the measuring device is started, the temperature sensor detects the ambient temperature and uses it as the food temperature, and sends the temperature data to the control module. The electromagnetic wave signal output port of the vector network analyzer sends an electromagnetic wave signal. The electromagnetic wave signal penetrates through the food through the coaxial transmission line structure and then returns to the electromagnetic wave signal input port of the vector network analyzer. The vector network analyzer calculates the electromagnetic parameters of the food based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, and sends the calculated electromagnetic parameters to the control module. The above steps are repeated at different temperatures to measure the temperature and electromagnetic parameters, and the corresponding temperature and electromagnetic parameters are sent to the control module. The control module constructs the mapping relationship between the two based on the received food temperature and electromagnetic parameters.

[0034] In this embodiment, the vector network analyzer determines the scattering parameters of the electromagnetic wave signal in the food based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, solves the reflection coefficient and transmission factor of the electromagnetic wave according to the scattering parameters, calculates the propagation constant according to the transmission factor, and calculates the electromagnetic parameters of the food according to the propagation constant and the reflection coefficient.

[0035] It can be understood that at different temperatures, when the electromagnetic wave vertically penetrates the food, the attenuation coefficient and phase delay of the electromagnetic wave can be calculated through the amplitude and phase changes of the electromagnetic wave before and after penetration, and then the electromagnetic parameters of the food can be deduced inversely. The amplitude attenuation is directly related to the loss characteristics of the medium. The greater the loss, the more obvious the amplitude attenuation of the electromagnetic wave; while the phase change is related to the influence of the medium on the propagation speed of the electromagnetic wave. Different electromagnetic parameters will change the propagation speed of the electromagnetic wave, resulting in a phase change. Using a vector network analyzer to accurately measure the amplitude and phase differences between the incident wave and the penetrated wave, and then through mathematical processing, the electromagnetic parameters such as the complex permittivity and complex permeability of the medium can be accurately calculated.

[0036] In this embodiment, the mapping relationship between the food temperature and the electromagnetic parameters is used for detecting the temperature of the grain heap. Specifically, the temperature dependence of the electromagnetic parameters of the grain heap stems from the coupling of multiple physical fields. The temperature change of the grain heap will cause moisture phase change, thermal expansion, biological metabolism and changes in the electromagnetic wave propagation characteristics, and then cause changes in the electromagnetic parameters. In this embodiment, the electromagnetic parameters can be permittivity, permeability or conductivity. Specifically, when the grain is heated and expanded, the porosity will be reduced and the packing density will be increased, which leads to an increase in the number of scattering interfaces in the electromagnetic wave propagation path and an increase in the equivalent permittivity; high temperature (>20°C) activates the respiration of microorganisms in the grain heap, releases and moisture, while increasing the ion concentration, significantly improving the conductivity; the permeability of trace metal impurities (such as iron filings) in the grain heap will be slightly adjusted due to temperature changes. For example, high temperature may reduce the ordered arrangement of magnetic impurities, resulting in a decrease in permeability.

[0037] In this embodiment, after the constructed mapping relationship is saved to the control module, the temperature of the grain pile in the granary can be detected according to this mapping relationship. The implementation method for detecting the temperature of the grain pile according to the mapping relationship is as follows: Step 41: Install a sensor matrix in the grain pile. Each sensor in the sensor matrix includes a temperature probe, an electromagnetic wave transmitting module, and an electromagnetic wave receiving module respectively.

[0038] Please refer to Figure 4 , in practical applications, multiple sensors can be distributed and set in the grain pile, and the distance between adjacent sensors can be dynamically adjusted according to the grain pile size and monitoring resolution requirements. Each sensor integrates a temperature probe (such as a thermocouple or a thermistor), an electromagnetic wave transmitting module, and an electromagnetic wave receiving module. The temperature probe is used to detect the temperature of the point where it is located, the electromagnetic wave transmitting module is used to transmit electromagnetic wave signals, and the electromagnetic wave receiving module is used to receive electromagnetic wave signals. Each sensor is communicatively connected to the main control device, and the main control device is used to receive the temperature detected by the sensor, control the sensor to emit electromagnetic wave signals, and receive the relevant data of the received electromagnetic wave signals sent by the sensor.

[0039] In this embodiment, each sensor in the sensor matrix adopts a passive sensor, which does not require battery power supply, and the sensor is encapsulated with a wave-transparent material (such as polypropylene) to reduce the interference to the electromagnetic wave signal and further improve the accuracy of temperature detection.

[0040] Step 42: Obtain the temperature of the point where the temperature probe of each sensor is located, and control each sensor to emit and receive electromagnetic wave signals. The frequency of the electromagnetic wave signal emitted by each sensor corresponds to the temperature of the point where it is located.

[0041] The temperature probe of each sensor detects the temperature of the point where it is located in real time, and the temperature data is transmitted to the main control device through analog-to-digital conversion or a direct digital interface. Please refer to Figure 5 , for any two sensors, the main control device generates an excitation signal with a corresponding electromagnetic wave frequency according to the temperature value to control the electromagnetic wave transmitting module of the sensor to emit electromagnetic wave signals with corresponding frequencies. The electromagnetic wave receiving module of each sensor receives the electromagnetic wave signals emitted by other sensors, and returns the relevant data of the received electromagnetic wave signals to the main control device.

[0042] Step 43: Construct an electromagnetic wave propagation equation between any two sensors in the grain pile to generate an electromagnetic wave propagation equation set.

[0043] In this embodiment, constructing the electromagnetic wave propagation equation between any two sensors in the grain pile specifically includes: Based on Maxwell's equations, the wave equation of the electric field strength of electromagnetic waves in a grain pile is determined, and an electromagnetic wave propagation equation is constructed according to the wave equation of the electric field strength of electromagnetic waves in a grain pile.

[0044] Maxwell's Equations is a set of partial differential equations that describe the relationships between electric fields, magnetic fields, charge density, and current density. The set of equations consists of four equations, namely Gauss's law that describes how charges generate electric fields, Gauss's magnetic law that indicates the non-existence of magnetic monopoles, Faraday's law of induction that explains how time-varying magnetic fields generate electric fields, and Maxwell-Ampere's law that shows how currents and time-varying electric fields generate magnetic fields.

[0045] In this embodiment, in a passive, linear, and isotropic grain pile medium, the differential form of Maxwell's equations is as follows: ; ; ; ; From Maxwell's equations, the wave equation of the electric field strength of electromagnetic waves in a grain pile can be derived as follows: ; Among them, represents the divergence operator, represents the curl operator, represents the Laplace operator, represents the electric displacement vector, represents the magnetic induction intensity, represents the electric field strength, represents the magnetic field strength, represents the current density, represents the magnetic permeability, represents the permittivity, represents the conductivity, represents the first-order derivative of the magnetic induction intensity with respect to time, represents the first-order derivative of the electric displacement vector with respect to time, represents the second-order derivative of the electric field strength with respect to time, represents the first-order derivative of the electric field strength with respect to time.

[0046] When electromagnetic waves propagate in a grain pile medium, the phase and amplitude changes are related to the path integral. Based on this, for any two sensors , an electromagnetic wave propagation equation can be established to describe the propagation of electromagnetic waves from the th sensor to the The electromagnetic wave propagation characteristics (phase delay and amplitude attenuation) of the sensors are as follows: ; ; ; ; ; wherein, represents the phase delay when the electromagnetic wave of the -th sensor propagates to the -th sensor, represents the propagation path of the electromagnetic wave of the -th sensor propagating to the -th sensor, represents the arc length parameter of the propagation path, which is used to describe the position on the propagation path, represents the position at which the phase constant is located, characterizing the phase change per unit length when the electromagnetic wave propagates in the medium, represents the integration variable, represents the amplitude attenuation when the electromagnetic wave of the -th sensor propagates to the -th sensor, represents the natural exponential function, represents the position at which the attenuation coefficient is located, characterizing the energy attenuation per unit length when the electromagnetic wave propagates in the medium, represents the real part of the dielectric constant at the position , represents the angular frequency of the electromagnetic wave signal, represents the pi, represents the frequency of the electromagnetic wave signal.

[0047] In the above electromagnetic wave propagation equation, the phase delay and amplitude attenuation of the electromagnetic wave propagation are related to the medium characteristics at each point on the path. By integrating the path, the propagation characteristics of the electromagnetic wave in the inhomogeneous medium can be accurately described, and the accuracy of temperature detection can be further improved. In addition, the attenuation of the electromagnetic wave is determined by the absorption characteristics of the medium, and the absorption process usually follows the exponential law. Therefore, the linear integral can be mapped to the actual attenuation amplitude through the exponential function. Through integration and the exponential function, the propagation behavior of the electromagnetic wave in the complex medium can be accurately modeled, providing a mathematical basis for the subsequent temperature inversion.

[0048] Step 44: Generate an electromagnetic wave distribution field for representing the electromagnetic parameter distribution according to the frequency of the electromagnetic wave signal emitted by each sensor, the amplitude and phase of the received electromagnetic wave signal, and based on the electromagnetic wave propagation equation set.

[0049] In this embodiment, generating an electromagnetic wave distribution field for representing the distribution of electromagnetic parameters includes: Discretizing the space where the grain pile is located into grain pile grids, calculating the electromagnetic parameters corresponding to each grain pile grid according to the frequency of the electromagnetic wave signal emitted by each sensor, the amplitude and phase of the received electromagnetic wave signal, and based on the electromagnetic wave propagation equations, and generating an electromagnetic wave distribution field for representing the distribution of electromagnetic parameters according to the electromagnetic parameters corresponding to each grain pile grid.

[0050] In practical applications, first divide the grain pile space into grain pile grids. The specific size of the grain pile grids can be set according to the detection resolution requirements (such as 1 cm³). At the same time, it is necessary to determine the position information of each grain pile grid relative to the sensor to determine the position of the electromagnetic wave on the propagation path; then, for any two sensors, discretize the path integral for each grain pile grid on the electromagnetic wave propagation path; then, determine the phase delay and amplitude attenuation of the electromagnetic wave signal on the propagation path according to the amplitude and phase of the received electromagnetic wave signal, and substitute the frequency of the electromagnetic wave signal emitted by each sensor and the phase delay and amplitude attenuation of the electromagnetic wave signal on the propagation path into the corresponding equations in the electromagnetic wave propagation equations, and the electromagnetic parameters of each grain pile grid can be inversely obtained; finally, map the electromagnetic parameters of each grain pile grid obtained by inversion to the three-dimensional space coordinates of the grain pile, and an electromagnetic wave distribution field representing the distribution of the electromagnetic parameters of the grain pile can be obtained.

[0051] By discretizing the grain pile into grids, constructing the electromagnetic wave propagation equations and inversely solving them, the finally generated electromagnetic parameter distribution field can reflect the distribution of the electromagnetic parameters inside the grain pile with high resolution.

[0052] Step 45: Generate a temperature distribution field for representing the temperature distribution based on the electromagnetic wave distribution field and based on the mapping relationship between the temperature and the electromagnetic parameters, and determine the temperature at any point in the grain pile according to the temperature distribution field.

[0053] Specifically, according to the electromagnetic parameters of each grain pile grid and based on the constructed mapping relationship between the temperature and the electromagnetic parameters, the temperature of each grain pile grid can be obtained. Map the temperature of each grain pile grid to the three-dimensional space coordinates of the grain pile, and an electromagnetic wave distribution field representing the distribution of the electromagnetic parameters of the grain pile can be obtained. When it is necessary to determine the temperature of a certain point in the grain pile, directly take the temperature of the grain pile grid where the point is located to realize determining the temperature at any point in the grain pile.

[0054] In this embodiment, by measuring the electromagnetic parameters of grains at different temperatures respectively, a mapping relationship between temperature and the electromagnetic parameters of grains is constructed. Based on this mapping relationship, the propagation characteristics of electromagnetic wave signals are dynamically correlated with the temperature field, so that the temperature of the grain heap can be inversely calculated by using the electromagnetic parameters. Determining the temperature by inversely calculating the electromagnetic parameters is more in line with the real physical process. When the temperature gradient of the grain heap changes sharply due to uneven ventilation, electromagnetic inversion can accurately reflect the mutation boundary, further improving the accuracy of temperature detection.

Claims

1. A measuring device for the electromagnetic parameters of grains, characterized in that, The measurement device includes a temperature sensor, a coaxial transmission line structure, a vector network analyzer, and a control module. The coaxial transmission line structure includes a cylindrical inner conductor and an outer conductor. The inner conductor is located on the central axis of the outer conductor, and a hollow structure is formed between the inner conductor and the outer conductor. The electromagnetic wave signal output port of the vector network analyzer is connected to one end of the coaxial transmission line structure, and the other end of the coaxial transmission line structure is connected to the electromagnetic wave signal input port of the vector network analyzer; The hollow structure is used to fill with grains. The temperature sensor is used to detect the grain temperature. The vector network analyzer is used to calculate the electromagnetic parameters of the grains according to the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal. The control module is used to construct a mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used for detecting the temperature of the grain heap; The radii of the inner conductor and the outer conductor satisfy the following conditions: ； Among them, represents the target characteristic impedance, represents the relative dielectric constant, represents the radius of the outer conductor, represents the radius of the inner conductor.

2. The measuring device for the electromagnetic parameters of grains according to claim 1, characterized in that The radii of the inner conductor and the outer conductor also satisfy the following conditions: ； Among them, represents the target maximum available frequency, represents the speed of light in vacuum.

3. The measuring device for the electromagnetic parameters of grains according to claim 1, characterized in that, The target characteristic impedance is 50Ω, the radius of the outer conductor is 50mm, and the radius of the inner conductor is 21.74mm.

4. The measuring device for the electromagnetic parameters of grains according to claim 1, characterized in that, The coaxial transmission line structure further includes a bakelite push plate, which is installed at the end of the outer conductor of the coaxial transmission line structure and can slide axially along the outer conductor.

5. The measuring device for the electromagnetic parameters of grains according to claim 1, characterized in that, The materials of the inner conductor and the outer conductor are aluminum.

6. The measuring device for the electromagnetic parameters of grains according to claim 1, characterized in that, The vector network analyzer is specifically used for: Determine the scattering parameters of the electromagnetic wave signal in the grains according to the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, solve the reflection coefficient and transmission factor of the electromagnetic wave according to the scattering parameters, calculate the propagation constant according to the transmission factor, and calculate the electromagnetic parameters of the grains according to the propagation constant and the reflection coefficient.

7. The measuring device for the electromagnetic parameters of grains according to claim 1, characterized in that, The mapping relationship is used for detecting the temperature of the grain heap, and its implementation method includes: Install a sensor matrix in the grain heap. Each sensor in the sensor matrix includes a temperature probe, an electromagnetic wave transmitting module, and an electromagnetic wave receiving module; Obtain the temperature of the location detected by the temperature probe of each sensor, and control each sensor to transmit and receive electromagnetic wave signals. The frequency of the electromagnetic wave signal transmitted by each sensor corresponds to the temperature of the location; Construct an electromagnetic wave propagation equation between any two sensors in the grain heap to generate an electromagnetic wave propagation equation set; Generate an electromagnetic wave distribution field for representing the distribution of electromagnetic parameters according to the frequency of the electromagnetic wave signal transmitted by each sensor and the amplitude and phase of the received electromagnetic wave signal and based on the electromagnetic wave propagation equation set; Generate a temperature distribution field for representing the temperature distribution according to the electromagnetic wave distribution field and based on the mapping relationship between the temperature and the electromagnetic parameters, and determine the temperature of any location in the grain heap according to the temperature distribution field.

8. The measuring device for the electromagnetic parameters of grains according to claim 7, characterized in that, The electromagnetic parameters are permittivity, permeability, or conductivity.

9. The measuring device for the electromagnetic parameters of grains according to claim 8, characterized in that, The electromagnetic wave propagation equation between any two sensors is as follows: ； ； ； ； ； Among them, represents the phase delay when the electromagnetic wave of the -th sensor propagates to the -th sensor, represents the propagation path of the electromagnetic wave of the -th sensor propagating to the -th sensor, represents the arc length parameter of the propagation path, which is used to describe the position on the propagation path, represents the position at the phase constant, represents the integration variable, represents the amplitude attenuation when the electromagnetic wave of the -th sensor propagates to the -th sensor, represents the natural exponential function, represents the attenuation coefficient at the position , represents the real part of the dielectric constant at the position , represents the angular frequency of the electromagnetic wave signal, represents pi, represents the frequency of the electromagnetic wave signal.

10. A method for measuring the electromagnetic parameters of grains, characterized in that, Applied to the measurement device for the electromagnetic parameters of grains as described in any one of claims 1 to 9, the method includes: Fill the grain sample in the hollow structure of the coaxial transmission line structure; The temperature sensor detects the grain temperature and sends it to the control module; The electromagnetic wave signal output port of the vector network analyzer outputs an electromagnetic wave signal. The electromagnetic wave signal penetrates the grain through the coaxial transmission line structure and then returns to the electromagnetic wave signal input port of the vector network analyzer. The vector network analyzer calculates the electromagnetic parameters of the grain based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal; The control module constructs a mapping relationship between the grain temperature and the electromagnetic parameters according to the received grain temperature and electromagnetic parameters. The mapping relationship is used for detecting the temperature of the grain pile.

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