Device and method for measuring electromagnetic parameters of grain

Abstract

The present invention relates to the field of grain detection technology and discloses a device and method for measuring grain electromagnetic parameters. This device aims to address the poor accuracy of existing electromagnetic parameter detection methods. The solution primarily comprises 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 being located on the central axis of the outer conductor, with a hollow structure formed between the inner and outer conductors. The hollow structure is used to hold grain, the temperature sensor is used to detect the grain temperature, the vector network analyzer is used to calculate the grain's electromagnetic parameters based on the amplitude and phase of the output and input electromagnetic wave signals, and the control module is used to establish a mapping relationship between the grain temperature and the electromagnetic parameters, which is used to detect the grain pile temperature. The radii of the inner and outer conductors meet impedance matching conditions. The present invention improves the accuracy of grain electromagnetic parameter measurement and is applicable to various types of grain.

Description

Technical Field

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

[0002] Electromagnetic parameters can reveal the internal state of grain, such as moisture content, mold, and impurities. For example, grain with a high moisture content may have a higher dielectric constant. Testing grain electromagnetic parameters can quickly determine if it meets these standards, preventing mold during storage. Furthermore, grains of varying quality have distinct electromagnetic properties, allowing for quality grading based on these parameters. Furthermore, electromagnetic parameters can be used to optimize processes during processing, such as drying or microwave treatment.

[0003] Existing electromagnetic parameter detection methods mainly include capacitance sensor method and microwave resonance method. Among them, the capacitance sensor method mainly fills the dielectric uniformly between the sensor electrodes, then uses an LCR meter or impedance analyzer to measure the capacitance and loss factor, and finally inverts the dielectric constant through an equivalent circuit model or empirical formula. However, due to the uneven distribution of grain particles or differences in bulk density, the application of the capacitance sensor method to grain electromagnetic parameter detection will lead to deviations in the dielectric constant measurement. In addition, the moisture content of grain and the ambient humidity both affect the dielectric properties, making it difficult to distinguish the influence of moisture content and other factors on capacitance. The microwave resonance method primarily uses a vector network analyzer to analyze the resonance characteristics of microwave signals in grain to invert its electromagnetic parameters. However, because grain is a complex medium with an inhomogeneous, porous structure, and fluctuating moisture content, and because the electromagnetic parameters of different grain varieties vary significantly, when the microwave resonance method is applied to grain electromagnetic parameter detection, microwave energy is easily reflected at the container-grain interface. Excessive reflectivity prevents the microwave signal from penetrating the grain, reduces the effective field strength of the grain, and weakens the detection sensitivity of the dielectric parameters. Furthermore, impurities or moisture gradients in the grain can cause local fluctuations in the dielectric constant, shifting the field distribution toward the container walls. This leads to insufficient field strength in the center of the grain, thus affecting the accuracy of the detection results. Furthermore, existing technologies fail to recognize the impact of grain temperature on electromagnetic parameters, resulting in poor detection accuracy of grain electromagnetic parameters. Summary of the Invention

[0004] The present invention aims to solve the problem of poor accuracy in existing electromagnetic parameter detection methods 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:

[0006] In a first aspect, the present invention provides a device for measuring electromagnetic parameters of grain, the device comprising 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 an outer conductor, the inner conductor being located on the central axis of the outer conductor, and a hollow structure being formed between the inner and outer conductors. 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.

[0007] The hollow structure is used to fill 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 based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, and the control module is used to establish a mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used to detect the temperature of the grain pile;

[0008] The radii of the inner conductor and the outer conductor satisfy the following conditions:

[0009] ;

[0010] in, represents the target characteristic impedance, represents the relative dielectric constant, represents the radius of the outer conductor, Indicates the radius of the inner conductor.

[0011] Furthermore, the radii of the inner conductor and the outer conductor also satisfy the following conditions:

[0012] ;

[0013] in, Indicates the target highest available frequency, Represents the speed of light in a vacuum.

[0014] Furthermore, the target characteristic impedance is 50Ω, the radius of the outer conductor is 50 mm, and the radius of the inner conductor is 21.74 mm.

[0015] Furthermore, the coaxial transmission line structure further comprises a bakelite push disk, which is mounted at the end of the outer conductor of the coaxial transmission line structure and can slide axially along the outer conductor.

[0016] Furthermore, the inner conductor and the outer conductor are made of aluminum.

[0017] Furthermore, the vector network analyzer is specifically used for:

[0018] The scattering parameters of the electromagnetic wave signal in the grain are determined based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, the reflection coefficient and transmission factor of the electromagnetic wave are solved based on the scattering parameters, the propagation constant is calculated based on the transmission factor, and the electromagnetic parameters of the grain are calculated based on the propagation constant and reflection coefficient.

[0019] Furthermore, the mapping relationship is used to detect the grain pile temperature, and its implementation method includes:

[0020] A sensor matrix is ​​installed in the grain pile, wherein each sensor in the sensor matrix includes a temperature probe, an electromagnetic wave transmitting module and an electromagnetic wave receiving module;

[0021] Obtain the temperature of the point 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 point;

[0022] Construct the electromagnetic wave propagation equation between any two sensors in the grain pile and generate the electromagnetic wave propagation equation group;

[0023] 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 equations;

[0024] According to the electromagnetic wave distribution field and based on the mapping relationship between temperature and electromagnetic parameters, a temperature distribution field for representing temperature distribution is generated, and the temperature of any point in the grain pile is determined according to the temperature distribution field.

[0025] Furthermore, the electromagnetic parameter is dielectric constant, magnetic permeability or electrical conductivity.

[0026] Furthermore, the electromagnetic wave propagation equation between any two sensors is as follows:

[0027] ;

[0028] ;

[0029] ;

[0030] ;

[0031] ;

[0032] in, Indicates the The electromagnetic wave of the first sensor propagates to the The phase delay of the sensor is Indicates the The electromagnetic wave of the first sensor propagates to the The propagation path of each sensor, Represents the arc length parameter of the propagation path, which is used to describe the position on the propagation path. Indicates location The phase constant at represents the integration variable, Indicates the The electromagnetic wave of the first sensor propagates to the The amplitude attenuation when the sensor is represents the natural exponential function, Indicates location The attenuation coefficient at Indicates location The real part of the dielectric constant at represents the angular frequency of the electromagnetic wave signal, represents pi, Indicates the frequency of the electromagnetic wave signal.

[0033] In a second aspect, the present invention provides a method for measuring electromagnetic parameters of grains, which is applied to the device for measuring electromagnetic parameters of grains as described in the first aspect, and the method comprises:

[0034] The grain sample is loaded into the hollow structure of the coaxial transmission line structure;

[0035] The temperature sensor detects the grain temperature and sends it to the control module;

[0036] The electromagnetic wave signal output port of the vector network analyzer outputs an electromagnetic wave signal, which passes through 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;

[0037] The control module constructs a 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 to detect the grain pile temperature.

[0038] The beneficial effects of the present invention are as follows: the device and method for measuring the electromagnetic parameters of grains provided by the present invention use a vector network analyzer to detect the electromagnetic parameters of grains based on electromagnetic wave signals before and after penetrating the grains. By optimizing the coaxial transmission line structure, its characteristic impedance is matched with the impedance of the vector network analyzer, thereby reducing the signal reflection of electromagnetic waves in complex grain media, improving energy utilization and the accuracy of electromagnetic parameter measurement, and when impurities and moisture gradients are present in the grains, the impedance matching can maintain the uniform distribution of the electromagnetic field of the grains and avoid electromagnetic field distortion, thereby accurately reflecting the dielectric properties of the grains as a whole, 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 temperature and grain electromagnetic parameters, and based on the mapping relationship, dynamically associates the electromagnetic wave signal propagation characteristics with the temperature field, thereby realizing the inversion of grain pile temperature using electromagnetic parameters. Determining the temperature by inverting electromagnetic parameters is more consistent with real physical processes. When the temperature gradient of the grain pile changes suddenly due to uneven ventilation, the electromagnetic inversion can accurately reflect the mutation boundary, further improving the accuracy of temperature detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the structure of a device for measuring electromagnetic parameters of grain provided in an embodiment;

[0040] Figure 2 A schematic structural diagram of a coaxial transmission line structure provided in an embodiment;

[0041] Figure 3 A schematic flow chart of a method for measuring electromagnetic parameters of grains provided in an embodiment;

[0042] Figure 4 A schematic diagram of the sensor matrix installation structure provided in the embodiment;

[0043] Figure 5 A schematic diagram of the transmission of electromagnetic wave signals provided in an embodiment. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of this embodiment will be clearly and completely described below in conjunction with the drawings in this embodiment.

[0045] 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 electromagnetic parameter measurement of rice, wheat, corn, etc.

[0046] Since grain itself is a complex medium with non-uniformity, porous structure, and fluctuating moisture content, when using microwave resonance method to detect electromagnetic parameters, uneven distribution of grain particles or differences in moisture content will cause local impedance mutations, triggering microwave signal reflection. Excessive reflectivity will prevent microwave signals from penetrating the grain, reduce the effective field strength of the grain, and weaken the detection sensitivity of dielectric parameters. At the same time, the grain may be mixed with impurities or moisture gradients, which will cause local dielectric constant fluctuations. In addition, the existing technology does not recognize the impact of grain temperature on electromagnetic parameters, resulting in poor detection accuracy of grain electromagnetic parameters.

[0047] In order to improve the accuracy of grain electromagnetic parameter detection, the technical solution of the present invention is proposed. In the present invention, a 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 load 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 based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, and the control module is used to establish a mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used to detect the temperature of the grain pile; the radii of the inner conductor and the outer conductor meet the following conditions: ;in, represents the target characteristic impedance, represents the relative dielectric constant, represents the radius of the outer conductor, Indicates the radius of the inner conductor.

[0048] Specifically, the present invention uses a vector network analyzer to detect the electromagnetic parameters of grain based on the electromagnetic wave signals before and after penetrating the grain. 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, and the inversion accuracy of the dielectric constant and dissipation factor can be improved, thereby improving the energy utilization rate and the accuracy of electromagnetic parameter measurement; and when there are impurities and moisture gradients in the grain, the impedance matching can suppress the formation of standing waves, maintain the integrity of the signal waveform, maintain the uniform distribution of the electromagnetic field of the grain, and avoid electromagnetic field distortion, thereby accurately reflecting the dielectric properties of the grain as a whole, and further improving the accuracy of the electromagnetic parameter measurement of the grain; in addition, the present invention can realize the inversion of the grain pile temperature using electromagnetic parameters by dynamically associating electromagnetic parameters with temperature. Determining the temperature by inverting electromagnetic parameters is more in line with real physical processes. When the temperature gradient of the grain pile changes sharply due to uneven ventilation, the electromagnetic inversion can accurately reflect the mutation boundary, further improving the accuracy of temperature detection.

[0049] The technical solution of this embodiment will be clearly and completely described below in conjunction with the drawings in this embodiment. Obviously, the described embodiment is only a part of the embodiments of the present invention, rather than all the embodiments.

[0050] Figure 1 A schematic diagram of a device for measuring electromagnetic parameters of grain is shown. 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.

[0051] See also 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. A hollow structure is formed between the inner conductor and the outer conductor, and the hollow structure is used to fill food.

[0052] In this embodiment, the radii of the inner conductor and the outer conductor meet the following conditions:

[0053] ;

[0054] in, Indicates the target characteristic impedance in ohms. represents the relative dielectric constant, dimensionless, Indicates the radius of the outer conductor in millimeters. It represents the radius of the inner conductor in millimeters. 138 represents a dimensionless constant that comes from the wave impedance and unit conversion process in electromagnetic field theory. Its essence is the approximate value obtained by adjusting the coefficient when converting the natural logarithm to the logarithm with base 10.

[0055] In this embodiment, the radii of the inner conductor and the outer conductor also meet the following conditions:

[0056] ;

[0057] in, Indicates the target maximum available frequency in Hertz. represents the speed of light in vacuum, take m / s.

[0058] It's understandable that coaxial transmission lines only support primary mode (TEM mode) transmission below the cutoff frequency. When the frequency exceeds the cutoff frequency, higher-order modes are generated. These higher-order modes cause signal energy dispersion and phase distortion, significantly reducing the measurement accuracy of electromagnetic parameters (such as dielectric constant and dissipation factor). Furthermore, an insufficient cutoff frequency can trigger signal reflection and dispersion effects, leading to amplitude and phase distortion of the transmitted signal. To further improve electromagnetic parameter measurement accuracy, this embodiment optimizes the coaxial transmission line structure under the aforementioned conditions, ensuring that the cutoff frequency of the coaxial transmission line covers the target frequency band and ensuring that the test system meets sensitivity requirements within the effective bandwidth.

[0059] In this embodiment, the target highest available frequency is Hz, the inner and outer conductors are made of 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 high-order mode is suppressed. The comprehensive design results in a coaxial transmission line structure with an outer conductor radius of 50mm and an inner conductor radius of 21.74mm, that is:

[0060] First, =50Ω, =50mm, =1 (air) Substituting into the above formula, we get =21.74mm;

[0061] Then calculate the cutoff frequency: Hz, that is, the highest usable frequency of the coaxial transmission line is Hz, meeting the target highest available frequency Requirements for frequencies below Hz to be available.

[0062] By optimizing the coaxial transmission line structure and matching its characteristic impedance with the impedance of the vector network analyzer, the team reduced electromagnetic wave signal reflections in complex grain media, improving energy utilization and the accuracy of electromagnetic parameter measurements. Furthermore, when impurities and moisture gradients are present in the grain, impedance matching maintains a uniform distribution of the grain's electromagnetic field, avoiding electromagnetic field distortion and accurately reflecting the grain's overall dielectric properties, further improving the accuracy of grain electromagnetic parameter measurements. Furthermore, the coaxial transmission line structure's cutoff frequency can cover the target frequency band, preventing the impact of multimode propagation on measurement results and ensuring that the measurement device meets sensitivity requirements within the effective bandwidth, further improving the reliability of the measurement device and the validity of the data.

[0063] In this embodiment, the hollow structure is used to fill 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 based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, and the control module is used to construct a mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used to detect the temperature of the grain pile.

[0064] In this embodiment, the coaxial transmission line structure also 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 to compress the grain. A scale is provided on the outside of the outer conductor to judge the degree of compression of the grain.

[0065] See also Figure 3 Based on the above-mentioned measuring device, the method for measuring electromagnetic parameters of grain provided in this embodiment includes the following steps:

[0066] Step 1: Fill the grain sample into the hollow structure of the coaxial transmission line structure;

[0067] Step 2: The temperature sensor detects the grain temperature and sends it to the control module;

[0068] Step 3: The electromagnetic wave signal output port of the vector network analyzer outputs an electromagnetic wave signal. The electromagnetic wave signal passes through 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.

[0069] Step 4: The control module constructs a mapping relationship between the grain temperature and the electromagnetic parameters based on the received grain temperature and electromagnetic parameters, and the mapping relationship is used to detect the grain pile temperature.

[0070] In practice, a grain sample is placed in the hollow structure of a coaxial transmission line and compressed, then the measuring device is activated. After activation, a temperature sensor detects the ambient temperature and uses it as the grain temperature. The temperature data is then sent to a control module. The electromagnetic wave signal output port of a vector network analyzer transmits an electromagnetic wave signal, which then penetrates the grain through the coaxial transmission line structure and returns to the electromagnetic wave signal input port of the vector network analyzer. The vector network analyzer calculates the electromagnetic parameters of the grain by combining the amplitude and phase of the output electromagnetic wave signal with the input electromagnetic wave signal, and then sends the calculated electromagnetic parameters to the control module. These steps are repeated at different temperatures to measure the temperature and electromagnetic parameters. The corresponding temperature and electromagnetic parameters are then sent to the control module, which then establishes a mapping relationship between the received grain temperature and electromagnetic parameters.

[0071] In this embodiment, the vector network analyzer determines the scattering parameters of the electromagnetic wave signal in the grain 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 based on the scattering parameters, calculates the propagation constant based on the transmission factor, and calculates the electromagnetic parameters of the grain based on the propagation constant and reflection coefficient.

[0072] It can be understood that at different temperatures, when electromagnetic waves vertically penetrate grain, the amplitude and phase changes before and after penetration can be used to calculate the attenuation coefficient and phase delay of the electromagnetic wave, and thus infer the electromagnetic parameters of the grain. Amplitude attenuation is directly related to the loss characteristics of the medium; the greater the loss, the more significant the electromagnetic wave amplitude attenuation. Phase change, on the other hand, is related to the medium's effect 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, the amplitude and phase differences between the incident and penetrating waves are precisely measured. After mathematical processing, electromagnetic parameters such as the complex dielectric constant and complex permeability of the medium can be accurately calculated.

[0073] In this embodiment, the mapping relationship between grain temperature and electromagnetic parameters is used to detect the temperature of the grain pile. Specifically, the temperature dependence of the electromagnetic parameters of the grain pile originates from the coupling of multiple physical fields. The temperature change of the grain pile will cause the water phase change, thermal expansion, biological metabolism and electromagnetic wave propagation characteristics to change, thereby causing the electromagnetic parameters to change. In this embodiment, the electromagnetic parameters can be dielectric constant, magnetic permeability or electrical conductivity. Specifically, the thermal expansion of grains will reduce the porosity and increase the packing density, which will lead to an increase in the scattering interface in the electromagnetic wave propagation path and an increase in the equivalent dielectric constant; high temperature (>20°C) activates the respiration of microorganisms in the grain pile, releasing and moisture, while increasing the ion concentration and significantly improving the electrical conductivity; the magnetic permeability of trace metal impurities (such as iron filings) in the grain pile will undergo slight adjustments due to temperature changes. For example, high temperature may reduce the orderly arrangement of magnetic impurities, resulting in a decrease in magnetic permeability.

[0074] In this embodiment, after the constructed mapping relationship is saved in the control module, the temperature of the grain pile in the granary can be detected according to the mapping relationship. The method for implementing the temperature detection of the grain pile according to the mapping relationship is as follows:

[0075] Step 41: Install a sensor matrix in the grain pile, where each sensor in the sensor matrix includes a temperature probe, an electromagnetic wave transmitting module, and an electromagnetic wave receiving module.

[0076] See also Figure 4 In practical applications, multiple sensors can be distributed throughout the grain pile, with the spacing between adjacent sensors dynamically adjusted based on the size of the pile and the required monitoring resolution. Each sensor integrates a temperature probe (such as a thermocouple or thermistor), an electromagnetic wave transmitter module, and an electromagnetic wave receiver module. The temperature probe detects the temperature at the location where it is located, the electromagnetic wave transmitter module transmits electromagnetic wave signals, and the electromagnetic wave receiver module receives electromagnetic wave signals. Each sensor is separately connected to a main control unit, which receives the temperature detected by the sensor, controls the sensor's electromagnetic wave transmission, and receives data related to the received electromagnetic wave signals.

[0077] In this embodiment, each sensor in the sensor matrix is ​​a passive sensor that does not require battery power, and the sensor is packaged with a wave-transmitting material (such as polypropylene) to reduce interference with electromagnetic wave signals and further improve the accuracy of temperature detection.

[0078] Step 42: Obtain the temperature of the point 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 point.

[0079] The temperature probe of each sensor detects the temperature of the point in real time, and the temperature data is transmitted to the main control device through analog-to-digital conversion or direct digital interface. Figure 5 For any two sensors, the main control device generates an excitation signal of the corresponding electromagnetic wave frequency according to the temperature value to control the electromagnetic wave transmitting module of the sensor to transmit the electromagnetic wave signal of the corresponding frequency. The electromagnetic wave receiving module of each sensor receives the electromagnetic wave signal transmitted by other sensors and returns the relevant data of the received electromagnetic wave signal to the main control device.

[0080] Step 43: Construct an electromagnetic wave propagation equation between any two sensors in the grain pile to generate an electromagnetic wave propagation equation group.

[0081] In this embodiment, the electromagnetic wave propagation equation between any two sensors in the grain pile is constructed, specifically including:

[0082] The wave equation of the electric field intensity of the electromagnetic wave in the grain pile is determined based on Maxwell's equations, and the electromagnetic wave propagation equation is constructed according to the wave equation of the electric field intensity of the electromagnetic wave in the grain pile.

[0083] Maxwell's equations are a set of partial differential equations that describe the relationship between electric fields, magnetic fields, charge density, and current density. The equations consist of four equations: Gauss's law describing how charges generate electric fields; Gauss's law of magnetism, which shows that magnetic monopoles do not exist; Faraday's law of induction, which explains how time-varying magnetic fields generate electric fields; and Maxwell-Ampere's law, which explains how current and time-varying electric fields generate magnetic fields.

[0084] In this embodiment, in a passive, linear, isotropic grain pile medium, the differential form of Maxwell's equations is as follows:

[0085] ;

[0086] ;

[0087] ;

[0088] ;

[0089] The wave equation of the electric field intensity of electromagnetic waves in the grain pile can be derived from Maxwell's equations as follows:

[0090] ;

[0091] in, 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 dielectric constant, represents the conductivity, represents the first-order derivative of 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 intensity with respect to time, It represents the first derivative of the electric field strength with respect to time.

[0092] When electromagnetic waves propagate in the grain pile medium, the phase and amplitude changes are related to the path integral. Based on this, we can use the wave equation of the electric field intensity of the electromagnetic wave in the grain pile to calculate the path integral of any two sensors. , establish an electromagnetic wave propagation equation to describe the electromagnetic wave from the The sensor propagates to the The electromagnetic wave propagation characteristics (phase delay and amplitude attenuation) of each sensor are as follows:

[0093] ;

[0094] ;

[0095] ;

[0096] ;

[0097] ;

[0098] in, Indicates the The electromagnetic wave of the first sensor propagates to the The phase delay of the sensor is Indicates the The electromagnetic wave of the first sensor propagates to the The propagation path of each sensor, Represents the arc length parameter of the propagation path, which is used to describe the position on the propagation path. Indicates location The phase constant at , which represents the phase change per unit length when the electromagnetic wave propagates in the medium, represents the integration variable, Indicates the The electromagnetic wave of the first sensor propagates to the The amplitude attenuation when the sensor is represents the natural exponential function, Indicates location The attenuation coefficient at the point represents the energy attenuation per unit length when the electromagnetic wave propagates in the medium. Indicates location The real part of the dielectric constant at represents the angular frequency of the electromagnetic wave signal, represents pi, Indicates the frequency of the electromagnetic wave signal.

[0099] In the above electromagnetic wave propagation equation, the phase delay and amplitude attenuation of electromagnetic wave propagation are related to the medium properties at each point along the path. By integrating the path, the propagation characteristics of electromagnetic waves in inhomogeneous media can be accurately described, further improving the accuracy of temperature detection. In addition, the attenuation of electromagnetic waves is determined by the absorption properties of the medium. The absorption process generally follows an exponential law, so the linear integral can be mapped to the actual attenuation amplitude through an exponential function. Through integration and exponential functions, the propagation behavior of electromagnetic waves in complex media can be accurately modeled, providing a mathematical foundation for subsequent temperature inversion.

[0100] Step 44: 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 equations.

[0101] In this embodiment, generating an electromagnetic wave distribution field for representing electromagnetic parameter distribution includes:

[0102] The space where the grain pile is located is discretized into grain pile grids. According to the frequency of the electromagnetic wave signal emitted by each sensor and the amplitude and phase of the received electromagnetic wave signal and based on the electromagnetic wave propagation equations, the electromagnetic parameters corresponding to each grain pile grid are calculated. According to the electromagnetic parameters corresponding to each grain pile grid, an electromagnetic wave distribution field is generated to represent the distribution of electromagnetic parameters.

[0103] In practical application, the grain pile space is first divided into The specific size of the grain pile grid can be set according to the detection resolution requirement (such as 1cm³), and the position information of each grain pile grid relative to the sensor needs to be determined to determine the position of the electromagnetic wave on the propagation path; then, for any two sensors, the path integral of each grain pile grid on the electromagnetic wave propagation path is discretized; then, according to the amplitude and phase of the received electromagnetic wave signal, the phase delay and amplitude attenuation of the electromagnetic wave signal on the propagation path are determined, and 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 are substituted into the corresponding equations in the electromagnetic wave propagation equation group to obtain the electromagnetic parameters of each grain pile grid by inversion; finally, the electromagnetic parameters of each grain pile grid obtained by inversion are mapped to the three-dimensional spatial coordinates of the grain pile to obtain the electromagnetic wave distribution field representing the distribution of the electromagnetic parameters of the grain pile.

[0104] By discretizing the grain pile into grids, constructing a set of electromagnetic wave propagation equations and inversely solving them, the electromagnetic parameter distribution field finally generated can reflect the electromagnetic parameter distribution inside the grain pile with high resolution.

[0105] Step 45: Generate a temperature distribution field for representing temperature distribution according to the electromagnetic wave distribution field and based on the mapping relationship between temperature and electromagnetic parameters, and determine the temperature of any point in the grain pile according to the temperature distribution field.

[0106] Specifically, the temperature of each grain pile grid can be determined based on the electromagnetic parameters of each grid and the mapping relationship between temperature and electromagnetic parameters. By mapping the temperature of each grid to the three-dimensional spatial coordinates of the grain pile, an electromagnetic wave distribution field representing the distribution of the grain pile's electromagnetic parameters can be obtained. To determine the temperature of a specific point in the grain pile, the temperature of the grid containing that point is directly taken, allowing the temperature of any point in the grain pile to be determined.

[0107] This embodiment measures the electromagnetic parameters of grain at different temperatures and constructs a mapping relationship between temperature and grain electromagnetic parameters. Based on this mapping relationship, the propagation characteristics of the electromagnetic wave signal are dynamically associated with the temperature field. This allows the grain pile temperature to be inverted using the electromagnetic parameters. Determining the temperature by inverting the electromagnetic parameters is more consistent with real physical processes. When the temperature gradient of the grain pile changes suddenly due to uneven ventilation, the electromagnetic inversion can accurately reflect the mutation boundary, further improving the accuracy of temperature detection.

Claims

1. A method for measuring electromagnetic parameters of grain, characterized in that: The method for measuring electromagnetic parameters of grain is implemented using a device for measuring electromagnetic parameters of grain. The 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, wherein 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 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 based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, and the control module is used to establish a mapping relationship between the grain temperature and the electromagnetic parameters, and the mapping relationship is used to detect the temperature of the grain pile; The radii of the inner conductor and the outer conductor satisfy the following conditions: ； in, represents the target characteristic impedance, represents the relative dielectric constant, represents the radius of the outer conductor, Indicates the radius of the inner conductor; The mapping relationship is used to detect the temperature of the grain pile, and its implementation method includes: A sensor matrix is ​​installed in the grain pile, wherein 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 point 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 point; Construct the electromagnetic wave propagation equation between any two sensors in the grain pile and generate the electromagnetic wave propagation equation group; 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 equations; generating a temperature distribution field for representing temperature distribution according to the electromagnetic wave distribution field and based on a mapping relationship between temperature and electromagnetic parameters, and determining the temperature of any point in the grain pile according to the temperature distribution field; The electromagnetic wave propagation equation between any two sensors is as follows: ； ； ； ； ； in, Indicates the The electromagnetic wave of the first sensor propagates to the The phase delay of the sensor is Indicates the The electromagnetic wave of the first sensor propagates to the The propagation path of each sensor, Represents the arc length parameter of the propagation path, which is used to describe the position on the propagation path. Indicates location The phase constant at represents the integration variable, Indicates the The electromagnetic wave of the first sensor propagates to the The amplitude attenuation when the sensor is represents the natural exponential function, Indicates location The attenuation coefficient at Indicates location The real part of the dielectric constant at represents the angular frequency of the electromagnetic wave signal, represents pi, Indicates the frequency of the electromagnetic wave signal, represents the magnetic permeability, Indicates conductivity.

2. The method for measuring electromagnetic parameters of grain according to claim 1, characterized in that: The radii of the inner conductor and the outer conductor also satisfy the following conditions: ； in, Indicates the target highest available frequency, Represents the speed of light in a vacuum.

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

4. The method for measuring electromagnetic parameters of grain according to claim 1, characterized in that: The coaxial transmission line structure further comprises a bakelite push disk, 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 method for measuring electromagnetic parameters of grain according to claim 1, characterized in that: The inner conductor and the outer conductor are made of aluminum.

6. The method for measuring electromagnetic parameters of grain according to claim 1, characterized in that: The vector network analyzer is specifically used for: The scattering parameters of the electromagnetic wave signal in the grain are determined based on the amplitude and phase of the output electromagnetic wave signal and the input electromagnetic wave signal, the reflection coefficient and transmission factor of the electromagnetic wave are solved based on the scattering parameters, the propagation constant is calculated based on the transmission factor, and the electromagnetic parameters of the grain are calculated based on the propagation constant and reflection coefficient.

7. The method for measuring electromagnetic parameters of grain according to claim 6, characterized in that: The electromagnetic parameter is dielectric constant, magnetic permeability or electrical conductivity.

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