A microwave heating in-situ dielectric dynamic measurement system and method based on waveguide switch switching

Abstract

This invention proposes an in-situ dynamic measurement system and method for dielectric constant of materials under microwave heating based on waveguide switch switching. It relates to the field of microwave measurement technology. The system includes: a waveguide cross-shaped switch switching module with a quarter-wavelength choke, an in-situ single-mode resonant cavity, a microwave heating module containing a microwave source, a circulator, and a water load, an electromagnetic parameter measurement module containing a vector network analyzer and a waveguide-coaxial converter, and a central measurement and control module. The method includes: using the TRL method to calibrate the measurement link, controlling the heating temperature using a PID algorithm, synchronously switching the switch state within 500ms, acquiring scattering parameters through frequency sweep measurement, completing full-temperature domain acquisition through cyclic heating, and inverting the dielectric constant using thermal expansion correction and the NRW algorithm. This invention achieves in-situ, quasi-isothermal, and high-precision dynamic measurement of the dielectric parameters of materials under high temperature and high power conditions through waveguide switch channel switching and choke high isolation design, combined with calibration, temperature control, rapid switching, and error correction methods.

Description

Technical Field

[0001] This invention relates to the field of microwave measurement technology, and more specifically, to a microwave heating in-situ dielectric dynamic measurement system and method based on waveguide switch switching. Background Technology

[0002] Microwaves, electromagnetic waves with frequencies between 300MHz and 300GHz, heat energy by converting electromagnetic energy directly into heat energy through polarization loss of polar molecules within a material under an alternating electromagnetic field. In agricultural engineering, microwave technology is widely used in grain drying, food sterilization, and biomass pyrolysis for oil or gas production. In these processes, the complex dielectric constant of the material is a key parameter determining microwave energy absorption efficiency, heating uniformity, and the progress of chemical reactions. However, agricultural and forestry biomass materials are typically porous, non-homogeneous, and highly heat-sensitive media. During microwave processing, their dielectric properties exhibit drastic nonlinear dynamic responses to temperature and composition changes. For example, in the drying stage, the dielectric constant rapidly decreases with the rapid evaporation of moisture; while in the pyrolysis and carbonization stage, the dielectric loss factor often increases exponentially with rising temperature and biochar formation, easily inducing localized thermal runaway, leading to material charring or reactor damage. Therefore, in-situ and dynamic monitoring of the electromagnetic parameters of materials throughout the microwave heating process is crucial for analyzing the interaction mechanism between microwaves and matter and optimizing process parameters.

[0003] Traditional microwave dielectric measurement technology employs a static offline mode. Sample transfer can lead to a sudden temperature drop and redistribution of moisture and heat due to the cooling effect, resulting in distorted measurement data. Furthermore, it fails to capture transient dielectric characteristics, causing data gaps. Online switching mechanisms lack isolation and safety, and high-power microwaves are prone to crosstalk to weak measurement signals and damage to precision instruments. Slow switching also creates measurement dead zones, and large sample temperature fluctuations cannot meet the requirements for quasi-isothermal measurements. Thermal expansion of metallic waveguides in a wide temperature range causes phase drift, and the lack of a dynamic phase compensation mechanism renders static calibration ineffective, resulting in a significant decrease in measurement accuracy at high temperatures.

[0004] Therefore, it is necessary to design a microwave heating in-situ dielectric dynamic measurement system and method based on waveguide switching to solve the problems of data distortion, lack of isolation and security, large system error and calibration failure in existing technologies. Summary of the Invention

[0005] In view of this, the present invention proposes a microwave heating in-situ dielectric dynamic measurement system and method based on waveguide switch switching, aiming to solve the problems of data distortion, lack of isolation and security, large system error and calibration failure in the existing technology.

[0006] In one aspect, the present invention proposes a microwave heating in-situ dielectric dynamic measurement system based on waveguide switching, comprising: A waveguide cross switch switching module includes a first waveguide cross switch and a second waveguide cross switch. The waveguide cross switch switching module is based on the choke groove cutting off the transmission mode of microwaves in the mating gap. An in-situ single-mode resonant cavity is electrically connected to the waveguide cross switch switching module. One end of the in-situ single-mode resonant cavity is connected to the cavity connection port of the first waveguide cross switch, and the other end of the in-situ single-mode resonant cavity is connected to the cavity connection port of the second waveguide cross switch. A microwave heating module is electrically connected to the waveguide cross switch switching module. The microwave heating module includes a microwave source, a circulator, and a water load. The output terminal of the microwave source is connected to the input terminal of the circulator, the output terminal of the circulator is connected to the heating input port of the first waveguide cross switch, and the isolation terminal of the circulator is connected to the water load. An electromagnetic parameter measurement module is electrically connected to the waveguide cross switch switching module. The electromagnetic parameter measurement module includes a vector network analyzer, a first waveguide coaxial converter, and a second waveguide coaxial converter. The first test port of the vector network analyzer is connected to the measurement input port of the first waveguide cross switch; the second test port of the vector network analyzer is connected to the measurement input port of the second waveguide cross switch. The central measurement and control module is electrically connected to the waveguide cross switch switching module, the in-situ single-mode resonant cavity, the microwave heating module, and the electromagnetic parameter measurement module, respectively. The central measurement and control module controls the switching between the heating state and the measurement state.

[0007] Furthermore, the first waveguide cross switch and the second waveguide cross switch have the same structure; Both the first waveguide cross switch and the second waveguide cross switch include a stator, a rotor, and a stepper motor drive unit; The stator is provided with four waveguide ports arranged in a cross shape; The rotor has a waveguide channel inside.

[0008] Furthermore, the four waveguide ports include: the heating input port, the cavity connection port, the measurement input port, and the load port; The choke groove is formed on the mating clearance surface between the stator and the rotor; The depth of the choke groove is one-quarter of a wavelength.

[0009] Furthermore, the first test port of the vector network analyzer is connected to the measurement input port of the first waveguide cross switch through the first waveguide coaxial converter; The second test port of the vector network analyzer is connected to the measurement input port of the second waveguide cross switch via the second waveguide coaxial converter.

[0010] Furthermore, when the central monitoring and control module controls the switching between the heating state and the measurement state, it includes: The central measurement and control module is electrically connected to the microwave source, the vector network analyzer, and the stepper motor drive unit, respectively. The central measurement and control module controls the rotor to rotate to the first position. The waveguide channel connects the heating input port and the cavity connection port. The measurement input port is physically blocked. Microwave energy enters the in-situ single-mode resonant cavity through the first waveguide cross switch. At this time, the measurement system is in a heating state. The central measurement and control module controls the rotor to rotate to the second position. The waveguide channel connects the measurement input port and the cavity connection port. The heating input port is physically blocked. The test signal of the vector network analyzer passes through the first waveguide cross switch and the second waveguide cross switch, and passes through the in-situ single-mode resonant cavity. At this time, the measurement system is in the measurement state.

[0011] Compared with the prior art, the beneficial effects of the microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching provided by the present invention are as follows: (1) By utilizing the flow channel switching mechanism of the waveguide cross switch, the alternation of "heating-measurement" can be achieved without moving the sample, which completely eliminates the sudden drop in temperature, redistribution of moisture and change of lattice state caused by sample transfer in offline measurement, ensuring that the measurement data can truly reflect the intrinsic characteristics of the material under the coupling effect of microwave thermal field.

[0012] (2) By designing a quarter-wavelength choke groove structure on the mating gap surface between the stator and rotor, a radio frequency short circuit is formed at the physical gap using the microwave choke principle, thus achieving high isolation between the heating path and the measurement path. This structure completely solves the problem of high-power heating source interfering with weak measurement signals in online measurement and effectively eliminates the risk of high-energy microwave leakage burning out the vector network analyzer.

[0013] On the other hand, this invention proposes a method for in-situ dynamic measurement of dielectric properties in microwave heating based on waveguide switching, comprising: The rotors of the first waveguide cross switch and the second waveguide cross switch are both rotated to the second position, and the measurement link is calibrated using the TRL calibration method to obtain the initial error term, which is then stored in the central measurement and control module. The sample to be tested is placed at the center of the in-situ single-mode resonant cavity, and the rotors of the first waveguide cross switch and the second waveguide cross switch are rotated to the first position. Based on the preset heating curve and PID algorithm, the output power of the microwave source is adjusted to heat the sample. The sample temperature is monitored in real time, and measurement commands are executed based on the sample temperature. In the measurement state, the vector network analyzer is used to perform frequency sweep measurement on the sample to obtain the scattering parameters at the current temperature, and the scattering parameters are transmitted to the central measurement and control module; Rotate the rotors of the first waveguide cross switch and the second waveguide cross switch to the first position, restore the power output of the microwave source, and continue heating to the next temperature point until all preset temperature points are measured. Based on the scattering parameters and the complex permittivity of the material obtained by the NRW algorithm, and by calling the pre-stored waveguide thermal expansion coefficient model, the physical size change of the in-situ single-mode resonant cavity and the waveguide channel at the current temperature is calculated. The phase of the scattering parameters is de-embedded and corrected to eliminate the system error introduced by thermal expansion.

[0014] Furthermore, when performing full two-port vector error calibration of the measurement link based on the TRL calibration method, it includes: The in-situ single-mode resonant cavity is removed, and a through-hole component, a reflector component, and a delay line standard component are sequentially connected to the position of the in-situ single-mode resonant cavity.

[0015] Furthermore, the measurement link includes: the waveguide channel, the first waveguide coaxial converter, and the second waveguide coaxial converter.

[0016] Furthermore, when executing a measurement command based on the sample temperature, it includes: If the sample temperature is greater than or equal to the preset sampling point temperature, a measurement interruption command is executed. If the sample temperature is lower than the preset sampling point temperature, the current state is maintained and the sample temperature is measured again.

[0017] Furthermore, when executing the measurement interrupt instruction, it includes: Control the microwave source to stop outputting or switch the high-power microwave energy generated by the microwave source to a dummy load; The rotors of the first waveguide cross switch and the second waveguide cross switch are synchronously rotated to the second position within 500ms.

[0018] Compared with existing technologies, the beneficial effects of the microwave heating in-situ dielectric dynamic measurement method based on waveguide switch switching provided by this invention are as follows: Relying on TRL full dual-port calibration to eliminate inherent errors in the measurement link, the PID algorithm achieves precise isothermal heating of the sample, and the dual-switch synchronous switching within 500ms enables quasi-isothermal measurement. Microwave energy is switched to a dummy load to ensure instrument safety, and cyclic heating measurement completes full-temperature-range data acquisition. Combining the NRW algorithm and thermal expansion de-embedding correction to eliminate high-temperature system errors, the instrument achieves in-situ, real-time, and high-precision dynamic measurement of material dielectric parameters under high-temperature and high-power conditions. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the planar structure layout of the integrated microwave heating and measurement device provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the test channel planar structure layout of the integrated microwave heating and measurement device provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the planar structure layout of the heating channel of the integrated microwave heating and measurement device provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the heating measurement conversion principle of the microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching provided in an embodiment of the present invention; Figure 5 This is a graph showing the complex dielectric constant and loss tangent of the ginger sample provided in this embodiment of the invention as a function of frequency. Figure 6 This is a graph showing the complex dielectric constant and loss tangent of a potato sample as a function of frequency, provided in an embodiment of the present invention. Figure 7 This is a graph showing the complex dielectric constant and loss tangent of the radish sample provided in this embodiment of the invention as a function of temperature. Figure 8 This is a functional block diagram of a microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching provided in an embodiment of the present invention. Figure 9 A flowchart of the in-situ dielectric dynamic measurement method for microwave heating based on waveguide switch switching provided in an embodiment of the present invention. Detailed Implementation

[0020] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art. It should be noted that, without conflict, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] It is important to note that: A choke slot is a groove structure with a depth of one-quarter wavelength that is formed on the mating gap between the stator and rotor of a waveguide cross switch. It is used to cut off the transmission mode of microwaves in the mating gap and improve the isolation of the system ports.

[0022] The mating gap refers to the tiny gap space reserved between the stator and rotor of a waveguide cross switch to allow the rotor to rotate. It provides space for the rotor to rotate and is a channel through which microwaves are prone to leakage.

[0023] The mating gap surface refers to the solid contact surface where the stator and rotor of a waveguide cross switch fit together to form a mating gap, which is used to create choke slots to achieve isolation and blocking of microwave transmission.

[0024] A waveguide channel refers to a microwave transmission channel opened inside the rotor of a waveguide cross switch, used to connect different waveguide ports and realize the switching of heating or measurement paths.

[0025] The first position refers to the specific position to which the waveguide cross switch rotor is rotated under the control of the central measurement and control module. This position is used to connect the waveguide flow channel to the heating input port and the cavity connection port, so that the system is in a heating state.

[0026] The second position refers to the specific position to which the waveguide cross switch rotor rotates under the control of the central measurement and control module. This position is used to connect the waveguide channel to the measurement input port and the cavity connection port, putting the system in a measurement state.

[0027] The first waveguide cross switch refers to the switching component in the waveguide cross switch switching module that is connected to one end of the in-situ single-mode resonant cavity, used to switch the microwave transmission path for heating and measurement.

[0028] The second waveguide cross switch refers to the switching component in the waveguide cross switch switching module that is connected to the other end of the in-situ single-mode resonant cavity. It is used to synchronously switch the microwave transmission path for heating and measurement with the first waveguide cross switch.

[0029] An in-situ single-mode resonant cavity is a cavity component in a system that houses the sample under test. It provides a stable single-mode microwave field to enable in-situ heating of the sample and measurement of its dielectric parameters.

[0030] A microwave source is a component in a microwave heating module that generates high-power microwaves to provide microwave energy for in-situ heating of samples.

[0031] A circulator is a component in a microwave heating module that directs microwave transmission, guiding microwave energy to the heating input port and isolating reflected microwaves.

[0032] Water load refers to the component in a microwave heating module that absorbs excess microwaves. It is used to absorb reflected microwave energy and protect the microwave source for safe operation.

[0033] A vector network analyzer is the core testing component of an electromagnetic parameter measurement module, used to transmit test signals and collect the scattering parameters of samples.

[0034] The first waveguide coaxial converter refers to the signal matching component of the electromagnetic parameter measurement module, which is used to connect the first test port of the vector network analyzer to the measurement input port of the first waveguide cross switch.

[0035] The second waveguide coaxial converter is a signal matching component of the electromagnetic parameter measurement module, used to connect the second test port of the vector network analyzer to the measurement input port of the second waveguide cross switch.

[0036] A stepper motor drive unit is a power component that drives the rotor of a waveguide cross switch to rotate, thereby switching between heating and measurement states.

[0037] The stator is the stationary base component in a waveguide cross switch, used to open four cross-shaped waveguide ports and provide a fixed microwave interface.

[0038] The rotor is a rotatable moving part in a waveguide cross switch, used to connect different ports through internal waveguide channels and switch microwave transmission paths.

[0039] The heating input port refers to the port on the waveguide cross switch stator that connects to the microwave heating module, used to receive heating energy from the microwave source.

[0040] The cavity connection port refers to the port on the waveguide cross switch stator that connects to the in-situ single-mode resonant cavity, used to realize the transmission docking between microwave and the resonant cavity.

[0041] The measurement input port refers to the port on the waveguide cross switch stator that connects to the electromagnetic parameter measurement module, used to input the test signals of the vector network analyzer.

[0042] The load port refers to the microwave matching port on the stator of the waveguide cross switch, which is used to meet the load matching requirements of the system's microwave transmission.

[0043] Reference Figure 1-4 and Figure 8 As shown in some embodiments of this application, a microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching includes: The waveguide cross switch switching module includes a first waveguide cross switch and a second waveguide cross switch. The waveguide cross switch switching module is based on the choke groove cutting off the transmission mode of microwaves in the mating gap.

[0044] Specifically, the first waveguide cross switch and the second waveguide cross switch have the same structure; Both the first waveguide cross switch and the second waveguide cross switch include a stator, a rotor, and a stepper motor drive unit; The stator is provided with four waveguide ports arranged in a cross shape; The rotor has a waveguide channel inside.

[0045] Specifically, the four waveguide ports include: the heating input port, the cavity connection port, the measurement input port, and the load port; The choke groove is formed on the mating clearance surface between the stator and the rotor; The depth of the choke groove is one-quarter of a wavelength.

[0046] It is understandable that, due to the fit gap between the stator and rotor of the waveguide cross switch for rotor rotation, microwaves can easily leak and crosstalk through this gap. This can cause high-power heating microwaves to interfere with the measurement signal and even burn out the vector network analyzer. Therefore, a choke groove needs to be made on the fit gap surface between the stator and rotor. Its function is to cut off the microwave transmission mode in the fit gap and block microwave leakage and crosstalk to achieve high isolation between the heating path and the measurement path. The choke groove depth is set to one-quarter wavelength because this depth is one-quarter of the waveguide wavelength corresponding to the system's operating frequency band. After the microwave enters the choke groove, the reflected return path and the incident path are superimposed to half the wavelength, which will cause the incident wave and the reflected wave to be out of phase and cancel each other out, forming an RF short circuit at the fit gap. This waveguide wavelength remains unchanged when the measurement device has a fixed operating frequency and waveguide model. The choke groove depth also remains fixed after machining. The wavelength and groove depth only need to be adjusted when the operating frequency or waveguide model is changed. In this way, microwave crosstalk and leakage are eliminated from the electromagnetic principle, ensuring the system's measurement accuracy and operational safety.

[0047] An in-situ single-mode resonant cavity is electrically connected to the waveguide cross switch switching module. One end of the in-situ single-mode resonant cavity is connected to the cavity connection port of the first waveguide cross switch, and the other end of the in-situ single-mode resonant cavity is connected to the cavity connection port of the second waveguide cross switch.

[0048] It can be understood that the function of the in-situ single-mode resonant cavity is to support the sample under test and provide a stable and uniform single-mode microwave field space for microwave heating and dielectric parameter measurement, thereby realizing in-situ heating and measurement of the sample. One end of the cavity is connected to the cavity connection port of the first waveguide cross switch, and the other end is connected to the cavity connection port of the second waveguide cross switch. This connection method allows the high-power heating microwaves from the microwave heating module to enter the resonant cavity through the cavity connection port of the first waveguide cross switch to heat the sample. At the same time, the test signal from the electromagnetic parameter measurement module can pass through the resonant cavity bidirectionally through the cavity connection ports of the first and second waveguide cross switches to complete the dual-port dielectric parameter measurement. This allows heating and measurement to share the same resonant cavity without moving the sample, ensuring the accuracy and continuity of in-situ dynamic measurement.

[0049] A microwave heating module is electrically connected to the waveguide cross switch switching module. The microwave heating module includes a microwave source, a circulator, and a water load. The output terminal of the microwave source is connected to the input terminal of the circulator, the output terminal of the circulator is connected to the heating input port of the first waveguide cross switch, and the isolation terminal of the circulator is connected to the water load.

[0050] It can be understood that the microwave heating module and the waveguide cross switch switching module achieve microwave transmission and electrical coordination. The microwave source, as the core component, generates high-power microwave energy. This microwave energy is first transmitted to the input end of the circulator. The circulator, with its unidirectional transmission characteristics, directs the microwaves to the heating input port of the first waveguide cross switch, providing a directional microwave path for system heating. At the same time, the reflected microwaves generated by sample heating cannot flow back to the microwave source. Instead, they are absorbed by the water load through the isolation end of the circulator, preventing the reflected microwaves from damaging the microwave source. This achieves directional supply of microwave energy, isolation and absorption of reflected waves, and ensures that the microwave heating module safely and stably provides the microwave energy required for system heating.

[0051] An electromagnetic parameter measurement module is electrically connected to the waveguide cross switch switching module. The electromagnetic parameter measurement module includes a vector network analyzer, a first waveguide coaxial converter, and a second waveguide coaxial converter. The first test port of the vector network analyzer is connected to the measurement input port of the first waveguide cross switch, and the second test port of the vector network analyzer is connected to the measurement input port of the second waveguide cross switch.

[0052] Specifically, the first test port of the vector network analyzer is connected to the measurement input port of the first waveguide cross switch through the first waveguide coaxial converter; The second test port of the vector network analyzer is connected to the measurement input port of the second waveguide cross switch via the second waveguide coaxial converter.

[0053] It can be understood that the electromagnetic parameter measurement module and the waveguide cross switch switching module achieve microwave transmission and electrical coordination. The vector network analyzer, as the core device for dual-port measurement, transmits the test signal output from its first test port to the measurement input port of the first waveguide cross switch after the coaxial signal and waveguide signal are matched and converted by the first waveguide coaxial converter. The second test port is connected to the measurement input port of the second waveguide cross switch after the signal is converted by the second waveguide coaxial converter, forming a complete dual-port measurement path. This ensures that the test signal can be transmitted stably and without loss to the in-situ single-mode resonant cavity and complete the acquisition of sample scattering parameters, thus ensuring the accuracy and stability of dielectric parameter measurement.

[0054] The central measurement and control module is electrically connected to the waveguide cross switch switching module, the in-situ single-mode resonant cavity, the microwave heating module, and the electromagnetic parameter measurement module, respectively. The central measurement and control module controls the switching between the heating state and the measurement state.

[0055] Specifically, when the central monitoring and control module controls the switching between the heating state and the measurement state, it includes: The central measurement and control module is electrically connected to the microwave source, the vector network analyzer, and the stepper motor drive unit, respectively. The central measurement and control module controls the rotor to rotate to the first position. The waveguide channel connects the heating input port and the cavity connection port. The measurement input port is physically blocked. Microwave energy enters the in-situ single-mode resonant cavity through the first waveguide cross switch. At this time, the measurement system is in a heating state. The central measurement and control module controls the rotor to rotate to the second position. The waveguide channel connects the measurement input port and the cavity connection port. The heating input port is physically blocked. The test signal of the vector network analyzer passes through the first waveguide cross switch and the second waveguide cross switch, and passes through the in-situ single-mode resonant cavity. At this time, the measurement system is in the measurement state.

[0056] It can be understood that the central measurement and control module, as the core of the system's overall control, coordinates the control of the waveguide cross switch switching module, the in-situ single-mode resonant cavity, the microwave heating module, and the electromagnetic parameter measurement module through electrical connections. Simultaneously, it directly connects to the microwave source, vector network analyzer, and stepper motor drive unit to achieve precise command transmission. By controlling the stepper motor drive unit to rotate the rotor, state switching is achieved. When the rotor is driven to the first position, the waveguide channel inside the rotor connects the heating input port and the cavity connection port while physically blocking the measurement input port. The microwave energy generated by the microwave source can smoothly enter the in-situ single-mode resonant cavity through the first waveguide cross switch, putting the system into heating mode to heat the sample. When the rotor is driven to the second position, the waveguide channel switches to connect the measurement input port and the cavity connection port while physically blocking the heating input port. The test signal from the vector network analyzer can sequentially pass through the first and second waveguide cross switches and through the in-situ single-mode resonant cavity, putting the system into measurement mode to collect the sample's dielectric parameters. Ultimately, this achieves automated, high-isolation, in-situ switching between heating and measurement states, ensuring the coordinated and orderly operation of all modules and the safe and accurate measurement process.

[0057] In the above embodiments, the flow channel switching mechanism of the waveguide cross switch enables alternating "heating-measurement" without moving the sample, completely eliminating the sudden temperature drop, moisture redistribution, and lattice state changes caused by sample transfer in offline measurements. This ensures that the measurement data can truly reflect the intrinsic characteristics of the material under the coupling effect of the microwave thermal field. By designing a quarter-wavelength choke groove structure on the mating gap surface of the stator and rotor, a radio frequency short circuit is formed at the physical gap using the microwave choke principle, achieving high isolation between the heating path and the measurement path. This structure completely solves the problem of high-power heating source interfering with weak measurement signals in online measurements and effectively eliminates the risk of high-energy microwave leakage burning out the vector network analyzer.

[0058] It is important to note that: The TRL calibration method refers to a microwave two-port calibration method implemented by sequentially connecting a through-hole component, a reflector, and a delay line standard component at the location of the in-situ single-mode resonant cavity. It is used to perform full two-port vector error calibration on the measurement link and obtain the initial error term.

[0059] The measurement link refers to a microwave signal transmission path that includes a waveguide channel, a first waveguide coaxial converter, and a second waveguide coaxial converter. It is used to transmit test signals from a vector network analyzer to complete the measurement of the sample's dielectric parameters.

[0060] Full two-port vector error calibration refers to the vector error calibration operation performed on both ports of the measurement link. This is used to eliminate inherent systematic errors in the measurement link and ensure the accuracy of scattering parameter measurements. The PID algorithm, or proportional-integral-derivative closed-loop control algorithm, is used to adjust the microwave source output power according to a preset heating curve, achieving precise isostatic heating of the sample under test.

[0061] Frequency sweep measurement refers to the operation of a vector network analyzer to continuously test the frequency of a sample within a set frequency band, in order to obtain the scattering parameters of the sample at the current temperature.

[0062] The NRW algorithm is a calculation method for retrieving the dielectric parameters of a material based on scattering parameters. It is used to deduce the complex dielectric constant of the sample under test from the measured scattering parameters.

[0063] De-embedding correction refers to the error correction operation performed on the phase of the scattering parameters, which is used to eliminate the systematic errors introduced by the thermal expansion of the in-situ single-mode resonator and waveguide channel at high temperatures.

[0064] A dummy load is a water-load component in the system used to absorb the high-power microwave energy generated by the microwave source, thus preventing microwave crosstalk from damaging the electromagnetic parameter measurement module.

[0065] The initial error term refers to the set of inherent vector error parameters of the measurement link obtained after calibration using the TRL calibration method. It is used to eliminate systematic errors in the measurement link and ensure the accuracy of scattering parameter measurement. The set of error parameters generated by performing full two-port vector error calibration on the measurement link, which includes waveguide channels and waveguide coaxial converters, is the initial error term.

[0066] The preset heating curve refers to the curve of sample heating temperature changing with time as preset by the central measurement and control module. It is used to control the microwave source to heat the sample according to the target rhythm. The temperature rise response data of the sample under different microwave powers is measured in advance through experiments. Combined with system safety and experimental target requirements, a complete temperature-time change relationship is planned and imported into the system, which is the preset heating curve.

[0067] Sample temperature refers to the real-time temperature of the sample under test inside the in-situ single-mode resonant cavity, used to determine whether a measurement command is triggered; temperature data is collected in real time by a temperature sensor deployed inside the resonant cavity, and the collected real-time value is the sample temperature.

[0068] Scattering parameters refer to the microwave transmission and reflection characteristic parameters of a sample measured by a vector network analyzer, which are used to invert and calculate the complex permittivity of the sample. The microwave transmission and reflection coefficient parameters measured by the vector network analyzer under measurement conditions are the scattering parameters.

[0069] Preset temperature points refer to the target temperature values ​​of the sample for which dielectric parameter measurements need to be performed, which are used to determine the measurement nodes. By planning the actual application temperature range of the sample to be tested, or by determining the key temperature nodes based on the material characteristics analysis, and then entering these target temperature values ​​into the system, these are the preset temperature points.

[0070] The complex permittivity is a core parameter characterizing the microwave dielectric properties of a sample under test, reflecting its microwave energy absorption and polarization capabilities. The complex permittivity is calculated by inverting the measured scattering parameters using the NRW algorithm.

[0071] The waveguide thermal expansion coefficient model is a pre-existing mathematical model relating the temperature and thermal expansion deformation of waveguide components. It is used to calculate the physical dimensional changes of components at high temperatures. By experimentally measuring the dimensional deformation of waveguide materials at different temperatures, a mathematical relationship model between temperature and thermal expansion is established. This model is the waveguide thermal expansion coefficient model.

[0072] The change in physical dimensions refers to the thermal expansion deformation of the in-situ single-mode resonant cavity and waveguide channel at high temperatures, which is used to correct the phase of the scattering parameters. The deformation value obtained by calling the waveguide thermal expansion coefficient model and substituting the actual temperature value of the current system is the change in physical dimensions.

[0073] The preset sampling point temperature refers to the temperature threshold that is set in advance to trigger the system to take measurements, and is used to determine when to collect data. By designing a sampling strategy with equal or non-equal intervals for the entire experimental temperature range, a series of temperature sampling nodes are determined, which are the preset sampling point temperatures.

[0074] Reference Figure 9 As shown, in some embodiments of this application, a method for in-situ dynamic measurement of dielectric properties in microwave heating based on waveguide switching is also provided, including: The rotors of both the first and second waveguide cross switches are rotated to the second position, and the measurement link is calibrated using the TRL calibration method to obtain the initial error term, which is then stored in the central measurement and control module.

[0075] Specifically, when performing full two-port vector error calibration of the measurement link based on the TRL calibration method, it includes: The in-situ single-mode resonant cavity is removed, and a through component, a reflector, and a delay line standard component are sequentially connected to the position of the in-situ single-mode resonant cavity. The measurement link includes: the waveguide channel, the first waveguide coaxial converter, and the second waveguide coaxial converter.

[0076] It is understandable that rotating the rotors of both the first and second waveguide cross switches to the second position switches switches the system to measurement mode, ensuring complete connectivity of the measurement link and physical blocking of the heating path. This guarantees that the calibration signal is transmitted only along the measurement link. Removing the in-situ single-mode resonant cavity and sequentially connecting the through-hole, reflector, and delay line standard at this location is because TRL calibration requires eliminating interference between the resonant cavity and the sample under test. Calibration is performed only on the measurement link itself, which includes the waveguide channel, the first waveguide coaxial converter, and the second waveguide coaxial converter. Furthermore, performing full two-port vector error calibration on the measurement link using the TRL calibration method can eliminate the inherent directional error and source matching issues of the measurement link. To prevent systematic errors such as load matching error and transmission tracking error from causing distortion in subsequent scattering parameter measurements and inaccurate complex dielectric constant inversion results, the initial error terms are obtained by measuring the two-port direct transmission characteristics using a through-hole device, measuring the reflection characteristics of each port using a reflector, and measuring the additional phase delay characteristics using a delay line. Then, a set of vector error parameters such as directionality, source matching, load matching, and transmission tracking are obtained by establishing a two-port error network model. The initial error terms are stored in the central measurement and control module, which can directly call these error parameters in real time to correct the collected scattering parameters during subsequent actual sample measurements. This eliminates the inherent systematic errors in the measurement link from the source and ensures the accuracy of dielectric parameter measurements.

[0077] The sample to be tested is placed at the center of the in-situ single-mode resonant cavity, and the rotors of the first waveguide cross switch and the second waveguide cross switch are rotated to the first position. Based on the preset heating curve and PID algorithm, the output power of the microwave source is adjusted to heat the sample.

[0078] It can be understood that: the sample to be tested is placed at the center of the in-situ single-mode resonant cavity, which allows the sample to be in the core region of the uniform and stable single-mode microwave field inside the resonant cavity, ensuring the uniformity of microwave heating. After the rotors of the first and second waveguide cross switches are rotated to the first position, the system switches to the heating working state. The waveguide flow channel inside the rotor connects the heating input port and the cavity connection port, and the measurement input port is physically blocked, forming a complete conductive path for microwave heating. The central measurement and control module calls the preset heating curve to extract the target temperature value at the corresponding moment, and at the same time acquires the actual temperature data of the sample in real time. The deviation between the actual temperature and the target temperature is used as the input. The PID algorithm completes the closed-loop calculation of proportional, integral, and derivative, generates an appropriate power control electrical signal, and transmits it to the microwave source. The microwave source dynamically adjusts its own microwave output power according to the electrical signal, so that the sample temperature accurately follows the change law of the preset heating curve, realizing constant temperature and controllable in-situ microwave heating of the sample.

[0079] The sample temperature is monitored in real time, and measurement commands are executed based on the sample temperature.

[0080] Specifically, when executing a measurement command based on the sample temperature, it includes: If the sample temperature is greater than or equal to the preset sampling point temperature, a measurement interruption command is executed. If the sample temperature is lower than the preset sampling point temperature, the current state is maintained and the sample temperature is measured again.

[0081] Specifically, executing the measurement interrupt instruction includes: Control the microwave source to stop outputting or switch the high-power microwave energy generated by the microwave source to a dummy load; The rotors of the first waveguide cross switch and the second waveguide cross switch are synchronously rotated to the second position within 500ms.

[0082] It can be understood that the core mechanism of temperature closed-loop feedback control, threshold logic triggering, high-energy microwave safe discharge, and rapid synchronous switching for temperature stabilization is based on real-time monitoring of sample temperature to construct a continuous feedback loop. A timing control logic is established using a preset sampling point temperature as a judgment threshold, enabling the system to automatically enter the measurement process when the sample temperature meets the target and continue heating when the target temperature is not met, ensuring that dielectric parameters are collected in situ at the target temperature, meeting the technical requirements of quasi-isothermal measurement. After triggering a measurement interruption, the high-power microwave energy from the microwave source is directed to a dummy load for absorption, relying on the principle of microwave directional transmission and energy dissipation to block high-energy... Microwaves enter the measurement path, fundamentally avoiding high-power microwave crosstalk signals and burning out the vector network analyzer. At the same time, the rotors of the first and second waveguide cross switches are synchronously rotated to the second position within 500ms. By relying on rapid switching, the heating interruption time is greatly compressed, preventing significant temperature fluctuations in the sample due to heating pauses. This ensures that the measurement is completed under quasi-isothermal conditions. Synchronous rotation ensures that the measurement paths on both sides are simultaneously turned on and the heating path is simultaneously blocked. Combined with the RF short-circuit characteristics of the choke groove, a high degree of isolation between the heating and measurement paths is achieved, providing safe and stable hardware conditions for the accurate acquisition of sample scattering parameters.

[0083] During measurement, the vector network analyzer is used to perform frequency sweep measurement on the sample to obtain the scattering parameters at the current temperature, and the scattering parameters are transmitted to the central measurement and control module.

[0084] It can be understood that, in the measurement state, the system forms a closed dual-port microwave measurement path consisting of a vector network analyzer, a first and second waveguide coaxial converter, a first and second waveguide cross switch, and an in-situ single-mode resonant cavity. The vector network analyzer continuously outputs broadband microwave test signals within a set frequency band to this path. The test signals are transmitted sequentially through the first waveguide coaxial converter and the first waveguide cross switch to the in-situ single-mode resonant cavity, where they undergo microwave polarization coupling, transmission, and reflection with the sample under test inside the cavity. The microwave signal carrying the dielectric characteristic information of the sample then flows back to the vector network analyzer through the second waveguide cross switch and the second waveguide coaxial converter. The vector network analyzer collects the amplitude and phase change data of the signal at different frequencies by frequency sweeping, and extracts scattering parameters that can characterize the microwave transmission and reflection characteristics of the sample. These scattering parameters carry the core information of the dielectric properties of the sample at the current temperature and are finally transmitted to the central measurement and control module, providing raw measurement data for subsequent dielectric parameter inversion and error correction.

[0085] Rotate the rotors of the first waveguide cross switch and the second waveguide cross switch to the first position, restore the power output of the microwave source, and continue heating to the next temperature point until all preset temperature points are measured.

[0086] It can be understood that, relying on the core mechanism of resetting and reconnecting the heating path, restoring microwave energy supply, and cyclic temperature range traversal, after rotating the rotors of the first and second waveguide cross switches to the first position, the internal waveguide flow channels of the rotors reconnect the heating input port and the cavity connection port, and the measurement input port is physically blocked. Combined with the RF short-circuit isolation characteristics of the choke slot, the system is reset from the measurement state to a high-isolation heating state, cutting off the interference path of the microwave signal to the measurement module. The central measurement and control module controls the microwave source to restore microwave power output. The high-power microwave energy is directionally transmitted to the first waveguide cross switch through the circulator and enters the in-situ single-mode resonant cavity through the cavity connection port, continuously acting on the sample to achieve microwave heating. At the same time, the module controls the output power according to the preset temperature rise curve and the PID algorithm in a closed loop, so that the sample temperature steadily rises to the next preset temperature point. After completing a single temperature point measurement, the above heating-switching-measurement process is repeated, traversing all preset temperature points one by one. Finally, the sample can complete continuous and complete in-situ dielectric dynamic measurement in the entire temperature range under the condition that there is no movement or state distortion throughout the process.

[0087] Based on the scattering parameters and the complex permittivity of the material obtained by the NRW algorithm, and by calling the pre-stored waveguide thermal expansion coefficient model, the physical size change of the in-situ single-mode resonant cavity and the waveguide channel at the current temperature is calculated. The phase of the scattering parameters is de-embedded and corrected to eliminate the system error introduced by thermal expansion.

[0088] It can be understood that: precise measurement is achieved by relying on the core mechanism of dielectric parameter inversion and phase error compensation based on thermal expansion deformation under microwave transmission theory. The scattering parameters carry the amplitude and phase characteristics of microwave transmission and reflection of the sample under test at the current temperature. The NRW algorithm is based on two-port microwave transmission theory, combined with the structural parameters of the in-situ single-mode resonant cavity and the sample thickness, to establish a mathematical model of amplitude attenuation and phase delay when electromagnetic waves pass through the sample. By solving this model, the complex permittivity that can characterize the microwave polarization and energy absorption characteristics of the sample can be obtained. Under high-temperature operating conditions, the metal structure of the in-situ single-mode resonant cavity and the waveguide channel will undergo thermal expansion. Expansion deformation alters the effective electrical length of the microwave transmission path, leading to phase drift in scattering parameters and introducing systematic errors. A pre-stored waveguide thermal expansion coefficient model incorporates a quantitative correspondence between waveguide material temperature and thermal expansion deformation. By substituting the current real-time temperature, the physical size changes of the resonant cavity and waveguide channel can be calculated. Based on this deformation value, the phase of the scattering parameters is de-embedded and corrected to compensate for the phase shift caused by thermal expansion, eliminating systematic errors caused by transmission path deformation. Ultimately, this ensures the authenticity of the scattering parameters and the accuracy of the complex permittivity inversion results, meeting the accuracy requirements for in-situ dynamic dielectric measurement under wide temperature ranges.

[0089] In the above embodiments, relying on TRL full dual-port calibration to eliminate inherent errors in the measurement link, the PID algorithm is used to achieve precise isothermal heating of the sample, the dual-switch synchronous switching within 500ms achieves quasi-isothermal measurement, the microwave energy is switched to a dummy load to ensure instrument safety, the cyclic heating measurement completes full-temperature-range data acquisition, and the NRW algorithm and thermal expansion de-embedding correction are combined to eliminate high-temperature system errors, thereby realizing in-situ, real-time, and high-precision dynamic measurement of material dielectric parameters under high-temperature and high-power conditions.

[0090] For example: Example 1 This embodiment is used to illustrate the stability and continuity of the device of the present invention in in-situ measurement of dielectric parameters of conventional high-moisture agricultural products.

[0091] Ginger was selected as the test material and prepared into a long cylindrical test sample with a thickness of d=16.93 mm. The test sample was then placed in the central region of the in-situ single-mode resonant cavity. The central measurement and control module set the scanning frequency band of the vector network analyzer to 2.6 GHz to 3.95 GHz. After the test was started, the central measurement and control module sent a synchronous switching command to the first and second waveguide cross switches, causing the rotors of the two waveguide cross switches to rotate synchronously to the measurement position within 500 ms, thereby connecting the measurement path between the vector network analyzer and the in-situ single-mode resonant cavity.

[0092] like Figure 5As shown, under the above measurement conditions, the vector network analyzer acquires the scattering parameters of the sample under test within a continuous frequency range, and the central measurement and control module calls the NRW inversion algorithm to calculate the dielectric parameters of the sample under test. The test results show that the real part of the dielectric constant of the ginger sample is 72.683 at 2.6 GHz, and shows a smooth decreasing trend with increasing frequency, decreasing to 68.610 at 3.95 GHz.

[0093] Throughout the testing process, the obtained dielectric constant frequency domain spectrum was continuous and smooth, without any obvious data breaks or abnormal jumps. This result demonstrates that the present invention, by setting a quarter-wavelength choke groove on the waveguide switch mating gap surface, can effectively suppress microwave leakage and undesired transmission modes under conditions of mechanical mating gaps, thereby improving the physical isolation between the heating and measurement paths. Simultaneously, the 500 ms synchronous rapid switching between the first and second waveguide cross switches avoids the temperature drop and moisture redistribution problems caused by sample transfer in traditional offline measurements, enabling continuous acquisition of dielectric parameters of the test material in situ under quasi-isothermal conditions.

[0094] Example 2 This embodiment illustrates the transient capture capability of the device of the present invention for materials prone to sudden changes in dielectric parameters during microwave heating, as well as its protective function for measuring instruments.

[0095] Fresh potatoes, a high-starch-based material, were selected as the test material and prepared into a test specimen with a thickness of d=11.34 mm. This specimen was then placed at the center of an in-situ single-mode resonant cavity. Under microwave conditions, this type of material is prone to abrupt changes in dielectric parameters due to factors such as localized moisture migration, changes in starch structure, and uneven temperature rise. Therefore, it is suitable for verifying the ability of the device of this invention to capture transient dielectric responses.

[0096] During the test, the central measurement and control module acquires the sample temperature signal in real time and, when the preset measurement conditions are met, controls the first and second waveguide cross switches to quickly switch from the heating state to the measurement state. Simultaneously, the central measurement and control module controls the output energy of the microwave source to switch from the in-situ single-mode resonant cavity to the water load, allowing the high-power microwave energy to be absorbed by the water load and preventing it from entering the low-power measurement branch of the vector network analyzer.

[0097] like Figure 6As shown, after the scattering parameters were collected by a vector network analyzer and inverted using the NRW algorithm, the real part of the dielectric constant of the fresh potato sample was 62.107 at 2.6 GHz, rapidly increasing to an extreme value of 63.181 at 2.647 GHz, and then gradually decreasing with increasing frequency, reaching 57.669 at 3.95 GHz. Simultaneously, the loss tangent nonlinearly increased from 0.36609 to 0.52270 in the range of 2.6 GHz to 3.95 GHz.

[0098] The above results demonstrate that the device of the present invention can switch between the heating and measurement paths in a short time and capture the rapid changes in the dielectric parameters of fresh potato samples. Furthermore, when a measurement interruption or measurement switching command is triggered, the central control module can synchronously control the position of the waveguide cross switch rotor and the microwave energy flow direction, ensuring that high-power microwave energy is introduced into the water load rather than into the vector network analyzer, thereby reducing the risk of damage to the measuring instruments caused by high-power microwave crosstalk. This proves that the device of the present invention can not only acquire high transient dielectric parameter data but also has high hardware security.

[0099] Example 3 This embodiment illustrates the phase error correction capability of the device of the present invention in broadband dielectric parameter measurement of thick dielectric samples.

[0100] A radish sample with a relatively large thickness was selected as the test material and prepared into a test block with a thickness of d=28.61 mm, which was then placed in the center of the in-situ single-mode resonant cavity. Since thick dielectric samples are prone to microwave transmission phase winding during broadband testing, and conventional dielectric parameter inversion methods are easily affected by phase multivalues, resulting in divergence points or abnormal inversion results, this embodiment is used to verify the phase de-embedding correction effect of the system of the present invention.

[0101] During testing, the central control module controlled the vector network analyzer to acquire scattering parameters of the sample under test within the 2.6 GHz to 3.95 GHz frequency band, and simultaneously obtained the temperature information of the in-situ single-mode resonator and waveguide channel. Based on a pre-stored waveguide thermal expansion coefficient model, the central control module calculated the changes in the physical dimensions of the in-situ single-mode resonator and waveguide channel under the current temperature conditions, and accordingly de-embedding the phase term in the scattering parameters. The corrected scattering parameters were then input into the NRW inversion algorithm to obtain the dielectric parameters of the radish sample.

[0102] like Figure 7As shown, within the 2.6 GHz to 3.019 GHz frequency band, the real part of the dielectric constant of the radish sample only fluctuates slightly within the range of 69.635 to 69.580. As the frequency continues to increase, the real part of the dielectric constant gradually converges, decreasing to 67.393 at 3.95 GHz. Meanwhile, the loss tangent remains stable between 0.306 and 0.334 within the wide bandwidth of the 2.6 GHz to 3.95 GHz test range, exhibiting a low overall slope.

[0103] Depend on Figure 7 As can be seen, the obtained broadband dielectric parameter spectrum exhibits good continuity and consistency, without any obvious divergence points caused by phase winding or phase multivalence. This result demonstrates that the present invention, by introducing a waveguide thermal expansion coefficient model into the central measurement and control module and performing temperature-related phase de-embedding correction on the scattering parameters, can effectively compensate for the changes in transmission electrical length caused by variations in the physical dimensions of the waveguide channel and resonant cavity during high-temperature or wide-temperature-range testing, thereby reducing phase drift errors and improving the accuracy and stability of broadband dielectric parameter inversion for thick dielectric samples.

[0104] It should be noted that: Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this application may be practiced without these specific details. In some instances, well-known structures and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0105] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of this application and form different embodiments.

[0106] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching, characterized in that, include: A waveguide cross switch switching module includes a first waveguide cross switch and a second waveguide cross switch. The waveguide cross switch switching module is based on the choke groove cutting off the transmission mode of microwaves in the mating gap. An in-situ single-mode resonant cavity is electrically connected to the waveguide cross switch switching module. One end of the in-situ single-mode resonant cavity is connected to the cavity connection port of the first waveguide cross switch, and the other end of the in-situ single-mode resonant cavity is connected to the cavity connection port of the second waveguide cross switch. A microwave heating module is electrically connected to the waveguide cross switch switching module. The microwave heating module includes a microwave source, a circulator, and a water load. The output terminal of the microwave source is connected to the input terminal of the circulator, the output terminal of the circulator is connected to the heating input port of the first waveguide cross switch, and the isolation terminal of the circulator is connected to the water load. An electromagnetic parameter measurement module is electrically connected to the waveguide cross switch switching module. The electromagnetic parameter measurement module includes a vector network analyzer, a first waveguide coaxial converter, and a second waveguide coaxial converter. The first test port of the vector network analyzer is connected to the measurement input port of the first waveguide cross switch; the second test port of the vector network analyzer is connected to the measurement input port of the second waveguide cross switch. The central measurement and control module is electrically connected to the waveguide cross switch switching module, the in-situ single-mode resonant cavity, the microwave heating module, and the electromagnetic parameter measurement module, respectively. The central measurement and control module controls the switching between the heating state and the measurement state.

2. The microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching according to claim 1, characterized in that, The first waveguide cross switch and the second waveguide cross switch have the same structure; Both the first waveguide cross switch and the second waveguide cross switch include a stator, a rotor, and a stepper motor drive unit; The stator is provided with four waveguide ports arranged in a cross shape; The rotor has a waveguide channel inside.

3. The microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching according to claim 2, characterized in that, The four waveguide ports include: the heating input port, the cavity connection port, the measurement input port, and the load port; The choke groove is formed on the mating clearance surface between the stator and the rotor; The depth of the choke groove is one-quarter of a wavelength.

4. The microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching according to claim 3, characterized in that, The first test port of the vector network analyzer is connected to the measurement input port of the first waveguide cross switch through the first waveguide coaxial converter; The second test port of the vector network analyzer is connected to the measurement input port of the second waveguide cross switch via the second waveguide coaxial converter.

5. The microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching according to claim 4, characterized in that, When the central control module controls the switching between heating and measurement states, it includes: The central measurement and control module is electrically connected to the microwave source, the vector network analyzer, and the stepper motor drive unit, respectively. The central measurement and control module controls the rotor to rotate to the first position. The waveguide channel connects the heating input port and the cavity connection port. The measurement input port is physically blocked. Microwave energy enters the in-situ single-mode resonant cavity through the first waveguide cross switch. At this time, the measurement system is in a heating state. The central measurement and control module controls the rotor to rotate to the second position. The waveguide channel connects the measurement input port and the cavity connection port. The heating input port is physically blocked. The test signal of the vector network analyzer passes through the first waveguide cross switch and the second waveguide cross switch, and passes through the in-situ single-mode resonant cavity. At this time, the measurement system is in the measurement state.

6. A method for in-situ dynamic measurement of dielectric properties in microwave heating based on waveguide switching, characterized in that, The microwave heating in-situ dielectric dynamic measurement system based on waveguide switch switching as described in any one of claims 1-5 includes: The rotors of the first waveguide cross switch and the second waveguide cross switch are both rotated to the second position, and the measurement link is calibrated using the TRL calibration method to obtain the initial error term, which is then stored in the central measurement and control module. The sample to be tested is placed at the center of the in-situ single-mode resonant cavity, and the rotors of the first waveguide cross switch and the second waveguide cross switch are rotated to the first position. Based on the preset heating curve and PID algorithm, the output power of the microwave source is adjusted to heat the sample. The sample temperature is monitored in real time, and measurement commands are executed based on the sample temperature. In the measurement state, the vector network analyzer is used to perform frequency sweep measurement on the sample to obtain the scattering parameters at the current temperature, and the scattering parameters are transmitted to the central measurement and control module; Rotate the rotors of the first waveguide cross switch and the second waveguide cross switch to the first position, restore the power output of the microwave source, and continue heating to the next temperature point until all preset temperature points are measured. Based on the scattering parameters and the complex permittivity of the material obtained by the NRW algorithm, and by calling the pre-stored waveguide thermal expansion coefficient model, the physical size change of the in-situ single-mode resonant cavity and the waveguide channel at the current temperature is calculated. The phase of the scattering parameters is de-embedded and corrected to eliminate the system error introduced by thermal expansion.

7. The method for in-situ dynamic measurement of dielectric properties in microwave heating based on waveguide switch switching according to claim 6, characterized in that, When performing full two-port vector error calibration of the measurement link based on the TRL calibration method, it includes: The in-situ single-mode resonant cavity is removed, and a through-hole component, a reflector component, and a delay line standard component are sequentially connected to the position of the in-situ single-mode resonant cavity.

8. The method for in-situ dynamic measurement of dielectric properties in microwave heating based on waveguide switch switching according to claim 7, characterized in that, The measurement link includes: the waveguide channel, the first waveguide coaxial converter, and the second waveguide coaxial converter.

9. The method for in-situ dynamic measurement of dielectric properties in microwave heating based on waveguide switch switching according to claim 8, characterized in that, When executing a measurement command based on the sample temperature, it includes: If the sample temperature is greater than or equal to the preset sampling point temperature, a measurement interruption command is executed. If the sample temperature is lower than the preset sampling point temperature, the current state is maintained and the sample temperature is measured again.

10. The method for in-situ dynamic measurement of dielectric properties in microwave heating based on waveguide switch switching according to claim 9, characterized in that, When executing a measurement interrupt instruction, the following are included: Control the microwave source to stop outputting or switch the high-power microwave energy generated by the microwave source to a dummy load; The rotors of the first waveguide cross switch and the second waveguide cross switch are synchronously rotated to the second position within 500ms.

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