A uniform electric field cavity design method for a single-mode liquid microwave resonant cavity

Abstract

The present invention discloses a method for designing a uniform electric field cavity of a single-mode liquid microwave resonant cavity, which belongs to the field of microwave heating technology. Starting from the dielectric properties of the liquid medium, the present invention designs a numerical simulation model of the single-mode liquid resonant cavity. First, the dielectric properties of the liquid medium are measured by the temperature reduction method to determine the thickness of the single-mode microwave heating cavity; then, the length and width of the simple model of the microwave resonant cavity are further determined by parametric scanning; the tapered waveguide design is further introduced to expand the microwave coverage range; finally, the single-mode microwave liquid resonant cavity is determined to be suitable for point frequency or variable frequency by frequency scanning. The present invention can effectively determine the optimal resonant cavity size and its limitations of a device that uses microwave energy as energy at a certain frequency, and can effectively improve the uniformity of the spatial distribution of the microwave electric field of the microwave liquid single-mode resonant cavity in the resonant cavity. The present invention provides technical support for the subsequent utilization of microwave energy and the development of microwave equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave heating, and in particular relates to a cavity design method for a single-mode microwave liquid resonant cavity. Background Art

[0002] The microwave field is invisible and heats unevenly, which severely limits the application of microwave technology. Single-mode resonant cavities have advantages that multi-mode resonant cavities cannot match: the thermal profile is relatively stable and the heating pattern is predictable. However, there are currently few designs for single-mode resonant cavities, and the distribution and uniformity of the electric field need to be improved. To further promote the development of microwaves in the industrial field, it is urgent to establish a method to regulate the application process of microwave resonant cavities. Currently, the control schemes for microwave fields are mainly limited to the air domain, rather than liquid resonant cavities. In addition, the design process of single-mode liquid resonant cavities in the existing technology still has some imperfections that need to be addressed. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for designing a uniform electric field cavity of a single-mode liquid microwave resonant cavity to remedy the problems of the prior art.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] The present invention designs a numerical simulation model of a single-mode liquid resonant cavity based on the dielectric properties of the liquid medium. First, the dielectric properties of the liquid medium are measured by a temperature reduction method to determine the thickness of the single-mode microwave heating cavity. Then, a parametric sweep is used to further determine the length and width of a simple model of the microwave resonant cavity. A tapered waveguide design is further introduced to expand the microwave coverage range. Finally, a frequency sweep is performed to determine whether the single-mode microwave liquid resonant cavity is suitable for point frequency or variable frequency.

[0006] A method for designing a uniform electric field cavity of a single-mode liquid microwave resonant cavity comprises the following specific steps:

[0007] S1: Determine the microwave frequency band f;

[0008] S2: Collect the dielectric constant of the liquid medium within the frequency range of ±20MHz. The temperature should include 90℃. When collecting, raise the temperature of the liquid medium to 95℃±2℃, remove the bubbles at the position of the dielectric characteristic probe, and naturally reduce the temperature over time.

[0009] Temperature, record the temperature and the dielectric constant and dielectric loss at that temperature;

[0010] S3: Calculate the wavelength of the microwave in the f-band in the liquid medium according to the wavelength formula;

[0011] When electromagnetic waves enter a liquid medium from a vacuum medium, their speed changes. At this time, the frequency of the electromagnetic waves does not change, but the wavelength changes. Since the electromagnetic wave speed v in the medium is the same as the wave speed in a vacuum, According to the relationship between microwave frequency and speed, the following formula can be obtained:

[0012]

[0013] Most foods are non-magnetic media, and for non-magnetic media, μ≈1. Therefore, the refractive index in food media is At this time, the speed of electromagnetic waves in the medium is The wavelength of electromagnetic waves in the medium is calculated as follows:

[0014]

[0015] Where c is the speed of light, which is 3×10 8 m / s; is the frequency of microwaves, in Hz; ε′ is the dielectric constant.

[0016] S4: According to the definition of a single-mode cavity, a single-mode cavity is formed when one of its length, width, and height dimensions is smaller than the wavelength of the microwave in the cavity medium. This creates a relatively stable electric field distribution and microwave heating pattern. To facilitate microwave processing of materials using a microwave cavity, the limiting factor for a single-mode cavity is generally set to the thickness of the microwave cavity. The thickness of the microwave cavity is determined based on the calculation of the microwave wavelength in the liquid medium in S3. Varying water quality may cause slight variations in the wavelength of microwaves in different water qualities. To account for these variations in water quality, the maximum thickness range is wavelength * 95%. Furthermore, based on the results of previous experimental electric field analysis and considerations of space and microwave energy utilization in mechanical design, the minimum thickness of the microwave field is set at wavelength * 80%. Therefore, the thickness of the microwave cavity is specified as λ * (80% to 95%).

[0017] S5: Select the rectangular waveguide specifications according to the microwave frequency and the relevant specifications of Hollow Metal Waveguide Part 2: Ordinary Rectangular Waveguide (GB / T11450.2-1989).

[0018] S6: Create a simple model consisting of only a rectangular waveguide, a microwave window, and a microwave resonant cavity.

[0019] S7: Perform a parametric sweep of the phases of the upper and lower microwave sources in a simple model to analyze the distribution of the microwave electric field within the resonant cavity. For most microwave applications, the microwave electric field should be distributed in the geometric center of the microwave single-mode device to facilitate the placement and removal of food. Therefore, when evaluating the phase effect, the dispersion, concentration, and intensity of the microwave electric field should be studied first.

[0020] The specific steps of determining the phase influence are as follows:

[0021] (1) Scan the initial phase, set the initial phase to prot, its range is 0~2pi, and the scanning step is pi / 4.

[0022] (2) Set the upper phase to prot + prot_1 and the lower phase to port. The range of prot_1 is 0 to 2pi, and the scan step is pi / 4. The scan range of prot is set to 0 to 2pi. Because the upper and lower microwave sources in this simple model are completely symmetrical, the phases of the upper and lower microwave sources can be swapped without affecting the results.

[0023] S8: Perform a parametric sweep of the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane. The long side of the rectangular waveguide is set to 1 unit a, the short side is set to 1 unit b, and half the wavelength (λ / 2) of a microwave at a certain frequency in a liquid medium is defined as a unit, represented by the letter c. The sweep parameters are as follows:

[0024] Table 1 Parametric sweep settings for microwave heating cavity length, width, and thickness

[0025]

[0026] S9: In order to reduce the application cost of microwave technology, in addition to being applicable to microwave sources with adjustable phase, the present invention also supplements the technical solution of using mechanical rectangular waveguides to control the phase. Calculate the waveguide wavelength at this frequency using the following formula 3. Add a height of λ on one side of the resonant cavity. g / 2 rectangular waveguide, the microwave in the resonant cavity will change half the phase cycle (2*pi).

[0027]

[0028] S10: Introduce a tapered waveguide. The schematic diagram of the tapered waveguide is as follows Figure 3 As shown, Figure 3 A is a picture of the actual processing of the tapered waveguide; Figure 3 B is the numerical simulation geometric model of the tapered waveguide. Figure 4 As shown, a vertically symmetrical microwave resonant cavity is established. Figure 5 The numerical simulation geometry model design shows the location of rectangular waveguide, tapered waveguide, microwave window, microwave heating cavity, and food. Figure 4The geometry shown in the Microwave Heating Module adds the microwave field as a physics field based on Maxwell's equations, and the study type is set to frequency domain. Similarly, the length of the rectangular waveguide specified in the national standard is defined as a, and the width of the rectangular waveguide is defined as b. The microwave window's primary function is to allow microwaves emitted by the microwave source to enter the rectangular waveguide and pass through it, thereby entering the microwave resonant cavity. Therefore, the size of the microwave window affects the electric field distribution within the heating cavity.

[0029] S11: Parametric sweeps are established for the length and width of the microwave window: Parametric sweeps are performed for the microwave window length (1.0a to 2.5a), width (0.5b to 1.5b), and height of the tapered waveguide. Similarly, the long side of the rectangular waveguide is set to 1 unit a, and the short side of the rectangular waveguide is set to 1 unit b.

[0030] Specifically, S11-1 sets the microwave window width to 1.0 Å and performs a parametric sweep of the length, defining the parameters as range (1.0 Å, 0.5 Å, 2.5 Å) and 1.75 Å, 2.15 Å, 2.25 Å, and 2.35 Å. Based on the electric field distribution and actual application requirements, an optimal microwave window length and several alternative, better microwave window lengths are determined.

[0031] S11-2 fixes the microwave window length and performs parameter sweep on the microwave window width, with the parameter set to range (0.5b, 0.1b, 1.5b). The microwave window width is determined based on actual sample production needs and energy utilization.

[0032] After the length and width of S11-3 are determined, a parameter scan is performed on the height of the tapered waveguide. The parameter scan range and step size are range (0.25a, ​​0.25a, ​​2a). The height of the tapered waveguide is selected according to the electric field distribution and reflection conditions.

[0033] Furthermore, the design method also includes S12: exploring the impact of microwave frequency changes on electric field distribution, and determining whether to use point-frequency microwaves or band-frequency microwaves. Exploring the impact of frequency fluctuations within the specified frequency range of f±20MHz on electric field distribution, the judgment is based on the electric field distribution and reflection conditions in the XY plane at Z=0. The microwave heating cavity size is set to the above-mentioned optimal microwave resonant cavity x*y*z, the microwave window size is set to wx*wy, and the horn height is set to hh. The frequency scanning scheme is set to range (f-20, 5, f±20) in MHz.

[0034] Furthermore, the numerical simulation models are mainly finite element method (FEM), finite difference time domain method (FDTD) and method of moments (MoM). Especially for microwave heating problems, finite element method (FEM) and finite difference time domain (FDTD) are the two most widely used methods. Current simulation software is mainly divided into finite element software and finite difference time domain software. Commercial software such as QuickwaveTM (QWED, Poland), Ansys (ANSYS, Pennsylvania, USA) and COMSOL Multiphysics (COMSOL multiphysics, Sweden) use the same method to simulate heat transfer and Maxwell's equations. The above software differs in the choice of numerical methods.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention performs highly accurate dielectric property measurements on liquid single-mode resonant cavities, specifies specific steps for designing such cavities, visualizes the electric field distribution, and achieves optimal cavity design for liquid single-mode resonants. This invention can effectively determine the optimal cavity dimensions and limitations for microwave-powered devices at a specific frequency, and can effectively improve the uniformity of the microwave electric field distribution within the resonant cavity of a microwave liquid single-mode resonant cavity. This invention provides technical support for the subsequent utilization of microwave energy and the development of microwave equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a numerical simulation geometric model of a simplified microwave heating cavity model.

[0038] Figure 2 is the composition of the simplified model of the microwave heating cavity. Figure 2 A is a rectangular waveguide, Figure 2 B is the microwave window, Figure 2 C is the microwave heating cavity (also called microwave resonant cavity).

[0039] Figure 3 It is the entity diagram and numerical simulation geometric model of the tapered waveguide. Figure 3 A is a tapered waveguide entity, Figure 3 B is the tapered waveguide geometric model.

[0040] Figure 4 This is the numerical simulation geometric model of the microwave heating module.

[0041] Figure 5 The composition of the microwave heating module containing a tapered waveguide. Figure 5 A is a rectangular waveguide, Figure 5 B is a tapered waveguide, Figure 5 C is the microwave window, Figure 5 D is the microwave heating cavity (also called the resonant cavity), Figure 5 E is the location of the food.

[0042] Figure 6 The dielectric properties of water at 433 MHz and 915 MHz are measured using the cooling method. Figure 6 A is the dielectric constant, Figure 6 B is the dielectric loss.

[0043] Figure 7 The dielectric properties of water at 433 MHz and 915 MHz are measured using the conventional heating method. Figure 7 A is the dielectric constant, Figure 7 B is the dielectric loss.

[0044] Figure 8 Figure 8 shows the effect of a 433 MHz microwave on the electric field distribution (heating pattern) when the phase difference between the upper and lower microwave sources is pi. 8A shows the electric field distribution in the XY plane, 8B shows the electric field distribution in the YZ plane, and 8C shows the electric field distribution in the XZ plane.

[0045] Figure 9 Figure 9 shows the effect of a 433 MHz microwave on the electric field distribution (heating mode) when the phase difference between the upper and lower microwave sources is 0. 9A shows the electric field distribution in the XY plane, 9B shows the electric field distribution in the YZ plane, and 9C shows the electric field distribution in the XZ plane.

[0046] Figure 10 Figure 10A shows the electric field distribution (heating pattern) when the phase difference between the upper and lower microwave sources is pi / 2. 10B shows the electric field distribution in the YZ plane, and 10C shows the electric field distribution in the XZ plane.

[0047] Figure 11 The electric field distribution of a 433MHz microwave using a BJ5 waveguide and a resonant cavity thickness of 80mm (89.14% of the wavelength) is shown in Figure 11A. The electric field distribution in the XY plane is shown in Figure 11B. The electric field distribution in the YZ plane is shown in Figure 11C.

[0048] Figure 12 The electric field distribution of a 433MHz microwave using a BJ5 waveguide and a resonant cavity thickness of 107.7mm (120% of the wavelength) is shown in Figure 12A, where 12B is the electric field distribution in the YZ plane, and 12C is the electric field distribution in the XZ plane.

[0049] Figure 13This is the electric field distribution when the 433MHz microwave uses the BJ5 waveguide and the microwave window width is 1.0b, where 13A is the electric field distribution in the XY plane; 13B is the electric field distribution in the YZ plane; and 13C is the electric field distribution in the XZ plane.

[0050] Figure 14 This is the electric field distribution when the BJ5 waveguide is used for 433MHz microwave and the microwave window width is 0.5b, where 14A is the electric field distribution in the XY plane; 14B is the electric field distribution in the YZ plane; and 14C is the electric field distribution in the XZ plane.

[0051] Figure 15 This is the electric field distribution when the BJ5 waveguide is used for 433MHz microwave and the microwave window is 1.2b, where 15A is the electric field distribution in the XY plane; 15B is the electric field distribution in the YZ plane; and 15C is the electric field distribution in the XZ plane.

[0052] Figure 16 This shows how the reflection changes with microwave frequency in the range of 433MH±20MHz, where the multi-excitation reflection coefficient component 1 is the upper microwave source and the multi-excitation reflection coefficient component 2 is the lower microwave source.

[0053] Figure 17 This is the effect of microwave frequency in the range of 433MHz±20MHz on the electric field distribution (heating mode).

[0054] Figure 18 The electric field distribution of a 915 MHz microwave using a BJ8 waveguide with a resonant cavity of 40 mm (wavelength 94.11%) is shown in Figure 18A, where 18B is the electric field distribution in the YZ plane, and 19C is the electric field distribution in the XZ plane.

[0055] Figure 19 The electric field distribution of a 915 MHz microwave resonant cavity using a BJ8 waveguide with a thickness of 30 mm (71% of the wavelength) is shown in Figure 19A, where 19B is the electric field distribution in the YZ plane, and 19C is the electric field distribution in the XZ plane.

[0056] Figure 20 This is the electric field distribution when the thickness of the 915MHz microwave resonant cavity using the BJ8 waveguide is 47mm (111% of the wavelength). Figure 20 A is the electric field distribution in the XY plane; Figure 20 B is the electric field distribution in the YZ plane; Figure 20 C is the electric field distribution in the XZ plane.

[0057] Figure 21The electric field distribution of a 915MHz microwave resonant cavity with a thickness of 36mm (84.59%) using a BJ9 waveguide is shown in Figure 21A, where 21B is the electric field distribution in the YZ plane, and 21C is the electric field distribution in the XZ plane.

[0058] Figure 22 This is the electric field distribution when the thickness of the 915MHz microwave resonant cavity using the BJ9 waveguide is 30mm (71% of the wavelength), where 22A is the electric field distribution in the XY plane; 22B is the electric field distribution in the YZ plane; and 22C is the electric field distribution in the XZ plane.

[0059] Figure 23 The electric field distribution of a 915 MHz microwave resonant cavity using a BJ9 waveguide with a thickness of 47 mm (111% of the wavelength) is shown in Figure 1. A is the electric field distribution in the XY plane; B is the electric field distribution in the YZ plane; and C is the electric field distribution in the XZ plane.

[0060] Figure 24 The effect of a microwave window width of 14 mm (88% of the wavelength) on the electric field distribution when using a BJ22 waveguide for 2450 MHz microwaves. 24A is the electric field distribution in the XY plane; 24B is the electric field distribution in the YZ plane; and 24C is the electric field distribution in the XZ plane.

[0061] Figure 25 The effect of a microwave window width of 17 mm (106% of the wavelength) on the electric field distribution when using a BJ22 waveguide for 2450 MHz microwaves. 25A is the electric field distribution in the XY plane; 25B ​​is the electric field distribution in the YZ plane; and 25C is the electric field distribution in the XZ plane.

[0062] Figure 26 The effect of a microwave window width of 14 mm (88% of the wavelength) on the electric field distribution when using a BJ26 waveguide for 2450 MHz microwaves. 26A is the electric field distribution in the XY plane; 26B is the electric field distribution in the YZ plane; and 26C is the electric field distribution in the XZ plane.

[0063] Figure 27 When using BJ26 waveguide for 2450MHz microwave, the microwave window width is 17.5mm (110% of the wavelength) and the influence on the electric field distribution is shown. Figure 27 A is the electric field distribution in the XY plane; Figure 27 B is the electric field distribution in the YZ plane; Figure 27 C is the electric field distribution in the XZ plane. DETAILED DESCRIPTION

[0064] The technical solution of the present invention is further described below with reference to the embodiments and drawings.

[0065] Example 1: For microwaves in the 433MHz and 915MHz frequency bands, the dielectric constant of water was measured using the cooling method. The dielectric constant and dielectric loss results are shown in the figure below: Figure 6 The specific operation steps are as follows, among which step S2 is closely related to this embodiment.

[0066] S1 determines the microwave frequencies f to be 433 MHz and 915 MHz.

[0067] S2 collects the dielectric constant of the medium at a frequency of 433 MHz, with a temperature of 90°C. During the collection process, the medium temperature is raised to approximately 95°C and then naturally cooled down over time.

[0068] S2-1 Specifically, use a beaker or other glass container, measure 500 mL of purified water, and cover the container with a sealing film to prevent water vapor loss due to temperature rise.

[0069] S2-2 Place the beaker containing purified water in a heatable water bath, and place a temperature probe in the lower middle part of the purified water. An optical fiber or other temperature measuring device can be used.

[0070] S2-3 uses a vector network analyzer (E5071C, 8417E, or other equivalent network analyzer) and a probe (85070B, N1501A, or other equivalent probe) for calibration. Calibrate the instrument using air, a metal correction module, and 25°C deionized water.

[0071] S2-4 Gradually raise the temperature of the purified water to 95°C and place the dielectric properties measurement probe in the water. Use a gentle plastic rod that will not scratch the probe to remove any bubbles formed in the water around the probe.

[0072] S2-5: Stop heating the water bath and allow the purified water in the beaker to cool naturally. Record the real-time temperature change. Use a network analyzer and probe to collect the dielectric constant and dielectric loss of the purified water in the 413MHz-443MHz and 895MHz-925MHz ranges. Match the temperature to the dielectric constant and dielectric loss at that moment.

[0073] S3: According to formula 2, the wavelength of microwaves in the 433MHz frequency band in purified water is 89.75mm, and the wavelength of microwaves in the 915MHz frequency band in purified water is 42.56mm.

[0074] S4: Based on the formation principle of single-mode cavities and the actual application scenarios of microwave resonant cavities, the thickness of the 433MHz resonant cavity is set as the limiting factor. The thickness range is wavelength * (80% to 95%), which is 71.80mm to 86.26mm. The thickness of the 915MHz resonant cavity is set to 34.08mm to 40.32mm.

[0075] S5: According to the microwave frequency and the relevant specifications of Hollow Metal Waveguide Part 2: Ordinary Rectangular Waveguide (GB / T11450.2-1989), the 433MHz rectangular waveguide specification is selected as BJ5, and the 915MHz rectangular waveguide is selected as BJ8 or BJ9 waveguide.

[0076] S6: Create a simple model with only rectangular waveguide, microwave window, and microwave resonant cavity (such as Figure 1 In addition, Figure 2 This figure shows the distribution of rectangular waveguide, microwave window and microwave heating cavity in a simple model. Here, the phase difference design of pi is realized by using the waveguide wavelength / 2. Figure 1 Numerical simulation model of a simple rectangular waveguide shown.

[0077] S7: Perform a parametric sweep of the phases of the upper and lower microwave sources in a simple model to analyze the distribution of the microwave electric field within the resonant cavity. For most microwave applications, the microwave electric field should be distributed in the geometric center of the microwave single-mode device to facilitate the placement and removal of food. Therefore, when evaluating the phase effect, the dispersion, concentration, and intensity of the microwave electric field should be studied first.

[0078] The specific steps to determine the phase impact are as follows:

[0079] (1) Scan the initial phase, set the initial phase to prot, its range is 0~2pi, and the scanning step is pi / 4.

[0080] (2) Set the upper phase to prot+prot_1 and the lower phase to port. The range of prot_1 is 0 to 2pi, and the scanning step is pi / 4. The scanning range of prot is set to 0 to 2pi.

[0081] S8: Perform a parametric sweep of the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane. For 433MHz microwaves: The long side of the rectangular waveguide is set to 1 unit a (457.2mm), the short side of the rectangular waveguide is set to 1 unit b (228.6mm), and half the wavelength of the microwave at a certain frequency in the liquid medium (λ / 2, 4.88mm) is defined as a unit, represented by the letter c. The sweep parameters are as follows:

[0082]

[0083] For 915MHz microwaves (using BJ8 as an example): the length of the long side of the rectangular waveguide is set to 1 unit a (292.1mm), the short side of the rectangular waveguide is set to 1 length unit b (146.05mm), and half the wavelength of microwaves at a certain frequency in a liquid medium (λ / 2, 21.28mm) is defined as a unit, represented by the letter c. The scanning parameters are as follows:

[0084]

[0085] S9: In order to reduce the application cost of microwave technology, in addition to the microwave source with adjustable phase, the following supplements the technical solution of using mechanical rectangular waveguide to control the phase. Calculate the waveguide wavelength at 433MHz. According to the following formula 3, the waveguide wavelength is 1065.1mm. Add a height of λ on one side of the resonant cavity. g / 2 (532.55mm) rectangular waveguide, the microwave in the resonant cavity will change half the phase cycle (pi).

[0086]

[0087] Calculate the waveguide wavelength at 915MHz. According to formula 3, the waveguide wavelength at 915MHz is 303.36mm. Add a height of λ on one side of the resonant cavity. g / 2 (151.68mm) rectangular waveguide. The microwaves in the resonant cavity will change by half a phase cycle (pi).

[0088] S10: Introduce a tapered waveguide. The schematic diagram of the tapered waveguide is as follows Figure 3 As shown, Figure 3 A is a picture of the actual processing of the tapered waveguide; Figure 3 B is the numerical simulation geometric model of the tapered waveguide. Figure 4 As shown, a vertically symmetrical microwave resonant cavity is established. Figure 5 The numerical simulation geometry model design shows the location of rectangular waveguide, tapered waveguide, microwave window, microwave heating cavity, and food. Figure 4 The microwave heating module geometry shown in the figure uses Maxwell's equations as a physics field, with the study type set to frequency domain. Similarly, the length of the rectangular waveguides for the 433 MHz and 915 MHz frequencies specified in the national standard is defined as a, and the width of the rectangular waveguide is defined as b. The microwave window's primary function is to allow microwaves emitted by the microwave source to enter the rectangular waveguide and pass through it, thereby entering the microwave resonant cavity where the food is heated. Therefore, the size of the microwave window affects the electric field distribution within the heating cavity.

[0089] S11: Parametric sweeps are established for the length and width of the microwave window: Parametric sweeps are performed for the microwave window length (1.0a to 2.5a), width (0.5b to 1.5b), and height of the tapered waveguide. Similarly, the long side of the rectangular waveguide is set to 1 unit a, and the short side of the rectangular waveguide is set to 1 unit b.

[0090] Specifically, S11-1 sets the microwave window width to 1.0 Å and performs a parametric sweep of the length, defining the parameters as range (1.0 Å, 0.5 Å, 2.5 Å) and 1.75 Å, 2.15 Å, 2.25 Å, and 2.35 Å. Based on the electric field distribution and actual application requirements, an optimal microwave window length and several alternative, better microwave window lengths are determined.

[0091] S11-2 fixes the microwave window length and performs parameter sweep on the microwave window width, with the parameter set to range (0.5b, 0.1b, 1.5b). The microwave window width is determined based on actual sample production needs and energy utilization.

[0092] After the length and width of S11-3 are determined, a parameter scan is performed on the height of the tapered waveguide. The parameter scan range and step size are range (0.25a, ​​0.25a, ​​2a). The height of the tapered waveguide is selected according to the electric field distribution and reflection conditions.

[0093] S12: Using the above-mentioned optimal microwave heating cavity length, width, and thickness, and the optimal tapered waveguide height, a frequency sweep is performed, where the frequency sweep scheme is defined as range (413 MHz, 5 MHz, 443 MHz).

[0094] The specific results of the cooling method are as follows: Figure 6 shown. Figure 6 Figure A shows the temperature variation of purified water. At 433MHz and 915MHz, the dielectric constant and dielectric loss of both devices change relatively steadily, showing a good pattern. This is consistent with research on the dielectric constant and dielectric loss of related water media. The dielectric constant shows a relatively stable and uniform decrease with increasing temperature. The dielectric loss gradually decreases with increasing temperature and gradually stabilizes with further temperature increases.

[0095] Comparative Example 1:

[0096] Using the temperature rising method: directly measure the dielectric constant of water at 433MHz.

[0097] The same research steps as in Example 1 were used, and the temperature was increased at S2. Specifically:

[0098] S2 collects the dielectric constant of the medium at a frequency of 433 MHz, and the temperature is inclusive of 90°C.

[0099] S2-1 Specifically, use a beaker or other glass container, measure 500 mL of purified water, and cover the container with a sealing film to prevent water vapor loss due to temperature rise.

[0100] S2-2 Place the beaker containing purified water in a heatable water bath, and place a temperature probe in the lower middle part of the purified water. An optical fiber or other temperature measuring device can be used.

[0101] S2-3 uses a vector network analyzer (E5071C, 8417E, or other capable network analyzer) and a probe (85070B, N1501A, or other capable probe) for calibration. Calibrate the instrument using air, a metal correction module, and 25°C deionized water.

[0102] S2-4 gradually raises the temperature of the purified water to 95°C and records the temperature change in real time. Use a network analyzer and a probe to collect the dielectric constant and dielectric loss of the purified water in the 418MHz to 438MHz range. Match the temperature to the dielectric constant and dielectric loss at that moment.

[0103] The results of dielectric properties measurement at 433MHz using the temperature rising method are as follows: Figure 7 As shown. Figure 7 As shown in Figure A, the dielectric constant at 433MHz and 915MHz changes with temperature in a sawtooth pattern. This is because water vapor continuously adheres to the detection area of ​​the probe during the heating process, resulting in the measured dielectric constant being a mixed dielectric constant of water, water vapor, and oxygen in the bubbles. This dielectric constant deviates significantly from the actual value and will produce huge errors when used to calculate the wavelength of microwaves in water. Figure 7 As shown in Figure B, the dielectric loss of water decreases gradually with increasing temperature. At around 80°C, the dielectric loss at 433 MHz is less than 0, indicating that the parameters measured by the instrument have produced impossible distortion data. Therefore, the traditional temperature increase method is difficult to accurately measure the changes in liquid media with temperature.

[0104] Example 2: Influence of the phase difference of the upper and lower microwave sources on the electric field distribution when the 433 MHz microwave adopts the BJ5 waveguide.

[0105] By using the phase difference pi as the upper and lower phase difference of the microwave resonant cavity, the electric field distribution in the XY plane of the middle layer of the microwave resonant cavity can be obtained, such as Figure 8As shown in the figure. When the phase difference of 433MHz microwaves is pi, the XY plane shifts toward red, indicating a higher electric field intensity in the center region. In the YZ plane, a higher electric field distribution is observed in the middle layer, followed by a relatively strong electric field at the top and bottom. In the XZ plane, it is noticeable that the electric field is concentrated almost in the center of the microwave heating cavity in both the X and Z directions, typically where the food is located.

[0106] Comparative Example 2: The effect of a phase difference of 0 (or 2pi) between the upper and lower microwave sources on the electric field distribution when a 433MHz microwave adopts a BJ5 waveguide.

[0107] For S7, when the phase difference between the upper and lower microwave sources of the microwave heating cavity is 2pi or 0, the electric field distribution in the XY plane is as follows: Figure 9 As shown in Figure .A. The electric field intensity is smaller in the center of the XY plane. In addition, it presents four relatively dispersed strips, which may cause uneven heating of the food, with higher temperatures at the strips and lower temperatures in the middle of the strips.

[0108] The electric field distribution in the YZ plane when the phase difference is 2pi or 0 is as follows Figure 9 As shown in Figure B, the electric field is divided into four lobes around the center, forming a region in the middle where the electric field is almost zero. When food is placed in this region, the center of the food will not be heated. This does not conform to the principle of using a microwave cavity to heat food.

[0109] The electric field distribution in the XZ plane when the phase difference is 2pi or 0 is as follows Figure 9 As shown in Figure 1, the electric field is concentrated in the upper and lower parts of the Z direction. The electric field distribution in the middle is blue, indicating that the electric field strength is almost zero.

[0110] Figure 10 The electric field distribution when the phase difference between the upper and lower microwave sources is pi / 2 is shown. Overall, the electric field distribution in the XY plane, YZ plane, and XZ plane is similar to that when the phase difference is pi. It should be noted that, if Figure 10 In the YZ plane shown in Figure B, the microwave electric field is smaller on the upper side than on the lower side, which means that the temperature of the upper part of the food will be lower than that of the lower part. Heating the entire food will exacerbate the temperature unevenness between the upper and lower sides.

[0111] Example 3: When a 433 MHz microwave uses a BJ5 waveguide, the effect of a resonant cavity thickness of 80% to 95% on the electric field distribution.

[0112] S1 determines the microwave frequency f to be 433 MHz.

[0113] S2 collects the dielectric constant of the medium at a frequency of 433 MHz, with a temperature of 90°C. During the collection process, the medium temperature is raised to approximately 90°C and then naturally cooled down over time.

[0114] S3: According to formula 2, the wavelength of 433MHz frequency band microwaves in purified water is 89.75mm.

[0115] S4: According to the formation principle of the single-mode cavity and the actual application scenario of the microwave resonant cavity, the thickness of the resonant cavity is set as the limiting factor, and the thickness range is wavelength*(80%~95%), which is 71.80mm~86.26mm.

[0116] S5: According to the microwave frequency, select the rectangular waveguide specification BJ5 in accordance with the relevant specifications of Hollow Metal Waveguide Part 2: Ordinary Rectangular Waveguide (GB / T11450.2-1989).

[0117] S6: Create a simple model consisting of only a rectangular waveguide, a microwave window, and a microwave resonant cavity.

[0118] S7: Perform a parametric scan on the phases of the upper and lower microwave sources of the simple model to analyze the distribution of the microwave electric field within the resonant cavity. For most microwave application scenarios, the microwave electric field should be distributed in the geometric center area of ​​the microwave single-mode device to facilitate the placement or removal of food. Therefore, when determining the results of the phase impact, the dispersion, concentration, and electric field strength of the microwave electric field should be studied first. The specific steps for determining the phase impact are the same as those in Example 1.

[0119] S8: Perform a parametric sweep of the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane. The long side of the rectangular waveguide is set to one unit a (457.2 mm), the short side is set to one unit b (228.6 mm), and half the wavelength of a microwave at a certain frequency in a liquid medium (λ / 2, 4.88 mm) is defined as one unit, represented by the letter c. The sweep parameters are the same as in Example 1.

[0120] S9: In order to reduce the application cost of microwave technology, in addition to the microwave source with adjustable phase, the following supplements the technical solution of using mechanical rectangular waveguide to control the phase. Calculate the waveguide wavelength at this frequency and calculate it according to the following formula 3 to get the waveguide wavelength of 1065.1mm. Add a height of λ on one side of the resonant cavity. g / 2 (532.55mm) rectangular waveguide, the microwave in the resonant cavity will change half the phase cycle (pi).

[0121]

[0122] S10: Introduce a tapered waveguide. The schematic diagram of the tapered waveguide is as follows Figure 3 As shown, Figure 3 A is a picture of the actual processing of the tapered waveguide; Figure 3 B is the numerical simulation geometric model of the tapered waveguide. Figure 4 As shown, a vertically symmetrical microwave resonant cavity is established. Figure 5 The locations of the rectangular waveguide, tapered waveguide, microwave window, microwave heating cavity, and food in the numerical simulation geometric model design are shown.

[0123] Use finite element or finite time-domain difference principle-based software to establish Figure 4 The geometry of the microwave heating module shown here uses Maxwell's equations as a physics field, with the study type set to frequency domain. Similarly, the length of the rectangular waveguide specified in the national standard is defined as a (457.2 mm), and the width as b (228.6 mm). The microwave window's primary function is to allow microwaves emitted by the microwave source to enter the rectangular waveguide and pass through it, thereby entering the microwave resonant cavity where the food is heated. Therefore, the size of the microwave window affects the electric field distribution within the heating cavity.

[0124] S11: Parametric sweeps are established for the length and width of the microwave window: a microwave window length of 1.0a to 2.5a (457.2 mm to 1143 mm), a width of 0.5b to 1.5b (114.3 mm to 342.9 mm), and a tapered waveguide height of 0.25a to 2a (114.3 mm to 914.4 mm) are parametrically swept. Similarly, the long side of the rectangular waveguide is set to a unit of 457.2 mm, and the short side of the rectangular waveguide is set to a unit of 228.6 mm, respectively, as b.

[0125] Specifically, S11-1 sets the microwave window width to 1.0 Å and performs a parametric sweep of the length, defining the parameters as range (1.0 Å, 0.5 Å, 2.5 Å) and 1.75 Å, 2.15 Å, 2.25 Å, and 2.35 Å. Based on the electric field distribution and actual application requirements, an optimal microwave window length and several alternative, better microwave window lengths are determined.

[0126] S11-2 fixes the microwave window length and performs parameter sweep on the microwave window width, with the parameter set to range (0.5b, 0.1b, 1.5b). The microwave window width is determined based on actual sample production needs and energy utilization.

[0127] After the length and width of S11-3 are determined, a parameter scan is performed on the height of the tapered waveguide. The parameter scan range and step size are range (0.25a, ​​0.25a, ​​2a). The height of the tapered waveguide is selected according to the electric field distribution and reflection conditions.

[0128] S12: Using the above-mentioned optimal microwave heating cavity length, width, and thickness, and the optimal tapered waveguide height, a frequency sweep is performed, where the frequency sweep scheme is defined as range (413 MHz, 5 MHz, 443 MHz).

[0129] Taking 433MHz as an example, when the thickness of the resonant cavity is 80% to 95%, the thermal diagram is as follows: Figure 11 The results show that when the cavity thickness is 90% of the 433MHz water wavelength, the electric field distribution in the XY plane, YZ plane, and XZ plane is concentrated in the center of the microwave cavity. In the YZ plane, it can be seen that there is no electric field concentration at the microwave window, and there will be no sparking caused by excessive electric field intensity.

[0130] Comparative Example 3: When using a BJ5 waveguide for 433MHz microwaves, the effect of the resonant cavity thickness not meeting the 80% to 95% threshold on the electric field distribution.

[0131] When the thickness of the resonant cavity is 1.2 times the wavelength, the size requirement of the single-mode resonant cavity is no longer met. Figure 12 As shown in Figure A, the overall electric field distribution in the XY plane consists of two high-field intensity regions at the top and bottom, and four sub-high-field intensity regions distributed at the corners. The overall electric field distribution is quite chaotic. Figure 12 Figure B shows the electric field distribution in the YZ direction. Similarly, there are six regions of high electric field intensity, distributed in the middle, upper, and lower layers. In this case, microwaves create numerous cold spots when used to process food, making effective localization impossible. This also prevents the desired uniform heating.

[0132] Example 4: When a 433MHz microwave uses a BJ5 waveguide, the microwave window width conforms to 0.8b to 1.1b, and the electric field distribution when it is 1.0b.

[0133] The electric field distribution in the XY, YZ, and XZ planes shows that when the microwave window is 1.0b, the middle layer where the food is located can be effectively heated by microwaves, and the interior of the food can be effectively and rapidly heated. When there is a certain temperature difference between the external water medium and the food, the food can be effectively heated externally.

[0134] Comparative Example 4: When using BJ5 waveguide for 433MHz microwave, the microwave window width does not conform to 0.8b~1.1b, and the electric field distribution is 0.5b and 1.2b

[0135] When the width of the microwave window is 0.5b. Figure 14 As shown in A, the larger electric field area in the XY plane is divided into three ellipses and two upper and lower semi-ellipses. Figure 14 As shown in B, the YZ plane has a secondary high electric field region in the central area, but there is an electric field concentration phenomenon at the microwave window.

[0136] When the width of the microwave window is 1.2b, Figure 15 As shown in Figure A, in the XY plane, the high electric field areas are on the upper and lower sides. At this time, the food in the center of the cavity cannot be effectively heated. Figure 15 As shown in Figure .B, in the YZ plane, the situation is similar to that in the XY plane. The microwave electric field is concentrated on both sides of the cavity, near the microwave window, rather than in the central area where the food should be. Therefore, when the microwave window width is 0.5b or 1.2b, it is not possible to effectively heat the food.

[0137] Example 5: Electric field distribution at a frequency of 433 MHz or a possible fluctuation frequency (±20 MHz)

[0138] The results are as follows Figure 16 、 17 shown.

[0139] Use S11 to study the reverse situation and electric field distribution in the 433MHz±15MHz frequency band. Figure 16 As shown in Figure 1, the multi-excitation reflection coefficient of the upper and lower microwave sources gradually decreases with the change of microwave frequency. Therefore, the electric field distribution is bound to be different for different frequencies.

[0140] In order to more clearly display the electric field distribution, step S13 is added to add food with the same material parameters into the microwave resonant cavity within the range of 433 MHz ± 15 MHz to observe the electric field distribution.

[0141] The results showed that at 413 MHz, the electric field distribution within the food was relatively uniform, forming a regular circular shape. As the microwave frequency increased, the electric field distribution within the food gradually split at 418 MHz, and at 423 MHz, the electric field intensity increased at the two ellipses on the left and right sides of the food. At 428 MHz, the ellipses on both sides gradually converged, forming a new, smaller elliptical electric field at the center, where the highest electric field distribution was observed.

[0142] When the frequency is further increased to 448 MHz, the electric field begins to split further, and at 453 MHz the electric field splits into three superimposed ellipses.

[0143] Therefore, in order to maintain a relatively stable microwave heating mode, the microwave source should be as stable as possible, preferably with a point frequency, so as to minimize the changes in the microwave electric field.

[0144] Example 6: Electric field distribution when BJ8 waveguide is used for 915MHz microwave and the cavity thickness is 80% to 95%, with the thickness being 94%.

[0145] S1 determines the microwave frequency f to be 915 MHz.

[0146] S2 collects the dielectric constant of the medium at a frequency of 915MHz, with a temperature of 90°C. During the collection process, the medium temperature is raised to approximately 95°C and then naturally cooled down over time.

[0147] S3: According to formula 2, the wavelength of 915MHz frequency band microwaves in purified water is 42.56mm.

[0148] S4: According to the formation principle of the single-mode cavity and the actual application scenario of the microwave resonant cavity, the thickness of the resonant cavity is set as the limiting factor, and the thickness range is wavelength*(80%~95%), which is 34.08mm~40.32mm.

[0149] S5: According to the microwave frequency, select the rectangular waveguide specification BJ8 in accordance with the relevant specifications of Hollow Metal Waveguide Part 2: Ordinary Rectangular Waveguide (GB / T11450.2-1989).

[0150] S6: Create a simple model consisting of only a rectangular waveguide, a microwave window, and a microwave resonant cavity.

[0151] S7: Perform a parametric scan on the phases of the upper and lower microwave sources of the simple model to analyze the distribution of the microwave electric field within the resonant cavity. For most microwave application scenarios, the microwave electric field should be distributed in the geometric center area of ​​the microwave single-mode device to facilitate the placement or removal of food. Therefore, when determining the results of the phase impact, the dispersion, concentration, and electric field strength of the microwave electric field should be studied first. The specific steps for determining the phase impact are the same as those in Example 1.

[0152] S8: Perform a parametric sweep of the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane. The long side of the rectangular waveguide is set to 1 unit a (292.1 mm), the short side is set to 1 unit b (146.05 mm), and half the wavelength of a microwave at a certain frequency in a liquid medium (λ / 2, 21.28 mm) is defined as a unit, represented by the letter c. The sweep parameters are as follows:

[0153]

[0154]

[0155] like Figure 18 As shown in the figure, at 915 MHz, using a BJ8 rectangular waveguide, when the resonant cavity thickness is 40 mm, the electric field distribution in the XY plane is relatively uniform, with the larger electric field concentrated in the center. The electric field distribution in the YZ and XZ planes shows that when the food is in the center, the geometric center of the food is well heated.

[0156] Comparative Example 6: When the BJ8 waveguide is used at a microwave frequency of 915 MHz, the thickness of the resonant cavity does not meet the electric field distribution at 80% to 95%.

[0157] Figure 19 This figure shows the electric field distribution when using a BJ8 waveguide at 915 MHz and the resonant cavity thickness is 30 mm (71%). The XY plane shows that the microwave electric field is concentrated above and below the microwave window. In addition, three long elliptical high-field regions appear above and below the microwave window.

[0158] Figure 20 This image shows the electric field distribution when using a BJ8 waveguide at 915 MHz and the cavity thickness is 47 mm (111%). The XY plane shows that when the cavity length exceeds 100%, the microwaves within the microwave window region in the center of the cavity split into two long, elliptical regions of high electric field and one short, elliptical region of high electric field. In this case, microwave heating using this cavity will result in numerous cold spots, which is detrimental to uniform heating. The YZ plane further demonstrates the discontinuity of the electric field in the YZ direction.

[0159] Example 7: 915MHz microwave uses BJ9 waveguide, and the thickness of the resonant cavity meets the electric field distribution at 80%-95%.

[0160] S1 determines the microwave frequency f to be 915 MHz.

[0161] S2 collects the dielectric constant of the medium at a frequency of 915MHz, with a temperature of 90°C. During the collection process, the medium temperature is raised to approximately 95°C and then naturally cooled down over time.

[0162] S3: According to formula 2, the wavelength of 915MHz frequency band microwaves in purified water is 42.56mm.

[0163] S4: According to the formation principle of the single-mode cavity and the actual application scenario of the microwave resonant cavity, the thickness of the resonant cavity is set as the limiting factor, and the thickness range is wavelength*(80%~95%), which is 34.05mm~40.43mm.

[0164] S5: According to the microwave frequency, select the rectangular waveguide specification BJ9 in accordance with the relevant specifications of Hollow Metal Waveguide Part 2: Ordinary Rectangular Waveguide (GB / T11450.2-1989).

[0165] S6: Create a simple model consisting of only a rectangular waveguide, a microwave window, and a microwave resonant cavity.

[0166] S7: Perform a parametric scan on the phases of the upper and lower microwave sources of the simple model to analyze the distribution of the microwave electric field within the resonant cavity. For most microwave application scenarios, the microwave electric field should be distributed in the geometric center area of ​​the microwave single-mode device to facilitate the placement or removal of food. Therefore, when determining the results of the phase impact, the dispersion, concentration, and electric field strength of the microwave electric field should be studied first. The specific steps for determining the phase impact are the same as those in Example 1.

[0167] S8: Perform a parametric sweep of the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane. The long side of the rectangular waveguide is set to 1 unit a (249.65 mm), the short side is set to 1 unit b (123.82 mm), and half the wavelength of a microwave at a certain frequency in a liquid medium (λ / 2, 21.28 mm) is defined as a unit, represented by the letter c. The sweep parameters are as follows:

[0168]

[0169] Figure 21 The electric field distribution of a 915MHz microwave using a BJ9 waveguide with a resonant cavity thickness of 36mm (84.59 of the dielectric wavelength) is shown. The results show that the high electric field concentration area in the XY plane, YZ plane, and XZ plane is located at the center of the resonant cavity, which is beneficial for heating food.

[0170] Comparative Example 7: 915MHz microwave uses BJ9 waveguide, and the thickness of the resonant cavity does not meet the electric field distribution when it is 80%-95%.

[0171] Figure 22 The electric field distribution for a 915 MHz microwave using a BJ9 waveguide with a resonant cavity thickness of 30 mm (71% of the wavelength) is shown. The results show that the electric field is high in the XY, YZ, and XZ planes at the geometric center of the resonant cavity. However, three oblong electric fields are present above and below the microwave window in the XY plane, with field strengths nearly identical to those at the center. These fields are located at locations where almost no electric field passes through, indicating that nearly half of the microwave energy is absorbed by the dielectric within the cavity.

[0172] Figure 23 The electric field distribution for a 915 MHz microwave using a BJ9 waveguide with a resonant cavity thickness of 47 mm (111% of the wavelength) is shown. The results show a different electric field distribution pattern than when using a BJ8 waveguide. This demonstrates that the same values ​​cannot be applied to different waveguides, requiring specific implementation using the methods described in this invention. Figure 23Figure A shows the electric field distribution in the XY plane when the cavity thickness is 47mm. The electric field at the microwave window splits into a central region of highest intensity and two regions of lower intensity above and below. The YZ plane further illustrates the results when the cavity thickness exceeds 95%. At this point, the central electric field is almost identical to the approximately ten circular regions of lower intensity on its left and right sides. This indicates that this cavity cannot be used for heating food.

[0173] Example 8: 2450MHz microwave uses BJ22 waveguide, and the thickness of the resonant cavity meets the electric field distribution at 80% to 95%.

[0174] S1 determines the microwave frequency f to be 2450 MHz.

[0175] S2 collects the dielectric constant of the medium at a frequency of 2450MHz, with a temperature of 90°C. During the collection process, the medium temperature is raised to approximately 95°C and then naturally cooled down over time.

[0176] S3: According to formula 2, the wavelength of 2450MHz frequency band microwaves in purified water is 15.9mm.

[0177] S4: According to the formation principle of the single-mode cavity and the actual application scenario of the microwave resonant cavity, the thickness of the resonant cavity is set as the limiting factor, and the thickness range is wavelength*(80%~95%), which is 12.75mm~15.11mm.

[0178] S5: According to the microwave frequency, select the rectangular waveguide specification BJ22 in accordance with the relevant specifications of Hollow Metal Waveguide Part 2: Ordinary Rectangular Waveguide (GB / T11450.2-1989).

[0179] S6: Create a simple model consisting of only a rectangular waveguide, a microwave window, and a microwave resonant cavity.

[0180] S7: Perform a parametric scan on the phases of the upper and lower microwave sources of the simple model to analyze the distribution of the microwave electric field within the resonant cavity. For most microwave application scenarios, the microwave electric field should be distributed in the geometric center area of ​​the microwave single-mode device to facilitate the placement or removal of food. Therefore, when determining the results of the phase impact, the dispersion, concentration, and electric field strength of the microwave electric field should be studied first. The specific steps for determining the phase impact are the same as those in Example 1.

[0181] S8: Perform a parametric sweep of the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane. The long side of the rectangular waveguide is set to 1 unit a (109.22 mm), the short side is set to 1 unit b (54.61 mm), and half the wavelength of a microwave at a certain frequency in a liquid medium (λ / 2, 7.95 mm) is defined as a unit, represented by the letter c. The sweep parameters are as follows:

[0182]

[0183] Figure 24 This figure shows the electric field distribution when using a BJ22 rectangular waveguide at 2450 MHz and a resonant cavity thickness of 14 mm. The results show that high electric field regions in the XY plane, YZ plane, and XZ plane are located in the center of the resonant cavity in the X, Y, and Z directions. This allows for high energy efficiency when used for food heating.

[0184] Comparative Example 8: 2450MHz microwave uses BJ22 waveguide, and the resonant cavity thickness does not meet the electric field distribution when it is 80% to 95%.

[0185] Figure 25 The electric field distribution is shown when a 2450MHz microwave uses a BJ22 waveguide and the resonant cavity thickness is 17mm (106% of the medium wavelength). The results show that the electric field in the XY plane consists of two elliptical high electric field areas. At this time, the electric field intensity at the center is relatively small. When food is present, the upper and lower sides of the food will be heated, rather than the middle area. This cavity is not conducive to uniform heating of food, and the heating efficiency of food in the center and on the left and right sides is low. The YZ plane also shows that the center of the food is not heated enough. The XZ plane shows that the electric field intensity in its central area is similar to that of the upper and lower sides, and is at an intermediate level.

[0186] Example 9: 2450MHz microwave uses BJ26 waveguide, and the thickness of the resonant cavity meets the electric field distribution at 80% to 95%.

[0187] S1 determines the microwave frequency f to be 2450 MHz.

[0188] S2 collects the dielectric constant of the medium at a frequency of 2450MHz, with a temperature of 90°C. During the collection process, the medium temperature is raised to approximately 95°C and then naturally cooled down over time.

[0189] S3: According to formula 2, the wavelength of 2450MHz frequency band microwaves in purified water is 15.9mm.

[0190] S4: According to the formation principle of the single-mode cavity and the actual application scenario of the microwave resonant cavity, the thickness of the resonant cavity is set as the limiting factor, and the thickness range is wavelength*(80%~95%), which is 34.05mm~40.43mm.

[0191] S5: According to the microwave frequency, select the rectangular waveguide specification BJ26 in accordance with the relevant specifications of Hollow Metal Waveguide Part 2: Ordinary Rectangular Waveguide (GB / T11450.2-1989).

[0192] S6: Create a simple model consisting of only a rectangular waveguide, a microwave window, and a microwave resonant cavity.

[0193] S7: Perform a parametric scan on the phases of the upper and lower microwave sources of the simple model to analyze the distribution of the microwave electric field within the resonant cavity. For most microwave application scenarios, the microwave electric field should be distributed in the geometric center area of ​​the microwave single-mode device to facilitate the placement or removal of food. Therefore, when determining the results of the phase impact, the dispersion, concentration, and electric field strength of the microwave electric field should be studied first. The specific steps for determining the phase impact are the same as those in Example 1.

[0194] S8: Perform a parametric sweep of the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane. The long side of the rectangular waveguide is set to 1 unit a (86.36 mm), the short side is set to 1 unit b (43.18 mm), and half the wavelength of a microwave at a certain frequency in a liquid medium (λ / 2, 7.95 mm) is defined as a unit, represented by the letter c. The sweep parameters are as follows:

[0195]

[0196] Figure 26 The electric field distribution of a 2450MHz microwave BJ26 waveguide with a resonant cavity thickness of 14mm (88% of the wavelength) is shown. The results show that high electric field regions in the XY, YZ, and XZ planes all occur in the center of the resonant cavity, exhibiting a relatively uniform, elliptical shape. These results demonstrate that the technical approach of this invention can achieve uniform design of microwave resonant cavity dimensions.

[0197] Comparative Example 9: 2450MHz microwave uses BJ26 waveguide, and the thickness of the resonant cavity does not meet the electric field distribution when it is 80% to 95%.

[0198] Figure 27The electric field distribution at 2450MHz using a BJ26 rectangular waveguide and a resonant cavity thickness of 17.5mm (110%) is shown. The results show that the XY plane electric field has two elliptical high electric field regions that are about to separate, with a relatively uniform high electric field region still existing in the middle. The YZ plane electric field distribution shows that the middle layer has a similar electric field distribution to the upper and lower layers, indicating low microwave energy utilization. The XZ plane electric field distribution also shows that the electric field strength in the middle layer is almost the same as that in the upper and lower layers. Approximately half of the microwave energy is used to heat the medium rather than the food, and approximately half of the energy is wasted.

Claims

1. A method for designing a uniform electric field cavity for a single-mode liquid microwave resonant cavity, characterized in that: The design method includes the following specific steps: S1: Determine the microwave frequency f; S2: Collect the dielectric constant of the liquid medium within the frequency range of ±20MHz at the f frequency point. During the collection, the temperature of the liquid medium is raised to 95±2℃, and then naturally cooled down over time. The temperature, dielectric constant, and dielectric loss at this temperature are recorded. S3: Calculate the wavelength of the microwave in the f-band in the liquid medium according to the wavelength formula; S4: Determine the thickness of the microwave resonant cavity based on the calculation of the wavelength of microwaves in the liquid medium in S3; S5: Select rectangular waveguide specifications according to GB / T 11450.2-1989 based on microwave frequency; S6: Establish a simple model consisting of only a rectangular waveguide, a microwave window, and a microwave resonant cavity; S7: performing a parametric sweep on the phases of the upper and lower microwave sources of the simple model to analyze the distribution of the microwave electric field in the resonant cavity; S8: Perform parametric scanning on the length and width of the microwave resonant cavity; observe the electric field distribution and reflection in the XY plane; S9: Calculate the waveguide wavelength at the frequency determined by S1 based on formula 3, and add a waveguide with a height of λ on one side of the resonant cavity. g / 2 rectangular waveguide, the microwave in the resonant cavity will change half the phase cycle (2*pi); S10: Introducing tapered waveguide based on numerical simulation model; S11: Perform parameterized scans of the microwave window length and width and the tapered waveguide height to complete the electric field cavity design.

2. The uniform electric field cavity design method according to claim 1, characterized in that: During the cooling process in S2, the temperature is within 90°C.

3. The uniform electric field cavity design method according to claim 1, wherein: In the above S4, the thickness of the microwave resonant cavity is defined as λ*(80% to 95%).

4. The uniform electric field cavity design method according to claim 1, wherein: In S7, when determining the phase influence result, the dispersion, concentration, and electric field intensity of the microwave electric field should be studied first. The specific steps for determining the phase influence are as follows: (1) Scan the initial phase, set the initial phase to prot, its range is 0~2pi, and the scanning step is pi / 4; (2) Set the upper phase to prot+prot_1 and the lower phase to port; the range of prot_1 is 0~2pi, the scanning step is pi / 4, and the scanning range of prot is set to 0~2pi.

5. The uniform electric field cavity design method according to claim 1, wherein: In S8, the length of the long side of the rectangular waveguide is set to 1 unit a, the short side of the rectangular waveguide is set to 1 length unit b, and half the wavelength (λ / 2) of microwaves at a certain frequency in the liquid medium is defined as 1 unit, represented by the letter c. The scanning parameters are as follows: Table 1 Parametric sweep settings for microwave heating cavity length, width, and thickness 6. The method for designing a uniform electric field cavity according to claim 1, wherein: In S10, a geometric model of the microwave heating module is established using the finite element method or the finite time-domain difference principle, the microwave field is added as a physical field based on the Maxwell equations, and the research type is set to the frequency domain; the length of the relevant rectangular waveguide is defined as a, and the width of the rectangular waveguide is defined as b.

7. The uniform electric field cavity design method according to claim 1, wherein: In the above S11, the length of the long side of the rectangular waveguide is set to 1 unit a, and the short side of the rectangular waveguide is set to 1 length unit b; specifically: S11-: First, the microwave window width is set to 1.0a, and the length is parametrically scanned, with the parameters defined as range(1.0a, 0.5a, 2.5a) and 1.75a, 2.15a, 2.25a, ​​and 2.35a; S11-2: Fixed microwave window length, performed parameter sweep on microwave window width, and set the parameter to range (0.5b, 0.1b, 1.5b); S11-3: After the length and width are determined, a parameter scan is performed on the height of the tapered waveguide. The parameter scan range and step size are range (0.25a, ​​0.25a, ​​2a). The height of the tapered waveguide is selected based on the electric field distribution and reflection conditions.

8. The uniform electric field cavity design method according to claim 1, wherein: The method also includes S12: exploring the influence of microwave frequency changes on electric field distribution, and determining whether to use point-frequency microwaves or band-frequency microwaves; exploring the influence of frequency fluctuations within the specified frequency range of f±20 MHz on electric field distribution, and judging based on the electric field distribution and reflection conditions in the XY plane at Z=0; setting the size of the microwave heating cavity to the above-mentioned optimal microwave resonant cavity x*y*z, the microwave window size to wx*wy, and the horn height to hh; and setting the frequency scanning scheme to range (f-20, 5, f±20) in MHz.

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