CN113950176B - Magnetron anode power supply ripple mixing multi-frequency heating device and method - Google Patents

Abstract

The invention discloses a magnetron anode power supply ripple mixing multi-frequency heating device and a method, which belong to the field of microwave heating, wherein a magnetron power supply is connected with a first cathode power supply line and a second cathode power supply line; the first cathode power line and the second cathode power line are respectively connected with two ends of a cathode of the magnetron; one end of the first capacitor is connected with the intermediate frequency signal generator, and the other end of the first capacitor is connected with a first cathode power line; a feed port is arranged on the cavity; the magnetron inputs microwaves of a plurality of frequencies into the cavity through the feed port. Based on nonlinear response characteristics of a magnetron, the intermediate frequency signal is equivalent to ripple of anode voltage of the magnetron to be loaded on the anode voltage of the magnetron, and a resonance signal excited by the magnetron is used as a local oscillation signal, and the magnetron is used for mixing to enable the output end of the magnetron to generate microwaves with multiple frequencies so as to uniformly heat materials.

Description

Magnetron anode power supply ripple mixing multi-frequency heating device and method

Technical Field

The invention belongs to the field of microwave heating, and in particular relates to a magnetron anode power supply ripple frequency mixing multi-frequency heating device and method.

Background Art

As a new type of clean energy, microwaves are widely used in many fields such as food, chemical industry, metallurgy and sewage treatment. Microwaves directly act on polar molecules and charged particles inside the heated material, so microwave heating has the advantages of selective heating, volume heating and clean heating. However, microwaves generally have the problem of uneven heating in the actual heating process. Uneven heating causes local excessive temperature and forms "hot spots". The absorption capacity of many substances for electromagnetic waves is positively correlated with temperature. The temperature in the "hot spot" area rises faster, eventually forming a "thermal runaway" phenomenon, which greatly restricts the large-scale application of microwave energy.

With the development of science and technology and the improvement of people's living standards, microwave ovens are becoming more and more popular among consumers and are gradually becoming a must-have household appliance in the kitchen. Microwave heating has the advantages of fast heating speed, low energy consumption and convenient control at any time, so microwave ovens have gradually been widely used. However, with the continuous development of technology, consumers' requirements for microwave ovens are gradually increasing, especially in terms of heating uniformity and heating efficiency of food. The operating frequency of traditional microwave ovens is 2450MHz, and only a single microwave source and a single frequency are used for heating. Although the microwave oven cavity is a multi-mode resonant cavity, it can excite multiple electromagnetic modes in the cavity, but the number of excited modes is limited after all, and there is still the phenomenon of uneven heating.

Scholars have done a lot of work to improve the uniformity of microwave heating. In 1989, Ji Tianren proposed the concept of a rotating antenna, that is, the antenna changes the mode field in the cavity as the driver rotates, resulting in a change in the field distribution and improving the uniformity of heating. In 1995, Yan Liping and others mainly explored the influence of the rotation of the turntable in the microwave oven cavity on the uniformity of heating and the relationship between the load size and area and the output power of the microwave oven. In 2001, Sung Yi and Lie Liu used FEM, the finite element method, to simulate and analyze regular rectangular waveguides and resonant cavities, and concluded that the more resonant frequencies excited in the cavity, the more uniform the field distribution. In 2006, Shinya Watanabe and others used the THE method to calculate heat conduction and the FDTD method to calculate the electromagnetic field, and studied the temperature distribution on the surface of the heated object. In 2017, Sang-Hyeon Bae and Min-GyoJeong studied a microwave conveyor belt dryer with sustainable power control made of multiple 2.45GHz microwave sources. By sequentially controlling the input power of the microwave source, the uniformity of cavity heating can be improved. Intermediate frequency signal refers to the frequency signal ranging from 300KHz to 3000KHz. In the radio frequency communication system, the signal before modulation is called the baseband signal, and the signal after mixing is called the radio frequency (or high frequency) signal. The signal between these two levels is the intermediate frequency signal.

At present, there has been no research in the art on how to enable a single microwave source to output microwaves of multiple frequencies to evenly heat the material, so as to improve the problem of uneven microwave heating of the material. Even if it is considered to use microwaves of multiple frequencies to heat the material, the number of microwave sources will generally increase, which will inevitably lead to an increase in cost. Or even if a single microwave source can output microwaves of multiple frequencies, a separately set mixer and a large number of auxiliary accessories must be used, which also leads to an increase in cost. The present invention realizes the output of microwaves of multiple frequencies by a single microwave source at a low cost, and the frequency of the output microwaves is controllable and adjustable, thereby ensuring the uniformity of microwave heating.

Summary of the invention

The purpose of the present invention is to provide a magnetron anode power supply ripple mixing multi-frequency heating device and method to solve the problems of uneven microwave heating in the prior art. To achieve the above purpose, the present invention provides the following technical solutions:

A magnetron anode power supply ripple mixing multi-frequency heating device comprises a magnetron power supply 1, a magnetron 2, an intermediate frequency signal generator 3, a first capacitor 41 and a cavity 8; the magnetron power supply 1 is connected to a first cathode power line 71 and a second cathode power line 72; the first cathode power line 71 and the second cathode power line 72 are respectively connected to the cathode ends of the magnetron 2; one end of the first capacitor 41 is connected to the intermediate frequency signal generator 3, and the other end is connected to the first cathode power line 71; a feed port is provided on the cavity 8; the magnetron 2 inputs microwaves of multiple frequencies into the cavity 8 through the feed port.

Furthermore, a first inductor 51 is provided on the first cathode power line 71 between the intersection of the first capacitor 41 and the first cathode power line 71 and the magnetron power supply 1 .

Furthermore, a second inductor 52 is disposed on the second cathode power line 72 .

Furthermore, a third inductor 53 is included; one end of the third inductor 53 is connected to the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected to the intermediate frequency signal generator 3, and the other end is grounded.

Furthermore, a fourth capacitor 44 is included; one end of the fourth capacitor 44 is connected to the first cathode power line 71 between the magnetron power supply 1 and the first inductor 51, and the other end is grounded.

Furthermore, a fifth capacitor 45 is included; one end of the fifth capacitor 45 is connected to the second cathode power line 72 between the magnetron power supply 1 and the second inductor 52, and the other end is grounded.

Furthermore, it also includes a first resistor 61, a second resistor 62 and a third resistor 63; the first resistor 61 and the third inductor 53 are connected in parallel; the second resistor 62 and the first inductor 51 are connected in parallel; the third resistor 63 and the second inductor 52 are connected in parallel.

Furthermore, it also includes an impedance matching regulator; the impedance matching regulator includes a second adjustable capacitor 42 and a third adjustable capacitor 43; one end of the second adjustable capacitor 42 is connected to the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected to the intermediate frequency signal generator 3, and the other end is grounded; one end of the third adjustable capacitor 43 is connected to the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected to the intermediate frequency signal generator 3, and the other end is grounded.

Furthermore, it also includes a circuit board; the first capacitor 41, the first inductor 51, the second inductor 52, the third inductor 53, the fourth capacitor 44, the fifth capacitor 45, the first resistor 61, the second resistor 62 and the third resistor 63 are integrated on the circuit board; the circuit board includes a first port, a second port, a third port, a fourth port and a fifth port; the first port is located on the first cathode power line 71 between the first inductor 51 and the magnetron power supply 1; the second port is located on the second cathode power line 72 between the second inductor 52 and the magnetron power supply 1; the third port is located on the first cathode power line 71 between the first inductor 51 and the magnetron 2; the fourth port is located on the second cathode power line 72 between the second inductor 52 and the magnetron 2; the fifth port is located between the intermediate frequency signal generator 3 and the first capacitor 41, so that the intermediate frequency signal generator 3 and the first capacitor 41 are connected.

A magnetron anode power supply ripple mixing multi-frequency heating method adopts any of the above-mentioned magnetron anode power supply ripple mixing multi-frequency heating devices; the specific steps are: the magnetron power supply 1 supplies power to the magnetron 2; the intermediate frequency signal generator 3 generates an intermediate frequency signal, and the intermediate frequency signal is input to the first cathode power supply line 71 through the first capacitor 41. At this time, the intermediate frequency signal is equivalent to the ripple of the anode voltage of the magnetron 2 loaded on the anode voltage of the magnetron 2, and the resonant signal excited by the magnetron 2 itself is used as the local oscillation signal. When the intermediate frequency signal acts as the anode voltage ripple and the resonant signal of the magnetron 2, the nonlinear response characteristics of the magnetron 2 cause the output end of the magnetron 2 to generate microwaves of multiple frequencies, and the microwaves of multiple frequencies are input into the cavity 8 through the feed port to heat the material 9.

The beneficial effects of the present invention are:

The invention discloses a magnetron anode power supply ripple frequency mixing multi-frequency heating device and method. The magnetron power supply is connected with a first cathode power line and a second cathode power line; the first cathode power line and the second cathode power line are respectively connected to the cathode ends of the magnetron; one end of the first capacitor is connected to an intermediate frequency signal generator, and the other end is connected to the first cathode power line; a feed port is provided on the cavity; the magnetron inputs microwaves of multiple frequencies into the cavity through the feed port. The magnetron anode power supply ripple frequency mixing multi-frequency heating device and method of the invention are based on the nonlinear response characteristics of the magnetron, and the intermediate frequency signal is equivalent to the ripple of the magnetron anode voltage, which is loaded on the magnetron anode voltage, and the resonance signal excited by the magnetron itself is used as a local oscillation signal, and the magnetron is used for frequency mixing to generate microwaves of multiple frequencies at the output end of the magnetron, so as to evenly heat the material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the circuit principle of the magnetron anode power supply ripple mixing multi-frequency heating device of the present invention, without showing the cavity;

FIG2 is an equivalent circuit diagram of a magnetron; according to the research on the structure and function of the magnetron resonant cavity, the magnetron resonant cavity can be equivalent to an RLC parallel resonant circuit, g+jb is the equivalent magnetron source part, G+jB is the equivalent load, R, L, C are the equivalent resistance, equivalent inductance and equivalent capacitance respectively;

FIG3 is a time domain image of the output signal of the magnetron; the expression of the output signal of the free oscillation magnetron in the steady state with the intermediate frequency signal in the anode voltage derived is plotted, the depth of the sideband envelope represents the amplitude of the loaded intermediate frequency signal, and the frequency of the sideband envelope is related to the frequency of the intermediate frequency signal;

FIG4 is a frequency domain image of the output signal of the magnetron; the image is obtained by fast Fourier transforming the derived expression. The frequency point with the highest intensity in the image represents the center frequency of the free oscillation magnetron, and the sub-frequency points with slightly weaker intensity on both sides of the center frequency represent the new frequency points obtained after mixing the magnetron local oscillation frequency with the intermediate frequency signal frequency. The frequency difference between the center frequency and the sub-frequency component is the frequency of the intermediate frequency signal.

FIG5 is a waveform diagram of the anode voltage of a magnetron loaded with an intermediate frequency signal; the ideal anode voltage is a DC voltage, and the loaded intermediate frequency signal is reflected as a ripple component on the DC voltage. Here, the complex intermediate frequency signal carrying information is simplified to a single-frequency sinusoidal signal;

FIG6 is a time domain image of the output signal of the magnetron in the free oscillation state. The magnetron is modeled by electromagnetic simulation software, and the time domain output image of the magnetron in the free oscillation stable state is obtained by simulation calculation. The sideband envelope characteristics are similar to the image derived in FIG3.

FIG. 7 is a frequency domain image of the magnetron output signal in a free oscillation state, and is a magnetron output spectrum obtained by simulation calculation. The relationship characteristics between the center frequency and the sub-frequency components on the image are similar to the image derived from FIG. 4 ;

FIG8 is a frequency domain image of the magnetron output signal when no intermediate frequency signal is loaded. This spectrum is the output spectrum of the 2M244-M1 magnetron produced by Panasonic in a free oscillation state;

FIG9 is a frequency domain image of the magnetron output signal when a 2 MHz intermediate frequency signal is loaded. The relationship characteristics between the center frequency and the sub-frequency components on the image are similar to the image derived from FIG4 ;

FIG10 is a frequency domain image of the magnetron output signal when a 3 MHz intermediate frequency signal is loaded. The relationship characteristics between the center frequency and the sub-frequency components on the image are similar to the image derived from FIG4 ;

FIG11 is a frequency domain image of the magnetron output signal when a 4 MHz intermediate frequency signal is loaded. The relationship characteristics between the center frequency and the sub-frequency components on the image are similar to the image derived from FIG4 ;

FIG12 is a formula for solving the real part expression to obtain the high-frequency output voltage VRF(t) of the magnetron in the free oscillation state;

FIG13 is a formula for solving the imaginary part expression to obtain the transient output frequency ω(t) of the magnetron in the free oscillation state;

FIG14 is a schematic diagram of a material located in a cavity;

Figure 15 is a heating simulation diagram of a rectangular cavity with a cavity design of 405×295×340 mm, a potato located 50 mm below the center of the cavity, an initial temperature of 293.15 K, a heating time of 20 s, a single-frequency input of 2.45 GHz microwave, and a power of 600 W. It can be seen that the average temperature ave＝313.68 K, cov＝0.5352;

FIG16 is a heating simulation diagram of a rectangular cavity of 405×295×340 mm, with the potato located 50 mm below the center of the cavity, an initial temperature of 293.15 K, a heating time of 20 s, and an input three-frequency difference of 4 MHz (2.45 GHz,

2.446GHz, 2.454GHz) microwaves, power 200W, it can be seen that the average temperature ave = 310.63K, cov = 0.3738;

Figure 17 shows that the experimental results of the output powers of the three main microwave frequencies are nearly consistent.

In the accompanying drawings: 1-magnetron power supply, 2-magnetron, 3-intermediate frequency signal generator, 41-first capacitor, 42-second adjustable capacitor, 43-third adjustable capacitor, 44-fourth capacitor, 45-fifth capacitor, 51-first inductor, 52-second inductor, 53-third inductor, 61-first resistor, 62-second resistor, 63-third resistor, 71-first cathode power line, 72-second cathode power line, 8-cavity, 9-material.

DETAILED DESCRIPTION

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods, but the present invention is not limited to the following embodiments.

Embodiment 1:

See Figures 1 to 11 and 14. The magnetron anode power supply ripple mixing multi-frequency heating device comprises a magnetron power supply 1, a magnetron 2, an intermediate frequency signal generator 3, a first capacitor 41 and a cavity 8; the magnetron power supply 1 is connected to a first cathode power line 71 and a second cathode power line 72; the first cathode power line 71 and the second cathode power line 72 are respectively connected to the cathode ends of the magnetron 2; one end of the first capacitor 41 is connected to the intermediate frequency signal generator 3, and the other end is connected to the first cathode power line 71; a feed port is provided on the cavity 8; the magnetron 2 inputs microwaves of multiple frequencies into the cavity 8 through the feed port.

The working principle of a single magnetron being able to output microwaves of multiple frequencies:

The present invention makes full use of the characteristics of the magnetron as an amplitude nonlinear response device, combines the influence of the magnetron anode voltage ripple on its output spectrum characteristics, and uses the magnetron as a mixer. The magnetron power supply 1 supplies power to the magnetron 2; the intermediate frequency signal generator 3 generates a modulated intermediate frequency signal, and the intermediate frequency signal is input to the first cathode power line 71 through the first capacitor 41. At this time, the intermediate frequency signal is equivalent to the ripple of the anode voltage of the magnetron 2 loaded on the anode voltage of the magnetron 2, and the resonance signal excited by the magnetron 2 itself is used as the local oscillation signal. When the intermediate frequency signal acts as the anode voltage ripple and the resonance signal of the magnetron 2, the nonlinear response characteristics of the magnetron 2 cause the output end of the magnetron 2 to generate microwaves of multiple frequencies, and these frequencies are the results of linear operations between the frequency of the intermediate frequency signal and the frequency of the resonance signal. At the same time, microwaves of multiple frequencies can be directly input into the cavity 8 through the feed port to uniformly heat the material 9.

Magnetron structure: The magnetron has a cylindrical anode, the anode blade is radially mounted on the inner wall of the anode, the spiral filament is used as the cathode, the cathode is located at the center of the magnetron, the antenna is mounted on one of the anode blades, a plurality of cooling fins are arranged on the outer circumferential surface of the anode, and two magnets are respectively mounted on the top and bottom of the anode to form a magnetic field. The magnetron power supply 1 supplies power to the cathode through the first cathode power supply line 71 and the second cathode power supply line 72, heats the cathode filament to emit thermal electrons, and the thermal electrons, under the action of the electric field and the magnetic field, with the help of several resonant cavities formed by the anode blades, convert the electronic energy into high-frequency energy, i.e. microwaves, while doing cycloidal motion, and the microwaves are emitted through the antenna. The magnetron power supply 1 provides a 3.3V voltage to the cathode, the anode is grounded, and there is a negative high voltage of about 4kV between the cathode and the anode.

The first cathode power line 71 and the second cathode power line 72 are directly or indirectly connected to the two ends of the cathode of the magnetron 2 respectively; the two ends of the cathode can be connected to the first cathode power line 71 and the second cathode power line 72 respectively through a choke coil. The first capacitor 41 is used to block the direct current from passing the alternating current, preventing the high-voltage direct current of the magnetron power supply 1 from running into the intermediate frequency signal generator 3, and at the same time ensuring that the modulated intermediate frequency signal generated by the intermediate frequency signal generator 3 can be input to the first cathode power line 71.

Theoretical derivation:

See FIG2 . Based on the magnetron equivalent RLC resonant circuit model, the circuit equation of the magnetron in the free oscillation stable state is:

in,

ω is the oscillation frequency of the magnetron, that is, the oscillation frequency of the signal generated at the output end of the magnetron; ω ₀ is the local oscillation frequency of the resonant cavity, that is, the frequency of the resonant signal excited by the magnetron itself as the local oscillation signal; Q ₀ is the inherent quality factor of the resonant circuit; Q _ext is the external quality factor of the resonant circuit; V _dc is the anode voltage of the magnetron, that is, the voltage between the cathode and anode of the magnetron, and the anode is grounded; V _RF is the high-frequency voltage, that is, the voltage of the signal generated at the output end of the magnetron; A is the amplitude of the intermediate frequency signal; f is the frequency of the intermediate frequency signal; g+jb is the equivalent magnetron source part, g is the magnetron source electronic conductance, and b is the magnetron source electronic susceptance; G+jB is the equivalent load, G is the load end electronic conductance, and B is the load end electronic susceptance; j is an imaginary unit; b ₀ and tanα are constants; R, L, and C are equivalent resistance, equivalent inductance, and equivalent capacitance, respectively; t is a time variable. JC Slater published a paper titled “THE PHASING OF MAGNETRONS” on April 3, 1947, which specifically described the above theoretical principles. These are now common knowledge in this field and can be used directly.

In order to analyze the starting process of the magnetron, during its initial oscillation, it can be assumed that the amplitude of its voltage changes exponentially with time, and the frequency is expressed as a complex number, and its imaginary part represents the exponential growth relationship, that is:

ω＝ω ₁ +jω ₂

因此定义

则ω＝ω₁+jГ(t)。此时，磁控管自由振荡稳定状态下的电路方程可以改写为：The relationship between high frequency voltage and time is expressed as

So define

Then ω＝ω ₁ +jГ(t). At this time, the circuit equation of the magnetron in the free oscillation stable state can be rewritten as:

Separating the real and imaginary parts of the equation yields:

in

Solving the real part expression, we can get the high-frequency output voltage of the magnetron in the free oscillation state:

Similarly, solving the imaginary part expression yields the transient output frequency of the magnetron in the free oscillation state:

in,

It shows that after the magnetron works stably, its frequency consists of three parts:

代表由电子束引起的频率前推效应；

代表由负载引起的频率牵引效应。ω ₀ represents the local oscillator frequency of the resonant cavity;

represents the frequency-forward effect caused by the electron beam;

Represents the frequency pulling effect caused by the load.

In summary, when the intermediate frequency signal is loaded onto the anode voltage of the magnetron, which is equivalent to the anode voltage ripple, the output signal expression of the magnetron in the free oscillation stable state is:

V(t)=V _RF (t)·sin(ω(t)·t)

By performing a fast Fourier transform on the magnetron output expression derived from the theory in the previous article, we can get the frequency domain diagram corresponding to the expression. Figure 3 is a time domain image of the magnetron output signal; the expression of the output signal of the free oscillation magnetron in the steady state with the intermediate frequency signal in the anode voltage derived is plotted, the depth of the sideband envelope represents the amplitude of the loaded intermediate frequency signal, and the frequency of the sideband envelope is related to the frequency of the intermediate frequency signal. Figure 4 is a frequency domain image of the magnetron output signal; the graph obtained by performing a fast Fourier transform on the derived expression, the frequency point with the highest intensity in the image represents the center frequency of the free oscillation magnetron, the sub-frequency points with slightly weaker intensity on both sides of the center frequency represent the new frequency points obtained after the magnetron local oscillation frequency is mixed with the intermediate frequency signal frequency, and the frequency difference between the center frequency and the sub-frequency component is the frequency of the intermediate frequency signal. According to the frequency domain image of the magnetron output, slightly weaker sub-frequency components appear on both sides of the center frequency of the magnetron output signal, and the frequency difference between the center frequency and the sub-frequency components is the frequency of the intermediate frequency signal loaded on the anode voltage, which means that the magnetron plays the expected role of a mixer.

Figure 5 is a waveform of the anode voltage of a magnetron loaded with an intermediate frequency signal; the ideal anode voltage is originally a DC voltage, and the loaded intermediate frequency signal is reflected as a ripple component on the DC voltage. Here, the complex intermediate frequency signal carrying information is simplified into a single-frequency sinusoidal signal. Figure 6 is a time domain image of the output signal of the magnetron in the free oscillation state. The magnetron is modeled by electromagnetic simulation software, and the time domain output image of the magnetron in the free oscillation stable state is obtained by simulation calculation. The sideband envelope characteristics are similar to the image derived from Figure 3. Figure 7 is a frequency domain image of the output signal of the magnetron in the free oscillation state. The output spectrum of the magnetron obtained by simulation calculation, the relationship characteristics between the center frequency and the sub-frequency components on the image are similar to the image derived from Figure 4. The electromagnetic simulation software CST Studio Suite simulates the free oscillation state magnetron with the intermediate frequency signal loaded on the anode voltage as an equivalent ripple, and the output spectrum results obtained also verify that the magnetron can play the role of a mixer.

On this basis, the present invention builds a test system to verify the results of numerical calculation and software simulation. The system uses the 2M244-M1 type magnetron produced by Panasonic. When the intermediate frequency signal is not loaded, the output spectrum of the magnetron is shown in Figure 8; after loading the intermediate frequency signals of different frequencies, the output spectrum of the magnetron is shown in Figures 9, 10 and 11. The relationship characteristics between the center frequency and the sub-frequency components on the image are similar to the image derived from Figure 4. The frequency difference between the center frequency and the sub-frequency components is the frequency of the intermediate frequency signal loaded on the anode voltage, indicating that the intermediate frequency signal is equivalent to the ripple of the magnetron anode voltage loaded on the magnetron anode voltage, and the resonance signal excited by the magnetron itself is used as the local oscillation signal. The magnetron can be used for mixing to generate the main three-frequency microwaves at the output end of the magnetron, that is, the center frequency and the sub-frequency components with slightly weaker intensity appearing on both sides of the center frequency. Therefore, the intermediate frequency signal can not only make the output end of the magnetron generate the main three-frequency microwaves, but also affect the frequency distribution, so that the frequency is adjustable and controllable, and the main three-frequency microwaves can evenly heat the material.

Embodiment 2:

See Figures 1 to 11 and 14. Based on the first embodiment, a first inductor 51 is provided on the first cathode power line 71 between the intersection of the first capacitor 41 and the first cathode power line 71 and the magnetron power supply 1. As can be seen from the above structure, the first inductor 51 is used to separate the AC from the DC, preventing the intermediate frequency signal from entering the magnetron power supply 1, while ensuring that the high-voltage DC and low-frequency DC filament current can enter the magnetron.

The second cathode power line 72 is provided with a second inductor 52. As can be seen from the above structure, the second inductor 52 is used to isolate the AC and pass the DC to prevent the intermediate frequency signal from entering the magnetron power supply 1, while ensuring that the high-voltage DC and low-frequency DC filament current can enter the magnetron.

The third inductor 53 is also included; one end of the third inductor 53 is connected to the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected to the intermediate frequency signal generator 3, and the other end is grounded. As can be seen from the above structure, when the first capacitor 41 fails and short-circuits, the high voltage is directly applied to the intermediate frequency signal generator 3, so the third inductor 53 is added, and when the first capacitor 41 fails and short-circuits, the high voltage DC is grounded through the third inductor 53. The third inductor 53 plays a role in protecting the intermediate frequency signal generator 3.

The fourth capacitor 44 is also included; one end of the fourth capacitor 44 is connected to the first cathode power line 71 between the magnetron power supply 1 and the first inductor 51, and the other end is grounded. As can be seen from the above structure, the fourth capacitor 44 prevents high-frequency signals from returning to the magnetron power supply 1.

The fifth capacitor 45 is also included; one end of the fifth capacitor 45 is connected to the second cathode power line 72 between the magnetron power supply 1 and the second inductor 52, and the other end is grounded. As can be seen from the above structure, the fifth capacitor 45 prevents high-frequency signals from returning to the magnetron power supply 1.

It also includes a first resistor 61, a second resistor 62 and a third resistor 63; the first resistor 61 is connected in parallel with both ends of the third inductor 53; the second resistor 62 is connected in parallel with both ends of the first inductor 51; the third resistor 63 is connected in parallel with both ends of the second inductor 52. As can be seen from the above structure, the first resistor 61, the second resistor 62 and the third resistor 63 are used to reduce the Q value of the third inductor 53, the first inductor 51 and the second inductor 52 respectively to avoid resonance of the inductors.

It also includes an impedance matching regulator; the impedance matching regulator includes a second adjustable capacitor 42 and a third adjustable capacitor 43; one end of the second adjustable capacitor 42 is connected to the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected to the intermediate frequency signal generator 3, and the other end is grounded; one end of the third adjustable capacitor 43 is connected to the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected to the intermediate frequency signal generator 3, and the other end is grounded. It can be seen from the above structure that the impedance matching regulator is used to perform impedance matching with the circuit.

It also includes a circuit board; the first capacitor 41, the first inductor 51, the second inductor 52, the third inductor 53, the fourth capacitor 44, the fifth capacitor 45, the first resistor 61, the second resistor 62 and the third resistor 63 are integrated on the circuit board; the circuit board includes a first port, a second port, a third port, a fourth port and a fifth port; the first port is located on the first cathode power line 71 between the first inductor 51 and the magnetron power supply 1; the second port is located on the second cathode power line 72 between the second inductor 52 and the magnetron power supply 1; the third port is located on the first cathode power line 71 between the first inductor 51 and the magnetron 2; the fourth port is located on the second cathode power line 72 between the second inductor 52 and the magnetron 2; the fifth port is located between the intermediate frequency signal generator 3 and the first capacitor 41, so that the intermediate frequency signal generator 3 and the first capacitor 41 are connected. It can be seen from the above structure that the first capacitor 41, the first inductor 51, the second inductor 52, the third inductor 53, the fourth capacitor 44, the fifth capacitor 45, the first resistor 61, the second resistor 62 and the third resistor 63 are integrated on the circuit board, which is convenient for modular use. The intermediate frequency signal generator 3, the magnetron power supply 1, and the magnetron 2 are directly connected to the corresponding ports of the circuit board respectively, and the structure is more simplified.

Generally, the three main microwave frequencies that appear are the center frequency and the slightly weaker sub-frequency components on both sides of the center frequency. By adjusting the matching of the modulation circuit, the center frequency intensity of the magnetron output can be made the same as the sub-frequency component intensity, that is, the power is consistent, which will be more conducive to uniform heating of the material.

Embodiment three:

See Figures 1 to 11 and 14. A magnetron anode power supply ripple frequency mixing multi-frequency heating method, using any magnetron anode power supply ripple frequency mixing multi-frequency heating device of the above embodiments; the specific steps are: the magnetron power supply 1 supplies power to the magnetron 2; the intermediate frequency signal generator 3 generates an intermediate frequency signal, and the intermediate frequency signal is input to the first cathode power supply line 71 through the first capacitor 41. At this time, the intermediate frequency signal is equivalent to the ripple of the anode voltage of the magnetron 2, which is loaded on the anode voltage of the magnetron 2, and the resonance signal excited by the magnetron 2 itself is used as the local oscillation signal. When the intermediate frequency signal acts as the anode voltage ripple and the resonance signal of the magnetron 2, the nonlinear response characteristics of the magnetron 2 cause the output end of the magnetron 2 to generate microwaves of multiple frequencies, and the microwaves of multiple frequencies are input into the cavity 8 through the feed port to heat the material 9. The method of the present invention makes full use of the characteristics of the magnetron as an amplitude nonlinear response device, combines the influence of the anode voltage ripple of the magnetron on its output spectrum characteristics, uses the magnetron as a mixer, and can enable the output end of the magnetron 2 to generate multiple microwaves with controllable and adjustable frequencies without the need to separately set up a mixer and cooperate with a large number of auxiliary accessories. The microwaves of multiple frequencies are input into the cavity 8 through the feed port to uniformly heat the material 9.

In fact, the magnetron outputs a large number of microwaves of different frequencies, but the microwave intensities of the three main frequencies are relatively high, so only the microwaves of these three frequencies are considered, and the other low-intensity microwaves can be ignored. It is only necessary to verify that the magnetron outputs three different frequency microwaves to improve the uniformity of material heating in the COMSOL Multiphysics simulation software:

Experimental description: Because it is not possible to feed sources with different frequencies simultaneously in this software, the present invention uses a single frequency source to feed in COMSOL Multiphysics, and exports the temperature rise results obtained at different frequencies to MATLAB software for calculation, so as to simulate the effect of simultaneous output of three frequencies of the magnetron.

First, the cavity is designed as a rectangular cavity of 405×295×340mm, the magnetron is fed by a BJ-26 rectangular waveguide, and potatoes of 50×50×50mm are placed in the cavity as materials. In the simulation verification, a single microwave source with a frequency of 2.45GHz and a power of 600W is used, and three microwaves with a center frequency of 2.45GHz, a frequency difference of 2 to 8MHz (for example, a frequency difference of 2MHz means three microwave frequencies of 2.448GHz, 2.45GHz, and 2.452GHz), and a power of 200W are used for feeding respectively. Then the temperature rise data is imported into MATLAB for calculation, and the three-frequency heating results are simulated. This method is used to compare and verify the improvement effect of heating uniformity.

The average temperature (ave) and temperature coefficient of variation (cov) in each case were calculated using MTALAB software. The temperature coefficient of variation (cov) is the ratio of the standard deviation of the original data to the average of the original data, reflecting the absolute value of the degree of data dispersion. The smaller the cov value, the more uniform the heating. At the same time, the improvement of heating uniformity at different potato positions was calculated.

The following table shows the data when the potato is 50 mm below the center of the cavity:

The following table shows the data when the potato is 80 mm below the center point:

The cavity is designed as a rectangular cavity of 450×350×340 mm. The following table shows the data when the potato is 80 mm below the center point:

From the above data, it can be concluded that the modulation circuit that modulates the intermediate frequency signal to the high voltage power supply of the magnetron makes the magnetron mix to generate a microwave signal with a specified frequency difference, and realizes microwave heating with three-frequency output, which has a good effect on improving heating uniformity and can achieve the expected purpose. According to the experiment, the optimal frequency of the intermediate frequency signal can be selected to optimize the heating uniformity of the material.

Figure 15 is a heating simulation diagram of a rectangular cavity with a cavity design of 405×295×340 mm, a potato located 50 mm below the center of the cavity, an initial temperature of 293.15 K, a heating time of 20 s, a single-frequency input of 2.45 GHz microwave, and a power of 600 W. It can be seen that the average temperature ave＝313.68 K, cov＝0.5352;

Fig. 16 is a heating simulation diagram of a rectangular cavity of 405×295×340 mm, with the potato located 50 mm below the center of the cavity, an initial temperature of 293.15 K, a heating time of 20 s, and a microwave input with a frequency difference of 4 MHz (2.45 GHz, 2.446 GHz, 2.454 GHz) and a power of 200 W. It can be seen that the average temperature ave = 310.63 K, cov = 0.3738;

From the comparison of Figures 15 and 16, it can be seen that the maximum temperature and average temperature of triple-frequency heating are not as high as those of single-frequency heating, but the difference in average temperature is small, and from the temperature distribution on the body surface, it can be seen that triple-frequency heating does have a certain improvement effect on uniformity.

As can be seen from Figure 17, by changing the power of the intermediate frequency signal, the experiment can make the output powers of the three main frequencies of microwaves close to each other. The closer they are, the more uniform the heating.

The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims (10)

1. A magnetron anode power supply ripple mixing multi-frequency heating device, characterized in that it includes a magnetron power supply (1), a magnetron (2), an intermediate frequency signal generator (3), and a first capacitor (41) and cavity (8); the magnetron power supply (1) is connected with a first cathode power supply line (71) and a second cathode power supply line (72); the first cathode power supply line (71) and the second cathode power supply line The power lines (72) are respectively connected to both ends of the cathode of the magnetron (2); one end of the first capacitor (41) is connected to the intermediate frequency signal generator (3), and the other end is connected to the first cathode power line (71) ; The cavity (8) is provided with a feed port; the magnetron (2) inputs microwaves of multiple frequencies into the cavity (8) through the feed port. 2. The magnetron anode power supply ripple-mixing multi-frequency heating device according to claim 1, characterized in that: the first capacitor (41) connects the intersection with the first cathode power line (71) and the magnetron A first inductance (51) is provided on the first cathode power line (71) between the power sources (1). 3. The magnetron anode power supply ripple mixing multi-frequency heating device according to claim 2, characterized in that a second inductance (52) is provided on the second cathode power line (72). 4. The magnetron anode power supply ripple mixing multi-frequency heating device according to claim 3 is characterized in that: it also includes a third inductance (53); one end of the third inductance (53) is connected to the intermediate frequency signal generator (3) and one end of the first capacitor (41) connected to the intermediate frequency signal generator (3) are both connected, and the other end is grounded. 5. The magnetron anode power supply ripple mixing multi-frequency heating device according to claim 4, characterized in that: it also includes a fourth capacitor (44); one end of the fourth capacitor (44) is connected to the magnetron power supply (1) is connected to the first cathode power line (71) between the first inductor (51), and the other end is grounded. 6. The magnetron anode power supply ripple mixing multi-frequency heating device according to claim 5, characterized in that: it also includes a fifth capacitor (45); one end of the fifth capacitor (45) is connected to the magnetron power supply (1) is connected to the second cathode power line (72) between the second inductor (52), and the other end is grounded. 7. The magnetron anode power supply ripple mixing multi-frequency heating device according to claim 6, characterized in that: it also includes a first resistor (61), a second resistor (62) and a third resistor (63); Two ends of the first resistance (61) and the third inductance (53) are connected in parallel; two ends of the second resistance (62) and the first inductance (51) are connected in parallel; the third resistance (63) and the second inductance (52) two ends are connected in parallel. 8. magnetron anode power supply ripple frequency mixing multi-frequency heating device according to claim 7, is characterized in that: also comprise impedance matching regulator; Described impedance matching regulator comprises the second adjustable capacitor (42) and The third adjustable capacitor (43); one end of the second adjustable capacitor (42) is connected to the intermediate frequency signal generator (3) and the first capacitor (41) is connected to one end of the intermediate frequency signal generator (3), and the other end Grounding; one end of the third adjustable capacitor (43) is connected to the intermediate frequency signal generator (3) and one end of the first capacitor (41) connected to the intermediate frequency signal generator (3), and the other end is grounded. 9. The magnetron anode power supply ripple mixing multi-frequency heating device according to claim 8, characterized in that: it also includes a circuit board; the first capacitor (41), the first inductor (51), the second The inductor (52), the third inductor (53), the fourth capacitor (44), the fifth capacitor (45), the first resistor (61), the second resistor (62) and the third resistor (63) are integrated on the circuit board on; the circuit board includes a first port, a second port, a third port, a fourth port and a fifth port; the first port is located between the first inductor (51) and the magnetron power supply (1) On the first cathode power supply line (71); the second port is located on the second cathode power supply line (72) between the second inductor (52) and the magnetron power supply (1); the third port is located at the second cathode power supply line (72) On the first cathode power line (71) between an inductor (51) and the magnetron (2); the fourth port is located at the second cathode between the second inductor (52) and the magnetron (2) On the power line (72); the fifth port is located between the intermediate frequency signal generator (3) and the first capacitor (41), connecting the intermediate frequency signal generator (3) and the first capacitor (41). 10. A magnetron anode power supply ripple-mixing multi-frequency heating method, characterized in that: the magnetron anode power ripple-mixing multi-frequency heating device described in any one of claims 1 to 9 is used; the specific steps are: The magnetron power supply (1) supplies power for the magnetron (2); the intermediate frequency signal generator (3) produces an intermediate frequency signal, and the intermediate frequency signal is input to the first cathode power line (71) through the first capacitor (41) , the intermediate frequency signal is equivalent to the ripple of the anode voltage of the magnetron (2) being loaded on the anode voltage of the magnetron (2), and the resonant signal excited by the magnetron (2) itself is used as a local oscillation signal, When the intermediate frequency signal acts as the anode voltage ripple and the resonant signal of the magnetron (2), the characteristic of the nonlinear response of the magnetron (2) causes the output terminal of the magnetron (2) to generate microwaves of multiple frequencies, Microwaves of multiple frequencies are input into the cavity (8) through the feed port to heat the material (9).

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