CN113950176A - Magnetron anode power supply ripple mixing multi-frequency heating device and method - Google Patents
Magnetron anode power supply ripple mixing multi-frequency heating device and method Download PDFInfo
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- CN113950176A CN113950176A CN202111196131.8A CN202111196131A CN113950176A CN 113950176 A CN113950176 A CN 113950176A CN 202111196131 A CN202111196131 A CN 202111196131A CN 113950176 A CN113950176 A CN 113950176A
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
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- H05B6/687—Circuits for monitoring or control for cooking
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/70—Feed lines
- H05B6/701—Feed lines using microwave applicators
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/80—Apparatus for specific applications
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Abstract
The invention discloses a magnetron anode power supply ripple frequency mixing multi-frequency heating device and a method, belonging 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 the 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 the first cathode power line; a feed port is arranged on the cavity; the magnetron inputs microwaves of multiple frequencies into the cavity through the feed port. The invention relates to a magnetron anode power supply ripple frequency mixing multi-frequency heating device and a method, which are based on the nonlinear response characteristic of a magnetron, wherein an intermediate frequency signal is equivalent to the ripple of the anode voltage of the magnetron and is loaded on the anode voltage of the magnetron, a resonance signal excited by the magnetron is used as a local oscillation signal, and the magnetron is used for carrying out frequency mixing to enable the output end of the magnetron to generate microwaves with a plurality of frequencies so as to uniformly heat materials.
Description
Technical Field
The invention belongs to the field of microwave heating, and particularly relates to a magnetron anode power supply ripple mixing multi-frequency heating device and method.
Background
Microwave is widely applied to various fields such as food, chemical industry, metallurgy, sewage treatment and the like as a novel clean energy. The microwave directly acts on the polar molecules and the charged particles in the heated material, so the microwave heating has the advantages of selective heating, body heating, cleaning heating and the like. However, the microwave generally has the problem of uneven heating in the actual heating process, uneven heating causes local overhigh temperature to form a 'hot spot', the absorption capacity of a plurality of substances to electromagnetic waves is in positive correlation with the temperature, the temperature of the 'hot spot' area rises faster, and finally, a 'thermal runaway' phenomenon is formed, so that the large-scale application of the microwave energy is greatly restricted.
With the development of science and technology and the improvement of the living standard of people, microwave ovens are more and more paid attention by consumers and slowly become necessary household appliances in kitchens. Since microwave heating has the advantages of high heating speed, low energy consumption, convenient control at any time and the like, the microwave oven is gradually widely applied. However, with the continuous development of the technology, the requirements of consumers for microwave ovens are gradually increased, especially in terms of the heating uniformity and heating efficiency of food. The traditional microwave oven has the working frequency of 2450MHz, only a single microwave source and single frequency are adopted for heating, and although the cavity of the microwave oven is a multi-mode resonant cavity and can excite a plurality of electromagnetic modes in the cavity, the number of the excited modes is limited, and the phenomenon of uneven heating still exists.
In the aspect of improving the heating uniformity of the microwave oven, a lot of work is done by students. In 1989, a concept of rotating an antenna was proposed, namely, the antenna rotates along with a driver, and a mode field in a cavity is changed, so that field distribution is changed, and heating uniformity is improved. In 1995, Yan Limni et al worked primarily to explore the effect of disk rotation in the cavity of a microwave oven on heating uniformity and the relationship between load size and area and microwave oven output power. In 2001, the regular rectangular waveguide and the resonant cavity are subjected to simulation analysis by using FEM (finite element method) of Sung Yi and Lie Liu, and the more the excited resonant frequency in the cavity is, the more uniform the field distribution is. In 2006, Shinya Watanabe et al calculated THE heat conduction by THE che method and THE electromagnetic field by THE FDTD method, and studied THE temperature distribution on THE surface of THE object to be heated. In 2017, Sang-Hyeon Bae and Min-Gyo Jeong researched microwave conveyor belt type dryers with sustainable power control made of multiple 2.45GHz microwave sources, and the input power of the microwave sources was sequentially controlled, so that the uniformity of cavity heating could be improved. The intermediate frequency signal refers to a frequency signal with a frequency range from 300KHz to 3000KHz, and in a radio frequency communication system, a signal before modulation is called a baseband signal, a signal after mixing is called a radio frequency (or high frequency) signal, and an intermediate frequency signal is between the two stages.
The prior art has not studied how to enable a single microwave source to output microwaves with multiple frequencies to uniformly heat materials so as to solve the problem of non-uniformity of materials heated by microwaves. Even if it is considered that the material is heated by microwaves of a plurality of frequencies, the number of microwave sources is generally increased, which inevitably leads to an increase in cost. Or even if a single microwave source can output microwaves of multiple frequencies, a mixer and a large number of auxiliary components which are separately provided must be used, which also results in an increase in cost. The invention realizes that a single microwave source outputs microwaves with a plurality of frequencies at low cost, and the frequency of the output microwaves is controllable and adjustable, thereby ensuring the uniformity of microwave heating.
Disclosure of Invention
The invention aims to provide a magnetron anode power supply ripple mixing multi-frequency heating device and method aiming at the defects, and aims to solve the problems that the microwave heating in the prior art is uneven and the like. In order to achieve the purpose, the invention provides the following technical scheme:
the magnetron anode power supply ripple frequency 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 with a first cathode power supply line 71 and a second cathode power supply line 72; the first cathode power line 71 and the second cathode power line 72 are respectively connected with two ends of the cathode of the magnetron 2; one end of the first capacitor 41 is connected with the intermediate frequency signal generator 3, and the other end is connected with a first cathode power line 71; a feed port is arranged 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 source 1.
Further, a second inductor 52 is disposed on the second cathode power line 72.
Further, a 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.
Further, a fourth capacitor 44 is also included; the fourth capacitor 44 has one end connected to the first cathode power line 71 between the magnetron power supply 1 and the first inductor 51, and the other end grounded.
Further, a fifth capacitor 45 is also included; the fifth capacitor 45 has one end connected to the second cathode power line 72 between the magnetron power supply 1 and the second inductor 52, and the other end grounded.
Further, a first resistor 61, a second resistor 62 and a third resistor 63 are included; the first resistor 61 and the third inductor 53 are connected in parallel; the second resistor 62 is connected in parallel with the first inductor 51; the third resistor 63 is connected in parallel with the second inductor 52.
Further, the device also comprises an impedance matching adjuster; the impedance matching regulator comprises a second adjustable capacitor 42 and a third adjustable capacitor 43; one end of the second adjustable capacitor 42 is connected with the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected with 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.
Further, the device also comprises 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 a circuit board; the circuit board comprises a first port, a second port, a third port, a fourth port and a fifth port; the first port is located on a 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 supply 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, and communicates the intermediate frequency signal generator 3 with the first capacitor 41.
The magnetron anode power supply ripple frequency mixing multi-frequency heating method adopts any one of the magnetron anode power supply ripple frequency mixing multi-frequency heating devices; the method comprises the following specific steps: the magnetron power supply 1 supplies power to the magnetron 2; the intermediate frequency signal generator 3 generates an intermediate frequency signal, 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 a ripple wave of an anode voltage of the magnetron 2 and is loaded to the anode voltage of the magnetron 2, a resonance signal excited by the magnetron 2 is used as a local oscillation signal, when the intermediate frequency signal is used as the anode voltage ripple and is acted with the resonance signal of the magnetron 2, the output end of the magnetron 2 generates microwaves with multiple frequencies through the nonlinear response characteristic of the magnetron 2, and the microwaves with multiple frequencies are input into the cavity 8 through the feed port to heat the material 9.
The invention has the beneficial effects that:
the invention discloses a magnetron anode power supply ripple frequency mixing multi-frequency heating device and a method, 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 the 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 the first cathode power line; a feed port is arranged on the cavity; the magnetron inputs microwaves of multiple frequencies into the cavity through the feed port. The invention relates to a magnetron anode power supply ripple frequency mixing multi-frequency heating device and a method, which are based on the nonlinear response characteristic of a magnetron, wherein an intermediate frequency signal is equivalent to the ripple of the anode voltage of the magnetron and is loaded on the anode voltage of the magnetron, a resonance signal excited by the magnetron is used as a local oscillation signal, and the magnetron is used for carrying out frequency mixing to enable the output end of the magnetron to generate microwaves with a plurality of frequencies so as to uniformly heat materials.
Drawings
FIG. 1 is a schematic diagram of the circuit of the magnetron anode power supply ripple mixing multi-frequency heating device of the present invention, not showing the cavity;
FIG. 2 is an equivalent circuit diagram of a magnetron; according to the research on the structure and the effect of the resonant cavity of the magnetron, the resonant cavity of the magnetron can be equivalent to an RLC parallel resonant circuit, G + jB is an equivalent magnetron source part, G + jB is an equivalent load, and R, L, C is an equivalent resistor, an equivalent inductor and an equivalent capacitor respectively;
FIG. 3 is a time domain image of the magnetron output signal; plotting the expression of the output signal of the free oscillation magnetron in a stable state, wherein the derived anode voltage contains an intermediate frequency signal, 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;
FIG. 4 is a frequency domain plot of the magnetron output signal; performing fast Fourier transform on the derived expression to obtain a graph, wherein the frequency point with the highest intensity in the graph represents the central frequency of the free oscillation magnetron, the secondary frequency points with the weaker intensities on two sides of the central frequency represent new frequency points obtained after the local oscillation frequency of the magnetron and the frequency of the intermediate frequency signal are mixed, and the frequency difference between the central frequency and the secondary frequency components is the frequency of the intermediate frequency signal;
FIG. 5 is a graph of magnetron anode voltage waveforms loaded with intermediate frequency signals; the original ideal anode voltage is direct current voltage, the loaded intermediate frequency signal is reflected as ripple wave component on the direct current voltage, and the complex intermediate frequency signal carrying information is simplified into a sinusoidal signal with single frequency;
FIG. 6 is a time domain image of magnetron output signals in a free oscillation state, modeling is performed on the magnetron through electromagnetic simulation software, the time domain output image of the magnetron in a free oscillation stable state is obtained through simulation calculation, and the sideband envelope characteristics are similar to the image obtained through derivation in FIG. 3;
FIG. 7 is a frequency domain image of magnetron output signals in a free oscillation state, a magnetron output spectrum graph obtained through simulation calculation, and the relationship characteristics between the central frequency and the secondary frequency components on the image are similar to the image derived from FIG. 4;
FIG. 8 is a frequency domain image of the magnetron output signal when no IF signal is applied, the spectrum being the output spectrum of a loosely produced 2M244-M1 type magnetron in a free-running state;
FIG. 9 is a frequency domain image of the magnetron output signal when a 2MHz IF signal is applied, the characteristics of the relationship between the center frequency and the secondary frequency components in the image being similar to the image derived from FIG. 4;
FIG. 10 is a frequency domain image of the magnetron output signal when a 3MHz IF signal is applied, the characteristics of the relationship between the center frequency and the secondary frequency components on the image being similar to the image derived from FIG. 4;
FIG. 11 is a frequency domain image of the magnetron output signal when a 4MHz IF signal is applied, the characteristics of the relationship between the center frequency and the secondary frequency components in the image being similar to the image derived from FIG. 4;
FIG. 12 is a formula for solving the real expression to obtain the high-frequency output voltage VRF (t) in the free oscillation state of the magnetron;
FIG. 13 is a formula for solving the imaginary expression to obtain the transient output frequency ω (t) of the free oscillation state of the magnetron;
FIG. 14 is a schematic view of a material located within a cavity;
fig. 15 is a heating simulation diagram of a rectangular cavity with a cavity design of 405 × 295 × 340mm, where a potato is located 50mm right below the center point of the cavity, the initial temperature is 293.15K, and the heating time is 20s, a microwave with 2.45GHz is input at a single frequency, the power is 600W, and it can be seen that the average temperature ave is 313.68K, and cov is 0.5352;
fig. 16 is a heating simulation diagram of a rectangular cavity with a cavity design of 405 × 295 × 340mm, potatoes located 50mm right below the center point of the cavity, an initial temperature of 293.15K, and a heating time of 20s, microwaves with three frequency differences of 4MHz (2.45GHz, 2.446GHz, 2.454GHz) are input, a power of 200W, and it can be seen that an average temperature ave is 310.63K, and cov is 0.3738;
fig. 17 shows that the output power of microwaves of three main frequencies can be close to the same experimental result.
In the drawings: the power supply comprises a magnetron power supply 1, a magnetron 2, a medium frequency signal generator 3, a first capacitor 41, a second adjustable capacitor 42, a third adjustable capacitor 43, a fourth capacitor 44, a fifth capacitor 45, a first inductor 51, a second inductor 52, a third inductor 53, a first resistor 61, a second resistor 62, a third resistor 63, a first cathode power line 71, a second cathode power line 72, a cavity 8 and a material 9.
Detailed Description
The present invention will be described in further detail below with reference to the drawings and the embodiments, but the present invention is not limited to the following examples.
The first embodiment is as follows:
see figures 1-11, 14. The magnetron anode power supply ripple frequency 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 with a first cathode power supply line 71 and a second cathode power supply line 72; the first cathode power line 71 and the second cathode power line 72 are respectively connected with two ends of the cathode of the magnetron 2; one end of the first capacitor 41 is connected with the intermediate frequency signal generator 3, and the other end is connected with a first cathode power line 71; a feed port is arranged on the cavity 8; the magnetron 2 inputs microwaves of multiple frequencies into the cavity 8 through the feed port.
The working principle that a single magnetron can output microwaves with multiple frequencies is as follows:
the invention fully utilizes the characteristic of the magnetron as an amplitude nonlinear response device, combines the influence of the anode voltage ripple of the magnetron on the output frequency spectrum characteristic thereof, 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, 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 a ripple wave of an anode voltage of the magnetron 2 and is loaded on the anode voltage of the magnetron 2, a 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 output end of the magnetron 2 generates microwaves with a plurality of frequencies due to the nonlinear response characteristic of the magnetron 2, and the frequencies are the result of linear operation between the frequency of the intermediate frequency signal and the frequency of the resonant signal. Meanwhile, microwaves with multiple frequencies can be directly input into the cavity 8 through the feed port to uniformly heat the material 9.
The magnetron structure: the magnetron has a cylindrical anode, anode vanes installed on an inner wall of the anode in a radial direction, a coiled filament as a cathode, the cathode being located at a center of the magnetron, an antenna installed on one of the anode vanes, a plurality of cooling fins installed on an outer circumferential surface of the anode, and two magnets installed on top and bottom of the anode, respectively, to form a magnetic field. The magnetron power supply 1 supplies power to the cathode through a first cathode power line 71 and a second cathode power line 72, heats the cathode filament to emit thermal electrons, and the thermal electrons convert the electronic energy into high-frequency energy, namely microwaves, by virtue of a plurality of resonance cavities formed by anode blades under the action of an electric field and a magnetic field while performing cycloidal motion. The magnetron power supply 1 supplies 3.3V voltage to the cathode, the anode is grounded, and negative high voltage of about 4kV is arranged between the cathode and the anode.
The first cathode power line 71 and the second cathode power line 72 are respectively connected with two ends of the cathode of the magnetron 2 directly or indirectly; the cathode terminals may be connected to a first cathode power supply line 71 and a second cathode power supply line 72 through choke coils, respectively. The first capacitor 41 is used to block the direct current from flowing through the alternating current, so as to prevent the high voltage direct current of the magnetron power supply 1 from flowing into the intermediate frequency signal generator 3, and to ensure 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:
referring to fig. 2, the circuit equation of the invention is based on the equivalent RLC resonant circuit model of the magnetron in the free oscillation stable state:
wherein the content of the first and second substances,
omega is the oscillation frequency of the magnetron, namely the oscillation frequency of the signal generated by the output end of the magnetron; omega0The local oscillation frequency of the resonant cavity, namely the frequency of the local oscillation signal which is the resonance signal excited by the magnetron itself; q0Is the intrinsic quality factor of the resonant circuit; qextIs the external quality factor of the resonant circuit; vdcThe anode is the voltage of the anode of the magnetron, namely the voltage between the cathode and the anode of the magnetron, and the anode is grounded; vRFIs a high frequency voltage, i.e. the voltage of the signal generated at the output 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 electron conductance, b is the magnetron source electron susceptance; g + jB is an equivalent load, G is the load end electronic conductance, and B is the load end electronic susceptance; j is an imaginary unit; b0Tan alpha is a constant; r, L, C is equivalent resistance, equivalent inductance and equivalent capacitance; t is a time variable. Slater published a paper entitled "THE PHASING OF MAGNETRONS" on 3.4.1947, specifically describing the above theoretical principles, and is now well known in the art and can be directly used.
In order to analyze the oscillation starting process of the magnetron, during the initial oscillation, it can be assumed that the amplitude of the voltage thereof changes exponentially with time, and the frequency is expressed as a complex number, and the imaginary part thereof represents the relationship of exponential increase, namely:
ω＝ω1+jω2
the relationship of the high-frequency voltage with time is expressed as
Thus define
Then ω is equal to ω1+ j r (t). At this time, the circuit equation in the steady state of free oscillation of the magnetron can be rewritten as:
separating the real and imaginary parts in the equation yields:
wherein
Solving the expression of the real part to obtain the high-frequency output voltage of the magnetron in the free oscillation state as follows:
similarly, the transient output frequency of the free oscillation state of the magnetron obtained by solving the imaginary expression is as follows:
wherein the content of the first and second substances,
the frequency of the magnetron after stable operation is shown to consist of three parts:
ω0representing the local oscillator frequency of the resonant cavity;
representing the frequency push-forward effect caused by the electron beam;
representing the frequency pulling effect caused by the load.
In summary, when the intermediate frequency signal is applied to the anode voltage of the magnetron, which is equivalent to the anode voltage ripple, the magnetron output signal under the free oscillation stable state has the following expression:
V(t)＝VRF(t)·sin(ω(t)·t)
the magnetron output expression obtained by theoretical derivation in the foregoing is subjected to fast fourier transform, and a frequency domain diagram corresponding to the expression can be obtained. FIG. 3 is a time domain image of the magnetron output signal; the derived representation of the output signal at steady state in a free-running magnetron with anode voltage containing an intermediate frequency signal is plotted, the depth of the sideband envelope representing the amplitude of the loaded intermediate frequency signal, the frequency of the sideband envelope being related to the frequency of the intermediate frequency signal. FIG. 4 is a frequency domain plot of the magnetron output signal; and performing fast Fourier transform on the derived expression to obtain a graph, wherein the frequency point with the highest intensity in the image represents the central frequency of the free oscillation magnetron, the secondary frequency points with the weaker intensities on two sides of the central frequency represent new frequency points obtained after the local oscillation frequency of the magnetron is mixed with the intermediate frequency signal frequency, and the frequency difference between the central frequency and the secondary frequency components is the frequency of the intermediate frequency signal. According to the frequency domain image output by the magnetron, secondary frequency components with weaker intensity appear at two sides of the central frequency of the output signal of the magnetron, and the frequency difference between the central frequency and the secondary frequency components is the frequency of the intermediate frequency signal loaded on the anode voltage, which means that the magnetron plays the role of the expected mixer.
FIG. 5 is a graph of magnetron anode voltage waveforms loaded with intermediate frequency signals; the original ideal anode voltage is direct current voltage, the loaded intermediate frequency signal is reflected as ripple wave component on the direct current voltage, and the complex intermediate frequency signal carrying information is simplified into a sinusoidal signal with single frequency. FIG. 6 is a time domain image of magnetron output signals in a free oscillation state, modeling is performed on the magnetron through electromagnetic simulation software, the time domain output image of the magnetron in a free oscillation stable state is obtained through simulation calculation, and the sideband envelope characteristics are similar to the image obtained through derivation in FIG. 3. Fig. 7 is a magnetron output signal frequency domain image in a free oscillation state, a magnetron output spectrum graph is obtained through simulation calculation, and the relation characteristic between the central frequency and the secondary frequency component on the image is similar to the image obtained by derivation of fig. 4. The magnetron in the free oscillation state, in which the anode voltage is loaded with the intermediate frequency signal as the equivalent ripple, is simulated by the CST Studio Suite of the electromagnetic simulation software, and the obtained output frequency spectrum result also verifies that the magnetron can play the role of a mixer.
On the basis, the test system is set up to verify the results of numerical calculation and software simulation, the system uses a 2M244-M1 type magnetron produced loosely, and when the intermediate frequency signal is not loaded, the output frequency spectrum of the magnetron is as shown in figure 8; after loading the intermediate frequency signals with different frequencies, the output frequency spectrum of the magnetron is shown in fig. 9, fig. 10 and fig. 11. The characteristics of the relationship between the center frequency and the sub-frequency components on the image are similar to the image derived from fig. 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, which means that the intermediate frequency signal is equivalent to the magnetron anode voltage with the ripple loaded on the magnetron anode voltage, the resonant signal excited by the magnetron itself is used as a local oscillation signal, the magnetron can be utilized to carry out frequency mixing, so that the output end of the magnetron generates microwaves of three main frequencies, namely, a central frequency and secondary frequency components with weaker intensity appearing at two sides of the central frequency, the intermediate frequency signal not only causes the output of the magnetron to generate microwaves of mainly three frequencies, and the distribution of frequency can be influenced, so that the frequency can be adjusted and controlled, and the microwave with three main frequencies can uniformly heat the material.
Example two:
see figures 1-11, 14. In 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 source 1. With the above structure, the first inductor 51 is used to isolate ac current from dc current, so as to prevent the if signal from entering the magnetron power supply 1, and ensure 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. With the above structure, the second inductor 52 is used to isolate ac and dc to prevent the if signal from entering the magnetron power supply 1, and to ensure that the high voltage dc and low frequency dc filament current can enter the magnetron.
A third inductance 53; 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 is short-circuited, the high voltage is directly applied to the if signal generator 3, so that the third inductor 53 is added, and when the first capacitor 41 fails and is short-circuited, the high voltage dc is grounded through the third inductor 53. The third inductor 53 functions to protect the if signal generator 3.
A fourth capacitor 44; the fourth capacitor 44 has one end connected to the first cathode power line 71 between the magnetron power supply 1 and the first inductor 51, and the other end grounded. As can be seen from the above structure, the fourth capacitor 44 prevents the high frequency signal from returning to the magnetron power supply 1.
A fifth capacitor 45; the fifth capacitor 45 has one end connected to the second cathode power line 72 between the magnetron power supply 1 and the second inductor 52, and the other end grounded. As can be seen from the above structure, the fifth capacitor 45 prevents the high frequency signal from returning to the magnetron power supply 1.
Also include the first resistance 61, the second resistance 62 and the third resistance 63; the first resistor 61 and the third inductor 53 are connected in parallel; the second resistor 62 is connected in parallel with the first inductor 51; the third resistor 63 is connected in parallel with 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 values of the third inductor 53, the first inductor 51 and the second inductor 52, respectively, so as to avoid the resonance of the inductors.
Also includes an impedance matching adjuster; the impedance matching regulator comprises a second adjustable capacitor 42 and a third adjustable capacitor 43; one end of the second adjustable capacitor 42 is connected with the intermediate frequency signal generator 3 and one end of the first capacitor 41 connected with 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. As can be seen from the above structure, the impedance matching adjuster is used for impedance matching with a circuit.
The circuit board is also included; 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 a circuit board; the circuit board comprises a first port, a second port, a third port, a fourth port and a fifth port; the first port is located on a 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 supply 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, and communicates the intermediate frequency signal generator 3 with the first capacitor 41. According to the structure, 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, so that the modular use is facilitated, the intermediate frequency signal generator 3, the magnetron power supply 1 and the magnetron 2 are directly connected with the corresponding ports of the circuit board respectively, and the structure is simplified and simpler.
The microwave frequency with three main intensities is the central frequency, and the secondary frequency components with weaker intensity are arranged at two sides of the central frequency, so that the central frequency intensity output by the magnetron is the same as the secondary frequency components in intensity, namely the power is consistent, after the matching of the modulation circuit is adjusted, which is more beneficial to uniformly heating materials.
Example three:
see figures 1-11, 14. The magnetron anode power supply ripple frequency mixing multi-frequency heating method adopts any magnetron anode power supply ripple frequency mixing multi-frequency heating device in the embodiment; the method comprises the following specific steps: the magnetron power supply 1 supplies power to the magnetron 2; the intermediate frequency signal generator 3 generates an intermediate frequency signal, 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 a ripple wave of an anode voltage of the magnetron 2 and is loaded to the anode voltage of the magnetron 2, a resonance signal excited by the magnetron 2 is used as a local oscillation signal, when the intermediate frequency signal is used as the anode voltage ripple and is acted with the resonance signal of the magnetron 2, the output end of the magnetron 2 generates microwaves with multiple frequencies through the nonlinear response characteristic of the magnetron 2, and the microwaves with multiple frequencies are input into the cavity 8 through the feed port to heat the material 9. The method of the invention fully utilizes the characteristic of the magnetron as an amplitude nonlinear response device, combines the influence of the anode voltage ripple of the magnetron on the output frequency spectrum characteristic, uses the magnetron as a frequency mixer, can enable the output end of the magnetron 2 to generate a plurality of microwaves with controllable and adjustable frequencies without independently setting the frequency mixer and matching a large number of auxiliary accessories, and inputs the microwaves with a plurality of frequencies into the cavity 8 through the feed port to uniformly heat the material 9.
In practice, the magnetron outputs a large number of microwaves of different frequencies, but the microwaves of the main three frequencies have high intensity, so that only the microwaves of the three frequencies are considered, and the microwaves of the other low frequencies can be ignored. The verification of improving the material heating uniformity by outputting microwaves with three different frequencies by a magnetron in COMSOL Multiphysics simulation software is only needed:
description of the experiment: because the software can not realize the simultaneous feeding of the sources with different frequencies, the invention adopts the mode that a single frequency source is used for feeding in the COMSOL Multiphysics, and the temperature rise results obtained under different frequencies are exported to MATLAB software for calculation, thereby simulating the effect of magnetron tri-frequency simultaneous output.
Firstly, the cavity is designed to be a rectangular cavity with the size of 405 multiplied by 295 multiplied by 340mm, the magnetron adopts BJ-26 rectangular waveguide feed, and potatoes with the size of 50 multiplied by 50mm are placed in the cavity as materials. In simulation verification, a single microwave source with the frequency of 2.45GHz and the power of 600W and three microwaves with different frequencies, the central frequency of which is 2.45GHz and the frequency difference of which is 2-8 MHz (for example, the frequency difference of 2MHz is that the frequency of the three microwaves is 2.448GHz, 2.45GHz and 2.452GHz), and the power of which is 200W are respectively fed, temperature rise data are led into MATLAB for calculation, and a three-frequency heating result is simulated, so that the improvement effect of the heating uniformity is verified by comparing the method.
The mean temperature (ave) and the temperature coefficient of variation (cov) were calculated for each case using MTALAB software, with the temperature coefficient of variation (cov) being the ratio of the standard deviation of the raw data to the mean of the raw data, reflecting the absolute value of the degree of dispersion of the data, with smaller cov values indicating more uniform heating. The improved heating uniformity of the potatoes at different positions was also calculated.
The following table is data of a potato positioned 50mm directly below the center point of the cavity:
the following table is data for a potato positioned 80mm directly below the center point:
the cavity is designed to be a rectangular cavity of 450 × 350 × 340mm, and the following table shows data of 80mm directly below the center point of the potato:
the conclusion can be drawn from the data, the intermediate frequency signal is modulated to the modulation circuit on the magnetron high-voltage power supply, so that the magnetron is mixed to generate a microwave signal with specified frequency difference, the microwave heating of three-frequency output is realized, the good effect on improving the heating uniformity is achieved, and the expected purpose can be achieved. The optimal frequency of the intermediate frequency signal can be selected according to experiments, so that the material heating uniformity is optimal.
Fig. 15 is a heating simulation diagram of a rectangular cavity with a cavity design of 405 × 295 × 340mm, where a potato is located 50mm right below the center point of the cavity, the initial temperature is 293.15K, and the heating time is 20s, a microwave with 2.45GHz is input at a single frequency, the power is 600W, and it can be seen that the average temperature ave is 313.68K, and cov is 0.5352;
fig. 16 is a heating simulation diagram of a rectangular cavity with a cavity design of 405 × 295 × 340mm, potatoes located 50mm right below the center point of the cavity, an initial temperature of 293.15K, and a heating time of 20s, microwaves with three frequency differences of 4MHz (2.45GHz, 2.446GHz, 2.454GHz) are input, a power of 200W, and it can be seen that an average temperature ave is 310.63K, and cov is 0.3738;
as can be seen from comparison of fig. 15 and 16, the maximum temperature and the average temperature of the triple-frequency heating are not higher than those of the single-frequency heating, but the average temperature difference is smaller, and the temperature distribution of the surface of the body shows that the triple-frequency heating has certain improvement effect on the uniformity.
As can be seen from fig. 17, by changing the power of the intermediate frequency signal, the output power of the microwave with three main frequencies can be obtained by experiments to be close to the same, and the closer the output power is, the more uniform the heating is.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (10)
1. Magnetron anode power supply ripple frequency mixing multifrequency heating device, its characterized in that: the 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 with a first cathode power supply line (71) and a second cathode power supply line (72); the first cathode power line (71) and the second cathode power line (72) are respectively connected with two ends of the cathode of the magnetron (2); one end of the first capacitor (41) is connected with the intermediate frequency signal generator (3), and the other end of the first capacitor is connected with a first cathode power line (71); a feed port is arranged on the cavity (8); the magnetron (2) inputs microwaves of multiple frequencies into the cavity (8) through the feed port.
2. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 1, wherein: and a first inductor (51) is arranged on the first cathode power line (71) between the connection intersection point of the first capacitor (41) and the first cathode power line (71) and the magnetron power supply (1).
3. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 2, wherein: and a second inductor (52) is arranged on the second cathode power line (72).
4. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 3, wherein: further comprising a third inductance (53); one end of the third inductor (53) is connected with the intermediate frequency signal generator (3) and one end of the first capacitor (41) connected with the intermediate frequency signal generator (3), and the other end of the third inductor is grounded.
5. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 4, wherein: further comprising a fourth capacitance (44); one end of the fourth capacitor (44) is connected with a first cathode power line (71) between the magnetron power supply (1) and the first inductor (51), and the other end of the fourth capacitor is grounded.
6. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 5, wherein: further comprising a fifth capacitance (45); one end of the fifth capacitor (45) is connected with a second cathode power line (72) between the magnetron power supply (1) and the second inductor (52), and the other end of the fifth capacitor is grounded.
7. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 6, wherein: the circuit also comprises 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) is connected with the two ends of the first inductor (51) in parallel; the third resistor (63) is connected with the second inductor (52) in parallel.
8. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 7, wherein: also includes an impedance matching adjuster; the impedance matching regulator comprises a second adjustable capacitor (42) and a third adjustable capacitor (43); one end of the second adjustable capacitor (42) is connected with the intermediate frequency signal generator (3) and one end of the first capacitor (41) connected with the intermediate frequency signal generator (3), and the other end of the second adjustable capacitor is grounded; one end of the third adjustable capacitor (43) is connected with the intermediate frequency signal generator (3) and one end of the first capacitor (41) connected with the intermediate frequency signal generator (3), and the other end of the third adjustable capacitor is grounded.
9. The magnetron anode power supply ripple mixing multifrequency heating apparatus of claim 8, wherein: the circuit board is also included; 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 a circuit board; the circuit board comprises a first port, a second port, a third port, a fourth port and a fifth port; the first port is located on a first cathode power line (71) between the first inductor (51) and the magnetron power supply (1); the second port is located on a second cathode power line (72) between the second inductor (52) and the magnetron power supply (1); the third port is located on a first cathode power line (71) between the first inductor (51) and the magnetron (2); the fourth port is positioned on a second cathode power line (72) between the second inductor (52) and the magnetron (2); the fifth port is positioned between the intermediate frequency signal generator (3) and the first capacitor (41) to communicate the intermediate frequency signal generator (3) with the first capacitor (41).
10. The magnetron anode power supply ripple frequency mixing multi-frequency heating method is characterized in that: the magnetron anode power supply ripple mixing multi-frequency heating device of any one of claims 1 to 9 is adopted; the method comprises the following specific steps: the magnetron power supply (1) supplies power to the magnetron (2); the medium frequency signal generator (3) generates a medium frequency signal, the medium frequency signal is input to a first cathode power line (71) through a first capacitor (41), the medium frequency signal is equivalent to a ripple of an anode voltage of the magnetron (2) and is loaded to the anode voltage of the magnetron (2), a resonance signal excited by the magnetron (2) is used as a local oscillation signal, when the medium frequency signal is used as the anode voltage ripple and is acted with the resonance signal of the magnetron (2), the output end of the magnetron (2) generates microwaves with multiple frequencies due to the nonlinear response characteristic of the magnetron (2), and the microwaves with multiple frequencies are input into the cavity (8) through the feed port to heat the material (9).
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