CN1528107A - microwave material heating device - Google Patents

Abstract

The invention concerns a microwave heating device designed for use in an oven for cooking food. Said device comprises a microwave generator (1) and means for diffusing (2) said energy in a working zone (3). The invention is characterised in that at least a patch antenna (10) adapted to sense the microwaves is arranged in the working zone. Said antenna is connected to an electromagnetic wave propagating line (11) of length L to ensure propagation of the microwaves sensed by the antenna, and whereof the end (12) is adapted to reflect part of said waves towards the antenna. The antenna (10) then retransmits said reflected waves into the chamber (26) with a specific phase shift determined by the length L of the propagation line.

Description

microwave material heating device

technical field

The present invention resides in an apparatus for heating matter by applying microwave energy, comprising a microwave generator and means for distributing the microwave energy in the working area. The invention is particularly, but not limited to, electromagnetic microwave ovens for food cooking.

Background technique

A problem encountered with devices using microwave energy to heat matter is the distribution of microwave energy intensity over the working area. In fact, it is very difficult to obtain a uniform distribution of microwave energy. Furthermore, the reflection of the microwaves leads to the formation of standing waves; regions with weak microwave energy intensity and thus less heating there. The first solution for microwave ovens was to place a mixer called a "stirrer" inside the microwave field. A conventional agitator consists of a rotating propeller whose blades agitate and reflect waves in the oven chamber in a random fashion. Another kind of solution is the method commonly used now, is to place food on a rotating table, so that food constantly passes through the high-energy zone and low-energy zone of microwave.

These two methods can not fully meet the needs, especially in the central region of the microwave cavity can not get enough energy. In fact, it is impossible to make a pizza without special auxiliary devices to distribute the microwaves better. These two methods also do not allow the distribution of microwave energy to be varied according to the type of food or as cooking progresses. Moreover, the manufacturing cost caused by the motor and mechanical device driving the rotating disk cannot be ignored.

Contents of the invention

The object of the present invention is to compensate the above-mentioned drawbacks by controlling the distribution of microwave energy in the working area and controlling the distribution of standing waves.

According to the present invention, in the working area, at least one planar antenna that can obtain microwaves is placed, and this antenna is connected with an electromagnetic wave transmission line with a length L to ensure the transmission of microwaves obtained by the antenna, and the end of the transmission line can be connected to the antenna. Reflected part of the microwave.

The antenna then re-radiates the microwaves reflected from the end of the transmission line with a defined phase difference with respect to the incident microwaves. This phase difference is determined by the length L of the transmission line and can be chosen such that the incident wave and the re-emitted wave are effectively superimposed. By means of this measure it is possible to intensify the microwave energy in selected parts of the working area, in particular to obtain a more uniform overall energy distribution.

According to a particularly useful feature of the invention, the length of the transmission line can be varied from L to L + ΔL by means of at least one actuator which changes the position of the end of the transmission line. This measure makes it possible to vary the microwave energy intensity in a given area according to heating needs. For example, when heating food, the length L of the transmission line can be changed according to the nature, shape, position in the working area or cooking progress of the food. This measure also makes it possible to change the position of the standing wave during the heating process.

Description of drawings

The features and advantages of the present invention will become further apparent in the ensuing description with reference to the accompanying drawings. The following description is exemplary and not limiting. Attached is:

- Figure 1 is a vertical sectional view of a microwave oven with heating means for applying microwave energy implemented according to the present invention;

- Figures 2a and 2b are top views of two panel antennas for implementing the invention;

- Figure 3 shows a temperature height map in each of the 25 blocks divided in a microwave oven according to the prior art.

- Figure 4 shows the temperature height diagram achieved by adding the device according to the invention to the aforementioned microwave oven.

- Fig. 5 shows another embodiment of the heating device, in which a schematic view of a cooking chamber floor with a planar antenna grid is shown.

Detailed ways

As shown in FIG. 1 , in an apparatus for heating matter using microwave energy there is a microwave generator 1 and means 2 for distributing microwave energy in a working area 3 . The microwave generator 1 is a magnetron whose antenna 4 propagates the microwaves into the waveguide 5 which spreads the microwave energy into the working area 3 through the opening 6 . The magnetron 1 is connected to a current supply circuit 7 of known type. Of course, other types of microwave generators, especially solid state generators, may be used without departing from the scope of the present invention. For electromagnetic devices for food cooking, the frequency of the microwave generator used is 2.45 GHz, but the invention can also be used for microwave generators operating at other frequencies, especially for industrial applications at 915 MHz.

According to the present invention, at least one planar antenna 10 capable of obtaining microwave energy is placed in the work area 3, and this antenna is connected to an electromagnetic wave transmission line 11 with a length L to ensure that the energy obtained by the antenna is transmitted. 12 is capable of reflecting at least a portion of the microwaves towards the antenna 10.

The flat plate antenna, English is "patch antenna (patch antenna)", is familiar to people, and generally has one or more substantially flat radiation plates 13 made of conductive materials, and the radiation plates 13 are generally in line with the ground. The connected conductor planes are parallel, and this conductor plane is called the ground plane, and dielectric or air insulation can be used between the radiation plane called the antenna and the ground plane. The most commonly used radiant panels are rectangular, but it will be seen later that other shapes can be used. The size of the radiant panel should be suitable for capturing microwaves in the work area. Preferably both the longitudinal and transverse dimensions of the plate are between λ/4 and λ, where λ is the wavelength of the microwaves dispersed in the working area. Naturally, this antenna suitable for obtaining microwaves can also emit microwaves of the same wavelength.

There is usually a conductor 15 in the electromagnetic wave transmission line 11, which is located near the ground plane 16, and the insulation between the two can be realized by dielectric material or air.

The end 12 of the transmission line is adapted for good reflection of electromagnetic waves. To this end, the end 12 can be free in air. Preferably, however, this terminal is in contact with a face 17 which is perpendicular to the transmission line and which is connected to ground. This enables most of the electromagnetic waves to be reflected toward the antenna. Such reflected waves are different from electromagnetic waves which generate reflections on the walls 20 of the cooking chamber. In fact, the absence of conductors in the cooking chamber walls means that the phase of the reflected and incident electromagnetic fields is reversed, resulting in energy losses.

The antenna 10 is connected to the transmission line 11 through the contact 21 between the radiation plate 13 and the conductor 15 of the transmission line 11 . The position of the contacts 21 is chosen such that the energy picked up by the antenna 10 is well transferred to the transmission line 11 . According to a good method, the contacts 21 are on the lower surface of the radiating plate 13, between its center and its periphery, as shown in FIGS. 2a and 2b.

Then, the antenna 10 in the working area acquires the incident microwaves reaching its surface, and transmits the acquired microwave energy to the transmission line 11 . The end 12 of the transmission line reflects the microwave to the antenna, and the antenna 10 re-radiates the microwave to the working area 3, and the phase difference Δφ of the re-radiated microwave relative to the incident wave is given by the formula

ΔΦ=(4π/λ)× L is given. Here λ is the wavelength of the microwaves dispersed in the working area, and L is the length of the transmission line 11 , that is, the length of the conductor 15 from its contact with the radiation plate 13 to the end 12 of the transmission line.

The choice of length L then determines the phase difference between the incident wave and the re-emitted wave. If L is selected so that the phases of the incident wave and the re-emitted wave are opposite, then the microwave superposition and cancellation will be obtained, which will weaken the microwave energy in the antenna area. On the contrary, if L is chosen so that the superposition of the incident wave and the re-emitted wave is mutually reinforced, the energy of the microwave in the antenna area is enhanced, resulting in a high ability to heat the material. Of course, various choices for the length L are possible between the two cases.

Preferably, the shape of the panel antenna 10 is adapted to emit a circularly polarized field, and there are various shapes of planar antennas to obtain such fields. Such antennas are generally characterized by substantially equal longitudinal and transverse dimensions. Two circularly offset antennas 10, 10' are shown in Figs. 2a and 2b. Figure 2a shows a first shape 10 of the antenna as a square with two diagonal corners 22,23 cut off. Figure 2b shows a second shape 10' of the antenna as a circle with two rectangular grooves 22', 23' on opposite half-lengths. This type of antenna creates a rotational movement of the field and enables a good distribution of the microwave energy in the working area.

With such a device, it is possible to reliably change the distribution of microwaves in the working area, or to increase or decrease the energy. The present invention can be used in various microwave heating devices, especially domestic appliances for cooking food, such as microwave ovens.

In order to realize such a microwave oven, as shown in Figure 1, the working area 3 is separated from the cooking chamber 26 which prevents microwave leakage, the wall 20 of the cooking chamber is connected to the ground, and there is at least a top 27 and a bottom in the wall 28 and a door (not shown) that food is introduced. The cooking chamber 26 mentioned, the microwave generator 1 and the function programming device 29 of the generator 1 are all located in the casing 30 constituting the oven box.

As the programming device 29, various known devices can be used for such household appliances. Simple timers can be used, or more complex programming systems can be used to control the power and process according to the type and condition of the food being cooked. In this case, the programming device 29 will be connected with a plurality of touch keys not shown in the figure, and be used for selecting an appropriate program.

Ideally, the antenna 10 is separated from the cooked food by a microwave-transparent protective plate 31, which avoids all splashes onto the antenna 10, which could damage or alter the antenna. characteristic. The protective plate 31 here is realized with a glass plate placed parallel to the base plate 28 . Of course, the present invention does not exclude the use of a rotating platform on the upper layer of the protective plate 31 .

As shown in FIG. 1, a part 14 of the wall of the cooking chamber 26 is used as the grounding plate of the antenna 10, so that the volume of the antenna 10 in the cooking chamber can be reduced, and the cost can also be reduced.

The insulation between the radiating plate 13 and the grounding plate 14 is guaranteed by an air layer, which can carry large power and also be used as a dielectric material with a long life.

The radiating plate 13 of the antenna can be kept at a distance d from the part 14 of the wall of the cooking chamber 26 using an insulating support, and in an ideal embodiment only a The conductor support 32 of the wall portion 14, generally this electromagnetic neutral point corresponds to the geometric center of the antenna, as shown at points 33 and 33' in Figures 2a and 2b. This simplifies the installation of the antenna.

The length L of the computer transmission line 11 makes the superposition of the microwaves dispersed in the cooking chamber and the microwaves re-radiated by the antenna realize the uniform distribution of the microwaves in the cooking chamber 26.

According to a particularly advantageous feature of the invention, changing the position of the end 12 of the transmission line 11 by means of at least one actuator 35 varies the length of the transmission line 11 between L and L + ΔL . Referring to Figure 1, the end 12 of the transmission line can transition from position 36 to position 37 shown in phantom. By means of this arrangement, different distributions of the microwave energy in the cooking chamber can be obtained.

According to a convenient method, the worker 35 is connected to the programming device 29 . In the programming device 29 there is a control device 39 of the worker and a storage device 38 of different lengths of transmission lines that are suitable for different cooking programs.

For example, for defrosting, it may be desirable to have more microwave energy in the center of the food, while for cooking snacks, it is desirable that the microwave energy be evenly distributed. It is also possible to change the distribution of microwave energy according to the shape and position of the food. According to the program selected by the user, the programming device 29 selects the length L suitable for this program from the stored lengths, and this value is transmitted to the worker 35 using the control device 39 as a reference value.

The programming device 29 can also vary the length of the transmission line 11 in a cyclic manner during the heating operation. This configuration moves the standing waves in the cooking chamber, thus eliminating the need for a turntable. Of course, various algorithms for the control of the transmission line length variation can be used.

The length variation ΔL required to cover various desired microwave energy distribution structures is less than or equal to a quarter wavelength λ, eg, 3 cm for 2.45 GHz microwaves spreading in the cooking chamber.

In a preferred embodiment, the transmission line 11 is a coaxial cable of circular cross-section, insulated by air between its conductor 15 and the surrounding tubular shield formed by at least the face 16 . The termination 12 of the transmission line is realized with an annular conductor plunger 41 in the space between the center conductor 15 and the shield 16 of the transmission line. This piston 41 is displaceable along the axis 11 by the linear work 35 . The front surface 17 of the piston 41 thus mounted in the transmission line 11 constitutes a surface connected to ground, constituting the end of the transmission line, where a large part of the electromagnetic waves are reflected. This arrangement is particularly advantageous because it allows the length of the transmission line to be varied continuously and is relatively simple to implement. Of course, other methods can also be used, such as using a telescope barrel-type coaxial line, or using a transmission line with a length L connected to a transmission line segment with a length ΔL .

The antenna 10 can be mounted anywhere in the cooking chamber 26 to control the electromagnetic field, however it is preferably mounted in the central portion of the base plate 28 . In fact, as can be seen in Fig. 3, the microwave energy of prior art microwave ovens is generally weaker above this zone A, B, C, D, E, F. Mounting the antenna 10 according to the invention in the central area of the base plate 28 results in stronger heating energy in areas A, B, C, D, E, F, as shown in FIG. 4 .

In another embodiment according to the invention shown in FIG. 4, there is an antenna network 50 consisting of n panel antennas A1, A2...An in the cooking chamber 26, each panel antenna A1, A2...An They are respectively connected to transmission lines 51, 52, ... 65 with lengths L1 , L2 ... Ln . In the case shown in the figure, the antenna network 50 is formed by 25 antennas arranged in a square. This net 50 can be arranged parallel to the sides of a wall 20 of the cooking chamber 26 . The lengths L 1 , L 2 . . . Ln of the individual transmission lines can be calculated such that the re-emitted microwaves are superimposed and enhanced at a point 49 of the cooking chamber called the focal point, where the resulting microwave energy is particularly strong. Preferably, this antenna network can form the base plate of the microwave oven and be protected, for example, by a microwave-transparent screen.

The aforementioned antennas A ₁ , A ₂ ... A _n can be connected to the previously described variable-length transmission lines, preferably the lengths of the transmission lines 51, 52, ... 65 can be changed by means of actuators 71, 72, ..., 85 L 1 , L 2 . . . L n to vary the position of the focal point 49 during the cooking operation, with the help of which configuration scans the volume of the food and ensures uniform cooking.

Claims (15)

1. utilize the device of microwave energy to material heating, comprising a microwave generator (1) is arranged and in service area (3) device (2) of dispersing microwave energy,

It is characterized in that placing at least in service area (3) planar antennas (10) that is suitable for obtaining microwave, antenna of addressing and length are LElectromagnetic transmission line (11) connect, with the microwave transmission that antenna was obtained, the termination of this transmission lines (12) are suitable near small part electromagnetic wave and reflect to antenna (10).

2. according to the heater that utilizes microwave energy of claim 1, it is characterized in that the shape of the planar antennas addressed is suitable for launching the circular polarization electromagnetic field.

3. according to the heater that utilizes microwave energy of claim 1 or 2, it is characterized in that the termination (12) of transmission line (11) and a face (17) of ground connection contact.

4. according to each the heater that utilizes microwave energy in the claim 1 to 3, it is characterized in that its service area is to define with a chamber (26) of cooking with microwave seal, cook a wall (20) ground connection of chamber (26), cook have a top (27) in the chamber (26) at least, (28) and the door that food is put at the bottom of one, the programmer of addressing (29) of cooking chamber (26), microwave generator (1) and generator operation is all in the casing (30) that constitutes furnace shell.

5. according to the heater that utilizes microwave energy of claim 4, it is characterized in that antenna (10) wherein separates with the chamber of cooking by a baffle to microwave (31).

6. according to the heater that utilizes microwave energy of claim 4 or 5, the ground plate that it is characterized in that antenna (10) wherein is to use the part (14) of the wall of cooking chamber (26) to constitute.

7. according to each the heater that utilizes microwave energy in the claim 4 to 6, the radiant panel (13) that it is characterized in that antenna (10) wherein extends to an electric conductor holder (32) of cooking locular wall by an electromagnetism neutral point (33) from antenna, and to keep and cook the distance of the wall of chamber (26) be d.

8. according to each the heater that utilizes microwave energy in the claim 4 to 7, it is characterized in that calculating the length of transmission line L, make the microwave of distribution in cooking chamber (26) and the microwave that antenna (10) is launched again superpose to be implemented in the even distribution of cooking indoor microwave.

9. according to each the heater that utilizes microwave in the claim 4 to 8, it is characterized in that the length of transmission line being existed by means of the final controlling element (35) of the position of a termination (12) that changes transmission line (11) LArrive L+ Δ LBetween change.

10. according to the heater that utilizes microwave energy of claim 9, it is characterized in that work device (35) wherein links to each other with a programmer (30), in this programmer, have the control device (39) of work device and storage to be suitable for difference and to cook the storage device of the different length of transmission line of program running (38).

11., it is characterized in that the variable quantity of length of transmission line wherein according to the heater that utilizes microwave energy of claim 9 or 10 Δ LBe less than or equal to 1/4th of the microwave wavelength in the service area, scattered.

12. according to each the heater that utilizes microwave energy in the claim 9 to 11, it is characterized in that electromagnetic transmission line (11) wherein is a coaxial line, its termination (12) is to realize that by the ring-type electric conductor piston (41) in the space that is between central conductor (15) and the shielding on every side (16) this piston can move along axis direction by linear actuating means (35).

13., it is characterized in that wherein antenna is installed in the central area of base plate (28) according to each the heater that utilizes microwave energy in the claim 4 to 12.

14. according to each the heater that utilizes microwave energy in the claim 4 to 12, it is characterized in that cooking and have in the chamber (26) wherein by n plate aerial (A1, A2 ... An) antenna networks of Zu Chenging (50), each plate aerial (A1, A2 ... An) with length be respectively L1, L2 LThe transmission line of n (51,52 ... 65) link to each other, calculate the length of these transmission lines, make the microwave of emission again cook indoor point (a 49) superposition enhancing that is called focus point.

15. according to the heater that utilizes microwave energy of claim 14, it is characterized in that can by means of change transmission line (51,52 ... the final controlling element of termination 65) (71,72 ..., 85), change the length of transmission line L1, L2 LN cooks the focus point (49) of operating process with change.

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