JPS6092A - High frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is characterized by 1. Uses a high frequency generator whose oscillation frequency is the 915MH2 band, which is one of the S, M (industrial, scientific, and medical) frequency bands, and is especially suitable for consumer use where the heating chamber is within twice the wavelength (approximately 330a). This invention relates to an improvement in the configuration of an antenna that is applied to a heating device and guides radio waves generated by a high-frequency generator to a heating chamber.

Conventional configurations and their problems In recent years, with advances in transistor technology, high-frequency generators have been constructed with solid-state active elements such as transistors instead of the conventionally widely used magnetrons, resulting in lower voltage, lighter weight, and smaller size.
Efforts to extend the lifespan are being considered. However, the ability of a transistor generally ranges from the 1st power to the 2nd power of the operating frequency f.
It is said that the power decreases in proportion to the power of the product, and the output is high at the frequency of 2450MH2, which has been widely used in consumer high-frequency heating devices.

It is extremely difficult to create highly efficient transistors.

Therefore, in order to make it into a transistor, another 1, S,
There is no choice but to use a low frequency of 915 MHz, which is the M frequency band.

However, if a frequency of 915 MHz is used, the wavelength will be approximately three times that of 2450 MHz, so 2
A different problem arises at 450 MHz.

FIG. 1 is only meant to explain this problem. If the heating chamber 2 is a rectangular parallelepiped and the lengths of each side are W, D, and H, the resonant frequency f of the heating chamber 2 is f-( 1/ff)x
(m/W)2+(n/D)2+(s door...
・Represented by Formula 1. Here, ε and μ are the dielectric constant and magnetic permeability of the medium in the heating chamber 2. m, n, and S are positive or zero integers indicating the order of the excited mode.

For example, W = 366”, D = 365mm, H
: Consider the case of a heating chamber 2 with dimensions of 240".

There are 27 modes that can resonate within the same wave number range of ±5% around 2450 MHZ, whereas 915 MHZ
z, modes that can resonate within the same ±5% range have orders of (m, n, 5) = (2, 0, 1) and (1, 0
, 2), and these are generally TE , TE20
This is a mode called 1 102. Therefore, even if the heating chamber 2 has the same dimensions, if the frequency used is 2460 MHz,
Because there are so many resonant modes, a single excitation antenna can excite many modes, whereas the 915M
In the case of Hz, for example, as shown in FIG. 1, if the probe antenna 3 is protruded from approximately the center of the left half of the upper surface of the heating chamber 2 and excited, only TE2o1 is strongly excited.

As mentioned above, the fact that the resonance frequency is extremely low in the 915 MHz band specifically causes the following problems.

The first problem is heating distribution. That is, in the previous example, T
Considering the case where only E2o1 is excited, the power density distribution of the electric field becomes as shown by the solid line in FIG. 2. This is the distribution when there is no object to be heated, and the distribution when there is an object to be heated is often quite different, but in any case, the heating distribution depends on the mode pattern, and the excited Since this is basically the TE2° mode, there is a problem in that the heating distribution is not uniform.

The second problem is the synthesis of radio wave outputs from a plurality of high frequency generators. In other words, if the desired heating output cannot be obtained with the output of one high-frequency generator, the outputs of two or more high-frequency generators are fed to the heating chamber with their corresponding separate antennas, combined, and doubled or tripled. The method of obtaining twice the output is a technique that has been very commonly used when a magnetron is used as a high frequency generator in the 2450 MHz band. In the case of a high-frequency generating device constituted by transistors, it is truly difficult to increase the power of the transistors more than that of a magnetron, so the above-described power combination becomes even more necessary.

However, the reason why such a method was established without special consideration in the past is that in the case of 2450 MHz, even if multiple antennas are used to excite, the number of modes excited by each antenna is extremely large, and as a result, the number of modes excited by each antenna is very large. A major reason for this is that specific interference conditions do not hold between the modes excited by each antenna. In other words, even if excited with multiple oscillation sources and antennas,
This results in a state where they can be considered as mutually independent power supply systems.

On the other hand, in the case of the frequency of the 915 MH2 band, the essential difference appears to be that the number of excited modes is extremely small. For example, consider the configuration shown in FIGS. 3a and 3b with two high-frequency generators and two corresponding antennas. According to this configuration, since the antennas 3a and 3b are located at the two maximum electric field points of the TE2°1 mode, it appears that TE2o1 is efficiently excited. However, since the electric field strength distribution in the cross section including the antennas 3a and 3b, including the direction of the electric field, becomes as shown in Figure 3, in order for TE2゜1 to be excited efficiently, the antennas 3a, 3b It can be seen that the phase difference between the excitation currents flowing in the excitation current must always be 1800 at the excitation point. To do this, it is first necessary that the oscillation phases of the two high-frequency generators be fixed to each other, and then the phase difference between the two must be set appropriately. Therefore, the conventional 2450
It is not possible to use power combining methods as in the case of magnetrons in the MHz band.

As explained above, in the case of high-frequency heating devices that use the 915 MHz band, there are extremely few modes excited in the heating chamber, which may cause uneven heating or make it difficult to combine the power of multiple high-frequency generators. There was such a problem.

OBJECTS OF THE INVENTION The present invention solves the problems of the prior art.
The aim is to eliminate heating unevenness in a high-frequency heating device using the MH2 band, and to provide a simple means for combining power using a plurality of high-frequency generators.

Structure of the Invention In order to achieve the above object, the present invention provides two or more antennas that guide high frequency waves generated by a high frequency generator to a heating chamber,
Each is configured to excite different modes.

As a result of the different modes being excited, the electric field distributions of the respective modes are superimposed and the heating distribution is made uniform.

In addition to the above configuration, if a configuration is adopted in which each antenna is powered by a separate high-frequency generator, each antenna has a different excitation mode, so they act independently of each other, and therefore the mutual oscillation phase difference etc. Regardless, the individual powers will be combined.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 4a, b, and a. FIG. 4 shows the electromagnetic field distribution inside the heating chamber 2 and the positions of the two antennas 3a and 3b.

Broken lines in the plan view indicate the basic direction of magnetic lines of force, and solid lines in each cross-sectional view indicate the electric field strength distribution including its polarity. In the case of this embodiment, the heating chamber 2 is W:D
, = 365'', H = 240'', which are the same dimensions as the conventional example, and 22011102 modes called TE can be excited. On the other hand, radio wave feeding is 2
The two excitation antennas 3a and 3b are connected to two modes TE T
The antenna 3a is provided near the maximum electric field point of E, and the antenna 3a is provided with TE2゜1, and the antenna 3b is provided with TE.
It is configured to excite each of them.

02 TE2o1. The power density distribution of the electric field in the TE1o2 mode is as shown in FIG. 2 by solid lines and broken lines, respectively. As can be seen from this distribution diagram, only one TE2o1 mode is excited, whereas in this example two antennas are used to excite TE and TEl. If both modes of 201 are excited, the heating patterns of both modes will be superimposed, and the heating distribution will be greatly improved.

What should be noted here is that, as can be understood from each cross-sectional view, the antenna 3b is at the zero position of the electric field 01 in the TE mode, and the antenna 3a is at the position where the electric field is 01 in the TE mode. Since the antennas 3a and 3b are at the zero electric field position of the two modes, each of the antennas 3a and 3b does not excite TE TE , and therefore both modes are basically excited independently of each other. Therefore, regarding the high-frequency power to the antennas 3a and 3b, it goes without saying that the power of one high-frequency generator may be divided into two and supplied, but it is also possible to supply power using two separate high-frequency generators for each. good. In the latter case, the power of the two high-frequency generators is combined, so it is an effective means for increasing the power when using a high-frequency generator using transistors, which is difficult to increase the power.

Father In the above example TE TE 22011 1
Although this is a case where two modes are excited simultaneously and independently, a similar configuration is possible for other excitation modes with the natural heating chamber dimensions.For example, when two modes, TE4゜1 and TE, Combinations can be considered. Furthermore, excitation using three or more antennas is also possible, and the easiest example from the above example is W=D=
If H=36s”, TEL.2.TE2゜1゜TE
Six independent modes called TE TE TE can be excited, and can be excited by up to six antennas including the side of the heating chamber.

Furthermore, in the above example, only an embodiment in which one feeding point corresponding to one antenna is provided is described.
For example, it goes without saying that it is also possible to use a multi-element antenna in which there is one feeding point and a plurality of antenna elements that serve as radio wave radiators are connected, and different modes are excited by each antenna element.

As described in the detailed description of the invention, according to the means of the present invention in which two or more antennas excite different modes, when one antenna is excited, the heating distribution is determined by a few excited mode patterns; In addition to greatly improving the conventional problem of uneven distribution, even if each antenna is fed with a separate high-frequency generator, there is little mutual interference, and the output is the sum of each high-frequency generator. , it is possible to easily increase the power of the high-frequency heating device.

Furthermore, even if the output of one high-frequency generator is distributed and fed, there is no need to adjust the excitation phases of the antennas, and a simple configuration is possible.

In the above explanation, the frequency bands used are 1, S, M.
We considered the 915MHz band, which is one of the frequency bands, but this frequency band is legally allocated depending on the radio wave usage situation in each country, and generally 916J = 13
MHz is often used.

In the present invention, the reason why the 916 MHz band is specifically specified is due to this legal background, and technically it is 915 MHz band. The configuration of the present invention can be applied to a range of about 915 to 100 MHz, which is far from the S and M frequency bands. Therefore, although some countries have adopted a frequency band that is somewhat different from this (915 MHz), it goes without saying that the present M-tpf3 holds true in exactly the same way even in such frequency bands.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a conventional high-frequency heating device, Fig. 2 is a power density distribution diagram of an electric field in a heating chamber for explaining a high-frequency heating device according to an embodiment of the present invention, and Fig. 3a is a diagram of a conventional high-frequency heating device. Figure 3 shows the electromagnetic field distribution diagram showing the antenna excitation means.
FIG. 4a is a sectional view taken along the line A-8 in FIG. It is a sectional view taken along line A and A4 in FIG. 4a. 1... High frequency generator, 2-... Heating chamber, 3...
antenna. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 1 Figure 3 α

Claims (2)

[Claims] (1) Equipped with a high frequency generator and a heating chamber that stores an object to be heated, radiates the high frequency generated by the high frequency generator to the heating chamber using at least two antennas, and excites different modes with each antenna. high frequency heating device. (2) The high-frequency heating device according to claim 1, comprising at least two high-frequency generators that feed power to each antenna.