JPS643039B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a high-frequency heating device in which the oscillation frequency of the high-frequency heating source is 915MHz, which is one of the ISM (industrial, scientific, and medical) frequency bands. This relates to the improvement of heating chambers for consumer equipment whose chambers are within several times the wavelength (approximately 33 cm).

Conventional configurations and their problems In the case of microwave ovens, which are widely used for consumer use as conventional high-frequency heating devices, most of them are I.
Although the 2450MHz band, which is one of the SM frequency bands, is used, the 915MHz according to the present invention is
When using high frequencies in the Hz band, there are the following characteristics.

First of all, compared to using 2450MHz,
In the case of 915MHz, the half-life depth with respect to water and fat, which are the main components of food, is large, and high-frequency energy is not concentrated only in localized areas or on the surface of food, which is advantageous for uniform heating of food.

Second, when considering semiconductor devices as high-frequency oscillation sources, in recent years, even in the high-frequency region, large amounts of power and
Even though the development of highly efficient semiconductor devices has progressed, there is a theory that the output limit of a semiconductor device is inversely proportional to the square of the frequency ( ² ). It's advantageous.

From the above points of view, it can be said that high-frequency heating devices using the 915 MHz band are superior to those using 2450 MHz. in
There are different problems than 2450MHz.

Next, I will explain the problem. FIG. 1 is a basic conceptual diagram showing the basic configuration of a high-frequency heating device.
The high-frequency heating device basically consists of a high-frequency oscillation source 1 that generates high-frequency waves, a heating chamber 2 for storing and heating an object to be heated 4, and a heating chamber 2 for guiding the high-frequency energy generated by the high-frequency oscillation source 1 to the heating chamber 2. coupler 3 of 3
It is made up of parts. The most common method for efficiently guiding the high frequency waves generated by the high frequency oscillation source 1 into the heating chamber 2 and heating the object to be heated 3 is to cause a resonator, which is the heating chamber, to resonate at that frequency. This is what electrical engineering teaches.

On the other hand, when heating chamber 2 is a rectangular parallelepiped and the lengths of each side are W, D, and H, the resonant frequency of heating chamber 2 is f=(1/√2)×√() ² +() ₂ +
(S/H) ₂ ... Represented by Formula 1. Here, ε and μ are heating chamber 2
The dielectric constant and magnetic permeability of the medium, m, n, and s are zero or positive integers indicating the order of the excited resonance mode. As predicted from the fact that Equation 1 is a function of the dielectric constant ε of the medium in the heating chamber 2, the resonant frequency of the resonator that is the heating chamber 2 depends on the load (the object to be heated 4) inside the resonator. Varies depending on quantity, shape, and quality.

By the way, in the case of a high-frequency heating device using 2450 MHz, the dimensions of the heating chamber 2 are sufficiently large compared to the wavelength (12 cm) even when considering consumer equipment. Therefore, since there are many adjacent modes that can be excited, it is difficult to excite a specific mode, but even if the load changes and the resonant frequency changes, one of the multiple modes will resonate or Since the state is close to that of the heating chamber 2, the high frequency energy is guided into the heating chamber 2 even if the load changes slightly.

On the other hand, for 915MHz, the free space wavelength is
Since the free space wavelength of 2450 MHz is 33 cm, which is approximately 2.7 times the free space wavelength of 12 cm, the number of modes that can resonate in the heating chamber 2 of the same size is greatly reduced. For example, D=365mm, H
When considering a resonator with dimensions of = 240 mm and W = 365 mm, there are 27 resonant modes that exist within a frequency range of ±5% around 2450 MHz, but within a frequency range of ±5% around 915 MHz. In the frequency range of (m, n, s) = (1, 0, 2) and (m, n, s) =
There are only two (2, 0, 1). This means that
915MHz for a specific mode (in this example (1,
0, 2) or (2, 0, 1) mode)
Although it is easy to excite, if the supplied frequency deviates from the resonant frequency of that mode, impedance matching in electrical engineering terms cannot be achieved completely, resulting in the problem that high frequency energy will not enter into the heating chamber 2. It was hot.

OBJECTS OF THE INVENTION The present invention aims to solve the problem of impedance matching that occurs when using the 915 MHz band, and to realize an efficient but highly reliable high-frequency heating device.

Structure of the Invention In order to achieve the above object, the high frequency heating device of the present invention uses the 915MHz band, which is one of the ISM frequency bands, and also operates in the TE201 and TE102 modes that do not have standing waves in the height direction in the frequency band. It is characterized by a configuration in which heating chambers are provided with different dimensions in depth and width so that the resonant frequencies of the two modes TE201 and TE102 are different.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Figure 2 shows the configuration of the heating chamber 2 including the probe antenna 3, which is the excitation part of the high-frequency heating device according to the present invention, and the two excited modes.
The electric field strength distributions A and B of TE201 and TE102 are shown, and the width W and depth D are always different.

Figure 3 is a plan view of the heating chamber viewed from above (X-
This shows the basic direction of the magnetic field lines of the above mode in the Z plane). Now width W of heating chamber 2 = 360mm, depth D
= 370 mm (in the case of the present invention, the electric field is uniform in the height direction)
Since we are considering TE201 and TE102 modes, H is optional) With no load in heating chamber 2, this heating chamber 2 has a frequency of (201) = 926MHz (1, 0,
2) Has a close resonant frequency of =912MHz
It can excite modes TE201 and TE102. This is because the width W and depth D are different, so W=
This is because the resonant frequencies of TE201 and TE102, which had degenerated into a single resonant frequency in the case of the square D, have separated. Figure 4 shows the relationship between W, D, and resonance frequency in more detail, where W = 350 mm and 355 mm.
The resonant frequencies are plotted when D is changed for each case of mm and 360 mm, and it can be seen that by appropriately combining D and W, which are not equal to each other, it is possible to set any two resonant frequencies that are close to each other. . On the other hand, the basic patterns of the magnetic lines of force for the two modes TE201 and TE102 as seen in the X-Z plane are as shown in C and D in Figure 3. If it is placed diagonally from the corner at a position 1/4 of the diagonal length from the top surface downward into the heating chamber 2, both the TE201 and TE102 modes can be excited as long as their frequencies match.

Now, the change in the resonance frequency with respect to the load amount varies depending on the components and shape of the load (heated object 4) used, the height of the heating chamber, etc., but according to the configuration of the present invention described above, By appropriately setting two adjacent resonant frequencies (201) and (102) according to the load conditions, impedance matching can be achieved over a wide range that cannot be achieved with a single mode in the 915 MHz band.

Therefore, in a consumer high-frequency heating device that uses the 915MHz band, a heating chamber that is efficient for a wide range of loads can be realized.

Also, the fact that no energy enters the heating chamber 2 means that there is a lot of energy reflected back to the oscillator.
In particular, devices using semiconductor elements are susceptible to reflection, so
Improving efficiency will directly lead to improved reliability.

Effects of the Invention As explained above, according to the configuration of the present invention
By varying the depth D and width W of the heating chamber while using the low frequency band of 915 MHz, TE ₂₀₁ and TE, which had degenerated to a single resonant frequency in the case of a square where W = D, were created. The ₁₀₂ resonant frequencies can be separated and any two adjacent resonant frequencies can be set. This makes it possible to achieve impedance matching over a wide range, which cannot be achieved with a single mode, in response to changes in the resonant frequency caused by differences in load. Furthermore, since the antenna probe can be placed near the corner of the heating chamber, there is also the effect that the effective volume of the heating chamber can be increased.

In addition, in the above explanation, the frequency band used is I.
We considered the 915MHz band, which is one of the SM frequency bands, but this frequency band is legally allocated depending on the radio wave usage status of each country, and generally the band width is 915±13MHz. many.

In the present invention, the reason why the 915MHz band is specifically designated is due to this legal background, and technically it is far from the 915MHz ISM frequency band.
The configuration method of this patent can be applied to a range of approximately 915±100MHz. Therefore, although some countries have adopted a frequency band that is slightly different from this (915MHz), it goes without saying that the present invention can be applied in exactly the same way even in such a frequency band.

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of a conventional high-frequency heating device.
Figure 2 shows two excited modes TE201 in the heating chamber of a high-frequency heating device that is an embodiment of the present invention.
Fig. 3 is a diagram of the electric field strength distribution of TE102 and TE102; Fig. 3 is a diagram of the basic pattern of the magnetic field lines of two excited modes TE201 and TE102 in a plan view (X-Z plane) of the heating chamber shown in Fig. 2; The figure is a characteristic diagram of the resonance frequency of both the TE201 and TE102 modes when the width W and depth D of the heating chamber are changed. DESCRIPTION OF SYMBOLS 1... High frequency oscillation source, 2... Heating chamber, 3... Coupling part (probe antenna), 4... Heated object.

Claims (1)

[Claims] 1. The 915 MHz band, which is one of the ISM frequency bands, is used, and the TE201 and TE102 modes that do not have standing waves in the height direction can be generated in the frequency band, and the two modes A high-frequency heating device that has heating chambers with different depth and width so that the resonance frequencies of TE201 and TE102 are different. 2. The high-frequency heating device according to claim 1, which is provided with an excitation section that can simultaneously excite both TE201 and TE102 modes.