JPS6040158B2 - High frequency heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The object of the present invention is to effectively supply high frequency energy of an oscillation tube to an object to be heated in high frequency heating.

In conventional high-frequency heating devices, the oscillation tube and the heating chamber in which food is placed and heated are connected, and the waveguide that guides the high-frequency waves to the heating chamber is generally rectangular in shape due to impedance matching and ease of processing. The chamber is also shaped like a rectangular hexahedral box for the same reason, and the radio waves propagated through the rectangular waveguide are radiated to the food from the husband side of the heating chamber, which is a rectangular hexahedral cavity resonator, to heat the food. Therefore, the excitation mode of the waveguide is TE in terms of space and economy.

mode was the mainstream. As is well known, TM,. If it is a mode, all sides of the rectangle of the waveguide must be longer than the cutting wavelength, but TE. This is because if it is a mode, it can be excited if the long side is longer than the cutting wavelength. Also, in this case, there are many various documents, and for ease of analysis, the position where the oscillator tube antenna is inserted into the waveguide is TE. In the mode, it was usual to set the waveguide approximately at the center of the long side. The present invention intentionally goes against the conventional methods described above and has undergone various studies, and provides a high-frequency power feeding system with a wide frequency band without changing the excitation mode of the waveguide.

An example in which the present invention is implemented in a household microwave oven will be described below.

Figure 1a shows the TE in a conventional microwave oven.

This shows the electric field distribution inside the waveguide excited by the mode. Here, the propagation direction is normally regulated by providing a shorting plate at a distance of about 4/4 from the antenna 1, but in reality, this is not necessarily 4/4 due to structural reasons. Also, Fig. 1 b, c,
d is a Rieke diagram showing the operation of the oscillator tube when a load (in this case water load) is placed in the heating chamber using the above waveguide, and b is a Rieke diagram showing the oscillation tube rated oscillation frequency c is the oscillation frequency + 1 day. 2
d is the value at the oscillation frequency of 1 and 2. In the figure, the operation at a certain level at each load is due to a radio wave mechanism (for example, a rotating saucer, starch, etc.) provided in the heating chamber. What is clear from FIGS. 1b, c, and d is that the fluctuations in each operating point due to fluctuations in the oscillation frequency of the oscillation tube are extremely large. In particular, the operating point at light load at c is VSWR. I can see that it is working above. However, with the same specifications, it is clear that it is unavoidable to operate in the maximum output range at rated load.
FIG. 2a shows the electric field distribution within the waveguide in the microwave oven according to the present invention.

The major difference from FIG. 1a is the insertion position of the oscillating tube antenna 1, TE. Although they are exactly the same in that they are excited in a mode, they are deviated in a direction perpendicular to the direction of radio wave propagation in this mode. In other words, the antenna is not located on the central axis in the long side direction of the rectangular wave tube.
Figures 2b, c, and d show an embodiment of the present invention, in which a waveguide is used in which the antenna is deviated to about one-eighth of the long side of the waveguide in the cross-sectional shape of the waveguide. This is a diagram when the waveguide is loaded with the same heating chamber as in the figure, and the oscillation frequencies are similarly viewed at b rated oscillation frequency, c oscillation frequency + IQHz, and d oscillation frequency -11 Hz. The point to note here is that the operating strength is VSW at any of the above frequencies b, c, and d.
The point is that it operates at R5 or lower. As a characteristic of an oscillation tube, when operated at a high VSWR, the radio waves emitted from the oscillation tube propagate through the waveguide and are carried into the heating chamber, but they are not absorbed by the load and return to the oscillation tube, causing damage to the oscillation tube itself. High temperatures will significantly shorten its lifespan. In addition, as a characteristic of the oscillator tube, the operating range in which the high frequency energy can be used to the maximum differs depending on the oscillator tube, but it is usually located at a point slightly larger than the VSWRI (VSWR2 to 3), and its phase is at the reference plane ( Since it is usually located at a certain phase advance from the antenna surface of the oscillator tube, perfect matching (in VSWR) is not required, but it has an appropriate reflection.

However, the VSWR does not seem to be high.
The condition of maintaining the range of is what produces maximum efficiency. Considering the conditions described above, the present invention can sufficiently absorb fluctuations in oscillation frequency and maintain a predetermined NSWR (VSWRI.5 to VSWR7 in the oscillation tube used in this experiment). I would like to add what I found out through this experiment: TE. It is expressed by the linear equation of the wavelength in the waveguide in the mode. Input: Free space wavelength, Input c: Waveguide shear wavelength, or the waveguide shear wavelength is twice the long side a of the waveguide in the TE and o modes, so the following equation can be written in the same equation: It is expressed as

When we measured the standing wave inside the waveguide using the method described above, we found that the wavelength within the tube obtained using the above formula was somewhat shorter than that of the oscillation tube in the range of 2 degrees. According to the wave tube, there is no big difference, but the value was close to the calculated value.

The above results revealed that even if the oscillation tube antenna position is shifted, the TE remains the same. It can be seen that it is excited by the mode. Further experiments revealed that there is a relationship between the eccentric position of the antenna and the width of the frequency band.

In other words, when the antenna's polarization position is shifted to about 1/16 or more of the long side of the waveguide or more than 1/32 of the cutoff wavelength ^c, the effect starts to occur, and the relationship with the waveguide's internal wavelength changes. I also understood that there was one. Moreover, if the offset position is set above the 1' peak of the long side of the waveguide, or more than 1/8 of the blockage or breakage wavelength c, the operating point on the -ke diagram changes significantly, and it is no longer a regular TE.
,. It also became clear that the mode could not be maintained. What can be said experimentally above is that the antenna insertion position of the oscillation tube is shifted.

With just the basic components, we can fully demonstrate the capabilities of the oscillation tube,
It also provides a high frequency power supply system that extends life.

[Brief explanation of the drawing]

Figure 1a is a diagram showing the waveguide configuration and its electric field distribution in a conventional microwave oven, b, c, and d are Rieke diagrams showing operating points using a conventional waveguide, Figure 2a is a diagram showing a waveguide configuration and its electric field distribution in a microwave oven showing an embodiment of the present invention, and b, c, and d are Rieke diagrams showing operating points using the waveguide of the present invention. . Figure 1 Figure 2

Claims (1)

[Claims] 1 In a device that heats food using high frequency waves, the oscillation antenna coupling position of the waveguide excited in the TE_1_0 mode that guides the high frequency waves radiated from the oscillation tube to the heating chamber is determined from the central axis of the waveguide in the direction of radio wave propagation. 1/32 of the cutting wavelength λc
High frequency heating device with deviation in the range of ~1/8.