DE1046219B - High frequency furnace - Google Patents

Description

GERMAN

The present invention relates to ovens in which the one to be heated or from others Grounds to be treated with high-frequency energy in a property delimited by metal walls Cavity is located in which energy is introduced in the form of high-frequency electrical radiation will. This type of facility includes, for. B. the so-called microwave oven, which can be used to heat food.

Such devices have the disadvantage that pronounced standing waves are formed in the cavity. Therefore, the energy absorption of the good is strongly dependent on its position in the cavity, and it is also a satisfactory electrical adaptation of the cavity to the high-frequency generator Difficult to achieve, especially with low loads.

It is known to mitigate this disadvantage in that a constantly moving, z. B. rotating Body is arranged, which can take about the shape of a fan. This moved Body influences the self-electromagnetic resonance of the cavity and causes one on average more even distribution of high frequency energy; however, its use introduces a complication The construction and operation of the furnace.

It is also known to supply the high-frequency power locally distributed and through the furnace suitable design of the insertion slots a certain To force polarization of the introduced vibrations. Part of the reflected in the furnace Naturally, power also returns to the generator through the slots. This disadvantage can by the arrangement of a damping resistor, although mitigated, but despite great effort (cooling!) not be eliminated; this measure also brings about a reduction in efficiency with himself.

The disadvantage mentioned several times, with its complicating consequences for the handling of the oven can now be eliminated in the simplest way that means for changing the polarization direction in the cavity the high-frequency radiation are arranged, in such a way that the in the cavity reflected vibrations can no longer escape through the insertion point. A microwave oven according to the invention is therefore characterized in that in the interior of the cavity at at least one of its walls a polarization grating is arranged, which is parallel to the wall and the Direction of polarization of the radiation reflected on this wall in relation to the direction of polarization the radiation hitting the wall changed by at least approximately 90 °.

High frequency furnace

Applicant:

"Patelhold"

Patent exploitation & electr ο holding
A.-G., Glarus (Switzerland)

Representative: Dr.-Ing. E. Sommerfeld, patent attorney,
Munich 23, Dunantstr, 6

Claimed priority:
Switzerland from April 16, 1957

Dipl.-Ing. Gustav Guanella, Zurich (Switzerland),
has been named as the inventor

The mode of operation of the furnace according to the invention will be explained with reference to FIGS. 1 and 2. 1 shows, as an exemplary embodiment, the cavity delimited by rectangular metallic walls B, D, W into which high-frequency energy is introduced through the waveguide L. The polarization direction E _{0 of} the introduced radiation lies parallel to the plane of the drawing. A polarization grating G _{x is} arranged near the wall B of the cavity opposite the waveguide L. The structure and mode of operation of such grids are well known per se; For the sake of completeness, it should therefore be remembered that they consist of conductors running parallel to one another, and that they reflect vibrations whose direction of polarization coincides with the direction of the conductor, while vibrations with a direction of polarization perpendicular thereto are allowed to pass. In the present case, the conductor direction is rotated by 45 ° with respect to the polarization direction E _{0 of} the introduced radiation, and the distance of the grating G _x from the wall B is equal to a quarter of the wavelength λ of the introduced radiation or equal to an odd multiple of this A value. At the grating, the component E located in guide direction is thus (s. Fig. 2) ₀ 'of the inserted vibration E ₀ reflects (-E ₀₎ to lying component E is transmitted through ₀ "while the vertical. This component reaches the wall B, on which it is reflected (-E ₀ "). It then passes through the grid G _{1 again} . Since they in-

809 698/408

between a to λ / 2 (or an odd-numbered ^{multiplicity!} multiple of this value) longer path has traveled as the component E _0, it enters above the grid G ₁ with a phase shift of 180 ° when + E ₀ "united in appearance and with the component - Ti ₀ 'to an oscillation E ₁ , the direction of polarization of which is rotated by 90 ° with respect to that of the introduced oscillation E ₀ .

It is now very easy to keep this reflected oscillation away from the high frequency generator. For this purpose a polarization grid G ₀ may be arranged for example in the mouth of the waveguide L, which transmits the introduced vibration E ₀ and the twisted by 90 ^D E ₁ vibration is reflected back into the cavity. The conductor direction of the grating G ₀ must therefore be perpendicular to the polarization direction E _{0 of} the radiation introduced. If the high-frequency energy is not introduced via a waveguide, but rather via a coupling loop or a dipole, special measures are not even necessary, since such elements as receivers are insensitive to vibrations, whose polarization direction is 90 ° compared to the polarization direction of the radiated vibrations is twisted.

A substantial improvement over the arrangement discussed so far can be achieved if a further polarization grating G _{2 is} provided near the wall D containing the waveguide L , which is parallel to the wall B. Its conductor direction is rotated by 45 ~ ^O with respect to the polarization direction of the introduced radiation; it is therefore parallel or perpendicular to that of the grating G ₁ . The grating G ₂ leaves the cross section required for the introduction of the radiation free; it is also constructed and arranged according to the aspects explained for the grating G _1. It is easy to see that the oscillation E _{1 impinging on the grating G 1} experiences a renewed rotation of its polarization direction by 90 °. The oscillation process in the cavity is then composed of two waves running in opposite directions, the polarization directions of which are perpendicular to one another. The wave running from top to bottom in FIG. 1 is thus parallel to the plane of the drawing (E ₀ ), the wave running from bottom to top is polarized perpendicular to it (.E ₁ ). So these two waves cannot unite to form a standing wave. There are therefore no places in the cavity with extremely large or extremely small energy densities, so that the effect of the high frequency energy on the material is practically no longer dependent on its location in the cavity. The reaction of the processes in the cavity on the high-frequency generator and thus the adjustment difficulties mentioned at the beginning are also largely eliminated. In the case of certain goods with a special nature or shape, the fact that waves with different polarization directions act on them at the same time has an additional effect.

For structural reasons, it can be advantageous if the conductor directions of the grids G ₁ and G ₂ run parallel to the side walls W of the cavity. Then the direction of polarization of the element introducing the energy (waveguide, coupling loop or dipole) must be rotated by 45 ° from the position shown in FIG. The outline of the cavity can be square or, as shown in FIG. 1, rectangular. The invention is of course in no way restricted to cavities with a square cross-section, but it can just as well be used, for example, in cylindrical cavities.

Incidentally, if the polarization grating G _{1 is} not arranged at the above-mentioned distance from the wall B , but for example at a distance of 2/8, the reflected wave traveling upwards is circularly polarized. With a corresponding arrangement of the polarization grating G ₂ , a linearly polarized wave running downwards is again produced. Even if the abovementioned advantages of the measure according to the invention no longer occur in their entirety with such an arrangement, this arrangement can nevertheless be expedient under certain circumstances, for example when space is limited.

In certain cases, an arrangement in which the distance at least of a polarization grating from the associated wall can be changed. It is then possible to find the optimal Conditions, for example with regard to a minimum of those that have an effect on the high-frequency generator Energy to cease in operation.

Instead of the polarization grating of parallel conductors described in the exemplary embodiment other means for changing the polarization direction can of course also be provided, see above for example mutually parallel strips of material with a high dielectric constant. In any case, a grid can be designed as a carrier for the good.

The concept of the invention can also be used to advantage when energy from one or also from several high-frequency generators is introduced into the cavity at several points. In a device according to FIG. B. to provide a second waveguide which opens into the wall B and which introduces an oscillation whose direction of polarization is perpendicular to the plane of the drawing (ie perpendicular to E ₀ and therefore parallel to E ₁ ) . In this case, too, the oscillation process in the cavity is composed of two waves running in opposite directions, the polarization directions of which are perpendicular to one another. When fed by two independent high-frequency generators, each of these waves is composed of two components, the frequencies of which will generally be somewhat different from one another.

Claims (6)

Patent claims: 1. High-frequency furnace in which the material to be treated is in one of metal walls limited cavity is located in which energy in the form of high frequency electromagnetic Radiation is introduced, characterized in that inside the cavity at at least a polarization grid is arranged on one of its walls, which is parallel to the wall and the direction of polarization of the radiation reflected on this wall in relation to the direction of polarization the radiation hitting the wall changed by at least approximately 90 °. 2. High-frequency furnace according to claim 1, characterized in that parallel to the wall opposite the point of introduction of the high-frequency power and at a distance of at least approximately (2n- 1) · Λ / 4 from this wall is a mutually parallel Conductors existing polarization grid is arranged, the direction of the conductor by 45 ° opposite the polarization direction of the introduced radiation is twisted (λ = wavelength of the radiation, η = whole number). 3. High-frequency furnace according to claim 2, in which the energy is introduced via a waveguide, characterized in that a polarization grating also in the mouth of the waveguide is arranged, the conductor direction perpendicular to the polarization direction of the radiation introduced stands. 4. High-frequency furnace according to claim 2, characterized in that a polarization grating is arranged parallel to the wall containing the point of introduction of the high-frequency energy and at a distance (2n- 1) · A / 4 from this wall, the conductor direction of which is 45 ° with respect to the polarization direction introduced radiation is twisted. 5. High-frequency furnace according to claim 1, characterized in that the distance between the polarization grating is changeable from the wall. 6. High frequency furnace according to claim 1, characterized in that high frequency energy to two Places is introduced, which lie in two mutually parallel walls of the cavity, wherein the polarization directions of the introduced vibrations are perpendicular to each other and that a polarization grating is arranged parallel to each of these walls, the conductor directions of which are rotated by 45 ° with respect to the directions of the introduced vibrations. Considered publications:
U.S. Patent Booklet No. 2,704,802. 1 sheet of drawings