News Column

Researchers Submit Patent Application, "Magnetron and Device Using Microwaves Related Applications", for Approval

July 30, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor ISHII, Takeshi (Shiga, JP), filed on January 6, 2014, was made available online on July 17, 2014.

The patent's assignee is Panasonic Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to a magnetron used in a device using microwaves, such as a microwave oven and a thermotherapy device, and more particularly to a structure of a connecting portion of an exhaust pipe and an antenna cap.

"Conventionally, as a magnetron of this type, there has been known, for example, a structure shown in FIG. 4.

"In FIG. 4, a conventional magnetron is provided with an anode portion 101, a cathode portion 102, an output portion 103, and an output antenna 104.

"The anode portion 101 has a cylindrical anode cylinder 111, and a plurality of vanes 112 radially arranged inside the anode cylinder 111. The plurality of vanes 112 is electrically connected in an alternate manner to every other strap rings 113 having different diameters. In addition, an input side opening and an output side opening of the anode cylinder 111 are provided with pole pieces 114 and 115, respectively, for concentrating a magnetic field on a central portion of the anode cylinder 111.

"The cathode portion 102 is arranged in a central portion of the anode portion 101, and is provided with a cathode filament 121 that emits thermal electrons. A lead wire 122 is connected to the cathode filament 121. The lead wire 122 passes through an inside of a side pipe 123 attached to the pole piece 114 on the input side, and then penetrates through a ceramic stem 124 provided so as to block the input side opening of the side pipe 123, to be connected to a connecting terminal 125.

"The output portion 103 is provided with a side pipe 131 attached to the pole piece 115 on the output side, a cylindrical antenna ceramic 132 attached to the output side opening of the side pipe 131, and an exhaust pipe 133 attached to the output side opening of the antenna ceramic 132 to serve as a part of a vacuum tube.

"The antenna 104 is connected to one of the plurality of vanes 112 of the anode portion 101. In addition, the antenna 104 passes through a hole 115a provided in the pole piece 115 of the output side, and then passes through insides of the side pipe 131 and the antenna ceramic 132 to be extended to an inside of the exhaust pipe 133. The exhaust pipe 133 has a chip-off portion 133a. After gas in the anode portion 101, the cathode portion 102, and the output portion 103 is exhausted, the chip-off portion 133a is formed by being pressure-bonded with the antenna 104 interposed therein and removing an unnecessary portion. Microwave energy generated in the anode portion 101 is extracted from the anode portion 101 with the antenna 104 connected to the one of vanes 112 to be emitted outside from the chip-off portion 133a.

"The chip-off portion 133a formed in an edge shape is a portion which is easily damaged. Accordingly, as shown in FIGS. 5 and 6, an antenna cap 134 is attached so as to cover the chip-off portion 133a. The antenna cap 134 is fixed by being press-fitted to an outer circumferential surface of an end portion 133b serving as a connecting portion with the antenna ceramic 132 of the exhaust pipe 133.

"Generally, the exhaust pipe 133 is made of oxygen-free copper, and the antenna ceramic 132 is made of ceramic. That is, the exhaust pipe 133 and the antenna ceramic 132 are made of materials having different thermal expansion coefficients. In addition, the exhaust pipe 133 and the antenna ceramic 132 are generally heated to 800.degree. C. or more to be connected to each other by brazing. Therefore, the end portion 133b of the exhaust pipe 133 is brazed with the antenna ceramic 132 in an expanded state. On the other hand, the antenna ceramic 132 having a small thermal expansion coefficient does not contract so much even when it is cooled. Accordingly, the end portion 133b of the exhaust pipe 133 is formed in a tapered shape in which the diameter of the end portion 133b is larger on the side close to the antenna ceramic 132, and decreases with distance from the antenna ceramic 132.

"When the magnetron is operated (ON), the temperature of the output portion 103 increases, for example, to about 300.degree. C. On the other hand, when the magnetron is not operated (OFF), the temperature of the output portion 103 returns to a normal temperature. When switching ON/OFF of the magnetron is repeated, temperature fluctuations (so-called heat cycle) of the output portion 103 weaken the strength of a press-fitting portion of the antenna cap 134 and the exhaust pipe 133. In addition, because the end portion 133b of the exhaust pipe 133 is formed in a tapered shape, the antenna cap 134 is likely to be removed. When the antenna cap 134 is removed, the chip-off portion 133a is damaged, and it becomes impossible to suppress occurrence of failures, such as electric discharge, vacuum leakage, and the like.

"As a structure for suppressing removal of the antenna cap 134, there have been known structures disclosed in, for example, Patent Document 1 (JP-A-08-185806) and Patent Document 2 (JP-A-2007-066673).

"Patent document 1 discloses a magnetron in which a projection is provided on an inner circumferential surface of the antenna cap, and a concave groove is provided in an outer circumferential surface of the exhaust pipe, such that the projection of the antenna cap and the concave groove of the exhaust pipe are fitted to each other.

"On the other hand, Patent document 2 discloses a magnetron in which the end portion of the exhaust pipe, to which the antenna cap is press-fitted, has a length ranging from 8 mm to 10 mm in a tubular axial direction."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "In the conventional magnetrons, generally, each portion thereof has been designed based on the assumption that the magnetrons have an oscillation frequency of 2.45 GHz band. In recent years, however, there has been developed a magnetron having an oscillation frequency of 5.8 GHz band. This is because, in the magnetron having the oscillation frequency of 5.8 GHz band, a wavelength of the oscillation frequency is approximately a half of that of the magnetron having an oscillation frequency of 2.45 GHz band, so that the sizes of peripheral devices, such as a waveguide and the like, are approximately halved to allow the peripheral devices to be greatly reduced in size.

"In the magnetron having the oscillation frequency of 5.8 GHz band, it is necessary to reduce a length of the end portion (outer circumferential surface) of the exhaust pipe in the tubular axial direction (e.g., from 10 mm to 5 mm). In this case, since a press fit length of the antenna cap and the exhaust pipe becomes short, the structures of Patent documents 1 and 2 cannot fully suppress removal of the antenna cap.

"As a method of solving this problem, there can be considered, for example, a structure in which the antenna cap and the exhaust pipe are bonded with a conductive adhesive, such as a silver paste or the like. However, in this structure, under a condition of heat cycle caused by repeating switching ON/OFF of the magnetron, it is difficult to continuously maintain the adhesive strength between the antenna cap and the exhaust pipe.

"Therefore, an object of the present invention is to solve the conventional problem described above, and to provide a magnetron which can suppress removal of the antenna cap.

"In order to achieve the above described object, the magnetron according to the present invention includes an anode portion, a cathode portion arranged in a central portion of the anode portion, an output antenna connected to the anode portion, an exhaust pipe arranged around the output antenna to serve as a part of a vacuum tube, and an antenna cap covering a chip-off portion included in the exhaust pipe, wherein the antenna cap and the exhaust pipe are welded to each other.

"The magnetron according to the present invention can further reliably suppress the removal of the antenna cap, since the antenna cap and the exhaust pipe are welded to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

"These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:

"FIG. 1 is a longitudinal sectional view of a magnetron according to an embodiment of the present invention.

"FIG. 2 is a partially enlarged sectional view showing a structure of the vicinity of an antenna cap included in the magnetron shown in FIG. 1.

"FIG. 3 is a perspective view showing a structure of the vicinity of an antenna cap included in the magnetron shown in FIG. 1.

"FIG. 4 is a longitudinal sectional view of a conventional magnetron.

"FIG. 5 is a partially enlarged sectional view showing a structure of the vicinity of an antenna cap included in the magnetron shown in FIG. 4.

"FIG. 6 is a perspective view showing a structure of the vicinity of an antenna cap included in the magnetron shown in FIG. 4."

For additional information on this patent application, see: ISHII, Takeshi. Magnetron and Device Using Microwaves Related Applications. Filed January 6, 2014 and posted July 17, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4527&p=91&f=G&l=50&d=PG01&S1=20140710.PD.&OS=PD/20140710&RS=PD/20140710

Keywords for this news article include: Electronics, Magnetron, Panasonic Corporation.

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Source: Electronics Newsweekly


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