Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J65/00—Lamps without any electrode inside the vessel; Lamps with at least one main electrode outside the vessel
  • H01J65/04—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels
  • H01J65/042—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels by an external electromagnetic field
  • H01J65/044—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels by an external electromagnetic field the field being produced by a separate microwave unit
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J65/00—Lamps without any electrode inside the vessel; Lamps with at least one main electrode outside the vessel
  • H01J65/04—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels

Definitions

• the present invention relates to a microwave powered lamp, and particularly to such a lamp which has a compact structure.
• Such microwave lamps may be used as illumination sources, which find a particular use in commercial or industrial lighting.
• These parts include a quartz bulb to contain the arc plasma housed within a microwave cavity having a metal mesh to contain the microwaves but allow the escape of light, a magnetron to produce the microwaves, a waveguide to carry the microwaves from the magnetron to the cavity, a power supply to drive the magnetron and cooling fans or other means to cool the magnetron and its power supply.
• the lamp bulb is rotated within the microwave cavity to stabilize the discharge which adds a motor to the system as well.
• the lamp itself does not include a reflector. Rather the lamp is to be inserted through a hole in reflectors of several designs, suitable for use in applications requiring light dispersal over different areas. This requires the light source to extend outward from the lamp case a distance of at least 100 mm. Keeping the entry hole to a small diameter increases the efficiency of the reflector.
• the bulb stem is fed through the coupling slot and the waveguide, and the motor and coupler are located on the other side of the waveguide, resulting in a very long stem which is subject to breakage.
• the waveguide must have a sufficiently narrow width so that the cutoff frequency is high enough to eliminate spurious interference signals from being generated, but must have a height sufficient to prevent arcing at the location of the magnetron antenna.
• a conventional WR-284 waveguide is narrow enough to eliminate interference signals, but because of its height which correlates to its width in a conventional ratio of about 1 to 2, arcing results.
• a microwave lamp wherein the coupling slot is located in the cavity end wall to one side of center, while the bulb stem passes through the end plate to the other side of center and is at an angle of other than 90° in relation to the end wall, so that the bulb is supported centrally in relation to the cavity wall structure.
• a motor and shaft coupling to the bulb stem are located at the end of the stem outside the cavity. In this manner, the bulb stem which is provided is not particularly long, and therefore provides a more rugged and durable support structure.
• the waveguide which feeds the coupling slot is oriented so that its long dimension is parallel to the cavity end wall, thus minimizing the overall length of the lamp.
• a novel waveguide structure is used, wherein the waveguide has about the height of a WR-340 waveguide, while it has the width of a WR-284 waveguide. In this way, the height of the magnetron antenna is accommodated without arcing, while spurious signals which might cause interference are eliminated.
• Figure 1 is a side view of a lamp in accordance with an embodiment of the invention.
• Figure 2 is a top view of the waveguide portion of the lamp depicted in Figure 1.
• Figure 3 is a sectional view of the waveguide of the lamp of Figure 1 taken perpendicular to the coupling slot.
• Figure 4 is a plan view which depicts how the magnetron and associated components are mounted in the lamp of Figure 1.
• the lamp is comprised of bulb 2 which is located in a microwave cavity.
• the bulb may be made of quartz and encloses a discharge forming medium, for example, a sulfur or selenium based fill.
• the microwave cavity is cylindrical, and is comprised of a side wall structure, and two end walls.
• the side wall structure and top end wall in the orientation of Figure 1 are made of a cylindrical metallic mesh, shown in part at reference numeral 3, which allows light to exit but is substantially opaque to microwave radiation.
• the bottom end wall of the cavity in the orientation of Figure 1 is the outside surface 8 of waveguide 10.
• the microwave lamp depicted in Figure 1 may be used to replace existing non-microwave lamps, and it is therefore desirable for the lamp to be made as compact as possible so as to fit within the general outline of existing lamps.
• the bulb stem extends from an end wall, it passes through the waveguide which feeds the cavity, and the motor and coupling ferrule are mounted on the opposite side of the waveguide, far enough away to be clear of microwave fields.
• Such an arrangement may have the effect of increasing the overall length of the lamp, as well as the length of the bulb stem, thereby making it subject to breakage.
• the coupling slot is located to one side of center in the cavity end wall, while the bulb stem is fed through the end wall to the other side of center canted in relation to the end wall, with the motor and ferrule being mounted outside the cavity and away from the waveguide.
• the long direction of the waveguide extends parallel to the end wall of the cavity, so as to not extend the length of the lamp. The result is a more compact lamp of shorter overall length, wherein the bulb is more ruggedly supported on a shorter stem.
• rectangular waveguide 10 is shown, having inside wall 12 and outside wall 8.
• the top walls of the waveguide have coupling slot 14 therein, which is shown in Figure 2.
• end wall 16 of the waveguide extends just beyond the coupling slot.
• Magnetron 18 having antenna 20 is mounted to the waveguide, as shown.
• Microwave power is fed into the waveguide and through coupling slot 14 to the microwave cavity, where it excites the fill in bulb 2.
• hole 21 is shown, through which the magnetron antenna and a gasket protrude.
• bulb stem 22 is passed through hole 24 an angle of other than 90°, (about 77° in the preferred embodiment) so that the bulb is centrally located in relation to the mesh side wall structure of the cavity.
• the motor 26 is mounted to motor support 28, while ferrule 30 couples the motor shaft to the bulb stem, which is typically made of quartz.
• Extension 34 of support 28 is secured to the bottom outside surface of the waveguide, while gap 36 is present between the motor support and the end wall of the waveguide.
• top wall 8 of the waveguide extends to the left at reference numeral 40 past the end of the waveguide. Additionally, the top of the waveguide is flush against plate 32, which is secured to plate 42 at the ends thereof with flanges 44 and 46.
• metallic ring 52 is mounted on the top surface of the waveguide (cavity end) .
• the cylindrical mesh is secured to this ring by a clamp, and the mesh passes through a hole in plate 42.
• a transparent cylindrical envelope 54 which may be made of glass or quartz surrounds the screen, and is mounted on plate 42, for example by retainer 56. Thermal insulation is disposed in the space between plates 32 and 42.
• microwave power generated by the magnetron is fed through the waveguide and the coupling slot into the cavity in which bulb 2 is located.
• magnetron antenna 20 is located 1/4 guide wavelength (the wavelength of signals propagating within the waveguide) from coupling slot 14.
• a waveguide having a width sufficiently narrow to have a cut-off frequency sufficiently high to eliminate spurious signals was necessary.
• a waveguide which was tried which accommodated the magnetron antenna produced out of band signals 200 Mhz below the normal operation point of 2450 Mhz, and the use of the 1/4 wavelength waveguide length referred to above tends to aggravate this situation.
• a WR-284 (equivalent IEC designation, R-32) waveguide was sufficiently narrow to eliminate spurious signals, but it was found that the height of this waveguide was too small to accommodate the magnetron antenna without arcing.
• a non- conventional waveguide having about the width of the WR-284 waveguide and about the height of the WR-340 (equivalent IEC designation, R-26) waveguide. This blocks the transmission of signals below 2078 Mhz and helps to suppress the low frequency out of band signals by reducing the phase shift between the magnetron and the coupling slot. At the same time, the height of the waveguide is sufficient to accommodate the magnetron antenna without arcing.
• the waveguide end wall behind the magnetron is moved farther away than is the usual practice.
• a metal tuning knob was used to match the impedance of the lamp to the waveguide. This knob functioned as a capacitor at its location. With the length reduction to one quarter wavelength, this position became the same as the magnetron antenna.
• a tuning knob might have been placed beside the antenna, taking care to avoid arcing, however, the magnetron antenna itself is a capacitor across the waveguide. This is usually compensated by placing the end wall in an inductive position, closer to the antenna than a quarter wavelength. By moving the wall farther out, the inductance is reduced and the antenna is seen as the desired tuning capacitance. The best position was found experimentally by using a movable waveguide end wall.
• tuning knob In many previous microwave lamps, matching is accomplished by placing a tuning knob in the waveguide.
• dielectric member 62 which may be made of mica is depicted. This member rests against the inside end wall of the waveguide and protrudes through coupling slot 14 while resting against the edge of the slot. It may be substantially as wide as the slot. The purpose of member 62 is to prevent arcing across the slot.
• Figure 4 is a plan view of the magnetron and associated components, which are located on plate 32 shown in Figure 1.
• Magnetron 18 receives filament power from filament transformer 70, while stepdown transformer 72 may be used to provide power for bulb rotator motor 26, shown in connection with motor mount 28 and capacitor 74.
• magnetron cooling air blower 76 is depicted as is PC control board 78.
• waveguide 10 is shown feeding coupling slot 14.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Electromagnetism (AREA)
• Discharge Lamps And Accessories Thereof (AREA)
• Constitution Of High-Frequency Heating (AREA)
• Circuit Arrangements For Discharge Lamps (AREA)
• Non-Portable Lighting Devices Or Systems Thereof (AREA)
• Vessels And Coating Films For Discharge Lamps (AREA)

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Publications (2)

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• 1996
  • 1996-04-18 IL IL11797296A patent/IL117972A/xx not_active IP Right Cessation
  • 1996-04-22 JP JP8531981A patent/JPH11511892A/ja active Pending
  • 1996-04-22 EP EP96913001A patent/EP0821832B1/de not_active Expired - Lifetime
  • 1996-04-22 WO PCT/US1996/005556 patent/WO1996033509A1/en not_active Ceased
  • 1996-04-22 AU AU55637/96A patent/AU5563796A/en not_active Abandoned
  • 1996-04-22 ZA ZA963179A patent/ZA963179B/xx unknown
  • 1996-04-22 HU HU9802761A patent/HUP9802761A3/hu unknown
  • 1996-04-22 KR KR1019970707485A patent/KR19990007961A/ko not_active Ceased
  • 1996-04-22 CA CA002218500A patent/CA2218500A1/en not_active Abandoned
  • 1996-04-22 DE DE69624472T patent/DE69624472D1/de not_active Expired - Lifetime
  • 1996-04-22 AT AT96913001T patent/ATE226759T1/de not_active IP Right Cessation

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