Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Distributed parameter resonator-type magnetron
Reexamination Certificate
2002-02-20
2003-11-11
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Distributed parameter resonator-type magnetron
C315S039510, C315S248000
Reexamination Certificate
active
06646384
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to microwave excited lamps and to microwave gaskets therein.
2. Description of the Prior Art
FIGS. 1 and 2
illustrate a schematic diagram of a prior art microwave excited lamp
10
of the type manufactured by the Assignee of the present invention. The microwave lamp
10
has a magnetron
12
. The magnetron
12
is rated with maximum sustained output power of at least 1,000 watts and typically at least 2,000 watts. The magnetron
12
includes a housing
14
of a conventional design including heat radiating fins (not illustrated) thereon to dissipate heat generated therein. The magnetron
12
typically oscillates at a frequency, such as 2.45 GHz, to produce the aforementioned output power. The magnetron
12
includes an antenna
18
which radiates microwaves within a microwave structure
20
. The microwaves are coupled to the UV electrodeless bulb
24
within a reflector
22
to cause the emission of UV light therefrom. The microwave structure
20
is manufactured from a metallic material, such as aluminum or stainless steel and contains the reflector
22
. The reflector
22
has a curved reflective surface
23
which reflects the UV wavelengths of the light produced by the UV bulb
24
through a metallic mesh
28
to a target (not illustrated). The metallic mesh
28
contains the microwaves within the reflector
22
but is transparent to the UV rays. The microwaves are coupled into the reflector
22
by slots
30
.
It should be understood that the magnetron
12
of
FIG. 1
has been omitted from
FIG. 2
in order to illustrate the backside surface
34
of the reflector
22
extending along the microwave structure
20
and the prior art usage of silver-plated brass wire mesh microwave gaskets
40
which provide microwave seals against aluminum structures within the microwave structure. The arcuate section
31
set off by dotted lines is a surface area where it has been discovered that at least one standing wave microwave current maxima exists during operation.
A pair of rails
32
connect the back surface
34
of the reflector
22
to opposed side walls
36
of the microwave structure
20
to provide a support structure for the reflector. The microwave structure
20
is electrically conductive and comprises aluminum. The microwaves transmitted from the antenna
18
flow on the surface
34
of the reflector
22
and through the slots
30
. The microwaves are prevented from leaking below the rails
34
by the silver-plated brass wire mesh microwave gaskets
40
and outside the end walls
44
by silver-plated brass wire mesh microwave gaskets
42
which each are of identical construction, and are manufactured from multiple wire filaments. The microwave gaskets
40
provide a microwave tight seal between the back surface
34
of the reflector
22
and the opposed side walls
36
of the microwave structure
20
. The microwave gaskets
42
seal the microwaves from leaking beyond the end plates
44
.
The current maxima in location
31
has been discovered to occur approximately in the middle third of the microwave structure
20
therewith discussed below regarding FIG.
3
. Oxidation of the silver-plated brass wire mesh gasket material occurs due to the presence of ozone, UV light, and heat during lamp operation. The progressive oxidation process increases the amount of contact resistance between the gasket and the reflector and the rails.
The gaskets
40
′ (new) and the gasket
40
″ (after use) of
FIG. 3
are identical to the gasket
40
of FIG.
2
and are wire manufactured-from silver-plated brass filaments. Silver plating was chosen because of low electrical resistance. The new silver gasket
40
′ is not oxidized and, as a result, provides the low electrical resistance between the gasket and aluminum of the reflector
22
and the rails
32
to the substantial alternating microwave current flow occurring within the area
31
over the back surface
34
of the aluminum reflector
22
, the surfaces of gasket
40
, the surface of the longitudinally extending aluminum rails
32
, and the surface of the opposed aluminum walls
36
of the microwave structure
20
. Alternating current circulates in a loop back and forth on the surface of the aforementioned parts and causes a voltage drop across the contact resistance between the silver-plated brass wire mesh gasket
40
and the aluminum reflector
22
and the aluminum rails
32
.
The silver-plated brass wire mesh gasket
40
″ has been used for 3,059 hours in a lamp of the design of
FIGS. 1 and 2
for generating UV light. It has been discovered by the inventor that the substantial oxidation of the silver-plated brass wire mesh gasket
40
″ is a result of the presence of heat, ozone and UV light. It has been further discovered by the inventor that the substantial oxidation in the vicinity of the area
31
increases the electrical contact resistance inherent in the electrical contact between the dissimilar materials of the aluminum used in the manufacture of the reflector
22
and rails
32
and the silver-plated brass of the gasket
40
. The increase in contact resistance caused by the oxidation of the silver plating in the vicinity of the current maxima in area
31
is so substantial that a sealing failure of the gaskets
40
and a heat related failure of the reflector
22
of
FIGS. 1 and 2
occurs. The highly oxidized state of the gasket
40
″ produces an increased contact resistance causing localized heating at the gasket interface with the back surface
34
of the reflector
22
. The heating destroys the reflector requiring both the gasket
40
and the reflector
22
to be replaced to maintain operational status of the lamp
10
. The rails
32
may also be locally damaged by the heat in the vicinity of the area
31
.
SUMMARY OF THE INVENTION
The present invention is an improved microwave excited lamp and gasket for use therein having a substantially longer life than the aforementioned prior art silver-plated brass wire mesh gasket and associated reflector of aluminum in electrical contact therewith. In accordance with the invention, a light reflector in a microwave excited lamp, the gasket and optionally at least one other metallic part of the microwave structure all comprise a common metallic material, such as elemental aluminum or stainless steel which substantially eliminates contact resistance. Since materials containing the same metal do not have appreciable contact resistance, the aforementioned problem of increased contact resistance caused by oxidation in the area of a current maxima inside the microwave structure which flows on the surfaces of the reflector, gasket, and at least one other part is eliminated. The metallic material used in the gasket, reflector and optionally any other parts may comprise, may consist essentially of or may consist of aluminum or stainless steel. In accordance with the invention, the reflector, microwave gasket, and optionally the at least one other part, do not have to be manufactured from identical metallic materials with it being within the scope of the invention to have different alloys comprising the metallic material, such as elemental aluminum or different alloys of stainless steel containing different percentages of ingredients.
Test results show that the failure of the prior art gasket
40
″ illustrated in
FIG. 3
does not occur with the invention as a result of the reflector, gasket and optionally at least one other part comprising the same metallic material, such as elemental aluminum or stainless steel.
A microwave excited lamp in accordance with the invention includes a microwave source; a microwave structure including a reflector comprising a metallic material and containing a microwave excited bulb which emits light in response to coupling of microwave power thereto from the microwave source; and at least one microwave gasket which provides a microwave tight seal between a surface of the reflector and at least one other part of the microwave structure with
Fusion UV Systems Inc.
Philogene Haissa
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