US3790852A

US3790852A - Microwave-excited light emitting device

Info

Publication number: US3790852A
Application number: US00248478A
Authority: US
Inventors: L Bolin; C Hopper; S Jolly
Original assignee: General Electric Co
Current assignee: General Electric Co; INDIANA NATIONAL BANK
Priority date: 1972-04-28
Filing date: 1972-04-28
Publication date: 1974-02-05
Anticipated expiration: 1991-02-05

Abstract

A microwave-excited light emitting device is provided comprising an electrodeless evacuated discharge lamp containing ionizable elements and mounted in the frequency determining resonator of a microwave oscillator. The oscillator resonator is tuned to provide a microwave frequency of sufficiently high frequency to provide ionization and excitation of the elements within the electrodeless discharge lamp while mitigating deterious ion bombardment of the walls of the electrodeless discharge lamp. By placing the lamp in the oscillator resonator any changes in the electrical characteristics of the lamp after firing will cause a frequency change in the oscillator allowing the lamp and the oscillator to remain in tuned relationship. However, the oscillator is further provided with thermal isolation means to isolate the lamp from the active device within the oscillator such as a vacuum tube or a solid state device. The light-emitting device is further provided with heating means to conduct externally generated heat to the lamp thermally independently of the active device. In this manner the lamp may be operated at a steady, and preferably elevated, temperature without exposing the active device to excessive heat which would have a deleterious effect on the life of the active device.

Description

United States Patent 1191 Bolin et al.

[111 I 3,790,852 [451 Fees, 1974 [5 1 MICROWAVE-EXCITED LIGHT EMITTING DEVICE [75] Inventors: Larry R. Bolin; Claude Hopper, .lr.,

both of Owensboro, Ky.; Shelby A. Jolly, Rockport, Ind.

[73] Assignee: General Electric Company,

Owensboro, Ky.

[22] Filed: Apr. 28, 1972 [21] Appl. No.: 248,478

Primary Examiner-John Kominski Attorney, Agent, or FirmNathan J. Cornfeld; Dennis A. Dearing; Frank L. Neuhauser [57] ABSTRACT A microwave-excited light emitting device is provided comprising an electrodeless evacuated discharge lamp containing ionizable elements and mounted in the frequency determining resonator of a microwave oscillator. The oscillator resonator is tuned to provide a microwave frequency of sufficiently high frequency to provide ionization and excitation of the elements within the electrodeless discharge-lamp while mitigating deterious ion bombardment of the'walls of the electrodeless discharge lamp. By placing the lamp in the oscillator resonator any changes in the electrical characteristics of the lamp after firing will cause a frequency change in the oscillator allowing the lamp and the oscillator to remain in tuned relationship. However, the oscillator is further provided with thermal isolation means to isolate the lamp from the active device within the oscillator such as a vacuum tube or a solid state device. The light-emitting device is further provided with heating means to conduct externally generated heat to the lamp thermally independently of the active device. In this manner the lamp may be operated at a steady, and preferably elevated, temperature without exposing the active device to excessive heat which would have a deleterious effect on the life of the active device.

9 Claims, 1 Drawing Figure MICROWAVE-EXCITED LIGHT EMITTING DEVICE CROSS-REFERENCE TO RELATED APPLICATION This application is related to U. S. patent application, Ser. No. 248,477 (G. E. Docket No. 36-08-0598) filed concurrently in the names of L. R. Bolin and S. A. Jolly and assigned to the assignee of the invention herein.

BACKGROUND OF THE INVENTION This invention relates to light-emitting devices excited to emit light by electromagnetic energy of microwave wavelength. More particularly, this invention relates to a microwave device comprising a microwave cavity oscillator having a liht emitting electrodeless lamp integrally mounted therein and thermally isolated from the active device within the oscillator.

In certain types of apparatus, such as, for example, spectroscopic analysis equipment for the identification of the presence of certain elements in samples, a modulated beam of a light spectrum of the element in question is produced to excite the sample. This modulated light source has been produced using hollow cathode electron discharge devices. However, for certain elements this has proved unsatisfactory because the presence of the particular element shortens the life of the hollow cathode.

It has therefore been proposed to produce the desired light spectrum by exciting such elements using microwaves. The element is encapsulated, together with an inert gas, in an electrodeless lamp comprising a sealed envelope transparent to the desired wavelengths of light, such as, for example, quartz or other glasses. The lamp is placed in a microwave cavity resonator in the particular location desired for light emission and coupled to a microwave cavity oscillator resonator to provide the power source for the excitation.

However, it has been found that at low frequencies, i.e., lower than about 500 mHz, the excited ions within the lamp bombard the glass envelope of the lamp with the resultant undesirable shortening of lamp life. At higher frequencies this problem is mitigated or eliminated butother problems are encountered which are thought to be due to an untuned condition between the two cavity resonators housing, respectively, the ocsillator and the lamp. This is apparently due to the lamp cavity resonator resonating a different frequency when the lamp is in an unexcited or unfired state than when the elements are excited. In the aforementioned patent application of Bolin and Jolly this problem is solved by placing the electrodeless discharge lamp in the same resonator which determines the frequency of the oscillator. Thus, changes in the electrical characteristics of the lamp which occur after firing will result in a frequency shift in the oscillator which allows the lamp and the oscillator to remain in tuned relationship.

However, it has been further found that it is desirable to operate the electrodeless discharge lamp at a given temperature which is usually hotter than that normally found in the oscillator. Normally the temperature in the oscillator will fluctuate due to warmup of the active device or the like. Also the presence of elevated temperatures, while desirable for the operation of the electrodeless discharge lamp, may be deleterious to the active device thereby shortening its life.

It is therefore an object of the invention to provide an integral, microwave stimulated, light-emitting device comprising a microwave oscillator cavity resonator containing an electrodeless light-emitting lamp which is thermally isolated from the active device in the oscillator. It is another object of the invention to provide means for stabilizing the temperature of the electrodeless discharge lamp. It is yet another object of the invention to provide supplemental heating means to raise the operating temperature of the electrodeless discharge lamp. These and other objects of the invention will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING The sole drawing of the invention is a partially cutaway cross-sectional view of the oscillator.

DESCRIPTION OF THE INVENTION The invention generally comprises a light emitting device comprising a microwave oscillator generally indicated at 2 having a composite outer electrically conductive shell comprising

shell sections

6, 8, and 10 and containing an electrodeless discharge lamp 60 adjacent one end thereof, an active device 30 adjacent an opposite end, and means therebetween comprising a resonant cavity generally indicated at numeral 40 which cooperated with the active device 30 to provide an oscillator to provide a sustained emission of microwave energy at the resonant frequency of the device as determined by the various parameters of the associated circurt.

Shell section 10 comprises a hollow metal shell which may be provided with a cylindrical bore therein. A metal end cap 12 is fitted into the central bore in shell 10 to provide an end wall 12 therein. End wall 12, in turn, communicates with a hollow metal tube 14 and a larger diameter metal tube 16 within shell 10 to electrically couple end wall 12 with a cathode terminal 32 of active device 30 which, in the illustrated embodiment, comprises a triode electron discharge device having the usual cathode, grid, and anode electrodes (not shown). Heater wires for the cathode are connected by leads 34 to terminal 17 and 18 on end wall 12. Terminal 17 is grounded to the end wall 12 while terminal 18 is brought out through an insulator 19.

Device 30 is also provided with a grid terminal ring 38 which is connected to a metallic grid cylinder 44 having a dielectric coating thereon to insulate it from shell 10. The grid of device 30 is connected to a terminal 24 via a lead 22 in grid resistor 23 leading from the grid cylinder 44. Terminal 24 is mounted in end wall 12 and insulated therefrom by an insulator 25.

Device 30 has an anode stud 36 thereon which is coupled to an anode line comprising solid cylinder member 46 and hollow sleeve member 48 which will be described in more detail below. Power is supplied to anode stud 36 through a terminal 50 mounted to end wall 12 and insulated therefrom by an insulator S2. A lead wire 54 connected to cylinder member 46 passes through a shield 55 to terminal 50 through an RF choke 58.

Feedback fingers 15 electrically connnected to the cathode 32 pass through openings in the end wall of grid cylinder 44 feed energy from the plate surface back to the cathode surface to sustain oscillation of the device.

The oscillator provides microwave energy in a manner well known to those skilled in the art and described, for example, in Chapter 6 of Electronic Designers Handbook; by R. W. Lande, D. C. Davis, and A. P. Albrecht; McGraw-l-lill Book Company, Inc.; 1957.

As previously mentioned above, anode stud 36 is coupled to an anode line comprising a solid cylinder or cylindrical member 46 and a hollow cylinder 48. Cylinder or rod 46 is threadedly secured to stud 36 and comprises a copper or aluminum or other good heat conducting and electrical conducting material. Sleeve 48 is then connected as by a threaded or press fit to a reduced end portion of cylinder 46. Sleeve 48 comprises a cylinder of poor heat conducting material such as, for example, lnvar. Cylinder 48 is plated with copper or other suitable metal to provide good electrical-characteristics.

Surrounding cylinder 46 is a sleeve 72 of good heat conducting and electrically insulating material such as beryllia. Sleeve 72 has a central bore therein approximately the same diameter as cylinder 46 to insure a tight fit to provide a good thermal coupling therebetween. The outer diameter of sleeve 72 is approximately the same as the inner diameter of shell 10 to, in turn, provide good thermal coupling therebetween. Heat generated by active device 30, particularly adjacent the anode portion, is thereby connected through cylinder 46 and sleeve 72 to the outer shell 10 from whence it may be dissipated to the surrounding environment.

As previously stated, the outer shell of the oscillator is a composite comprising

shell portions

6, 8, and 10. Shell portion 6, like shell portion 10, comprises a good heat conducting metal having a cylindrical bore therein. Shell portion 6 is separated from shell portion 10 by an intermediate shell 8 which is constructed of, for example, lnvar or other poor heat conducting material plated with copper or other suitable material to provide good electrical materials. The adjoining ends of the respective shell portions may be suitably joined together by threaded connections, press fitting, or metallurgical bonding.

Electrodeless discharge lamp 60 comprises a sealed, hollow ampule comprising silica or glass or the like and containing gas of the particular elements, for example, mercury vapor, and inert gas such as argon. The lamp 60 is mounted, in the illustrated embodiment, in a central bore of a sleeve 74 which is constructed of a good heat conducting material such as beryllia. Sleeve 74, in turn, has an external dimension matching the internal configuration of shell 6 so that it may be tightly fitted therein in good thermal communication therewith.

Sleeve 48 of the anode line is dimensioned to extend toward the electrodeless discharge lamp 60 mounted in sleeve 74 so that the narrow end 62 of lamp 60 fits within the end of sleeve 48. The length of the anode line and the length of shell 8 are dimensioned to be, electrically, one-half wavelength long, taking into account the foreshortening of the capacitance at the anode end of the anode line. Thus, the electrodeless discharge lamp 60 is placed approximately in a position of maximum electrical field strength. This is desirable to provide maximum intensity of the field and therefore maximum brilliance of the emitted light resulting from the excitation from the ions within the lamp by the microwave energy. Slight adjustments, of course, of the position of lamp 60 to provide the maximum impedance matching of the lamp to the anode line may be necessary to provide the most efficient operation.

In the illustrated embodiment, an end wall 13 is also provided on the end of the oscillator shell 6. End wall 13 has a central window 1321 which provides a columnated beam of light from the electrodeless discharge lamp. It should be noted, however, that this is not necessary for the operation of the device but may be preferred for certain uses.

In a preferred embodiment, shell 6 is surrounded by a heater coil which is capable of supplying additional heat to the electrodeless discharge lamp through thermal conduction via shell 6 and sleeve 74. in this manner the lamp may be heated to a preselected temperature above the normal operating temperature of the oscillator and then maintained at that temperature.

The device operates by initiation of oscillation between the cavity resonator and the amplifier means at a preselected frequency. Microwave energy generated thereby is transmitted to the electrodeless discharge lamp whereby the ions therein are excited to emit light therefrom. The sustained emission oflight based on excitation of the vapor or gas therein can result in a frequency shift in the oscillator. While this effect is not fully understood, it is believed to be the result of a change in the impedance of the load resulting from a change in the reactance of the lamp under excitation conditions as opposed to the unexcited state. These changes in reactance change the resonant frequency of the cavity which, in turn, results in the shift in frequency of the oscillator. This frequency shift, however, affects both the oscillator and the lamp. Hence, the oscillator and the lamp remain in a tuned condition resulting in maximum efficiency of operation.

However, due to the construction of shell 8 and anode line portion 48 of poor heat conducting material, the oscillator, although electrically functioning as an integral device, is thermally isolated into two shell chambers, the shell chamber housing active device 30 adjacent shell portion 10 and the chamber housing electrodeless discharge lamp 60 adjacent shell portion 6. Each of these chambers comprises an outer shell portion (10-6) of good heat conducting material, a sleeve of insulating material which is a good heat conductor, and a central device from which heat is either conducted toward or away from. In this manner the electrodeless discharge lamp may be operated at a temperature preselected for maximum efficiency of the lamp. The active device, on the other hand, may be operated at a reduced temperature with any heat generated from the device being conducted to the outer shell 10 and dissipated to the atmosphere thereby providing a lower operating temperature for the active device resulting in longer life.

Thus, the invention provides an integral device wherein an electrodeless discharge lamp is mounted in the frequency determinating resonator of a microwave oscillator, yet is thermally isolated from the active device in the oscillator. While the invention has been described with regard to a particular configuration and particular materials it should be readily apparent that minor modifications as well as substitutions of other materials having similar properties may be made without departing from the scope of the invention which is to be limited only by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A light-emitting device comprising:

a. a microwave oscillator including:

1. 'a composite electrically conductive shell defining a resonant cavity, said conductive shell being dimensioned to be electrically one-half the operating frequency wavelength, and thus creating at least two positions of maximum electric field intensity;

2. an active device disposed within said cavity adjacent one of said at least two positions for providing asustained emission of microwave energy at a predetermined operating frequency;

b. an electrodeless discharge lamp disposed within said cavity and spaced from said active means at least a distance one-half the operating frequency wavelength of said cavity and thereby being disposed of another of said at least two positions of maximum electric intensity in said cavity;

c. a first heat transmitting means, interposed between said active device and said lamp, for conducting heat generated by the active device to the surrounding environment, said first heat transmitting means being constructed of an electrically nonconductive material.

2. The device of claim 1 wherein said shell comprises a first shell portion adjacent said active device, having good heat conducting properties, said first shell portion being thermally coupled to said first heat transmitting means; a second shell portion adjacent said lamp, havinggood heat conducting properties; and a third shell portion interposed between said first and second members, having poor thermal conducting properties.

3. The device of claim 2 wherein said oscillator fur- 'ther comprises a central electrode having a first portion electrically coupled to said active device and a second portion comprising a poor thermal conductor extending from said first portion toward said lamp, said central electrode first portion extending through and being thermally coupled to said first heat-transmitting means.

4. The light-emitting device of claim 3 wherein said lamp is disposed in said second portion of said central electrode and a second heat transmitting means is thermally coupled between said lamp and said second portion of said shell for conducting heat to and away from said lamp, said second heat transmitting means being constructed of an electrically non-conductive material.

5. The light-emitting device of claim 4 wherein heat generating means is thermally coupled to said second shell portion.

6. A light-emitting device comprising:

a. a microwave oscillator including:

1. a composite electrically conductive shell defining a resonant cavity, said conductive shell dimensioned to be electrically one-half the operating frequency wavelength and thus creating at least two positions of maximum electric field intensity;

2. means dividing said resonant cavity into first and second shell chambers;

3. an active device, disposed within said first shell chamber, adjacent one of said at least two positions for providing a sustained emission of microwave energy at a predetermined operating frequency;

b. an electrodeless discharge lamp disposed within said second shell chamber and spaced from said active means at least a distance one-half the operating frequency wavelength of said cavity and thereby being disposed at another of said at least two positions.

7. The device of claim 6 wherein said shell comprises a first shell portion having good heat conductive properties, said first shell portion defining said first shell chamber, and a second shell portion having good heat conducting properties, said second shell portion defining said second shell chamber; and said dividing means includes a first heat transmitting means thermally coupled to said first shell portion for transmitting heat generated by the active device to said first shell portion for dissipation to the surrounding environment and a second heat transmitting means thermally coupled between said lamp and said second shell portion for conducting heat to and away from said lamp, said first and second heat transmitting means constructed of electrically non-conductive material. 8. The device of claim 7 wherein said shell further comprises a third shell portion interposed between said first and second shell portions having poor thermal conducting properties.

9. The device of claim 7 wherein heat generating means is thermally coupled to said second shell por- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patmfl1No. 3,790,852 Datai February 5, 1974 Invmumr(s) Larry R. Bolin; Claude Hopper, Jr.; Shelby A. Jolly It is certified that error appears in the above-identified patefit and that said Letters Patent are hereby corrected as shown below:

Column 5, Claim 1, Line 17, cancel "of" (first occurrence) and insert at.

Signed and sealed this 10th day of September 197h."

v (SEAL) I Attestz v 'MccoY M. GIBSON; JR; 0. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC 60376-P69 i: use sovzrgunsflfgnmrms orncs: Isa d-ase-au I I

Claims

1. A light-emitting device comprising: a. a microwave oscillator including: 1. a composite electrically conductive shell defining a resonant cavity, said conductive shell being dimensioned to be electrically one-half the operating frequency wavelength, and thus creating at least two positions of maximum electric field intensity; 2. an active device disposed within said cavity adjacent one of said at least two positions for providing a sustained emission of microwave energy at a predetermined operaTing frequency; b. an electrodeless discharge lamp disposed within said cavity and spaced from said active means at least a distance one-half the operating frequency wavelength of said cavity and thereby being disposed of another of said at least two positions of maximum electric intensity in said cavity; c. a first heat transmitting means, interposed between said active device and said lamp, for conducting heat generated by the active device to the surrounding environment, said first heat transmitting means being constructed of an electrically non-conductive material.

2. The device of claim 1 wherein said shell comprises a first shell portion adjacent said active device, having good heat conducting properties, said first shell portion being thermally coupled to said first heat transmitting means; a second shell portion adjacent said lamp, having good heat conducting properties; and a third shell portion interposed between said first and second members, having poor thermal conducting properties.

2. an active device disposed within said cavity adjacent one of said at least two positions for providing a sustained emission of microwave energy at a predetermined operaTing frequency; b. an electrodeless discharge lamp disposed within said cavity and spaced from said active means at least a distance one-half the operating frequency wavelength of said cavity and thereby being disposed of another of said at least two positions of maximum electric intensity in said cavity; c. a first heat transmitting means, interposed between said active device and said lamp, for conducting heat generated by the active device to the surrounding environment, said first heat transmitting means being constructed of an electrically non-conductive material.

2. means dividing said resonant cavity into first and second shell chambers;

3. an active device, disposed within said first shell chamber, adjacent one of said at least two positions for providing a sustained emission of microwave energy at a predetermined operating frequency; b. an electrodeless discharge lamp disposed within said second shell chamber and spaced from said active means at least a distance one-half the operating frequency wavelength of said cavity and thereby being disposed at another of said at least two positions.

3. The device of claim 2 wherein said oscillator further comprises a central electrode having a first portion electrically coupled to said active device and a second portion comprising a poor thermal conductor extending from said first portion toward said lamp, said central electrode first portion extending through and being thermally coupled to said first heat-transmitting means.

6. A light-emitting device comprising: a. a microwave oscillator including:

7. The device of claim 6 wherein said shell comprises a first shell portion having good heat conductive properties, said first shell portion defining said first shell chamber, and a second shell portion having good heat conducting properties, said second shell portion defining said second shell chamber; and said dividing means includes a first heat transmitting means thermally coupled to said first shell portion for transmitting heat generated by the active device to said first shell portion for dissipation to the surrounding environment and a second heat transmitting means thermally coupled between said lamp and said second shell portion for conducting heat to and away from said lamp, said first and second heat transmitting means constructed of electrically non-conductive material.

8. The device of claim 7 wherein said shell further comprises a third shell portion interposed between said first and second shell portions having poor thermal conducting properties.

9. The device of claim 7 wherein heat generating means is thermally coupled to said second shell portion.