Radiant energy – Radiant energy generation and sources – With radiation modifying member
Reexamination Certificate
1998-11-12
2001-06-19
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Radiant energy generation and sources
With radiation modifying member
C250S493100, C250S495100
Reexamination Certificate
active
06249005
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO MICROFICHE APPENDIX
Not Applicable
FIELD OF THE INVENTION
The field of the invention is electro-optical radiation sources and a method of production of a specifically tuned radiation source. The focus of the invention is a novel filament contained within a packaged radiation source device, configured to be a component in an instrumentation application. The specific application and embodiment described is an infrared radiation source for use in various calibration, reference and measurement instruments; but the filament component and the method of wavelength tuning that component in the manufacturing process may be applied widely to a variety of other radiation emission requirements.
BACKGROUND OF THE INVENTION
The tradeoffs and requirements of radiation sources for electromagnetic and optical radiation sources, and in particular the use of enclosed electrically-excited filaments, have been the subject of development for over 100 years. As this development addressed more narrow and specific radiation requirements of controlled wavelength emission for accuracy and precision, power efficiency requirements for economy, and loss reduction and temperature control, the problems involved in design and manufacture of suitable radiation sources have become correspondingly more complex.
A particular application environment that has received a great deal of inquiry is the area of infrared radiation, which is efficiently useful and necessary in a variety of measurement and detection instrumentation. Many such applications are limited in power, space and cooling ability and require efficient illumination within a limited spectral band. Some considerations of this environment and difficulties of emitter design are discussed in U.S. Pat. No. 3,875,413 to Bridgham for Infrared Radiation Source, which particularly recognizes the difficulty of achieving stability and control of temperature and emission wavelength in a thin, flat, electrically heated radiator.
Temperature stability has been a particular development objective of traditional IR sources for calibration and measurement applications, which rely on steady state heating of an object with relatively large thermal mass. This in turn requires a long turn-on and settling time for stable operation and produces a large amount of waste heat.
As will be seen in the following descriptions, the invention may be compared favorably as an improvement over many previous radiation sources and could usefully replace such traditional reference emission sources as wire filament bulbs, LEDs, lead salt lasers, and rare earth oxide line emitters in measurement applications. Although these narrow band emitters produce isolated line radiation, they can only be tuned with difficulty and over narrow ranges. Incandescent sources typically produce a radiation spectrum described by the Planck curve with very little of the total radiation in the desired band for a particular measurement. Specifically, again in the infrared field, sources of the prior art include developments such as pulsed radiation sources using a thin plate form of radiation filament.
The prior art generally teaches the necessity of a thin plate element for radiation cooling, the '413 patent referenced above, for instance, specifying 1-2 &mgr;m. U.S. Pat. No. 5,220,173 to Kanstad for Pulsating Infrared Radiation Source proposes a formula for required thinness. The '173 patent proposes that thin flat plate elements will efficiently radiate in the IR range as the low mass of the thin material will radiate greater heat than stored thermal energy delivered by a pulsed driving circuit, and predicts the thinness of material necessary to produce this effect at the 1-2 micron range. As the focus of the prior art is on radiation source thinness for cooling effect, problems of emissivity, wavelength control and resistance control have been unaddressed.
SUMMARY OF THE INVENTION
The inquiry leading to the invention sought to examine the prior art and to practically implement an improved IR source. A new approach to fabrication of the filament emitter was required, as manufacture of the emitter described in the prior art proved problematic in that the flat plate configuration of the emitter could not be made to reliably radiate the desired radiation wavelength range, or to produce radiation outside the desired wavelength spectrum with efficient power consumption. An improved method of temperature and wavelength control was sought, and a different direction from merely specifying the thickness of material used for the emitter was taken, involving texturing the surface of the filament material to produce a microscale topography on the radiating surface that will enhance radiation while providing precise control of source temperature and emission wavelengths. As surface texture primarily produces the efficacious improvements in emissivity, radiative surface area, and wavelength control, the invention does not depend, as does the prior art, on the native properties of the source element material to achieve the desired optical effects, nor are coatings necessary which undesirably increase mass of the radiator.
The design of the radiation filament of the invention seeks to improve or remedy deficiencies noted in the prior art to the effect that conventional low thermal mass incandescent sources, including metal ribbons, thin flat plates and wire coils, which might otherwise be desirable for use as a filament, suffer from low emissivity and low electrical resistance which causes difficulty in assuring that the drive power warms the radiator and not the leads and contacts. By simultaneously improving the emissivity, thinning the source, and increasing electrical resistance, the present invention overcomes both problems.
A principal objective of the invention in its development was to provide a practical method of design and manufacture of an incandescent radiation element spectrally tuned to produce high emissivity within a narrow spectral band. More specifically, an infrared radiation source was sought such that the source emits with the efficiency close to that of an ideal black body in the desired emission band, but which has low emissivity outside that band. This was achieved by controlling the source's surface topography on a micron scale.
Another important objective is to utilize existing but untested technologies for fabricating a radiation filament designed for specific wavelength emissions. Another objective is to provide a radiating emission source that would be stable, essentially self-correcting, and mechanically simple. A specific application objective is to develop a high brightness precision controlled infrared spectrum source emitter that can be packaged with no moving parts and used in rugged environments.
These and other objectives were achieved and put into practice by development of techniques for modifying the surface characteristics of the radiation filament. By producing a random distribution of features of controlled size, surfaces were produced with high emissivity for short wavelengths and low emissivity for long wavelengths. By making the feature sizes very uniform, surface emissivity spectra were exhibited in sample materials with a sharp long wavelength cut-off, and refinements in feature size produced adjustments to the exact wavelength of the cut-off point.
A surface that can be produced with microscopic feature topology tailored to produce specific emitted frequencies when electrically stimulated proved practical as various texturing methods—mechanical, chemical, electro-chemical and particle bombardment—were examined. For any choice of material, differing feature patterns were produced under a variety of texturing methods and variables involved in application of those methods, as will be particularly described later in discussion of the preferred embodiment. Texturing by any of these means produces a pattern of relatively long “fingers” or peaks and valleys that not only increase the radiating
Ion Optics, Inc.
McDermott & Will & Emery
Nguyen Kiet T.
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