Radiant energy – Radiant energy generation and sources – With radiation modifying member
Reexamination Certificate
2000-12-22
2003-06-03
Lee, John R. (Department: 2881)
Radiant energy
Radiant energy generation and sources
With radiation modifying member
C250S493100, C250S495100, C250S505100, C219S209000, C219S553000, C338S306000, C338S307000
Reexamination Certificate
active
06573521
ABSTRACT:
This invention relates to a radiation source for emitting radiation in pulses with a duration and at intervals within chosen ranges, comprising at least one plate-shaped radiant element and at least two electrical conductors coupled to the element(s).
Infrared radiation e.g. for use in gas analysers, are typically generated using a thermal radiation source whose surface is heated to such a temperature that the surface in accordance with Plancks radiation law and the spectral emissivity of the surface emits the required radiant power at the wavelengths measured by the gas analyser.
A number of this type of emitters are known, being adapted to emit pulsed or continuous black or grey body radiation. Examples are shown in the following patent applications: EP 692.702, EP 729.016, NO 149.679, PCT/GB95/02446, PCT/NO96/00216, U.S. Pat. No. 4,644,141 and U.S. Pat. No. 5,220,173.
In EP 692.702 a source is described in which the radiant element is surrounded by an insulating material to minimize the heat loss. The source is not prepared for pulsing.
A problem related to pulsed infrared transmitters is the need for effective cooling of the source to obtain sufficient contrast between radiation in the pulses and during the intervals. At the same time, the heat conduction must be sufficiently small to let the source obtain the required temperature during the pulse.
EP 729.016 describes a pulsed infrared source using filaments being heated by an electrical current. The filaments are positioned at a chosen distance from a surface, this distance being dependant on the required cooling of the filaments.
In PCT/GB95/02446 an infrared emitting device is shown comprising a foil provided with resistive elements being heated by an electrical current. The device is cooled by radiation, and thus has to be thin.
A problem related to the use of filaments and thin foils is their relatively short life span, as they are vulnerable and may easily break as a result of overheating or mechanical shock.
A solution discussed in PCT/NO96/00216 and NO 149.679 comprises electrically conductive, planar surfaces adapted to emit infrared radiation. The emitter is mounted on a substrate supporting the emitter and conducting the excess heat away. A problem with this solution is that the heat is conducted transversally through the substrate to the environment, resulting in large dynamic differences in temperature and corresponding thermic stress in the material making the lifetime of the source unpredictable, or limiting the temperatures which may be used on the source.
U.S. Pat. No. 5,220,173 is another example showing a radiation cooled source being sufficiently thin to radiate more energy during the pulse than is stored in the element. This, however, is not a practical solution, as it is difficult to produce a sufficiently thin membrane being able to withstand the high temperature of the source when radiating and the mechanical strain on the membrane at rapid changes in temperature. Also, when the membrane is sufficiently thin, the material will become transparent, reducing or destroying the capability of radiating the supplied energy. A similar solution is shown in U.S. Pat. No. 4,644,141, in which a radiator comprising a resistance layer is arranged on a thin substrate.
The required temperature of the source is usually obtained by adjusting the.provided electrical current in the source, thus demanding a system capable of adjusting the current through the source.
It is an object of this invention to provide a pulsed radiation source having sufficient contrast in radiation between the exited and the relaxation periods. This is especially important when-used in gas detection instruments using two or more pulsed radiation elements radiating on different wavelengths, the radiation of which being separated in time, so that the radiation from the different sources in their relaxation periods do not disturb the radiation from the emitting source.
It is also an object of this invention to provide a radiation source being capable of controlling the temperature, and thus the emitted wavelength, of the source in a simple way.
The objects of the invention is obtained using a radiation source as described above, being characterized in that it also includes at least one plate-shaped surrounding, thermally conductive element being thermally coupled to a radiation element at its inner edge, and being thermally coupled to a cooling element at its outer surface.
REFERENCES:
patent: 4644141 (1987-02-01), Werner et al.
patent: 5220173 (1993-06-01), Kanstad
patent: 5369277 (1994-11-01), Knodle
patent: 5939726 (1999-08-01), Wood
patent: 6297511 (2001-10-01), Syllaios et al.
patent: 0 692 702 (1996-01-01), None
patent: 0 729 016 (1996-08-01), None
patent: 2 117 957 (1983-10-01), None
patent: WO 97/09593 (1997-03-01), None
Hashmi Zia R.
Lee John R.
Rothwell Figg Ernst & Manbeck
Simrad Optronics ASA
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