Radiant energy – Radiant energy generation and sources – Plural radiation sources
Reexamination Certificate
1999-04-01
2001-10-02
Anderson, Bruce (Department: 2881)
Radiant energy
Radiant energy generation and sources
Plural radiation sources
C250S494100, C250S493100, C250S50400H
Reexamination Certificate
active
06297511
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to infrared emitters and infrared imaging systems, and more particularly to a high frequency infrared emitter.
BACKGROUND OF THE INVENTION
Infrared (IR) imaging systems are often employed to detect objects such as fires, planes, vehicles and people, and to control temperature sensitive industrial processes. A specific type of IR imaging systems, thermal imaging systems, generally operate by detecting the differences in thermal radiance of various objects in a scene and by displaying the differences as a visual image of the scene.
The basic components of a thermal imaging system generally include optics for collecting and focusing IR radiation from a scene, a thermal detector having a plurality of thermal sensors for converting IR radiation to an electrical signal, and electronics for amplifying and processing the electrical signal into a visual display or for storage in an appropriate medium. A chopper may be included in the thermal imaging system to provide a reference signal indicating the amount of background radiation being received by the detector. Choppers may periodically interrupt the transmission of IR radiation to the detector in order to provide this reference signal. For example, the chopper may be a rotating disk with openings that intermittently block incoming IR radiation.
In order to detect and create an image of an object, thermal imaging systems generally rely on infrared radiation that is either emitted by that object or that is reflected off the object. Thermal imaging systems may include a infrared source that emits IR radiation. Such an IR emitter can be used to actively create an image of an object by reflecting IR radiation off of the object and to the thermal detector(s) of the imaging system.
SUMMARY OF THE INVENTION
In many applications, an IR emitter is required that can produce intermittent pulses of IR radiation. Such an IR emitter might be used to replace a mechanical chopper in a thermal imaging system. In order for such an imaging system to have good detectivity, the pulses of IR radiation are preferably produced at a high frequency. Accordingly, a need has arisen for an IR emitter that is capable of producing IR radiation modulating at high frequencies. The present invention provides a high frequency infrared emitter that meets this need.
According to one aspect of the present invention, an IR emitter is provided that is capable of producing infrared radiation modulating at high frequency. This modulating frequency may be selected by the operator. The IR emitter includes a resistive membrane having a low thermal mass. The membrane is suspended by thermal isolation arms over a substrate such that a resonant emitting cavity is formed between the membrane and the substrate. The low thermal mass, thermally isolated membrane design maximizes the temperature change induced by Joule heating of the resistive membrane and allows the emitted IR radiation to be modulated at selected high frequencies.
IR emitters incorporating the present invention may function as broadband near-IR and mid-IR sources that can be electrically modulated at frequencies on the order of one hundred to one thousand hertz, both in emission intensity and spatially. IR emitters incorporating the teachings of the present invention can be used in gas or liquid sensors and various other spectroscopic applications, IR signal or pattern generation, and IR displays.
Embodiments of the present invention provide numerous technical advantages. IR emitters incorporating teachings of the present invention are capable of providing electronic chopping of emitted IR radiation at frequencies greater than one hundred Hertz. Furthermore, in one embodiment of the present invention, the use of a resonant emitting cavity provides the IR emitter with an emissivity of greater than eighty percent. Another advantage of IR emitters incorporating teachings of the present invention is the ability to emit IR radiation over a broad spectral band. For example, one embodiment of the present invention is operable to emit IR radiation with a wavelength of three to fourteen micrometers (&mgr;m).
Yet another technical advantage of IR emitters incorporating the teachings of the present invention is their high efficiency due to the efficient thermal isolation of the emitter. In addition, embodiments of the present invention can be surface micromachined using a micro-electromechanical systems (MEMS) process.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
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Carlos H. Mastrangelo, James Hsi-Jen Yeh, and Richard S. Muller, “Electrical and Optical Characteristics of Vacuum-Sealed Polysilicon Microlamps,”IEEE Transactions on Electron Devices, vol. 39, No. 6, pp. 1363-1375, Jun. 1992.
Gooch Roland W.
McCardel William L.
Schimert Thomas R.
Syllaios Athanasios J.
Anderson Bruce
Baker & Botts L.L.P.
Raytheon Company
Wells Nikita
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