Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-10-26
2001-03-20
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S349000, C250SDIG001
Reexamination Certificate
active
06204502
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for detecting thermal radiation, and to presence detection apparatus based on such a device. The invention can be used particularly, but not exclusively, for detecting intrusion into a security zone under surveillance.
2. Related Art
In the field of high-security surveillance, e.g. monitoring premises for storing nuclear material, it is essential for monitoring objects that are in the zone under surveillance failure and without interruption.
At present, in order to ensure continuity of knowledge concerning a situation that is under surveillance, e.g. a quantity of fissile material, and in order to keep a zone of finite dimensions under surveillance, use is made of systems based on seals, whether electronic or otherwise (with identity and/or integrity), of optical surveillance systems (using cameras), and of a range of conventional detectors.
Systems based on seals are generally insufficient because most of them can be used only once, and they are incapable of providing remote surveillance.
With video surveillance systems, the large amount of investment that is required, the image and signal processing that is necessary for detecting an intrusion, and the possibility of error by a spurious image, lead to enormous drawbacks when used in high security surveillance setups.
In most detection applications, traditional surveillance systems based on ultrasound are used for measuring radiation from moving sources. The principle on which they are based is difficult to use for remote surveillance while still allowing movement to take place in a portion of the same premises that is not under surveillance.
Surveillance by means of ultrasound detectors becomes impossible whenever some movement is to be expected around the boundaries of the zone under surveillance since such detectors respond specifically to movement and molecular vibration.
Numerous pyroelectrical and semiconductor devices are commonly used for detecting thermal radiation emitted by a moving source. Since thermal radiation varies with the emissivity of a surface, such detectors suffer from the major drawback of having their responsiveness dependant on wavelength. It is therefore necessary to select a detector as a function of the source to be detected since the detector operates in a narrow frequency band. In addition, detectors of those types are themselves heated by the radiation they receive, and they always require a cooling system.
It can thus be deduced that for an application seeking to provide high security surveillance of a specified zone, the systems mentioned above present at least one of the following drawbacks:
responsiveness is nearly always dependent on wavelength, thereby making it necessary to select a specific detector as a function of the source to be detected;
with infrared or ultrasound systems, only movement is detected in the detection area. Such systems provide detection information due only to the movement of a source of thermal radiation in the zone under surveillance, but no information concerning presence;
an optical lens is generally used for focusing incident rays, thereby giving rise to an undesirable filter effect;
encapsulation is normally necessary in order to eliminate external noise resulting from convection currents;
a cooling device needs to be provided in many cases; and
with ultrasound systems, it is not possible to focus surveillance on a particular zone of finite dimensions without suffering disturbances from people or objects moving around the boundaries of said zone.
Thus, an object of the present invention is to provide a device for detecting thermal radiation that does not suffer from the above-mentioned drawbacks.
SUMMARY OF THE INVENTION
The device of the invention is characterized in that it comprises:
a detector having one or more portions designed to be exposed to the thermal radiation, and one or more portions designed to be protected from the thermal radiation, the detector delivering a detection signal on the basis of a temperature difference between the exposed portions and the protected portions; and
a reflector type concentrator associated with said detector to concentrate thereon the thermal radiation coming from a predetermined three-dimensional zone.
Combining a reflector type of concentrator with a detector of the above-specified type makes it possible to define a zone under surveillance accurately and to detect any change in the state of thermal unbalance in the zone under surveillance. It will be observed that the detector responds to a small temperature difference representative of the difference between the amount of energy absorbed and transformed into heat flux in exposed regions and in non-exposed regions.
Advantageously, the concentrator is a parabolic reflector.
In a preferred embodiment, the detector is mounted to move relative to an axis of the concentrator in order to make it easy to adapt the detection field merely by adjusting position.
Also, the use of a concentrator advantageously replaces the use of an optical lens for focusing the incident thermal radiation, thereby avoiding transmission losses or losses due to the capacitive effect of the lens material.
The operating principle and the manufacturing technology used for the detector make it possible to avoid conventional cooling problems which require cryostats or Peltier effect devices which are expensive and consume power.
Even at very low temperature, the detector is sensitive to any object that emits thermal radiation in a very broad band extending from 0.75 micrometers (&mgr;m) to 1,000 &mgr;m, i.e. covering the range from the visible to microwaves. It makes it possible to provide information representative of instantaneous variations in energy unbalance between a system and its environment, and can thus operate as a heat flux meter under varying conditions.
In a preferred embodiment, the detector is made up of at least one pair of planar thermocouple elements having a cold junction in thermal contact with a protected portion of the detector, and at least one hot junction in thermal contact with an exposed portion of the detector.
The exposed portion(s) and the protected portion(s) of the detector may constitute a common active surface of the detector, being respectively constituted by surface elements that are substantially absorbent and by surface elements that are substantially reflective relative to thermal radiation.
In an embodiment having a shape that is particularly advantageous, the detector comprises a plurality of pairs of thermocouple elements mounted in series and disposed in a plurality of lines interconnected at their ends so as to form a meandering path, the cold and hot junctions being disposed in respective alternate rows extending across the lines and being in thermal contact with a material which presents the sensitive surface in the form of reflective strips and absorbent strips arranged in rows of alternating phase in alignment respectively with the cold junctions and with the hot junctions.
By way of example, the thermocouple elements are made up of alternating elements of copper and of constantan deposited on a substrate of electrically insulating material such as the material known under the name “KAPTON” which is a trademark registered by Dupont de Nemours, and the thermocouple elements are covered in a material that is substantially transparent to thermal radiation, which may also be KAPTON, the portions of the material covering the cold junction being coated in a layer of reflecting material. The reflective portions may be obtained by depositing gold on the surface of the material covering the thermocouples.
Advantageously, the surface of the substrate opposite from its surface supporting the thermocouple elements is coated in a layer of metal for being put into contact with a mechanical support surface.
The invention also provides presence detection apparatus comprising at least one thermal radiation detector device of the above-specified type, and control means receiv
Guilmain Pierre
Korn Christophe
Thery Pierre
Bacon & Thomas PLLC
Communaute Europeene de l'Energie Atomique (Euratom)
Hannaher Constantine
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