IR intrusion detector using scattering to prevent false alarms
First Claim
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1. An infrared intrusion detector comprising:
- a radiation-impermeable housing with an infrared-radiation permeable window;
at least one infrared sensor disposed in the housing, comprising a plurality of pyroelectric sensor elements;
reflector means having a plurality of mirror surfaces for reflecting and focusing infrared radiation entering the housing through the window onto the pyroelectric sensor elements;
filter means for filtering radiation reflected by the reflector means;
whereinthe mirror surfaces have a surface roughness such that radiation having a wavelength in an approximate range from 6 to 15 micrometers is focused onto the infrared sensor elements, and such that radiation of wavelengths below approximately 3 micrometers is scattered by the mirror surfaces.
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Abstract
An infrared intrusion detector uses infrared-sensitive sensors with pyroelectric sensor elements for detecting infrared radiation from a spatial region to be monitored. Infrared radiation passes through an entrance window and reaches the sensor elements via focusing mirrors. Extraneous radiation, outside the useful radiation band, is eliminated by filtering at the entrance window and by an optical transmission filter, and by scattering at suitable rough surfaces of the focusing mirrors. As a result, the infrared intrusion detector is less sensitive to extraneous radiation and less likely to produce false alarms.
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Citations
7 Claims
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1. An infrared intrusion detector comprising:
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a radiation-impermeable housing with an infrared-radiation permeable window; at least one infrared sensor disposed in the housing, comprising a plurality of pyroelectric sensor elements; reflector means having a plurality of mirror surfaces for reflecting and focusing infrared radiation entering the housing through the window onto the pyroelectric sensor elements; filter means for filtering radiation reflected by the reflector means;
whereinthe mirror surfaces have a surface roughness such that radiation having a wavelength in an approximate range from 6 to 15 micrometers is focused onto the infrared sensor elements, and such that radiation of wavelengths below approximately 3 micrometers is scattered by the mirror surfaces. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification