Pyroelectric detectors
AssigneePlessey Handel und Investments AG
InventorDavid Appleby
Life of this patent
Estimating the term…
Abstract
An intruder detector consists of an element of pyroelectric material having three defined regions; two being active to infra-red radiation and one being relatively inactive to infra-red radiation. The inactive region and one of the active regions are connected together in parallel and the other active region is connected in series with these two. The arrangement has full cancellation of environment effects while being partially unbalanced for infra-red detection so that isolated areas of infra-red radiation (such as an intruder) can be detected at long and short ranges. The element is used with a concave mirror for increased zonal coverage. Each of the regions of pyroelectric material has a substantially constant thickness and all of the three regions have the same thickness.
Claims34
A pyroelectric detector comprising an element of pyroelectric material, said element having first and second regions, said first and second regions being connected in parallel with each other, said first region being active to infra-red radiation to produce a first output, said second region being relatively inactive to infra-red radiation so as to produce a null output, said element having a third region, said third region being connected in series with said first and second regions, said third region being oppositely polarized and active to infra-red radiation to produce a further output, wherein said first and further outputs are compared to each other, and are each compared to said null output, whereby to detect intrusion at both near and far ranges.
A pyroelectric detector as claimed in any one of claims, 1, 2, 3 or 4 wherein said first and third regions of said element which are active to infra-red radiation have a ratio of areas of approximately 3:2.
A pyroelectric detector as claimed in 5 wherein said first and third regions of said element which are active to infra-red radiation have a ratio of areas of approximately 3:2.
A pyroelectric detector as claimed in 6 wherein said first and third regions of said element which are active to infra-red radiation have a ratio of areas of approximately 3:2.
A pyroelectric detector as claimed in 7 wherein said first and third regions of said element which are active to infra-red radiation have a ratio of areas of approximately 3:2.
Dependencies are inferred from the claim text.