Patent ID: 9711018
Date: 2017-07-18
CPC Classifications: G01J,G02B,G08B

Claim:
1. A passive infra red detector comprising a plurality of passive infra red sensors and a lens member arranged to direct radiation from a target area onto the sensors, wherein the lens member forms a substantially hemispherical dome about the infrared sensors, the dome having a central axis and comprising a plurality of contiguous facets distributed about the central axis, each facet having an outer surface and an inner surface that forms a lens to direct radiation onto the sensors, wherein the plurality of contiguous facets comprises a plurality of lenslets distributed about the central axis, wherein the detector comprises a first passive infra red sensor aligned with the central axis of the dome and having a sensitive surface substantially normal to the central axis, and a plurality of second passive infra red sensors distributed about the central axis of the dome, wherein the second passive infra red sensors are inclined such that the outward normal from the sensitive surface of each second passive infra red sensor makes an acute angle with the outward direction of the central axis, and wherein an optical centre of each lenslet is located closer, along the surface of the dome, to the central axis than a geometrical centre of the lenslet.