Range insensitive infrared intrusion detector

Abstract From the Canadian patent

An infrared detector is described for monitoring a corridor like room having a plurality of focusing means for the collection of infrared radiation emitted by an intruder. The field of view of each focusing means is oriented so as to form a continuous field of coverage in the space to be monitored, without gaps or areas of limited sensitivity. furthermore the solid angle subtended by each focusing means is chosen so that the sum of the energy received from the intruder in the monitored area and focused onto the infrared sensor by the multiple focusing means is insensitive to and independent of the range of the intruder from the monitoring device.