| 摘要 |
<p>Arrays of Fresnel lenses moulded in a single sheet of plastics 29 are used in conjunction with a thermal radiation detector 1 to provide intruder alarm apparatus. Each lens defines one detection direction in a fan of such directions 26,27,28. Such arrays have been moulded as a curved surface 22 centered on the detector. To reduce moulding costs while maintaining the optical efficiencies of all lenses in the array, a flat array of lenses is provided in which each lens is moulded as an angled facet 30,31,32, the poles 36,37,38 of the lenses lying in a plane.</p> |
