Infrared radiation detector with integral fresnel lens window

摘要

An infrared radiation detector comprises a pyroelectric detector element in a hermetically sealed housing. The housing comprises a base and cover with an aperture. A Fresnel lens, for example made of polyethylene transmissive in the 8-14 mu m wavelength range, is fastened over the aperture on the inside of the cover for condensing the radiation to be detected onto the detector element. In one example the Fresnel lens is held against a flange surrounding the aperture by a press-fit ring. Alternatively, the Fresnel lens is glued to a silicon window which in turn is fastened to the flange surrounding the aperture. The Fresnel lens thus forms an integral part of the detector housing avoiding the need for external mirrors or lenses.