Finel lens effect has two: one is the focusing effect, the pyroelectric infrared signal refraction (reflection) in PIR, second is the detection region is divided into a number of area and a dark area, make into the detection region of the moving object to temperature changes in the form of PIR produce changes in pyroelectric infrared signal.

Finel lens main role is to detect spatial infrared effectively focus on sensor.Through the distribution in the lens of the concentric band (Windows) used to achieve infrared aggregation, equivalent to the function of convex lens.This part is mainly to see the band selection lens design and lens material.Consideration of lens parameters mainly include: the luminous flux, different lens concentricity, thickness uniformity, the optical axis of the lens and shape the concentricity, transmittance, focal length error.Finel lens narrowband (Windows) design is generally uneven, from top to bottom is divided into several rows above, below, are less dense, sparse, generally intermediate sides.Because the human face, knee, arm infrared radiation is stronger, just in front of the above lens; the less, because the lower body infrared radiation is weak, the two is to prevent small animal surface infrared radiation interference.Generally made of organic glass with.