Guide for material selection
- Choosing a high transmittance material for 8-14um wavelength
PIR motion detectors operate in the 7 to 14 μm infrared band and cannot detect motion through standard glass or most plastic materials (except polyethylene, PE).
To achieve proper functionality, special PIR-transmissive materials are required for manufacturing Fresnel lenses, optical elements, and PIR windows.
System performance is a function of both sensor capabilities and optical stack design. Optimal lens transmittance in the far-infrared (FIR) spectrum is critical.
For example, the Far Infrared transmittance of Poly FIR200 is 67.5% (at 0.2mm thickness)
This transmittance is attenuated per thickness. With 0.6mm thickness, which is typical for PIR lens, Poly FIR200 has around 40% of transmittance.
(그래프) Transmittance of Poly FIR200, 0.2mm thick
TMOS00-05 FT-IR
Thickness of the material and transmittance has a strong correlation, as the lens material typically has higher transmissivity the thinner the material. You want to properly size the thickness in a way that ensures mechanical structure integrity while maintaining high transmissivity in FIR wavelengths.
- Choosing a stable and UV-resistant material
When integrating a PIR sensor, selecting the right material for optical components is crucial not only for maximizing transmittance in the 8–14 μm FIR range but also for ensuring long-term UV resistance and maintaining aesthetic quality over time.
To achieve both high optical performance and durability, we strongly recommend using pre-compounded materials such as SBK150 or HGW335, which are based on Poly FIR200 combined with carefully selected additives (e.g., UV stabilizers, antioxidants, pigments). These materials are specifically engineered to minimize UV-induced degradation, maintain lens appearance, and prevent surface brittleness or discoloration even after prolonged exposure.
This approach ensures stable transmittance, reliable sensor performance, and consistent aesthetic quality throughout the product's lifetime, making SBK150 and HGW335 the preferred choices for PIR sensor lens or cover applications.
- Explanation of above UV resist test result
SBK150 is a black compounded material supplied by Fresnel Factory to multiple customers. It is produced by combining Poly FIR200 with various additives in carefully optimized proportions.
Even after receipt of UV radiation equivalent to five years of exposure, SBK150 retains over 92.5% of its initial performance, whereas a competing product retains only 46.6%. This significant difference in lens transmittance attenuation is a major factor in degrading the overall performance of devices that use PIR sensors.
Furthermore, attenuation differences affect not only transmittance (or lens performance) but also the appearance and aesthetic quality of the lens. Changes in surface color and increased brittleness are typical examples of these issues.
- How to test accelerated UV test
This UV resist test is conducted by Korea Research Institute of Chemical Technology according to request of Fresnel Factory Inc.
KRICT has conducted this acerated test as possible as to meet the ISO 4892 : Plastics — Methods of exposure to laboratory light sources.
300MJ is equivalent amount of UV energy of a year in Korea.
1500MJ is equivalent amount as 5 years.
- Material Selection for Both Product Performance and Design
Since Far Infrared (FIR) used by PIR sensors cannot pass through materials other than polyethylene (PE), commonly used finishing materials for other sensors—such as polycarbonate or glass—cannot be applied. That's why, PIR sensors require a PE-based cover or lens that is directly exposed on the product surface.
Therefore, it is essential to select a material that not only offers high FIR transmittance and strong UV resistance but also suitable colors and shapes that align with the product identity.
Compounded materials such as SBK150 and HGW335, based on Fresnel Factory’s Poly FIR, provide a wide range of color options, high transmittance, and a high Melt Flow Index (MFI). These properties make it possible to maintain the product’s design identity while ensuring high sensor performance.
