We’ve covered why standard glass blocks PIR detection. But what if you absolutely must detect through a window? This article covers advanced, sometimes experimental, solutions.<\/p>\n
Ordinary soda-lime glass is opaque to 8-14\u00b5m infrared due to molecular absorption. It may transmit visible light but blocks thermal IR completely.<\/p>\n
If you can replace a small pane of glass with an IR-transparent material, detection becomes possible. Options include:<\/p>\n
Thin (0.1-0.5mm) high-density polyethylene (HDPE) film transmits IR well. It’s flexible, cheap, but not durable for long-term outdoor use. Can be stretched over a frame.<\/p>\n
Excellent IR transmission from visible to beyond 14\u00b5m. Used in laser optics. Extremely expensive and fragile. Not practical for most applications.<\/p>\n
Good IR transmission, but expensive and brittle. Requires anti-reflection coating.<\/p>\n
Transmits from UV to mid-IR, but hygroscopic (absorbs moisture).<\/p>\n
Some manufacturers produce IR-transparent plastics for sensor windows. These are proprietary and may be available as custom components.<\/p>\n
Instead of relying on passive body heat, use an active IR source and look for reflections. This is essentially an active IR sensor, not PIR.<\/p>\n
A pulsed IR LED (850-940nm) and a photodiode can detect reflections from people, even through glass. The LED must be bright enough to penetrate the glass and return a signal. This is how many automatic door sensors work.<\/p>\n
mmWave radar (24GHz, 60GHz, 77GHz) penetrates glass easily and detects motion and presence. It’s a completely different technology but solves the through-glass problem elegantly. Modules like the HLK-LD2410 are now under $10.<\/p>\n
This experimental technique uses two sensors: one with a view through the glass, one with a view of the glass itself. By subtracting the signals, you might cancel out the glass’s thermal signature. This is complex and not commercially common.<\/p>\n
For most users, the best solution is to avoid putting the sensor behind glass. Mount it outside in a weatherproof enclosure. If that’s impossible, consider switching to mmWave radar.<\/p>\n
While standard glass remains a barrier, advanced materials and alternative technologies offer solutions for through-window detection.<\/p>\n","protected":false},"excerpt":{"rendered":"
Introduction We’ve covered why standard glass blocks PIR detection. But what if you absolutely must detect through a window? This article covers advanced, sometimes experimental, solutions. Why Standard Glass Blocks IR (Recap) Ordinary soda-lime glass is opaque to 8-14\u00b5m infrared due to molecular absorption. It may transmit visible light but blocks thermal IR completely. Advanced […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-3426","post","type-post","status-publish","format-standard","hentry","category-troubleshooting"],"blocksy_meta":[],"yoast_head":"\r\n