What type of lens focuses infrared radiation onto the sensor in a PIR?

In passive infrared (PIR) sensors, a Fresnel lens is utilized to focus infrared radiation onto the sensor. This type of lens is specifically designed to capture and direct the subtle changes in infrared radiation that are emitted by objects, such as humans and animals, moving within its field of view.

The unique structure of a Fresnel lens, which consists of many small prisms arranged in a flat sheet, allows it to effectively concentrate these infrared emissions onto the sensor. This design not only reduces the bulkiness and weight of traditional convex lenses, but it also enables a broader detection area, enhancing the sensor's sensitivity and accuracy.

The efficient focusing of infrared radiation by the Fresnel lens plays a crucial role in the functioning of PIR sensors, allowing them to detect motion based on temperature variations in the environment. This capability is fundamental for applications like security systems, automated lighting, and occupancy sensing, ensuring that the sensor can reliably respond to any activity detected within its range.