Infrared Sensors

There are all sorts of sensors all over the world, each with their own respective functions. Biological, Vibrational, Auditory, Radiation, Optical, Mechanical, Chemical, Electromagnetic, Thermal and more, they are basically used to monitor various properties or characteristics of various physical systems.

Included in this roster is the infrared sensor.

As infrared (Infrared radiation is part of the electromagnetic spectrum, which includes radio waves, microwaves, visible light, ultraviolet light and gamma rays and x rays) is part of the electromagnetic spectrum, it exists at a wavelength farther than visible light. It cannot be seen, but can be detected. Objects which are capable of generating heat also generate infrared radiation. This includes animals and human beings, whose radiation is the strongest (at a wavelength of 9.4u) of all. This generated heat is what infrared motion sensors utilize for its successful operation.

An infrared sensor (or the passive infrared sensor often called PIR) can be found in most homes as part of home security systems, as motion detectors. In an infrared motion detector, the PIR sensor is typically mounted on a printed circuit board which contains all electronics needed to interpret sent and/or received signals. The entire circuit package is contained in a housing case which is then mounted in a location where the sensor can “view” the area to be monitored.

Let’s utilize the trip wire setup to illustrate how motion is detected by infrared motion sensors. An infrared signal (or stream) is established within the effective range of the motion detector. Once something “trips” this already established signal, motion is detected and the system’s alert functions are put into play.

Hardware wise, an infrared signal will not pass through types of material that visible light is capable of (like a window glass or plastic). However, with some attenuation, material that is opaque to visible light like germanium and silicon have no problems dealing with infrared radiation. An unprocessed silicon wafer makes a good IR window. It also provides additional filtering for light in the visible range.

The prime source of an infrared sensor’s successful operation relies on pyroelectric sensors. Pyroelectric sensors are made of a crystalline material that generates a surface electric charge when exposed to heat in the form of infrared radiation. The sensor’s elements are sensitive to radiation over a wide range, thus its functional capabilities.

For optimum optical performance (in terms of distributing the infrared signal) a Fresnel (pronounced Frennel) lens is utilized. It’s a Plano convex lens that has been collapsed on itself to form a flat lens that retains its optical characteristics, but is much smaller in thickness and therefore has less absorption losses.

Certain brands and models boast “customization” features that somewhat come as entertaining. For example, certain body signature data could be stored in memory, and the detection of such could call in certain activity.

Imagine going home to a dark empty house. One could utilize motion sensors as light switches, making that dangerous climb up the stairs a breeze. Also, one could utilize motion sensors as deterrents against potential intruders. Picture the same scene, only this time it’s a burglar en route to your dark home. Once his presence is detected, lights inside the house could automatically turn on. This activity could appear to the intruder as his presence is now compromised and would have to rethink his intentions of breaking in.

Infrared motion detectors are good investments as home security devices. Wireless models are now out in the market, making the installation of these devices simple. One wouldn’t need to employ the services of a hardware installation specialist, to successfully install them.

A real plus for home security systems.