Infrared
Infrared Sensor The
Infrared spectrum includes light waves that are too low in frequency for our eyes to detect. The category of infrared light is most popularly associated with thermal and heat signatures, however most of the everyday infrared spectrum devices we commonly use operate in the near Infrared spectrum (NIR).
Infrared sensors that detect thermal emissions are based around the mid and far infrared spectrum and are what we see in the thermal imaging and FLIR (forward looking Infrared) systems on TV. Those “thermal” types of sensors use specific materials that when exposed to heat, change voltage. These types of sensors are used most popularly in motion detection systems, however they are also used in heat-seeking devices and remote temperature monitoring systems. Infrared detection can be used on a robot to detect the presence of a human.
Near Infrared sensors are present in a lot of devices ranging from our TV remotes to our digital cameras, and do not detect thermal emissions. They can be used to send information wirelessly, or use the reflected light for edge detection as such in a roomba's cliff sensor. The light from these emitters can be directed and focused and commonly come in the form of LED’s (Light emitting diodes). Their use is very similar to a normal colored LED, except that when powered, the light is not visible to the human eye (sometimes you can see a small faint red color emanating from the LED).
The LEDs can be used for active “night vision”, where they are used to light up the surrounding area to be recorded on a digital camera. As it turns out, digital cameras will pick up light in the NIR spectrum. Many digital cameras have filters that will filter the NIR out, however without this filter, the cameras can pick up light outside the visible spectrum - and are used a lot on security monitoring systems in conjunction with these NIR light emitting diodes. Robots can use this active “night vision” to navigate in the darkness.
Single point detectors that are used to detect light are called photo-diodes. They can be made to respond to all sorts of light, however typically it is best to pick ones designed for the particular wavelength of light your emitter is transmitting on. A photo-diode will output a voltage that is proportional to the intensity of light received.
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