Infrared Detectors & Systems
Infrared detectors and systems operate using two infrared light-emitting diodes (LEDs). One diode is wired to send out an infrared light signal. A second infrared LED is wired to produce a small electric signal when it receives an infrared light signal. Objects passing close enough to the LED emitting the infrared signal will reflect light back to the detector LED and trigger the system.
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LEDs
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IR LEDs emit light beyond the visible spectrum. LEDs are designed to produce light energy directly from an input electric current. They are designed to emit light of a certain wavelength, and infrared (IR) LEDs emit light in the infrared spectrum. IR light has a longer wavelength than visible light, and is invisible to the naked eye. Typical IR LEDs emit light in the near-infrared region of about 720 to 1500 nanometers in wavelength.
Detectors
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Remote controls use near-IR signals. An IR LED identical to the LED used to emit the light is used as a detector. The detector LED is wired so that the LED will produce a small electric signal when it is exposed to the same wavelength of IR that is emitted by the first LED. The detector LED is shielded from direct exposure to the emitting LED. When an object comes within range of the emitted IR, it reflect the IR back onto the detector LED. This causes the detector LED to produce an electric signal that is sent into the detection system.
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Detector System
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IR detectors operate automatic sliding doors. A detector system is able to amplify and analyze the signal from the detector LED. The system can be tuned for higher or lower sensitivity depending on the requirements needed. Making the system more sensitive allows objects to be detected from farther away. The system can also interpret the signal's strength to determine how far away an object is.
Applications
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Motion detectors can be used for security or warning purposes. IR detector systems are used for a variety of purposes. Contrary to popular belief, they work just as well in daylight as they do in darkness. IR systems are used to operate automatic doors on commercial establishments like grocery stores and shops. As you approach the door, an IR signal is reflected off you and your clothing. When the intensity of the reflected IR reaching the detector is sufficient (you are close enough to the door), the electronic signal from the detector LED will trigger the system to open the door.
Thermal Imaging
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Thermal imaging requires complex and expensive equipment. Thermal imaging uses special cameras that are sensitive to much longer wavelengths of IR light than is used in typical infrared detectors. Thermal imaging detects the radiant IR given off by objects as "black body radiation." The special cameras required for thermal imaging detect mid- and far-range infrared light, usually from about 4,000 to 15,000 nanometers in wavelength. The human body emits infrared light at about 9,400 nanometers in wavelength. Thermal imaging is used to detect flaws in electrical wiring, insulation of buildings, any many other industrial applications.
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References
- Photo Credit eye image by Pali A from Fotolia.com red led image by Kir from Fotolia.com remote control 3 image by Kelly Kane from Fotolia.com Row of glass doors image by Lucid_Exposure from Fotolia.com security camera image by Igor Zhorov from Fotolia.com thermal hand image by Adrian Hillman from Fotolia.com
