[航空航天]红外技术英文资料.doc
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1、6 Infrared Detection TechnologyInfrared is an electromagnetic spectrum at a wavelength that is longer than visible light. It can not be seen but it can be detected. Objects that generate heat also generate infrared radiation and those objects include animals and the human body whose radiation is str
2、ongest at a wavelength of 9.4 m. Infrared in this range will not pass through many types of material that pass visible light such as ordinary window glass and plastic. However, it can pass through, with some attenuation, material that is opaque to visible light such as germanium and silicon. The inf
3、rared (IR) detection region of the electromagnetic spectrum ranges from 0.78 to 1000 microns(m) and can be further subdivided into the near, mid and far IR regions which range from 0.78 m to 2.5m, 2.5m to 50 m and 50 m to 1000 m respectively. The most common wavelengths for detection applications oc
4、cur in the mid IR region and range between 2.5m and 15m.A blackbody is a theoretical construct that absorbs all the radiant energy striking it and radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature.In quantum mechanics, the dependence of the radia
5、tion density on its frequency and temperature is given by Planck radiation formula: (1)Where h=6.6210-34Js is Planck constant; c=3105km/s is the velocity of electromagnetic waves in vacuum; k=1.3810-23J/K is the Boltzmann constant; T K is the absolute temperature of the radiating body; f Hz is frequ
6、ency; RO is the spectral density of radiation equal to power radiation on frequency f in the band of 1.0 Hz by 1.0 m2 of the radiator.The frequency fm on which the spectral density of radiation has the maximum is determined by Wien formula: (2)At present, there are several different detection techni
7、ques that utilize IR spectroscopy. They include passive IR detection technology, active infrared detection technology and thermal infrared remote sensing technology etc.6.6.1 Active infrared detection technology for house security systemAn active infrared detector includes a radiation source and an
8、infrared sensor which is sensitive to interruptions in the radiation sensed from the source. These detectors are used as intrusion detectors by providing a path of radiation from the source to the sensor in a place where the path is likely to be interrupted by an intruder. The proposed active infrar
9、ed method of motion detection has the advantage of fast response speed of a relatively large sensor. This advantage permits simpler optical system design, especially for wide fields of view. Besides, it is insensitivity to mechanical and acoustic noise, which presents substantial problems in the pas
10、sive infrared (PIR) sensors. Low production cost is another advantage of these active infrared detectors. In active infrared systems, there are two-piece elements which are consisting of an infrared transmitter and an infrared receiver. And there is a 3/8 inch infrared beam between the transmitter w
11、hich is placed on one side of the trail and the receiver which is placed on the other side of the trail. The transmitter and the receiver can be separated whose distance is as much as 150 feet. The transmitter emits a beam of light into the scan zone. The light, which is reflected by the background
12、returns to the receiver, which constantly monitors the scan zone. The infrared light is interrupted when a person or object enters the zone. It then sends a signal to the controller system, which is wired into the door controls. One variation of this operating mode is called fibakground suppression.
13、 The receiver only detects a change in the reflected light when a person or object enters the scan zone thus causing a reflectance variation of the light, sending a signal to the microcontroller in oder to trigger the alarm of the security system.House security system is one of security that truly r
14、elated to burglar or safety alarm system. Burglar and safety alarms are found in electronic form nowadays. Sensors connected to a control unit via either a low-voltage hardwire which in turn connects to a means for announcing the alarm to elicit response. In a new construction systems, wireless syst
15、ems may be more economical and certainly quicker to install. Some systems are dedicated to one mission: handle fire, intrusion, and safety alarms simultaneously. In common security system, the lights are triggered by motion and give the impression to user that someone is at home and able to see the
16、burglar. Infrared motion detectors placed in house security system in crucial areas of the house can detect any burglars and alert the home owner or police. The first security system invented, house alarms are triggered by the release of a pressure button fitted into a door or window frame. This bas
17、ic alarm is fundamentally flawed as the entire intruder need to silence the alarm to close the door or window. The various systems on the market ranging from inexpensive house security alarms to highly sophisticated systems require the professional installation. All modern alarms are based on the sa
18、me foundation, the electric circuit which is completed either when the door is opened or closed depending on the security system designed. The alarm is triggered when the circuit is altered and will not be silenced until a code is punched into the control panel. The most expensive and complicated al
19、arm systems might also involve a combination of motion sensors and pressure pads to ensure even the most cunning intruder cant get his hands on treasures.For the infrared transmitter which is also known as emitter circuit, it is on a basic design of timer 555 astable operation. The output of timer i
20、s connected to the infrared transmitter which is used to produce pulse using an astable timer circuit. In astable circuit operation, pulse will continually generated until the power supplied through the circuit is removed. The astable circuit produces a continuous train of pulses at any frequency re
21、quired. This means that the 555 timer can operate repeatedly, it will switch on and off continually to generate data for the infrared transmission.The infrared receiver which is also known as infrared detector receives the data transmitted by the infrared transmitter circuit. It is a simple electron
22、ics device on detecting infrared signal. This infrared detector can be directly connected into the controller circuit to produce logic high 1 or low 0 from the output terminal thus activate or deactivate the controller system operation. The range of infrared detector components according to datashee
23、t states that the infrared detector can fully operate on detecting the infrared signal of 38 to 45 kHz. 6.6.2 Theory and application of the passive infrared (PIR) detection technologyPIR motion detectors always use thermal sensors, detecting the small temperature increase when the sensor element is
24、exposed to radiation and absorbs it. Quantum detectors are not practical for PIR due to their need for cooling.We will see that thermal radiation is represented by Planks law. The corresponding theory was developed from a theoretical physical model of a radiator: the blackbody, while the radiation f
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