INTRODUCTION TO IR SENSOR
An IR LED, also known as IR transmitter, is a special purpose LED that transmits infrared rays in the range of 760 nm wavelength. Such LEDs are usually made of gallium arsenide or aluminum gallium arsenide. They, along with IR receivers, are commonly used as sensors.
The appearance is same as a common LED. Since the human eye cannot see the infrared radiations, it is not possible for a person to identify whether the IR LED is working or not, unlike a common LED. To overcome this problem, the camera on a cell phone can be used. The camera can show us the IR rays being emanated from the IR LED in a circuit.
PRINCIPLES OF OPERATION:
We have already discussed how a light sensor works. IR Sensors work by using a specific light sensor to detect a select light wavelength in the Infra-Red (IR) spectrum. By using an LED which produces light at the same wavelength as what the sensor is looking for, you can look at the intensity of the received light. When an object is close to the sensor, the light from the LED bounces off the object and into the light sensor. This results in a large jump in the intensity, which we already know can be detected using a threshold.
DETECTING BRIGHTNESS:
Since the sensor works by looking for reflected light, it is possible to have a sensor that can return the value of the reflected light. This type of sensor can then be used to measure how "bright" the object is. This is useful for tasks like line tracking.
EVOLUTION OF INFRARED COMMUNICATION SYSTEMS
Optical wireless communication systems have experienced a huge development since the late1970s when IR was first proposed as an alternative way (to radio) to connect computer networks without cables. IBM was one of the first organizations to work on wireless IR networks. The first reports on IBM’s experimental work were published between 1978 and 1981. They have described a duplex IR link that achieved a bit rate of 64 kbps using PSK and a carrier frequency of 256 kHz.
In 1983, Minami et al. from Fujitsu described a full-duplex LOS system that operated under the same principles as the network described by Gfeller. That system consisted of an optical satellite attached to the ceiling and connected to a network node via a cable, and of a number of computer terminals that communicated to the server via the optical satellite. It operated at 19.2 kbps (over 10 m) with an error rate of 10−6 when working under fluorescent illumination. By 1985, the Fujitsu team had managed to improve the data rate of its system to 48 kbps, as reported by Takahashi and Touge.
In the same year (1985), researchers from two other companies (Hitachi and HP Labs) presented their own work in the area of wireless IR communications. In the case of Hitachi,Nakata et al. reported a directed-LOS network system that replaced the optical satellite on the ceiling with an optical reflector. This system achieved a data rate of up to 1 Mbps of less than 10−7 for a distance of 5 m.[ 4] In 1987, AT&T Bell presented their work on optical wireless communications. They reported a directed-LOS system that operated at 45 Mbps over a wavelength of 800 nm.
More recently, Showa Electric reported a 100-Mbps short-range IR wireless transceiver that operated over a maximum range of 20 m and used LEDs for the transmitter and avalanche photo detector (APDs) for the receiver. Another system, proposed by Singh et al. in 2004 , was based on the idea of a base station attached to the ceiling and connected to the network k via a backbone. The proposed network operated at 100 Mbps and was based on DPPM with carrier sense multiple access with collision detection (CSMA/CD) for the Media Access Control (MAC) protocol.
In the same year (1985), researchers from two other companies (Hitachi and HP Labs) presented their own work in the area of wireless IR communications. In the case of Hitachi,Nakata et al. reported a directed-LOS network system that replaced the optical satellite on the ceiling with an optical reflector. This system achieved a data rate of up to 1 Mbps of less than 10−7 for a distance of 5 m.[ 4] In 1987, AT&T Bell presented their work on optical wireless communications. They reported a directed-LOS system that operated at 45 Mbps over a wavelength of 800 nm.
Chronology Of Indoor Optical Wireless Communication Research
PROPERTIES OF INFRARED SYSTEM
Infrared radiation (IR) is electromagnetic radiation with a wavelength between 0.7 and 300micrometres, which equates to a frequency range between approximately 1 and 430 THz. Its wavelength is longer (and the frequency lower) than that of visible light, but the
Infrared Spectrum
Infrared Radiation behaves similar to the visible light, so it exhibits all the properties that light does such as
a) Reflection
b) Refraction
c) Diffraction
d) Diffusion
ATTENUATION
Atmospheric attenuation is defined as the process whereby some or all of the energy of an
Electromagnetic wave is lost (absorbed and/or scattered) when traversing the atmosphere.
ABSORPTION
Absorption, in the context of electromagnetic waves and light, is defined as the process of conversion of the energy of a photon to internal energy, when electromagnetic radiation is captured by matter. When particles in the atmosphere absorb light, this absorption provokes a transition (or excitation) in the particle’s molecules from a lower energy level to a higher one
SCATTERING
Scattering is defined as the dispersal of a beam of particles or of radiation into a range of directions as a result of physical interactions. When a particle intercepts an electromagnetic wave, part of the wave’s energy is removed by the particle and re-radiated into a solid angle centered at it. The scattered light is polarized, and of the same wavelength as the incident wavelength, which means that there is no loss of energy to the particle
ORIGINS OF THE TERM
The name means below red, the Latin infra meaning "below". Red is the color of the longest wavelengths of visible light. Infrared light has a longer wavelength (and so a lower frequency) than that of red light visible to humans, hence the literal meaning of below red.
DIE DIVISION SCHEME
The International Commission on Illumination (CIE) recommended the division of infrared radiation into the following three bands:
§ IR-A: 700 nm–1400 nm (0.7 µm – 1.4 µm)
§ IR-B: 1400 nm–3000 nm (1.4 µm – 3 µm)
§ IR-C: 3000 nm–1 mm (3 µm – 1000 µm)
A commonly used sub-division scheme is:
§ Near-infrared (NIR, IR-A DIN): 0.75-1.4 µm in wavelength, defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles.
§ Short-wavelength infrared (SWIR, IR-B DIN): 1.4-3 µm, water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the dominant spectral region for long-distance telecommunications.
§ Mid-wavelength infrared (MWIR, IR-C DIN) also called intermediate infrared (IIR): 3-8 µm. In guided missile technology the 3-5 µm portion of this band is the atmospheric window in which the homing heads of passive IR 'heat seeking' missiles are designed to work, homing on to the IR signature of the target aircraft, typically the jet engine exhaust plume.
ADVANTAGES OVER RF
WIDER AND UNREGULATED SPECTRUM
From a spectrum management point of view, for example, IR offers potentially huge bandwidths that are currently unregulated worldwide. The radio part of the spectrum, on the other hand, gets more congested every year, and the allocation of radio frequencies is increasingly difficult and expensive. Moreover, due the fact that the authorities that regulate the allocation of radio frequencies vary from one country to another. Device needs to remodeled accordingly for different country so as to avoid a potential risk of system or product incompatibility in different geographical locations.
HIGH NOISE IMMUNITY
Another advantage of IR over radio is its immunity to electromagnetic interference (EMI).This makes IR the preferred option in environments where interference must be minimized or eliminated. In addition, IR does not interfere with and is not affected by radio frequencies, which is particularly relevant in hospitals, as explained in a number of published articles in the area.
HIGHER SECURITY
IR also presents advantages over radio in terms of security. Because IR radiation behaves like visible light, it does not penetrate walls, which means that the room where the energy is generated encloses the emitted signal completely (assuming there are no windows or transparent barriers between rooms). This prevents the transmitted information from being detected outside and implies intrinsic security against eavesdropping. In addition, IR offers the possibility of rapid wireless deployment and the flexibility of establishing temporary communication links.
Further advantages of IR over radio include the
D) low cost,
E) The small size (Portable) and
F) The limited power consumption.
This is explained by the fact that wireless IR communication systems make use of the same opto-electronic devices that have been developed and improved over the past decades for optical fiber communications and other applications. One such component is the light-emitting diode (LED), which, due to its now faster response times, high radiant output power, and improved efficiency, is becoming the preferred option for short-distance optical wireless applications.
DISADVANTAGES
DIRECT LINE OF SIGHT COMMUNICATION
Optical wireless links are susceptible to blocking from persons and objects, which can result in the attenuation of the received signal or in the disruption of the link (depending on the configuration of the system. That is; the Wireless IR systems operate only in direct line of sight communication.
SHORTER RANGE
Wireless IR systems generally operate in environments where other sources of illumination are present. This background illumination has part of its energy in the spectral region used by wireless IR transmitters and receivers, and introduces noise in the photo detector, which limits the range of the system. Moreover, optical wireless systems are also affected by the high attenuation suffered by the IR signal when transmitted through air, and by atmospheric phenomena such as fog and snow that further reduce the range of the system and deteriorate the quality of the transmission when operating outdoors
.
· Restrictions to the emitted optical power due to eye safety.
APPLICATIONS
INFRARED FILTER
Infrared (transmitting/passing) filters can be made from many different materials. One type is made of polysulfide plastic that blocks over 99% of the visible light spectrum from white light sources such as incandescent filament bulbs. Infrared filters allow a maximum of infrared output while maintaining extreme covertness. Currently in use around the world, infrared filters are used in Military, Law Enforcement, Industrial and Commercial applications. Active-infrared night vision: the camera illuminates the scene at infrared wavelengths invisible to the human eye. Despite a dark back-lit scene, active-infrared night vision delivers identifying details, as seen on the display monitor.
Night Vision
ACTIVE-INFRARED NIGHT VISION
The camera illuminates the scene at infrared wavelengths invisible to the human eye. Despite a dark back-lit scene, active-infrared night vision delivers identifying details, as seen on the display monitor. Infrared is used in night vision equipment when there is insufficient visible light to see. Night vision devicesoperate through a process involving the conversion of ambient light photons into electrons which are then amplified by a chemical and electrical process and then converted back into visible light. Infrared light sources can be used to augment the available ambient light for conversion by night vision devices, increasing in-the-dark visibility without actually using a visible light source.
THERMOGRAPHY
A Thermo graphic Image Of A Dog
Infrared radiation can be used to remotely determine the temperature of objects (if the emissivity is known). This is termed grapy, or in the case of very hot objects in the NIR or visible it is termed pyrometer. Thermographs (thermal imaging) are mainly used in military and industrial applications but the technology is reaching the public market in the form of infrared cameras on cars due to the massively reduced production costs. Thermo graphic cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 900–14,000 nanometers or 0.9–14 μm) and produce images of that radiation. Since infrared radiation is emitted by all objects based on their temperatures, according to the black body radiation law, thermo grapy makes it possible to "see" one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature, therefore thermograpy allows one to see variations in temperature
TRACKING
Infrared tracking, also known as infrared homing, refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiationin the infrared part of the spectrum to track it. Missiles which use infrared seeking are often referred to as "heat-seekers", since infrared (IR) is just below the visible spectrum of light in frequency and is radiated strongly by hot bodies. Many objects such as people, vehicle engines, and aircraft generate and retain heat, and as such, are especially visible in the infrared wavelengths of light compared to objects in the background.
HEATING
Infrared radiation can be used as a deliberate heating source. For example it is used in infrared saunas to heat the occupants, and also to remove ice from the wings of FIR is also gaining popularity as a safe method of natural health care & physiotherapy. Infrared heating is also becoming more popular in industrial manufacturing processes, e.g. curing of coatings, forming of plastics, annealing, plastic welding, and print drying. In these applications, infrared heaters replace convection ovens and contact heating. Efficiency is achieved by matching the wavelength of the infrared heater to the absorption characteristics of the material.
COMMUNICATIONS
IR data transmission is also employed in short-range communication among computer peripherals and personal digital assistants. These devices usually conform to standards published by IrDA, the Infrared Data Association. Remote controls and IrDA devices use infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current.. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Infrared is the most common way for remote controls to command appliances.
SPECTROSCOPY
Infrared vibrational spectroscopy is a technique which can be used to identify molecules by analysis of their constituent bonds. Each chemical bonding a molecule vibrates at a frequency which is characteristic of that bond. A group of atoms in molecule (e.g. CH2) may have multiple modes of oscillation caused by the stretching and bending motions of the group as a whole. If an oscillation leads to a change in dipole in the molecule, then it will absorb a photon which has the same frequency. Typically, the technique is used to study organic compounds using light radiation from 4000–400 cm−1, themed-infrared. A spectrum of all the frequencies of absorption in a sample is recorded. This can be used to gain information about the sample composition in terms of chemical groups present and also its purity
No comments:
Post a Comment