According to Maxwell, electromagnetic waves are the waves in which energy is been transported through spaces in periodic disturbances in the form of electric and magnetic field components. The two field components have the same frequency and wavelength and travel mutually perpendicular to each other. All electromagnetic waves travels in the space with the same speed i.e. the speed of light, C=2.99792458 x 10^8 m/s. The wavelength and frequency are related to the speed of light by the following relation:
Speed of light= frequency x wavelength
There is a wide range of frequency encountered our physical world, form the low frequency of the electric waves generated by the power transmission lines to the very high frequency of the gamma rays originating from the atomic nuclei. This frequency range of the electromagnetic waves forms the electromagnetic spectrum.
The electromagnetic spectrum are generally divided into several regions of wavelength, of which only a narrow band is visible to our human eyes and is that called the visible region .On the immediate high energy side of the visible spectrum lies the ultraviolet rays and on the low energy side is the infrared rays. The portion of the infrared region that is most useful for analysis of organic compounds is not immediately adjacent to the visible spectrum, but it is having a wavelength ranging from 2500 to 16000 nm with corresponding frequency ranging from 1.9 x 10^13 to 1.2 x 10^14 Hz.
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The name "infrared" means below red, where infra is a Latin word meaning below and red is the color of the longest wavelength of the visible region. Infrared light has a longer wavelength and so have shorter frequency than that of the red light visible to human eyes.
DIFFERENT REGIONS IN INFRARED:
Usually objects emit infrared radiation across a spectrum of wavelength, but only certain region of the spectrum is of interest since sensors are usually designed only to collect radiation within a specific bandwidth. As a result, the infrared band in been divided into smaller sections:
According to the international commission on illumination (CIE) recommended the infrared radiation has been divided into the following three bands:
IR-A: 700-1400 (0.7-1.4 micrometer)
IR-B: 1400-3000 (1.4-3 micrometer)
IR-C: 3000-1 (3-1000 micrometer)
It has wavelength of 0.75 to 1.4 micrometer, defined by the water absorption and usually used in fiber optic.
SHORT-WAVELENGHT INFRARED (SWIR):
It has wavelength of 1.4-3 micrometer, the 1530 to 1560 nm is the dominant spectral region for long- distance telecommunications.
MID-WAVELENGHT INFRARED (MWIR):
Mid-wavelength infrared is also known as intermediate infrared of wavelength 3 to 8 micrometer.
LONG-WAVELENGHT INFRARED (LWIR):
Long wavelength infrared is the 'thermal imaging' in which sensors can obtain a completely passive picture of the outside world based on thermal emissions and requiring no external light or thermal source like the sun, the moon or infrared illumination.
Near infrared and short-wavelength infrared is sometimes known as 'reflected infrared' while mid-wavelength infrared and long-wavelength infrared is also referred to as 'thermal infrared'.
Infrared radiation is popularly known as 'heat' or known as 'heat radiation'. Light and electromagnetic waves of any frequency heats the surfaces that absorb them. Infrared light from the sun accounts for about 49% of the heating of the Earth with the rest being caused by visible light that is absorbed then re-radiated at long wavelengths. Visible light or ultraviolet emitting lasers can charge paper and incandescently not objects emit visible radiation.
Heat energy is in transient form that flows due to temperature difference, unlike heat transmitted by thermal conduction or thermal convection, radiation can propagate through a vacuum. The concept of emissivity is important in understanding the infrared emission of objects. This is a property of a surface which describes its thermal emission s deviate from the ideal of a black body. Two objects at the same physical temperature will not appear the same temperature in an infrared image if they have different emissivity.
Infrared radiation can be used as a deliberate heating source. For example, it is used in infrared to heat the occupants and also to remove ice from the wings of aircraft (de-icing). Far infrared has also increased its popularity as a safe method of natural health care and physiotherapy. Infrared radiation can also be used in cooking and heating food as it pre-dominantly heats the opaque, absorbent objects rather than the air around them. Infrared radiation is extensively used in manufacturing process. For example ,curing coat, forming of plastics, annealing, and plastic welding. In these applications, infrared heaters replaced convection ovens and contact heating. Efficiency is achieved by matching the wavelength of the infrared heater to the absorption characteristics of the materials.
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Heating with infrared radiation is a very popular use of infrared technology. An infrared heater for ultrapure water offers an infrared heater which provides rapid and efficient heating of liquids without any possibility of contamination.
Active-infrared radiation night vision: The camera illuminates the scene at infrared wavelength which is visible to the human eyes. Despite of the dark back light scene, active infrared night vision delivers identifying the details seen in the displayed monitor. Infrared radiation is used in night vision equipment when the visible light not sufficient to our eyes. Night vision devices operates by a process which involves the conversion of ambient light photons into electrons, it is then amplified by a chemical and electrical process and again it is converted back into visible light, infrared light sources can be used to augment the available devices increasing in the dark visibility without actually using a visible light sources. Infrared light and night vision are not same with thermal imaging, in thermal imaging images are created based on the difference in the temperature of the surfaces.
Infrared radiation is also used to remotely determine the temperature difference of the object provided the emissivity is known is termed as thermography. If it is in the case of very hot objects in the near infrared or in the visible region it is termed as pyrometry. Thermography/thermal imaging is mostly used in military and industrial application but this technology has reached to the public market in the form infrared cameras etc. thermographic cameras can detect radiation in the range of infrared range of the electromagnetic spectrum and can produce images of that radiation. The amount of radiations emitted by an object increases with temperature and for this reason thermography allows us to see radiation in temperature.
Infrared photography is another application of near infrared lights. In IR photography, infrared filters are being to capture the near infrared spectrum. A digital camera often uses infrared blockers. Cheaper digital cameras, camera phones etc have less filters and can be seen at intense near infrared radiation appearing as a bright white color.
Infrared tracking, also known as the infrared homing refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track it. Missiles in which infrared radiation is being used are often referred to as 'heating seekers' as infrared radiation is just the visible spectrum of light in frequency and radiated strongly by hot bodies. Many objects like human, vehicle engines and aircraft generate and retain heat and are therefore these are especially visible in the infrared wavelengths of light as compared objects in the background.
Infrared data transmission is also employed in short range communication among computer peripherals and personal digital assistants. These devices are generally confirmed to standards published by IrDA, the infrared radiation 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. switch on or off to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal created by the transmitter and filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. Infrared radiation does not penetrate walls and therefore it does not interfere with other devices in adjoining rooms. Infrared is the most common way for remote controls to command appliances.
Wireless communication, allows information to be exchanged between the two devices without the use of wires or cables. A wireless keyboard sends information to the computer without the use of a keyboard cables; a cellular telephone sends information to another telephone without using any wires or cables. In all such case, information is being transmitted and received using electromagnetic waves or energy also referred to electromagnetic radiation. The electromagnetic spectrum classifies electromagnetic energy according to frequency and wavelength.
Free space optical communication using laser can be relatively inexpensive way to install communication link in an urban area operating at up to 4gigabits, compared cost of burying fiber optic cables. Infrared lasers are being used to provide the light of optical fiber communication systems. Infrared light with a wavelength around 1330 nm or 1550 nm are the best choice for standard silica fibers. Infrared data transmission of encoded audio versions of printed signs is being researched as an aid for visually impaired people through RIAS ( remote infrared audible signal).
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Infrared vibrational spectroscopy is a technique which can be used to identify the molecules by analyzing its constituent bonds. Each chemical bond in a molecule vibrates at a frequency which is a characteristic of that bond. A group of atoms in a molecule may have multiple modes of oscillation caused by the stretching and bending motion of a group as a whole. When the oscillation leads to a change in dipole in the molecule, then it will absorb a photon having same frequency. The vibrational frequencies of most molecules correspond to the frequencies of IR light. Photon associated with this part of the infrared are not large enough to excite electrons, but may induce vibrational excitation of covalently bonded atoms and groups. the covalent bonds in molecules are not rigid sticks or rod , such as found in molecular model kits, but are more likely stiff spring that can be stretched and bent.
In addition to the facile rotation of groups about single bonds, molecules experience a wide variety of vibrational motions, characteristic of their component atoms. Consequently, virtually all organic compounds will absorb infrared radiation that corresponds in energy to three vibrations. Infrared spectroscopy is similar in principle of ultraviolet-visible spectrometer. The complexity of this spectrum is typical of most infrared spectra and illustrates their use in identifying substances. The gap in the spectrum between 700 and 800 per cm is due to solvent absorption. This spectrum also indicates the presence of an aldehyde function, a phenol, hydroxyl and a substituted benzene ring. Infrared spectra may be obtained from samples in all phases i.e. solids, liquids and gases. Liquids usually examined as a thin film sandwiched between two polished plate. If solvents are used to dissolve solid, care must be taken in order to avoid obscuring important spectral regions by solvent absorption.
A molecules composed of n-atoms has 3n degrees of freedom, six of which are translations and rotations of the molecules itself. This leaves 3n-6 degrees of vibrational freedom (3n-5 if the molecule is linear). Vibration modes are often given descriptive names such as stretching, bending, and scissoring. Rocking and twisting. Simple diatomic molecules have only one bond and one vibrational bond. If the molecule is symmetrical, for example N2 the bond is not observed in the infrared spectrum, but only one in the Raman spectrum. Unsymmetrical diatomic molecules, for example Co absorbs in the infrared spectrum. More complex molecules have many bonds, and their vibrational spectra are corresponding more complex i.e. big molecules have many peaks in their infrared spectra.
USES AND ITS APPLICATIONS OF SPECTROSCOPY:
Infrared spectroscopy is widely used in research and industry as a simple and reliable technique for measurement, quality central and dynamic measurement. It is also used in forensic analysis in both criminal and civil cases, enabling identifying of polymer degradation. By measuring at a specific frequency overtime change in the character or quality of a particular bond can be measured. This is especially useful in measuring the degree of polymerization in polymer manufacture. This makes the observation of chemical reaction and processes quicker and more accurate. Infrared spectroscopy has been highly successful for application in both organic and inorganic chemistry. Infrared spectroscopy has also been successfully utilized in the field of semiconductor microelectronics. For example infrared spectroscopy can be applied to semi-conductors like silicon, gallium arsenide etc.
In the field of climatology, atmospheric infrared radiation is monitored to detect trends in the energy exchange between the earth and the atmosphere. These trends provide information on long term changes in the earth's climate. It is one of the primary parameters studied in research into global warming together with solar radiations.
Infrared astronomy is the branch of astronomy or astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometer. Infrared astronomy started few decades ago after the discovery of infrared light. It was discovered by William Herschel in 1800. The early progresses of infrared spectroscopy were very limited and it was not until the early 20th century that conclusion detections of astronomical objects other than the sun and the moon were detected in the infrared light. Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components including mirrors, lenses and solid state digital detectors. Infrared and optical astronomy are usually been practiced using the same telescopes, since the same mirrors and lenses are usually more effective over a wavelength range that includes both the visible and optical light. Infrared light can be absorbed at many wavelengths by water vapors in the Earth's atmosphere. For this reason, infrared telescopes are at high elevation in dry places above as much of the atmosphere as possible.
Infrared radiation having wavelength just longer than the visible light is known as near infrared and it behaves in a very similar way like the visible light which can be detected by using similar solid state devices. Therefore the near infrared region of the spectrum is often incorporated as part of the optical spectrum along with the near ultraviolet.
Infrared radiation is used by the astronomers to study the universe, like all the other forms of electromagnetic radiations. Infrared telescopes which includes major optical telescopes and few dedicated infrared telescopes are needed to be chilled with liquid nitrogen and shielded from warm objects. This is been done because of the reason that objects of temperature of few hundred Kelvin emit most of their thermal energy at infrared wavelengths. Suppose the infrared detectors were not kept cooled, the radiation from the detectors itself would contribute noise that would dwarf the radiation from any celestial source. It is very important particularly in the mid infrared (MID) and far infrared (FIR) regions of the spectrum.
The infrared part of the spectrum has several useful benefits for astronomers. Cold, dark molecular clouds of gas and dust in our galaxy glows with radiation heat when they are being radiated by imbedded stars. Infrared can also be used to detect protostars before they begin to emit visible light . stars emit a smaller portion of their energy in the infrared spectrum, so nearly cool objects such as planets can be more readily detected. In the visible region , the glare that comes from the stars drowns out the reflected light from a planet. Infrared light is also important and useful for observing the cores of active galaxies which are often cloaked in gas and dust. Distant galaxies with a red shift will have the peak portion of their spectrum shifted towards longer wavelength, so they are more readily observed in the infrared.
INFRA RED TECHNOLOGY
Infra red radiation is the region of the EM spectrum between microwaves and visible light. One of the most common IR detector arrays used at research telescopes is Hg Cd Te arrays. These operate well between 0.6- 5 micrometers wavelengths. For longer wavelength observations or higher sensitivity other detectors may be used like narrow gap semi-conductors. Some of the common applications of infra -red technology are :
Augmentative communication devices
Car locking system
Environmental control system
Telephones, television, CD players etc.
Low power requirements; therefore it is ideal for laptops, telephones, personnel digital assistance.
High noise immunity
Line of sight: transmitter and receiver must be almost directly aligned to communicate.
It can be blocked by common materials like people, walls, and plants.
Short range: performance drops off with longer distance.
Light, weather sensitive.
Data rate transmission is lower than typical wire transmission.
Strong infrared radiation in certain industry high heat setting may constitutes a health hazards to the eyes and the vision. More so, since the radiation is invisible. Therefore special infrared proof protection eyeglasses must be worn in such places.