Broadcasting technology

08-Mar-17

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Optical F ibers , Radars Optical F ibers , Radars and Satel l i tesand Satel l i tes

The Development and Evolution of Broadcasting Technology

Farseem M. Mohammedy PhD

Associate Professor, ECE 424,

Dept of EEE, B.U.E.T., Dhaka-1000.

https://www.facebook.com/farseem

Dept of EEE, BUET Dr. Farseem M. Mohammedy 2

Optical Fiber TechnologyOptical Fiber Technology

Dept of EEE, BUET

History of Optical FibersHistory of Optical Fibers

Dr. Farseem M. Mohammedy 3

Circa 2500 B.C. Earliest known glass; Roman times-glass drawn into fibers;Venice Decorative Flowers made of glass fibers1609-Galileo uses optical telescope1626-Snell formulates law of refraction1668-Newton invents reflection telescope1840-Samuel Morse Invents Telegraph1841-Daniel Colladon-Light guiding demonstrated in water jet

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1870-Tyndall observes light guiding in a thin water jet1873-Maxwell electromagnetic waves1876-Elisha Gray and Alexander Bell Invent Telephone1877-First Telephone Exchange1880-Bell invents Photophone1888-Hertz Confirms EM waves and relation to light1880-1920 Glass rods used for illumination1897-Rayleigh analyzes waveguide1899-Jagdish Bose and Marconi Radio Communication1902-Marconi invention of radio detector1910-1940 Vacuum Tubes invented and developed1930-Lamb experiments with silica fiber1931-Owens-Fiberglass1936-1940 Communication using a waveguide

1876-Alexander Graham Bell

1876 First commercial Telephone

J. C. Bose

08-Mar-17

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Dept of EEE, BUET

Bells Bells PhotophonePhotophone


1880 - Photophone Transmitter

1880 - Photophone Receiver

“The ordinary man…will find a little difficulty in comprehending how sunbeams are to be used. Does Prof. Bell intend to connect Boston and Cambridge…with a line of sunbeams hung on telegraph posts, and, if so, what diameter are the sunbeams to be…?…will it be necessary to insulate them against the weather…?…until (the public) sees a man going through the streets with a coil of No. 12 sunbeams on his shoulder, and suspending them from pole to pole, there will be a general feeling that there is something about Prof. Bell’s photophone which places a tremendous strain on human credulity.”

New York Times Editorial, 30 August 1880

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1951-Heel, Hopkins, Kapany image transmission using fiber bundles1957-First Endoscope used in patient1958-Goubau et. al. Experiments with the lens guide1958-59 Kapany creates optical fiber with cladding1960-Ted Maiman demonstrates first laser in Ruby1960-Javan et. al. invents HeNe laser1962-4 Groups simultaneously make first semiconductor lasers1961-66 Kao, Snitzer et al conceive of low loss single mode fiber communications and develop theory1970-First room temp. CW semiconductor laser-Hayashi & PanishApril 1977-First fiber link with live telephone traffic-

GTE Long Beach 6 Mb/sMay 1977-First Bell system 45 mb/s links

GaAs lasers 850nm Multimode -2dB/km lossEarly 1980s-InGaAsP 1.3 µm Lasers

- 0.5 dB/km, lower dispersion-Single modeLate 1980s-Single mode transmission at 1.55 µm -0.2 dB/km1989-Erbium doped fiber amplifier1 Q 1996-8 Channel WDM4th Q 1996-16 Channel WDM1Q 1998-40 Channel WDM

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How the Fiber contains LightHow the Fiber contains Light

Dr. Farseem M. Mohammedy 7 Dept of EEE, BUET

MirageMirage


Warm mirage Cold mirage

08-Mar-17

3

Dept of EEE, BUET

Total Internal ReflectionTotal Internal Reflection


A laser bouncing down an acrylic rod, illustrating the total internal reflection of light in a multi-mode optical fiber

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Single mode / multi modeSingle mode / multi mode


Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics.

Dept of EEE, BUET Dr. Farseem M. Mohammedy 11 Dept of EEE, BUET

BitrateBitrate--Distance productDistance product


Agrawal-Fiber Optic Communications, 3rd Ed.

08-Mar-17

4

Dept of EEE, BUET

Progress In Progress In LightwaveLightwave Communication Communication TechnologyTechnology


Modes of Modes of LightwaveLightwave CommunicationCommunication


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LightwaveLightwave Application Application AreasAreas


Optical interconnects

Chip to Chip (Unlikely in near future)Board to Board (>1foot eg. CPU-Memory)Subsystem-Subsystem (Optics used Low Speed)

Rack -To-Rack

Chip-to-Chip

Board-to-Board

µp

89

86

NE7809

NE7809

NE7809

LaserDriver

D-F/FRetiming

N:1Mux

LaserDiode

Data

Clock

Optical

OpticalPreamp

PhotoDetector

Preamp MainAmp

ClockRecovery

D-F/FDecision

1:NDeMux

Data

Clock

Receiver

Transmitter

Telecommunications

Long Haul (Small Market-High Performance)LANs (Large Market Lower Performance)

High-Speed Analog (CATV-Remote Satellite)

Dept of EEE, BUET

Why fiberWhy fiber??


Palais-Fiber Optic Communications

08-Mar-17

5

Dept of EEE, BUET

Optical Fiber Optical Fiber Attenuation and Fiber Amplifier GainAttenuation and Fiber Amplifier Gain

Dr. Farseem M. Mohammedy 17 Dept of EEE, BUET Dr. Farseem M. Mohammedy 18

Dept of EEE, BUET

Modern Optical Modern Optical Fiber Fiber SystemSystem


Image Transmission by Fiber BundleImage Transmission by Fiber Bundle


08-Mar-17

6

Dept of EEE, BUET

The InternetThe Internet


Growth of the Internet: Demand Driver for High Bandwidth Communications

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Land CablesLand Cables


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Fibers OverheadFibers Overhead


Metro NetworkMetro Network


08-Mar-17

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Dept of EEE, BUET

Undersea CablesUndersea Cables


World Fiber MapWorld Fiber Map



One of the largest network provider in Bangladesh, Summit Communications Ltd. aggregate a state-of-the-art fiber optic network, has built access to over 33,000 KM nationwide network connecting all 64 districts, 340 upazillasand more than 3650 government offices, serving all the mobile phone operators, major ISPs and call centers all over the country.

http://summitcommunications.net/Dept of EEE, BUET Dr. Farseem M. Mohammedy 28

SensorsSensors

08-Mar-17

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Dept of EEE, BUET

Why do we need sensorsWhy do we need sensors

• Our brain understands electro-chemical signal

• A computer understands electrical signal

• So if we want to get our job done by a computer, we must seek for something that can convert a physical signal into electrical signal

• Sensors are ‘Eyes’ and ‘Ears’ for your computer


Optical signal in

Audio Signal in

Dept of EEE, BUET

What is a SensorWhat is a Sensor

• Wiki says-

– "A sensor is a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an (today mostly electronic) instrument. "

• For example, a thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, most sensors are calibrated against known standards.

• A good sensor obeys the following rules:– Is sensitive to the measured property only

– Is insensitive to any other property likely to be encountered in its application

– Does not influence the measured property


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The World of SensorsThe World of Sensors


Sensors EverywhereSensors Everywhere


08-Mar-17

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Optical Sensors Optical Sensors


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Why Optical SensorsWhy Optical Sensors

• Advantages: – Electromagnetic immunity

– Electrical isolation

– Compact and light

– Both point and distributed configuration

– Wide dynamic range

– Amenable to multiplexing


Optical SensorsOptical Sensors

• Optical sensors convert light signal into electric signal

• This is done by absorbing photons and then creating free electron-hole pairs (EHPs) out of them

• This is the principle of photodiodes (PDs) and photoconductors

• Pyrolytic detectors work by absorbing photons and converting photon energies into heat

• Increase in temperature changes its polarization which in turn changes its relative permittivity

36Dr. Farseem M. Mohammedy

Light signal (photons) Electric signal (EHPs)PD

08-Mar-17

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PhotodetectorsPhotodetectors

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CurrentCurrent--VoltageVoltage


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PhotodetectorsPhotodetectors

• Junction diodes

– pn photodiodes

– pin photodiodes

• Avalanche photodiodes

• Photoconductors


DetectivityDetectivity


• This is a very important figure-of-merit in detector design

• This is defined as the ratio of the signal power to the noise power

• The higher the SNR for a detector, the better

• Noise equivalent power is the optical signal power required to generate a photocurrent that is equal to the total noise current in the photodetectorat a given wavelength within a bandwidth of 1 Hz

• Detectivity (D*) is the reciprocal of NEP: The higher the D*, the lower the noise floor, the better for a detector;

• The unit for D* is cm.Hz1/2/W or Jones; D* is a normalized SNR

power noise

power signalSNR

08-Mar-17

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Dept of EEE, BUET Dr. Farseem M. Mohammedy 41 Dept of EEE, BUET Dr. Farseem M. Mohammedy 42

Infrared Sensors Infrared Sensors

Dept of EEE, BUET

MMidid--IR ApplicationsIR Applications


•Mid Infrared lasers/detectors for

•Biomedical applications•Defense and security applications•Next generation non-silica fibers

•Possibilities to explore interesting structures

•Extra freedom in wavelength selection

http://www.satimagingcorp.com/gallery/landsat-hydrology-lg.htmlhttp://www.spectroscopymag.com/spectroscopy/article/articleDetail.jsp?id=309539&sk=&date=&&pageID=4

P. Norton, Opto-Electronics Review, 16(2), 105–117, 2008.

well

barrier

Absorption layer

InGaSb

Dept of EEE, BUET

EEnvironment Sensingnvironment Sensing


Bacteria/toxic element/process elements

Top layer n+ In0.18Ga0.82Sb

Undoped layerIn0.18Ga0.82Sb

Bottom layerp+In0.18Ga0.82Sb

Metamorphically Graded Buffer from GaSb to In0.15Ga0.85Sb

p GaSb Substrate

Pre

-Am

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fier

Cir

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an

d D

isp

lay

InAs substrate

http

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qd.

ece.

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.edu

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h.h

tml

http://www.roithner-laser.com/LED_MID_IR.htm

P. Norton, Opto-Electronics Review, 16(2), 105–117, 2008.

08-Mar-17

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Dept of EEE, BUET

MMidid--IR signature environmental gasesIR signature environmental gases


A LA Lookook--back on IR Detectorsback on IR Detectors


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IR DetectorsIR Detectors

"At present efforts in infrared detector research are directed towards improving the performance of single element devicessingle element devices, large electronically scanned arraysarrays and higher operating temperature." – Antoni Rogalski

• Another important aim is to make IR detectors cheaper and more convenient to use.

• There are two major IR Detector classes – infrared thermal detectors and photon detectors

• Due to fundamental different types of noise, these two classes of detectors have different dependencies of detectivities on wavelength and temperature.


CComparison of IR Detectorsomparison of IR Detectors**


*Rogalski, Prog. Quant. Electron., 27, pp. 59-210, 2003

08-Mar-17

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Receiver CircuitReceiver Circuit

Dept of EEE, BUET

Receiver DesignReceiver Design


•Requirements •Low noise

•High bandwidth

•Choice of amplifier topology•Depends on application (bandwidth vssensitivity)•Front-end photodetector (PIN or

Avalanche detector)

detector amp Decision circuit signalOptical power

Key issues

•Speed/bandwidth

•Noise

•Cost/Technology

•Power consumption

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Choice of TransistorsChoice of Transistors


FET•Thermal noise associated with channel conductance•Shot noise from gate leakage current•Other FET noises

BJT•Shot noise from base and collector current•Thermal noise from base resistance

•Speed/bandwidth •Noise •Cost •Technology

HBT•High speed•SiGe and III-V technology

HEMT•High speed•III-V technology•Lower noise and power consumption than FETs

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Monolithically Integrated OEICMonolithically Integrated OEIC


•Reported performance at 1.55m

•~50 Gb/s bandwidth•Low sensitivity

•High efficiency

•Major considerations•Material compatibilities •Desired device and amplifier characteristics•Single-step fabrication in a MBE•Involved processing•Cost

K. Kato, IEEE Trans. Microwave Theory Tech., 47, p.1265, 1999

•Monolithic integration of detector and amplifier on the same chip is possible using shared layer growth techniques

08-Mar-17

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SatellitesSatellites

Dept of EEE, BUET

HistoryHistory

• The concept of the geostationary communications satellite was first proposed by Arthur C. Clarke (1917-2008).

• In October 1945 Clarke published an article titled "Extraterrestrial Relays" in the British magazine Wireless World.

• The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals.


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First Artificial SatelliteFirst Artificial Satellite

• The first artificial Earth satellite was Sputnik 1.

• Put into orbit by the Soviet Union on October 4, 1957, it was equipped with an on-board radio-transmitter that worked on two frequencies: 20.005 and 40.002 MHz.

• The first artificial satellite used solely for global communications was a balloon named Echo 1 launched by NASA.

• It soared 1,600 kilometres (1,000 mile) above the planet after its Aug. 12, 1960 launch, yet relied on humanity's oldest flight technology — ballooning.


Two Types of SatellitesTwo Types of Satellites

• Two major classes of communications satellites –

– passive and

– active. • Passive satellites only reflect the signal coming from the source,

toward the direction of the receiver without amplification.

• Active satellites, on the other hand, amplify the received signal before re-transmitting it to the receiver on the ground.

• Passive satellites were the first communications satellites, but are little used now.

• Telstar was the second active, direct relay communications satellite. Belonging to AT&T as part of a multi-national agreement between AT&T, Bell Telephone Laboratories, NASA, the British General Post Office, and the French National PTT (Post Office) to develop satellite communications, it was launched by NASA from Cape Canaveral on July 10, 1962.


08-Mar-17

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Dept of EEE, BUET

OrbitsOrbits

• GEO – Geostationary orbits

• MEO – Medium Earth Orbit

• LEO – Low Earth Orbit


GeoGeo

• Geostationary orbit is 35,786 kilometres (22,236 mi) from Earth’s surface.

• This orbit is special in that the apparent position of the satellite in the sky, viewed by a ground observer, does not change - the satellite appears to "stand still" in the sky.

• This is because the satellite's orbital period is the same as the rotation rate of the Earth. The advantage of this orbit is that ground antennas do not have to track the satellite across the sky.


The first geostationary satellite was Syncom 3, launched on August 19, 1964, and used for communication across the Pacific starting with television coverage of the 1964 Summer Olympics.

Dept of EEE, BUET

MeoMeo

• A MEO is a satellite in orbit somewhere between 2,000 and 35,786 kilometres (1,243 and 22,236 mi) above the earth’s surface.

• Visible for much longer periods of time than LEO satellites, usually between 2 and 8 hours.

• Have a larger coverage area than LEO satellites.

• As such, fewer satellites are needed in a MEO network than a LEO network.

• One disadvantage is that a MEO satellite’s distance gives it a longer time delay (<50 ms) and weaker signal than a LEO satellite.

• In 1962, the first communications satellite, Telstar, was launched. It was a medium earth orbit satellite designed to help facilitate high-speed telephone signals.


LeoLeo

• A low Earth orbit (LEO) typically is a circular orbit about 160 to 2,000 km (99 to 1,243 miles) above the earth's surface and, correspondingly, a period (time to revolve around the earth) of about 90 minutes.

• Because of low altitude, these satellites are only visible from within a radius of roughly 1,000 km (620 miles) from the sub-satellite point.

• In addition, satellites in LEO change their position relative to the ground position quickly. So a large number of satellites are needed if the mission requires uninterrupted connectivity.

• LEO satellites are less expensive to launch into orbit than geostationary satellites and, due to proximity to the ground, do not require as high signal strength.

• Thus there is a trade off between the number of satellites and their cost.


08-Mar-17

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Dept of EEE, BUET

GeoGeo--MeoMeo--LeoLeo



Telephone Traffic on SatellitesTelephone Traffic on Satellites

• The first and historically most important application for communication satellites was in intercontinental long distance telephony.

• The fixed Public Switched Telephone Network relays telephone calls from land line telephones to an earth station, where they are then transmitted to a geostationary satellite. The downlink follows an analogous path.

• Improvements in submarine communications cables through the use of fiber-optics caused some decline in the use of satellites for fixed telephony in the late 20th century.

• Satellite communications are still used in many applications today. Remote islands such as Saint Helena, Easter Island, where no submarine cables are in service, need satellite telephones.

• There are also regions of some continents and countries where landline telecommunications are rare to nonexistent, for example large regions of South America, Africa, Canada, China, Russia, and Australia. Satellite communications also provide connection to the edges of Antarctica and Greenland. Other land use for satellite phones are rigs at sea, a back up for hospitals, military, and recreation. Ships at sea, as well as planes, often use satellite phones.


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Television Traffic on SatelliteTelevision Traffic on Satellite

• The first public satellite television signals from Europe to North America were relayed via the Telstar satellite over the Atlantic ocean on 23 July 1962, [a test broadcast was on 11 July].

• The signals were received and broadcast in North American and European countries and watched by over 100 million.

• Launched in 1962, the Relay 1 satellite was the first satellite to transmit television signals from the US to Japan.


The first geosynchronous communication satellite, Syncom 2, was launched on 26 July 1963.

Dept of EEE, BUET

History of Satellite CommunicationHistory of Satellite Communication

• 1965 – World's first commercial communications satellite, called Intelsat I and nicknamed "Early Bird", was launched into geosynchronous orbit.

• 1967 – First national network of television satellites, called Orbita, was created by the Soviet Union.

• 1972 – First commercial North American satellite to carry television transmissions was Canada's geostationary Anik 1.

• 1974 – ATS-6, the world's first experimental educational and Direct Broadcast Satellite (DBS), was launched. It transmitted at 860 MHz using wideband FM modulation and had two sound channels. The transmissions were focused on the Indian subcontinent but experimenters were able to receive the signal in Western Europe using home constructed equipment that drew on UHF television design techniques already in use.

• 1976 – The first in a series of Soviet geostationary satellites to carry Direct-To-Home (DTH) television, Ekran 1, was launched. It used a 714 MHz UHF downlink frequency so that the transmissions could be received with existing UHF television technology rather than microwave technology.


ATS-6

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Dept of EEE, BUET

Satellite TV IndustrySatellite TV Industry

• 1976 – The satellite television industry developed first in the US from the cable tv industry as communication satellites were being used to distribute television programming to remote cable tv head-ends. Home Box Office (HBO), Turner Broadcasting System (TBS), were among the first to use satellite television to deliver programming.

• 1978 – Public Broadcasting Service(PBS), a non-profit public broadcasting service, began to distribute its television programming by satellite.

• 1979 – Soviet engineers developed the Moskva system of broadcasting / delivering TV signals via satellites. They launched the Gorizont GEO satellites later that same year.

• 1979 – Federal Communications Commission (FCC) began allowing people to have home satellite earth stations without a federal government license. First home satellite TV stations dishes were nearly 20 feet in diameter and were remote controlled.


Satellite TV IndustrySatellite TV Industry

• 1980 – Satellite televisions were well established in the USA and Europe.

• 1982 – First satellite channel in the UK, Satellite Television Ltd. (later Sky1), was launched.

• 1984 – The U.S. Congress passed the Cable Communications Policy Act of 1984, which gave those using Television Receive Only (TVRO) systems the right to receive signals for free.

• 1988 – Luxembourg launched Astra 1A, the first satellite to provide medium power satellite coverage to Western Europe.


C-Band satellite dish

Dept of EEE, BUET

Standard Satellite TVStandard Satellite TV

• Satellite television is a service that delivers television programming to customers (usually paying subscribers) by relaying it from a communications satellite orbiting the Earth directly to the customer's location.

• The signals are received via an outdoor parabolic antenna usually referred to as a satellite dish and a low-noise block downconverter(LNB).

• A satellite receiver then decodes the desired television programmefor viewing on a television set.

• Receivers can be external set-top boxes, or a built-in television tuner. • Satellite television provides a wide range of channels and services. It

is the only television available in many remote geographic areas without terrestrial television or cable television service.


08-Mar-17

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Dept of EEE, BUET

Digital Digital TelevisionTelevision

• Digital television (DTV) is the transmission of audio and video by digitally processed and multiplexed signal, in contrast to the totally analog and channel separated signals used by analog television.

• DTV can support more than one program in the same channel bandwidth. It is an innovative service that represents the first significant evolution in television technology since color television in the 1950s.


Dept of EEE, BUET

Block DiagramsBlock Diagrams


MicrowavesMicrowaves

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Dept of EEE, BUET

MicrowavesMicrowaves• Microwaves are a form of electromagnetic radiation with wavelengths

ranging from one meter to one millimeter; with frequencies between 300 MHz (100 cm) and 300 GHz (0.1 cm).

• A more common definition in radio engineering is the range between 1 and 100 GHz (300 and 3 mm).

• The prefix “micro-” in microwave indicates that microwaves are "small", not wavelength in the micrometer range, compared to waves used in typical radio broadcasting, in that they have shorter wavelengths.

• Microwaves travel by line-of-sight.


Microwaves are extremely widely used in point-to-point communication links, wireless networks, microwave radio relay networks, radar, satellite and spacecraft communication, medical diathermy and cancer treatment, remote sensing, radio astronomy, particle accelerators, spectroscopy, industrial heating, collision avoidance systems, garage door openers and keyless entry systems, and for cooking food in microwave ovens.


Dept of EEE, BUET

First Microwave LinkFirst Microwave Link

• 1931 – Anglo-French consortium headed by Andre C. Clavier demonstrated an experimental microwave relay link across the English Channel using 10 foot (3 m) dishes. Telephony, telegraph and facsimile data was transmitted over the bidirectional 1.7 GHz beams 64 km (40 miles) between Dover, UK and Calais, France. The radiated power, produced by a miniature Barkhausen-Kurz tube located at the dish's focus, was one-half watt.

• 1933 – Military microwave link between airports at St. Inglevert, UK and Lympne, France, a distance of 56 km (35 miles).


Antennas of 1931 experimental 1.7 GHz microwave relay link across the English Channel. The receiving antenna (background, right) was located behind the transmitting antenna to avoid interference.

Dept of EEE, BUET

History of Microwave LinksHistory of Microwave Links

• 1940s – The development of radar in World War II provided the technology for practical exploitation of microwave communication.

• 1950s – Large transcontinental microwave relay networks, consisting of chains of repeater stations linked by line-of-sight beams of microwaves were built in Europe and America to relay long distance telephone traffic and television programs between cities.

• 1960s – Communication satellites which transferred data between ground stations by microwaves took over much long distance traffic in the 1960s.

• In recent years there has been an explosive increase in use of the microwave spectrum by new telecommunication technologies such as wireless networks, and direct-broadcast satellites which broadcast television and radio directly into consumers' homes.


Modern communication tower

08-Mar-17

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Dept of EEE, BUET

World War IIWorld War II

• The development of radar during World War II provided much of the microwave technology which made practical microwave communication links possible, particularly the klystronoscillator and techniques of designing parabolic antennas.

• Though not commonly known, the US military used both portable and fixed-station microwave communications in the European Theater during World War II.


Post War DevelopmentsPost War Developments• The main motivation in 1946 to use microwave radio instead of cable was that a large capacity could be installed

quickly and at less cost. It was expected at that time that the annual operating costs for microwave radio would be greater than for cable. There were two main reasons that a large capacity had to be introduced suddenly: Pent up demand for long distance telephone service, because of the hiatus during the war years, and the new medium of television, which needed more bandwidth than radio.

• The prototype was called TDX and was tested with a connection between New York City and Murray Hill, the location of Bell Laboratories in 1946. The TDX system was set up between New York and Boston in 1947. The TDX was upgraded to the TD2 system, which used [the Morton tube, 416B and later 416C, manufactured by Western electric ] in the transmitters, and then later to TD3 that used solid state electronics.

• During the 1950s a unit of the US telephone carrier, AT&T Long Lines, built a transcontinental system of microwave relay links across the US that grew to carry the majority of US long distance telephone traffic, as well as television network signals.

• Military microwave relay systems continued to be used into the 1960s, when many of these systems were supplanted with tropospheric scatter or communication satellite systems. When the NATO military arm was formed, much of this existing equipment was transferred to communications groups.

• The typical communications systems used by NATO during that time period consisted of the technologies which had been developed for use by the telephone carrier entities in host countries. One example from the USA is the RCA CW-20A 1–2 GHz microwave relay system which utilized flexible UHF cable rather than the rigid waveguide required by higher frequency systems, making it ideal for tactical applications.

• The typical microwave relay installation or portable van had two radio systems connecting two line of sight sites. These radios would often carry 24 telephone channels frequency division multiplexed on the microwave carrier (i.e. Lenkurt 33C FDM).

• Long distance microwave relay networks were built in many countries until the 1980s when the technology lost its share of fixed operation to newer technologies such as fiber-optic cable and communication satellites, which offer lower cost per bit.


Dept of EEE, BUET

Antenna Research Under the 'Turkey Shed'Antenna Research Under the 'Turkey Shed'


Microwave Relay Microwave Relay linkslinks

• Because the radio waves travel in narrow beams confined to a line-of-sight path from one antenna to the other, they don't interfere with other microwave equipment, and nearby microwave links can use the same frequencies.

• Antennas used must be highly directional (High gain); these antennas are installed in elevated locations such as large radio towers in order to be able to transmit across long distances.

• Their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter.

• Parabolic ("dish") antennas are the most widely used directive antennas at microwave frequencies, but horn antennas, slot antennas and dielectric lens antennas are also used.


C band horn-reflector antennas on the roof of a telephone switching center , U.S. AT&T Long Lines microwave relay network.

Waveguide is used to carry microwaves.

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Dept of EEE, BUET

Microwave Relay linksMicrowave Relay links

• A microwave link is a communication system that uses a beam of radio waves in the microwave frequency range to transmit video, audio, or data between two locations, which can be from just a few feet or meters to several miles or kilometers apart.

• Microwave links are commonly used by television broadcasters to transmit programmes across a country. Mobile units can be camera mounted, allowing cameras the freedom to move around without trailing cables. These are often seen on the touchlines of sports fields on Steadicam systems.

• Properties of microwave links– Involve line of sight (LOS) communication technology– Affected greatly by environmental constraints, including rain fade– Have very limited penetration capabilities through obstacles such as hills, buildings and trees– Sensitive to high pollen count[citation needed]– Signals can be degraded[citation needed]during Solar proton events

• Uses of microwave links– In communications between satellites and base stations– As backbone carriers for cellular systems– In short range indoor communications– Telecommunications, in linking remote and regional telephone exchanges to larger (main)

exchanges without the need for copper/optical fiber lines.


Microwave Sources Microwave Sources

• All warm objects emit low level microwave black-body radiation, depending on their temperature.

• High-power microwave sources use specialized vacuum tubes to generate microwaves. These devices operate using the ballistic motion of electrons in a vacuum under the influence of controlling electric or magnetic fields, and include

– magnetron (used in microwave ovens), – klystron, – traveling-wave tube (TWT), and – gyrotron. These devices work on the basis of clumps of electrons flying ballistically through them, rather than using a continuous stream of electrons.

• Low-power microwave sources use solid-state devices such as the

– field-effect transistor (at least at lower frequencies), – tunnel diodes, Gunn diodes, and IMPATT diodes. Low-power sources are available as benchtop instruments, rackmount instruments, embeddable modules and in card-level formats.

• A maser is a solid state device which amplifies microwaves using similar principles to the laser, which amplifies higher frequency light waves.


Dept of EEE, BUET

KKlystronlystron

• The klystron was the first significantly powerful source of radio waves in the microwave range.

• Before its invention the only sources were the Barkhausen-Kurz tube and split anode magnetron, which were limited to very low power.

• A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range.

• Low-power klystrons are used as oscillators in terrestrial microwave relay communications links, while high-power klystrons are used as output tubes in UHF television transmitters, satellite communication, and radar transmitters, and to generate the drive power for modern particle accelerators.

• In a klystron, an electron beam interacts with radio waves as it passes through resonant cavities, metal boxes along the length of a tube. The electron beam first passes through a cavity to which the input signal is applied. The energy of the electron beam amplifies the signal, and the amplified signal is taken from a cavity at the other end of the tube. The output signal can be coupled back into the input cavity to make an electronic oscillator to generate radio waves. The gain of klystrons can be high, 60 dB (one million) or more, with output power up to tens of megawatts, but the bandwidth is narrow, usually a few percent although it can be up to 10% in some devices.


Two Cavity KlystronsTwo Cavity Klystrons


The first prototype klystron, manufactured by Westinghouse in 1940. On the left are the cathode and accelerating anode, which create the electron beam. In the center between the wooden supports is the drift tube, surrounded by the two donut-shaped cavity resonators, the "buncher" and the "catcher". The output terminal is visible at top. On the right is the cone shaped collector anode, which absorbs the electrons. It could generate 200 W of power at 40 centimeters (750 MHz) with 50% efficiency.

Klystron oscillator from 1944. The electron gun is on the right, the collector on the left. The two cavity resonators are in center, linked by a short coaxial cable to provide positive feedback.

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Reflex KlystronReflex Klystron


Early external cavity klystron tubes developed by Bell Labs. also including cascade types.

Low-power Russian reflex klystron from 1963. The cavity resonator from which the output is taken, is attached to the electrodes labeled Externer Resonator.

Reflex klystrons are almost obsolete now and has been replaced by semiconductor devices.

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Use of KlystronsUse of Klystrons• Klystrons can produce far higher microwave power outputs than solid state

microwave devices such as Gunn diodes.

• In modern systems, they are used from UHF (hundreds of MHz) up through hundreds of GHz (as in the Extended Interaction Klystrons in the CloudSatsatellite).

• Klystrons can be found at work in radar, satellite and wideband high-power communication (very common in television broadcasting and EHF satellite terminals), medicine (radiation oncology), and high-energy physics (particle accelerators and experimental reactors).

• At SLAC, for example, klystrons are routinely employed which have outputs in the range of 50 MW (pulse) and 50 kW (time-averaged) at 2856 MHz.

• The Arecibo Radar uses two klystrons that provide a total power output of 1 MW (continuous) at 2380 MHz.


cloudsat Gunn diodes Arecibo

Large klystrons

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MagnetronsMagnetrons

• The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity resonators).

• Electrons pass by the openings to these cavities and cause radio waves to oscillate within, similar to the way a guitar resonates sound from its sound box via the oscillation of its strings. The frequency of the microwaves produced, the resonant frequency, is determined by the cavities' physical dimensions.

• Unlike other vacuum tubes such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier in order to increase the intensity of an applied microwave signal; the magnetron serves solely as an oscillator, generating a microwave signal from direct current electricity supplied to the vacuum tube.

• An early form of magnetron was invented by H. Gerdien in 1910. Another form of magnetron tube, the split-anode magnetron, was invented by Albert Hull in 1920, but it wasn't capable of high frequencies and was of little use.

• Similar devices were experimented with by many teams through the 1920s and 1930s. However, the more stable klystron was preferred for most German radars during World War II.

• The cavity magnetron tube was later improved by John Randall and Harry Boot in 1940 at the University of Birmingham, England.

• The high power of pulses from their device made centimeter-band radar practical for the Allies of World War II, with shorter wavelength radars allowing detection of smaller objects from smaller antennas. The compact cavity magnetron tube drastically reduced the size of radar sets so that they could be more easily installed in night-fighter aircraft, anti-submarine aircraft and escort ships.


“The “The most valuable cargo ever brought to our most valuable cargo ever brought to our shores,,shores,,

• In 1940, at the University of Birmingham in the United Kingdom, John Randall and Harry Boot produced a working prototype of cavity magnetron. Instead of abandoning the magnetron due to its frequency instability, they sampled the output signal and synchronized their receiver to whatever frequency was actually being generated. In 1941, the problem of frequency instability was solved by coupling ("strapping") alternate cavities within the magnetron.

• Because France had just fallen to the Nazis and Britain had no money to develop the magnetron on a massive scale, Churchill agreed that Sir Henry Tizard should offer the magnetron to the Americans in exchange for their financial and industrial help (the Tizard Mission). An early 10 kW version, built in England by the General Electric Company Research Laboratories, Wembley, London (not to be confused with the similarly named American company General Electric), was given to the US government in September 1940.

• The British magnetron was a thousand times more powerful than the best American transmitter at the time. At the time the most powerful equivalent microwave producer available in the US (a klystron) had a power of only 10W.

• The cavity magnetron was widely used during World War II in microwave radar equipment and is often credited with giving Allied radar a considerable performance advantage over German and Japanese radars, thus directly influencing the outcome of the war. It was later described by the historian James Phinney Baxter III as "[t]he most valuable cargo ever brought to our shores".

• The Bell Telephone Laboratories made a producible version from the magnetron delivered to America by the Tizard Mission, and before the end of 1940, the Radiation Laboratory had been set up on the campus of the Massachusetts Institute of Technology to develop various types of radar using the magnetron.

• By early 1941, portable centimetric airborne radars were being tested in American and British aircraft. In late 1941, the Telecommunications Research Establishment in Great Britain used the magnetron to develop a revolutionary airborne, ground-mapping radar codenamed H2S. The H2S radar was in part developed by Alan Blumlein and Bernard Lovell.


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TizardTizard MissionMission


Henry Thomas Tizard (center), British physicist and head of the Tizard Mission, visits with MIT researchers. The 1940 Tizard Mission introduced to the U.S. the newly invented resonant-cavity magnetron and other British radar developments, and helped establish MIT as a major federally funded research university.

Photo courtesy of the MIT Museum. Read: http://news.mit.edu/2015/how-tizard-mission-paved-way-for-MIT-research-1123

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H2S Radar H2S Radar –– a game changera game changer


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Cavity MagnetronCavity Magnetron

• The great advance in magnetron design was the cavity magnetron or electron-resonance magnetron, which works on entirely different principles. In this design the oscillation is created by the physical shaping of the anode, rather than external circuits or fields.


All cavity magnetrons consist of a heated cathode placed at a high negative potential created by a high-voltage, dc power supply. The cathode is placed in the center of an evacuated, lobed, circular chamber. A magnetic field parallel to the filament is imposed by a permanent magnet. The magnetic field causes the electrons, attracted to the (relatively) positive outer part of the chamber, to spiral outward in a circular path, a consequence of the Lorentz force. Spaced around the rim of the chamber are cylindrical cavities. Slots are cut along the length of the cavities that open into the central, common cavity space. As electrons sweep past these slots, they induce a high-frequency radio field in each resonant cavity, which in turn causes the electrons to bunch into groups. A portion of the radio frequency energy is extracted by a short antenna that is connected to a waveguide (a metal tube, usually of rectangular cross section). The waveguide directs the extracted RF energy to the load, which may be a cooking chamber in a microwave oven or a high-gain antenna in the case of radar. Dept of EEE, BUET

Working PrincipleWorking Principle


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Features of Cavity Magnetron Features of Cavity Magnetron

• The sizes of the cavities determine the resonant frequency, and thereby the frequency of the emitted microwaves. However, the frequency is not precisely controllable. Where precise frequencies are needed, other devices, such as the klystron are used.

• The magnetron is a self-oscillating device requiring no external elements other than a power supply.

• The modern magnetron is a fairly efficient device. In a microwave oven, for instance, a 1.1-kilowatt input will generally create about 700 watts of microwave power, an efficiency of around 65%. (The high-voltage and the properties of the cathode determine the power of a magnetron.) Large S band magnetrons can produce up to 2.5 megawatts peak power with an average power of 3.75 kW. Some large magnetrons are water cooled. The magnetron remains in widespread use in roles which require high power, but where precise control over frequency and phase is unimportant.


Magnetron in a Microwave OvenMagnetron in a Microwave Oven


Watch a video:https://youtu.be/RrOw03gIIQQ

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CutCut--away View away View


Idea FactoriesIdea Factories

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Bell LaboratoriesBell Laboratories


The historic laboratory originated in the late 19th century as the Volta Laboratory and Bureau created by Alexander Graham Bell. Bell Labs was also at one time a division of the American Telephone & Telegraph Company (AT&T Corporation), half-owned through its Western Electric manufacturing subsidiary.Currently named Nokia Bell Labs (formerly named AT&T Bell Laboratories, Bell Telephone Laboratories and Bell Labs) is an American research and scientific development company, owned by Finnish company Nokia. Its headquarters are located in Murray Hill, New Jersey, in addition to other laboratories around the rest of the United States and in other countries.

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Bell and Her LegacyBell and Her Legacy


http://www.beatriceco.com/bti/porticus/bell/longlines_book1.html

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Bell Labs Bell Labs BLuesBLues


Alan White at Bell Labs, working on a red helium-neon laser in a very cluttered laboratory, which captures the place well.


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Bell BuildingsBell Buildings


Bell Laboratories Building in 1936

Bell Labs Holmdel Complex in Holmdel, NJ. Now abondoned.

Bell Laboratories in Murray Hill, New Jersey

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Modern DaysModern Days


https://www.wired.com/2014/09/coupland-bell-labs/

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MITMIT


MIT Radiation Laboratory, Roof laboratory main room, 1941

Building 22 at MIT was constructed to house the Radiation Laboratory during World War II.


BlueBlue LEDLED

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Beginnings, 1900's to 1920'sBeginnings, 1900's to 1920's

• 1907 - Henry J Round, working in Marconi Electronics reports on emission of light from a crystal of silicon carbide when a current was applied to it, a phenomenon called electroluminescence


A 24-line note by Round, H. J. Electr. World, 49, 308 (1907).

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Losev's Radio and 'Light Relay'Losev's Radio and 'Light Relay'


“In the 16 papers published between 1924 and 1930 he provided a comprehensive study of the LED and outlined its applications. Losev understood the ‘cold’ (non-thermal) nature of the emission, measured its current threshold, recognized that LED emission is related to diode action and measured the current–voltage characteristics of the device in detail. He also studied the temperature dependence of the emission down to the temperature of liquefied air (a predominantly nitrogen-based mixture of gases used at the time) and modulated the LED emission up to the frequency of 78.5 kHz by applying an a.c. current to the contact.

From Nikolay Zheludev, Nature Photonics, vol 1, April 2007, pp189-192.

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EElectroluminescence lectroluminescence


Came the SemiconductorsCame the Semiconductors


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The First Transistor 1947The First Transistor 1947


Integrated Circuits by Jack KilbyIntegrated Circuits by Jack Kilby



TThe pnhe pn--junctionjunction


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Forward biased pnForward biased pn--junction as LEDjunction as LED


Blue LEDBlue LED


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Material ConsiderationMaterial Consideration


Nick Holonyak and the GaAsP LEDNick Holonyak and the GaAsP LED

• In 2012, it’s certainly 50 years since Nick Holonyak, working at GEC’s Syracuse, New York facility, developed what is considered the first LED capable of generating visible light. Holonyak’s LED was also the first to be in form ready for commercial usage. He wrote up his work and sent it off to Applied Physics Letters on 17 October 1962. The journal published the work in December 1962 under the headline ‘Coherent (visible) Light Emission from GaAs1-xPx Junctions’.


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New Growth MachinesNew Growth Machines

• In the 1970s, new crystal growth techniques, MBE (Molecular Beam Epitaxy) and MOVPE (Metalorganic Vapour Phase Epitaxy) were developed.


Heterostructures and Quantum WellsHeterostructures and Quantum Wells

• Thanks to the development of heterostructures (Nobel Prize 2000 to Z.I. Alferov and H. Kroemer), and later quantum wells, allowing for a better confinement of the carriers while reducing the losses. The development of infrared LEDs and laser diodes had shown that heterojunctions and quantum wells were essential to achieve high efficiency. In such structures holes and electrons are injected in a small volume where recombination occurs more efficiently and with minimal losses.


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Long Series of BreakthroughsLong Series of Breakthroughs

" Today’s efficient GaN-based LEDs result from a long series of breakthroughs in basic materials physics and crystal growth, in device physics with advanced heterostructure design, and in optical physics for the optimization of the light out-coupling. "


Nobel Prize for Physics 2014Nobel Prize for Physics 2014

• Press Release• 7 October 2014

• The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2014 to

• Isamu AkasakiMeijo University, Nagoya, Japan and Nagoya University, Japan

• Hiroshi AmanoNagoya University, Japan

• Shuji NakamuraUniversity of California, Santa Barbara, CA, USA

• “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources”


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• "“for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources”

• Incandescent light bulbs lit the 20th century; the 21st century will be lit by LED lamps!


Nobel Prize for Physics 2014Nobel Prize for Physics 2014

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White LEDWhite LED

• RGB method

• A mix of red, green and blue LEDs in one module according to the RGB colour model, white light is produced by the proper mixture of red, green and blue light. The RGB white method produces white light by combining the output from red, green and blue LEDs. This is an additive colour method.

• The Phosphor Method

• The Phosphor white method produces white light in a single LED by combining a short wavelength LED such as blue or UV, and a yellow phosphor coating. Phosphor white offers much better colour rendering that RGB white, often on a par with florescent sources.

• Phosphor white light is also much more efficient than RGB white. Because of its superior efficient and colourrendering, phosphor white is the most commonly used method of producing white light with LEDs.


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Efficiency TrendsEfficiency Trends


A Bird's Eye View of LED EventsA Bird's Eye View of LED Events


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A Journey of LightA Journey of Light

• Today, GaN-based LEDs provide the dominant technology for back-illuminated liquid crystal displays in many mobile phones, tablets, laptops, computer monitors, TV screens, etc. Blue and UV-emitting GaN diode lasers are also used in high-density DVDs, which has advanced the technology for storing music, pictures and movies. Future application may include the use of UV-emitting AlGaN/GaN LEDs for water purification, as UV light destroys the DNA of bacteria, viruses and microorganisms. In countries with insufficient or non-existent electricity grids, the electricity from solar panels stored in batteries during daylight, powers white LEDs at night.


“ We witness a direct transition from kerosene lamps to white LEDs. ”


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LED ApplicationsLED Applications

• LED is mainly used in these fields:

1. Indoor residential lighting.2. Commercial and office building lighting.3. Hard to reach areas like: high ceiling and central dome area.4. 24-hours full time operation facilities like: store, mart, underground parking lot, elevator etc.5. Subway and tunnel area.6. High risk of fire area like: gas station and fuel depot.7. Vessel and shore operation area.8. Food production facilities and exhibition space.9. Clean room environment with air pollution control like: semiconductor manufacturing facilities.10. Need to block harmful UV lights area like: museums and art center.11. High-tech devices display area.12. Area requires long-term light exposure like: schools and libraries.


http://www.bestlightingbuy.com/led-applications.html

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ApplicationsApplications

• Illumination technology is presently going through a revolution, namely the transition from light bulbs and fluorescent tubes to LEDs.

• The light bulb, invented by Thomas Edison in 1879, has a low efficiency ≈16 lm/W , approximately 4% energy efficiency from electricity into light.

• A lumen is a unit used to characterize the light flux, which takes into account the eye's spectral response.

• The fluorescent tube, containing mercury and invented by P. Cooper Hewitt in 1900, reaches an efficiency of 70 lm/W.

• White LEDs currently reach more than 300 lm/W, representing more than 50% wallplug efficiency. White LEDs used for lighting are often based on efficient blue LEDs that excite a phosphor so that the blue light is converted to white light. These high-quality LEDs with their very long lifetime (100 000 hours) are getting cheaper, and the market is currently exploding. A little further on in the future, three-colour LEDs may replace the combination of blue LED and phosphor for efficient lighting.

• Replacing light bulbs and fluorescent tubes with LEDs will lead to a drastic reduction of electricity requirements for lighting. Since 20-30% of the electricity consumed in industrial economies is used for lighting, considerable efforts are presently being devoted to replacing old lighting technologies with LEDs.


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Usage TrendsUsage Trends


SourcesSources

– www.nobelprize.org

– http://www.bbc.com/news/technology-19886534


http://www.priyo.com/2014/10/20/113973.html

��র Mon, 20/10/2014


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