electromagnetic waves - hong kong polytechnic...
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Electromagnetic Waves
Electromagnetic waves are transverse waves that have some electrical and magnetic properties. They do not need a medium, matter, to travel through.Electromagnetic waves transfer energy by means of changing electric and magnetic fields.
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Speed of Light
c = f λWavelength (m)
Frequency (Hz)
Speed of light3 x 108 m/sec
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Electromagnetic Spectrum
The electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.
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Radio WavesLongest wavelength EM wavesApplications:
TV broadcasting AM and FM broadcast radioWireless control Heart rate monitorsCordless phone communication
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Microwaves Wavelengths from 1 mm - 1 mApplications:
Microwave ovens Bluetooth headsets Wi-FiRadar GPS
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Infrared Radiation
Wavelengths in between microwaves and visible lightApplications:
Night vision gogglesRemote controlsThermographs
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IR Emission from a Cold-blooded Lizard
Optical Image Far-Infrared Image
“Room Temperature”
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Electrical Work
One of the conductor terminals is hot. Hot Terminal Temperature…..203FLeft Terminal Temperature….156FTemperature difference is …… 47F
癋119.7
癋179.5
120
140
160
AR01
SP01
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Visible spectrum
Visible Spectrum
Prism
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RedOrangeYellowGreen Blue Indigo Violet
Colour Spectrum
lowest frequency
highest frequency
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Eye Sensitivity to Colour
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Ultraviolet
Shorter wavelengths than visible lightApplications:
Sterilizing medical equipmentWater disinfectionSecurity images on money
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X-rays
Tiny wavelength, high energy wavesApplications:
Medical imagingAirport securityInspecting industrial welds
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Illumination Level
Summer shade10000-15000
Full moon:0.5
Cloudy25000
Sunny50000-100000
Lux
Office400-500
Workshop300-1000
Warehouse125-300
Studio2000
Shop500-1000
Flat200
Street20-70
20 lux 2000 luxArtificial light
Natural light
> Technical Appendix
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Commonly used Lighting Sources
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Incandescent Lamp
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Colour Temperature
Object
YouHeat LampCandle FlameBulb FilamentSun’s Surface
Temperature
~ 30 C ≈ 300 K~ 500 C ≈ 770 K
~ 1700 C ≈ 2000 K~ 2500 C ≈ 2800 K~ 5500 C ≈ 5800 K
Colour
Infrared (invisible)Dull redDim orangeYellowBrilliant white
The hotter it gets, the “bluer” the emitted lightThe hotter it gets, the more intense the radiation
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Colour TemperatureThis is a measurement of "warmth" or "coolness" provided by the lamp.People usually prefer a warmer source in lower illuminance areas, such as dining areas and living rooms, and a cooler source in higher illuminance areas, such as grocery stores. Colour temperature refers to the colour of a blackbody radiator at a given absolute temperature, expressed in Kelvin.A blackbody radiator changes colour as its temperature increases ( first to red, then to orange, yellow, and finally bluish white at the highest temperature.A "warm" colour light source actually has a lower colour temperature. For example, a cool-white fluorescent lamp appears bluish in colour with a colour temperature of around 4100 K. A warmer fluorescent lamp appears more yellowish with a colour temperature around 3000 K.
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Problems with Thermal Light
Temperature too low, too redIncandescent light bulb, 2500°CThe sun, 5800°C
Not energy efficientLots of invisible infrared lightOnly a small fraction of thermal power is visible
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Incandescent Lamp1879 (Thomas Edison) Lamp power: 15 to 1000 W Light Output: up to 15,000 lumensClass G to E: Europe has decided to remove these lights from the EU market before 2012
E27 (ES) E14(SES)B22 (BC)
S14S15 S19
Efficiency: Lifetime: Output (lm): Colour: On/off : FrequentControl: Direct
Advantages
Bright point light source (if transparent glass)
Disadvantages
Energy-guzzler – very low efficiency(E, F or G-class)
Full compatibility with existing luminaries Risks due to high operating temperature
Full dimmable on any dimmer
Good quality and performance
Short lifetime (1000 hours)
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Photon Absorption and Emission
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Emission Colours of Various Gases
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The fluorescent lamp produces light by the passage of an electric current flowing through a vapor of mercury.
1.Electron emitted from electrode collides with mercury atom.2.Impact produces ultraviolet rays3.Phosphor converts ultraviolet to visible light.
This process is known as “fluorescence,” hence the name fluorescent lamp.
Fluorescent Lamp
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Fluorescent Light
Bulb Wall
Phosphor
UV
Mercury
Electricity
Visible Light
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Phosphors
A mercury lamp emits mostly invisible UV lightTo convert its UV light to visible, use a phosphorPhosphors absorb photons and reemit new photonsNew photon energy is less than old photon energyFluorescent lamps → phosphors emit white light
(De luxe) warm white, (de luxe) cool white phosphors
Specialty lamps → phosphors emit colored lightBlue, green, yellow, orange, red, violet, etc.
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Fluorescent Tubes
The most frequently used!Accept frequent On/Off switchingLamp power: 4 to 140 W, light output up to 14000 LumensLifetime of fluorescent tubes depends on daily On / Off frequency and type of ballastSeveral types of fixtures according to use: 3m to 12m height (high efficiency), hanging, surface or flush mounted, single, twin or multiple tube fixture, IP 65 version...
> Overview of building lighting
T12(40-65lm/W)
T8(80-95 lm/W)
T5(95-105 lm/W)
38mm26mm 16mm
Lighting/consumption: Lifetime: Output: Colour:
On/off: FrequentControl: BallastDimmable: Yes
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THE BULB•Most fluorescent lamps are made in straight tubular bulbs in various diameters.
•Circline lamps are in the form of a circle.
•U-Bent lamps are essentially straight lamps bent to form a U shape.
Elements of a Fluorescent Lamp
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Elements of a Fluorescent Lamp
THE ELECTRODES•Coiled tungsten wires coated with an emission material•When heated, emit electrons•Electrons bombard mercury atoms producing ultraviolet rays.
THE PHOSHPORSPhosphors are the coated powders on the inside of the bulb that convert the
ultraviolet rays to visible light. There are two basic types:• Halophosphates• Trichromatics or Triband Phosphors
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BallastsAll fluorescent lamps require a ballast for starting and operation. The ballast has two basic functions:•Limit the lamp’s operating current•Provide the required voltage to start the lampLIMITING THE CURRENT•When a fluorescent lamp is started, its resistance to the current flow decreases dramatically.•If not controlled, the current would increase rapidly and destroy the lamp virtually instantaneously.•The ballast limits the current.
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Fluorescent lamp that is small in size (~2 in. diameter, 3 to 5 in. in length).Developed as replacement for incandescent lamps.Two Main Types
Ballast-integrated.Ballast non-integrated (allows only lamp to be replaced).
Compact Fluorescent Lamps (CFLs)
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Use ¼ the power of an incandescent for an equivalent amount of light. (an 18-watt CFL is equivalent to a 75-watt incandescent.)
10,000 hour life. (10 times an incandescent).
Compact Fluorescent Lamps (CFLs)
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Control Circuits For Fluorescent Tubes
Electronic ballast
Please note: Most Compact Fluorescent Lamps (CFL) have an electronic ballast built into the base
● Magnetic ballast
or
Dimmable
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Light-emitting diodes (LEDs)
Very long lifetimeQuickly emerging technology with recent progress in efficiency For room lighting, only in the first phases of commercialisation and rarely meets all consumer expectations in terms of light output and other functions. Likely to become true alternative to CFLs very rapidly.Electric power: 0.05-0.1 W (1 LED) to several Watts (LED array), Light Output: a few Lumens (1 LED) to thousands lm (LED array)
G10G5.3
E27 E14
● Main use: Traffic lights, signalling / display boards, decoration spotlights, portable or isolated ELV DC lighting (battery, photovoltaic), etc.
> Overview of home & small office lighting
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Silicon
Semiconductors
Adding a very small amount of P or As to Si makes an n-type semi-conductor with an extra electron
Adding a very small amount of B or Ga to Si makes a p-type semi-conductor with a missing electron (a hole)
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N-type Semiconductor
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P-type Semiconductor
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P-N Junction
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Reverse Biased
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Forward Biased
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Ideal CharacteristicsBias conditionsForward bias : vd > 0 — current can flow and id > 0.Reverse bias : vd < 0 — current cannot flow and id = 0.
vd
id
vd
id
0.7 V
with finite forward drop(more realistic)
Ideal diode
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Getting DC out of ACAC provides a means for us to distribute electrical power, but most devices actually want DC
bulbs, toasters, heaters, fans don’t care: plug straight insophisticated devices care because they require a certain polarity
rather than oscillating polarity derived from ACthis is why battery orientation matters in most electronics
Use diodes to “rectify” AC signalSimplest rectifier uses one diode:
AC source load
input voltage
voltage seen by loaddiode only conductswhen input voltage is positive
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Full-wave Rectifier
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Smoothing OutStill a bumpy ride, but we can smooth this out with a capacitor
capacitors have capacity for storing chargeacts like a reservoir to supply current during low spotsvoltage regulator smoothes out remaining ripple
A
C
B
D
AC source
load
capacitor
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LEDsMain difference is material is more exotic than silicon used in ordinary diodes/transistors
typically 2-volt drop instead of 0.7 V drop (3.6V for blue LED)When electron flows through LED, loses energy by emitting a photon of light rather than vibrating lattice (heat)Anything with an LED cares about the battery orientation (it’s still a diode, after all)LED efficiency is over 30% (compare to incandescent bulb at 10%)
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LED Materials
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LED ConstructionAn LED is a semiconductor device that converts electrical energy directly into a discrete colour of lightThe diode is made from different materials and substratesLEDs are made in chip fabrication factories. White LEDs are blue LEDs plus phosphor
Wire Bond
Anode Lead
Cathode Lead
Epoxy Case
Epoxy LensSemiconductor Diode
Reflective Cup
©2004 Color Kinetics Incorporated
Sapphire Substrate
GaP Base
N-type GaP:N etc...
P-type GaP: N etc… +- Yellow phosphor coating
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Dot matrixStarburst7-segmentBargraph
Some Types of LEDs
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Incandescent
Fluorescent
Source: Lumileds
Lum
inou
s Ef
ficie
ncy
(lum
ens
/ wat
t)
Halogen
LED
White LED
Reflector
0
50
100
150
200
1920 1940 1960 1980 2000 2020
LED Efficiency Trends
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Monochrome IndicatorsTraffic lights, automotive, exit signs etcPortable appliances, cell phones, PDAsSignageDirect view displays; video screens
Emerging ApplicationsTransportation: marine, auto, aviation etcLighting niches
FutureGeneral Illumination
©2004 Color Kinetics Incorporated
LED Applications
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LED Replacement for a 4-ft. Fluorescent Lamp
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Hard Rock Hotel & Casino, Las Vegas
•Energy Costs
•Previous metal halide fixtures about $18,000/yr.
•The LED-based units projected to draw about $1,900/yr.
•Maintenance Costs
•Previous fixtures $25K/yr (plus filters and ballasts)
•LED-based units: $600/yr
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Missouri Theater, St. Joseph, MO
•Lighting designer originally considered neon for this architectural/ceiling application.
•Neon required too much power for the existing wiring system.
•400+ LED-based fixtures installed using existing wiring.
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History of Microwave Heating Cooking food with microwaves was discovered by Percy Spencer while he was building magnetrons for radar sets with the company Raytheon. He was working on an active radar set when he noticed that a peanut chocolate bar he had in his pocket started to melt. The radar had melted his candy bar with microwaves.The first food to be deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.On October 8, 1945 Raytheon filed a U.S. patent for Spencer's microwave cooking process and an oven that heated food using microwave energy was placed in a Boston restaurant for testing.
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What are Microwaves?
Microwaves are a form of electromagnetic energy, like light waves or radio waves
Microwaves are used extensively in telecommunications
Good for transmitting information because it can penetrate haze, light rain and snow, clouds, and smoke.
Also used in radars and in detecting speeding cars.
Microwave has become most familiar as the energy source for cooking food.
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Water Molecules
Water molecules are unusually polarAn electric field orients water moleculesA fluctuating electric field causes water molecules to fluctuate in orientation
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Microwave HeatingMicrowave means time-varying electric fieldAs electric field changes direction, water flips back and forth: they can’t help it
oscillating electric field
time
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Microwave Heating
Microwaves have fluctuating electric fieldsWater molecules orient back and forthLiquid water heats due to molecular “friction”Ice doesn’t heat due to orientational stiffnessSteam doesn’t heat due to lack of “friction”Food’s liquid water content heats the food
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At 2.45 GHz, microwaves penetrate into food (looks partially transparent) and excite water molecules internally
2.45 GHz is a good compromise: lower frequency would not be readily absorbed (food too transparent); higher frequency would not penetrate well, heating the outside (food too opaque)
Ideally, food cooks uniformly throughouteliminating restriction of thermal diffusion timeexcept for ice, which isn’t warmed by microwaves
Still, cold spots can develop if radiation pattern is not uniformmicrowaves are reflected by walls, and set up standing-wave interference patterns leaving hot spots and cold spotshelps to rotate food through this stationary radiation pattern
Microwave Heating
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Generating MicrowavesMagnetron tube has tank circuits in itStreams of electrons amplify tank oscillationsA loop of wire extracts energy from tanksA short ¼-wave antenna emits the microwaves
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Microwave Oven
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Microwave Oven
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Efficiency of Microwave HeatingA microwave oven converts only part of its electrical input into microwave energy.A typical consumer microwave oven consumes 1100 W of electricity in producing 700 W of microwave power, an efficiency of 64%.The other 400 W are dissipated as heat, mostly in the magnetron tube. Additional power is used to operate the lamps, AC power transformer, magnetron cooling fan, food turntable motor and the control circuits. This waste heat, along with heat from the food, is exhausted as warm air through cooling vents.
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Health Hazards
It is known that microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn
the lens of the eye ~ exposure to high levels of microwaves can cause cataracts.
Microwave oven used low level of microwaves, within the region of non-ionizing radiationStill uncertain in the effects of humans from long term exposure to low level of microwaves
Still experimentingBest to stay a way (an arm’s length) in reducing exposure to microwaves
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Induction Cooker
The water in the metal pot is boiling. Yet, the water in the glass pot is not boiling, and the stove top is cool to the touch.
The stove operates in this way by using electromagnetic induction.
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AC Coil Example
220 volts at 50 Hz is applied to the coil.
The changing magnetic field induces a voltage in the coil which is sufficient to light the bulb if it is close enough.
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Inductive Charging
BB
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Generation of Eddy CurrentsWhen an electrically conductive material is placed in the coil’s dynamic magnetic field electromagnetic, induction will occur and eddy currents will be induced in the material.
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Metal Detector
A pulsing current is applied to the coil, which then induces a magnetic field shown in blue. When the magnetic field of the coil moves across metal, such as the coin in this illustration, the field induces electric currents (called eddy currents) in the coin. The eddy currents induce their own magnetic field, shown in red, which generates an opposite current in the coil, which induces a signal indicating the presence of metal. A metal detector can also be used to detect mines buried underground.
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Induction Cooker
The induction cooker uses coils of wire with high frequency AC to produce large eddy currents in the metal cooking pot placing above. The heating effect of the eddy current cooks the food.Moreover, since eddy current is not induced in its plastic case which is made up of non-metallic material, the cooker is not hot to touch.
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Induction Cooker
The induction coil is installed underneath the ceramic glass. The coil is energised by a frequency converter that converts mains power into higher-frequency alternating current. This generates an electromagnetic alternating field (with a frequency between 20,000Hz and 30,000Hz) that penetrates the ceramic glass and concatenates with the ferromagnetic bottom of the pan. This magnetic field produces heat generating eddy current into the bottom of the pans.The food in the pots heats up for Joule effect.
A pot above the induction coil can be regarded as the secondary of a transformer
Inverter/user interface
coil
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induction compatible cookware
non-induction compatible
enamel cast iron stainless steel FAGORcookware
copper glass aluminum
Induction Cooker
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* Melting chocolate without using a double boileris only possible with induction
Wide Range of Power Options
50 Watts 3600 Watts
gentle heat* simmer
deep fry
sautégrill
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safer: there are no open flames and the surface remains cool to the touch
quicker: heating and adjustments are immediate, saving you up to 50% of the cooking time when compared to more traditional methods
even heating: hot spots and rings are avoided because the bottom of your cookware heats uniformly
easy cleaning: the surface is flat and smooth; spills and overflows do not stick to the cooktop, so they can easily be wiped away
Induction Cooker
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Resistive Heating: Coffee Maker
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Radio FrequenciesA radio wave is an electromagnetic wave propagated by an antenna.Radio waves have different frequencies and by tuning a radio receiver to a specific frequency, you can pick up a specific signal.
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Radio Frequencies
Frequency Band10 kHz to 30 kHz Very Low Frequency (VLF)30 kHz to 300 kHz Low Frequency (LF)300 kHz to 3 MHz Medium Frequency (MF)3 MHz to 30 MHz High Frequency (HF)30 MHz to 328.6 MHz Very High Frequency (VHF)328.6 MHz to 2.9 GHz Ultra High Frequency (UHF)2.9 GHz to 30 GHz Super High Frequency (SHF)30 GHz and above Extremely High Frequency (EHF)
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Production of Electromagnetic Waves
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Dipole Antenna
Transmission of TV and RadioTransmitter: wire half a wavelengthPushes electrons back and forthReceiver: wire half a wavelength
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Reception of Radio Waves Receiving antenna works best
when ‘tuned’ to the wavelength of the signal, and
has proper polarizationB
E
Optimum antenna length is λ/4: one-quarter wavelength
Electrons in antenna are “jiggled”by passage of electromagnetic wave
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More on AntennasOften radio stations use extremely tall antenna towers to transmit their signals.Antenna at radio transmitter: launch radio signals into space.Antenna at radio receiver: pick up as much of the transmitter’s power as possible and feed it to the tuner.
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Modulation
If you have a sine wave and a transmitter that is transmitting the sine wave into space using an antenna (more antennas later), you have a radio station.
Problem with plain sine wave: does not contain information.
Sine wave has to modulated in some way so that it contains information, e.g., voice message.
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Modulation Method
Amplitude Modulation (AM): Amplitude (peak-to-peak voltage) of sine wave is changed so as to contain information.
AM radio stations and picture part of TV signals use amplitude modulation to encode information signal.
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AM Broadcasting
AM was the dominant method of broadcasting during the first eighty years of the 20th century and remains widely used into the 21st.AM radio began with the first, experimental broadcast in 1906 by Reginald Fessenden, and was used for small-scale voice and music broadcasts up until World War I.AM radio technology is simpler than FM radio. An AM receiver detects amplitude variations in the radio waves at a particular frequency. It then amplifies changes in the signal voltage to drive a loudspeaker or earphones. AM radio is broadcast on several frequency bands: Long wave, Medium wave, Short wave.Because of its susceptibility to atmospheric and electrical interference and the generally lower sound fidelity of super-heterodyne receivers, AM broadcasting has attracted mostly talk radio and news programming, while music radio and public radio mostly shifted to FM broadcasting.
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AM Radio in Practice
Uses frequency range from 535 kHz to 1700 kHzeach station uses 9 kHzspacing is 10 kHz (a little breathing room) → 117 channels9 kHz of bandwidth means 4.5 kHz is highest audio frequency that can be encoded
falls short of 20 kHz capability of human ear
Audio signal changes slowly with respect to radio carriertypical speech sound of 500 Hz varies 1000 times slower than carrierthus will see 1000 cycles of carrier to every one cycle of audio
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AM Modulation Example
Car radio is tuned to radio station, say 880 AM. Transmitter’s sine wave is transmitting at 880,000 Hz (sine wave repeats 880,000 times per second).DJ’s voice is modulated onto sine wave, i.e., amplitude of sine wave is varied as DJ’s voice varies.A power amplifier magnifies power of modulated sinewave, e.g., to 50,000 Watts for a large AM station. Antenna then sends radio waves into space. High power amplification helps waves travel large distances.
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Transmitter Description
Information(voice message)
Combine
SineWave
Radio Transmitter
Antenna
Radio Waves
Transmitter generates its own sine wave using oscillators.
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AM ReceptionTuners operate using a principle called resonance. That is, tuners resonate at and amplify one particular frequency and ignore all other frequencies in the air.
After tuning in, radio receiver has to extract the DJ’s voice signal from the sine waves.
This is done using a demodulator (aka detector).
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Receiver Description
Separate
Sine Wave
Radio Transmitter
Antenna
Information(voice message)
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Frequency Modulation (FM): Radio transmitter changes frequency of sine wave according to information signal.
Frequency modulation is most popular. Used by FM radio stations, sound part of TV signal, cordless phones, etc.
Modulation Method
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FM Broadcasting
FM broadcasting is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio.Throughout the world, the broadcast band is 87.5 to 108.0 MHz (i.e. in the VHF range). The frequency of an FM broadcast station (more strictly its assigned nominal centre frequency) is usually an exact multiple of 100 kHz.For FM stereo, the maximum distance covered is significantly reduced. This is due to the presence of the 38 kHz subcarrier modulation. Vigorous audio processing improves the coverage area of an FM stereo station.Despite having been developed in 1933, FM broadcasting took a long time to be adopted by the majority of radio listeners.The first FM broadcasting stations were in the United States, but initially they were primarily used to broadcast classical music to an upmarket listenership in urban areas and for educational programming. By the late 1960s FM had been adopted by fans of "alternative rock" music, but it wasn't until 1978 (the first year that listenership to FM stations exceeded that of AM stations) that FM became mainstream.
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FM Radio in PracticeSpans 87.8 MHz to 108.0 MHz in 200 kHz intervals
101 possible stationsexample: 91X runs from 91.0–91.2 MHz (centered at 91.1)
Nominally uses 150 kHz around center75 kHz on each side30 kHz for L + R (mono) → 15 kHz audio capability30 kHz offset for stereo difference signal (L - R)
75 kHz from band center, modulation is slower than carrier, so many cycles go by before frequency noticeably changes
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AM vs. FM
FM is not inherently higher frequency than AMthese are just choicesaviation band is 108–136 MHz uses AM technique
Besides the greater bandwidth (leading to stereo and higher audio frequencies), FM is superior in immunity to environmental influences
there are lots of ways to mess with an EM-wave’s amplitudepass under a bridgere-orient the antenna
no natural processes mess with the frequency
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Digital Audio Broadcasting
Digital Audio Broadcasting (DAB) is a digital radio technology used in several countries for broadcasting radio stations. Particularly used in Europe, the DAB standard was initiated as aEuropean research project and was launched by BBC in 1995.DAB technology offers more radio programs when compared to analogue FM radio. It is more effective with regard to noise andmultipath fading for mobile listening.Digital audio broadcasting offers several benefits over analoguesystems that include improved end-user features, lower cost, more stations, better reception quality, less pirate interference andvariable bandwidth.
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Analog audioAnalog audiosignalsignal
DataData
Signal Processor
A/D Converter
A/D Converter
Single FrequencyNetwork
The quick brown fox jumps right over the lazy dog tail
Digital Audio SignalDigital Audio Signal
Digital Audio Broadcasting
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FM vs. DAB
FM DAB
Sound Quality Long Playing Record Near CD
Mobile Reception
Slightly Interfered
Interference free
Network Frequency
Multi-frequencies
Single Frequency
Image Broadcasting
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Benefits of using DAB
No tuning anymoreRadio 1 : 92.6 ~ 94.4MHzRadio 2 : 94.8 ~ 96.9MHzRadio 4 : 97.6 ~ 98.9MHz
88 108
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Benefits of using DAB
Interference free mobile reception
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DAB’s capability:
Enhanced service and better Enhanced service and better sound quality for sound quality for audienceaudience
New market for the New market for the media sectormedia sector
AudioAudio + + DataData = = DDigital igital AAudio udio BBroadcastingroadcasting
FMFM DABDAB
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The DAB system in HK
Digital Audio Broadcasting Steering Committee
80 88 90 94 97 98 99
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FM Station
AM Station
Castle Peak
CloudyHill
GoldenHill
BeaconHill
KowloonPeak
MountGough
LammaIsland
PengChau
Transmitter Site Map
DAB Station
Beacon Hill
Mt. Gough
Transmitter Site Map
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Internet RadioInternet radio is essentially the same as regularly broadcast radio, with a few distinguishing characteristics.Internet radio is streamed, and so does not involve downloading. You simply log on to the particular site and in it comes.Several formats are on offer, but the MP3 and ACC formats are currently the most frequently used.www.livme365.com, www.radiotower.com, MyOpusRadio.com,RadioJoyAlukkas.com
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Analog Television TerrestrialBroadcasting Standards
Abbrev Name Main Geographic UsePAL Phase Alternating Line Most of Europe, Australia, Parts
of Asia (including India & China), Most of Africa, Eastern South America
NTSC National Television System Committee
North & Central America, Western South America, Japan, Philippines, Thailand, Taiwan, South Korea
SECAM Sequential Color with Memory
France, Russia & former Soviet republics, portions of Africa, Madagascar
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Analog TV Standards Worldwide
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NTSC Television Broadcasting50-890 MHz (6 MHz Channels)FM Audio, AM (SSB) Video525 Lines @ 30 Frames / secondInterlacing (Alternating Lines)Synch PulsesLuminance / Chrominance
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Frequency AllocationTV channels require 6 MHz of bandwidth each
2, 3, 4 cover 54–72 MHz5, 6 cover 76–88 MHz7–13 cover 174–216 MHz14–83 cover 470–890 MHz (UHF)
Amplitude modulation (AM) + all kinds of sneaky trickshad to add on color after-the-factbasically treat video signal as waveform, and AM accordinglyaudio is FM (Frequency Modulation), however
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TV Receiver
The electronic signal is decoded by the receiver; splitting the FM wave to the audio section and the AM wave to the video section of the television.http://www.howstuffworks.com/tv.htm
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TV Signal• In a black-and-white TV, the
screen is coated with white phosphor and the electron beam "paints" an image onto the screen by moving the electron beam across the phosphor a line at a time.
•To "paint" the entire screen, electronic circuits inside the TV use the magnetic coils to move the electron beam in a "raster scan" pattern across and down the screen. The beam paints one line across the screen from left to right. It then quickly flies back to the left side, moves down slightly and paints another horizontal line, and so on down the screen, like this:
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The video signal tells the TV how and when to sweep
Every 63.5 μs, get a signal to start a new line (5 μs dip)called horizontal sync
At bottom of screen, get 400 μs dip to signal arrival at bottomcalled vertical sync
In between is brightness information:E.g., 2 V means white, 0.5 V means black
TV signal
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Making ColourSo far we can paint black and white pictures (actually grayscale) by varying brightnessGenerating colour requires three tricks:
use coloured phosphors (red, green, blue) instead of just whiteuse three separate electron guns, one for each colormask the phosphor screen so that the green gun can only hit green phosphor, etc.
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Colour TV Screen
• A colour TV screen differs from a black-and-white screen in three ways: • Three electron beams (Red, Green, Blue)that
move simultaneously across the screen. • The screen is coated with red, green and blue
phosphors arranged in dots or stripes. • On the inside of the tube, very close to the
phosphor coating, there is a thin metal screen called a shadow mask. This mask is perforated with very small holes that are aligned with the phosphor dots (or stripes) on the screen.
Components of a CRT Monitor
Electron GunsThree electron guns locatedat the back of the monitor’s cathode-ray tube send out three electron beamsfor each of the primary colors.
Magnetic Deflection YokeThis mechanism uses electromagneticfields to bend the paths of the electronstreams.
Shadow MaskThe beams pass through holes in a metal plate called a shadow mask. The mask keeps the electron beams precisely aligned, so that colors are accurate. The monitor’s dot pitch is a measure of how closely the holes are spaced apart.
Phosphor CoatingThe phosphor coating is a material that glows when struck by an electronbeam. The screen is made up of triads of red, green, and blue phosphor dots. As the energy in the electron beam increases, the phosphor dots glow brighter. To create different colors, the intensity of each of the three beams is varied.
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Liquid Crystal Displays (LCDs)
LCD displays use totally different technologyLCD is backlit with fluorescent tubes (usually around side)each pixel “addressed” with horizontal conductor on back, transparent vertical on front, forming matrix of connectivityamount of current through pixel determines its brightnessfilters in front of R, G, B pixels create coloreach pixel usually has own transistor (TFT on glass!) and capacitor to switch and hold charge
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What is a plasma : fourth state of Matter
Increasing Temperature
A plasma is electrically conducting and very reactive
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Plasma Display
Note the patterns of the address and display electrodes To excite an address, both voltages must be applied
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Fujitsu ALIS display More complex electrodes but better use of surface area for display
Plasma Display
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Analogue SatelliteTelevision
AnalogueTerrestrialTelevision
Television
Analogue Broadcasting
AnalogueCableTelevision
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Digital Television Worldwide
Worldwide, terrestrial TV broadcasts are switching from analog to digital modulation
Different countries have different schedules for switching over (most by 2015)Some satellite TV broadcasting has been digital for more than 15 years
Japan is deploying ISDB-T technology, replacing NTSC and analog HDTV MUSE standards
ISDB-T also being widely deployed in South AmericaNorth America is deploying ATSC digital TV to replace NTSC analog standard
U.S. digital transition is completed for “full-service” broadcasts; legacy NTSC remains for low-power stations
Australia and Europe are deploying DVB-TChina is rolling its own (DMB-T)
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Digital TV Terrestrial Broadcasting Standards
Abbrev NameOver-the-Air Modulation Type
Main Geographic Use
DVB-T Digital Video Broadcasting –Terrestrial
Coded Orthogonal Frequency Division Multiplexing (COFDM) (QPSK, 16QAM, and 64QAM)
Europe, Russia, Australia, Parts of Asia
ISDB-T Integrated Services Digital Broadcasting -Terrestrial
Coded Orthogonal Frequency Division Multiplexing (COFDM) (DQPSK, QPSK, 16QAM, and 64QAM)
Japan, South America (ISDB-T International)
ATSC Advanced Television Systems Committee
8-level Vestigial Sideband (8VSB)
North America, South Korea
DMB-T/H Digital Multimedia Broadcast –Terrestrial/Handheld
Time Domain Synchronous Orthogonal Frequency Division Multiplexing (TDS-OFDM)
China only
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Digital TV Standards Worldwide
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Production
STB
TV
Receive Digital TV with Analogue TV
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Digital Terrestrial TelevisionFeatures
Spectrum Efficiency
Multi-channel Capability
Immunity to Disturbance
Portable & Mobile TV
Enhanced services (such as Electronic Programme Guide)
Lower Power Operation
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Digital Terrestrial Television
Received signal quality affected by environment
Excellent signal qualityRobust reception
ANALOGUE DIGITALFeatures - Immunity to Disturbance
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DTT Supports High Definition Television
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DTT Supports Multi-channel Programmes and Multimedia Contents
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DTT Supports Reception by Mobile / Portable Devices
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Broadcast Development in HK
TV on Cable andSatellite,
MUSE analog HD
1960 1970 1980 1990 2000
DABTV
• DTT/ HDTV• IPTV• Mobile TV
(T-DMB, DVB-H, MediaFLO, One Seg)
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TV - IPTV
(Internet Protocol TV)
Use of Internet Protocol (IP) for home TV transmission, can be over phone lines, via optical fibre trunks.
Flexibility of including interactive services and HDTV. Offers many TV channels, viewer-targeting.
For HDTV, application of MPEG4 AVC (H.264)/ VC-1 (WMV) coding, VDSL2/ ADSL2+ technologies or Fibre to the Home/ Building (FTTH/ FTTB).
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Broadcast to hand-sets (mobile phones, PDAs), notebook PCs, etc. Interactive and audio services.
T-DMB (Terrestrial-DMB)Evolved from DAB. Allows video, audio and data to be transmitted to mobile devices. More efficient audio coding. Backward compatible with DAB audio (MUSICAM).
DVB-H (Digital Video Broadcasting – Handheld)Tailored for transmitting multiple TV channels to mobile devices. Time-slicing technology conserves battery power of mobile devices.
Mobile TV
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FCC and Frequency BandsIn the U.S., the Federal Communications Commission (FCC) who is able to use which frequencies for which purposes.
It issues licenses to stations for specific frequencies.
For example, AM radio stations must use frequencies in 535 kHz to 1.7 MHz band.
FM radio stations transmit in band of frequencies from 88 MHz to 108 MHz.
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US Frequency Allocation – the FCC
(300 MHz has a wavelength of 1 meter)
“Radio” frequency-space is allocated to the hilt!Here’s a sample region from 300–600 MHz
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Frequency Allocation