ENGLISH ASSIGNMENT ABOUT
“MICROWAVES”
CREATED BY:
1.
Fathria
Nurul Fadillah
2.
Hani
Marta Putri
3.
Herlina
Fitri Handayani
4.
Yuris
Ramadhona
Class : 2TEA
Lecturer : Yusri,S.Pd,.M.Pd
STATE POLYTECHNIC OF SRIWIJAYA
PALEMBANG
2016
MICROWAVES
a. Definition
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). This broad
definition includes both UHF and EHF (millimeter waves), and various
sources use different boundaries. In all cases, microwave includes the
entire SHF band (3
to 30 GHz, or 10 to 1 cm) at minimum, with RF engineeringoften
restricting the range between 1 and 100 GHz (300 and 3 mm).
The prefix micro- in microwave is
not meant to suggest a wavelength in the micrometer range. It indicates that
microwaves are "small", compared to waves used in typical radio
broadcasting, in that they have shorter wavelengths. The boundaries
between far infrared, terahertz
radiation, microwaves, and ultra-high-frequency radio waves are
fairly arbitrary and are used variously between different fields of study.
Beginning at about 40 GHz, the atmosphere becomes less transparent to
microwaves, at lower frequencies to absorption from
water vapor and at higher frequencies from oxygen. A spectral band structure
causes absorption peaks at specific frequencies (see graph at right). Above
100 GHz, the absorption of electromagnetic radiation by Earth's atmosphere
is so great that it is in effect opaque, until the
atmosphere becomes transparent again in the so-called infrared and optical window frequency
ranges.
The term microwave also has a more technical meaning
in electromagnetics and circuit theory. Apparatus and
techniques may be described qualitatively as "microwave" when the
frequencies used are high enough that wavelengths of signals are roughly the
same as the dimensions of the equipment, so that lumped-element
circuit theory is inaccurate. As a consequence, practical
microwave technique tends to move away from the discrete resistors, capacitors, and inductors used with
lower-frequency radio waves.
Instead, distributed
circuit elements and transmission-line theory are more useful
methods for design and analysis. Open-wire and coaxial transmission lines used at
lower frequencies are replaced by waveguides and stripline, and
lumped-element tuned circuits are replaced by cavity resonatorsor resonant
lines. In turn, at even higher frequencies, where the wavelength of the
electromagnetic waves becomes small in comparison to the size of the structures
used to process them, microwave techniques become inadequate, and the methods
of optics are used.
b.
Microwaves Sources
There are 2 kind of microwave
sources:
1.
High-power microwave sources use specialized vacuum tubes to
generate microwaves. These devices operate on different principles from
low-frequency vacuum tubes, using the ballistic motion of electrons in a vacuum
under the influence of controlling electric or magnetic fields, and include
the magnetron (used
in microwave
ovens), klystron,traveling-wave
tube (TWT),
and gyrotron. These devices
work in the density modulated
mode, rather than the currentmodulated mode.
This means that they work on the basis of clumps of electrons flying
ballistically through them, rather than using a continuous stream of electrons.
2.
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.
All warm
objects emit low level microwave black-body
radiation, depending on their temperature, so in
meteorology andremote
sensing microwave
radiometers are used to measure the temperature of objects or
terrain. The sun and other astronomical radio sources such as Cassiopeia A emit low
level microwave radiation which carries information about their makeup, which
is studied by radio astronomersusing receivers
called radio
telescopes. The cosmic
microwave background radiation (CMBR), for example, is a weak microwave noise
filling empty space which is a major source of information on cosmology's Big Bang theory of
the origin of the Universe.
c.
Microwave Uses
Microwave technology is extensively used for point-to-point
telecommunications (i.e. non-broadcast uses). Microwaves are
especially suitable for this use since they are more easily focused into
narrower beams than radio waves, allowing frequency reuse; their
comparatively higher frequencies allow broad bandwidth and
high data
transmission rates, and antenna sizes are smaller than at lower frequencies
because antenna size is inversely proportional to transmitted frequency.
Microwaves are used in spacecraft communication, and much of the world's data,
TV, and telephone communications are transmitted long distances by microwaves
between ground stations and communications
satellites. Microwaves are also employed in microwave ovens and
in radar technology.
1. Communication
Before the advent of fiber-optic transmission,
most long-distance telephone calls were
carried via networks of microwave
radio relay links run by carriers such as AT&T Long Lines. Starting in
the early 1950s, frequency
division multiplex was used to send up to 5,400 telephone channels on
each microwave radio channel, with as many as ten radio channels combined into
one antenna for the hop to the next site, up to 70 km
away.
Wireless LAN protocols, such as Bluetooth and
the IEEE 802.11 specifications
used for Wi-Fi, also use microwaves in the 2.4 GHz ISM band,
although 802.11a uses ISM bandand U-NII frequencies
in the 5 GHz range. Licensed long-range (up to about 25 km) Wireless
Internet Access services have been used for almost a decade in many countries
in the 3.5–4.0 GHz range. The FCC recently[when?] carved
out spectrum for carriers that wish to offer services in this range in the U.S.
— with emphasis on 3.65 GHz. Dozens of service providers across the
country are securing or have already received licenses from the FCC to operate
in this band. The WIMAX service offerings that can be carried on the
3.65 GHz band will give business customers another option for
connectivity.
Metropolitan
area network (MAN) protocols, such as WiMAX (Worldwide
Interoperability for Microwave Access) are based on standards such as IEEE 802.16, designed to
operate between 2 and 11 GHz. Commercial implementations are in the
2.3 GHz, 2.5 GHz, 3.5 GHz and 5.8 GHz ranges.
Mobile
Broadband Wireless Access (MBWA) protocols based on standards specifications
such as IEEE 802.20 or
ATIS/ANSI HC-SDMA (such
as iBurst) operate
between 1.6 and 2.3 GHz to give mobility and in-building penetration
characteristics similar to mobile phones but with vastly greater spectral
efficiency.
Some mobile phone networks,
like GSM, use the
low-microwave/high-UHF frequencies around 1.8 and 1.9 GHz in the Americas
and elsewhere, respectively. DVB-SH and S-DMBuse 1.452 to
1.492 GHz, while proprietary/incompatible satellite radio in the
U.S. uses around 2.3 GHz for DARS.
Microwave radio is used in broadcasting and telecommunication transmissions
because, due to their short wavelength, highly directional
antennas are smaller and therefore more practical than they would be at longer
wavelengths (lower frequencies). There is also more bandwidth in the
microwave spectrum than in the rest of the radio spectrum; the usable bandwidth
below 300 MHz is less than 300 MHz while many GHz can be used above
300 MHz. Typically, microwaves are used in television news to
transmit a signal from a remote location to a television station from a
specially equipped van. See broadcast
auxiliary service (BAS), remote
pickup unit (RPU), and studio/transmitter
link (STL).
Most satellite
communications systems operate in the C, X, Ka, or Ku bands
of the microwave spectrum. These frequencies allow large bandwidth while
avoiding the crowded UHF frequencies and staying below the atmospheric
absorption of EHF frequencies. Satellite TV either
operates in the C band for the traditional large dish fixed
satellite serviceor Ku band for direct-broadcast
satellite. Military communications run primarily over X or Ku-band links,
with Ka band being used for Milstar.
2. Navigation
Global
Navigation Satellite Systems (GNSS) including the Chinese Beidou, the
American Global
Positioning System((introduced in 1978)GPS) and the Russian GLONASSbroadcast
navigational signals in various bands between about 1.2 GHz and
1.6 GHz.
3. Radar
Radar uses
microwave radiation to detect the range, speed, and other characteristics of
remote objects. Development of radar was accelerated during World War II due to
its great military utility. Now radar is widely used for applications such
as air
traffic control, weather forecasting, navigation of ships, and speed
limit enforcement.
Microwaves cannot be carried with usable efficiency in ordinary transmission lines but
require waveguide, such as a
metal pipe.
4. Radio Astronomy
Most radio
astronomy uses microwaves. Usually the naturally-occurring microwave radiation
is observed, but active radar experiments have also been done with objects in
the solar system, such as determining the distance to the Moon or
mapping the invisible surface of Venus through
cloud cover.
The Atacama
Large Millimeter Array, located at more than 5,000 meters (16,597 ft)
altitude in Chile, observes the universe in themillimetre
and submillimetre wavelength ranges. The world's largest ground-based
astronomy project to date consists of more than 66 dishes and was built in an
international collaboration by Europe, North America, East Asia and Chile.
The cosmic
microwave background radiation (CMBR) has been mapped by a number of instrument at
an ever increasing resolution. The CMBR is understood to be a "relic
radiation" from the Big Bang. Due to the
expansion and thus cooling of the Universe, the originally high-energy
radiation has been shifted into the microwave region of the radio spectrum.
Sufficiently sensitive radio telescopes can
detected the CMBR as a faint background glow, almost exactly the same in all
directions, that is not associated with any star, galaxy, or other object.
5. Heating and Power Application
A microwave
oven passes
(non-ionizing) microwave radiation at a frequency near 2.45 GHz (12 cm) through
food, causing dielectric
heating primarily by absorption of the energy in water. Microwave ovens
became common kitchen appliances in Western countries in the late 1970s,
following the development of less expensive cavity magnetrons. Water in the
liquid state possesses many molecular interactions that broaden the absorption
peak. In the vapor phase, isolated water molecules absorb at around
22 GHz, almost ten times the frequency of the microwave oven.
Microwave heating is used in industrial processes for drying and curing products. Many semiconductor
processing techniques use microwaves to generate plasma for such
purposes as reactive
ion etching and plasma-enhanced chemical
vapor deposition(PECVD).
Microwave frequencies typically ranging from 110 – 140 GHz are used
in stellarators and tokamak experimental
fusion reactors to help heat the fuel into a plasma state. The upcoming ITER thermonuclear
reactor is expected to range from 110–170 GHz and will employ
electron cyclotron resonance heating (ECRH).
Microwaves can be used to transmit
power over long distances, and post-World War II research
was done to examine possibilities. NASA worked in
the 1970s and early 1980’s to research
the possibilities of using solar
power satellite (SPS) systems with large solar
arrays that would beam power down to the Earth's surface via microwaves.
Less-than-lethal weaponry
exists that uses millimeter waves to heat a thin layer of human skin to an
intolerable temperature so as to make the targeted person move away. A
two-second burst of the 95 GHz focused beam heats the skin to a
temperature of 54 °C (129 °F) at a depth of 0.4 millimetres (1⁄64 in).
The United
States Air Force and Marinesare currently using
this type of active
denial system in fixed installations.
6. Spectroscopy
Microwave radiation is used in electron
paramagnetic resonance (EPR or ESR) spectroscopy, typically in the X-band
region (~9 GHz) in conjunction typically with magnetic fieldsof 0.3 T. This
technique provides information on unpaired electrons in
chemical systems, such as free radicals or transition metal ions such
as Cu(II). Microwave radiation is also used to perform rotational
spectroscopy and can be combined with electrochemistry as
in microwave
enhanced electrochemistry.
d.
Microwave Frequency Bands
Rough plot of
Earth's atmospheric transmittance (or opacity) to various wavelengths of
electromagnetic radiation. Microwaves are strongly absorbed at wavelengths
shorter than about 1.5 cm (above 20 GHz) by water and other molecules in
the air.
|
Microwave frequency bands
|
|||
|
Designation
|
Frequency range
|
Wavelength range
|
Typical uses
|
|
1
to 2 GHz
|
15 cm
to 30 cm
|
military
telemetry, GPS, mobile phones (GSM), amateur radio
|
|
|
2
to 4 GHz
|
7.5 cm
to 15 cm
|
weather
radar, surface ship radar, and some communications satellites (microwave
ovens, microwave devices/communications, radio astronomy, mobile phones,
wireless LAN, Bluetooth, ZigBee, GPS, amateur radio)
|
|
|
4
to 8 GHz
|
3.75 cm
to 7.5 cm
|
long-distance
radio telecommunications
|
|
|
8
to 12 GHz
|
25 mm
to 37.5 mm
|
satellite
communications, radar, terrestrial broadband, space communications, amateur
radio
|
|
|
12
to 18 GHz
|
16.7 mm
to 25 mm
|
satellite
communications
|
|
|
18
to 26.5 GHz
|
11.3 mm
to 16.7 mm
|
radar,
satellite communications, astronomical observations, automotive radar
|
|
|
26.5
to 40 GHz
|
5.0 mm
to 11.3 mm
|
satellite
communications
|
|
|
33
to 50 GHz
|
6.0 mm
to 9.0 mm
|
satellite
communications, terrestrial microwave communications, radio astronomy,
automotive radar
|
|
|
40
to 60 GHz
|
5.0 mm
to 7.5 mm
|
||
|
50
to 75 GHz
|
4.0 mm
to 6.0 mm
|
millimeter
wave radar research and other kinds of scientific research
|
|
|
75
to 110 GHz
|
2.7 mm
to 4.0 mm
|
satellite
communications, millimeter-wave radar research, military radar targeting and
tracking applications, and some non-military applications, automotive radar
|
|
|
90
to 140 GHz
|
2.1 mm
to 3.3 mm
|
SHF
transmissions: Radio astronomy, microwave devices/communications, wireless
LAN, most modern radars, communications satellites, satellite television
broadcasting, DBS, amateur radio
|
|
|
110
to 170 GHz
|
1.8 mm
to 2.7 mm
|
EHF
transmissions: Radio astronomy, high-frequency microwave radio relay,
microwave remote sensing, amateur radio, directed-energy weapon, millimeter
wave scanner
|
|
P band is
sometimes used for Ku Band. "P" for
"previous" was a radar band used in the UK ranging from
250 to 500 MHz and now obsolete per IEEE Std 521.
When radars were first developed at K band
during World War II, it was not known that there was a nearby absorption band
(due to water vapor and oxygen in the atmosphere). To avoid this problem, the
original K band was split into a lower band, Ku, and upper band, Ka.
e.
Effects on health
Microwaves do not contain sufficient energy to chemically change substances
by ionization, and so are an example of non-ionizing radiation.
The word "radiation" refers to energy radiating from a source and not
to radioactivity. It has not
been shown conclusively that microwaves (or other non-ionizing electromagnetic
radiation) have significant adverse biological effects at low levels. Some, but
not all, studies suggest that long-term exposure may have a carcinogenic effect. This
is separate from the risks associated with very high-intensity exposure, which
can cause heating and burns like any heat source, and not a unique property of
microwaves specifically.
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