Extremely high frequency
Encyclopedia
Extremely high frequency is the highest radio frequency
band. EHF runs the range of frequencies
from 30 to 300 gigahertz, above which electromagnetic radiation
is considered to be low (or far) infrared
light
, also referred to as terahertz radiation
. This band has a wavelength
of ten to one millimetre, giving it the name millimeter band or millimetre wave, sometimes abbreviated MMW or mmW.
Compared to lower bands, terrestrial radio
signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distance
s. In particular, signals in the 57–64 GHz region are subject to a resonance
of the oxygen
molecule and are severely attenuated. Even over relatively short distances, rain fade
is a serious problem, caused when absorption by rain
reduces signal strength
. In climates other than deserts absorption due to humidity also has an impact on propagation. While this absorption limits potential communications range, it also allows for smaller frequency reuse distances than lower frequencies. The small wavelength
allows modest size antennas to have a small beam width, further increasing frequency reuse potential.
and remote sensing
. Ground-based radio astronomy
is limited to high altitude sites such as Kitt Peak
and Atacama Large Millimeter Array (ALMA
) due to atmospheric absorption issues. Satellite-based remote sensing near 60 GHz can determine temperature in the upper atmosphere by measuring radiation emitted from oxygen molecules that is a function of temperature and pressure. The ITU
non-exclusive passive frequency allocation at 57-59.3 is used for atmospheric monitoring in meteorological and climate sensing applications,and is important for these purposes due to the properties of oxygen absorption and emission in Earth’s atmosphere. Currently operational U.S. satellite
sensors such as the Advanced Microwave
Sounding Unit (AMSU) on one NASA satellite (Aqua) and four NOAA (15-18) satellites and the Special Sensor Microwave Imager Sounder (SSMI/S) on Department of Defense satellite F-16 make use of this frequency range.
/s. It is used commonly in flat terrain.
The 71-76, 81-86 and 92–95 GHz bands are also used for point-to-point high-bandwidth communication links. These frequencies, as opposed to the 60 GHz frequency, require a transmitting license in the US from the Federal Communications Commission
(FCC), though they do not suffer from the effects of oxygen absorption as the 60 GHz does. There are plans for 10 Gbit/s links using these frequencies as well. In the case of the 92–95 GHz band, a small 100 MHz range has been reserved for space-borne radios, making this reserved range limited to a transmission rate of under a few gigabits per second.
The band is essentially undeveloped and available for use in a broad range of new products and services, including high-speed, point-to-point wireless local area networks and broadband Internet access
. WirelessHD
is another recent technology that operates near the 60 GHz range. Highly directional, "pencil-beam" signal characteristics permit systems in these bands to be engineered in close proximity to one another without causing interference. Potential applications include radar
systems with very high resolution.
Uses of the millimeter wave bands include point-to-point communications, intersatellite links, and point-to-multipoint communications.
Because of shorter wavelengths, the band permits the use of smaller antennas than would be required for similar circumstances in the lower bands, to achieve the same high directivity and high gain. The immediate consequence of this high directivity, coupled with the high free space loss at these frequencies, is the possibility of a more efficient use of the spectrum for point-to-multipoint applications. Since a greater number of highly directive antennas can be placed in a given area than less directive antennas, the net result is higher reuse of the spectrum, and higher density of users, as compared to lower frequencies. Furthermore, because one can place more voice channels or broadband information using a higher frequency to transmit the information, this spectrum could potentially be used as a replacement for or supplement to fiber optics.
ASELSAN, a Turkish Armed Forces
owned company, is currently working on an on-board processing EHF satellite transponder in conjunction with the Scientific and Technological Research Council of Turkey (TUBITAK) and Bilkent University. ASELSAN's aim is to produce an indegenous on-board processing EHF satellite transponder and its phased array antenna.
As reported in incisor.tv monthly magazine, the WiMedia Alliance
is looking at using the 60 GHz range in their road map.
has developed a nonlethal weapon system called Active Denial System
(ADS) which emits a beam of radiation with a wavelength of 3 mm. The weapon is reportedly not dangerous and causes no physical harm, but is extremely painful and causes the target to feel an intense burning pain, as if his or her skin is going to catch fire.
The TSA
has deployed a $170,000 machine, in the month of February 2009, for use in Tulsa International Airport
according to USA Today. Machines will follow in Las Vegas
, San Francisco, Albuquerque and Salt Lake City by May 2009. Similar units have been deployed in Baltimore (BWI) and Raleigh (RDU) for some time. These machines were deployed in the Jersey City PATH train system for two weeks in 2006.
Currently the technology does not mask any part of the bodies of the people who are being scanned. However, passengers' faces are deliberately masked by the system. The photos are screened by technicians in a closed room, then deleted immediately upon search completion. Currently, passengers can decline scanning and be screened via a metal detector and patted down. The machines do allow the screener to see muted or slightly blurred images of body parts. Privacy advocates are concerned. "We're getting closer and closer to a required strip-search to board an airplane," said Barry Steinhardt of the American Civil Liberties Union. In at least one airport, Indianapolis International, upgrades have eliminated the need for an officer in a separate viewing area. The new software generates a generic image of a human. There is no anatomical differentiation between male and female on the image, and if an object is detected, the software only presents a yellow box in the area. If the device does not detect anything of interest, no image is presented.
Three security scan
ners using millimeter waves were put into use at Schiphol Airport in Amsterdam on 15 May 2007, with more expected to be installed later. The passenger's head is masked from the view of the security personnel.
According to Farran Technologies, a manufacturer of one model of the millimeter wave scanner, the technology exists to extend the search area to as far as 50 meters beyond the scanning area which would allow security workers to scan a large number of people without their awareness that they are being scanned.
Medicine
Most widely used in former USSR nations, low intensity
(usually 10 mW/cm2 or less) electromagnetic radiation of extremely high frequency (especially in the range 40 - 70 GHz
, which corresponds to wavelength
of 7.5 - 4.3 mm) is used in human medicine for the treatment of many types of diseases. This type of therapy is called Millimeter Wave (MMW) Therapy or Extremely High Frequency (EHF) Therapy. More than 10 000 devices are used for Millimeter Wave Therapy worldwide and more than a million people have been successfully treated with millimeter wave therapy during its documented history. Established in 1992, the Russian Journal Millimeter waves in biology and medicine is dedicated to the scientific basis and clinical applications of Millimeter Wave Therapy. More than 50 issues of it have been published.
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
band. EHF runs the range of frequencies
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
from 30 to 300 gigahertz, above which electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
is considered to be low (or far) infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
, also referred to as terahertz radiation
Terahertz radiation
In physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It is synonymously termed submillimeter radiation, terahertz waves, terahertz light, T-rays, T-waves, T-light, T-lux, THz...
. This band has a wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of ten to one millimetre, giving it the name millimeter band or millimetre wave, sometimes abbreviated MMW or mmW.
Compared to lower bands, terrestrial radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distance
Distance
Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
s. In particular, signals in the 57–64 GHz region are subject to a resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
of the oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
molecule and are severely attenuated. Even over relatively short distances, rain fade
Rain fade
Rain fade refers primarily to the absorption of a microwave radio frequency signal by atmospheric rain, snow or ice, and losses are especially prevalent at frequencies above 11 GHz. It also refers to the degradation of a signal caused by the electromagnetic interference of the leading edge of a...
is a serious problem, caused when absorption by rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
reduces signal strength
Signal strength
In telecommunications, particularly in radio, signal strength refers to the magnitude of the electric field at a reference point that is a significant distance from the transmitting antenna. It may also be referred to as received signal level or field strength. Typically, it is expressed in...
. In climates other than deserts absorption due to humidity also has an impact on propagation. While this absorption limits potential communications range, it also allows for smaller frequency reuse distances than lower frequencies. The small wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
allows modest size antennas to have a small beam width, further increasing frequency reuse potential.
Scientific research
This band is commonly used in radio astronomyRadio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
and remote sensing
Remote sensing
Remote sensing is the acquisition of information about an object or phenomenon, without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth by means of propagated signals Remote sensing...
. Ground-based radio astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
is limited to high altitude sites such as Kitt Peak
Kitt Peak
Kitt Peak is a mountain in the U.S. state of Arizona. It is the location of the Kitt Peak National Observatory. The radio telescope at the Observatory is one of ten dishes comprising the Very Long Baseline Array ....
and Atacama Large Millimeter Array (ALMA
Atacama Large Millimeter Array
The Atacama Large Millimeter/sub-millimeter Array is an array of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter wavelength operations, the array is being constructed on the Chajnantor plateau at 5000 metres altitude...
) due to atmospheric absorption issues. Satellite-based remote sensing near 60 GHz can determine temperature in the upper atmosphere by measuring radiation emitted from oxygen molecules that is a function of temperature and pressure. The ITU
Itu
Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...
non-exclusive passive frequency allocation at 57-59.3 is used for atmospheric monitoring in meteorological and climate sensing applications,and is important for these purposes due to the properties of oxygen absorption and emission in Earth’s atmosphere. Currently operational U.S. satellite
sensors such as the Advanced Microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
Sounding Unit (AMSU) on one NASA satellite (Aqua) and four NOAA (15-18) satellites and the Special Sensor Microwave Imager Sounder (SSMI/S) on Department of Defense satellite F-16 make use of this frequency range.
Telecommunications
In the United States, the band 38.6 - 40.0 GHz is used for licensed high-speed microwave data links, and the 60 GHz band can be used for unlicensed short range (1.7 km) data links with data throughputs up to 2.5 GbitGigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
/s. It is used commonly in flat terrain.
The 71-76, 81-86 and 92–95 GHz bands are also used for point-to-point high-bandwidth communication links. These frequencies, as opposed to the 60 GHz frequency, require a transmitting license in the US from the Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC), though they do not suffer from the effects of oxygen absorption as the 60 GHz does. There are plans for 10 Gbit/s links using these frequencies as well. In the case of the 92–95 GHz band, a small 100 MHz range has been reserved for space-borne radios, making this reserved range limited to a transmission rate of under a few gigabits per second.
The band is essentially undeveloped and available for use in a broad range of new products and services, including high-speed, point-to-point wireless local area networks and broadband Internet access
Broadband Internet access
Broadband Internet access, often shortened to just "broadband", is a high data rate, low-latency connection to the Internet— typically contrasted with dial-up access using a 56 kbit/s modem or satellite Internet with inherently high latency....
. WirelessHD
WirelessHD
WirelessHD is an industry-led effort to define a specification for the next generation wireless digital network interface for wireless high-definition signal transmission for consumer electronics products. The consortium currently has over 40 adopters; key members behind the specification include...
is another recent technology that operates near the 60 GHz range. Highly directional, "pencil-beam" signal characteristics permit systems in these bands to be engineered in close proximity to one another without causing interference. Potential applications include radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
systems with very high resolution.
Uses of the millimeter wave bands include point-to-point communications, intersatellite links, and point-to-multipoint communications.
Because of shorter wavelengths, the band permits the use of smaller antennas than would be required for similar circumstances in the lower bands, to achieve the same high directivity and high gain. The immediate consequence of this high directivity, coupled with the high free space loss at these frequencies, is the possibility of a more efficient use of the spectrum for point-to-multipoint applications. Since a greater number of highly directive antennas can be placed in a given area than less directive antennas, the net result is higher reuse of the spectrum, and higher density of users, as compared to lower frequencies. Furthermore, because one can place more voice channels or broadband information using a higher frequency to transmit the information, this spectrum could potentially be used as a replacement for or supplement to fiber optics.
ASELSAN, a Turkish Armed Forces
Turkish Armed Forces
The Turkish Armed Forces are the military forces of the Republic of Turkey. They consist of the Army, the Navy , and the Air Force...
owned company, is currently working on an on-board processing EHF satellite transponder in conjunction with the Scientific and Technological Research Council of Turkey (TUBITAK) and Bilkent University. ASELSAN's aim is to produce an indegenous on-board processing EHF satellite transponder and its phased array antenna.
As reported in incisor.tv monthly magazine, the WiMedia Alliance
WiMedia Alliance
The WiMedia Alliance is a non-profit open industry association that promotes and enables the rapid adoption, regulation, standardization and multi-vendor interoperability of ultra-wideband worldwide....
is looking at using the 60 GHz range in their road map.
Weapons systems
With Raytheon the U.S. Air ForceAir force
An air force, also known in some countries as an air army, is in the broadest sense, the national military organization that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an army, navy or...
has developed a nonlethal weapon system called Active Denial System
Active Denial System
The Active Denial System is a non-lethal, directed-energy weapon developed by the U.S. military. It is a strong millimeter-wave transmitter primarily used for crowd control . Some ADS such as HPEM ADS are also used to disable vehicles. Informally, the weapon is also called the heat ray...
(ADS) which emits a beam of radiation with a wavelength of 3 mm. The weapon is reportedly not dangerous and causes no physical harm, but is extremely painful and causes the target to feel an intense burning pain, as if his or her skin is going to catch fire.
Security screening
A recent development has been imagers for security applications as clothing and other organic materials are translucent in some mm-wave atmospheric windows. Privacy advocates are concerned about the use of this technology because it allows screeners to see airport passengers as if without clothing.The TSA
Transportation Security Administration
The Transportation Security Administration is an agency of the U.S. Department of Homeland Security that exercises authority over the safety and security of the traveling public in the United States....
has deployed a $170,000 machine, in the month of February 2009, for use in Tulsa International Airport
Tulsa International Airport
Tulsa International Airport is a city-owned public-use airport located five miles northeast of downtown Tulsa, a city in Tulsa County, Oklahoma, United States. It was originally named Tulsa Municipal Airport, when the city acquired it in 1929...
according to USA Today. Machines will follow in Las Vegas
Las Vegas, Nevada
Las Vegas is the most populous city in the U.S. state of Nevada and is also the county seat of Clark County, Nevada. Las Vegas is an internationally renowned major resort city for gambling, shopping, and fine dining. The city bills itself as The Entertainment Capital of the World, and is famous...
, San Francisco, Albuquerque and Salt Lake City by May 2009. Similar units have been deployed in Baltimore (BWI) and Raleigh (RDU) for some time. These machines were deployed in the Jersey City PATH train system for two weeks in 2006.
Currently the technology does not mask any part of the bodies of the people who are being scanned. However, passengers' faces are deliberately masked by the system. The photos are screened by technicians in a closed room, then deleted immediately upon search completion. Currently, passengers can decline scanning and be screened via a metal detector and patted down. The machines do allow the screener to see muted or slightly blurred images of body parts. Privacy advocates are concerned. "We're getting closer and closer to a required strip-search to board an airplane," said Barry Steinhardt of the American Civil Liberties Union. In at least one airport, Indianapolis International, upgrades have eliminated the need for an officer in a separate viewing area. The new software generates a generic image of a human. There is no anatomical differentiation between male and female on the image, and if an object is detected, the software only presents a yellow box in the area. If the device does not detect anything of interest, no image is presented.
Three security scan
Security scan
A full-body scanner is a device that creates an image of a person's nude body through their clothing to look for hidden objects without physically removing their clothes or making physical contact...
ners using millimeter waves were put into use at Schiphol Airport in Amsterdam on 15 May 2007, with more expected to be installed later. The passenger's head is masked from the view of the security personnel.
According to Farran Technologies, a manufacturer of one model of the millimeter wave scanner, the technology exists to extend the search area to as far as 50 meters beyond the scanning area which would allow security workers to scan a large number of people without their awareness that they are being scanned.
MedicineEHF – therapyEHF therapy is a biophysical theory studying mechanisms of action on the living organism of electromagnetic radiation of millimeter range high frequency of low intensity, and medical practice using effects of the above mentioned action at treatment of different ailments.Electromagnetic waves of...
Most widely used in former USSR nations, low intensityIntensity (physics)
In physics, intensity is a measure of the energy flux, averaged over the period of the wave. The word "intensity" here is not synonymous with "strength", "amplitude", or "level", as it sometimes is in colloquial speech...
(usually 10 mW/cm2 or less) electromagnetic radiation of extremely high frequency (especially in the range 40 - 70 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
, which corresponds to wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of 7.5 - 4.3 mm) is used in human medicine for the treatment of many types of diseases. This type of therapy is called Millimeter Wave (MMW) Therapy or Extremely High Frequency (EHF) Therapy. More than 10 000 devices are used for Millimeter Wave Therapy worldwide and more than a million people have been successfully treated with millimeter wave therapy during its documented history. Established in 1992, the Russian Journal Millimeter waves in biology and medicine is dedicated to the scientific basis and clinical applications of Millimeter Wave Therapy. More than 50 issues of it have been published.
See also
- Electromagnetic shieldingElectromagnetic shieldingElectromagnetic shielding is the process of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive and/or magnetic materials. Shielding is typically applied to enclosures to isolate electrical devices from the 'outside world' and to cables to isolate...
- Knife-edge effectKnife-edge effectIn electromagnetic wave propagation, the knife-edge effect or edge diffraction is a redirection by diffraction of a portion of the incident radiation that strikes a well-defined obstacle such as a mountain range or the edge of a building....
- MicrowaveMicrowaveMicrowaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
- Terahertz radiationTerahertz radiationIn physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It is synonymously termed submillimeter radiation, terahertz waves, terahertz light, T-rays, T-waves, T-light, T-lux, THz...
External links
- FCC bulletin on MMW propagation
- Asyrmatos Millimeter Wave Communication System
- L-3 Communications ProVision Body Screening System
- FCC 70/80/90 GHz overview.
- FCC 57–64 GHz rules.
- Civil mm-wave Regulation in US
- Definition of frequency bands (VLF, ELF... etc.)
- Millimetre-Wave Technology Group at Rutherford-Appleton Laboratory
- Overview of active methods for shielding spacecraft from energetic space radiation
- St. Andrews University mm-wave group
- A Survey of University Capabilities for a New Canadian Radio Telescope
- US Patent 7220488 - Deflecting magnetic field shield