Extremely high frequency

Extremely high frequency Frequency range 30 to 300 GHz

ITU Radio Band Numbers 1 2 3 4 5 6 7 8 9 10 11 12 ITU Radio Band Symbols ELF SLF ULF VLF LF MF HF VHF UHF SHF EHF THF NATO Radio bands A B C D E F G H I J K L M IEEE Radar bands HF VHF UHF L S C X Ku K Ka Q V W v d e

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 distances. 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.

Applications

Scientific research

This band is commonly used in radio astronomy 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.^[1]

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 Gbit/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. ^[2]

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.^{[citation needed]}

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.^[3]

As reported in incisor.tv monthly magazine, the WiMedia Alliance is looking at using the 60 GHz range in their road map.^{[4][dead link]}

Weapons systems

With Raytheon the U.S. Air Force has developed a nonlethal weapon system called Active Denial System (ADS) which emits a beam of radiation with a wavelength of 3 mm.^[5] 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

Main article: Millimeter wave scanner

A recent development has been imagers for security applications as clothing and other organic materials are translucent in some mm-wave atmospheric windows.^{[6][dead link]} Privacy advocates are concerned about the use of this technology because it allows screeners to see airport passengers as if without clothing.

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.^[7] 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.^[8]

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.^{[citation needed]} 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.^[7] 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 scanners 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.^{[9][dead link]}

Medicine

Most widely used in former USSR nations,^[10][11] 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.^[11][12] 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 ^[13] and more than a million people have been successfully treated with millimeter wave therapy during its documented history.^[13] 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.^[14] More than 50 issues of it have been published.

See also

• Electromagnetic shielding
• Knife-edge effect
• Microwave
• Terahertz radiation

References

1. ^ FCC.gov, Comments of IEEE Geoscience and Remote Sensing Society, FCC RM-11104, 10/17/07
2. ^ Rfdesign.com, Multigigabit wireless technology at 70 GHz, 80 GHz and 90 GHz, RF Design, May 2006
3. ^ "Processed EHF Transponder And Antenna Design And Production". http://www.aselsan.com.tr/urun.asp?urun_id=229&lang=en. Retrieved 5 June 2009. 
4. ^ Incisor.tv
5. ^ "Slideshow: Say Hello to the Goodbye Weapon". http://www.wired.com/news/technology/0,72134-0.html. Retrieved 4 June 2009. 
6. ^ Newscientisttech.com
7. ^ ^{a b} Frank, Thomas (18 February 2009). "Body scanners replace metal detectors in tryout at Tulsa airport.". USA Today. http://www.usatoday.com/travel/flights/2009-02-17-detectors_N.htm. Retrieved 2 May 2010. 
8. ^ "Mirror for Star Ledger Article "PATH riders to face anti-terror screening -- Program will begin at station in Jersey City". 2006/07/12 Wed. p. 014. http://www.hudsoncity.net/tubes/securitytesting.html. 
9. ^ Scenta.co.uk
10. ^ M. Rojavin and M. Ziskin, Medical application of millimetre waves, QJM: An International Journal of Medicine, vol. 91, no. 1, p. 57, 1998, Qjmed.oxfordjournals.org
11. ^ ^{a b} Pakhomov, A. G., Murphy, P. R., Low-intensity millimeter waves as a novel therapeutic modality, IEEE Transactions on Plasma Science, 2000, vol. 28, no. 1, DX.doi.org
12. ^ Betskii, O. V. , Devyatkov, N. D., Kislov, V., Low Intensity Millimeter Waves in Medicine and Biology, Critical Reviews in Biomedical Engineering, 2000, vol. 28 no. 1&2, p. 247-268 Begellhouse.com
13. ^ ^{a b} Betskii, O. V., Kotrovskaya T. I., Lebedeva, N. N., Millimeter Waves in Biology and Medicine, III Всероссийская конференция «Радиолокация и радиосвязь» – ИРЭ РАН, 26-30 октября 2009, JRE.cplire.ru
14. ^ Benran.ru

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