Extremely high frequency

Last updated
Extremely high frequency
Extremely high frequency
Frequency range
30 to 300 GHz
Wavelength range
10–1 mm
Related bands
  • K  / L  / M (NATO)
  • Ka  / V  / W  /mm (IEEE)
Millimetre band (IEEE)
Frequency range
110 to 300 GHz
Wavelength range
2.73 to 1 mm
Related bands
EHF (IEEE)

Extremely high frequency is the International Telecommunication Union designation specifically included in the electromagnetic spectrum classification group with 8 other principal dedicated channel allocation. Extremely high frequency or commonly known as "EHF", is a large broadband that span a radius of about (30 GHz to 300 GHz) for the molecular spectra of radio frequencies. It lies between the super high frequency (3 GHz to 30 GHz) band and the far infrared band (300 GHz to 1015), for which the lower part is the terahertz band. Radio waves in this band have wavelengths from ten to one millimeter, so it is also called the millimeter band and radiation in this band is called millimeter waves, sometimes abbreviated MMW or mmWave. Millimeter-length electromagnetic waves were first investigated by Jagadish Chandra Bose, who generated waves of frequency up to 60 GHz during experiments in 1894–1896. [1]

Contents

Compared to lower bands, radio waves in this band have high atmospheric attenuation: they are absorbed by the gases in the atmosphere. Absorption increases with frequency until at the top end of the band the waves are attenuated to zero within a few meters. Absorption by humidity in the atmosphere is significant except in desert environments, and attenuation by rain (rain fade) is a serious problem even over short distances. However the short propagation range allows smaller frequency reuse distances than lower frequencies. The short wavelength allows modest size antennas to have a small beam width, further increasing frequency reuse potential. Millimeter waves are used for military fire-control radar, airport security scanners, short range wireless networks, and scientific research.

In a major new application of millimeter waves, certain frequency ranges near the bottom of the band are being used in the newest generation of cell phone networks, 5G networks. [2] The design of millimeter-wave circuit and subsystems (such as antennas, power amplifiers, mixers and oscillators) also presents severe challenges to engineers due to semiconductor and process limitations, model limitations and poor Q factors of passive devices. [3]

Propagation

Atmospheric attenuation in dB/km as a function of frequency over the extremely high frequency band. Peaks in absorption at specific frequencies are a problem, due to atmosphere constituents such as water vapour ( .mw-parser-output .template-chem2-su{display:inline-block;font-size:80%;line-height:1;vertical-align:-0.35em}.mw-parser-output .template-chem2-su>span{display:block;text-align:left}.mw-parser-output sub.template-chem2-sub{font-size:80%;vertical-align:-0.35em}.mw-parser-output sup.template-chem2-sup{font-size:80%;vertical-align:0.65em} H2O) and molecular oxygen ( O2). The vertical scale is double logarithmic, as dB are themselves logarithmic. Micrwavattrp.png
Atmospheric attenuation in dB/km as a function of frequency over the extremely high frequency band. Peaks in absorption at specific frequencies are a problem, due to atmosphere constituents such as water vapour (H2O) and molecular oxygen (O2). The vertical scale is double logarithmic, as dB are themselves logarithmic.

Millimeter waves propagate solely by line-of-sight paths. They are not refracted by the ionosphere nor do they travel along the Earth as ground waves as lower frequency radio waves do. [4] At typical power densities they are blocked by building walls and suffer significant attenuation passing through foliage. [4] [5] [6] Absorption by atmospheric gases is a significant factor throughout the band and increases with frequency. However, this absorption is maximum at a few specific absorption lines, mainly those of oxygen at 60 GHz and water vapor at 24 GHz and 184 GHz. [5] At frequencies in the "windows" between these absorption peaks, millimeter waves have much less atmospheric attenuation and greater range, so many applications use these frequencies. Millimeter wavelengths are the same order of size as raindrops, so precipitation causes additional attenuation due to scattering (rain fade) as well as absorption. [5] [6] The high free space loss and atmospheric absorption limit useful propagation to a few kilometers. [4] Thus, they are useful for densely packed communications networks such as personal area networks that improve spectrum utilization through frequency reuse. [4]

Millimeter waves show "optical" propagation characteristics and can be reflected and focused by small metal surfaces and dielectric lenses around 5 to 30 cm (2 inches to 1 foot) diameter. Because their wavelengths are often much smaller than the equipment that manipulates them, the techniques of geometric optics can be used. Diffraction is less than at lower frequencies, although millimeter waves can be diffracted by building edges. At millimeter wavelengths, surfaces appear rougher so diffuse reflection increases. [4] Multipath propagation, particularly reflection from indoor walls and surfaces, causes serious fading. [6] [7] Doppler shift of frequency can be significant even at pedestrian speeds. [4] In portable devices, shadowing due to the human body is a problem. Since the waves penetrate clothing and their small wavelength allows them to reflect from small metal objects they are used in millimeter wave scanners for airport security scanning.

Applications

Scientific research

Part of the Atacama Large Millimeter Array (ALMA), Chile, America, a millimeter wave radio telescope The Atacama Compact Array.jpg
Part of the Atacama Large Millimeter Array (ALMA), Chile, America, a millimeter wave radio telescope

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 International Telecommunication Union non-exclusive passive frequency allocation at 57–59.3 GHz 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 (SSMI/S) on Department of Defense satellite F-16 make use of this frequency range. [8]

Telecommunications

In the United States, the band 36.0–40.0 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 higher frequencies do not suffer from oxygen absorption, but require a transmitting license in the US from the Federal Communications Commission (FCC). 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, limiting this reserved range to a transmission rate of under a few gigabits per second. [9]

A CableFree MMW link installed in the UAE installed for Safe City applications, providing 1 Gbit/s capacity between sites. The links are fast to deploy and have a lower cost than fibre optics. CableFree MMW Link installed in UAE.jpg
A CableFree MMW link installed in the UAE installed for Safe City applications, providing 1 Gbit/s capacity between sites. The links are fast to deploy and have a lower cost than fibre optics.

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 different systems to operate close to one another without causing interference. Potential applications include radar systems with very high resolution.

The Wi-Fi standards IEEE 802.11ad and IEEE 802.11ay operate in the 60 GHz (V band) spectrum to achieve data transfer rates as high as 7 Gbit/s and at least 20 Gbit/s, respectively.

Uses of the millimeter wave bands include point-to-point communications, intersatellite links, and point-to-multipoint communications. In 2013 it was speculated that there were plans to use millimeter waves in future 5G mobile phones. [10] In addition, use of millimeter wave bands for vehicular communication is also emerging as an attractive solution to support (semi-)autonomous vehicular communications. [11]

Shorter wavelengths in this band permit the use of smaller antennas to achieve the same high directivity and high gain as larger ones in lower bands. 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 frequencies for point-to-multipoint applications. Since a greater number of highly directive antennas can be placed in a given area, the net result is greater frequency reuse, and higher density of users. The high usable channel capacity in this band might allow it to serve some applications that would otherwise use fiber-optic communication or very short links such as for the interconnect of circuit boards. [12]

Weapons systems

Millimeter wave fire control radar for CIWS gun on Soviet aircraft carrier Minsk, Russia Minsk port bow AK-630 CIWS gun fire control radar.JPG
Millimeter wave fire control radar for CIWS gun on Soviet aircraft carrier Minsk, Russia

Millimeter wave radar is used in short-range fire-control radar in tanks and aircraft, and automated guns (CIWS) on naval ships to shoot down incoming missiles. The small wavelength of millimeter waves allows them to track the stream of outgoing bullets as well as the target, allowing the computer fire control system to change the aim to bring them together. [ citation needed ]

With Raytheon the U.S. Air Force has developed a nonlethal antipersonnel weapon system called Active Denial System (ADS) which emits a beam of millimeter radio waves with a wavelength of 3 mm (frequency of 95 GHz). [13] The weapon causes a person in the beam to feel an intense burning pain, as if their skin is going to catch fire. The military version had an output power of 100 kilowatts (kW), [14] and a smaller law enforcement version, called Silent Guardian that was developed by Raytheon later, had an output power of 30 kW. [15]

Security screening

Millimeter wave security scanner at Bonn airport NRW-Verkehrsminister Hendrik Wust - Vorstellung Easy Security-6274.jpg
Millimeter wave security scanner at Bonn airport

Clothing and other organic materials are transparent to millimeter waves of certain frequencies, so a recent application has been scanners to detect weapons and other dangerous objects carried under clothing, for applications such as airport security. [16] Privacy advocates are concerned about the use of this technology because, in some cases, it allows screeners to see airport passengers as if without clothing.

The TSA has deployed millimeter wave scanners to many major airports.

Prior to a software upgrade the technology did not mask any part of the bodies of the people who were being scanned. However, passengers' faces were deliberately masked by the system. The photos were screened by technicians in a closed room, then deleted immediately upon search completion. 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. [17] To address this issue, 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. [18] Passengers can decline scanning and be screened via a metal detector and patted down. [19]

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. [20]

Thickness gauging

Recent studies at the University of Leuven have proven that millimeter waves can also be used as a non-nuclear thickness gauge in various industries. Millimeter waves provide a clean and contact-free way of detecting variations in thickness. Practical applications for the technology focus on plastics extrusion, paper manufacturing, glass production and mineral wool production.

Medicine

Low intensity (usually 10 mW/cm2 or less) electromagnetic radiation of extremely high frequency may be used in human medicine for the treatment of diseases. For example, "A brief, low-intensity MMW exposure can change cell growth and proliferation rates, activity of enzymes, state of cell genetic apparatus, function of excitable membranes and peripheral receptors." [21] This treatment is particularly associated with the range of 40–70 GHz. [22] This type of treatment may be called millimeter wave therapy or extremely high frequency therapy. [23] This treatment is associated with eastern European nations (e.g., former USSR nations). [21] The Russian Journal Millimeter waves in biology and medicine studies the scientific basis and clinical applications of millimeter wave therapy. [24]

Police speed radar

Traffic police use speed-detecting radar guns in the Ka-band (33.4–36.0 GHz). [25]

See also

Related Research Articles

<span class="mw-page-title-main">Electromagnetic spectrum</span> Range of frequencies or wavelengths of electromagnetic radiation

The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high frequency these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications.

<span class="mw-page-title-main">Microwave</span> Electromagnetic radiation with wavelengths from 1 m to 1 mm

Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz and 300 GHz, broadly construed. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz, or between 1 and 3000 GHz . The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range; rather, it indicates that microwaves are small, compared to the radio waves used in prior radio technology.

The Ku band is the portion of the electromagnetic spectrum in the microwave range of frequencies from 12 to 18 gigahertz (GHz). The symbol is short for "K-under", because it is the lower part of the original NATO K band, which was split into three bands because of the presence of the atmospheric water vapor resonance peak at 22.24 GHz, (1.35 cm) which made the center unusable for long range transmission. In radar applications, it ranges from 12 to 18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521–2002.

<span class="mw-page-title-main">Radio wave</span> Type of electromagnetic radiation

Radio waves are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths greater than 1 millimeter, about the diameter of a grain of rice. Radio waves with frequencies above about 1 GHz and wavelengths shorter than 30 centimeters are called microwaves. Like all electromagnetic waves, radio waves in vacuum travel at the speed of light, and in the Earth's atmosphere at a slightly lower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects.

<span class="mw-page-title-main">Ultra high frequency</span> Electromagnetic spectrum 300–3000 MHz

Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter. Radio waves with frequencies above the UHF band fall into the super-high frequency (SHF) or microwave frequency range. Lower frequency signals fall into the VHF or lower bands. UHF radio waves propagate mainly by line of sight; they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception. They are used for television broadcasting, cell phones, satellite communication including GPS, personal radio services including Wi-Fi and Bluetooth, walkie-talkies, cordless phones, satellite phones, and numerous other applications.

<span class="mw-page-title-main">Microwave radiometer</span> Tool measuring EM radiation at 0.3–300-GHz frequency

A microwave radiometer (MWR) is a radiometer that measures energy emitted at one millimeter-to-metre wavelengths (frequencies of 0.3–300 GHz) known as microwaves. Microwave radiometers are very sensitive receivers designed to measure thermally-emitted electromagnetic radiation. They are usually equipped with multiple receiving channels to derive the characteristic emission spectrum of planetary atmospheres, surfaces or extraterrestrial objects. Microwave radiometers are utilized in a variety of environmental and engineering applications, including remote sensing, weather forecasting, climate monitoring, radio astronomy and radio propagation studies.

<span class="mw-page-title-main">Terahertz radiation</span> Range 300-3000 GHz of the electromagnetic spectrum

Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahertz (THz), although the upper boundary is somewhat arbitrary and is considered by some sources as 30 THz. One terahertz is 1012 Hz or 1,000 GHz. Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm = 100 μm. Because terahertz radiation begins at a wavelength of around 1 millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy. This band of electromagnetic radiation lies within the transition region between microwave and far infrared, and can be regarded as either.

Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres. These frequencies fall within the microwave band, so radio waves with these frequencies are called microwaves. The small wavelength of microwaves allows them to be directed in narrow beams by aperture antennas such as parabolic dishes and horn antennas, so they are used for point-to-point communication and data links and for radar. This frequency range is used for most radar transmitters, wireless LANs, satellite communication, microwave radio relay links, satellite phones, and numerous short range terrestrial data links. They are also used for heating in industrial microwave heating, medical diathermy, microwave hyperthermy to treat cancer, and to cook food in microwave ovens.

The Ka band is a portion of the microwave part of the electromagnetic spectrum. The designation "Ka-band" is from Kurz-above, which stems from the German word kurz, meaning "short".

The V band ("vee-band") is a standard designation by the Institute of Electrical and Electronics Engineers (IEEE) for a band of frequencies in the microwave portion of the electromagnetic spectrum ranging from 40 to 75 gigahertz (GHz). The V band is not heavily used, except for millimeter wave radar research and other kinds of scientific research. It should not be confused with the 600–1,000 MHz range of Band V of the UHF frequency range.

The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).

Non-line-of-sight (NLOS) radio propagation occurs outside of the typical line-of-sight (LOS) between the transmitter and receiver, such as in ground reflections. Near-line-of-sight conditions refer to partial obstruction by a physical object present in the innermost Fresnel zone.

<span class="mw-page-title-main">Waveguide (radio frequency)</span> Hollow metal pipe used to carry radio waves

In radio-frequency engineering and communications engineering, a waveguide is a hollow metal pipe used to carry radio waves. This type of waveguide is used as a transmission line mostly at microwave frequencies, for such purposes as connecting microwave transmitters and receivers to their antennas, in equipment such as microwave ovens, radar sets, satellite communications, and microwave radio links.

The W band of the microwave part of the electromagnetic spectrum ranges from 75 to 110 GHz, wavelength ≈2.7–4 mm. It sits above the U.S. IEEE-designated V band (40–75 GHz) in frequency, and overlaps the NATO designated M band (60–100 GHz). The W band is used for satellite communications, millimeter-wave radar research, military radar targeting and tracking applications, and some non-military applications.

<span class="mw-page-title-main">Microwave transmission</span> Transmission of information via microwaves

Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300 MHz to 300 GHz of the electromagnetic spectrum. Microwave signals are normally limited to the line of sight, so long-distance transmission using these signals requires a series of repeaters forming a microwave relay network. It is possible to use microwave signals in over-the-horizon communications using tropospheric scatter, but such systems are expensive and generally used only in specialist roles.

The Q band is a range of frequencies contained in the microwave region of the electromagnetic spectrum. Common usage places this range between 33 and 50 GHz, but may vary depending on the source using the term. The foregoing range corresponds to the recommended frequency band of operation of WR22 waveguides. These frequencies are equivalent to wavelengths between 6 mm and 9.1 mm in air/vacuum. The Q band is in the EHF range of the radio spectrum.

Microwave imaging is a science which has been evolved from older detecting/locating techniques in order to evaluate hidden or embedded objects in a structure using electromagnetic (EM) waves in microwave regime. Engineering and application oriented microwave imaging for non-destructive testing is called microwave testing, see below.

The waveguide E band is the range of radio frequencies from 60 GHz to 90 GHz in the electromagnetic spectrum, corresponding to the recommended frequency band of operation of WR12 waveguides. These frequencies are equivalent to wave lengths between 5 mm and 3.333 mm. The E band is in the EHF range of the radio spectrum.

The IEEE K-band is a portion of the radio spectrum in the microwave range of frequencies from 18 to 27 gigahertz (GHz). The range of frequencies in the center of the K-band between 18 and 26.5 GHz are absorbed by water vapor in the atmosphere due to its resonance peak at 22.24 GHz, 1.35 cm (0.53 in). Therefore these frequencies experience high atmospheric attenuation and cannot be used for long-distance applications. For this reason, the original K-band has been split into three bands: Ka-band, K-band, and Ku-band as detailed below.

<span class="mw-page-title-main">Lens antenna</span> Microwave antenna

A lens antenna is a directional antenna that uses a shaped piece of microwave-transparent material to bend and focus microwaves by refraction, as an optical lens does for light. Typically it consists of a small feed antenna such as a patch antenna or horn antenna which radiates radio waves, with a piece of dielectric or composite material in front which functions as a converging lens to collimate the radio waves into a beam. Conversely, in a receiving antenna the lens focuses the incoming radio waves onto the feed antenna, which converts them to electric currents which are delivered to a radio receiver. They can also be fed by an array of feed antennas, called a focal plane array (FPA), to create more complicated radiation patterns.

References

  1. ↑ "Milestones: First Millimeter-wave Communication Experiments by J.C. Bose, 1894-96". List of IEEE milestones . Institute of Electrical and Electronics Engineers. 14 June 2022.
  2. ↑ User Equipment (UE) radio transmission and reception; Part 3: Range 1 and Range 2 Interworking operation with other radios (PDF) (Technical Specification). 3GPP TS 38.101-3 version 15.2.0 Release 15. ETSI. July 2018. p. 11. Retrieved 5 December 2019.
  3. ↑ du Preez, Jaco; Sinha, Saurabh (2017). Millimeter-Wave Power Amplifiers. Springer. pp. 1–35. ISBN   978-3-319-62166-1.
  4. 1 2 3 4 5 6 Huang, Kao-Cheng; Zhaocheng Wang (2011). Millimeter Wave Communication Systems. John Wiley & Sons. pp. Sections 1.1.1–1.2. ISBN   978-1-118-10275-6.
  5. 1 2 3 "Millimeter Wave Propagation: Spectrum Management Implications" (PDF). Office of Engineering and Technology, Bulletin No. 70. Federal Communications Commission (FCC), US Dept. of Commerce. July 1997. Retrieved May 20, 2017.
  6. 1 2 3 du Preez, Jaco; Sinha, Saurabh (2016). Millimeter-Wave Antennas: Configurations and Applications. Springer. pp. 13–14. ISBN   978-3-319-35068-4.
  7. ↑ Seybold, John S. (2005). Introduction to RF Propagation. John Wiley and Sons. pp. 55–58. ISBN   0-471-74368-2.
  8. ↑ FCC.gov [ permanent dead link ], Comments of IEEE Geoscience and Remote Sensing Society, FCC RM-11104, 10/17/07
  9. ↑ Rfdesign.com Archived 2012-07-16 at the Wayback Machine , Multigigabit wireless technology at 70 GHz, 80 GHz and 90 GHz, RF Design, May 2006
  10. ↑ Rappaport, T.S.; Sun, Shu; Mayzus, R.; Zhao, Hang; Azar, Y.; Wang, K.; Wong, G.N.; Schulz, J.K.; Samimi, M. (2013-01-01). "Millimeter Wave Mobile Communications for 5G Cellular: It Will Work!". IEEE Access. 1: 335–349. Bibcode:2013IEEEA...1..335R. doi: 10.1109/ACCESS.2013.2260813 . ISSN   2169-3536.
  11. ↑ Asadi, Arash; Klos, Sabrina; Sim, Gek Hong; Klein, Anja; Hollick, Matthias (2018-04-15). "FML: Fast Machine Learning for 5G mmWave Vehicular Communications". IEEE Infocom'18.
  12. ↑ Peter Smulders (2013). "The Road to 100 Gb/s Wireless and Beyond: Basic Issues and Key Directions". IEEE Communications Magazine. 51 (12): 86–91. doi:10.1109/MCOM.2013.6685762. S2CID   12358456.
  13. ↑ "Slideshow: Say Hello to the Goodbye Weapon". Wired. 5 December 2006. Retrieved 16 August 2016.
  14. ↑ "Active Denial System: a terahertz based military deterrent for safe crowd control". Terasense Group Inc. 2019-05-29. Retrieved 2020-05-03.
  15. ↑ Hambling, David (2009-05-08). "'Pain ray' first commercial sale looms". Wired. Retrieved 2020-05-03.
  16. ↑ Newscientisttech.com Archived March 11, 2007, at the Wayback Machine
  17. ↑ Frank, Thomas (18 February 2009). "Body scanners replace metal detectors in tryout at Tulsa airport". USA Today. Retrieved 2 May 2010.
  18. ↑ "Statement of Robert Kane to House of Representatives" (PDF). 2011-11-03. p. 2. Archived from the original (PDF) on 2011-11-25.
  19. ↑ Cortez, Joe. "The Three Inspection Options at TSA Checkpoints". Trip Savvy. Retrieved 11 January 2024.
  20. ↑ esa. "Bat inspires space tech for airport security". esa.int. Retrieved 7 April 2018.
  21. 1 2 Pakhomov, A. G.; Murphy, P. R. (2000). "Low-intensity millimeter waves as a novel therapeutic modality". IEEE Transactions on Plasma Science. 28 (1): 34–40. Bibcode:2000ITPS...28...34P. doi:10.1109/27.842821. S2CID   22730643.
  22. ↑ Betskii, O. V.; Devyatkov, N. D.; Kislov, V. (2000). "Low Intensity Millimeter Waves in Medicine and Biology". Critical Reviews in Biomedical Engineering. 28 (1&2). Begellhouse.com: 247–268. doi:10.1615/CritRevBiomedEng.v28.i12.420. PMID   10999395.
  23. ↑ M. Rojavin; M. Ziskin (1998). "Medical application of millimetre waves". QJM: An International Journal of Medicine. 91 (1): 57–66. doi: 10.1093/qjmed/91.1.57 . PMID   9519213.
  24. ↑ Benran.ru Archived 2011-07-18 at the Wayback Machine
  25. ↑ "Radio and Radar Frequency Bands". copradar.com. Retrieved 30 April 2020.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.