Misplaced Pages

#383616

44-444: (Redirected from G-band ) G band may refer to: G band (IEEE) , a millimetre wave band from 110 to 300 GHz G band (NATO) , a radio frequency band from 4 to 6 GHz G band, representing a green hued wavelength of 464 nm in the photometric systems adopted by astronomers G banding , in cytogenetics The G Band , alternative name of The Glitter Band Topics referred to by

88-475: 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. 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

132-568: A combination of centrifugal and gravitational forces to obtain any ratio of lateral and normal forces. For example, it can apply a normal force at zero lateral force for the drop to fly off away from the surface in the normal direction or it can induce a lateral force at zero normal force (simulating zero gravity ). The term droplet is a diminutive form of 'drop' – and as a guide is typically used for liquid particles of less than 500 μm diameter. In spray application , droplets are usually described by their perceived size (i.e., diameter) whereas

176-431: A drop falling through a gas is actually more or less spherical for drops less than 2 mm in diameter. Larger drops tend to be flatter on the bottom part due to the pressure of the gas they move through. As a result, as drops get larger, a concave depression forms which leads to the eventual breakup of the drop. The capillary length is a length scaling factor that relates gravity , density, and surface tension , and

220-409: A droplet has a radius larger than the capillary length, they are known as macrodrops and the gravitational forces will dominate. Macrodrops will be 'flattened' by gravity and the height of the droplet will be reduced. Raindrop sizes typically range from 0.5 mm to 4 mm, with size distributions quickly decreasing past diameters larger than 2-2.5 mm. Scientists traditionally thought that

264-429: A few kilometers. Thus, they are useful for densely packed communications networks such as personal area networks that improve spectrum utilization through frequency reuse . 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

308-536: 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. 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. Millimeter waves propagate solely by line-of-sight paths. They are not refracted by

352-424: 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. 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

396-581: A sphere of radius 4.5 mm) are theoretically stable and could be levitated in a wind tunnel. The largest recorded raindrop was 8.8 mm in diameter, located at the base of a cumulus congestus cloud in the vicinity of Kwajalein Atoll in July 1999. A raindrop of identical size was detected over northern Brazil in September 1995. In medicine , this property is used to create droppers and IV infusion sets which have

440-444: Is a small column of liquid , bounded completely or almost completely by free surfaces . A drop may form when liquid accumulates at the end of a tube or other surface boundary, producing a hanging drop called a pendant drop. Drops may also be formed by the condensation of a vapor or by atomization of a larger mass of solid . Water vapor will condense into droplets depending on the temperature. The temperature at which droplets form

484-436: Is also a drop held together by surface tension. Some substances that appear to be solid, can be shown to instead be extremely viscous liquids, because they form drops and display droplet behavior. In the famous pitch drop experiments , pitch – a substance somewhat like solid bitumen – is shown to be a liquid in this way. Pitch in a funnel slowly forms droplets, each droplet taking about 10 years to form and break off. In

SECTION 10

#1732880724384

528-402: Is called the dew point . Liquid forms drops because it exhibits surface tension . A simple way to form a drop is to allow liquid to flow slowly from the lower end of a vertical tube of small diameter. The surface tension of the liquid causes the liquid to hang from the tube, forming a pendant. When the drop exceeds a certain size it is no longer stable and detaches itself. The falling liquid

572-412: Is different from Wikidata All article disambiguation pages All disambiguation pages G band (IEEE) 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

616-473: Is directly responsible for the shape a droplet for a specific fluid will take. The capillary length stems from the Laplace pressure , using the radius of the droplet. Using the capillary length we can define microdrops and macrodrops. Microdrops are droplets with radius smaller than the capillary length, where the shape of the droplet is governed by surface tension and they form a more or less spherical cap shape. If

660-412: 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. Passengers can decline scanning and be screened via a metal detector and patted down. According to Farran Technologies, a manufacturer of one model of the millimeter wave scanner,

704-454: Is particularly associated with the range of 40–70 GHz . This type of treatment may be called millimeter wave therapy or extremely high frequency therapy . This treatment is associated with eastern European nations (e.g., former USSR nations). The Russian Journal Millimeter waves in biology and medicine studies the scientific basis and clinical applications of millimeter wave therapy. Traffic police use speed-detecting radar guns in

748-542: 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,

792-603: 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. 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

836-568: The ionosphere nor do they travel along the Earth as ground waves as lower frequency radio waves do. At typical power densities they are blocked by building walls and suffer significant attenuation passing through foliage. 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. At frequencies in

880-484: 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

924-418: 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. The high free space loss and atmospheric absorption limit useful propagation to

SECTION 20

#1732880724384

968-450: 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

1012-730: The Ka-band (33.4–36.0 GHz). ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km VLF 3 kHz/100 km 30 kHz/10 km LF 30 kHz/10 km 300 kHz/1 km MF 300 kHz/1 km 3 MHz/100 m HF 3 MHz/100 m 30 MHz/10 m VHF 30 MHz/10 m 300 MHz/1 m UHF 300 MHz/1 m 3 GHz/100 mm SHF 3 GHz/100 mm 30 GHz/10 mm EHF 30 GHz/10 mm 300 GHz/1 mm THF 300 GHz/1 mm 3 THz/0.1 mm Raindrop A drop or droplet

1056-527: 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

1100-580: 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), and a smaller law enforcement version, called Silent Guardian that was developed by Raytheon later, had an output power of 30 kW. 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. Privacy advocates are concerned about

1144-599: The distance to get to terminal velocity increases sharply. An example is a drop with a diameter of 2 mm that may achieve this at 5.6 m . Due to the different refractive index of water and air , refraction and reflection occur on the surfaces of raindrops , leading to rainbow formation. The major source of sound when a droplet hits a liquid surface is the resonance of excited bubbles trapped underwater. These oscillating bubbles are responsible for most liquid sounds, such as running water or splashes, as they actually consist of many drop-liquid collisions. Reducing

1188-492: The dose (or number of infective particles in the case of biopesticides ) is a function of their volume. This increases by a cubic function relative to diameter; thus, a 50 μm droplet represents a dose in 65 pl and a 500 μm drop represents a dose in 65 nanolitres. A droplet with a diameter of 3 mm has a terminal velocity of approximately 8 m/s. Drops smaller than 1 mm in diameter will attain 95% of their terminal velocity within 2 m . But above this size

1232-507: 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. Multipath propagation , particularly reflection from indoor walls and surfaces, causes serious fading. Doppler shift of frequency can be significant even at pedestrian speeds. In portable devices, shadowing due to

1276-470: The force due to surface tension is given by where d is the tube diameter. The mass m of the drop hanging from the end of the tube can be found by equating the force due to gravity ( F g = m g {\displaystyle F_{g}=mg} ) with the component of the surface tension in the vertical direction ( F γ sin ⁡ α {\displaystyle F_{\gamma }\sin \alpha } ) giving

1320-520: The force required to slide a drop on the surface, namely the force to detach the drop from its position on the surface only to translate it to another position on the surface. Normal adhesion is the adhesion required to detach a drop from the surface in the normal direction, namely the force to cause the drop to fly off from the surface. The measurement of both adhesion forms can be done with the Centrifugal Adhesion Balance (CAB). The CAB uses

1364-417: The formula where α is the angle of contact with the tube's front surface, and g is the acceleration due to gravity. The limit of this formula, as α goes to 90°, gives the maximum weight of a pendant drop for a liquid with a given surface tension, γ {\displaystyle \gamma } . This relationship is the basis of a convenient method of measuring surface tension, commonly used in

G band - Misplaced Pages Continue

1408-535: 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. 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

1452-444: 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. In addition, use of millimeter wave bands for vehicular communication is also emerging as an attractive solution to support (semi-)autonomous vehicular communications. Shorter wavelengths in this band permit

1496-517: 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. 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

1540-407: The pendant drop test, a drop of liquid is suspended from the end of a tube or by any surface by surface tension . The force due to surface tension is proportional to the length of the boundary between the liquid and the tube, with the proportionality constant usually denoted γ {\displaystyle \gamma } . Since the length of this boundary is the circumference of the tube,

1584-422: The petroleum industry. More sophisticated methods are available to take account of the developing shape of the pendant as the drop grows. These methods are used if the surface tension is unknown. The drop adhesion to a solid can be divided into two categories: lateral adhesion and normal adhesion. Lateral adhesion resembles friction (though tribologically lateral adhesion is a more accurate term) and refers to

1628-409: The same term [REDACTED] This disambiguation page lists articles associated with the title G band . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=G_band&oldid=1226658459 " Category : Disambiguation pages Hidden categories: Short description

1672-403: The stream of outgoing bullets as well as the target, allowing the computer fire control system to change the aim to bring them together. 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). The weapon causes a person in

1716-412: The surface tension of a body of liquid makes possible to reduce or prevent noise due to droplets falling into it. This would involve adding soap , detergent or a similar substance to water. The reduced surface tension reduces the noise from dripping. The classic shape associated with a drop (with a pointy end in its upper side) comes from the observation of a droplet clinging to a surface. The shape of

1760-541: 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. 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

1804-519: The technology focus on plastics extrusion , paper manufacturing , glass production and mineral wool production . Low intensity (usually 10 mW/cm 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." This treatment

G band - Misplaced Pages Continue

1848-400: 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,

1892-423: 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

1936-419: The variation in the size of raindrops was due to collisions on the way down to the ground. In 2009, French researchers succeeded in showing that the distribution of sizes is due to the drops' interaction with air, which deforms larger drops and causes them to fragment into smaller drops, effectively limiting the largest raindrops to about 6 mm diameter. However, drops up to 10 mm (equivalent in volume to

#383616