Radio frequency

Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around twenty thousand times per second (20 kHz) to around three hundred billion times per second (300 GHz). This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies;[1][2] these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range.

Electric current

Electric currents that oscillate at radio frequencies (RF currents) have special properties not shared by direct current or alternating current of lower frequencies.

  • Energy from RF currents in conductors can radiate into space as electromagnetic waves (radio waves). This is the basis of radio technology.
  • RF current does not penetrate deeply into electrical conductors but tends to flow along their surfaces; this is known as the skin effect.
  • RF currents applied to the body often do not cause the painful sensation and muscular contraction of electric shock that lower frequency currents produce.[3][4] This is because the current changes direction too quickly to trigger depolarization of nerve membranes. However this does not mean RF currents are harmless; they can cause internal injury as well as serious superficial burns called RF burns.
  • RF current can easily ionize air, creating a conductive path through it. This property is exploited by "high frequency" units used in electric arc welding, which use currents at higher frequencies than power distribution uses.
  • Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric insulator of a capacitor. This is because capacitive reactance in a circuit decreases with frequency.
  • In contrast, RF current can be blocked by a coil of wire, or even a single turn or bend in a wire. This is because the inductive reactance of a circuit increases with frequency.
  • When conducted by an ordinary electric cable, RF current has a tendency to reflect from discontinuities in the cable such as connectors and travel back down the cable toward the source, causing a condition called standing waves. Therefore, RF current must be carried by specialized types of cable called transmission line, such as coaxial cables.

Frequency bands

The radio spectrum of frequencies is divided into bands with conventional names designated by the International Telecommunications Union (ITU):

Frequency
range
Wavelength
range
ITU designation IEEE bands[5]
Full name Abbreviation[6]
3–30 Hz 105–104 km Extremely low frequency ELF N/A
30–300 Hz 104–103 km Super low frequency SLF N/A
300–3000 Hz 103–100 km Ultra low frequency ULF N/A
3–30 kHz 100–10 km Very low frequency VLF N/A
30–300 kHz 10–1 km Low frequency LF N/A
300 kHz – 3 MHz 1 km – 100 m Medium frequency MF N/A
3–30 MHz 100–10 m High frequency HF HF
30–300 MHz 10–1 m Very high frequency VHF VHF
300 MHz – 3 GHz 1 m – 10 cm Ultra high frequency UHF UHF, L, S
3–30 GHz 10–1 cm Super high frequency SHF S, C, X, Ku, K, Ka
30–300 GHz 1 cm – 1 mm Extremely high frequency EHF Ka, V, W, mm
300 GHz – 3 THz 1 mm – 0.1 mm Tremendously high frequency THF N/A

Frequencies of 1 GHz and above are conventionally called microwave,[7] while frequencies of 30 GHz and above are designated millimeter wave. More detailed band designations are given by the standard IEEE letter- band frequency designations[5] and the EU/NATO frequency designations.[8]

In communication

Radio frequencies are generated and processed within very many functional units such as transmitters, receivers, computers, and televisions to name a few. Radio frequencies are also applied in carrier current systems including telephony and control circuits.

In medicine

Radio frequency (RF) energy, in the form of radiating waves or electrical currents, has been used in medical treatments for over 75 years,[9] generally for minimally invasive surgeries using radiofrequency ablation including the treatment of sleep apnea.[10]

Effects on the human body

Radio frequency current through tissue will generate heat in the tissue and can cause burns.

Measurement

Test apparatus for radio frequencies can include standard instruments at the lower end of the range, but at higher frequencies the test equipment becomes more specialized.

Mechanical oscillations

While RF usually refers to electrical oscillations, mechanical RF systems are not uncommon: see mechanical filter and RF MEMS.

See also

References

  1. ^ J. A. Fleming, The Principles of Electric Wave Telegraphy and Telephony, London: Longmans, Green & Co., 1919, p. 364
  2. ^ A. A. Ghirardi, Radio Physics Course, 2nd ed. New York: Rinehart Books, 1932, p. 249
  3. ^ Curtis, Thomas Stanley (1916). High Frequency Apparatus: Its Construction and Practical Application. USA: Everyday Mechanics Company. p. 6.
  4. ^ Mieny, C. J. (2003). Principles of Surgical Patient Care (2nd ed.). New Africa Books. p. 136. ISBN 9781869280055.
  5. ^ a b IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands Archived 2013-12-21 at the Wayback Machine, Institute of Electrical and Electronics Engineers, 2002. (Convenience copy at National Academies Press.)
  6. ^ Jeffrey S. Beasley; Gary M. Miller (2008). Modern Electronic Communication (9th ed.). pp. 4–5. ISBN 978-0132251136.
  7. ^ Kumar, Sanjay; Shukla, Saurabh (2014). Concepts and Applications of Microwave Engineering. PHI Learning Pvt. Ltd. p. 3. ISBN 978-8120349353.
  8. ^ Leonid A. Belov; Sergey M. Smolskiy; Victor N. Kochemasov (2012). Handbook of RF, Microwave, and Millimeter-Wave Components. Artech House. pp. 27–28. ISBN 978-1-60807-209-5.
  9. ^ Ruey J. Sung & Michael R. Lauer (2000). Fundamental approaches to the management of cardiac arrhythmias. Springer. p. 153. ISBN 978-0-7923-6559-4. Archived from the original on 2015-09-05.
  10. ^ Melvin A. Shiffman; Sid J. Mirrafati; Samuel M. Lam; Chelso G. Cueteaux (2007). Simplified Facial Rejuvenation. Springer. p. 157. ISBN 978-3-540-71096-7.

External links

Channel (broadcasting)

In broadcasting, a channel or frequency channel is a designated radio frequency (or, equivalently, wavelength), assigned by a competent frequency assignment authority for the operation of a particular radio station, television station or television channel.

Directed-energy weapon

A directed-energy weapon (DEW) is a ranged weapon that damages its target with highly focused energy, including laser, microwaves and particle beams. Potential applications of this technology include weapons that target personnel, missiles, vehicles, and optical devices.In the United States, the Pentagon, DARPA, the Air Force Research Laboratory, United States Army Armament Research Development and Engineering Center, and the Naval Research Laboratory are researching directed-energy weapons and railguns to counter ballistic missiles, hypersonic cruise missiles, and hypersonic glide vehicles. These systems of missile defense are expected to come online no sooner than the mid to late-2020s.Russia, China, India, and the United Kingdom are also developing directed-energy weapons.

After decades of R&D, directed-energy weapons are still at the experimental stage and it remains to be seen if or when they will be deployed as practical, high-performance military weapons.

Electromagnetic interference

Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data. Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras (Northern/Southern Lights). EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy.

EMI can be used intentionally for radio jamming, as in electronic warfare.

Frequency allocation

Frequency allocation (or spectrum allocation or spectrum management) is the allocation and regulation of the electromagnetic spectrum into radio frequency bands, which is normally done by governments in most countries. Because radio propagation does not stop at national boundaries, governments have sought to harmonise the allocation of RF bands and their standardization.

ISO/IEC 18000

ISO/IEC 18000 is an international standard that describes a series of diverse RFID technologies, each using a unique frequency range.

ISO/IEC 18000 consists of the following parts, under the general title Information technology — Radio frequency identification for item management:

Part 1: Reference architecture and definition of parameters to be standardized

Part 2: Parameters for air interface communications below 135 kHz

Part 3: Parameters for air interface communications at 13,56 MHz

Part 4: Parameters for air interface communications at 2,45 GHz

Part 6: Parameters for air interface communications at 860 MHz to 960 MHz

Part 7: Parameters for active air interface communications at 433 MHzThe ISO/IEC 18000-6 is a large document. In 2012 it was split into 5 parts for publication:

Part 6: Parameters for air interface communications at 860 MHz to 960 MHz General

Part 61: Parameters for air interface communications at 860 MHz to 960 MHz Type A

Part 62: Parameters for air interface communications at 860 MHz to 960 MHz Type B

Part 63: Parameters for air interface communications at 860 MHz to 960 MHz Type C

Part 64: Parameters for air interface communications at 860 MHz to 960 MHz Type DThe various parts of ISO/IEC 18000 describe air interface communication at different frequencies in order to be able to utilize the different physical behaviors. The various parts of ISO/IEC 18000 are developed by ISO/IEC JTC1 SC31, "Automatic Data Capture Techniques".

Conformance test methods for the various parts of ISO/IEC 18000 are defined in the corresponding parts of ISO/IEC 18047. (See RFID testing)

Performance test methods are defined in ISO/IEC 18046. (See RFID testing)

Radio-frequency engineering

Radio-frequency engineering, or RF engineering, is a subset of electrical and electronic engineering involving the application of transmission line, waveguide, antenna and electromagnetic field principles to the design and application of devices that produce or utilize signals within the radio band, the frequency range of about 20 kHz up to 300 GHz.It is incorporated into almost everything that transmits or receives a radio wave, which includes, but is not limited to, mobile phones, radios, Wi-Fi, and two-way radios.

RF engineering is a highly specialized field that typically includes the following areas of expertise:

Design of antenna systems to provide radiative coverage of a specified geographical area by an electromagnetic field or to provide specified sensitivity to an electromagnetic field impinging on the antenna.

Design of coupling and transmission line structures to transport RF energy without radiation.

Application of circuit elements and transmission line structures in the design of oscillators, amplifiers, mixers, detectors, combiners, filters, impedance transforming networks and other devices.

Verification and measurement of performance of radio frequency devices and systems.To produce quality results, the RF engineer needs an in-depth knowledge of mathematics, physics and general electronics theory as well as specialized training in areas such as wave propagation, impedance transformations, filters and microstrip printed circuit board design to name a few.

Radio-frequency identification

Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. The tags contain electronically stored information. Passive tags collect energy from a nearby RFID reader's interrogating radio waves. Active tags have a local power source (such as a battery) and may operate hundreds of meters from the RFID reader. Unlike a barcode, the tag need not be within the line of sight of the reader, so it may be embedded in the tracked object. RFID is one method of automatic identification and data capture (AIDC).RFID tags are used in many industries. For example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly line; RFID-tagged pharmaceuticals can be tracked through warehouses; and implanting RFID microchips in livestock and pets enables positive identification of animals.

Since RFID tags can be attached to cash, clothing, and possessions, or implanted in animals and people, the possibility of reading personally-linked information without consent has raised serious privacy concerns. These concerns resulted in standard specifications development addressing privacy and security issues. ISO/IEC 18000 and ISO/IEC 29167 use on-chip cryptography methods for untraceability, tag and reader authentication, and over-the-air privacy. ISO/IEC 20248 specifies a digital signature data structure for RFID and barcodes providing data, source and read method authenticity. This work is done within ISO/IEC JTC 1/SC 31 Automatic identification and data capture techniques. Tags can also be used in shops to expedite checkout, and to prevent theft by customers and employees.

In 2014, the world RFID market was worth US$8.89 billion, up from US$7.77 billion in 2013 and US$6.96 billion in 2012. This figure includes tags, readers, and software/services for RFID cards, labels, fobs, and all other form factors. The market value is expected to rise to US$18.68 billion by 2026.

Radiofrequency ablation

Radiofrequency ablation (RFA) is a medical procedure in which part of the electrical conduction system of the heart, tumor or other dysfunctional tissue is ablated using the heat generated from medium frequency alternating current (in the range of 350–500 kHz). RFA is generally conducted in the outpatient setting, using either local anesthetics or conscious sedation anesthesia. When it is delivered via catheter, it is called radiofrequency catheter ablation.

Two important advantages of radio frequency current (over previously used low frequency AC or pulses of DC) are that it does not directly stimulate nerves or heart muscle and therefore can often be used without the need for general anesthetic, and that it is very specific for treating the desired tissue without significant collateral damage.Documented benefits have led to RFA becoming widely used during the 21st century. RFA procedures are performed under image guidance (such as X-ray screening, CT scan or ultrasound) by an interventional pain specialist (such as an anesthesiologist), interventional radiologist, otolaryngologists, a gastrointestinal or surgical endoscopist, or a cardiac electrophysiologist, a subspecialty of cardiologists.

Transmitter

In electronics and telecommunications, a transmitter or radio transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves.

Transmitters are necessary component parts of all electronic devices that communicate by radio, such as radio and television broadcasting stations, cell phones, walkie-talkies, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, ships, spacecraft, radar sets and navigational beacons. The term transmitter is usually limited to equipment that generates radio waves for communication purposes; or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not usually called transmitters, even though they often have similar circuits.

The term is popularly used more specifically to refer to a broadcast transmitter, a transmitter used in broadcasting, as in FM radio transmitter or television transmitter. This usage typically includes both the transmitter proper, the antenna, and often the building it is housed in.

Visible (optical)
Microwaves
Radio
Wavelength types
History
Pioneers
Transmission
media
Network topology
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Multiplexing
Networks
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Video
Sound
Modulation
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Frequencies & Bands
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