Radio frequency

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Radio frequency (RF) is a rate of oscillation in the range of about kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations; however, mechanical RF systems do exist (see mechanical filter and RF MEMS).

Although radio frequency is a rate of oscillation, the term "radio frequency" or its abbreviation "RF" are also used as a synonym for radio – i.e. to describe the use of wireless communication, as opposed to communication via electric wires. Examples include:

Special properties of RF current[edit]

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

Radio communication[edit]

To receive radio signals an antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune into a particular frequency (or frequency range).[4] This is typically done via a resonator – in its simplest form, a circuit with a capacitor and an inductor form a tuned circuit. The resonator amplifies oscillations within a particular frequency band, while reducing oscillations at other frequencies outside the band.

Frequencies[edit]

FrequencyWavelengthDesignationAbbreviation[5]
3 – 30 Hz105 – 104 kmExtremely low frequencyELF
30 – 300 Hz104 – 103 kmSuper low frequencySLF
300 – 3000 Hz103 – 100 kmUltra low frequencyULF
3 – 30 kHz100 – 10 kmVery low frequencyVLF
30 – 300 kHz10 – 1 kmLow frequencyLF
300 kHz – 3 MHz1 km – 100 mMedium frequencyMF
3 – 30 MHz100 – 10 mHigh frequencyHF
30 – 300 MHz10 – 1 mVery high frequencyVHF
300 MHz – 3 GHz1 m – 10 cmUltra high frequencyUHF
3 – 30 GHz10 – 1 cmSuper high frequencySHF
30 – 300 GHz1 cm – 1 mmExtremely high frequencyEHF
300 GHz - 3000 GHz1 mm - 0.1 mmTremendously high frequencyTHF

The inverse relation between frequency and wavelength deduces that the higher the frequency of the RF Signal, the smaller its wavelength and vice versa. Thus, under similar conditions of propagation, the higher frequency signal attenuates faster than the lower frequency signal and becomes too weak to be detected at the end of the receiver, located at larger distances. An RF power amplifier is used to amplify the power level of such a transmitter RF Signal, so that it can travel larger distances with less attenuation.

In medicine[edit]

Radio frequency (RF) energy has been used in medical treatments for over 75 years,[6] generally for minimally invasive surgeries, using radiofrequency ablation and cryoablation, including the treatment of sleep apnea.[7] Magnetic resonance imaging (MRI) uses radio frequency waves to generate images of the human body.

Radio frequencies at non-ablation energy levels are sometimes used as a form of cosmetic treatment that can tighten skin, reduce fat, or promote healing.[8]

RF diathermy is a medical treatment that uses RF induced heat as a form of physical or occupational therapy and in surgical procedures. It is commonly used for muscle relaxation. It is also a method of heating tissue electromagnetically for therapeutic purposes in medicine. Diathermy is used in physical therapy and occupational therapy to deliver moderate heat directly to pathologic lesions in the deeper tissues of the body. Surgically, the extreme heat that can be produced by diathermy may be used to destroy neoplasms, warts, and infected tissues, and to cauterize blood vessels to prevent excessive bleeding. The technique is particularly valuable in neurosurgery and surgery of the eye. Diathermy equipment typically operates in the short-wave radio frequency (range 1–100 MHz) or microwave energy (range 434–915 MHz).

Pulsed electromagnetic field therapy (PEMF) is a medical treatment that purportedly helps to heal bone tissue reported in a recent NASA study. This method usually employs electromagnetic radiation of different frequencies - ranging from static magnetic fields, through extremely low frequencies (ELF) to higher radio frequencies (RF) administered in pulses.

RF Effects on the human body[edit]

Extremely Low frequency RF with electric field levels in the low Kv/m range are known to induce perceivable currents within the human body that create an annoying tingling sensation. These currents will typically flow to ground through a body contact surface such as the feet, or arc to ground where the body is well insulated.[9][10]

Canadian safety code 6, also, recommends electric field limits of 100 kV/m for pulsed EMF to prevent air breakdown and spark discharges. Additional rational for EMF restrictions is to avoid auditory effect and energy-induced unconsciousness in rats.[11]

Also, see Microwave burn and Electromagnetic radiation and health

As a weapon[edit]

A heat ray is a RF harassment device that makes use of microwave radio frequencies to create an unpleasant heating effect in the upper layer of the skin. A publically known heat ray weapon called the Active Denial System was developed by the US military as an experimental weapon to deny the enemy access to an area. Also, see death ray which is a heat ray weapon that delivers electromagnetic energy at levels that injure human tissue. The inventor of the death ray, Harry Grindell Matthews, claims to have lost sight in his left eye while developing his death ray weapon based on a primitive microwave magnetron from the 1920s. (Note that a typical microwave oven induces a tissue damaging cooking effect inside the oven at about 2 kV/m.)

Also, see, directed energy weapons

See also[edit]

References[edit]

  1. ^ "ISO/IEC 14443-2:2001 Identification cards — Contactless integrated circuit(s) cards — Proximity cards — Part 2: Radio frequency power and signal interface". Iso.org. 2010-08-19. Retrieved 2011-11-08. 
  2. ^ Curtis, Thomas Stanley (1916). High Frequency Apparatus: Its Construction and Practical Application. USA: Everyday Mechanics Company. p. 6. 
  3. ^ Mieny, C. J. (2003). Principles of Surgical Patient Care (2nd ed.). New Africa Books. p. 136. ISBN 9781869280055. 
  4. ^ Brain, Marshall (2000-12-07). "How Radio Works". HowStuffWorks.com. Retrieved 2009-09-11. 
  5. ^ Jeffrey S. Beasley; Gary M. Miller (2008). Modern Electronic Communication (9th ed.). pp. 4–5. ISBN 978-0132251136. 
  6. ^ Ruey J. Sung and Michael R. Lauer (2000). Fundamental approaches to the management of cardiac arrhythmias. Springer. p. 153. ISBN 978-0-7923-6559-4. 
  7. ^ Melvin A. Shiffman, Sid J. Mirrafati, Samuel M. Lam and Chelso G. Cueteaux (2007). Simplified Facial Rejuvenation. Springer. p. 157. ISBN 978-3-540-71096-7. 
  8. ^ Noninvasive Radio Frequency for Skin Tightening and Body Contouring, Frontline Medical Communications, 2013
  9. ^ Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency Range from 3 kHz to 300 GHz, Canada Safety Code 6, page 63
  10. ^ Extremely Low Frequency Fields Environmental Health Criteria Monograph No.238, chapter 5, page 121, WHO
  11. ^ Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency Range from 3 kHz to 300 GHz, Canada Safety Code 6, page 62

External links[edit]