Radio frequency (RF) is a rate of oscillation in the range of about 30 kHz The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of sine wave, particularly those used in radio and audio applications to 300 GHz, which corresponds to the frequency of electrical signals normally used to produce and detect radio waves Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally-occurring radio waves are made by lightning, or by astronomical objects. Artificially-generated radio waves are used for fixed and mobile. RF usually refers to electrical rather than mechanical oscillations, although mechanical RF systems do exist (see mechanical filter and RF MEMS The RF MEMS acronym stands for radio frequency microelectromechanical system, and refers to components of which moving sub-millimeter-sized parts provide RF functionality. RF functionality can be implemented using a variety of RF technologies. Besides RF MEMS technology, ferrite, ferroelectric, GaAs, GaN, InP, RF CMOS, SiC, and SiGe technology are).
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Radio communication
In order to receive radio signals an antenna An antenna is a transducer designed to transmit or receive electromagnetic waves. In other words, antennas convert electromagnetic waves into electrical currents and vice versa. They are used with waves in the radio part of the electromagnetic spectrum, that is, radio waves, and are a necessary part of all radio equipment. Antennas are used in must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner A radio tuner receives radio broadcasts and converts them into audio-frequency signals which can be fed into an amplifier driving a loudspeaker. FM tuner, AM tuner, DAB tuner, etc. are types of radio tuner dealing with transmissions using different methods of modulation. The term tuner is used both for part of a radio receiver which also contains is necessary to tune in to a particular frequency (or frequency range).[1] This is typically done via a resonator – in its simplest form, a circuit with a capacitor A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors a static electric field develops in the dielectric that stores energy and produces a mechanical force between the conductors. An ideal capacitor is and an inductor An inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries. Typically an inductor is a conducting wire shaped as a coil, the loops helping to create a strong forming a tuned circuit An LC circuit is a resonant circuit or tuned circuit that consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C. When connected together, an electric current can alternate between them at the circuit's resonant frequency. The resonator amplifies oscillations within a particular frequency band A frequency range or frequency band is a range of wave frequencies. It most often refers to either a range of frequencies in sound or a range of frequencies in electromagnetic radiation, which includes light and radio waves, while reducing oscillations at other frequencies outside the band. Often the inductor or the capacitor of the tuned circuit is adjustable allowing the user to change the frequencies at which it resonates.[2] The resonant frequency of a tuned circuit is given by the formula
where f0 is the frequency in Hertz The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of sine wave, particularly those used in radio and audio applications, L is inductance Inductance is the property in an electrical circuit where a change in the electric current through that circuit induces an electromotive force that opposes the change in current (See Induced EMF) in Henries In physics, and electronics, the henry is the SI unit of inductance. It is named after Joseph Henry (1797-1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791-1867) in England. The magnetic permeability of the vacuum is 4π×10−7 H/m (henry per metre), and C is capacitance In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge. Capacitance is also a measure of the amount of electrical energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor. In a parallel plate capacitor, capacitance is directly proportional to in Farads The farad is the SI unit of capacitance. The term farad is named after the English physicist Michael Faraday.
Special properties of RF electrical signals
Electrical currents that oscillate at RF have special properties not shared by direct current Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through semiconductors, insulators, or even through a vacuum as in signals. One such property is the ease with which they can ionize air, creating a conductive path through it. This property is exploited by 'high frequency' units used in electric arc welding Arc welding uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a, although strictly speaking these machines do not typically employ frequencies within the HF band. Another special property is that RF current cannot penetrate deeply into electrical conductors but flows along the surface of conductors; this is known as the skin effect Skin effect is the tendency of an alternating electric current to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core. That is, the electric current tends to flow at the "skin" of the conductor, at an average depth called the skin depth. The skin effect. Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric A dielectric is an electrical insulator that may be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, insulator of a capacitor. The degree of effect of these properties depends on the frequency of the signals.
Frequencies
In medicine
Radio frequency (RF) energy has been used in medical treatments for over 75 years,[3] generally for minimally invasive surgeries, using radiofrequency ablation Radio frequency ablation is a medical procedure where part of the electrical conduction system of the heart, tumor or other dysfunctional tissue is ablated using high frequency alternating current to treat a medical disorder. An important advantage of RF current (over previously used low frequency AC or pulses of DC) is that it does not directly and coagulation Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis , wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel. Disorders of coagulation can lead to an increased risk of bleeding (hemorrhage) or obstructive clotting, including the treatment of sleep apnea Sleep apnea is a sleep disorder characterised by abnormal pauses in breathing or instances of abnormally low breathing, during sleep. Each pause in breathing, called an apnea, can last from a few seconds to minutes, and may occur 5 to 30 times or more an hour. Similarly, each abnormally low breathing event is called a hypopnea. Sleep apnea is.[4]
See also
- Electromagnetic radiation Electromagnetic radiation is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to
- Frequency allocation The radio frequency electromagnetic spectrum is an aspect of the physical world which, like land, water, and air, is subject to usage limitations. Use of radio frequency bands of the electromagnetic spectrum is regulated by governments in most countries, in a Spectrum management process known as frequency allocation or spectrum allocation. Radio
- Frequency bandwidth
- Radio waves Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally-occurring radio waves are made by lightning, or by astronomical objects. Artificially-generated radio waves are used for fixed and mobile
- Plastic Sealing/Welding Technologies The purpose of this article is to outline the most commonly used heat sealing technologies in the Industrial Fabrics market using Engineered Textiles with Polymer coatings. Advancements in industrial materials/fabrics, such as greater heat resistance and strength, stronger weaves and coatings, and consistency roll to roll have opened the market up
- RF connector A coaxial RF connector is an electrical connector designed to work at radio frequencies in the multi-megahertz range. RF connectors are typically used with coaxial cables and are designed to maintain the shielding that the coaxial design offers. Better models also minimize the change in transmission line impedance at the connection. Mechanically
- Spectrum management
References
- ^ Brain, Marshall (2000-12-07). "How Radio Works". HowStuffWorks.com. http://electronics.howstuffworks.com/radio8.htm. Retrieved 2009-09-11.
- ^ Brain, Marshall (2000-12-08). "How Oscillators Work". HowStuffWorks.com. http://electronics.howstuffworks.com/oscillator3.htm. Retrieved 2009-09-11.
- ^ Ruey J. Sung and Michael R. Lauer (2000). Fundamental approaches to the management of cardiac arrhythmias. Springer. p. 153. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 9780792365594. http://books.google.com/books?id=S1fWhl2c5zIC&pg=PA153&dq=rf+coagulation+75-years&lr=&as_brr=3&ei=IIhuSpfBJ6aqlQT-n7nmDg.
- ^ Melvin A. Shiffman, Sid J. Mirrafati, Samuel M. Lam and Chelso G. Cueteaux (2007). Simplified Facial Rejuvenation. Springer. p. 157. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 9783540710967. http://books.google.com/books?id=w1fQK21WK28C&pg=RA1-PA157&dq=rf+coagulation+sleep-apnea&lr=&as_brr=3&ei=ZYduSumzKJCckgT_-bHdDg.
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