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Near-field Acoustic Levitation
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Near field may refer to: * Near-field (mathematics), an algebraic structure * Near-field region, part of an electromagnetic field * Near field (electromagnetism) ** Magnetoquasistatic field, the magnetic component of the electromagnetic near field ** Near-field communication (NFC) using the magnetic component of the electromagnetic near field (magnetoquasistatic field) See also * Near-field magnetic induction communication, a technique for deliberately limited-range communication between devices ** Near-field communication (NFC), a set of application protocols based on this * Near-field optics * Near-field scanning optical microscope Near-field scanning optical microscopy (NSOM) or scanning near-field optical microscopy (SNOM) is a microscopy technique for nanostructure investigation that breaks the far field resolution limit by exploiting the properties of evanescent waves ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-field (mathematics)
In mathematics, a near-field is an algebraic structure similar to a division ring, except that it has only one of the two distributive laws. Alternatively, a near-field is a near-ring in which there is a multiplicative identity and every non-zero element has a multiplicative inverse. Definition A near-field is a set Q together with two binary operations, + (addition) and \cdot (multiplication), satisfying the following axioms: :A1: (Q, +) is an abelian group. :A2: (a \cdot b) \cdot c = a \cdot (b \cdot c) for all elements a, b, c of Q (The associative law for multiplication). :A3: (a + b) \cdot c = a \cdot c + b \cdot c for all elements a, b, c of Q (The right distributive law). :A4: Q contains an element 1 such that 1 \cdot a = a \cdot 1 = a for every element a of Q (Multiplicative identity). :A5: For every non-zero element a of Q there exists an element a^ such that a \cdot a^ = 1 = a^ \cdot a (Multiplicative inverse). Notes on the definition # The above is, strictly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-field Region
The near field and far field are regions of the electromagnetic (EM) field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative ''near-field'' behaviors dominate close to the antenna or scattering object, while electromagnetic radiation ''far-field'' behaviors dominate at greater distances. Far-field E (electric) and B (magnetic) field strength decreases as the distance from the source increases, resulting in an inverse-square law for the radiated ''power'' intensity of electromagnetic radiation. By contrast, near-field E and B strength decrease more rapidly with distance: the radiative field decreases by the inverse-distance squared, the reactive field by an inverse-cube law, resulting in a diminished power in the parts of the electric field by an inverse fourth-power and sixth-power, respectively. The rapid drop in power contained in the near-field ensures that effects due to the near-field essentially vanish a f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromagnetic Radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, Light, (visible) light, ultraviolet, X-rays, and gamma rays. All of these waves form part of the electromagnetic spectrum. Classical electromagnetism, Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric field, electric and magnetic fields. Depending on the frequency of oscillation, different wavelengths of electromagnetic spectrum are produced. In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted ''c''. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. The position of an electromagnetic wave w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetoquasistatic Field
A magnetoquasistatic field is a class of electromagnetic field in which a slowly oscillating magnetic field is dominant. A magnetoquasistatic field is typically generated by ''low-frequency'' induction from a magnetic dipole or a current loop. The magnetic near-field of such an emitter behaves differently from the more commonly used far-field electromagnetic radiation. At low frequencies the rate of change of the instantaneous field strength with each cycle is relatively slow, giving rise to the name "magneto-quasistatic". The near field or quasistatic region typically extends no more than a wavelength from the antenna, and within this region the electric and magnetic fields are approximately decoupled. Weakly conducting non-magnetic bodies, including the human body and many mineral rocks, are effectively transparent to magnetoquasistatic fields, allowing for the transmission and reception of signals through such obstacles. Also, long-wavelength (i.e. low-frequency) signals are bett ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-field Communication
Near-field communication (NFC) is a set of communication protocols that enables communication between two electronic devices over a distance of 4 cm (1 in) or less. NFC offers a low-speed connection through a simple setup that can be used to bootstrap more-capable wireless connections. Like other "proximity card" technologies, NFC is based on inductive coupling between two so-called antennas present on NFC-enabled devices—for example a smartphone and a printer—communicating in one or both directions, using a frequency of 13.56 MHz in the globally available unlicensed radio frequency ISM band using the ISO/IEC 18000-3 air interface standard at data rates ranging from 106 to 424 kbit/s. The standards were provided by the NFC Forum. The forum was responsible for promoting the technology and setting standards and certifies device compliance. Secure communications are available by applying encryption algorithms as is done for credit cards and if they fit the crite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-field Magnetic Induction Communication
A near-field magnetic induction (NFMI) communication system is a short range wireless physical layer that communicates by coupling a tight, low-power, non-propagating magnetic field between devices. The concept is for a transmitter coil in one device to modulate a magnetic field which is measured by means of a receiver coil in another device. Background: technical concepts NFMI systems differ from other wireless communications in that most conventional wireless RF systems use an antenna to generate, transmit, and propagate an electromagnetic wave. In these types of systems all of the transmission energy is designed to radiate into free space. This type of transmission is referred to as "far-field." According to Maxwell's equation for a radiating wire, the power density of far-field transmissions attenuates or rolls off at a rate proportional to the inverse of the range to the second power (1/r2) or −20 dB per decade. This slow attenuation over distance allows far-field ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-field Optics
Near-field optics is that branch of optics that considers configurations that depend on the passage of light to, from, through, or near an element with subwavelength features, and the coupling of that light to a second element located a subwavelength distance from the first. The barrier of spatial resolution imposed by the very nature of light itself in conventional optical microscopy contributed significantly to the development of near-field optical devices, most notably the near-field scanning optical microscope, or NSOM. The relatively new optical science of dressed photons (DPs) can also find its origin in near-field optics. Size constraints The limit of optical resolution in a conventional microscope, the so-called diffraction limit, is in the order of half the wavelength of the light used to image. Thus, when imaging at visible wavelengths, the smallest resolvable features are several hundred nanometers in size (although point-like sources, such as quantum dots, can be res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
