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Therefore, in addition to electrical and fire safety concerns, such cables may also be required to be pressure-resistant where they penetrate a vessel's bulkheads. They must also resist corrosion caused by salt water or salt spray, which is accomplished through the use of thicker, specially constructed jackets, and by ... | Wikipedia - Electrical wiring - Cables > Modern wiring materials | 161 | 827 | null |
Section: Cables > Aluminium conductors. Aluminium wire was common in North American residential wiring from the late 1960s to mid-1970s due to the rising cost of copper. Because of its greater resistivity, aluminium wiring requires larger conductors than copper. For instance, instead of 14 AWG (American wire gauge) cop... | Wikipedia - Electrical wiring - Cables > Aluminium conductors | 334 | 1,805 | null |
This is sometimes addressed by coating aluminium conductors with an antioxidant paste (containing zinc dust in a low-residue polybutene base) at joints, or by applying a mechanical termination designed to break through the oxide layer during installation. Some terminations on wiring devices designed only for copper wir... | Wikipedia - Electrical wiring - Cables > Aluminium conductors | 261 | 1,458 | null |
Section: Raceways and cable runs. Insulated wires may be run in one of several forms between electrical devices. This may be a specialised bendable pipe, called a conduit, or one of several varieties of metal (rigid steel or aluminium) or non-metallic (PVC or HDPE) tubing. Rectangular cross-section metal or PVC wire tr... | Wikipedia - Electrical wiring - Raceways and cable runs | 342 | 1,707 | null |
Section: Bus bars, bus duct, cable bus. For very high currents in electrical apparatus, and for high currents distributed through a building, bus bars can be used. (The term "bus" is a contraction of the Latin omnibus – meaning "for all".) Each live ("hot") conductor of such a system is a rigid piece of copper or alumi... | Wikipedia - Electrical wiring - Bus bars, bus duct, cable bus | 347 | 1,659 | null |
Section: Early wiring methods. The first interior power wiring systems used conductors that were bare or covered with cloth, which were secured by staples to the framing of the building or on running boards. Where conductors went through walls, they were protected with cloth tape. Splices were done similarly to telegra... | Wikipedia - Electrical wiring - Early wiring methods | 171 | 935 | null |
Section: Early wiring methods > Knob and tube (US). The earliest standardized method of wiring in buildings, in common use in North America from about 1880 to the 1930s, was knob and tube (K&T) wiring: single conductors were run through cavities between the structural members in walls and ceilings, with ceramic tubes f... | Wikipedia - Electrical wiring - Early wiring methods > Knob and tube (US) | 202 | 1,053 | null |
Section: Early wiring methods > Metal-sheathed wires. In the United Kingdom, an early form of insulated cable, introduced in 1896, consisted of two impregnated-paper-insulated conductors in an overall lead sheath. Joints were soldered, and special fittings were used for lamp holders and switches. These cables were simi... | Wikipedia - Electrical wiring - Early wiring methods > Metal-sheathed wires | 335 | 1,637 | null |
Section: Early wiring methods > Other historical wiring methods. Armored cables with two rubber-insulated conductors in a flexible metal sheath were used as early as 1906, and were considered at the time a better method than open knob-and-tube wiring, although much more expensive. The first rubber-insulated cables for ... | Wikipedia - Electrical wiring - Early wiring methods > Other historical wiring methods | 338 | 1,702 | null |
US Type THN, THHN, etc.) became common. The simplest form of cable has two insulated conductors twisted together to form a unit. Such non-jacketed cables with two (or more) conductors are used only for extra-low voltage signal and control applications such as doorbell wiring. Other methods of securing wiring that are n... | Wikipedia - Electrical wiring - Early wiring methods > Other historical wiring methods | 349 | 1,757 | null |
Article: Electroactive polymer. An electroactive polymer (EAP) is a polymer that exhibits a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. A typical characteristic property of an EAP is that they will undergo a large amou... | Wikipedia - Electroactive polymer - Summary | 182 | 892 | null |
Section: History. The field of EAPs emerged back in 1880, when Wilhelm Röntgen designed an experiment in which he tested the effect of an electrostatic field on the mechanical properties of a stripe of natural rubber. The rubber stripe was fixed at one end and was attached to a mass at the other. Electric charges were ... | Wikipedia - Electroactive polymer - History | 350 | 1,692 | null |
In 1977 the first electrically conducting polymers were discovered by Hideki Shirakawa et al. Shirakawa, along with Alan MacDiarmid and Alan Heeger, demonstrated that polyacetylene was electrically conductive, and that by doping it with iodine vapor, they could enhance its conductivity by 8 orders of magnitude. Thus th... | Wikipedia - Electroactive polymer - History | 335 | 1,602 | null |
Section: Types > Dielectric. Dielectric EAPs are materials in which actuation is caused by electrostatic forces between two electrodes which squeeze the polymer. Dielectric elastomers are capable of very high strains and are fundamentally a capacitor that changes its capacitance when a voltage is applied by allowing th... | Wikipedia - Electroactive polymer - Types > Dielectric | 153 | 712 | null |
Section: Types > Ionic. Ionic EAPs are polymers in which actuation is caused by the displacement of ions inside the polymer. Only a few volts are needed for actuation, but the ionic flow implies that higher electrical power is needed for actuation, and energy is needed to keep the actuator at a given position. Examples... | Wikipedia - Electroactive polymer - Types > Ionic | 181 | 809 | null |
Section: Types > Ionic > Ionic polymer-metal composite. Ionic polymer-metal composites consist of a thin ionomeric membrane with noble metal electrodes plated on its surface. It also has cations to balance the charge of the anions fixed to the polymer backbone. They are very active actuators that show very high deforma... | Wikipedia - Electroactive polymer - Types > Ionic > Ionic polymer-metal composite | 152 | 740 | null |
Section: Types > Ionic > Stimuli-responsive gels. Stimuli-responsive gels (hydrogels, when the swelling agent is an aqueous solution) are a special kind of swellable polymer networks with volume phase transition behaviour. These materials change reversibly their volume, optical, mechanical and other properties by very ... | Wikipedia - Electroactive polymer - Types > Ionic > Stimuli-responsive gels | 175 | 910 | null |
Section: Comparison of dielectric and ionic EAPs. Dielectric polymers are able to hold their induced displacement while activated under a DC voltage. This allows dielectric polymers to be considered for robotic applications. These types of materials also have high mechanical energy density and can be operated in air wi... | Wikipedia - Electroactive polymer - Comparison of dielectric and ionic EAPs | 169 | 824 | null |
Section: Characterization > Dynamic mechanical thermal analysis (DMTA). Dynamic mechanical analysis is a non destructive technique that is useful in understanding the mechanism of deformation at a molecular level. In DMTA a sinusoidal stress is applied to the polymer, and based on the polymer's deformation, the elastic... | Wikipedia - Electroactive polymer - Characterization > Dynamic mechanical thermal analysis (DMTA) | 168 | 846 | null |
Section: Applications > Tactile displays. In recent years, "electro active polymers for refreshable Braille displays" has emerged to aid the visually impaired in fast reading and computer assisted communication. This concept is based on using an EAP actuator configured in an array form. Rows of electrodes on one side o... | Wikipedia - Electroactive polymer - Applications > Tactile displays | 240 | 1,210 | null |
Section: Applications > Microfluidics. EAP materials have huge potential for microfluidics, e.g. as drug delivery systems, microfluidic devices and lab-on-a-chip. A first microfluidic platform technology reported in the literature is based on stimuli-responsive gels. To avoid the electrolysis of water, hydrogel-based m... | Wikipedia - Electroactive polymer - Applications > Microfluidics | 332 | 1,641 | null |
Another technology that can benefit from the unique properties of EAP actuators is optical membranes. Due to their low modulus, the mechanical impedance of the actuators, they are well-matched to common optical membrane materials. Also, a single EAP actuator is capable of generating displacements that range from microm... | Wikipedia - Electroactive polymer - Applications > Microfluidics | 175 | 878 | null |
Section: Future directions. The field of EAPs is far from mature, which leaves several issues that still need to be worked on. The performance and long-term stability of the EAP should be improved by designing a water impermeable surface. This will prevent the evaporation of water contained in the EAP, and also reduce ... | Wikipedia - Electroactive polymer - Future directions | 213 | 1,056 | null |
Article: Field electron emission. Field electron emission, also known as field-induced electron emission, field emission (FE) and electron field emission, is the emission of electrons from a material placed in an electrostatic field. The most common context is field emission from a solid surface into a vacuum. However,... | Wikipedia - Field electron emission - Summary | 319 | 1,594 | null |
In some contexts (e.g. spacecraft engineering), the name "field emission" is applied to the field-induced emission of ions (field ion emission), rather than electrons, and because in some theoretical contexts "field emission" is used as a general name covering both field electron emission and field ion emission. Field ... | Wikipedia - Field electron emission - Summary | 307 | 1,518 | null |
In the modern context, cold field electron emission (CFE) is the name given to a particular statistical emission regime, in which the electrons in the emitter are initially in internal thermodynamic equilibrium, and in which most emitted electrons escape by Fowler–Nordheim tunneling from electron states close to the em... | Wikipedia - Field electron emission - Summary | 285 | 1,375 | null |
Section: Terminology and conventions. Equations in this article are written using the modern International System of Quantities (ISQ). Older field emission literature (and papers that directly copy equations from old literature) often work with Gaussian units such that they omit the physical constant ε0. In this articl... | Wikipedia - Field electron emission - Terminology and conventions | 158 | 806 | null |
Section: Early history of field electron emission. In retrospect, it seems likely that the electrical discharges reported by J.H. Winkler in 1744 were started by CFE from his wire electrode. However, meaningful investigations had to wait until after J.J. Thomson's identification of the electron in 1897, and until after... | Wikipedia - Field electron emission - Early history of field electron emission | 330 | 1,623 | null |
V were not straight. Walter H. Schottky suggested in 1923 that the effect might be due to thermally induced emission over a field-reduced barrier. If so, then plots of log(i) vs. √V should be straight, but they were not. Nor is Schottky's explanation compatible with the experimental observation of only very weak temper... | Wikipedia - Field electron emission - Early history of field electron emission | 322 | 1,495 | null |
Oppenheimer had mathematical details of his theory seriously incorrect. There was also a small numerical error in the final equation given by Fowler–Nordheim theory for CFE current density, corrected in a 1929 paper. If the barrier field in Fowler–Nordheim 1928 theory is exactly proportional to the applied voltage, and... | Wikipedia - Field electron emission - Early history of field electron emission | 340 | 1,673 | null |
The Fowler–Nordheim 1928 work suggested that thermions did not need to exist as a separate class of internal electrons: electrons could come from a single band occupied in accordance with Fermi–Dirac statistics, but would be emitted in statistically different ways under different conditions of temperature and applied f... | Wikipedia - Field electron emission - Early history of field electron emission | 208 | 1,044 | null |
Section: Practical applications: past and present > Field electron microscopy and related basics. As already indicated, the early experimental work on field electron emission (1910–1920) was driven by Lilienfeld's desire to develop miniaturized X-ray tubes for medical applications. However, it was too early for this te... | Wikipedia - Field electron emission - Practical applications: past and present > Field electron microscopy and related basics | 319 | 1,403 | null |
When the emitter surface is clean, this FEM image is characteristic of: (a) the material from which the emitter is made: (b) the orientation of the material relative to the needle/wire axis; and (c) to some extent, the shape of the emitter endform. In the FEM image, dark areas correspond to regions where the local work... | Wikipedia - Field electron emission - Practical applications: past and present > Field electron microscopy and related basics | 345 | 1,537 | null |
A consequence of FEM development, and subsequent experimentation, was that it became possible to identify (from FEM image inspection) when an emitter was "clean", and hence exhibiting its clean-surface work-function as established by other techniques. This was important in experiments designed to test the validity of t... | Wikipedia - Field electron emission - Practical applications: past and present > Field electron microscopy and related basics | 233 | 1,146 | null |
Section: Practical applications: past and present > Field electron spectroscopy (electron energy analysis). Energy distribution measurements of field-emitted electrons were first reported in 1939. In 1959 it was realized theoretically by Young, and confirmed experimentally by Young and Mueller that the quantity measure... | Wikipedia - Field electron emission - Practical applications: past and present > Field electron spectroscopy (electron energy analysis) | 210 | 1,179 | null |
Section: Practical applications: past and present > Atomically sharp emitters. Nowadays it is possible to prepare very sharp emitters, including emitters that end in a single atom. In this case, electron emission comes from an area about twice the crystallographic size of a single atom. This was demonstrated by compari... | Wikipedia - Field electron emission - Practical applications: past and present > Atomically sharp emitters | 163 | 789 | null |
Section: Practical applications: past and present > Vacuum breakdown and electrical discharge phenomena. As already indicated, it is now thought that the earliest manifestations of field electron emission were the electrical discharges it caused. After Fowler–Nordheim work, it was understood that CFE was one of the pos... | Wikipedia - Field electron emission - Practical applications: past and present > Vacuum breakdown and electrical discharge phenomena | 231 | 1,244 | null |
Section: Fowler–Nordheim tunneling. Fowler–Nordheim tunneling is the wave-mechanical tunneling of an electron through an exact or rounded triangular barrier. Depending on the material's structure, the electron may be initially localized to the surface or delocalized into the bulk and best represented by a travelling wa... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling | 253 | 1,311 | null |
Section: Fowler–Nordheim tunneling > Motive energy. For an electron, the one-dimensional Schrödinger equation can be written in the form where Ψ(x) is the electron wave-function, expressed as a function of distance x measured from the emitter's electrical surface, ħ is the reduced Planck constant, m is the electron mas... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling > Motive energy | 313 | 1,347 | null |
Section: Fowler–Nordheim tunneling > Escape probability. For an electron approaching a given barrier from the inside, the probability of escape (or "transmission coefficient" or "penetration coefficient") is a function of h and F, and is denoted by D(h, F). The primary aim of tunneling theory is to calculate D(h, F). F... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling > Escape probability | 341 | 1,376 | null |
Section: Fowler–Nordheim tunneling > Correction factor for the Schottky–Nordheim barrier. The Schottky–Nordheim barrier, which is the barrier model used in deriving the standard Fowler–Nordheim-type equation, is a special case. In this case, it is known that the correction factor ν {\displaystyle {\it {\nu }}} is a fun... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling > Correction factor for the Schottky–Nordheim barrier | 252 | 963 | null |
Section: Fowler–Nordheim tunneling > Decay width. The decay width (in energy), dh, measures how fast the escape probability D decreases as the barrier height h increases; dh is defined by: When h increases by dh then the escape probability D decreases by a factor close to e ( ≈ 2.718282). For an elementary model, based... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling > Decay width | 275 | 931 | null |
Section: Fowler–Nordheim tunneling > Comments. A historical note is necessary. The idea that the Schottky–Nordheim barrier needed a correction factor, as in eq. (9), was introduced by Nordheim in 1928, but his mathematical analysis of the factor was incorrect. A new (correct) function was introduced by Burgess, Kroemer... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling > Comments | 331 | 1,569 | null |
For tunneling well below the top of a well-behaved barrier of reasonable height, the escape probability D(h, F) is given formally by: where ν(h, F) is a correction factor that in general has to be found by numerical integration. For the special case of a Schottky–Nordheim barrier, an analytical result exists and ν(h, F... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling > Comments | 328 | 1,465 | null |
When the emitter is so sharp that atomic-level detail cannot be neglected, and/or the tunneling barrier is thicker than the emitter-apex dimensions, then a more sophisticated approach is desirable. As noted at the beginning, the effects of the atomic structure of materials are disregarded in the relatively simple treat... | Wikipedia - Field electron emission - Fowler–Nordheim tunneling > Comments | 214 | 1,081 | null |
Section: Total-energy distribution. The energy distribution of the emitted electrons is important both for scientific experiments that use the emitted electron energy distribution to probe aspects of the emitter surface physics and for the field emission sources used in electron beam instruments such as electron micros... | Wikipedia - Field electron emission - Total-energy distribution | 314 | 1,571 | null |
This is also true (or nearly true) when the emission comes from a small field enhancing protrusion on an otherwise flat surface. To see how the total energy distribution can be calculated within the framework of a Sommerfeld free-electron-type model, look at the P-T energy-space diagram (P-T="parallel-total"). This sho... | Wikipedia - Field electron emission - Total-energy distribution | 349 | 1,336 | null |
This element of incident current density sees a barrier of height h given by: The corresponding escape probability is D(h, F): this may be expanded (approximately) in the form where DF is the escape probability for a barrier of unreduced height equal to the local work-function φ. Hence, the element dεdKp makes a contri... | Wikipedia - Field electron emission - Total-energy distribution | 218 | 815 | null |
Hence, the element dεdKp makes a contribution z S f F D D d ϵ d K p {\displaystyle z_{\mathrm {S} }f_{\mathrm {FD} }D\mathrm {d} {\it {\epsilon }}\mathrm {d} K_{\mathrm {p} }} to the emission current density, and the total contribution made by incident electrons with energies in the elementary range dε is thus where th... | Wikipedia - Field electron emission - Total-energy distribution | 330 | 1,020 | null |
For a given emitter, with a given field applied to it, j F {\displaystyle j_{\mathrm {F} }} is independent of F, so eq. (21) shows that the shape of the distribution (as ε increases from a negative value well below the Fermi level) is a rising exponential, multiplied by the FD distribution function. This generates the ... | Wikipedia - Field electron emission - Total-energy distribution | 176 | 728 | null |
Section: Cold field electron emission > Fowler–Nordheim-type equations > Introduction. Fowler–Nordheim-type equations, in the J–F form, are (approximate) theoretical equations derived to describe the local current density J emitted from the internal electron states in the conduction band of a bulk metal. The emission c... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Introduction | 203 | 1,000 | null |
Section: Cold field electron emission > Fowler–Nordheim-type equations > Zero-temperature form. Current density is best measured in A/m2. The total current density emitted from a small uniform region can be obtained by integrating the total energy distribution j(ε) with respect to total electron energy ε. At zero tempe... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Zero-temperature form | 327 | 1,204 | null |
The electron state at point "F" on the diagram ("state F") is the "forwards moving state at the Fermi level" (i.e., it describes a Fermi-level electron moving normal to and towards the emitter surface). At 0 K, an electron in this state sees a barrier of unreduced height φ, and has an escape probability DF that is high... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Zero-temperature form | 281 | 1,183 | null |
Section: Cold field electron emission > Fowler–Nordheim-type equations > Non-zero temperatures. To obtain a result valid for non-zero temperature, we note from eq. (23) that zSdFDF = J0/dF. So when eq. (21) is integrated at non-zero temperature, then – on making this substitution, and inserting the explicit form of the... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Non-zero temperatures | 346 | 1,157 | null |
Normal thinking has been that, in the CFE regime, λT is always small in comparison with other uncertainties, and that it is usually unnecessary to explicitly include it in formulae for the current density at room temperature. The emission regimes for metals are, in practice, defined, by the ranges of barrier field F an... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Non-zero temperatures | 230 | 1,054 | null |
Section: Cold field electron emission > Fowler–Nordheim-type equations > Physically complete Fowler–Nordheim-type equation. Result (23) also leads to some understanding of what happens when atomic-level effects are taken into account, and the band-structure is no longer free-electron like. Due to the presence of the at... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Physically complete Fowler–Nordheim-type equation | 268 | 1,175 | null |
Modinos has discussed how this factor might be calculated: he estimates that it is most likely to be between 0.1 and 1; it might lie outside these limits but is most unlikely to lie outside the range 0.01 < λB < 10. By defining an overall supply correction factor λZ equal to λT λB λd2, and combining equations above, we... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Physically complete Fowler–Nordheim-type equation | 298 | 1,138 | null |
The so-called elementary Fowler–Nordheim-type equation, that appears in undergraduate textbook discussions of field emission, is obtained by putting λZ → 1, PF → 1, ν F {\displaystyle {\nu }_{\mathrm {F} }} → 1; this does not yield good quantitative predictions because it makes the barrier stronger than it is in physic... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Physically complete Fowler–Nordheim-type equation | 313 | 1,154 | null |
Section: Cold field electron emission > Fowler–Nordheim-type equations > Recommended form for simple Fowler–Nordheim-type calculations. Explicitly, this recommended simplified standard Fowler–Nordheim-type equation, and associated formulae, are: where Fφ here is the field needed to reduce to zero a Schottky–Nordheim ba... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Recommended form for simple Fowler–Nordheim-type calculations | 324 | 1,291 | null |
Section: Cold field electron emission > Fowler–Nordheim-type equations > Comments. A historical note on methods of deriving Fowler–Nordheim-type equations is necessary. There are several possible approaches to deriving these equations, using free-electron theory. The approach used here was introduced by Forbes in 2004 ... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Comments | 344 | 1,694 | null |
Further, integrating via the normal-energy distribution does not generate experimentally measured electron energy distributions. In general, the approach used here seems easier to understand, and leads to simpler mathematics. It is also closer in principle to the more sophisticated approaches used when dealing with rea... | Wikipedia - Field electron emission - Cold field electron emission > Fowler–Nordheim-type equations > Comments | 165 | 889 | null |
Section: Cold field electron emission > CFE theoretical equations. The preceding section explains how to derive Fowler–Nordheim-type equations. Strictly, these equations apply only to CFE from bulk metals. The ideas in the following sections apply to CFE more generally, but eq. (30) will be used to illustrate them. For... | Wikipedia - Field electron emission - Cold field electron emission > CFE theoretical equations | 336 | 1,536 | null |
For a metal emitter, the β−value for a given position will be constant (independent of voltage) under the following conditions: (1) the apparatus is a "diode" arrangement, where the only electrodes present are the emitter and a set of "surroundings", all parts of which are at the same voltage; (2) no significant field-... | Wikipedia - Field electron emission - Cold field electron emission > CFE theoretical equations | 335 | 1,474 | null |
A parameter Ar, called the notional emission area (with respect to point "r"), is then defined by: where the integral is taken across the part of the emitter of interest. This parameter Ar was introduced into CFE theory by Stern, Gossling and Fowler in 1929 (who called it a "weighted mean area"). For practical emitters... | Wikipedia - Field electron emission - Cold field electron emission > CFE theoretical equations | 327 | 1,554 | null |
Section: Cold field electron emission > Modified equations for large-area emitters. The equations in the preceding section apply to all field emitters operating in the CFE regime. However, further developments are useful for large-area emitters that contain many individual emission sites. For such emitters, the notiona... | Wikipedia - Field electron emission - Cold field electron emission > Modified equations for large-area emitters | 274 | 1,304 | null |
The presence of αr in eq. (36) accounts for the difference between the macroscopic current densities often cited in the literature (typically 10 A/m2 for many forms of large-area emitter other than Spindt arrays) and the local current densities at the actual emission sites, which can vary widely but which are thought t... | Wikipedia - Field electron emission - Cold field electron emission > Modified equations for large-area emitters | 341 | 1,564 | null |
A "field enhancement factor" γ is then defined and related to the values of βr and βM by With eq. (31), this generates the following formulae: where, in accordance with the usual convention, the suffix "r" has now been dropped from parameters relating to the reference point. Formulae exist for the estimation of γ, usin... | Wikipedia - Field electron emission - Cold field electron emission > Modified equations for large-area emitters | 313 | 1,405 | null |
Various trade-offs and constraints exist. In practice, although the definition of macroscopic field used above is the commonest one, other (differently defined) types of macroscopic field and field enhancement factor are used in the literature, particularly in connection with the use of probes to investigate the i–V ch... | Wikipedia - Field electron emission - Cold field electron emission > Modified equations for large-area emitters | 162 | 814 | null |
Section: Cold field electron emission > Modified equations for nanometrically sharp emitters. Most of the theoretical derivations in the field emission theory are done under the assumption that the barrier takes the Schottky–Nordheim form eq. (3). However, this barrier form is not valid for emitters with radii of curva... | Wikipedia - Field electron emission - Cold field electron emission > Modified equations for nanometrically sharp emitters | 336 | 1,392 | null |
However, modern emitters are much sharper than this, with radii that of the order of a few nm. Therefore, the standard FN equation, or any version of it that assumes the SN barrier, leads to significant errors for such sharp emitters. This has been both shown theoretically and confirmed experimentally. The above proble... | Wikipedia - Field electron emission - Cold field electron emission > Modified equations for nanometrically sharp emitters | 333 | 1,288 | null |
(23). It yields where the functions λ d ( f ) {\displaystyle \lambda _{d}(f)} and ψ ( f ) {\displaystyle \psi (f)} are defined as and In equation (46), for completeness purposes, λd is not approximated by unity as in (29) and (30a), although for most practical cases it is a very good approximation. Apart from this, equ... | Wikipedia - Field electron emission - Cold field electron emission > Modified equations for nanometrically sharp emitters | 280 | 1,118 | null |
Section: Cold field electron emission > Empirical CFE i–V equation. At the present stage of CFE theory development, it is important to make a distinction between theoretical CFE equations and an empirical CFE equation. The former are derived from condensed matter physics (albeit in contexts where their detailed develop... | Wikipedia - Field electron emission - Cold field electron emission > Empirical CFE i–V equation | 322 | 1,505 | null |
However, it should now be possible to make reasonably accurate measurements of dlni/d(1/V) (if necessary by using lock-in amplifier/phase-sensitive detection techniques and computer-controlled equipment), and to derive κ from the slope of an appropriate data plot. Following the discovery of approximation (30b), it is n... | Wikipedia - Field electron emission - Cold field electron emission > Empirical CFE i–V equation | 286 | 1,184 | null |
Thus, it is clear that the factor v(f) in the exponent of the theoretical equation (30) gives rise to additional V-dependence in the pre-exponential of the empirical equation. Thus, (for effects due to the Schottky–Nordheim barrier, and for an emitter with φ = 4.5 eV) we obtain the prediction: Since there may also be v... | Wikipedia - Field electron emission - Cold field electron emission > Empirical CFE i–V equation | 325 | 1,427 | null |
Section: Fowler–Nordheim plots and Millikan–Lauritsen plots. The original theoretical equation derived by Fowler and Nordheim has, for the last 80 years, influenced the way that experimental CFE data has been plotted and analyzed. In the very widely used Fowler–Nordheim plot, as introduced by Stern et al. in 1929, the ... | Wikipedia - Field electron emission - Fowler–Nordheim plots and Millikan–Lauritsen plots | 315 | 1,396 | null |
In the common case of a film emitter generated on one plate of a two-plate arrangement with plate-separation W (so βM = 1/W) then Nowadays, this is one of the most likely applications of Fowler–Nordheim plots.] It subsequently became clear that the original thinking above is strictly correct only for the physically unr... | Wikipedia - Field electron emission - Fowler–Nordheim plots and Millikan–Lauritsen plots | 349 | 1,527 | null |
In practice, due to the extra complexity involved in taking the slope correction factor into detailed account, many authors (in effect) put σFN = 1 in eq. (49), thereby generating a systematic error in their estimated values of β and/or γ, thought usually to be around 5%. However, empirical equation (42) – which in pri... | Wikipedia - Field electron emission - Fowler–Nordheim plots and Millikan–Lauritsen plots | 336 | 1,354 | null |
1/V]. This is the form of plot used by Millikan and Lauritsen in 1928. Rearranging eq. (43) gives Thus, B can be determined, to a good degree of approximation, by determining the mean slope of a Millikan–Lauritsen plot over some range of values of 1/V, and by applying a correction, using the value of 1/V at the midpoin... | Wikipedia - Field electron emission - Fowler–Nordheim plots and Millikan–Lauritsen plots | 320 | 1,351 | null |
(4) This procedure takes into account all physical effects that influence the value of κ, whereas the Fowler–Nordheim-plot correction procedure (in the form in which it has been carried out for the last 50 years) takes into account only those effects associated with barrier shape – assuming, furthermore, that this shap... | Wikipedia - Field electron emission - Fowler–Nordheim plots and Millikan–Lauritsen plots | 201 | 989 | null |
Section: Further theoretical information. Developing the approximate theory of CFE from metals above is comparatively easy, for the following reasons. (1) Sommerfeld's free-electron theory, with its particular assumptions about the distribution of internal electron states in energy, applies adequately to many metals as... | Wikipedia - Field electron emission - Further theoretical information | 301 | 1,473 | null |
For materials other than metals (and for atomically sharp metal emitters) one or more of the above factors will be untrue. For example, crystalline semiconductors do not have a free-electron-like band-structure, do have surface states, are subject to field penetration and band bending, and may exhibit both internal vol... | Wikipedia - Field electron emission - Further theoretical information | 298 | 1,451 | null |
However, attempts to derive meaningful current density values will usually or always fail. Note that a straight line in a Fowler–Nordheim or Millikan–Lauritsen plot does not indicate that emission from the corresponding material obeys a Fowler–Nordheim-type equation: it indicates only that the emission mechanism for in... | Wikipedia - Field electron emission - Further theoretical information | 266 | 1,424 | null |
Article: Field-induced polymer electroluminescent technology. Field-induced polymer electroluminescent (FIPEL) technology is a low power electroluminescent light source. Three layers of moldable light-emitting polymer blended with a small amount of carbon nanotubes glow when an alternating current is passed through the... | Wikipedia - Field-induced polymer electroluminescent technology - Summary | 283 | 1,357 | null |
Article: First-order hold. First-order hold (FOH) is a mathematical model of the practical reconstruction of sampled signals that could be done by a conventional digital-to-analog converter (DAC) and an analog circuit called an integrator. For FOH, the signal is reconstructed as a piecewise linear approximation to the ... | Wikipedia - First-order hold - Summary | 284 | 1,290 | null |
Section: Basic first-order hold. First-order hold is the hypothetical filter or LTI system that converts the ideally sampled signal to the piecewise linear signal x F O H ( t ) = ∑ n = − ∞ ∞ x ( n T ) t r i ( t − n T T ) {\displaystyle x_{\mathrm {FOH} }(t)\,=\sum _{n=-\infty }^{\infty }x(nT)\mathrm {tri} \left({\frac ... | Wikipedia - First-order hold - Basic first-order hold | 345 | 855 | null |
Delayed first-order hold, sometimes called causal first-order hold, is identical to FOH above except that its output is delayed by one sample period resulting in a delayed piecewise linear output signal x F O H ( t ) = ∑ n = − ∞ ∞ x ( n T ) t r i ( t − T − n T T ) {\displaystyle x_{\mathrm {FOH} }(t)\,=\sum _{n=-\infty... | Wikipedia - First-order hold - Delayed first-order hold | 350 | 800 | null |
the triangular function. The effective frequency response is the continuous Fourier transform of the impulse response. where s i n c ( x ) {\displaystyle \mathrm {sinc} (x)\ } is the sinc function. The Laplace transform transfer function of the delayed FOH is found by substituting s = i 2 π f: The delayed output makes ... | Wikipedia - First-order hold - Delayed first-order hold | 196 | 805 | null |
Section: Predictive first-order hold. Lastly, the predictive first-order hold is quite different. This is a causal hypothetical LTI system or filter that converts the ideally sampled signal into a piecewise linear output such that the current sample and immediately previous sample are used to linearly extrapolate up to... | Wikipedia - First-order hold - Predictive first-order hold | 331 | 1,374 | null |
Section: A. abbreviated address callingCalling that enables a user to employ an address having fewer characters than the full address when initiating a call. absolute coordinatesThe absolute distances or angles that specify the position of a point with respect to the datum of a coordinate system. absolute coordinateOne... | Wikipedia - Glossary of industrial automation - A | 350 | 1,889 | null |
actuatorA power mechanism used to effect motion of the robot (e.g. a motor which converts electrical, hydraulic or pneumatic energy to effect motion of the robot). adaptive controlA control scheme that adjusts the control system parameters from conditions detected during the process. address (in numerical control)A cha... | Wikipedia - Glossary of industrial automation - A | 346 | 1,800 | null |
analog dataData a represented by a physical quantity that is considered to be continuously variable and whose magnitude is made directly proportional to the data or to a suitable function of the data. analog input channel amplifierAn amplifier attached to one or more analog input channels, that adapts the analog signal... | Wikipedia - Glossary of industrial automation - A | 320 | 1,732 | null |
argument (in numerical control)Data which qualifies a command. arm (primary axes)An interconnected set of links and powered joints comprising members of longitudinal shape which supports, positions and orientates the wrist and/or an end effector. articulated structureSet of links and joints which constitutes the arm an... | Wikipedia - Glossary of industrial automation - A | 349 | 1,851 | null |
Article: Glossary of power electronics. This glossary of power electronics is a list of definitions of terms and concepts related to power electronics in general and power electronic capacitors in particular. For more definitions in electric engineering, see Glossary of electrical and electronics engineering. For terms... | Wikipedia - Glossary of power electronics - Summary | 218 | 1,178 | null |
Section: A. AC capacitor A capacitor essentially designed for operation with alternating voltage.AC conversion factor For AC conversion, the ratio of the fundamental output power to the fundamental input power. AC converter A converter for AC conversion. AC filter A filter on the AC side of a converter, designed to red... | Wikipedia - Glossary of power electronics - A | 321 | 1,678 | null |
Section: B. basic converter connection The electrical arrangement of principal arms in a converter. boost converter step-up converter A direct DC converter providing an output voltage which is higher than the input voltage. boost and buck connection A series connection of two or more converter connections the direct vo... | Wikipedia - Glossary of power electronics - B | 242 | 1,264 | null |
Section: C. capacitor commutation A method of self-commutation in which the commutating voltage is supplied by capacitors included in the commutation circuit.capacitor element (or element) An indivisible part of a capacitor consisting of two electrodes separated by a dielectric.capacitor losses The active power consume... | Wikipedia - Glossary of power electronics - C | 315 | 1,496 | null |
circuit crest working reverse voltage The highest instantaneous value of the reverse voltage developed across a reverse blocking valve device or an arm consisting of such devices, excluding all repetitive and non-repetitive transient voltages. circuit non-repetitive peak off-state voltage The highest instantaneous valu... | Wikipedia - Glossary of power electronics - C | 350 | 1,967 | null |
commutation In a power converter the transfer of current from one conducting arm to the next to conduct in sequence, without interruption of the current, both arms conducting simultaneously during a finite time interval. commutation circuit The circuit consisting of the commutating arms and the source providing the com... | Wikipedia - Glossary of power electronics - C | 328 | 1,683 | null |
conduction interval (of a valve arm) That part of an elementary period in which the valve arm conducts. conduction ratio The ratio of the conduction interval to the sum of the conduction interval and the idle interval. conduction through In inverter operation, the situation that a valve arm continues conduction at the ... | Wikipedia - Glossary of power electronics - C | 347 | 1,918 | null |
constant voltage to constant current crossover The behavior of a stabilized power supply that automatically converts the mode of operation from voltage stabilization to current stabilization when the output current reaches a preset value, and vice versa. continuous flow (of direct current) A flow of direct current whic... | Wikipedia - Glossary of power electronics - C | 342 | 1,829 | null |
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