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Heat Sink

Heat sink

:This article is about heat sinks as cooling devices. For alternative meanings see Heat sink (disambiguation) Heat sink (disambiguation) A heat sink is an environment or object capable of absorbing heat from another object with which it is in thermal contact (either direct contact or radiational "contact"). In common use, it is a device made of metal brought into contact with the hot surface of a component (in most cases, some kind of thermal interface material is put between the heat sink and the heat source to increase thermal throughput), such as a microprocessor chip or other power handling semiconductor in order to stablise its temperature through increased thermal mass and heat dissipation (primarily by conduction and convection and to a lesser extent by radiation). Heat sinks are widely used in electronics, and have become almost essential to modern central processing units. A heat sink usually consists of a metal structure with one or more flat surfaces to ensure good thermal contact with the components to be cooled, and an array of comb or fin like protrusions to increase the surface contact with the air, and thus the rate of heat dissipation. A heat sink is often used in conjunction with a fan in order to increase the rate of airflow over the heat sink, thus maintaining a larger temperature gradient by replacing warmed air faster than would be by convection, this is known as a forced air system. gradient Heat sinks are commonly made of a good thermal conductor such as copper or aluminum. Copper is significantly more expensive than aluminum but is also a better thermal conductor. The contact surface of a heat sink must be highly polished in order to ensure the best thermal contact with the object to be cooled. Sometimes a thermally conductive grease is employed to ensure the best thermal contact, such greases often contain colloidal silver (an even better thermal conductor than copper.) It is claimed that some brands of thermal grease that are advertised as containing silver or silver oxide actually contain neither, most notably that of CompUSA. Due to recent technological developments and public interest, the market for commercial heat sink cooling for CPUs has reached an all time high; many companies now compete to make the best heat sink for PC overclocking enthusiasts. Some of the more prominent heat sink makers include: Thermalright, Thermaltake, Aero Cool, Cooler Master, Zalman, and Swiftech. A good heat sink is vital to overclocked computer systems because the cooler a microprocessor is, the faster it can be made to run without instability. Temporary heat sinks are sometimes used in soldering circuit boards in order to prevent the heat from damaging sensitive nearby electronics - in the simplest case, this means gripping part of a component to be soldered with a crocodile clip or similar.

Heat sink (disambiguation)

A heat sink is
- a device used to conduct heat away from an object.
- an urban area with a tendency to absorb sunlight and re-radiate it as heat, together with heat from energy usage. This may also be referred to as an urban heat island).

Microprocessor

]] A microprocessor (abbreviated as µP or uP) is a computer electronic component made from miniaturized transistors on a single semiconductor integrated circuit (IC) (aka microchip or just chip). The central processing unit (CPU) is the most well known microprocessor, but many other components in a computer have them, such as the GPU on a video card. Before the advent of microprocessors, electronic CPUs were made from individual small-scale integrated circuits containing the equivalent of only a few transistors. By integrating the processor onto one or a very few large-scale integrated circuit packages (containing the equivalent of thousands or millions of discrete transistors), the cost of processor power was greatly reduced. See History of computing hardware for pre-electronic and early electronic computers. The evolution of microprocessors has been known to follow Moore's Law when it comes to steadily increasing performance over the years. This law suggests that the complexity of an integrated circuit, with respect to minimum component cost will double in about 18 months. A rule that has been generally followed, unconsciously, since the early 1970's. From humble beginnings as the drivers for calculators, the continued increase in power has led to the dominance of microprocessors over every other form of computer; every system from the largest mainframes to the smallest handheld computers now use a microprocessor at their core.

History

The first chips

As with many advances in technology, the microprocessor was an idea whose time had come. Three projects arguably delivered a complete microprocessor at about the same time, Intel's 4004, Texas Instruments' TMS 1000, and Garrett AiResearch's Central Air Data Computer. In 1968 Garrett was invited to produce a digital computer to compete with electromechanical systems then under development for the main flight control computer in the US Navy's new F-14 Tomcat fighter. The design was complete by 1970, and used a MOS-based chipset as the core CPU. The design was smaller and much more reliable than the mechanical systems it competed against, and was used in all of the early Tomcat models. However the system was considered so advanced that the Navy refused to allow publication of the design, and continued to refuse until 1997. For this reason the CADC, and the MP944 chipset it used, are fairly unknown even today. TI developed the 4-bit TMS 1000 and stressed pre-programmed embedded applications, introducing a version called the TMS1802NC on September 17, 1971, which implemented a calculator on a chip. The Intel chip was the 4-bit 4004, released on November 15, 1971, developed by Federico Faggin. TI filed for the patent on the microprocessor. Gary Boone was awarded for the single-chip microprocessor architecture on September 4, 1973. It may never be known which company actually had the first working microprocessor running on the lab bench. In both 1971 and 1976, Intel and TI entered into broad patent cross-licensing agreements, with Intel paying royalties to TI for the microprocessor patent. A nice history of these events is contained in court documentation from a [http://www.mgt.buffalo.edu/courses/mgs/651/s1s/simha/Date-old/Intel-Cyrix/Cyrix-intel-11.htm legal dispute] between Cyrix and Intel, with TI as intervenor and owner of the microprocessor patent. Interestingly, a third party claims to have been awarded a patent which might cover the "microprocessor". See [http://www.me.utexas.edu/~me179/topics/patents/case6articles/case6article1.html a webpage] claiming an inventor pre-dating both TI and Intel, describing a "microcontroller", which may or may not count as a "microprocessor". A computer-on-a-chip is a variation of a microprocessor which combines the microprocessor core (CPU), some memory, and I/O (input/output) lines, all on one chip. The computer-on-a-chip patent, called the microcomputer patent at the time, , was awarded to Gary Boone and Michael J. Cochran of TI. Aside from this patent the proper meaning of microcomputer is a computer using a (number of) microprocessor(s) as its CPU(s), while the concept of the patent is somewhat more similar to a microcontroller. According to A History of Modern Computing, (MIT Press), pp. 220–21, Intel entered into a contract with Computer Terminals Corporation, later called Datapoint, of San Antonio TX, for a chip for a terminal they were designing. Datapoint later decided not to use the chip, and Intel marketed it as the 8008 in April, 1972. This was the world's first 8-bit microprocessor. It was the basis for the famous "Mark-8" computer kit advertised in the magazine Radio-Electronics in 1974. The 8008 and its successor, the world-famous 8080, opened up the microprocessor component marketplace.

Notable 8-bit designs

The 4004 was later followed by the 8008, the world's first 8-bit microprocessor. These processors are the precursors to the very successful Intel 8080, Zilog Z80, and derivative Intel 8-bit processors. The competing Motorola 6800 architecture was cloned and improved in the MOS Technology 6502, rivaling the Z80 in popularity during the 1980s. Both the Z80 and 6502 concentrated on low overall cost, through a combination of small packaging, simple computer bus requirements, and the inclusion of circuitry that would normally have to be provided in a separate chip (for instance, the Z80 included a memory controller). It was these features that allowed the home computer "revolution" to take off in the early 1980s, eventually delivering semi-usable machines that sold for US$99. Motorola trumped the entire 8-bit world by introducing the MC6809, arguably one of the most powerful, orthogonal, and clean 8-bit microprocessor designs ever fielded – and also one of the most complex hardwired logic designs that ever made it into production for any microprocessor. Microcoding replaced hardwired logic at about this point in time for all designs more powerful than the MC6809 – specifically because the design requirements were getting too complex for hardwired logic. Another early 8-bit microprocessor was the Signetics 2650, which enjoyed a brief flurry of interest due to its innovative and powerful instruction set architecture. A seminal microprocessor in the world of spaceflight was RCA's RCA 1802 (aka CDP1802, RCA COSMAC) which was used in NASA's Voyager and Viking spaceprobes of the 1970s, and onboard the Galileo probe to Jupiter (launched 1989, arrived 1995). The CDP1802 was used because it could be run at very low power,
- and because its production process (Silicon on Sapphire) ensured much better protection against cosmic radiation and electrostatic discharges than that of any other processor of the era; thus, the 1802 is said to be the first radiation-hardened microprocessor.

16-bit

The first multi-chip 16-bit microprocessor was the National Semiconductor IMP-16, introduced in early 1973. An 8-bit version of the chipset introduced in 1974 as the IMP-8. In 1975, National introduced the first 16-bit single-chip microproessor, the PACE, which was later followed by an NMOS version, the INS8900. Other early multi-chip 16-bit microprocessors include one used by Digital Equipment Corporation (DEC) in the LSI-11 OEM board set and the packaged PDP 11/03 minicomputer, and the Fairchild Semiconductor MicroFlame 9440, both of which were introduced in the 1975 to 1976 timeframe. The first single-chip 16-bit microprocessor was TI's TMS 9900, which was also compatible with their TI 990 line of minicomputers. The 9900 was used in the TI 990/4 minicomputer, the TI-99/4A home computer, and the TM990 line of OEM microcomputer boards. The chip was packaged in a large ceramic 64-pin DIP package package, while most 8-bit microprocessors such as the Intel 8080 used the more common, smaller, and less expensive plastic 40-pin DIP. A follow-on chip, the TMS 9980, was designed to compete with the Intel 8080, had the full TI 990 16-bit instruction set, used a plastic 40-pin package, moved data 8 bits at a time, but could only address 16 KB. A third chip, the TMS 9995, was a new design. The family later expanded to include the 99105 and 99110. Intel followed a different path, having no minicomputers to emulate, and instead "upsized" their 8080 design into the 16-bit Intel 8086, the first member of the x86 family which powers most modern PC type computers. Intel introduced the 8086 as a cost effective way of porting software from the 8080 lines, and succeeded in winning much business on that premise. Following up their 8086 and 8088, Intel released the 80186, 80286 and, in 1985, the 32-bit 80386, cementing their PC market dominance with the processor family's backwards compatibility. The integrated microprocessor memory management unit (MMU) was developed by Childs et al. of Intel, and awarded US patent number 4,442,484.

32-bit designs

16-bit designs were in the market only briefly when full 32-bit implementations started to appear. The world's first single-chip 32-bit microprocessor was the AT&T Bell Labs BELLMAC-32A, with first samples in 1980, and general production in 1982 (See [http://cm.bell-labs.com/cm/cs/bib/shoji.bib this webpage] for a bibliographic reference and [http://www.bell-labs.com/org/physicalsciences/timeline/span23.html this webpage] for a general reference). After the divestiture of AT&T in 1984, it was renamed the WE 32000 (WE for Western Electric), and had two follow-on generations, the WE 32100 and WE 32200. These microprocessors were used in the AT&T 3B5 and 3B15 minicomputers; in the 3B2, the world's first desktop supermicrocomputer; in the "Companion", the world's first 32-bit laptop computer; and in "Alexander", the world's first book-sized supermicrocomputer, featuring ROM-pack memory cartridges similar to today's gaming consoles. All these systems ran the original Bell Labs Unix Operating System, which included the first Windows-type software called xt-layers. The most famous of the 32-bit designs is the MC68000, introduced in 1979. The 68K, as it was widely known, had 32-bit registers but used 16-bit internal data paths, and a 16-bit external data bus to reduce pin count. Motorola generally described it as a 16-bit processor, though it clearly has 32-bit architecture. The combination of high speed, large (16 megabyte) memory space and fairly low costs made it the most popular CPU design of its class. The Apple Lisa and Macintosh designs made use of the 68000, as did a host of other designs in the mid-1980s, including the Atari ST and Commodore Amiga. Intel's first 32-bit microprocessor was the iAPX 432, which was introduced in 1981 but was not a commercial success. It had an advanced capability-based object-oriented architecture, but poor performance compared to other competing architectures such as the Motorola 68000. Motorola's success with the 68000 led to the MC68010, which added virtual memory support. The MC68020, introduced in 1985 added full 32-bit data and address busses. The 68020 became hugely popular in the Unix supermicrocomputer market, and many small companies (e.g., Altos, Charles River Data Systems) produced desktop-size systems. Following this with the MC68030, which added the MMU into the chip, the 68K family became the processor for everything that wasn't running DOS. The continued success led to the MC68040, which included a FPU for better math performance. An 68050 failed to achieve its performance goals and was not released, and the follow-up MC68060 was released into a market saturated by much faster RISC designs. The 68K family faded from the desktop in the early 1990s. Other large companies designed the 68020 and follow-ons into embedded equipment. At one point, there were more 68020s in embedded equipment than there were Intel Pentiums in PCs (See [http://www.embedded.com/98/9807sr.htm this webpage] for this embedded usage information). The ColdFire processor cores are derivatives of the venerable 68020. During this time (early to mid 1980s), National Semiconductor introduced a very similar 16-bit pinout, 32-bit internal microprocessor called the NS 16032 (later renamed 32016), the full 32-bit version named the NS 32032, and a line of 32-bit industrial OEM microcomputers. By the mid-1980s, Sequent introduced the first symmetric multiprocessor (SMP) server-class computer using the NS 32032. This was one of the designs few wins, and it disappeared in the late 1980s. Other designs included the interesting Zilog Z8000, which arrived too late to market to stand a chance and disappeared quickly. In the late 1980s, "microprocessor wars" started killing off some of the microprocessors. Apparently, with only one major design win, Sequent, the NS 32032 just faded out of existence, and Sequent switched to Intel microprocessors.

64 bit microchips on the desktop

Though high end RISC (see below) based designs featured the first crop of 64 bit processors long before the current mainstream PC microchips from IBM, AMD and Intel, 64 bit only began to trickle onto the desktop in 2003 with the official launches of the AMD Opteron in April, AMD Athlon 64 in September, the PowerPC G5 in June and the Intel Xeon in 2004. With AMD's introduction of the first ia32 backwards compatible 64-bit chip Athlon 64 in September 2003, followed by Intel's own 64 bit chips, the 64 bit desktop era began. Both processors can run 32 bit legacy apps as well as the new 64 bit software. With 64 bit Windows XP and Linux that run on 64 bits, the software too is geared to utilise the full power of such processors. In reality the move to 64 bits is more than just an increase in register size from the ia32 as it also includes a small increase in register quantity for the aging CISC designs. The move to 64 bits by PowerPC processors had been intended since the processors design in the early 90s and was not a major cause of incompatibility. Existing integer registers are extended as are all related data pathways but in common with the ia32 designs both floating point and vector units had been operating at or above 64 bits for several years. Unlike the ia32 no new general purpose registers are added so any performance for not using the 64 bit mode where available is minimal.

History of Operating System support for 64 bit microchips

- April 2003 Mandrakesoft released Mandrake Linux Corporate Server 2.1 for the AMD Opteron processor
- April 2003 Turbolinux Releases "Turbolinux 8 for AMD64"
- October 2003 Mac OS X v10.3 was the first to take some advantage of 64 bit processors although only for an enlarged address space
- November 2003 SuSE releases SUSE LINUX 9.0 for AMD64
- November 2004 Mandrakesoft released Mandrakelinux 10.1 for x86-64
- April 2005 Mac OS X v10.4 was the first version of the OS to take advantage of 64 bit integer calculations
- April 2005 Microsoft released Windows XP Professional x64 Edition

RISC

In the mid-1980s to early-1990s, a crop of new high-performance RISC (reduced instruction set computer) microprocessors appeared, which were initially used in special purpose machines and Unix workstations, but have since become almost universal in all roles except the Intel-standard desktop. The first commercial design was released by MIPS Technologies, the 32-bit R2000 (the R1000 was not released). The R3000 made the design truly practical, and the R4000 introduced the world's first 64-bit design. Competing projects would result in the IBM POWER and Sun SPARC systems, respectively. Soon every major vendor was releasing a RISC design, including the AT&T CRISP, AMD 29000, Intel i860 and Intel i960, Motorola 88000, DEC Alpha and the HP-PA. Market forces have "weeded out" many of these designs, leaving the POWER and the derived PowerPC as the main desktop RISC processor, with the SPARC being used in Sun designs only. MIPS continues to supply some SGI systems, but is primarily used as an embedded design, notably in Cisco routers. The rest of the original crop of designs have either disappeared, or are about to. Other companies have attacked niches in the market, notably ARM, originally intended for home computer use but since focussed at the embedded processor market. Today RISC designs based on the MIPS, ARM or PowerPC core power the vast majority of computing devices. Of course, in the IBM-compatible PC world, Intel, AMD, and now VIA of Taiwan all make x86-compatible microprocessors. In 64-bit computing, the DEC(-Intel) ALPHA, the AMD 64, and the HP-Intel Itanium are the most popular designs as of late 2004.

Design concepts

See the main article: CPU design.

Market statistics

In 2003, about 44 billion US$ worth of microprocessors were manufactured and sold. [http://www.wsts.org/press.html] Although about half of that money was spent on CPUs used in desktop or laptop personal computers, those count for only about 0.2% of all CPUs sold. About 55% of all CPUs sold in the world are 8-bit microcontrollers. Over 2 billion 8-bit microcontrollers were sold in 1997. [http://www.circuitcellar.com/library/designforum/silicon_update/3/index.asp] Less than 10% of all the CPUs sold in the world are 32-bit or more. Of all the 32-bit CPUs sold, about 2% are used in desktop or laptop personal computers. "Taken as a whole, the average price for a microprocessor, microcontroller, or DSP is just over $6." [http://www.embedded.com/shared/printableArticle.jhtml?articleID=9900861]

Common µPs; architectures

- AMD K5, K6, K6-2, K6-III, Duron, Athlon, Athlon_XP, Athlon_MP, Athlon_XP-M
- AMD Athlon 64, Athlon 64 FX, Athlon_64_X2, Sempron, Turion_64
- AMD Opteron
- ARM family, StrongARM, Intel PXA2xx
- Atmel AVR architecture (purely microcontrollers)
- RCA 1802 (aka RCA COSMAC, CDP1802)
- Cyrix M1, M2
- DEC Alpha
- Intel 4004, 4040
- Intel 8080, 8085, Zilog Z80
- Intel 8086, 8088, 80186, 80188, 80286, 80386, 80486 (Intel x86 architecture)
- Intel Pentium, Pentium Pro, Celeron, Pentium II, Pentium III, Xeon, Pentium 4, Pentium M, Pentium D, Celeron M, Celeron D (Intel x86; parents of IA-64, with HP PA-RISC)
- Intel Itanium (IA-64 architecture)
- Intel i860, i960
- MIPS architecture
- Motorola 6800, MOS Technology 6502, Motorola 6809, WDC 65816
- Motorola 68000 family, ColdFire
- Motorola 88000 (parents of the PowerPC family, with POWER)
- IBM POWER (parents of the PowerPC family, with 88000)
- NSC 320xx
- OpenCores OpenRISC architecture
- PA-RISC family (HP, parents to the IA-64 architecture, with x86)
- PowerPC family, G3, G4, G5
- National Semiconductor SC/MP ("scamp")
- Signetics 2650
- SPARC, UltraSPARC, UltraSPARC II–IV
- SuperH family
- Transmeta's Crusoe and Efficeon
- INMOS Transputer
- VIA's C3,C7,Eden Series

Notes

- The RCA 1802 had what is called a static design, meaning that the clock frequency could be made arbitrarily low; this let the Voyager/Viking/Galileo spacecraft run the processor at very low speeds (to the degree of 0 Hz, i.e. a total stop condition), hence using a minimum of electrical power for long uneventful stretches of the voyage. Timers and/or sensors would awaken/speed up the processor in time for important tasks, such as navigational updates, attitude control, data acquisition, and radio communication.

External links

Patents

- -- Memory System for a Multi-Chip Digital Computer (CPU)

Research

- [http://www.emlabs.info EMLabs.info] -- List of Universities and Research Groups engaged in microcontrollers development.

General

- [http://www.chiplist.com/ The ChipList] – By Adrian Offerman
- [http://www.sasktelwebsite.net/jbayko/cpu.html Great Microprocessors of the Past and Present] – By John Bayko
- [http://bwrc.eecs.berkeley.edu/CIC/ CPU Info Center] – At UC Berkeley
- [http://www-106.ibm.com/developerworks/library/pa-microhist.html?ca=dgr-mw08MicroHistory Microprocessor history] – Hosted by IBM
- [http://www.hkrmicro.com/course/micro.html A Simple Course on Microprocessors] – By Kenneth Richardson
- [http://vmoc.museophile.org/cards/ Microprocessor instruction set cards] – By Jonathan Bowen
- [http://www.tomshardware.com/ Tom's Hardware Guide]
- [http://www.anandtech.com/ AnandTech]
- [http://www.overclockersclub.com/ The Overclocker's Club]
- [http://www.cpu-collection.de/ CPU-Collection]
- [http://f-cpu.org/ Freedom CPU]
- [http://www.guide-to-laptops.com/guides/laptop-processors.html Laptop Processors]
- [http://computer.howstuffworks.com/microprocessor.htm HowStuffWorks "How Microprocessors Work"]

Historical documents

- [http://www.ti.com/corp/docs/company/history/calcchip.shtml TMS1802NC calculator chip press release] – Texas Instruments, 17 September 1971
- [http://www.ti.com/corp/docs/company/history/singlechip.shtml 1973: TI Receives first patent on Single-Chip Microprocessor]
- [http://www.ti.com/corp/docs/company/history/microcomputer.shtml TI Awarded Basic Microcomputer Patent] – TI, 17 February 1978 ("microcomputer" to be understood as a single-chip computer; a simple µC)
- [http://www-106.ibm.com/developerworks/library/pa-yearend.html?ca=dgr-lnxw01PowerYear Important discoveries in microprocessors during 2004] – Hosted by IBM

Processor company sites

- [http://www.amd.com/ Advanced Micro Devices]
- [http://www.intel.com/ Intel Semiconductor]
- [http://www-03.ibm.com/chips/ IBM Microelectronics]
- [http://www.amcc.com/ AMCC]
- [http://www.freescale.com/ Freescale] (formerly of Motorola)
- [http://www.arm.com/ ARM]
- [http://www.mips.com/ MIPS Technologies]
- [http://www.ti.com/home_p_allsc TI Semiconductors] Category:Digital electronics
- Microprocessor
- AAA Category:Communication engineering ko:마이크로프로세서 ja:マイクロプロセッサ th:ไมโครโพรเซสเซอร์ ko:마이크로프로세서 ja:マイクロプロセッサ th:ไมโครโพรเซสเซอร์

Semiconductors

A semiconductor is a material with an electrical conductivity that is intermediate between that of an insulator and a conductor. A semiconductor behaves as an insulator at very low temperature, and has an appreciable electrical conductivity at room temperature although much lower conductivity than a conductor. Commonly used semiconducting materials are silicon, germanium, and gallium arsenide. A semiconductor can be distinguished from a conductor by the fact that, at absolute zero, the uppermost filled electron energy band is fully filled in a semiconductor, but only partially filled in a conductor. The distinction between a semiconductor and an insulator is slightly more arbitrary. A semiconductor has a band gap which is small enough such that its conduction band is appreciably thermally populated with electrons at room temperature, whilst an insulator has a band gap which is too wide for there to be appreciable thermal electrons in its conduction band at room temperature.

Fundamental semiconductor physics

Band structure of a semiconductor

depletion zone In the parlance of solid-state physics, semiconductors (and insulators) are defined as solids in which at absolute zero (0 K), the uppermost band of occupied electron energy states, known as the valence band, is completely full. Or, to put it another way, the Fermi energy of the electrons lies within the forbidden bandgap. The Fermi energy, or Fermi level can be thought of as the energy up to which available electron states are occupied at absolute zero. At room temperatures, there is some smearing of the energy distribution of the electrons, such that a small, but not insignificant number have enough energy to cross the energy band gap into the conduction band. These electrons which have enough energy to be in the conduction band have broken free of the covalent bonds between neighbouring atoms in the solid, and are free to move around, and hence conduct charge. The covalent bonds from which these excited electrons have come now have missing electrons, or holes which are free to move around as well. (The holes themselves don't actually move, but a neighbouring electron can move to fill the hole, leaving a hole at the place it has just come from, and in this way the holes appear to move.) It is an important distinction between conductors and semiconductors that, in semiconductors, movement of charge (current) is facilitated by both electrons and holes. Contrast this to a conductor where the Fermi level lies within the conduction band, such that the band is only half filled with electrons. In this case, only a small amount of energy is needed for the electrons to find other unoccupied states to move into, and hence for current to flow. The ease with which electrons in a semiconductor can be excited from the valence band to the conduction band depends on the band gap between the bands, and it is the size of this energy bandgap that serves as an arbitrary dividing line between semiconductors and insulators. Materials with a bandgap energy of less than about 3 electronvolts (eV) are generally considered semiconductors, while those with a greater bandgap energy are considered insulators.. The current-carrying electrons in the conduction band are known as "free electrons", although they are often simply called "electrons" if context allows this usage to be clear. The holes in the valence band behave very much like positively-charged counterparts of electrons, and they are usually treated as if they are real charged particles.

Doping of semiconductors

One of the main reasons that semiconductors are useful in electronics is that their electronic properties can be greatly altered in a controllable way by adding small amounts of impurities. These impurities are called dopants. Heavily doping a semiconductor can increase its conductivity by a factor greater than a billion. In modern integrated circuits, for instance, heavily-doped polycrystalline silicon is often used as a replacement for metals.

Intrinsic and extrinsic semiconductors

An intrinsic semiconductor is a semiconductor which is pure enough that the impurities in it do not appreciably affect its electrical behavior. In this case, all carriers are created by thermally or optically excited electrons from the full valence band into the empty conduction band. Thus equal numbers of electrons and holes are present in an intrinsic semiconductor. Electrons and holes flow in opposite directions in an electric field, though they contribute to current in the same direction since they are oppositely charged. Hole current and electron current are not necessarily equal in an intrinsic semiconductor, however, because electrons and holes have different effective masses (crystalline analogues to free inertial masses). The concentration of carriers in an intrinsic semiconductor is strongly dependent on the temperature. At low temperatures, the valence band is completely full, making the material an insulator (see electrical conduction for more information). Increasing the temperature leads to an increase in the number of carriers and a corresponding increase in conductivity. This principle is used in thermistors. This behavior contrasts sharply with that of most metals, which tend to become less conductive at higher temperatures due to increased phonon scattering. An extrinsic semiconductor is a semiconductor that has been doped with impurities to modify the number and type of free charge carriers present.

N-type doping

The purpose of n-type doping is to produce an abundance of mobile or "carrier" electrons in the material. To help understand how n-type doping is accomplished, consider the case of silicon (Si). Si atoms have four valence electrons, each of which is covalently bonded with one of four adjacent Si atoms. If an atom with five valence electrons, such as those from group 15 (a.k.a. group VA) of the periodic table (e.g. phosphorus (P), arsenic (As), or antimony (Sb)), is incorporated into the crystal lattice in place of a Si atom, then that atom will have four covalent bonds and one unbonded electron. This extra electron is only weakly bound to the atom and can easily be excited into the conduction band. At normal temperatures, virtually all such electrons are excited into the conduction band. Since excitation of these electrons does not result in the formation of a hole, the number of electrons in such a material far exceeds the number of holes. In this case the electrons are the majority carriers and the holes are the minority carriers. Because the five-electron atoms have an extra electron to "donate", they are called donor atoms. Note that each movable electron within the semiconductor is never far from an immobile positive dopant ion, and the n-doped material normally has a net electric charge of zero.

P-type doping

The purpose of p-type doping is to create an abundance of holes. In the case of silicon, a trivalent atom (such as boron) is substituted into the crystal lattice. The result is that one electron is missing from one of the four covalent bonds normal for the silicon lattice. Thus the dopant atom can accept an electron from a neighboring atoms' covalent bond to complete the fourth bond. Such dopants are called acceptors. The dopant atom accepts an electron, causing the loss of one bond from the neighboring atom and resulting in the formation of a "hole". Each hole is associated with a nearby negative-charged dopant ion, and the semiconductor remains electrically neutral as a whole. However, once each hole has wandered away into the lattice, one proton in the atom at the hole's location will be "exposed" and no longer cancelled by an electron. For this reason a hole behaves as a quantity of positive charge. When a sufficiently large number of acceptor atoms are added, the holes greatly outnumber the thermally-excited electrons. Thus, the holes are the majority carriers, while electrons are the minority carriers in P-type materials. Blue diamonds (Type IIb), which contain boron (B) impurities, are an example of a naturally occurring P-type semiconductor.

Carrier concentrations

When a semiconductor is doped, its majority carrier concentration exceeds the intrinsic carrier concentration by a factor that is dependent on the doping level. However, the product of the majority and minority carrier concentrations continues to be equal to the square of the intrisic carrier concentration. For example, consider an intrinsic semiconductor at a temperature such that its carrier concentration (hole and electron) is 10¹³/cm³. If this is n-doped to 10¹⁶/cm³, then the hole concentration will be 10¹⁰/cm³. It also follows from this that minority carrier concentrations in doped semiconductors are dependent on temperature to the square of the extent that carrier concentrations in intrinsic semiconductors are, since the majority carrier concentration is effectively fixed at the doping level.

P-N junctions

A p-n junction may be created by doping adjacent regions of a semiconductor with p-type and n-type dopants. If a positive bias voltage is placed on the p-type side, the dominant positive carriers (holes) are pushed toward the junction. At the same time, the dominant negative carriers (electrons) in the n-type material are attracted toward the junction. Since there is an abundance of carriers at the junction, the junction behaves as a conductor, and the voltage placed across the junction produces a current. As the clouds of holes and electrons are forced to overlap, electrons fall into holes and become part of the population of immobile covalent bonds. However, if the bias polarity is reversed, the holes and electrons are pulled away from the junction. Since only very few new electron/hole pairs are created at the junction, the existing mobile carriers are swept away to leave a depletion zone; a region of relatively non-conducting silicon. The reverse bias voltage will produce only a very low current across the junction. The p-n junction is the basis of an electronic device called a diode, which allows electric charges to flow in only one direction. Similarly, a third semiconductor region can be doped n-type or p-type to form a three-terminal device, such as the bipolar junction transistor (which can be either p-n-p or n-p-n).

Required purity and perfection of semiconductor materials

Semiconductors with predictable, reliable electronic properties are necessary for mass production. The level of chemical purity needed is extremely high because the presence of impurities even in very small proportions can have large effects on the properties of the material. A high degree of crystalline perfection is also required, since faults in crystal structure (such as dislocations, twins, and stacking faults) interfere with the semiconducting properties of the material. Crystalline faults are a major cause of defective semiconductor devices. The larger the crystal, the more difficult it is to achieve the necessary perfection. Current mass production processes use crystal ingots between four and twelve inches in diameter which are grown as cylinders and sliced into wafers. Because of the required level of chemical purity, and the perfection of the crystal structure which are needed to make semiconductor devices, special methods have been developed to produce the initial semiconductor material. A technique for achieving high purity includes growing the crystal using the Czochralski process. An additional step that can be used to further increase purity is known as zone refining. In zone refining, part of a solid crystal is melted. The impurities tend to concentrate in the melted region, while the desired material recrystalizes leaving the solid material more pure and with fewer crystalline faults.

References

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External links

- [http://science.howstuffworks.com/diode.htm Howstuffwork's semiconductor page]
- [http://www.tpub.com/content/neets/14179/index.htm Electrical Engineering Training Series] A set of articles on Semiconductors and Transistors
- [http://www.semiconductor-technology.com Semiconductor Technology] Information on the Semiconductor Industry.
- [http://www.ioffe.rssi.ru/SVA/NSM/Semicond/index.html NSM-Archive] Physical Properties of Semiconductors (such as Si, GaAs and others), including band structure, mechanical, electrical, thermal and optical properies
- [http://hyperphysics.phy-astr.gsu.edu/hbase/solids/semcn.html Semiconductor Concepts at Hyperphysics], includes intrisic semiconductors, doping, junctures, band theorry, etc.
- [http://ece-www.colorado.edu/~bart/book/book/ Principles of Semiconductor Devices]
- [http://www.semi1source.com/ Semiconductor resource launch page]
- [http://www.semiconductorglossary.com/ Semiconductor glossary] Category:Condensed matter physics Category:Semiconductors ko:반도체 ja:半導体 th:สารกึ่งตัวนำ

Heat conduction

Heat conduction is the transmission of heat across matter. Heat transfer is always directed from a higher to a lower temperature. Denser substances are usually better conductors; metals are excellent conductors. The law of heat conduction also know as Fourier's law states that the time rate of heat flow Q through a slab (or a portion of a perfectly insulated wire, as shown in the figure) is proportional to the gradient of temperature difference: :

Q = K A \frac

A is the transversal surface area, Δ x is the thickness of the body of matter through which the heat is passing, K is a conductivity constant dependent on the nature of the material and its temperature, and ΔT is the temperature difference through which the heat is being transferred. This law forms the basis for the derivation of the heat equation.

Conductance

Writing :

U = \frac, \quad

Fourier's law can also be stated as: :

Q = U A\, \Delta T \quad

where U is the conductance. The reciprocal of conductance is resistance, equal to: :

\frac, \quad

and it is resistance which is additive when several conducting layers lie between the hot and cool regions, because A and Q are the same for all layers. In a multilayer partition, the total conductance is related to the conductance of its layers by: :

\frac = \frac + \frac + \frac+ \cdots

So, when dealing with a multilayer partition, the following formula is usually used: :

Q = \frac

When heat is being conducted from one fluid to another through a barrier, it is sometimes important to consider the conductance of the thin film of fluid which remains stationary next to the barrier. This thin film of fluid is difficult to quantify, its characteristics depending upon complex conditions of turbulence and viscosity, but when dealing with thin high-conductance barriers it can sometimes be quite significant.

Newton's law of cooling

A related principle, Newton's law of cooling, states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings. This form of heat loss principle, however, is not very precise; a more accurate formulation requires an analysis of heat flow based on the heat equation in an inhomogeneous medium. The general applicability of this simplification is characterized by the Biot number. Nevertheless, it is easy to derive from this principle the exponential decay of temperature of a body. If T is the temperature of the body, then :

\frac = - r (T - T_)

where r is some positive constant. From which, it follows that :

T(t) = T_ + (T(0) - T_) \ e^. \quad

For example, simplified climate models may use Newtonian cooling instead of a full (and computationally expensive) radiation code to maintain atmospheric temperatures.

Radiation

Radiation can refer to one of the following:
- Alpha radiation
- Beta radiation
- Gamma radiation
- Delta radiation
- Epsilon radiation
- Neutron radiation
- Cherenkov radiation, radiation by a particle moving through an insulating medium faster than the speed of light in that medium.
- Electromagnetic radiation, a stream of photons of a variety of different energies.
- Ionizing radiation, a stream of particles with sufficient energy to cause ionization.
- Gravitational radiation, a predicted consequence of general relativity.
- Non-ionizing radiation, electromagnetic radiation that does not carry enough energy to ionize living material.
- Particle radiation, any kind of radiation in which the individual elements behave like particles.
- Synchrotron radiation, the emission of radiation by a charged particle undergoing acceleration.
- Thermal radiation, the process by which a hot object emits electromagnetic radiation.
- Radiant energy, radiation emitted by a source into the surrounding environment.
- Adaptive radiation, in evolutionary biology, a process by which one species becomes many in order to adapt to specific ecological niches. In fiction, radiation can also refer to:
- Theta radiation and Omicron radiation, which are found in Star Trek

Electronics

The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.

Electronic devices today

Electronic devices are used to perform a wide variety of tasks. The main uses of electronic circuits are the controlling, processing and distribution of information, and the conversion and distribution of electric power. Both of these uses involve the creation or detection of electromagnetic fields and electric currents. While electrical energy had been used for some time to transmit data over telegraphs and telephones, the development of electronics truly began in earnest with the advent of radio.

CAD/CAM of electronic circuits

Today's electronics engineers enjoy the ability to design circuits using premanufactured building blocks such as power supplies, resistors, capacitors, semiconductors (such as transistors), and integrated circuits. Electronic design automation software programs include schematic capture programs such as ORCAD , used to make circuit diagrams and printed circuit board layouts.

Electronic systems

One way of looking at an electronic system is to divide it into the following parts: # Inputs – Electronic or mechanical sensors (or transducers), which take signals (in the form of temperature, pressure, etc.) from the physical world and convert them into current/voltage signals. # Signal processing circuits – These consist of electronic components connected together to manipulate, interpret and transform the signals. # Outputs – Actuators or other devices (also transducers) that transform current/voltage signals back into useful physical form. One example is a television set. Its input is a broadcast signal received by an antenna or fed in through a cable. Signal processing circuits inside the television extract the brightness, colour and sound information from this signal. The output devices are a cathode ray tube that converts electronic signals into a visible image on a screen and magnet driven audio speakers.

Electronic test equipment

- Ammeter, e.g. Galvanometer (Measure current)
- Ohmmeter, e.g. Wheatstone bridge (Measure resistance)
- Voltmeter (Measures voltage)
- Multimeter (Measures all of the above)
- Oscilloscope (Measures all of the above, except Ohm, as they change over time)
- Logic analyzer (Tests digital circuits)
- Spectrum analyzer (SA) (Measures spectral energy of signals)
- Vector signal analyzer (VSA) (Like the SA but it can also perform many more useful digital demodulation functions)
- Electrometer (Measures charge)
- Frequency counter (Measures frequency)
- Time-domain reflectometer for testing integrity of long cables

Electronic components

- Electronic components
- Electronic Devices and Circuits

Analog circuits

Most analog electronic appliances, such as radio receivers, are constructed from arrays of a few types of circuits.
- Analog computer
- Analog multipliers
- electronic amplifiers
- electronic filters
- electronic oscillators
- Phase-locked loops
- electronic mixers
- Power conversion
- Electronic Power Supply
- impedance matchers
- operational amplifiers
- comparators

Digital circuits

Computers, electronic clocks, and programmable logic controllers (used to control industrial processes) are constructed of digital circuits. Digital Signal Processors are another example. Building-blocks:
- logic gates
- flip-flops
- counters
- registers
- multiplexers
- Schmitt triggers Highly integrated devices:
- microprocessors
- microcontrollers
- DSP
- Field Programmable Gate Array

Mixed-signal circuits

Mixed-signal circuits, also known as hybrid circuits, are becoming increasingly common. Mixed circuits contain both analog and digital components. analog to digital converters and digital to analog converters are the primary examples. Other examples are transmission gates and buffers.

Heat dissipation

Heat generated by electronic circuitry must be dissipated to improve reliability. Techniques for heat dissipation can include heatsinks and fans for air cooling, and other forms of computer cooling such as liquid cooling for computers .

Noise

Associated with all electronic circuits is noise. Types of noise include
- Shot noise in resistors.
- Johnson-Nyquist noise (Thermal noise) in resistors.
- White noise
- 1/f noise (pink noise, or flicker noise)
- Gaussian noise

Electronics theory

- Mathematical methods in electronics
- Digital circuits
- Analog electronics

External links

Tutorials and projects

- [http://www.electronicsinfoline.com/ Electronics Infoline] Directory for electronics projects.
- [http://www.opamp-electronics.com/tutorials/index.htm Basic Electronic Tutorials On DC, AC, Semiconductor and Digital Theory] Extensive free tutorial material and store.
- [http://www.electronics-tutorials.com/ Electronics tutorials] Modest site, mostly focused on radio electronics, awkward layout.
- Williamson Labs' [http://www.williamson-labs.com/ Electronics tutorial]
- Ian Purdie's [http://my.integritynet.com.au/purdic Electronics tutorial]s
- Iguana Labs' [http://www.iguanalabs.com/maintut.htm Electronics Tutorials and Kits]
- [http://www.electronicdefinitions.com Electronic Meanings and Acronyms]
- [http://www.ibiblio.org/obp/electricCircuits/ Lessons in Electric Circuits] – A free series of textbooks on the subjects of electricity and electronics.
- [http://www.radio-electronics.com/ Radio-Electronics.Com] Free information and resources covering radio and electronics
- [http://www.electronicschat.org/echatwiki/ A hobbyist wiki]
- [http://www.falstad.com/circuit/ Circuit simulator with voltage and current visualization]
- [http://allaboutcircuits.com A comprehensive guide to making integrated circuits]
- [http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/etroncon.html HyperPhysics]
- [http://www.talkingelectronics.com/te_interactive_index.html "Talking Electronics"] Great for amateurs, commercial kits.
- [http://electronics.esolberg.com/ Electronic parts library]
- [http://www.work-readyelectronics.org Work Ready Electronics] Free instructional online course materials for Community College Electronics Instructors and Students.

Some other good sites

- [http://endtas.com/robot/ Endtas robotics community website with lots of free robotic projects. Do it yourself]
- [http://www.ieee.org/ IEEE]
- [http://www.spectrum.ieee.org/ IEEE spectrum]
- [http://www.elexp.com/links.htm Electronix Express]
- [http://www.electronicspoint.com/ Electronics Discussions] Web access to electronics related newsgroups. Category:Electronics Category:Electronic engineering ko:전자공학 ms:Elektronik ja:電子工学 simple:Electronics th:อิเล็กทรอนิกส์

Fan (implement)

A fan has two purposes – to move air for creature comfort or for ventilation and to move air or gas from one location to another for industrial purposes. Fans have broad surfaces that usually revolve. Leaves or flat objects, waved to produce a more comfortable atmosphere, are the simplest kind of fan. Applications include ornamental decorations, climate control, cooling system, refreshing air, personal wind-generation (e.g., an electric table fan), ventilation (e.g., an exhaust fan), winnowing (e.g., separating chaff of cereal grains), removing dust (e.g., sucking as in a vacuum cleaner), drying (usually in addition to heat) and to provide draft for a fire.

History

Etymology

Old English fann referred to a basket or shovel for winnowing. It was a loan from Latin vannus, with the same meaning, derived from ventus "wind" or a related root (cf. vates). In the sense of "device for moving air" the word is first attested 1390, the hand-held version is first recorded in 1555.

Ancient

1555 Fan history stretches back thousands of years. Since antiquity, fans have possessed a dual function – a status symbol and a useful ornament. In the course of their development, fans have been made of a variety of materials and have included decorative artwork. The simplest fans are leaves or flat objects, waved to produce a cooler atmosphere. These rigid or folding hand-held implements have been used for cooling, for air circulation, as a ceremonial device, and as a sartorial accessory throughout the world from ancient times. They are still widely used. The earliest known fans are called 'screen fans' or 'fixed leaf fans'. These were manipulated by hand to cool the body, to produce a breeze, and to ward off insects. Such early fans usually took the form of palm leaves. Some of the earliest known fans have come from Egyptian tombs. Early Assyria and Egypt employed slaves and servants to manipulate the fan. In Egyptian reliefs, fans were of the rigid type. Tutankhamum's tomb possessed gold fans with ostrich feathers, matching depictions on tomb walls. Long-handled, disk-shaped fans were carried by attendants in ancient times and were associated with regal and religious ceremonies. They had handles or sticks attached to a rigid leaf or to feathers. Plumage of birds was used in fans, such as those of the Egyptians and Native American Indians, that had both practical and ceremonial uses. In the ancient Americas, the Aztec, Maya, and South American cultures used bird feathers in their fans. Among the Aztec fans were used to depict merchants in illustrations of trades. The use of varios feather types had a religious connotation. The Paracas people of South America (modern Peru) have left numerous examples of ancient feather fans among their mummies. In India, the Hindi term for a fan is 'pankha' (a derivative of "a feather" or "a bird's wing"). Pictorial evidence records that the Greeks, the Etruscans, and the Romans used fans as cooling and ceremonial devices. In Greece, linen was stretched over leaf-shaped frames. In Rome, gilded and painted wooden fans were used. Roman ladies throughout the empire used circular fans. Chinese sources link the fan with mythical and historical characters.

Asia

In China, screen fans were used throughout society. The earliest known Chinese fans are a pair of woven bamboo side-mounted fans from the 2nd century BC. The Chinese character for "fan" (扇) is etymologically derived from a picture of feathers under a roof. The Chinese fixed fan, pien-mien, means 'to agitate the air'. Chinese character Fans were part of the social status for the Chinese people. A particular status and gender would accord a specific type of fan to an individual. The folding fan was invented in Japan and taken to China in the 9th century. The Akomeogi (or Japanese folding fan; 衵扇; Hiôgi) originated in the 6th century. These were fans held by aristocrats of the Heian period when formally dressed. They were made by tying thin stripes of hinoki (or Japanese cypress) together with thread. The number of strips of wood differed according to the person's rank. They are used today by Shinto priests in formal costume and are brightly painted. The Chinese dancing fan was developed in the 7th century. The Chinese form of the hand fan was a row of feathers mounted in the end of a handle. In China, the folding fan came into fashion during the Ming dynasty between the years of 1368 and 1644, and Hangzhou was a center of folding fan production. The Mai Ogi (or Chinese dancing fan) has ten sticks and a thick paper mount showing the family crest. Chinese painters crafted many fan decoration designs. The slats, of ivory, bone, mica, mother of pearl, or tortoise shell, were carved and covered with paper or fabric. Folding fans have "montures" which are the sticks and guards. The leaves are usually painted by craftsman. Social significance was attached to the fan in the Far East. The management of the fan became a highly regarded feminine art. The function and employment of the fan reached its high point of social significance (fans were even used as a weapon - called the iron fan, or tieshan in Chinese, tessen in Japanese). Printed fan leaves and painted fans are done on a paper ground. The paper was originally hand made and displayed the characteristic watermarks. Machine made paper fans, introduced in the 19th century, are smoother with an even texture. Folding fans (扇子 Japanese "sensu", Chinese: "shanzi";) continue to be important cultural symbols and popular tourist souvenirs in East Asia. See also: Chinese paper art

Europe

Chinese paper art In Europe, during the Middle Ages, the fan was absent. The West's earliest fan is a flabellum (or ceremonial fan), which dates to the 6th century. Hand fans were reintroduced to Europe in the 13th century and 14th century. Fans from the Middle East were brought back by Crusaders. In the 15th century, Portuguese traders brought fans to Europe from China and Japan. Fans became generally popular. In the 1600s, the folding fan, introduced from China, became popular in Europe. In the 17th century and 18th century, fans reached a high degree of artistry and were being made throughout Europe. Folded fans of lace, silk, or parchment were decorated and painted by artists. Fans were imported from China by the East India Companies at this time, also. Around the middle 1700s, inventors started designing mechanical fans. Wind-up fans (similar to wind-up clocks) were popular in the 1700s. In the 19th century in the West, European fashion caused fan decoration and size to vary.

Mechanical development

The first recorded mechanical fan was the punkah fan used in the Middle East in the 1500s. It had a canvas covered frame that was suspended from the ceiling. Servants, known as punkah wallahs, pulled a rope connected to the frame to move the fan back and forth. rope.]] The Industrial Revolution in the late 1800s introduced belt-driven fans powered by factory waterwheels. Attaching wooden or metal blades to shafts overhead that were used to drive the machinery, the first industrial fans were developed. When Thomas Edison and Nikola Tesla introduced electrical power in the late 1800s and early 1900s for the public, the personal electrical fan was introduced. Between 1882 and 1886, Dr. Schuyler Skaats Wheeler developed the two-bladed desk fan, a type of personal electric fan. It was commercially marketed by the American firm Crocker & Curtis. In 1882, Philip H. Diehl introduced the electric ceiling fan. Diehl is considered the father of the modern electric fan. In the late 1800s, electric fans were used only in commercial establishments or in well-to-do households. Heat-convection fans fueled by alcohol, oil, or kerosene were common around the turn of the 20th century. In the 1920s, industrial advances allowed steel to be mass-produced in different shapes, bringing fan prices down and allowing more homeowners to afford them. In the 1930s, the first art deco fan was designed. Before this fan, called the Silver Swan, most household fans were fairly plain. In the 1950s, fans were manufactured in colors that were bright and eye catching. Central air conditioning in the 1960s brought an end to the golden age of electric fan. In the 1970s, Victorian-style ceiling fans became popular. In the twentieth century, fans have become utilitarian. During the 2000s, fan aesthetics have become a concern to fan buyers. The fan is part of everyday life in the Far East, Japan, and Spain (among other places).

Mechanical devices

Spain Mechanically, a fan can be any revolving vane or vanes used for producing currents of air. Fans produce air flows with high volume and low pressure, as opposed to a gas compressor which produces high pressures at a comparatively low volume. Fans are useful for moving large quantities of air, which is suited for applications such as winnowing grain or blowing a fire, cooling and ventilation purposes, and in conjunction with a heat source for heating and drying. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as anemometers and wind turbines often have designs similar to that of a fan. Mechanical revolving blade fans are made in a wide range of designs. In a home you can find fans that can be put on the floor or a table, or hung from the ceiling, or are built into a window, wall, roof, chimney, etc. They can be found in electronic instruments such as computers where they cool the circuits inside, and in appliances such as hair dryers and space heaters. They are also used for cooling in air-conditioning systems, and in automotive engines, where they are driven by belts or by direct motor. Fans create a wind chill but do not lower temperatures directly.

Types

wind chill There are three main types of fans used for moving air, axial, centrifugal (also called radial) and cross flow (also called tangential). The axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate. Axial fans blow air across the axis of the fan, linearly, hence their name. This is the most commonly used type of fan, and is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in wind tunnels. The centrifugal fan has a moving component (called an impeller) that consists of a central shaft about which a set of blades form a spiral pattern. Centrifugal fans blow air at right angles to the intake of the fan, and spin (centrifugally) the air outwards to the outlet. An impeller rotates, causing air to enter the fan near the shaft and move perpendicularly from the shaft to the opening in the scroll-shaped fan casing. A centrifugal fan produces more pressure for a given air volume, and is used where this is desirable such as in leaf blowers, air mattress inflators, and various industrial purposes. They are typically more noisy than comparable axial fans. The cross flow fan has a squirrel cage rotor (a rotor with a hollow center and axial fan blades along the periphery). Tangential fans take in air along the periphery of the rotor, and expel it through the outlet in a similar fashion to the centrifugal fan. Cross flow fans give off an even airflow along the entire width of the fan, and are very quiet in operation. They are comparatively bulky, and the air pressure is low. Cross flow fans are often used for cooling in photocopiers. The action of a fan or blower causes pressures slightly above atmospheric, which are called plenums. Fans usually use electric power. Electric fans generally consist of a set of rotating blades that are placed in a protective housing that permits air to flow through it. The blades are rotated by an electric motor, for big industrial fans, 3-phase asynchronous motors are commonly used. Smaller fans are often powered by shaded pole AC motors, or brushed or brushless DC motors. AC-powered fans usually use mains voltage, while DC-powered fans use low voltage, typically 24V, 12V or 5V. Cooling fans for computer equipment exclusively use brushless DC motors, which produce much less EMI. In machines which already have a motor, the fan is often connected to this rather than being powered independently. This is commonly seen in cars, large cooling systems and winnowing machines.

Table fan

Basic elements of a typical table fan include the fan blade, base, armature and lead wires, motor, blade guard, motor housing, oscillator gearbox, and oscillator shaft. The oscillator is a mechanism that motions the fan from side to side. The axle comes out on both ends of the motor, one end of the axle is attached to the blade and the other is attached to the oscillator gearbox. The motor case joins to the gearbox to contain the rotor and stator. The oscillator shaft combines to the weighted base and the gearbox. A motor housing covers the oscillator mechanism. The blade guard joins to the motor case for safety. Electro-mechanical fans, among collectors, are rated according to their condition, size, age, and number of blades. Four-blade designs are the most common. Five-blade or six-blade designs are rare. The materials from which the components are made, such as brass, are important factors in fan desirability.

Ceiling fan

oscillator A fan suspended from the ceiling of a room is a ceiling fan. It usually has a light associated with it to replace any displaced light. These devices are generally used in homes without central air conditioning, or in conjunction with air conditioning to lower energy bills. Ceiling fan controls usually include one for speed (slow, medium, and fast), one for the light (on and off), and one for directional control of the fan blades (clockwise and counterclockwise). Ceiling fans can be used as a cooling device in warm months (pushing air down, thereby creating a wind chill effect) and a heat transferrer (pulling air up, thereby pushing the heat that stratifies by the ceiling, down along the walls so as not to create a wind chill) in colder months.

Solar powered fan

Electric fans used for ventilation may be powered by solar panels instead of mains current. This is an attractive option because once the capital costs of the solar panel have been covered, the resulting electricity is free. In addition, electricity is always available when the sun is shining and the fan needs to run. A typical example uses a detached 10 watt, 12x12 inch solar panel and is supplied with appropriate brackets, cables, and connectors. It can be used to ventilate up to 1250 square feet (100 m²) of area and can move air at up to 800 cubic feet per minute (400 L/s). Because of the wide availability of 12 V brushless DC electric motors and the convenience of wiring such a low voltage, such fans usually operate on 12 volts. The detached solar panel is typically installed in the spot which gets most of the sun light and then connected to the fan mounted as far as 20 to 25 feet (6 to 7 m) away. Other permanently-mounted and small portable fans include an integrated (non-detachable) solar panel.

Gas turbine fan

The low pressure compressor in a turbofan engine is often called a fan. Typically, these units absorb thousands of horsepower, the power being provided by the expansion of hot combustion gases through the low pressure turbine.

Aft fan

Several turbofans feature an aft fan, where the fan rotor blades are mounted radially outwards of the (LP) turbine rotor blades. This dispenses with the need for an (LP) shaft. In an early example, General Electric bolted a fan/turbine unit to the rear of a J79 turbojet, to convert it into the CJ805 turbofan. The GE36 UDF Demonstrator used a similar arrangement to convert an F404 mixed exhaust turbofan into a propfan.

Supersonic fan

Early gas turbine fans rotated at subsonic tip speeds, to avoid the generation of shock waves in the airflow. Modern fans, however, often rotate at supersonic tip speeds, and exploit the shock waves. Some advanced designs can generate a pressure ratio of more than 2.2:1 in a single stage, although 1.8:1 is more typical.

Supersonic through-flow fan

Although supersonic fans rotate at a supersonic tip speed, the axial flow is subsonic. However, some experimental devices have demonstrated supersonic axial flow. All the speed lines on the resulting fan map (or characteristic) are virtually horizontal, unlike those of more conventional units.

Variable pitch fan

Several ultra-high bypass ratio turbofan demonstrator engines (e.g. Rolls-Royce/SNECMA M45SD-02) have incorporated variable pitch fans, much like the variable pitch propellers on a turboprop engine. Varying the pitch of the rotor blades improves the low flight speed handling of the low pressure ratio fan unit, without the need to resort to a variable area cold or mixed flow nozzle. Reverse thrust down to zero aircraft speed is also practical.

Variable geometry fan

Some multi-stage, high pressure ratio, fans on military turbofan engines incorporate variable geometry, (e.g. F404). The variability is usually confined to the inlet guide vanes. Although the leading edge of the vane is static, a piano-type hinge allows the trailing edge to be adjusted in pitch, to redirect the airflow onto the first rotor. VIGV's enhance the surge margin of the fan in the mid-flow region.

Propfan

Some ultra-high bypass ratio turbofans dispense with the fan nacelle and have an unducted fan rotor. The fan blades, which resemble scimitars, are especially shaped to work efficiently at flight speeds up to about Mach 0.75. General Electric demonstrated a propfan engine, called the GE36 UDF, in the 1980's.

Overhung fan

Turbojets and early turbofans used the inlet guide vanes to support the front bearing of the (LP) compressor/fan rotor assembly. Today, the fans used in turbofan engines are often to an overhung design, where the fan rotor is cantilevered out forward, beyond the front bearing. This facilitates the removal of the inlet guide vanes. Consequently, the fan rotor blades are the first aerofoils encountered by the engine airflow.

Snubbered fan

Prior to the introduction of wide chord fan blades, fan blades fitted to turbofan engines often featured snubbers. These are protuberances that stick-out at right angles to the fan aerofoil, somewhere between mid-span and blade tip. The snubbers on adjacent fan blades butt-up against each other, in a peripheral sense, and improve the vibration characteristics of the blade. Wire lacing (e.g. Pegasus) is an alternative approach.

Wide chord fan

As might be expected, snubbers reduce the aerodynamic efficiency of fan aerofoils. Rolls-Royce pioneered a more efficient alternative: wide chord fan blades. The increased blade chord (i.e. width) is used to enhance the vibration characteristics. Wide chord first went into service in the RB311-535E4 for the Boeing 757 in 1984 and have been a feature of the RB211/Trent/V2500 engine family ever since. Potential weight increases are usually offset by making the blades hollow. Other engine manufacturers have now introduced wide chord fans.

Swept fan

Engine manufacturers are beginning to introduce so-called swept fan blades, which should yield benefits in aerodynamic efficiency and noise.

Other meanings

snubber
- In a fan heater, a fan (or blower) blows cool air past a heating element, heating the air (forced convection). It has a fan wheel with vanes fixed on a rotating shaft enclosed in a case or chamber, to create a blast of air (i.e., the fan blast) for forge purposes.
- In automobiles, a mechanical fan, driven with a belt and pulley off the engine's crankshaft, or an electric fan switched on/off by a thermo switch is used to blow or suck air through a coolant filled radiator, to prevent the engine from overheating.
- A fan is also a small vane or sail that is used to keep the large sail of a smock windmill always in the direction of the wind.
- A fan vault is a type of roof used in church architecture.
- Fan death is an urban legend common in South Korea.

Books

- Rhead, G. Wooliscroft. "The History of the Fan", Kegan Paul, 1910
- Irons, Neville John. "Fans of Imperial China". Kaiserreich Kunst Ltd, 1982.
- Irons, Neville John. "Fans of Imperial Japan". Kaiserreich Kunst Ltd, 1982.
- Armstrong, Nancy. "Book of Fans". Smithmark Publishing, 1984. ASIN 0831709529
- Armstrong, Nancy. "Fans", Souvenir Press, 1984
- Mayor, Susan. "Fans", Charles Letts, 1990
- Mayor, Susan. "The Letts Guide to Collecting Fans". Charles Letts, 1991.
- Alexander, Helene. "The Fan Museum", Third Millennium Publishing, 2001. ISBN 0-9540319-11
- Cowen, Pamela. "A Fanfare for the Sun King: Unfolding Fans for Louis XIV", Third Millennium Publishing (September, 2003) ISBN 1903942209
- Hutt, Julia & Alexander, Helene. "Ogi: A History of the Japanese Fan". Art Media Resources; Bilingual edition (February 1, 1992) ISBN 1872357083
- Qian, Gonglin. "Chinese Fans: Artistry and Aesthetics (Arts of China, #2)". Long River Press (August 31, 2004) ISBN 1592650201
- North, Audrey. "Australia's fan heritage". Boolarong Publications (1985). ISBN 0864390017
- Hart, Avril & Taylor, Emma. "Fans" (V & A Fashion Accessories Series). Publisher- V & A Publications. ISBN 1851772138
- Bennett, Anna G. "Unfolding beauty: The art of the fan : the collection of Esther Oldham and the Museum of Fine Arts, Boston". Thames and Hudson (1988). ISBN 0878462791
- Roberts, Jane. "Unfolding Pictures: Fans in the Royal Collection". Publisher -Royal Collection (January 30, 2006. ISBN 1902163168
- Gitter, Kurt A. "Japanese fan paintings from western collections". Publisher- New Orleans Museum of Art (1985). ISBN 089494021X

External links

: Hand Fans
- [http://www.fancircleinternational.org/ The Fan Circle International]
- [http://www.e-budokai.com/articles/weapons.htm Tessen warrior fan]
- [http://www.fanassociation.org/ Fan Association of North America]
- [http://www.ideco.com/fans/index.html A Cool Breeze Hand Fans]
- [http

Heat sink

See also

Heat sink (disambiguation)

Microprocessor

History

The first chips

Notable 8-bit designs

16-bit

32-bit designs

64 bit microchips on the desktop

History of Operating System support for 64 bit microchips

RISC

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Market statistics

Common µPs; architectures

Notes

See also

External links

Patents

Research

General

Historical documents

Processor company sites

Semiconductors

Fundamental semiconductor physics

Band structure of a semiconductor

Doping of semiconductors

Intrinsic and extrinsic semiconductors

N-type doping

P-type doping

Carrier concentrations

P-N junctions

Required purity and perfection of semiconductor materials

See also

Encompassing fields

Sub-fields

Concepts

References

External links

Heat conduction

Conductance

Newton's law of cooling

See also

Radiation

See also

Electronics

Electronic devices today

CAD/CAM of electronic circuits

Electronic systems

Electronic test equipment

Electronic components

Analog circuits

Digital circuits

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Noise

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See also

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Some other good sites

Fan (implement)

History

Etymology

Ancient

Asia

Europe

Mechanical development

Mechanical devices

Types

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Ceiling fan

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Propfan