تبادل لینک هوشمند 
Wi-Fi چیست و چگونه کار می کند؟
در فرودگاه، هتل، رستوران، کتابخانه و یا حتی دفتر کار، امروزه دیگر در هر کجا که تصور کنید ممکن است بتوانید به اینترنت متصل شوید. در آینده ای نزدیک شبکه های ارتباطی بدون سیم چنان گسترشی می یابند که در هر زمان و مکانی شاهد ارائه خدمات اینترنت بی سیم خواهید بود. به کمک شبکه هایی همچون Wi-Fi قادر خواهید بود تا رایانه های یک اطاق یا دفتر کار خود را به راحتی به یکدیگر متصل نمایید.
شبکه های ارتباطی بدون سیم همواره از امواج رادیویی استفاده می کنند. در این شبکه ها یک قطعه رایانه ای اطلاعات را تبدیل به امواج رادیویی می نماید و آنها را از طریق آنتن ارسال می کند. در طرف دیگر یک روتر بدون سیم، با دریافت سیگنال های فوق و تبدیل آنها به اطلاعات اولیه، داده ها را برای رایانه قابل فهم خواهد ساخت.
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شما ومیلیون ها نفر دیگر در سراسر جهان هر روز از اینترنت جهت برقرای ارتباط با دیگران استفاده می کنید. خرید، سرگرمی، کنترل وضعیت آب و هوا و کارهایی از این قبیل. حتما درباره دریافت نامه های الکترونیکی و یا اخبار بوسیله رایانه های جیبی و یا تلفن های همراه مطالبی را شنیده اید. در این مقاله قصد داریم تا شما را با پروتکلی به نام WAP یا Wireless Application Protocol آشنا کنیم.
یکی از مهمترین علل پیدایش اینترنت بی سیم در چند سال اخیر، استفاده اکثر مردم از گوشی هایی است که قابلیت های بالایی دارند. توسعه شبکه های سلولی دیجیتال و خدمات ارتباطی شخصی زمینه ایجاد چنین خدمتی را فراهم نموده است به طوریکه هم اکنون در حدود 60 میلیون تلفن همراه در حال فعالیت در شبکه های اینترنت بی سیم در سراسر دنیا برآورد می شود.
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فیبرنوری چیست؟
فیبرهای نوری رشته های بلند و نازکی از شیشه بسیار خالصند که ضخامتی در حدود قطر موی انسان دارند. آنها در بسته هایی بنام کابل‌های نوری کنار هم قرار داده می‌شوند و برای انتقال سیگنال‌های نوری در فواصل دور مورد استفاده قرار می‌گیرند. از آنها همچنین برای عکسبرداری پزشکی و معاینه های فنی در مهندسی مکانیک استفاده می‌شود.
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پرتوی ایکس
پرتو ایکس یا اشعه ایکس (اشعه رونتگن) نوعی از امواج الکترومغناطیس با طول موج حدود ۱۰ تا ۱۰-۲ آنگستروم است که در بلورشناسی و عکسبرداری از اعضای داخلی بدن و عکسبرداری از درون اشیای جامد و به عنوان یکی از روش‌های تست غیرمخرب در تشخیص نقص‌های موجود در اشیای ساخته شده (مثلاً در لوله‌هاو...) کاربرد دارد.
محتویات
[نهفتن]- ۱ تاریخچه
- ۲ انواع پرتو ایکس
- ۳ روش‌های تولید
- ۴ ایمنی
- ۵ منابع
- ۶ پیوندهای مفید به بیرون
- ۷ جستارهای وابسته
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پرتوی ایکس
پرتو ایکس یا اشعه ایکس (اشعه رونتگن) نوعی از امواج الکترومغناطیس با طول موج حدود ۱۰ تا ۱۰-۲ آنگستروم است که در بلورشناسی و عکسبرداری از اعضای داخلی بدن و عکسبرداری از درون اشیای جامد و به عنوان یکی از روش‌های تست غیرمخرب در تشخیص نقص‌های موجود در اشیای ساخته شده (مثلاً در لوله‌هاو...) کاربرد دارد.
محتویات
[نهفتن]- ۱ تاریخچه
- ۲ انواع پرتو ایکس
- ۳ روش‌های تولید
- ۴ ایمنی
- ۵ منابع
- ۶ پیوندهای مفید به بیرون
- ۷ جستارهای وابسته
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دید کلی با توجه به اینکه اشعه گاما دارای تشعشع الکترومغناطیسی می‌باشد، آن فاقد بار و جرم سکون است. اشعه گاما موجب برهمکنشهای کولنی نمی‌گردد و لذا آنها برخلاف ذرات باردار بطور پیوسته انرژی از دست نمی‌دهند. معمولا اشعه گاما تنها یک یا چند برهمکنش اتفاقی با الکترونها یا هسته‌های اتم‌های ماده جذب کننده احساس می‌کند. در این برهمکنش‌ها اشعه گاما یا بطور کامل ناپدید می گردد یا انرژی آن بطور قابل ملاحظه‌ای تغییر می‌یابد. اشعه گاما دارای بردهای مجزا نیست، به جای آن ، شدت یک باری که اشعه گاما بطور پیوسته با عبور آن از میان ماده مطابق قانون نمایی جذب کاهش می‌یابد
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سری فوریه، روشی در ریاضیات می‌باشد که به وسیله آن، هر تابع متناوبی به صورت جمعی از توابع سینوس و کسینوس می‌تواند نوشته شود. نام این قضیه به اسم ریاضیدان فرانسوی، ژوزف فوریه ثبت شده است. هدف از این کار، نمایش توابع در دامنه فرکانس می‌باشد.
محتویات
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Zener diode
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A Zener diode is a type of diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". The device was named after Clarence Zener, who discovered this electrical property.
A conventional solid-state diode will not allow significant current if it is reverse-biased below its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode will be permanently damaged due to overheating. In case of large forward bias (current in the direction of the arrow), the diode exhibits a voltage drop due to its junction built-in voltage and internal resistance. The amount of the voltage drop depends on the semiconductor material and the doping concentrations.
A Zener diode exhibits almost the same properties, except the device is specially designed so as to have a greatly reduced breakdown voltage, the so-called Zener voltage. By contrast with the conventional device, a reverse-biased Zener diode will exhibit a controlled breakdown and allow the current to keep the voltage across the Zener diode close to the Zener breakdown voltage. For example, a diode with a Zener breakdown voltage of 3.2 V will exhibit a voltage drop of very nearly 3.2 V across a wide range of reverse currents. The Zener diode is therefore ideal for applications such as the generation of a reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low-current applications.
The Zener diode's operation depends on the heavy doping of its p-n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material. In the atomic scale, this tunneling corresponds to the transport of valence band electrons into the empty conduction band states; as a result of the reduced barrier between these bands and high electric fields that are induced due to the relatively high levels of dopings on both sides.[1] The breakdown voltage can be controlled quite accurately in the doping process. While tolerances within 0.05% are available, the most widely used tolerances are 5% and 10%. Breakdown voltage for commonly available zener diodes can vary widely from 1.2 volts to 200 volts.
Another mechanism that produces a similar effect is the avalanche effect as in the avalanche diode. The two types of diode are in fact constructed the same way and both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the Zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a positive temperature coefficient.[1] In a 5.6 V diode, the two effects occur together and their temperature coefficients neatly cancel each other out, thus the 5.6 V diode is the component of choice in temperature-critical applications. Modern manufacturing techniques have produced devices with voltages lower than 5.6 V with negligible temperature coefficients, but as higher voltage devices are encountered, the temperature coefficient rises dramatically. A 75 V diode has 10 times the coefficient of a 12 V diode.
All such diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of "Zener diode".
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Electronic filter
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both. Electronic filters can be:
- passive or active
- analog or digital
- high-pass, low-pass, bandpass, band-reject (band reject; notch), or all-pass.
- discrete-time (sampled) or continuous-time
- linear or non-linear
- infinite impulse response (IIR type) or finite impulse response (FIR type)
The most common types of electronic filters are linear filters, regardless of other aspects of their design. See the article on linear filters for details on their design and analysis.
Contents
[hide]- 1 History
- 2 Classification by technology
- 3 The transfer function
- 4 Classification by topology
- 5 Classification by design methodology
- 6 See also
- 7 External links and references
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Electric power distribution
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This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (January 2008) |
Electricity distribution is the final stage in the delivery (before retail) of electricity to end users. A distribution system's network carries electricity from the transmission system and delivers it to consumers. Typically, the network would include medium-voltage (less than 50 kV) power lines, electrical substations and pole-mounted transformers, low-voltage (less than 1 kV) distribution wiring and sometimes electricity meters.
Contents
[hide]- 1 Modern distribution systems
- 2 History
- 3 Distribution network configurations
- 4 Distribution industry
- 5 See also
- 6 References
- 7 External links
- 8 Further reading
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Electrical conductor
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This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2009) |
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons (see electrical conduction). Positive charges may also be mobile in the form of atoms in a lattice that are missing electrons (known as holes), or in the form of ions, such as in the electrolyte of a battery. Insulators are non-conducting materials with fewer mobile charges, which resist the flow of electric current.
All conductors contain electric charges which will move when an electric potential difference (measured in volts) is applied across separate points on the material. This flow of charge (measured in amperes) is what is meant by electric current. In most materials, the direct current is proportional to the voltage (as determined by Ohm's law), provided the temperature remains constant and the material remains in the same shape and state.
Most familiar conductors are metallic. Copper is the most common material used for electrical wiring. Silver is the best conductor, but is expensive. Because it does not corrode, gold is used for high-quality surface-to-surface contacts. However, there are also many non-metallic conductors, including graphite, solutions of salts, and all plasmas. There are even conductive polymers. See electrical conduction for more information on the physical mechanism for charge flow in materials.
All non-superconducting materials offer some resistance and warm up when a current flows. Thus, proper design of an electrical conductor takes into account the temperature that the conductor needs to be able to endure without damage, as well as the quantity of electric current. The motion of charges also creates an electromagnetic field around the conductor that exerts a mechanical radial squeezing force on the conductor. A conductor of a given material and volume (length × cross-sectional area) has no real limit to the current it can carry without being destroyed as long as the heat generated by the resistive loss is removed and the conductor can withstand the radial forces. This effect is especially critical in printed circuits, where conductors are relatively small and close together, and inside an enclosure: the heat produced, if not properly removed, can cause fusing (melting) of the tracks.
Thermal and electrical conductivity often go together. For instance, most metals are both electrical and thermal conductors. However, some materials are practical electrical conductors without being good thermal conductors.
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Intel Corporation
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| Type | Public |
|---|---|
| Traded as | NASDAQ: INTC NYSE: INTC SEHK: 4335 Euronext: INCO Dow Jones Industrial Average Component NASDAQ-100 Component |
| Industry | Semiconductors |
| Founded | Mountain View, California (1968)[1] |
| Founder(s) | Gordon E. Moore Robert Noyce |
| Headquarters | Santa Clara, California, U.S.[2] |
| Area served | Worldwide |
| Key people | Jane E. Shaw (Chairman) Paul S. Otellini (President and CEO) |
| Products | Microprocessors Flash memory Motherboard Chipsets Network Interface Card Bluetooth Chipsets |
| Revenue |  US$ 43.623 billion (2010)[3] |
| Operating income | US$ 16.045 billion (2010)[3] |
| Net income | US$ 11.464 billion (2010)[3] |
| Total assets | US$ 63.186 billion (2010)[3] |
| Total equity | US$ 49.430 billion (2010)[3] |
| Employees | 82,500 (January 2010)[3] |
| Website | Intel.com |
Intel Corporation (NASDAQ: INTC) is an American global technology company and the world's largest semiconductor chip maker, based on revenue.[4] It is the inventor of the x86 series of microprocessors, the processors found in most personal computers. Intel was founded on July 18, 1968, as Integrated Electronics Corporation (though a common misconception is that "Intel" is from the word intelligence) and is based in Santa Clara, California, USA. Intel also makes motherboard chipsets, network interface controllers and integrated circuits, flash memory, graphic chips, embedded processors and other devices related to communications and computing. Founded by semiconductor pioneers Robert Noyce and Gordon Moore and widely associated with the executive leadership and vision of Andrew Grove, Intel combines advanced chip design capability with a leading-edge manufacturing capability. Though Intel was originally known primarily to engineers and technologists, its "Intel Inside" advertising campaign of the 1990s made it and its Pentium processor household names.
Intel was an early developer of SRAM and DRAM memory chips, and this represented the majority of its business until 1981. While Intel created the first commercial microprocessor chip in 1971, it was not until the success of the personal computer (PC) that this became its primary business. During the 1990s, Intel invested heavily in new microprocessor designs fostering the rapid growth of the computer industry. During this period Intel became the dominant supplier of microprocessors for PCs, and was known for aggressive and sometimes controversial tactics in defense of its market position, particularly against AMD, as well as a struggle with Microsoft for control over the direction of the PC industry.[5][6] The 2010 rankings of the world's 100 most powerful brands published by Millward Brown Optimor showed the company's brand value at number 48.[7]
Intel has also begun research in electrical transmission and generation.[8][9]
Contents
[hide]- 1 Corporate history
- 2 Product and market history
- 3 Corporate affairs
- 4 Competition
- 5 See also
- 6 References
- 7 External links
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Microprocessor
A microprocessor incorporates most or all of the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC, or microchip).[1][2]
The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic on 4-bit words. Other embedded uses of 4-bit and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc., followed soon after. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general-purpose microcomputers from the mid-1970s on.
During the 1960s, computer processors were often constructed out of small and medium-scale ICs containing from tens to a few hundred transistors. The integration of a whole CPU onto a single chip greatly reduced the cost of processing power. From these humble beginnings, continued increases in microprocessor capacity have rendered other forms of computers almost completely obsolete (see history of computing hardware), with one or more microprocessors used in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers.
Since the early 1970s, the increase in capacity of microprocessors has followed Moore's law, which suggests that the number of transistors that can be fitted onto a chip doubles every two years. Although originally calculated as a doubling every year,[3] Moore later refined the period to two years.[4] It is often incorrectly quoted as a doubling of transistors every 18 months.
Contents
[hide]- 1 Firsts
- 2 8-bit designs
- 3 12-bit designs
- 4 16-bit designs
- 5 32-bit designs
- 6 64-bit designs in personal computers
- 7 Multicore designs
- 8 RISC
- 9 Special-purpose designs
- 10 Market statistics
- 11 See also
- 12 Notes and references
- 13 External links
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Sonar
Sonar (originally an acronym for SOund Navigation And Ranging) is a technique that uses sound propagation (usually underwater, as in Submarine navigation) to navigate, communicate with or detect other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and SODAR (an upward looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.
Contents
[hide]- 1 History
- 2 Performance factors
- 3 Active sonar
- 4 Passive sonar
- 5 Warfare
- 6 Civilian applications
- 7 Scientific applications
- 8 See also
- 9 References
- 10 Bibliography
- 11 Further reading
- 12 External links
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Television
Television (TV) is a telecommunication medium for transmitting and receiving moving images that can be monochromatic (shades of grey) or multicolored. Images are usually accompanied by sound. "Television" may also refer specifically to a television set, television programming, television transmission.
The etymology of the word is derived from mixed Latin and Greek origin, meaning "far sight": Greek tele (τῆλε), far, and Latin visio, sight (from video, vis- to see, or to view in the first person.
Commercially available since the late 1920s, the television set has become commonplace in homes, businesses and institutions, particularly as a source of entertainment and news. Since the 1970s the availability of video cassettes, laserdiscs, DVDs and now Blu-ray Discs, have resulted in the television set frequently being used for viewing recorded as well as broadcast material. In recent years Internet television has seen the rise of television available via the Internet, e.g. iPlayer and Hulu.
Although other forms such as closed-circuit television (CCTV) are in use, the most common usage of the medium is for broadcast television, which was modeled on the existing radio broadcasting systems developed in the 1920s, and uses high-powered radio-frequency transmitters to broadcast the television signal to individual TV receivers.
Broadcast TV is typically disseminated via radio transmissions on designated channels in the 54–890 MHz frequency band.[1] Signals are now often transmitted with stereo and/or surround sound in many countries. Until the 2000s broadcast TV programs were generally transmitted as an analogue television signal, but in recent years public and commercial broadcasters have been progressively introducing digital television broadcasting technology.
A standard television set comprises multiple internal electronic circuits, including those for receiving and decoding broadcast signals. A visual display device which lacks a tuner is properly called a monitor, rather than a television. A television system may use different technical standards such as digital television (DTV) and high-definition television (HDTV). Television systems are also used for surveillance, industrial process control, and guiding of weapons, in places where direct observation is difficult or dangerous.
Amateur television (ham TV or ATV) is also used for experimentation, pleasure and public service events by amateur radio operators. Ham TV stations were on the air in many cities before commercial TV stations came on the air.[2]
Contents
[hide]- 1 History
- 2 Geographical usage
- 3 Content
- 4 Social aspects and effects on children
- 5 Environmental aspects
- 6 See also
- 7 References
- 8 Further reading
- 9 External links
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Telegraphy
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Telegraphy is the long-distance transmission of messages without physical transport of written messages. It is a compound term formed from the Greek words tele (τηλε) = far and graphein (γραφειν) = write. Radiotelegraphy or wireless telegraphy transmits messages using radio.
Contents
[hide]- 1 Terminology
- 2 Optical telegraph
- 3 Electrical telegraphs
- 4 Wireless telegraphy
- 5 Telegraphic improvements
- 6 Telex
- 7 Arrival of the Internet
- 8 E-mail displaces telegraphy
- 9 Worldwide status of telegram services
- 10 Social implications
- 11 Names of periodicals
- 12 See also
- 13 References
- 14 Further reading
- 15 External links
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Telephone
- "Phone" redirects here. For other uses, see Phone (disambiguation). This article is about the communications device. For other uses, see Telephone (disambiguation).
| Phone | |
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| An Olivetti rotary dial telephone, c.1940s |
The telephone (from the Greek: τῆλε, tēle, "far" and φωνή, phōnē, "voice"), often colloquially referred to as a phone, is a telecommunications device that transmits and receives sound, most commonly the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other. It is one of the most common appliances in the developed world, and has long been considered indispensable to businesses, households and governments. The word "telephone" has been adapted to many languages and is widely recognized around the world.
All telephones have a microphone to speak into, an earphone which reproduces the voice of the other person, a ringer which makes a sound to alert the owner when a call is coming in, and a keypad (or in older phones a telephone dial or no manual device) to enter the telephone number of the telephone being called. The microphone and earphone are usually built into a handset which is held up to the face to talk. The keypad may be part of the handset or of a base unit to which the handset would be connected. A landline telephone is connected by a pair of wires to the telephone network, while a mobile phone or cell phone is portable and communicates with the telephone network by radio. A cordless telephone has a portable handset which communicates by radio with a base station connected by wire to the telephone network, and can only be used within a limited range of the base station.
The microphone converts the sound waves to electrical signals, which are sent through the telephone network to the other phone, where they are converted back to sound waves by the earphone in the other phone's handset. Telephones are a duplex communications medium, meaning they allow the people on both ends to talk simultaneously. The telephone network, consisting of a worldwide net of telephone lines, fiberoptic cables, microwave transmission, cellular networks, communications satellites, and undersea telephone cables connected by switching centers, allows any telephone in the world to communicate with any other. Each telephone line has an identifying number called its telephone number. To initiate a telephone call, a conversation with another telephone, the user enters the other telephone's number into a numeric keypad on his/her phone. Graphic symbols used to designate telephone service or phone-related information in print, signage, and other media include ℡ (U+2121), ☎ (U+260E), ☏ (U+260F), and ✆ (U+2706).
Although originally designed for voice communication, the system has been adapted for data communication such as Telex, Fax and dial-up Internet communication.
Contents
[hide]- 1 History
- 2 Basic principles
- 3 Details of operation
- 4 Digital telephony
- 5 IP telephony
- 6 Usage
- 7 Telephone operating companies
- 8 Patents
- 9 See also
- 10 Notes
- 11 References
- 12 Further reading
- 13 External links
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Control system
A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.
There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls. There is also fuzzy logic, which attempts to combine some of the design simplicity of logic with the utility of linear control. Some devices or systems are inherently not controllable.
Contents
[hide]- 1 Overview
- 2 Logic control
- 3 On–off control
- 4 Linear control
- 5 Fuzzy logic
- 6 Physical implementations
- 7 See also
- 8 References
- 9 External links
Digital electronics
Digital electronics represent signals by discrete bands of analog levels, rather than by a continuous range. All levels within a band represent the same signal state. Relatively small changes to the analog signal levels due to manufacturing tolerance, signal attenuation or parasitic noise do not leave the discrete envelope, and as a result are ignored by signal state sensing circuitry.
In most cases the number of these states is two, and they are represented by two voltage bands: one near a reference value (typically termed as "ground" or zero volts) and a value near the supply voltage, corresponding to the "false" ("0") and "true" ("1") values of the boolean domain respectively.
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An industrial digital controller
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Intel 80486DX2 microprocessor
Digital techniques are useful because it is easier to get an electronic device to switch into one of a number of known states than to accurately reproduce a continuous range of values.
Digital electronic circuits are usually made from large assemblies of logic gates, simple electronic representations of Boolean logic functions.[1]
Contents
[hide]- 1 Advantages
- 2 Disadvantages
- 3 Analog issues in digital circuits
- 4 Construction
- 5 Non-electronic logic
- 6 Recent developments
- 7 See also
- 8 References
- 9 External links
Electronic engineering
Electronics engineering,[1] also referred to as electronic engineering,[2][3] is an engineering discipline where non-linear and active electrical components such as electron tubes, and semiconductor devices, especially transistors, diodes and integrated circuits, are utilized to design electronic circuits, devices and systems, typically also including passive electrical components and based on printed circuit boards. The term denotes a broad engineering field that covers important subfields such as analog electronics, digital electronics, consumer electronics, embedded systems and power electronics. Electronics engineering deals with implementation of applications, principles and algorithms developed within many related fields, for example solid-state physics, radio engineering, telecommunications, control systems, signal processing, systems engineering, computer engineering, instrumentation engineering, electric power control, robotics, and many others.[4][verification needed]
The Institute of Electrical and Electronics Engineers (IEEE) is one of the most important and influential organizations for electronics engineers.
Contents
[hide]- 1 Relationship to electrical engineering
- 2 History of electronic engineering
- 3 Electronics
- 4 Typical electronic engineering undergraduate syllabus
- 5 Education and training
- 6 Professional bodies
- 7 Subfields
- 8 See also
- 9 References
- 10 External links
Electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another.[1] Circuits can be constructed of discrete components connected by individual pieces of wire, but today it is much more common to create interconnections by photolithographic techniques on a laminated substrate (a printed circuit board or PCB) and solder the components to these interconnections to create a finished circuit. In an Integrated Circuit or IC, the components and interconnections are formed on the same substrate, typically a semiconductor such as silicon or (less commonly) gallium arsenide.[2]
Breadboards, perfboards or stripboards are common for testing new designs. They allow the designer to make quick changes to the circuit during development.
An electronic circuit can usually be categorized as an analog circuit, a digital circuit or a mixed-signal circuit (a combination of analog circuits and digital circuits).
Contents
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Engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of people.
The American Engineers' Council for Professional Development (ECPD, the predecessor of ABET)[1] has defined "engineering" as:
[T]he creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination; or to construct or operate the same with full cognizance of their design; or to forecast their behavior under specific operating conditions; all as respects an intended function, economics of operation and safety to life and property.[2][3][4]
One who practices engineering is called an engineer, and those licensed to do so may have more formal designations such as Professional Engineer, Chartered Engineer, Incorporated Engineer, Ingenieur or European Engineer. The broad discipline of engineering encompasses a range of more specialized subdisciplines, each with a more specific emphasis on certain fields of application and particular areas of technology.
Contents
[hide]- 1 History
- 2 Main branches of engineering
- 3 Methodology
- 4 Social context
- 5 Relationships with other disciplines
- 6 See also
- 7 References
- 8 Further reading
- 9 External links
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Triode
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This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (August 2010) |
A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube (or valve in British English) with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube is the first electronic amplification device. The word is derived from the Greek τρίοδος, tríodos, from tri- (three) and hodós (road, way), originally meaning the place where three roads meet.
Contents
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Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves. In addition to their use in broadcasting, transmitters are necessary component parts of many electronic devices that communicate by radio, such as cell phones, Wifi and Bluetooth enabled devices, garage door openers, two-way radios in aircraft, ships, and spacecraft, radar sets, and navigational beacons. The term transmitter is usually limited to equipment that generates radio waves for communication purposes; or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits.
The term is popularly used more specifically to refer to transmitting equipment used for broadcasting, as in radio transmitter or television transmitter. This usage usually includes both the transmitter proper as described above, and the antenna, and often the building it is housed in.
An unrelated use of the term is in industrial process control, where a "transmitter" is a device which converts measurements from a sensor into a signal, and sends it, usually via wires, to be received by some display or control device located a distance away.
Contents
[hide]- 1 Description
- 2 Legal restrictions
- 3 How it works
- 4 History
- 5 Broadcast transmitters
- 6 Transmitters in culture
- 7 Records
- 8 References
- 9 See also
- 10 External links
Receiver (radio)
A radio receiver is an electronic circuit that receives its input from an antenna, uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, amplifies it to a level suitable for further processing, and finally converts through demodulation and decoding the signal into a form usable for the consumer, such as sound, pictures, digital data, measurement values, navigational positions, etc.[1]
In consumer electronics, the terms radio and radio receiver are often used specifically for receivers designed for the sound signals transmitted by radio broadcasting services – historically the first mass-market radio application.
Contents
[hide]- 1 Types of radio receivers
- 2 Consumer audio receivers
- 3 History of radio receivers
- 4 See also
- 5 Notes
- 6 References
Wire
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It has been suggested that this article be split into articles titled Wire (electrical conductor) and Wire (metal rope), accessible from a disambiguation page. (Discuss) |
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various wire gauges. The term wire is also used more loosely to refer to a bundle of such strands, as in 'multistranded wire', which is more correctly termed a wire rope in mechanics, or a cable in electricity.
Although usually circular in cross-section, wire is also made in square or flattened rectangular cross-section, either for decorative purposes, or for technical purposes such as high-efficiency voice coils in loudspeakers. Edge-wound[1] coil springs, such as the "Slinky" toy, are made of special flattened wire.
Contents
[hide]- 1 History
- 2 Uses
- 3 Production
- 4 Finishing, jacketing, and insulating
- 5 Solid versus stranded
- 6 Varieties
- 7 See also
- 8 References
- 9 External links
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Transformer
A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp), and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np.
In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical.
Contents
[hide]- 1 History
- 2 Basic principles
- 3 Practical considerations
- 4 Equivalent circuit
- 5 Types
- 6 Classification
- 7 Construction
- 8 Applications
- 9 See also
- 10 Notes
- 11 References
- 12 External links
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Resistor
A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. This constant of proportionality is called conductance, G. The reciprocal of the conductance is known as the resistance R, since, with a given voltage V, a larger value of R further "resists" the flow of current I as given by Ohm's law:
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than 9 orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinking. In a high voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor.
The series inductance of a practical resistor causes its behavior to depart from ohms law; this specification can be important in some high-frequency applications for smaller values of resistance. In a low-noise amplifier or pre-amp the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology.[1] A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.
Contents
[hide]- 1 Units
- 2 Theory of operation
- 3 Construction
- 4 Variable resistors
- 5 Measurement
- 6 Standards
- 7 Resistor marking
- 8 Electrical and thermal noise
- 9 Failure modes
- 10 See also
- 11 References
- 12 External links
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.[1][2] The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts are touching and electricity can flow between them, or 'open', meaning the contacts are separated and nonconducting.
A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another workpiece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force, acting as sensors in a process and used to automatically control a system. For example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by another electrical circuit is called a relay. Large switches may be remotely operated by a motor drive mechanism. Some switches are used to isolate electric power from a system, providing a visible point of isolation that can be pad-locked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock.
Contents
[hide]- 1 In circuit theory
- 2 Contacts
- 3 Actuator
- 4 Special types
- 5 Light switches
- 6 Electronic switches
- 7 See also
- 8 References
- 9 External links
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Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion.[1][2]
Motors converting heat energy into motion are usually referred to as engines,[3] which come in many types. A common type is a heat engine such as an internal combustion engine which typically burns a fuel with air and uses the hot gases for generating power. External combustion engines such as steam engines use heat to generate motion via a separate working fluid.
Another common type of motor is the electric motor. This takes electrical energy and generates mechanical motion via varying electromagnetic fields.
Other motors including pneumatic motors that are driven by compressed air, and motors can be driven by elastic energy, such as springs. Some motors are driven by non combustive chemical reactions. Molecular motors like myosins in muscles generate useful mechanical motion in biological systems by chemical reactions like ATP hydrolysis.
Contents
[hide]- 1 Terminology
- 2 History of engines
- 3 Heat engine
- 4 Non thermal chemically powered motor
- 5 Electric motor
- 6 Physically powered motor
- 7 Sound levels
- 8 Engine efficiency
- 9 Engines by use
- 10 See also
- 11 References
- 12 External links
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Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy.[1] Since the invention of the first battery (or "voltaic pile") in 1800 by Alessandro Volta, batteries have become a common power source for many household and industrial applications. According to a 2005 estimate, the worldwide battery industry generates US$48 billion in sales each year,[2] with 6% annual growth.[3]
There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. Batteries come in many sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers.
Contents
[hide]- 1 History
- 2 Principle of operation
- 3 Categories and types of batteries
- 4 Battery capacity and discharging
- 5 Battery lifetime
- 6 Hazards
- 7 Battery chemistry
- 8 Homemade cells
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
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Relay
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This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (November 2009) |
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
A type of relay that can handle the high power required to directly control an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".
Contents
[hide]- 1 Basic design and operation
- 2 Types
- 3 Pole and throw
- 4 Applications
- 5 Relay application considerations
- 6 Protective relays
- 7 Railway signalling
- 8 See also
- 9 References
- 10 External links
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Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow (as opposed to ionic conductivity) intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter. Semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices. Such devices include transistors, solar cells, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits. Similarly, semiconductor solar photovoltaic panels directly convert light energy into electrical energy. In a metallic conductor, current is carried by the flow of electrons. In semiconductors, current is often schematized as being carried either by the flow of electrons or by the flow of positively charged "holes" in the electron structure of the material. Actually, however, in both cases only electron movements are involved.
Common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of proportions. Such compounds share with better known semiconductors intermediate conductivity and a rapid variation of conductivity with temperature, as well as occasional negative resistance. Such disordered materials lack the rigid crystalline structure of conventional semiconductors such as silicon and are generally used in thin film structures, which are less demanding for as concerns the electronic quality of the material and thus are relatively insensitive to impurities and radiation damage. Organic semiconductors, that is, organic materials with properties resembling conventional semiconductors, are also known.
Silicon is used to create most semiconductors commercially. Dozens of other materials are used, including germanium, gallium arsenide, and silicon carbide. A pure semiconductor is often called an “intrinsic” semiconductor. The electronic properties and the conductivity of a semiconductor can be changed in a controlled manner by adding very small quantities of other elements, called “dopants”, to the intrinsic material. In crystalline silicon typically this is achieved by adding impurities of boron or phosphorus to the melt and then allowing the melt to solidify into the crystal. This process is called "doping".[1]
Contents
[hide]- 1 Explaining semiconductor energy bands
- 2 Energy bands and electrical conduction
- 3 Holes: electron absence as a charge carrier
- 4 Energy–momentum dispersion
- 5 Carrier generation and recombination
- 6 Semi-insulators
- 7 Doping
- 8 Preparation of semiconductor materials
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
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Electronics
Electronics is the branch of science and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits. The nonlinear behaviour of these components and their ability to control electron flows makes amplification of weak signals possible, and is usually applied to information and signal processing. Electronics is distinct from electrical and electro-mechanical science and technology, which deals with the generation, distribution, switching, storage and conversion of electrical energy to and from other energy forms using wires, motors, generators, batteries, switches, relays, transformers, resistors and other passive components. This distinction started around 1906 with the invention by Lee De Forest of the triode, which made electrical amplification of weak radio signals and audio signals possible with a non-mechanical device. Until 1950 this field was called "radio technology" because its principal application was the design and theory of radio transmitters, receivers and vacuum tubes.
Today, most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solid state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This article focuses on engineering aspects of electronics.
Contents
[hide]- 1 Electronic devices and components
- 2 Types of circuits
- 3 Heat dissipation and thermal management
- 4 Noise
- 5 Electronics theory
- 6 Electronics lab
- 7 Computer aided design (CAD)
- 8 Construction methods
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
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Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals. It is made of a solid piece of semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things.
Contents
[hide]- 1 History
- 2 Importance
- 3 Simplified operation
- 4 Comparison with vacuum tubes
- 5 Types
- 6 Construction
- 7 See also
- 8 References
- 9 Further reading
- 10 External links
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Electronic band structure
In solid-state physics, the electronic band structure (or simply band structure) of a solid describes those ranges of energy an electron is "forbidden" or "allowed" to have. Band structure derives from the diffraction of the quantum mechanical electron waves in a periodic crystal lattice with a specific crystal system and Bravais lattice. The band structure of a material determines several characteristics, in particular the material's electronic and optical properties.
Contents
[hide]- 1 Why bands occur in materials
- 2 Basic concepts
- 3 Theory of band structures in crystals
- 4 References
- 5 Bibliography
- 6 Further reading
- 7 See also
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Electron
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| Composition: | Elementary particle[2] |
| Particle statistics: | Fermionic |
| Group: | Lepton |
| Generation: | First |
| Interaction: | Gravity, Electromagnetic, Weak |
| Symbol(s): | e− , β− |
| Antiparticle: | Positron (also called antielectron) |
| Theorized: | Richard Laming (1838–1851),[3] G. Johnstone Stoney (1874) and others.[4][5] |
| Discovered: | J. J. Thomson (1897)[6] |
| Mass: | 9.10938215(45)×10−31 kg[7] 5.4857990943(23)×10−4 u[7] [1,822.88850204(77)]−1 u[note 1] 0.510998910(13) MeV/c2[7] |
| Electric charge: | −1 e[note 2] −1.602176487(40)×10−19 C[7] −4.803×10−10 esu [8] |
| Magnetic moment: | −1.00115965218111 μB[7] |
| Spin: | 1⁄2 |
The electron is a subatomic particle carrying a negative electric charge. It has no known components or substructure. Therefore, the electron is generally believed to be an elementary particle.[2] An electron has a mass that is approximately 1/1836 that of the proton[9] The intrinsic angular momentum (spin) of the electron is a half-integer value in units of ħ, which means that it is a fermion. The antiparticle of the electron is called the positron. The positron is identical to the electron except that it carries electrical and other charges of the opposite sign. When an electron collides with a positron, both particles may either scatter off each other or be totally annihilated, producing a pair (or more) of gamma ray photons. Electrons, which belong to the first generation of the lepton particle family,[10] participate in gravitational, electromagnetic and weak interactions.[11] Electrons, like all matter, have quantum mechanical properties of both particles and waves, so they can collide with other particles and be diffracted like light. However, this duality is best demonstrated in experiments with electrons, due to their tiny mass. Since an electron is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle.[10]
The concept of an indivisible amount of electric charge was theorized to explain the chemical properties of atoms, beginning in 1838 by British natural philosopher Richard Laming;[4] the name electron was introduced for this charge in 1894 by Irish physicist George Johnstone Stoney. The electron was identified as a particle in 1897 by J. J. Thomson and his team of British physicists.[6][12][13]
In many physical phenomena, such as electricity, magnetism, and thermal conductivity, electrons play an essential role. An electron in motion relative to an observer generates a magnetic field, and will be deflected by external magnetic fields. When an electron is accelerated, it can absorb or radiate energy in the form of photons. Electrons, together with atomic nuclei made of protons and neutrons, make up atoms. However, electrons contribute less than 0.06% to an atom's total mass. The attractive Coulomb force between an electron and a proton causes electrons to be bound into atoms. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.[14]
According to theory, most electrons in the universe were created in the big bang, but they may also be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere. Electrons may be destroyed through annihilation with positrons, and may be absorbed during nucleosynthesis in stars. Laboratory instruments are capable of containing and observing individual electrons as well as electron plasma, whereas dedicated telescopes can detect electron plasma in outer space. Electrons have many applications, including welding, cathode ray tubes, electron microscopes, radiation therapy, lasers and particle accelerators.
Contents
[hide]- 1 History
- 2 Characteristics
- 3 Formation
- 4 Observation
- 5 Plasma applications
- 6 See also
- 7 Notes
- 8 References
- 9 External links
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Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations, and a graph of the system is drawn with the oscillating variable as the vertical axis and time as the horizontal axis, the amplitude is visually represented by the vertical distance between the extrema of the curve.
In older texts the phase is sometimes very confusingly called the amplitude.[1]
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Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency. Loosely speaking, 1 year is the period of the Earth's orbit around the Sun,[1] and the Earth's rotation on its axis has a frequency of 1 rotation per day.[2]
Contents
[hide]- 1 Definitions and units
- 2 Measurement
- 3 Frequency of waves
- 4 Examples
- 5 Period versus frequency
- 6 Other types of frequency
- 7 Frequency ranges
- 8 See also
- 9 References
- 10 Further reading
- 11 External links
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