ELECTRONICS

branch of physics that deals with the emission, behaviour, and effects of electrons (as in electron tubes and transistors) and with electronic devices. The beginnings of electronics can be traced to various experiments with electricity. In the 1880s Thomas A. Edison and others observed the flow of current between elements in an evacuated glass tube. Edison, who was experimenting to improve his incandescent light bulb, added a second element near the filament in the tube. Under certain conditions, he noticed a bluish glow in the tube. This Edison effect remained unexplained and unexploited for some years. In 1897 the British physicist J.J. Thomson determined that the Edison effect was due to the emission and passage of particles; through experiment, he identified these particles as electrons. A short time later the English engineer John A. Fleming constructed the so-called thermionic valve (a two-electrode thermionic vacuum tube) by which an electrical current could be restricted to flow only in one direction. This rectifying process, also known as detection and demodulation, produced an output current that could be used to operate a telephone receiver or recording device. Fleming's valve was greatly improved in 1907 by the American engineer Lee De Forest, who added a third element to the evacuated tube and produced the first triode, which could greatly amplify an electrical signal. From the triode the forms of the electron tube (q.v.) multiplied, giving rise to photomultiplier tubes, klystrons, magnetrons, and so forth. In 1947 three scientists at Bell LaboratoriesJohn Bardeen, William B. Shockley, and Walter H. Brattainintroduced the transistor, a simple device consisting of a small block of a semiconductor (q.v.) with three electrodes that could perform many of the functions of electron tubes. The invention of the transistor initiated a progressive miniaturization of electronic components that by the mid-1990s resulted in the manufacture of solid-state devices that contained more than 20,000,000 transistors on a single tiny silicon chip. Such high-density microcircuits, called microprocessors, have led to tremendous advances in computer technology and in computer-based automated systems (e.g., industrial robots and spacecraft-control systems). The availability of inexpensive microprocessors has also brought about the computerization of an enormous array of consumer products, ranging from self-focusing cameras and self-tuning televisions to programmable videocassette recorders and security systems. In addition, developments in optoelectronics ( i.e., an approach that makes use of both optical and electronic phenomena) have yielded efficient photodetectors and solar cells, as well as light-emitting diodes, semiconductor lasers, and optical fibres that are integral to many advanced communications systems. branch of physics that deals with the emission, behaviour, and effects of electrons (as in electron tubes and transistors) and with electronic devices. Electronics encompasses an exceptionally broad range of technology. The term originally was applied to the study of electron behaviour and movement. It came to be used in its broader sense with advances in knowledge about the fundamental nature of electrons and about the way in which the motion of these particles could be utilized. Today many scientific and technical disciplinesincluding physics, chemistry, materials science, mathematics, and electrical and electronic engineeringdeal with different aspects of electronics. Research in these fields has led to the development of such key devices as transistors, integrated circuits, lasers, and optical fibres. These in turn have made it possible to manufacture a wide array of electronic consumer, industrial, and military products. These products range from cellular radiotelephone systems and videocassette recorders to high-performance supercomputers and sophisticated weapons systems. By the mid-1980s the electronics industry was the largest manufacturing industry in the United States. Japan and the industrialized nations of western Europe also had flourishing electronics industries, while various developing countriesincluding South Korea, Taiwan, and Israelexperienced significant advances as well. The impact of electronics on modern life has been pervasive. It can be said that the world is in the midst of an electronic revolution at least as significant as the industrial revolution of the 19th century. Evidence of this is apparent everywhere. Electronics is essential, for example, in telecommunications. An ever-increasing volume of information is transmitted in digital form. Digital techniques, in which signals are converted into groups of pulses, allow the intermingling of voice, television, and computer signals into one very rapid series of pulses on a single channel that can be separated at the receiving end and reconstituted into the signals originally sent. Because the digital pulses can be regenerated perfectly after they become attenuated with distance, no noise or other degradation is apparent at the receiving end. Electronic controls for industrial machines and processes have made possible dramatic improvements in productivity and quality. Computer-aided design tools facilitate the designing of parts that have complex shapes, such as aircraft wings, or intricate structures, such as integrated circuits. The production of designs of this sort is done by computer-controlled machines that receive instructions directly from the design tools. Access to knowledge has been made far easier by computerized indexes of scientific and technical journals, which are accessible from centralized services over telephone lines. These central databases are being supplemented by new techniques derived from digital audio and video disc technology, which provide locally, and at low cost, access to vast amounts of information in text and graphic form. This article reviews the historical development of electronics, highlighting major discoveries and advances. It also describes some key electronic functions and the manner in which various devices carry out these functions. Additional reading The history of electronics Developments in electronics are outlined in Henry B.O. Davis, Electrical and Electronic Technologies: A Chronology of Events and Inventors to 1900 (1981), Electrical and Electronic Technologies: A Chronology of Events and Inventors from 1900 to 1940 (1983), and Electrical and Electronic Technologies: A Chronology of Events and Inventors from 1940 to 1980 (1985); G.W.A. Dummer, Electronic Inventions and Discoveries: Electronics from Its Earliest Beginnings to the Present Day, 3rd rev. and expanded ed. (1983); W.A. Atherton, From Compass to Computer: A History of Electrical and Electronics Engineering (1984); and Ernest Braun and Stuart Macdonald, Revolution in Miniature: The History and Impact of Semiconductor Electronics, 2nd ed. (1982). The science of electronics Fundamental principles and basic functions of electronics are presented in Paul Horowitz and Winfield Hill, The Art of Electronics, 2nd ed. (1989); S.W. Amos, Principles of Transistor Circuits: Introduction to the Design of Amplifiers, Receivers, and Digital Circuits, 7th ed. (1990), an elementary discussion of devices and circuits; J. Seymour, Electronic Devices and Components, 2nd ed. (1988); Robert J. Matthys, Crystal Oscillator Circuits, rev. ed. (1992), an introductory textbook covering a wide range of oscillators; Arthur H. Seidman (ed.), Integrated Circuits Applications Handbook (1983), an extensive coverage with many detailed examples; B. Jayant Baliga, Modern Power Devices (1987, reprinted 1992), a comprehensive textbook on devices for power frequency applications; Thomas M. Frederiksen, Intuitive CMOS Electronics: The Revolution in VLSI, Processing, Packaging, and Design, rev. ed. (1989), an excellent introduction to CMOS integrated circuits, devices, and processing; Robert Boylestad and Louis Nashelsky, Electronic Devices and Circuit Theory, 5th ed. (1992); and Robert E. Simpson, Introductory Electronics for Scientists and Engineers, 2nd ed. (1987). James T. Humphries and Leslie P. Sheets, Industrial Electronics, 4th ed. (1993), is also of interest.Reference works on electronics include Donald G. Fink and Donald Christiansen (eds.), Electronics Engineers' Handbook, 3rd ed. (1989); Christopher J. Booth (ed.), New IEEE Standard Dictionary of Electrical and Electronics Terms, 5th ed. (1993); Stan Gibilisco (ed.), Encyclopedia of Electronics, 2nd ed. (1990); Reference Data for Engineers: Radio, Electronics, Computer, and Communications, 8th ed. (1993); and John Douglas-Young, Illustrated Encyclopedic Dictionary of Electronics, 2nd ed. (1987). American Radio Relay League, The ARRL Handbook for Radio Amateurs, 1994, 71st ed. (1993), covers electronic and electrical principles and explains how devices work and how to apply them, assuming only modest technical knowledge. Robert I. Scace