ac (alternating current) - current that repeatedly alternates direction (like the tide of the ocean) from a positive maximum to a negative maximum, then back to the positive maximum and so on; standard house current alternates at a frequency of 60 such cycles per second (or 60 Hz)

ac voltage - voltage associated with an alternating-current (ac) signal; since it is constantly varying it is expressed in both "peak" and "average" (or rms) values; the normal home wall outlet supplies 120 Volts rms and has a peak voltage of 169.7 Volts.

A/D converter (analog-to-digital converter) - a device that converts continuously varying analog signals from instruments that monitor such conditions as movement, temperature, and sound into binary code (that is, 1s and 0s) for the computer.

analog - a representation of a signal that resembles the original; it implies a continuous, smoothly changing signal where any piece of information can take on any of an infinite set of values. Real-world phenomena, such as sound, heat, and pressure, are analog. For example, when someone says it is 55 degrees outside, it could really be 55.012492 degrees, or any value between that and 55.

arc lamp (see gas discharge lamp) - a gas discharge lamp in which light is produced by the passage of electricity, through a gas, across two electrodes enclosed in a quartz envelope; high-pressure arc lights (such as mercury vapor lamps, high-pressure sodium arc lamps, and metal-halide arc lamps) produce light in a physically small bulb of high-pressure gases; low-pressure arc lights (such as fluorescent lights, germicidal ultraviolet lamps, and neon sign lamps) employ a physically big tube of low-pressure gas plasma.

ASIC (application-specific integrated circuit) - unlike standard parts like microprocessors and general-purpose memory ICs, an ASIC can be pre-manufactured for a special application or it can be custom manufactured (typically using components from a "building block" library of components) for a particular customer application. Since the building blocks already exist in a library, it is much easier to produce a new ASIC than to design a new chip from scratch.

audio - relating to sound--or frequencies--that can be heard by the human ear; the audible frequency range extends from approximately 20 Hz to 20,000 Hz; the human voice extends over a frequency range of about 100 Hz to 3,000 Hz.

backlight - a light source typically placed behind a liquid-crystal display (LCD); several types of backlights are used including electroluminescent (EL) backlights, LED backlights, and cold-cathode fluorescent lamps (CCFLs); EL backlights are very thin, lightweight, and provide an even light; LED backlights consume more power, but offer a longer operating life and are brighter than ELs; CCFL backlights offer low power consumption and a very bright white light.

bipolar - one of two basic processes (MOS and bipolar) used to fabricate ICs, bipolar technology is based on transistors made from a sandwich of so-called n- and p-type semiconductor material, resulting in "npn" and "pnp transistors"; bipolar technology has more fabrication steps than CMOS technology, and therefore costs more. Bipolar circuits are often chosen for high-performance analog functions while CMOS circuits are often used for digital functions as well as analog functions (see CMOS).

bipolar transistor - invented over 50 years ago, the bipolar transistor is a current-controlled device made from a sandwich of "n-" and "p-type" semiconductor material, resulting in "npn" and "pnp" transistors. The middle section of the transistor is known as the "base" and the other two sections as the "collector" and "emitter" (see transistor and field-effect transistor).

Boolean logic (also see digital) - a form of algebra in which all values are reduced to either TRUE or FALSE; this is the basic theory behind digital systems, where functions--known as logic gates--change incoming "1's" and "0's" according to a set of rules. Logic gates are put together in a sequence to get complex results, but they actually only do a limited number of things: they invert a bit (a HIGH input becomes a LOW output, called a NOT operation), and they compare two bits and tell you if they are the same (an AND gate) or different (an OR gate). These can all be mixed to get AND and OR gates that also invert to give NAND and NOR gates. Gates can be built up into complex structures that add, multiply, and compare numbers.

capacitor - a passive component that stores a charge, measured in Farads (F); capacitors resist changes in voltage, and are an essential component in (for example) power supplies for filtering out unwanted ac noise from a dc signal

CAD (Computer Aided Design) - usually applied to that part of computer-aided engineering that involves the drawing or physical-layout steps of engineering design.

CAE (Computer Aided Engineering) - also called EDA (Electronic Design Automation), is a technique for using computers to help with all phases of engineering design work; similar to computer-aided design (CAD), but also involves the conceptual and analytical design steps; CAE tools help engineers capture and verify the functional and physical characteristics of their designs before they actually manufacture them, thus reducing the time and cost of the design process; CAE tools also allow designers to design much more complex products than they would otherwise be able to.

clock - a circuit or device that generates a periodic signal used for timing or synchronizing signals.

CMOS (Complementary MOS (Metal Oxide Semiconductor)) - one of two basic processes (MOS and bipolar) used to fabricate ICs, CMOS uses MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) as the principal circuit element. Noted for having low power consumption (see bipolar).

connector - the part of a cable that plugs into a port or interface to connect one device to another. Most connectors are either male (containing one or more exposed pins) or female (containing holes in which the male connector can be inserted).

CPLD (complex programmable-logic device) - high-density programmable logic device characterized by an architecture offering high speed, predictable timing, and simple software; generally the preferred type of device for implementing high-speed logic.

CRT (cathode-ray tube) - the technology used in most televisions and computer display screens. A CRT works by moving an electron beam back and forth across the back of the screen. Each time the beam makes a pass across the screen, it lights up phosphor dots on the inside of the glass tube, illuminating the active portions of the screen. By drawing many such lines from the top to the bottom of the screen, it creates an entire screenful of images.

current - the amount of electricity (electrons) flowing through a wire or circuit, measured in Amperes (A)

D/A converter (digital-to-analog converter) - a device that converts digital pulses into analog signals.

data network - any network of interconnected devices constructed for, and used for, the transfer of data between the devices.

dc (direct current) - current that flows in one direction only (like the water from a faucet).

dc/dc converter - an active device--similar to a switching power supply in its operation--that accepts a dc input and typically produces a different dc output voltage; sometimes the input and output are the same, in which case the converter is used for its noise isolation and/or regulation capabilities; dc/dc converters are important for applications where electronic equipment must be operated from a battery or other dc source; dc/dc converter modules typically offer full functionality, while dc/dc converter ICs usually require the addition of external components (like an inductor and capacitors) for complete operation

dc voltage - voltage associated with a dc signal, as from a battery; it is constant—, not varying.

density - a relative measure of the amount of logic, measured in gates, integrated into a single programmable logic device. Higher density equates to more gates; often used interchangeably with "complexity."

development tool - a hardware/software product used to analyze, test, and produce software code for embedded systems.

device programmer - a standalone piece of electronic equipment used to write instructions and data into PLDs via a socket.

digital - a digital system is based around the idea of ON or OFF, so an electrical signal is either there or it isn't. This means that numbers have to be represented as a combination of 0 (OFF) or 1 (ON). This is a binary system, and the 1's and 0's are called bits.

digital subscriber lines (DSL) - technologies that allow telephone companies to use conventional phone lines to deliver data at rates far higher than today's traditional modems or even ISDN

diode - a two-terminal semiconductor device that allows current to flow in one direction only; an essential component used in power supplies to convert ac into dc (a process called rectification)

discrete logic - circuits that perform simple digital functions presented in an individual package; discrete logic products often lack the complexity required for many of today's sophisticated electronic systems, since they offer low levels of integration (see Boolean logic).

discrete semiconductor - a semiconductor component--such as a transistor or diode--that is presented in an individual package.

drift - a gradual, normally permanent change in a signal’s or component’s characteristics; this is due to aging plus changes in the environment and other factors external to the component (usually an oscillator).

DSP - short for digital signal processing, which refers to manipulating analog information--such as sound or images--that has been converted into a digital form.

electromagnetic spectrum - the entire continuum of all kinds of electric, magnetic, and visible radiation; electromagnetic waves are characterized by their frequency and/or wavelength associated with that frequency; in order of increasing frequency--and decreasing wavelength--the spectrum consists of the following bands:

low/radio frequencies--0.001 Hz to about 300 MHz (i.e., 300,000,000 Hz)
microwave--from about 300 MHz to 300 GHz (i.e., 300,000,000,000 Hz)
infrared light--from about 300 GHz to 375 THz (i.e., 375,000,000,000,000 Hz)
visible light--from 375 THz to 750 THz
ultraviolet light--from about 750 THz to 300 PHz (i.e., 300,000,000,000,000,000 Hz)
x-rays and gamma rays--expressed in EHz

embedded system - typically an IC or pc board, it is a specialized computer system that is part of a larger system or machine.

EPROM (erasable programmable read-only memory) - a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM is similar to a PROM, but requires only electricity to be erased.

fault tolerant - a power supply system configuration to ensure the maintenance of system power despite the loss of any single power module. The usual technique is to provide redundant power modules on an n + 1 basis, with sufficient isolation that the failure of any one power module does not cause system failure.

FED (field-emissive display) - a new type of flat-panel display that operates in a similar fashion to a CRT. The advantage is that FEDs can be packaged in an ultra-thin, lightweight, low-power package. FED technology allows the thin panels of today's LCDs, offers a wider field-of-view, provides the image quality of CRT displays, and uses less power than CRTs. FEDs already exist in some special applications and are expected to be in high-volume production in 1998 and in stores in 1999.

fiberoptics - uses a bundle of fine glass or plastic to carry pulses of light much the way an electric current is carried by a copper wire; but a fiberoptic cable can carry millions of times as much information as a copper wire.

field-effect transistor (FET) - a voltage-controlled semiconductor device having three terminals--a gate, drain, and source--whose control, or gate, signal creates an electromagnetic field that controls the flow of current through the device (see transistor and bipolar transistor).

flat-panel display - a very thin display screen used in portable computers. Nearly all modern flat-panel displays use LCD technologies.

flip-flop - A digital logic circuit that can be in one of two states, which it switches between each time a "toggle" signal is sent to it.

fluorescent lamp - a type of gas discharge lamp that uses an electric charge to excite gaseous atoms in a glass tube; these atoms emit ultraviolet (UV) radiation that is absorbed by a phosphor coating on the walls of the lamp tube; the phosphor coating then transforms the UV light to visible light.

FPGA (field-programmable gate array) - a high-density (that is, containing more than 1,000 gates) programmable-logic chip containing small logic cells interconnected through an array of programmable switches. FPGAs can implement thousand of gates of logic in a single IC and can be programmed by users at their site in a few seconds or less depending on the type of device used. FPGAs are popular for prototype development, custom computing, digital signal processing, and logic emulation.

frequency - the number of times per second that a signal (or wave) alternates from positive to negative and back again, expressed in Hertz (Hz); the highest frequencies that a human ear can hear are those that oscillate at up to 15,000 to 20,000 times per second; the electromagnetic wave corresponding to the color red has a frequency of 428,570 GHz (pronounced gigahertz), which can also be stated as 428,570 billion cycles per second; when you look at red light, your eye receives over four hundred trillion waves every second.

frequency counter - a device that measures and displays the frequency of a signal under test.

gas discharge lamp - a lamp that produces light by discharging an electric arc through a mixture of gases and gaseous metals.

gate - the most basic logic element (such as an AND gate or an OR gate); more gates means higher density (see Boolean logic).

gate array - a digital IC that is customized by interconnecting an array of logic elements.

heat sink - a component generally made of aluminum or a zinc alloy and having fins designed to lower the temperature of an electronic device to which it is attached by dissipating heat into the surrounding air; most modern motherboards require either a heat sink, fan, or both.

HDL (Hardware Description Language) - allows designers to describe the desired functionality of their design at a higher level of abstraction using programming language code instead of schematic symbols; the two most common examples are VHDL and Verilog HDL.

hot swap - to remove and replace a system component while power is on and the system is functional (without first shutting the system down)

incandescent lamp - lamp in which a current flowing through a thin wire (or filament) heats the filament to such a high temperature that it gives off light; incandescent lights are the most familiar type of light source--for example, typical "light bulbs" are incandescent lamps.

IGBT (insulated-gate bipolar transistor) - a power semiconductor device available for use in power conversion circuits; usually found in high-voltage circuits (above 300 V) because it has significantly lower values of on-resistance than a power MOSFET with the same die size

inductor - a coiled conductor that tends to oppose any change in the flow of current; usually has coils wrapped around a ferrous core; may be used in power supply filtering.

infrared (IR) light - electromagnetic energy radiated in the wavelength range of about 770 to 1,106 nanometers--which is just below the red end of the visible spectrum; nearly all of the infrared portion of the spectrum is invisible to the human eye; infrared LEDs are used in sensing, data transmission, ambient light detection, and other various applications.

inverter - 1.) a logic gate that converts the input signal to the opposite state for output; if the input is "TRUE," the output is "FALSE," and vice versa. An inverter performs the Boolean NOT operation (see Boolean logic). 2.) Also, a power supply circuit that converts dc to ac.

jitter - the instability in the timing of a digital signal waveform associated with the loss of synchronization with a standard clock cycle; less is better.

lamp - a light source composed of a metal base, a glass or quartz tube filled with an inert gas or a vapor, and base pins to attach to a fixture; incandescent lamps contain filaments while gas discharge lamps contain electrodes.

LCD (liquid-crystal display) - a screen for displaying text/graphics based on a technology called liquid crystal, where small currents change the reflectiveness or transparency of the screen. LCD screens used in notebook computers are backlit to make them easier to read in bright environments.

LED (light-emitting diode) - a semiconductor device that produces either visible or infrared light when electricity is passed through it; they require very little power and are often used as indicator lights.

light pipe - an optical conduit made of molded plastic that directs the light from an LED to the viewing location, often at a right angle from the circuit board.

line driver - a device that ensures reliable and accurate signal transmission over long cable runs; it prevents signal degradation due to inherent cable characteristics as well as that caused by ambient electrical noise.

linear power supply - a power supply that uses a conventional 50- or 60-Hz power transformer followed by a diode rectifier, capacitor filter, and linear regulator; these supplies are about 40% to 55% efficient

linear regulator - a stabilization circuit in which a control device--such as a power MOSFET or bipolar transistor--is placed in series or parallel with the load to deliver a constant voltage across the load

logic (see Boolean logic) - a collection of circuit elements that use digital logic to perform a function or sequence of operations; one of the three major classes of digital ICs--microprocessors, memory, and logic--logic is used for data manipulation and control functions.

logic analyzer - a device that connects to a target system's microcontroller or microprocessor and monitors pins and other device signals to give an accurate real view of software/hardware interaction; useful for viewing the relationships of many signals at once. It presents data in the same general way that an oscilloscope does: the horizontal axis is time, but the vertical axis is logic "high" or "low," not voltage.

logic synthesis - the process of automating the translation of higher-level, abstract design descriptions--in the form of a hardware description language (HDL)--into gate-level hardware-specific implementations.

microcontroller - a highly integrated chip that contains all of the components needed--a central processing unit (CPU), random access memory (RAM), some form of read-only memory (ROM), input/output ports, and timers--to control a system. Unlike a general-purpose computer, which also includes all of these components, a microcontroller is designed for a very specific task—to control a particular system. As a result, the parts can be simplified and reduced, which cuts down on costs.

microprocessor - A silicon chip that contains a central processing unit (CPU)--the "brain" of a computer--where most calculations take place. Specialized microprocessors (see microcontrollers) control the logic of almost all other digital devices, from clock radios to fuel-injection systems for automobiles. Three basic characteristics differentiate microprocessors:

instruction set: The set of instructions that the microprocessor can execute (e.g., RISC or CISC).
bandwidth: The number of bits processed in a single instruction.
clock speed: Given in frequency, it determines how many instructions per second the processor can execute.

microwave frequency - very-short electromagnetic waves between about 30 centimeters and 1 millimeter in wavelength; microwave frequencies range from approximately 1 GHz (i.e., 1,000,000,000 Hz) to 300 GHz in frequency and are just below infrared light on the electromagnetic spectrum.

MOSFET (metal oxide semiconductor field-effect transistor) - offering several advantages over bipolar transistors, MOSFETs feature better thermal stability, switching speed, and bandwidth, and are similar to vacuum tubes in their operation. (see power MOSFET)

motion control - depending on the application, motion control can refer to simple on-off control or a sequencing of events, controlling the speed of a motor, moving objects from one point to another, or precisely constraining the speed, acceleration, and position of a system.

motor control - a form of motion control that involves controlling the speed of a motor.

MOV (metal-oxide varistor) - a voltage-sensitive breakdown device that is commonly used to limit overvoltage conditions (electrical surges) on power and data lines; when the applied voltage exceeds the breakdown point, the resistance of the MOV decreases from a very high level (thousands of ohms) to a very low level (a few ohms), shorting the voltage safely to ground

multimeter - an all-in-one measuring device, it usually combines a voltmeter, an ammeter, and an ohmmeter; it often contains a transistor tester and measures capacitance and inductance as well.

multimedia - the use of computers to present text, graphics, video, animation, and sound in an integrated way.

n + 1 - a power supply system configuration by which power supplies are wired in parallel and sized so that the total system power can be provided by n modules. If there are n + 1 modules, then one module may fail without interrupting operations of the system.

nanometer (nm) - a unit of metric measurement equal to one billionth of a meter, which is used to measure light wavelengths.

neon lamp - a gas discharge light that generates a blue or amber light by exciting a neon gas plasma with two heated electrodes; when the voltage is high enough between the electrodes, the neon gas will break down and begin to conduct electricity, giving off a glow in the process.

noise - a random unwanted signal that is imposed on the wanted output signal.

on-resistance - the output resistance of a power switching device--typically a power MOSFET--when it is in its fully "on" or conducting state; especially important in high-current switches, where the voltage drop across the power device must be minimized

off-line power supply - a power supply that operates directly off the ac power line, without using a power transformer prior to dc conversion (i.e., rectification and filtering)

operating system – the systems software on a computer that commands the computer’s resources, executes its programs, and manages its data and memory. Residing between applications programs and a computer's hardware, an operating system has three main functions:

to efficiently manage hardware
to support applications
to provide a user interface

optocoupler - a device that electrically isolates electronic circuits by converting electronic signal information to light pulses.

oscillator - a timing device consisting of quartz crystal and an oscillation circuit to generate an output signal at a constant specified frequency.

oscilloscope - a test instrument that displays electronic signals (waves and pulses) on a screen for measurement or visual inspection; especially useful for viewing small voltage changes on a signal. The horizontal axis on the screen represents time; the vertical axis is voltage.

passive component - a component that requires no external source of power for its functionality; does not provide any amplification or gain (see resistor, capacitor, and inductor).

PCB (printed-circuit board) - a glass fabric laminate containing one or more layers of conductive traces to interconnect ICs and other components.

PCB layout (pc-board layout) - the process of placing and routing the conductive pattern derived from the schematic circuit diagram onto the pc board--the laminate to which all the electronic components are soldered--with one or more layers of etched metal tracks making the connections; the layout defines the final physical form of the circuit.

PLD (programmable logic device) - a digital integrated circuit that can be programmed (or configured) by a designer to perform specific complex logic functions.

plasma display - a type of flat-panel display that works by sandwiching an ionized gas between two wired panels. When the gas is charged, it glows a bright orange. Plasma displays require much more power than LCD displays and are not used frequently today.

power - electrical energy measured according to voltage and current; usually given in Watts (W)

power factor - the ratio of ac power actually used by a piece of electrical equipment compared to the total apparent ac power supplied; a high apparent power yields a low power factor--meaning the equipment is using a higher current than it actually needs to satisfy its real power requirement; dc circuits always exhibit a power factor of 1.00 (i.e., real input power equals apparent input power)

power factor correction (PFC) - increases the portion of the ac input energy that an ac-input power supply can use, thus increasing overall efficiency

power MOSFET - a power semiconductor device often used as a power switch in dc/dc converters; capable of handling currents of more than 1 Ampere

power supply - an electrical device that provides a known voltage and current output. A power supply can be a standalone device--like a battery or a unit that plugs into a wall outlet--or a fundamental component of a larger electrical product.

programmable device - see FPGA and PLD.

programmable power supply - a power supply that is continuously controllable over both the current and voltage range; it provides the flexibility to power many different circuits and typically allows users to read and program output current and voltage either through front-panel controls or remotely via computer.

PROM (programmable read-only memory) - a permanent memory chip that is programmed by the customer rather than by the chip manufacturer. It differs from a ROM, which is programmed at the time of manufacture. PROMs have been mostly superseded by EPROMs, which can be reprogrammed.

PTC (positive temperature coefficient device) - a device that switches from a low-resistance to a high-resistance state at a specific temperature; placed in line with a circuit, it is widely used as a current limiter; if a short circuit occurs, the increasing current through the device causes it to heat up and increase its resistance, which in turn reduces current flow

real-time operating system (RTOS)- the description for an operating system that responds to an external event within a short and predictable time frame.

rectifier - a diode circuit that passes current in only the forward direction; is used to convert alternating current (ac) to direct current (dc).

RF (radio frequency) - electromagnetic waves ranging from a few kilohertz to over 100 gigahertz for transmitting data, audio, or video; may or may not include the microwave frequency band, depending on the definition used.

resistor - a passive component, measured in Ohms (W), that "resists" the flow of current through it; permits a predetermined current to flow with a given applied voltage

regulation - maintains the output voltage of a power supply to a constant value, regardless of changes in the input voltage or the demands of the load to which the power is being supplied

ripple - distinguished from noise by its periodic non-random nature, ripple is characterized by a series of small ac voltage or current peaks on a dc signal; it is typically a by-product of converting ac to dc.

schematic capture - the process of entering the logical design of an electronic circuit into a CAE system by creating a schematic representation of components and interconnections.

SCR - silicon-controlled rectifier, also known as a thyristor; like a diode it only allows electric current to flow through it in one direction, but in addition it can be controlled so that its "turn-on" can be delayed indefinitely.

semiconductor - a solid crystalline material that is neither a good conductor of electricity (like copper) nor a good insulator (like rubber); the most common semiconductor material is silicon; examples of semiconductor devices include integrated circuits and discrete (non-integrated) semiconductors like transistors and diodes.

sensor - an input device that sends information about its surroundings in the form of electronic signals, or data.

shielded enclosure - a metal or screened enclosure that prevents radio-frequency radiation from being emitted; the FCC standards for computers include limits on how much radiation may be emitted.

signal generator - a device used to generate electronic test signals (or waveforms) for injecting into a circuit input; the circuit's output may then be displayed on (for example) an oscilloscope.

simulation - software modeling/emulation of an electronic circuit design that replicates how a device will perform in terms of timing and results; helps eliminate the time-consuming need for constant physical prototyping.

spectrum analyzer - a device that shows the energy level within each section of a given frequency band (or spectrum).

surge - a transient wave of current, voltage, or power in an electric circuit. A transient causes a high rate of change of current or voltage in the system, but lasts for only a short amount of time.

surge protection - achieved through the use of surge suppression devices, which are used to protect equipment from transient overvoltages present on ac power, data, or telephone circuits. The suppressor may operate by absorbing the surge or by blocking the surge from flowing or by a combination of the two.

switching supply - usually an off-line device, it first converts ac line voltage to crude dc voltage, then "switches" the resulting dc signal on and off at up to 500,000 times per second; this "chopped" ac signal is then converted to dc again; because of the high frequency, the transformer and capacitors required to convert the signal to a stable dc signal can be much smaller than their 50/60-Hz counterparts; switching supplies are 60% to 80% efficient

switching frequency - the rate at which dc voltage is switched in a switching power supply or dc/dc converter

telecommunications - describes any system that is capable of transmitting data in electronic form. The signals can either be transmitted using cabling or by radio signals.

thyristor - (see also SCR) a component like a diode, but will not conduct until a voltage is applied to its third terminal known as the "gate."

transceiver - short for "transmitter-receiver"; a device that both transmits and receives signals.

transformer - passive electromagnetic component that transfers alternating-current (ac) power from one circuit to another; typically used to transform one ac voltage into another lesser or greater ac voltage.

transistor - a three-terminal semiconductor device used for amplifying or switching signals; today's microprocessor ICs contain tens of millions of microscopic transistors. Individually packaged discrete transistors are often used in power and control applications (see bipolar transistor and field-effect transistor).

ultraviolet (UV) light - the light that is above the blue/violet end of the visible spectrum; the wavelengths of UV light are smaller (and thus have a higher frequency) than that of infrared and visible light; wavelengths range from 1.0 to 400 nm.

visible spectrum - the portion of the electromagnetic spectrum visible to the human eye; wavelengths in this region extend from about 400 to 750 nm.

voltage - the electrical "pressure" that causes current in a circuit

waveform - the pattern of a sound wave or other electronic signal in analog form.

wavelength - measured in meters, it is the length from the peak of one wave to the peak of the next (or the length of one oscillation); the higher the frequency of a wave, the shorter its wavelength; for example, visible red light has a wavelength of only 700 nanometers, which means that one wave spans only 7 ten millionths of a meter.

waveform generator - see signal generator

wireless - refers to a communication, monitoring, or control system that uses electromagnetic or acoustic waves to carry a signal through atmospheric space rather than along a wire; in most wireless systems, radio-frequency (RF) or infrared (IR) waves are used.