Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to detection: Detection limit, Edge detection


Physics the act or process of extracting information, esp at audio or video frequencies, from an electromagnetic wave
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the conversion of electrical oscillations, as a result of which lower-frequency oscillations or a direct current is produced. The most widespread case of detection —demodulation—consists in the isolation of a low-frequency modulating signal from modulated high-frequency oscillations. Detection is used in radio receivers to isolate audiofrequency oscillations and in television to isolate image signals.

Figure 1. (a) Oscillations with constant amplitude at detector input, (b) current pulses l of identical amplitude at detector output. The detector records the constant component of the current.

In the simplest case, an amplitude-modulated oscillation is the aggregate of three high frequencies ω, ω + Ω, and ω - Ω, where ω is a high carrier frequency and Ω is a low modulation frequency. Since there is no signal of frequency Ω in a modulated oscillation, detection must entail frequency conversion. Electrical oscillations are fed to a device (a detector) that passes current only in one direction. In the process the oscillations are converted into a number of current pulses of the same sign. If the amplitude of the detected oscillations is constant, then the current pulses at the detector output have constant amplitude (Figure 1). If the amplitude of the oscillations at the detector input changes, the amplitude of the cur-rent pulses becomes different. Here the pulse envelope con-forms to the law governing the change in the amplitude of modulated oscillations fed to the detector (Figure 2). If the oscillations are only partially rectified—that is, if the current flows through the detector in both directions but the electric conductivity of the detector is different—detection also takes place. Thus, any device having different electric conductivity in different directions, such as a diode, may be used for detection. The frequency spectrum of the current passing through the diode is much richer than the spectrum of the initial modulated oscillation. It contains a constant component, an oscillation of frequency Ω, as well as components having frequencies ω, 2ω, 3ω, and so on. To isolate a signal of frequency Ω the diode current passes through a linear filter that has high resistance at frequency Ω and low resistance at frequencies ω, 2ω, and so on. The simplest filter consists of a resistor R and a capacitor C whose values are defined by the conditions ωRC > > 1 and ΩRC < < 1. The voltage at the output of the filter has frequency Ω and an amplitude proportional to the depth of modulation of the input high-frequency oscillation.

The detector examined above, which has a piecewise linear relationship between the current and the voltage (Figure 3,b), is called a linear detector and reproduces virtually without distortion the low-frequency oscillation Ω used to modulate the input signal (Figure 3,c). Much greater distortions are produced in a square-law detector,

Figure 2. (a) Oscillations with amplitude modulation at detector input, (b) current pulses at detector output. The detector records low-frequency alternating current (lower broken line).

will induce a current through a detector whose spectrum contains the frequencies Ω, 2Ω, ω - Ω, ω, ω + Ω, 2ω - Ω, 2ω + Ω, and so on, A linear filter easily screens all frequencies beginning with the third, but an oscillation of frequency 2O is weakly attenuated by the filter and is “noise” that distorts the signal Ω. It can be eliminated only when the modulation depth is small, since the amplitude of a current of frequency 2Ω is proportional to the square of the modulation depth of the input signal.

Figure 3. (a) Amplitude-modulated oscillation at detector input, (b) current-voltage characteristic of detector, (c) current oscillations at detector output

A given diode may function either as a square-law or linear detector, depending on the magnitude of the signal fed to it. For a weak signal the diode curve is square, but for a strong signal the curve may be considered “piecewise linear.” Thus, for detectors having low distortion it is desirable to feed a rather strong signal to the detector.

The nonlinearity of the dependence of current on voltage in vacuum and semiconductor diodes (diode detection), the nonlinearity of the curve of the grid-cathode section of a vacuum triode (grid detection), and the nonlinearity of the dependence of the anode current of a triode on the voltage at the grid (plate detection) are used for detection. In all cases the very process of detection reduces to diode detection; it is accompanied by signal amplification in the triode only in grid and plate detectors. Detection is also possible in the optical range, where it is accomplished by means of photocells (photoelectric cells, photoamplifiers, photodiodes, and so on) or nonlinear crystals.


Strelkov, S. P. Vvedenie v teoriiu kolebanii, 2nd ed. Moscow, 1964.
Siforov, V. I. Radiopriemnye ustroistva, 5th ed. Moscow, 1954. Chapter 6.
Gutkin, L. S. Preobrazovanie sverkhvysokikh chastot i detektirovanie. Moscow-Leningrad, 1953.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


The recovery of information from an electrical or electromagnetic signal.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In this paper, we propose a lane detection method that is suitable for all kinds of complex traffic situations, especially as driving speed in roads is too fast.
The latest TSA certification, based on the requirements for the "TSA Electronic Baggage Screening Program (EBSP) Requirements for Automated Detection of Explosives," formed out of a Congressional mandate for the screening of all passenger checked baggage for concealed explosives.
Anomaly detection has become an important area of intensive research for secured communication.
MIDC Cardiac is a Point of Care (POC) handheld device for the early detection of certain cardiac event biomarkers to significantly accelerate the triage, diagnosis, treatment and disposition of patients reporting chest pain and with suspected acute myocardial infarction (heart attack).
There are three key problems in aircraft detection from remote sensing images by the deep learning method.
The Global Insurance Fraud Detection Market size is expected to reach $10 billion by 2025, rising at a market growth of 26.6% CAGR during the forecast period.
EdgeWave's next generation email security platform is a cybersecurity solution that provides comprehensive predelivery protection, postdelivery detection and automated incident response to address emerging email threats like phishing, ransomware, and business email compromise.
Matt Clark, vice president technology and product development, Smiths Detection, said: "In doing so, it reduces the burden on image analysts and increases efficiency and detection accuracy."
The achievement of this paper lies that a multipattern sharing technology is successfully used to realize the high-efficient detection for multiple different complex events from massive manufacturing event streams with our scheme.
LeakTronics founder, Darren Merlob, is more than just a leak detection equipment developer.
Cross-lingual plagiarism detection (CLPD) deals with discovering and retrieving of the copied words and sentences in a bilingual scenario.
For UAV based applications in traffic monitoring, one essential task is vehicle detection. This task has become challenging due to the following reasons: varying illumination conditions, background motions due to UAV movements, complicated scenes, and different traffic conditions (congested or noncongested).

Full browser ?