detection

de·tec·tion

D0169000 (dĭ-tĕk′shən)n.1. The act or process of detecting; discovery: detection of a crime; detection of radiation from a distant galaxy.2. See demodulation.

detection

(dɪˈtɛkʃən) n1. the act of discovering or the fact of being discovered: detection of crime. 2. (Electronics) the act or process of extracting information, esp at audio or video frequencies, from an electromagnetic wave. See also demodulation

de•tec•tion

(dɪˈtɛk ʃən)

n. 1. the act of detecting or the state of being detected. 2. the process of demodulation. [1425–75; < Late Latin]

detection

1. In tactical operations, the perception of an object of possible military interest but unconfirmed by recognition.
2. In surveillance, the determination and transmission by a surveillance system that an event has occurred.
3. In arms control, the first step in the process of ascertaining the occurrence of a violation of an arms control agreement.
4. In nuclear, biological, and chemical (NBC) environments, the act of locating NBC hazards by use of NBC detectors or monitoring and/or survey teams. See also hazard; monitoring; nuclear, biological, and chemical environment.

Thesaurus

Noun	1.	detection - the perception that something has occurred or some state exists; "early detection can often lead to a cure"sensingperception - the process of perceiving
	2.	detection - the act of detecting something; catching sight of somethingespial, spotting, catching, spyingdiscovery, find, uncovering - the act of discovering something
	3.	detection - the detection that a signal is being receivedsignal detectionreception - quality or fidelity of a received broadcast
	4.	detection - a police investigation to determine the perpetrator; "detection is hard on the feet"detecting, detective work, sleuthingpolice investigation, police work - the investigation of criminal activities

detection

noun1. diagnosis, spotting, recognition, observation, perception, identification, discernment the early detection of cancer2. discovery, arrest, capture, exposure, uncovering, tracking down, unearthing, apprehension, rooting out, unmasking, ferreting out These criminals are sophisticated enough to avoid detection.

Translations

detection

Physics the act or process of extracting information, esp at audio or video frequencies, from an electromagnetic wave

Detection

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.

REFERENCES

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.

V. N. PARYGIN

detection

[di′tek·shən] (communications) The recovery of information from an electrical or electromagnetic signal.

detection

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detection

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Detection

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detection

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Patient discussion about detection

detection

Synonyms for detection

noun diagnosis

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noun discovery

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Synonyms for detection

noun the perception that something has occurred or some state exists

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noun the act of detecting something

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noun the detection that a signal is being received

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noun a police investigation to determine the perpetrator

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