Abus FUBW50120 Instructions D'installation Et D'utilisation page 37

Microwaves Microwaves is a trivial name for electromagnetic waves with a frequency of 1–
300 GHz, which corresponds to a wavelength of approx. 30 cm to 1 mm. The
frequency range of microwaves includes parts of the decimetric wave range, as
well as the centimetre and millimetre wave range; at its lower end, i.e. toward
the lower frequencies, the microwave range meets the infrared range; towards
its higher end it meets the infrared range of the optical spectrum.
Application
Microwaves are used in radar technology, microwave ovens and many other
technical applications including wireless communications systems (mobile
communications, Bluetooth, satellite broadcasting, Wi-Fi, amateur radio) and
sensor systems (e.g. radar).
Detector technology
Motion detectors utilise the Doppler effect produced by signals.
They work best when movement is longitudinal to the detector.
Motion detectors using microwaves respond optimally when the distance to the
sensor changes.
Doppler The Doppler effect is temporal compression or elongation of a signal caused by
effect changes in distance between the transmitter and receiver for the duration of the
signal. The cause is the change in duration. This purely kinematic effect occurs
for all signals which spread out at a specific speed, mostly the speed of light or
sound.
For periodic signals, the observed frequency increases or decreases. This
affects both pitches and modulation frequencies, e.g. the familiar change in pitch
of a passing police siren.
In the case of Doppler radar, a movement (approaching or moving away) of an
object is detected by the measured frequency change between the transmitted
and reflected signal.
Introduction
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