Page 214 - Electrical Engineering Dictionary

distance. Particles exhibit wave-like charac- diffuse density signal that has uniform
teristics in their passage through matter. In energy density, meaning that the energy flux
striking a target the incident beam scatters off is equal in all parts of a given region.
nucleons. The scattered waves then combine
according to the superposition principle, and diffuse intensity the energy scattered in
the peak of this scattered wave is called the all directions out of the forward or specular
diffracted beam. directions. Sometimes also called incoherent
component of the intensity.
diffraction (1) distortion of an electro-
magnetic wave due to the proximity of a diffuse multipath the result of multipath
boundary or aperture. propagation observed as overlapping signal
(2) a bending or scattering of electromag- components, due to delay differences of mul-
netic waves. Basically a redistribution within tipath components being less than the delay
resolutionofthesignal. Observableinthede-
a wavefront when it passes near the edge of
lay power spectrum as a continuous distribu-
an opaque object.
tion of power over delay. See also multipath
(3) the propagation of light in the presence
propagation, delay power spectrum.
of boundaries. It is the property of light that
causes the wavefront to bend as it passes an
diffuse scattering the component of the
edge.
scattering from a rough surface that is not in
the specular direction. It is caused by reflec-
diffractionangle anglecorrespondingap-
tions from local surfaces oriented in planes
proximately to the rate of spreading of an
different from that of the mean surface. See
electromagnetic wave that has been trans-
also specular scattering.
mitted through an aperture; with Gaussian
beams the far field half angle for a radius
diffuse transmittance a transmitted sig-
equal to the spot size.
nal that has uniform energy density.
diffraction coefficient in the Geometric
diffusion a region of a semiconductor into
Theory of Diffraction, the coefficient that is
which a very high concentration of impurity
proportional to the contribution to the scat-
has been diffused in order to substantially in-
tered field due to the fringe currents near an
crease the majority carrier concentration in
edge or corner of a scattering target.
that region.
diffraction efficiency of Bragg cell ra- diffusion pump second stage of the vac-
tio of the intensity of the principal diffracted uum system. Hot oil showers the particles in
beam to the intensity of the undiffracted a vacuum and creates a better vacuum. Af-
beam. ter a mechanical (roughing) pump is used to
remove about 99.99% of the air in the beam
diffraction grating an array of reflecting tube, the remaining air can then be removed
or transmitting lines that mutually enhance by a diffusion pump, down to about 1E −9
the effects of diffraction. torr.

diffraction loss loss from an electromag- diffusion under field (DUF) a local thin
netic beam due to finite aperture effects. layer of semiconductor with a very high car-
rier concentration located under and in con-
diffraction tomography generalization tact with the collector of a vertical bipolar
of computerized tomography incorporating transistor to provide a low-resistivity connec-
scattering effects. tion to it.

c
2000 by CRC Press LLC