·
The Doppler effect is a change
in the perceived frequency of sound emitted by a moving source.
·
Using echoes from moving
targets the frequency of the initial signal from an ultrasonic transducer is subtracted
from the frequency of the returning echoes – this is the Doppler shift.
·
Using this shift and by knowing
the angle of the receiver to the direction of movement of the target one can
work out the velocity of that target
o
Dn = (2ns/ v) x
cosQ
§ Dn = Doppler
shift (Hz)
§ n =
frequency of initial beam (Hz)
§ s = velocity of the target (m/s)
§ v = velocity of sound (in tissue 1540 m/s)
§ q = angle
between sound beam and direction of target movement
