Doppler effect is a change in the perceived frequency of sound emitted by a moving source

·         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