2. Doppler Physics

3. Waves from a static source Wave peaks evenly spaced around the source at 1 wavelength intervals

4. Waves from a moving source Source moving this way Old positions of source

5. http://www.kettering.edu/~drussell/Demos/doppler/doppler.html

6. Reflection off a static surface

7. Reflection off a moving surface

8. Back to waves If a wave reflects off a moving object the reflected frequency is changed This is called the Doppler effect “Doppler shift” (f d )given by: f r -f t =f d =f t *2*u/c Where f r =received frequency f t =transmitted frequency u=relative velocity of source and reflector c=speed of sound

9. Geometry Maximum Doppler shift here Moving reflectors – Blood cells Zero Doppler shift here

10. Angle effects Maximum Doppler shift at 0 degrees minimum at 90 degrees – proportional to the Cosine of the angle between the beam and direction of travel Direction of movement Alignment of beam

11. Change in F d with Angle f d =f t *2u*Cos(  )/c c*f d / 2*f t *Cos(  ) =u

13. Doppler Modes Color Power Spectral

15. CW doppler Always transmitting and receiving Just look at the difference in frequency So – don’t know depth ! Can avoid this (somewhat) by using intersecting beams.

18. Pulsed wave Doppler Pulses – just like real time scanning Can find depth Need to “gate” analysis of received pulse, so we know where the moving objects are…

21. Uterine Doppler

22. Umbilical Doppler

25. Common Carotid Artery