Doppler Physics

1
Doppler Physics
2
Waves from a static source
Wave peaks evenly spaced around the source at 1
wavelength intervals
3
Waves from a moving source
Old positions of source
Source moving this way
4
http//www.kettering.edu/drussell/Demos/doppler/d
oppler.html
5
Reflection off a static surface
6
Reflection off a moving surface
7
Back to waves

• If a wave reflects off a moving object the
  reflected frequency is changed
• This is called the Doppler effect
• Doppler shift (fd)given by
• fr-ftfdft2u/c
• Where frreceived frequency
• fttransmitted frequency
• urelative velocity of source and reflector
• cspeed of sound

8
Geometry
Moving reflectors Blood cells
9
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

Alignment of beam
Direction of movement
10
Change in Fd with Angle
fdft2uCos(q)/c
cfd/ 2ftCos(q) u
11
(No Transcript)
12
Doppler Modes Color Power
Spectral
13
(No Transcript)
14
CW doppler

• Always transmitting and receiving
• Just look at the difference in frequency
• So dont know depth !
• Can avoid this (somewhat) by using intersecting
  beams.

15
(No Transcript)
16
(No Transcript)
17
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

18
(No Transcript)
19
(No Transcript)
20
Uterine Doppler
21
Umbilical Doppler
22
(No Transcript)
23
(No Transcript)
24
Common Carotid Artery