PHY238Y Lecture 14

1
PHY238YLecture 14

• Doppler Effect (continued from Lecture 13 -
  slides 7-12)
• Ultrasound
• The Doppler flowmeter
• References
• Halliday, Resnick, Walker Fundamentals of
  Physics, 6th ed., Wiley 2003, Chapter 18 (18.8)
• Hallett et al. Physics for the life sciences,
  4th ed., 2003, Ch.2 (2.7)
• J. A. Tuszynski, J.M. Dixon Biomedical
  Applications of Introductory Physics, Wiley 2002,
  Ch.16

2
PHY238YLecture 14

• The term ultrasound includes anything over
  20kHz
• Sounds in the range 20kHz 100kHz are used in
  communication and navigation by bats and
  dolphins.
• The range 1 20MHz is used for medical
  applications. Such frequencies are produced by
  ultrasonic transducers.
• Medical applications of ultrasound are
• - diagnostic uses reflection at boundaries
  between organs
• - therapy produces heating in tissues (uses 10
  -100kW/m2)
• - surgery 1 - 40MW/m2 are used to destroy
  diseased tissue.

3
PHY238YLecture 14

• Arterial ultrasound scan
• Uses ultrasound in the range 7-12 MHz to scan
  arteries close to the surface of the body.
• General principle of imaging you cannot observe
  anything smaller than the wavelength you are
  using in your investigation.
• Limit of resolution with 7MHz is 0.2 mm

4
PHY238YLecture 14

• Doppler flow meter