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Doppler Effect & Ultrasound

  1. Apr 12, 2005 #1
    hey just wondering about the doppler effect and how it is used in meterology, law enforcment and astronomy.

    I know for law enforcment they use it in radar guns, and astronomy i think for finding the distance of planets?

    Any other ways it used? and also how is ultra sound used in medicine?
    any web links would be cool too, thanx.
  2. jcsd
  3. Apr 13, 2005 #2
    Just a little clarification on using the doppler effect to find the distance of planets. There are actually two sources of wavelength shifts around massive, moving objects, that due to the change in gravitational potential energy (very slight around objects even of earth's mass), and the more dominant velocity effect. It's not so much that you can find the distance between planets using the doppler effect because well the planet could potentially be in a galaxy that is moving toward you, but objects further away from us tend to have higher doppler redshifts (moving faster away), so it generally works consistently only for objects incredibly far away such as quasars. I should also note that an entire convention for long-distance objects has been built around the doppler effect, detailed at http://hyperphysics.phy-astr.gsu.edu/hbase/astro/redshf.html#c2 (the second block of text)

    As for your question, I found easy-to-understand answers from http://www.howstuffworks.com and simply seraching for "doppler"
    Last edited by a moderator: Apr 13, 2005
  4. Apr 13, 2005 #3

    Chi Meson

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    Modern ultrasould equipment uses the doppler effect to determine precise motion of membranes inside the body. At every interface within the body (such as the surface of the heart) a partial reflection of sound occurs. This reflection will be shifted by a certain amount if the membrane is moving toward or away from the source.

    The latest machines are so good that by changing the frequency just right, you can get a photograph of the face of a baby in the womb; it looks just like a black & white snapshot. A little twist of a dial, and then you can see the skeleton.

    Try a google search for ultrasound AND doppler
  5. Apr 13, 2005 #4
    Doppler is not required to visualize membranes. Doppler ultrasound is not used to visualize objects at all in fact. The most common use is to assess blood flow in arteries and veins.

    Actually ultrasound units (the transducers really) operate at a constant frequency, anywhere from 1 MHz to 12 MHz with a different transducer for each frequency. When the technologist twists the dial or moves the sliders, timing delays are being adjusted that let you visualize structures at different depths. By increasing the timing delay and waiting a longer or shorter time for echoes, you effectively change the depth of field in an ultrasound study (deeper for longer times, closer for shorter times).
    Last edited: Apr 13, 2005
  6. Apr 13, 2005 #5

    Chi Meson

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    I gotta get a new textbook!
  7. Apr 13, 2005 #6
    You are right Chi meson, but I was talking more about Doppler ultrasound, you were explaing the ultrasound that is more commonly used for viewing internal organs or pregnant women.
  8. Apr 14, 2005 #7

    Chi Meson

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    Yeah. Thing is, my son was born just two months ago, and I always made sure to be there for the ultrasound viewings during the pregnancy (it was a brand new machine and I'm still agog over it!).
    BTW: I had asked the technician "Does that [dial] change the frequency?" and she said "yes." It made sense at the time. :redface:
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