Doppler Effect


The Doppler effect is a phenomenon that has been used in conjunction with a number of different technologies to measure motion. The Doppler effect states that if a wave source and corresponding receiver are moving relative to each other the frequency observed by the receiver will be greater than or smaller than the actual source frequency. This is also known as the Doppler frequency shift. When the wave source and the receiver are moving towards each other the observed frequency will be greater than the actual frequency. If the source and receiver are moving away from each other, the observed frequency will be less than the actual frequency.


Perhaps the best known applications of the Doppler effect in medicine has been in conjunction with ultrasound. Electromagnetic waves or ultrasonic waves are reflected or emitted from a moving object. The resulting Doppler shift is detected with demodulators and filtering techniques.


The Doppler effect has also been used in conjunction with radioactive isotopes to detect motion in the 100 Angstroms range. A radioactive isotope which is a g-ray source is attached to the object of interest. A g-ray absorber is used to measure the Doppler shift of the g-rays. Velocity information can be extracted from this information.


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Support for the development of this module was provided by the National Science Foundation and The Cooper Union for the Advancement of Science and Art.

Please send questions or comments to Professor Ron Adrezin or Professor Daniel Raichel.