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10 Cards in this Set

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  • Back
245. What does the velocity of sound depend on? What is dispersion?
The velocity of sounds depends on the properities of the medium. Dispersion is the frequency dependence of the velocity of sound.
246. What does acoustic impedance depend on?
Acoustic impedance (Z) is linearly proportional to the density of the medium (p) and the velocity of the ultrasound (v). Z=pv
247. Enumerate the best known effects suitable for the generation of ultrasound!
-inverse piezoelectric effect
-electrostriction effect
-magnetostriction effect
248. Describe the relationship between the amplitude of the ultrasound-induced pressure fluctuation (P) and the intensity of ultrasound (I).

where Z is acoustic impedance.
249. What is cavitation?
Attractive forces between fluid particles may be overcome by the alternative pressure changes induced by ultrasound and microscopic cavities containing no fluid particles may be generated.
250. What does the value of cavitation threshold mainly depend on?
It depends on the frequence of ultrasound and the viscosity of the fluid.
251. How does the intensity of ultrasound decrease after passing through a given medium?

where Io is the intensity of the ultrasound entering the medium, a is the absorption coefficient
and x is the thickness of the medium.
252. List the primary effects of ultrasound.
- pressure fluctuation
- cavitation
- mechanical friction
- absorption
253. List the secondary effects of ultrasound.
- emulsification
- dispergation
- coagulation
- thermic effect
254. What is the basis of imaging with ultrasound?
A part of an ultrasound beam is reflected at the interfaces of different tissues with difference acoustim impedance, so the boundaries of different tissues can be mapped using the intensity and the delay of the echo compared to the impulsve leaving the transducer.