10 Sound, ultrasound Flashcards
Give the frequency range of sound waves audible by a normal human ear!
Lower limit: 16-20 Hz
Upper limit: 16000-20000 Hz.
Give the frequency range of sound waves audible by a normal human ear!
Lower limit: 16-20 Hz
Upper limit: 16000-20000 Hz.
What is ultrasound?
Sounds whose frequency is between 20000 Hz and 1010 Hz.
Give the definition and unit of sound intensity!
The energy carried by the sound wave perpendicularly through unit cross-sectional area per unit time. Its unit is Watt/m2.
Define in words the compressibility of a medium.
Compressibility is given by the relative volume decrease of the medium caused by a unit increase of pressure.
Define acoustic impedance of a medium and provide a formula showing how it depends on other properties of the medium.
Acoustic impedance is a material constant, which can be defined as the resistance of the medium against bringing its particles into motion. Acoustic impedance (Z)
depends on the density (d) and the compressibility (k) of the medium
Describe the relationship between the propagation speed of sound (c) characteristic of a given medium and the acoustic impedance of the medium (Z)!
c=Z/d, where d is the density of the medium.
List the most widespread effects suitable for the generation of ultrasound!
- inverse piezoelectric effect
- electrostriction effect
- magnetostriction effect
List the most widespread effects suitable for the generation of ultrasound!
- inverse piezoelectric effect
- electrostriction effect
- magnetostriction effect
Describe the relationship between the amplitude of the ultrasound-induced pressure fluctuation (ΔPmax) and the intensity of ultrasound (J)!
∆𝑝𝑚𝑎𝑥 = √2𝑍𝐽 , where Z is acoustic impedance.
What is cavitation?
Attractive forces between fluid particles may be overcome by the alternating pressure changes induced by ultrasound and microscopic cavities containing no fluid particles may be generated.
How does the intensity of ultrasound change while it passes through a certain medium?
𝐽 = 𝐽0𝑒−𝜇𝑥
where J0 is the intensity of the ultrasound entering the medium, μ is the absorption coefficient and x is the thickness of the medium.
What does the reflexivity (extent of reflection on the interface of two media) of ultrasound depend on?
Extent of reflection is determined by the accoustic impedances of the two media. The greater the difference in their acoustic impedances, the larger the reflected fraction of ultrasound is.
What is the basis of imaging with ultrasound?
A part of a ultrasound beam is reflected at the interfaces of different tissues with different acoustic impedance, so the boundaries of different tissues can be mapped using the intensity and the delay of the echo compared to the impulse leaving the transducer.
What is the basis of imaging with ultrasound?
A part of a ultrasound beam is reflected at the interfaces of different tissues with different acoustic impedance, so the boundaries of different tissues can be mapped using the intensity and the delay of the echo compared to the impulse leaving the transducer.
