Ch.3 Describing Sound Waves Flashcards
What are the 7 parameters that describe sound waves?
Period
Frequency
Amplitude
Power
Intensity
Wavelength
Speed
Define period
Time it take a wave to vibrate a single cycle. Units in time. 0.06-0.5 microseconds. Determined by source. Not adjustable by sonographer.
Define frequency
Number of events in a specific amount of time. Affects penetration and image quality. Units are hertz. Typical values are 2MHz-15 MHz. Determined by sound source. Not adjustable by sonographer.
Period x frequency=
- They are reciprocals of each other.
What are the 3 bigness parameters?
Amplitude, power, intensity
Define amplitude
Bigness of a wave. Units are pressure, density, or distance. Typical values are 1MPa-3MPa. Determined by sounds source, but decreases with propagation through body. Can be controlled by sonographer
Define power
Rate of energy transferred or rate which work is performed. Units are in watts. Typical values are 4-90 mW. Initially sound source but decreases as it goes through the body. Relies on medium and wave. Controlled by sonographer.
How are power and amplitude related?
Proportional to each other. Power is proportional to amplitude squared.
Define intensity
Concentration of energy in a sound beam. I=P/area
Units are W/cm^2
Typical values are 0.01-300 W/cm^2
Determined by sound source but changes as sound propagates in body. Sonographer can adjust.
Intensity proportional to amplitude ^2
Define wavelength
Distance of one complete cycle. Units mm/cm length. 0.1-0.8mm where 1MHz=1.54mm.
Determined by source and medium.
No controlled by sonographer.Affects image quality.
Inversely related to frequency.
What role does wavelength perform in image quality?
Shorter wavelengths create higher frequency sound therefore more detail.
Define propagation speed
Rate at which sound wave travels. meters per second. Typically mm/microsecond, 500-4000 m/s.
Determined by medium.
All sound travels at same speed through any medium. Not adjustable by sonographer.
Speed=
Frequency* wavelength
What is the speed of sound in soft tissue ?
1,540 m/s
Sound travels fastest in ____, slower in ___, and slowest in _____.
Solids, liquids, gases
What two characteristics of a medium affect speed of sound?
Stiffness and density
Define stiffness
Ability of an object to resist compression.
How does stiffness affect speed?
Directly related.
Other terms that describe stiffness?
Bulk modulus is the same as stiffness.
Elasticity and compressibility are opposites of stiffness.
Ex: Marshmallows low bulk modulus that are highly compressible and highly elastic.
Density define
Weight of a material.
How does density affect speed?
Inversely related. Sound traveled faster in media with low density.
What has the greatest influence on speed?
Stiffness.
Ex: air has low stiffness, therefore travels slowly in air
What is the source of a sound wave in an ultrasound?
The ultrasound system and transducer
