2 Sound Flashcards
What are biologic effects of sound?
The effects of the sound wave on biological tissue.
What are acoustic propagation properties?
The effects of the MEDIUM upon the sound wave.
What is sound?
A type of wave that carries energy, not matter, from place to place.
A series of COMPRESSIONS and RAREFACTIONS.
What type of wave makes up sound?
Mechanical and longitudinal wave
What is an acoustic variable?
They help identify which waves are sound waves.
Pressure, density and distance.
What are the units for the 3 acoustic variables (pressure, density and distance)?
Pascals (Pa), kg/cm^3, cm/ft/miles
What is the difference between transverse and longitudinal waves?
The difference is the direction in which particles move.
Transverse waves have particles that move in a perpendicular direction whereas longitudinal waves have particles that move in the same direction as the wave.
What are acoustic parameters?
They describe the feature of a particular sound wave.
Period, frequency, amplitude, power, intensity, wavelength, and speed.
What is a period?
The time required to complete a single cycle.
Typical values: 0.06-0.5 microsec
Determined by sound source
NOT changed by sonographer
What is frequency?
Number of certain events that occur in a particular time duration.
(Number of cycles of an acoustic variable that occur in 1sec)
1/second= Hertz, Hz
Typical values: 2MHz-15MHz
Determined by sound source
NOT changed by sonographer
What is the range of audible sound?
20 Hz-20,000 Hz
How are frequency and period related?
They are reciprocals or an inverse relationship.
Remember to use complementary units!
What are the 3 bigness parameters?
Amplitude, Power, Intensity
These describe a sound beam’s strength.
What is amplitude?
The difference between the average value and the max value of an acoustic variable, the variation of an acoustic variable.
Measured in decibels.
Determined by sound source.
YES can be changed by sonographer.
What is power?
The rate that work is performed, or rate of energy transfer.
Watts
Determined by sound source.
YES can be changed by sonographer.
What is the relationship between power and amplitude?
Power is proportional to Amplitude^2.
What is intensity?
The concentration of energy in a sound beam. watts/cm^2= power/beam area Typical values: 0.001-100 watts/cm^2 Determined by sound source YES can be changed by sonographer
What is the relationship between intensity and power?
They are proportional
What is wavelength?
The length or distance of a single cycle.
Typical values: 0.1-0.88 mm
Determined by BOTH source and medium.
NOT changed by sonographer.
What is the wavelength of sound with a frequency of 1 MHz in soft tissue? 2 MHz?
IN SOFT TISSUE, DIVIDE 1.54MM BY FREQUENCY IN MHZ.
1MHz– 1.54mm
2MHz–0.77mm
What is propagation speed?
The rate that sound travels through a medium.
Typical values: 1540m/s, 1.54km/s, 1.54mm/microsec
Determined by MEDIUM only (density and stiffness)
NOT changed by sonographer.
What is the relationship of speed to stiffness and density?
Stiffness and speed in SAME direction.
Density and speed in OPPOSITE direction.
List from slowest to fastest: how fast does speed pass through the following different mediums (solid, gas, liquid).
Gas(slower) < Liquid < Solid(faster)
What is interference?
When 2 waves overlap at the same location and at the same time to combine into a single new wave.
What is constructive interference?
When the amplitude of the new, combined wave is greater than the original 2 waves, occurs with in-phase waves.
What is destructive interference?
When the amplitude of the new wave is less than one of the original waves, occurs with out-of-phase waves.
