Ch 6 Sound in Media Flashcards
What two things do sound waves do when traveling?
Some reflect at the boundaries of 2 different media, remainder travels deeper to next medium boundary
Sound ______ as it travels.
weakens
Propagation
sound traveling through tissue
Reflection
portion of sound that bounces off medium boundaries
Receive
reflected wave traveling back to transducer
Attenuate
sound wave weakening while traveling
absorption
Amplified
US system strengthens reflected waves received by transducer
What are the 6 steps to signals traveling?
- Sound waves created & transmitted into body by US system & transducer
- Sound waves attenuate as they propagate
- Waves are reflected at boundary of 2 media
- Reflections received by transducer
- Waves converted to electrical signal
- Signal sent to US system to be amplified
What do decibels measure?
- strength of sound beams as they are created and propagate
- strength and brightness of images created by electrical signals
What is decibel notation?
- uses logarithms
- does not use absolute numbers
- reports relative change
Decibel notation is: (4 things)
- relative measurement
- a comparison
- a ratio
- logarithmic
Positive decibels report signals that are what?
Increasing in strength or getting larger
When intensity doubles, the relative change is ______?
3 dB
Negative decibels report what kind of signals?
- signals that are decreasing or getting smaller
When intensity is reduced to half the original value, the relative change is _____?
-3 dB
What is a logarithm?
- method of rating numbers
- represents the number of 10s multiplied to create the original number
If a log increases by 1, the number increases _____
10 fold
What is the log of 1000? 10000?
3, 4
Attenuation is a decrease in what 3 parameters as sound propagates?
Power, intensity, amplitude
What two factors is attenuation determined by?
Path length and frequency of sound
How does path length affect attenuation?
- directly affects it
- increased distance = increased attenuation
- increased distance = decreased strength
How does frequency affect attenuation?
- directly affects
- increased frequency = increased attenuation
- increased frequency = decreased strength
What 3 processes contribute to attenuation?
Reflection, scattering, absorption
What does reflection do to part of the wave that keeps traveling?
Weakens it