Ch. 1, & 2 Flashcards
Basics, Sound Variables, Sound Parameters & their Relationships
vertical axis
(Y)
horizontal axis
(X)
Unrelated
- two items that are not associated with one another
examples: - -propagation speed and frequency
- -wavelength and intensity
- -frequency and intensity
Related or Proportional
- two items are associated, can either be inverse or directly
- Power ∝ Intensity
Inversely Related
when one item increases the other decreases
ex) frequency and period
wavelength and frequency
acoustic velocity (speed) and density
Reciprocal relationships
Inverse numbers multiplied to equal 1
Example = period and frequency
Metric system
G giga, billion, 10^9 M mega, million, 10^6 k killo, thousand, 10^3 h hecto, hundred, 10^2 da deca, ten, 10^1 # d deci, tenth, 10^-1 c centi, hundredth, 10^-2 m milli, thousandth, 10^-3 u(mu) micro, millionth, 10^-6 n nano, billionth, 10^-9
Acoustic propagation properties
effects medium have on wave/ what happens when sound wave hits something
Biological effects
effects of sound wave upon the biologic tissue through which it passes (heat)
to be a sound wave…
- mechanical - vibrate back and forth in fixed position
- cannot travel through vacuum - must have medium
- molecules must have compression and rarefaction
- travel in straight, longitudinal line
transverse waves
particles more in perpendicular motions, up and down along the wave in right angles
longitudinal waves
sound waves
more left to right in same direction as sound propagation
acoustic variables
pressure - pascals (Pa)
density - concentration of mass in volume (kg/cm^3)
distance - measure of particle motion (cm,mm)
Out of phase
peaks and troughs at different times
correlate to destructive interference for a wave lower in amplitude
In phase
when peaks and troughs are at the same time and location
correlate to constructive interference for a wave length higher in amplitude
Acoustic parameters
- sound wave features/characteristics
- period, frequency amplitude, intensity, power
wavelength, propagation speed
Period - define, units, typical values, determination, adjustability
- time for a wave to vibrate a single cycle
- microseconds μs
- 0.06 - 0.5 μs
- sound source
- no adjusting
Frequency - define, units, typical values, determination, adjustability
- number of cycles in a given time
- hertz (same as saying X per second)
- 2 - 15 MHz
- sound source
- no adjusting
Infrasound
less than 20 Hz - inaudible
Audible
20 - 20,000 Hz (20 kHz)
Ultrasound/ ultrasonic
greater than 20 kHz (20,000 Hz) - too high for humans
Relationship between Frequency & Period
- INVERSE (means they are repricals)
- Frequency increases - Period decreases
- As Frequency decreases - Period increases
- Frequency X Period = 1
“Bigness” Parameters
Amplitude, Power, Intensity = strength of sound wave
Amplitude - define, units, typical values, determination, adjustability
- difference between the max and baseline value (or peak to peak, max and min)
- any of acoustic variables (Pa, g/cm^3, cm)
- 1MPa - 3MPa
- sound source
- Initially adjustable
Power - define, units, typical values, determination, adjustability
- Rate of energy transfer, strength of beam
- Watts
- 0.004 to 0.090 watts (4 - 90 milliwats)
- sound source
- Initially adjustable
Power & Amp. relationship
Power/Intensity ∝ Amp^2
- If amp decreases by a factor of 2, power is decreased by factor of 4
Intensity - define, units, typical values, determination, adjustability
- Concentration of energy in beam
- W/cm^2, watts from power and cm^2 from beam area
- 0.01 to 300 W/cm^2
- sound source
- initially can change
(intensity) W/cm^2 = (power) W ÷ cm^2 ( area)
Relationship in Bigness Parameters
- Intensity ∝ Power
- if amp doubles then power & intensity will quadruple
Wavelength - define, units, typical values, determination, adjustability
- Distance/ length of one complete cycle
- Any unit of length (cm, mm, m)
- Soft tissue wavelength typically 0.1 to 0.8 mm
- Sound source AND media
- Not adjustable
wavelength (mm) = 1.54 mm/μs ÷ frequency (MHz)
Wavelength & Frequency relationship
INVERSE
- Higher freq. has shorter wavelengths = higher quality
- Lower freq. has longer wavelengths
Propagation Speed - define, units, typical values, determination, adjustability
- Rate of which sound travels through medium
- mm/μs, or any distance divided by time
- 1540 m/s or 1.54 mm/μs
- Medium only
- Not adjustable
speed (m/s) = frequency (Hz) X wavelength (m)
Speed of sound in order of lowest to highest
Air (lung), soft tissues, liver, bone
Medium characteristics that determine speed propagation
Stiffness & Density
Stiffness
- Resists compression, maintains its shape
- Bulk modulus
- Directly related to speed
- –Increases & speed of sound increases
Density
- Relative weight
- Inversely related to speed
- –Increases & speed reduces
