SPI module 1 정리 - ②

* Frequency = 1 / period

 - number of events that occur in a specific period of time.

 - unit : hertz, Hz /  1Mz=1,000,000Hz

 - determined only by the sound source, not by the medium

 

* Period = 1 / frequency

 - period is the time takes for a sound wave to complete 1 cycle

 - unit : second, S, ms, μs

 

* wavelength

 - wavelength is the distance over which one complete wave cycle occurs.

 - wavelength is the distance between any two consecutive identical point on a wave.

 

F ↑ : P ↓ WL ↓

F ↓ : P ↑ WL ↑

 

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* wave equation

 

wavelength, (λ) = speed of sound / frequency

λ=C/f

 

wavelength (mm) =

1,540 m/s (=1.54mm/μs)

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frequency (MHz)

 

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* Amplitude = voltage

 - unit : Pascal

 - maximum variation in an acoustic variable

 - relates to the strength of the sound wave

 - determined by the US system

 

 - The loss of amplitude is called attenuation.

 

*  Power ;

 - unit : Watt; W, milliwatt; mW

 - energy per time

 

 - power α (amplitude^2)

 

 * Intensity ;

 - unit : W/cm^2, mW/cm^2

 - concentration of power.

 - intensity = power / area

 

 - intensity α power α (amplitude^2)

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* Speed of sound

 - is determined by medium

 - is not determined by frequency of wavelength

 

Medium	m/s
air	330
fat	1460
water (20˚C)	1480
6% saline (20˚C)	1540
soft tissue	1540
water (50˚C)	1540
muscle	1580
transducer crystal	3850
bone	4000

 

 

* What can affect the speed of sound?

1. Stiffness : hardness of a medium
2. Density

Speed α Stiffness

Speed α 1/ density

 

What has the most significan effect on propagation speed? = "Stiffness"

 

Dertermined by Sound Source	Dertermined by Medium	Dertermined by Sound Source & Medium
Period Frequency Amplitude, power, and intensity	Propagation speed Impedance	Wavelength ∵ WL(λ) = speed / frequency

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* Range equation

 - Distance = speed × time / 2

 

 - "time" is between the transmission of the pulse and the reception of the echo.

c

 - pulse-echo time = pulse round-trip time = time of flight = go-return time

 

 

distance	go-return time
1cm	13μs
2cm	26μs
3cm	39μs
10cm	130μs

 

Deep echo : long go-return time

Superficial echo : short go-return time

 

 

if "go return time = 117μs"?

depth is "9cm"