physics chapter 1

Time

any unit of duration - s, ms, micros

what is sound

pressure wave that requires a mechanical action

distance

any length measurement

frequency

cycles/second - Hz, MHz

velocity

unit of length divided by time

area

any distance unit squared

volume

any distance unit cubed or volume unit (cm³ or mL)

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what are the pirmary acoustic variables

pressure, density, distance

define pressure and units

concentration of force within an area, Pascals

define density and units

concentration of mass within a volume, kg/cm³

define distance and what units

measurement of particle motion, any length unit

defind wavelength

length of single cycle of sound - LENGTH

what are the 7 parameters of sound

period, frequency, amplitude, power, intensity, propogation speed, wavelength

what is period (T)

amount of time of one cycle (beginning of one to beg of another) TIME

what determines period

machine - not adjustable

if frequency of sound is 12 Hz, what is period

1/12 of second

what determines frequency

machine - not adjustable

period and freuqncy are ___________

inversely related, reciprocals

what is amplitude

amount of force

5 oscillations in 1 second = __________ Hz

5

define propogation speed

speed of soundwave through medium

what determines propogation speed

medium

what is formula for propogation speed

speed (C) = frequency (Hz) x wavelength (lambda)

what is standard for speed through soft tissue

1540 m/s (1.54 mm/microS)

what properties of the medium determine speed of sound

siffness and density

what determines wavelength

machine and medium, not adjustable - only acoustic parameter determined by both

lower the frequency, ___________ the wavelength

longer

formula for wavelength

propogation speed (1.54 Mhz)/frequency

what is wavelength of 2 MHz transducer

1.54 divided by 2 (soft tissue prop speed) = 0.77 mm

what parameters affect strength of a soundwave

amplitude, power, intensity

define amplitude

max increase or decrease of acoustic variable from baseline of that variable

what are amplitude variables

particle motion (pressure, density, distance)

what units are amplitude variables in

pascals, kg/cm³, mm, dB

what determines amplitude variables

machine initially, then medium causes decrease - it is adjustable by changing output power

define power

the rate at which work is performed or energy is transmitted

what determines power

initially machine, decreases w/medium - adjustable by sonographer

how is power proportional to amplitude

increase power = increase amplitude²

define intenstiy

power of a wave divided by area of which it is spread (W/cm²)

what unit is used for intensity

W (power)/cm²

what determines intensity

machine initially then decreases w/medium - adjustable by sonographer

intensity is _______ to power

directly proportional - equally

intensity is _____ to amplitude²

proportional - if amplitude² is doubled, intensity is x4

what is the amount of impedence dependt on

density and propogation speed

what unit is used for impedence

Rayls

what controls impedence

medium

transmission of Pulse echo converts _____________

electrical energy to sound

reception of pulse echo converts

sound into electricity

what are pulsed wave parameters

pulse repetition freqency (PRF), pulse repetition period (PRP), pulse duratoin (PD), duty factor (DF), spacial pulse length (SPL)

what is PRF/pulsed repetition frequency

number of pulses per second (one pulse can have mult. cycles)

the deeper the area of interest, the faster/slower the PRF

slower

define PRP/pulse repitition period

time taken for pulse to occur (on/trasmit and off/listening times)

PRP and PRF are _________ related

inversely related, reciprocals

pulse duration

“talking” time measurement - # cycles (n) x period (T)

pulse duration determined by

machine

what is spatial pulse length

number of cyclex (n) x wavelength

if wavelength increases, spatial pulse length __________

increases

SPL determined by

machine and medium

attenuation

decrease of amplitude, power, and intesity

what are mechanisms of attenuation

absorption, scattering, reflection

what is the unit for attenuation

decibels dB

absorption creates ___________

heat - thermal bioeffects - (sound to heat)

How are attenuation and frequency related

Directly

distance (path length) and attenuation are __________ related

directly

if intensity or power doubles, decibels changes by

3 dB

if intensity or power decreases by half, decibel changes by

-3 dB

what is wavelength of 1 MHz transducer

1.54

what is wavelength of 2 MHz transducer

0.77

Intensity formula

power/area W/cm²

formula for impedance

prop speed (p) x density

what is PRP

puls repetition period - one pulse length

what is spatial pulse length

length of pulse

formula for PD

pulse duration = n of cycles x period

formula for DF

duty factor - PD/PRP

when increaseing dB by 3, what is intensity/power

doubled

when decreasing dB by 3, what is intensity/power

1/2

when increasing dB by 6, what is intensity/power

quadrupled

when decreasing dB by 6, what is intensity/power

1/4th

when increasing dB by 10, what is intensity/power

10 x

when decreasing dB by 10, what is intensity/power

1/10th

when increasing dB by 20, what is intensity/power

100 (#0’s)

formula for attenuation coefficient

½ frequency

formula for HID/half intensity depth

6/f

what is specular reflectors

90 deg, smooth

what is Rayleigh scattering?

only seen in RBC, omnidirectional scattering

formula for Raleigh scattering

frequency to the 4th power

what are the two criteria required for reflection

normal incidence (90 degrees), media w/different impedances/PORNN

What does PORNN stand for

Perpendicular, orthogonal, right angle, 90°, normal - all same meaning

angle of reflection and angle of incidence will always equal

each other and add to 90 degrees

what is intensity transmission coefficient

% of sound transmitted at an interface

formula for intensity transmission coefficient

1 minus % of sound reflected at an interface/intensity reflection coefficient - ITC=1-IRC ITC and IRC = 100%

what is refraction

Angle of transmitted sound - a redirection of a sound beam, not reflection, Snell’s law

what are two requirements of refraction

oblique incidence, different prop speeds of 2 media

will media with faster speed have greater or lesser refraction/angle

greater

formula for inensity

power/area

what is PW “pulse”

talking time

what is PW temporal

all time - transmit and receive

where is spatial peak measured

at center of beam

what is BUR/beam uniformity ratio?

spatial peak/average

at what intensity is PW usually at

0% - usually listening, not transmitting