Sound waves for physics unit 1 exam

how do you define sound? what type of wave is it? what is it produced by, for sound to exist it must travel through what?

Sound: is a mechanical, longitudinal wave produced by

a vibrating source. For sound to exist, it must travel

through a medium

Sound Waves

•Ultrasound:

Transducer produces what?

Sound pulses travel through what?

Is reflected from the boundaries between?

•Ultrasound

• Transducer produces sound pulses

• Sound pulses travel through tissue (a media)

• Is reflected from the boundaries between structures and then

returned to the transducer

what do sound waves consists of?

• Consist of energy

sound waves consist of energy, carried from.?

what are the different types of waves

Carried from one location to another

• Heat, sound, magnetic and light are types of waves

Wave classification electromagnetic VS mechanical

Let’s talk about Electromagnetic

Alternating what field

what’s the direction

can travel in what

what does this produce/what is this used for

Electromagnetic

• Alternating electric and magnetic field

• Perpendicular

• Can travel in a vacuum

• Light / X-Ray

Mechanical wave classification

what does it pass through and…

energy is passed between?

this is what wave?

Mechanical

• Passes through a medium and vibrates molecules

• Energy is passed between the molecules

• Sound!

what is this showing you?

Mechanical “Longitudinal”

what is this showing you

electromagnetic

Wave Classification. Longitudinal- define (sound waves in what)

Particles vibrate in a motion that is parallel to the direction of wave

propagation

• Sound waves in liquid

Wave Classification define transverse

Transverse

• Particle motion is perpendicular to the direction of wave

propagation

this is representing what wave

Longitudinal

wave anatomy:

mechanical waves can’t travel in what?

what is required for it travel?

what are the acoustic propagation properties for sound to travel and bounce back?

IN what direction does it travel?

• Can’t travel in a vacuum

• Medium

• Required

• Molecules are compressed and rarefied

• Acoustic propagation properties

• Travel in a straight line - longitudinal

Define compression

Compression: squeeze together

Define Rarefied

Rarefied: stretched apart

what are the acoustic variables we used this method for identifying what? It Distinguish between what? Sound waves =/

what are the variables?

• Acoustic variables

• Method for identifying waves

• Distinguish between sound and other types of waves

• Sound Waves = Acoustic Waves

Variables: Pressure, Density, Distance

Define the variable and tell me the unit, Pressure

Pressure: concentration of force in an area: pascals (Pa)

Define the variable and tell me the unit, Density

• Density: concentration of mass in a volume: kg/cm3

Define the variable and tell me the unit, Distance

Distance: measure of particle motion: cm, m

what are the & Acoustic parameters

Acoustic parameters

• Describes the features

• Period

• Frequency

• Amplitude

• Power

• Intensity

• Wavelength

• Propagation speed

Remember that sound waves are a ______cyclical event that travels in a _____line

One cycle =

this _____wave

Compression =

Rarefaction =

Remember

• Sound waves are a reoccurring cyclical event that travels in a

straight line

• One cycle = one peak + one trough

• Sine wave

• Compression: high pressure area, crests

• Rarefaction: low pressure, trough

Phase

• Comparing where the peaks and troughs of two waves ____

• In-Phase: Peaks occur when

what type of interference

resulting wave is ?

• Phase

• Comparing where the peaks and troughs of two waves intersect

• In-Phase: peaks occur at the same time and location

• Constructive interference

• Resulting wave is larger than each individual wave

Out-of-Phase: peaks and troughs occur at ____time

what type of interference is this?

resulting wave is?

complete destructive of what

Out-of-Phase: peaks and troughs occur at different time

Destructive interference

• Resulting wave is smaller than each individual wave

• Complete destructive: wave amplitude match perfectly

• Phenomenon

• Waves with different?

one moment in time?

Phenomenon

• Waves with different frequencies

• One moment in time

• Constructive interference

• Destructive interference

what does frequency measure

complete cycle =

what are the units

Ultrasound imaging is in the range of ?

Doppler ultrasound is in the range of?

• Measurement

• Frequency = # of cycles

• Complete cycle = one crest + one trough

• Units

• Cycles / second = Hertz (Hz)

• Ultrasound imaging is in the range of MegaHertz (MHz)

• Doppler ultrasound is in the range of Hertz (Hz) to kiloHertz (kHz)

what is infrasound mean what is the frequency

• Infrasound

• Frequency < 20Hz

• Too low for humans to hear

what does Audible mean and what’s the frequency?

Audible

• Frequency 20Hz – 20kHz

what does Ultrasound mean and what’s the frequency?

•Ultrasound

• Frequency >20kHz

• Too high for humans to hear

Diagnostic Sonography

• Frequency determined by?

• Frequency determined by the transducer

• 2MHz – 20 MHz

what does Frequency affects?

• Affects penetration and resolution

High frequency=

High frequency = better resolution

Low Frequency =

Low frequency = better penetration

•Ultrasound system / transducer

• “Source”

Control some of the what?

Can sonographer adjust this?

Control some of the parameters

• Sonographer can adjust

Medium- its an actual what

sound travels …..

can determine what

• Medium

• Actual tissue

• Sound travels through the tissue

• Can determine some parameters

what is period and what are the units

what is it measuring and its determined by what? can sonographer change this? typical ultrasound wave=

p=

f=

Time it takes to complete one cycle

• Seconds, milliseconds, microseconds

• Measuring time from one point on the wave to a similar point on

consecutive waves

• Determined by the transducer

• Sonographer cannot change this

• Typical ultrasound wave

• .06 - .5 μs

P=1/f

f=frequency

Period and frequency have what type of relationship

High frequency= (what type of period)

Low Frequency= (what type of period)

• Period and frequency

• Inverse relationship

• High frequency = short period

• Low frequency = long period

Period and wavelength have what type of relationship?

measure how

• Period and wavelength

• Direct relationship

• Measure the same area, but with different units

Frequency

•Number of events that occur?

Ultrasound = # of….

units?

Determined by?

can or cannot be changed with the basic ultrasound system and transducer

whats the Typical ultrasound frequency range

Frequency

•Number of events that occur in a specific duration of time

• Ultrasound: # of cycles that occur in 1 second

• Units

• Hertz (Hz)

• Determined by the sound source (transducer)

• Can’t be changed with the basic ultrasound system and transducer

• 2MHz – 20MHz

Frequency

• Importance… its affects

Affects penetration and image quality (and resolution)

what type of relationship does frequency and period have

• Frequency and period

• Inversely related / reciprocal relationship (=1)

what does Amplitude describe?

Difference between?

what are the units?

•Describes wave magnitude (strength)

•Difference between max or minimum value and the baseline

•Units

• Variable

• Pressure – pascals

• Density – g/cm3

• Particle motion – any distance measurement

• Decibels

Amplitude

•Units

is it controlled by the sonographer?

•Units

• Ultrasound 1 MPa – 3 MPa (millions)

Yes Controlled by the sonographer its the Output power / power control

Amplitude will decrease when? this is called?

• Will decrease as wave travels in tissue

• Attenuation

How do you measure the wavelength of Amplitude (?)

Peak to Peak

• 2x the amplitude value or is the max and min amplitude value

Define Attenuation

Attenuation: weakening of the wave as it travels through tissue

Define Power

what’s the units?

• Rate of energy transfer or the rate at which work is performed

• Think of a light bulb

• 45 W bulb vs 100W bulb

• Rate of energy transmitted by the transducer into the body

•Units

• Watts (W)

• Ultrasound

• .004 - .09 W or 4 – 90 mW

is power controlled by the sonographer?

Yes, • Controlled by the sonographer

• Power output / power control button

• Power α Amplitude2

If one increases, what happens to the other

If one decreases, what happens to the other

If one increases, so does the other

• If one decreases, so does the other

what will decrease as wave travels through the tissue (power slide)

Attenuation

A sonographer increases the amplitude of a wave by a factor of 3. How has the

power changed?

Power α Amplitude2

Power = 3 x 3 = 9 (power has increased 9-fold)

When a sonographer decreases the amplitude of a wave to 1⁄2 of its original

value, how has the power changed?

Power α Amplitude2

Power = .5 x .5 = .25 (power is now 25% of its original value)

A sonographer will use full power for most exams they perform. Some exceptions when

the power would be decreased is:

Obstetrics (OB)

Infants and children

Transcranial Doppler (TCD)

and contrast

Intensity, its concentration of what

its describes what

and depends on

Intensity, Concentration of energy in sound beam

Describes how power in a wave is distributed in space

• Depends upon power and area

• Intensity = power/area

If power doubles what happens to intensity? what’s the relationship

what’s the units?

• If power doubles, intensity will double (directly related)

• Intensity α Amplitude2

•Units

• Watts/square (W/cm2)

when will intensity change

Intensity will change as wave travels into the tissue

Rate of change for intensity is dependent upon what

Rate of change is dependent upon wave characteristics and the

medium

• Intensity is dependent upon the ultrasound system

Is intensity controlled by the sonographer?

• Controlled by sonographer

• Power output / power control button

Determining Wave Strength

• Look at the relationship between

• Look at the relationship between amplitude, intensity and

power

Determining Wave Strength

• Look at the relationship between amplitude, intensity and

power

power=intensity

if one increases, what happens to the other

if one decreases what happens to the other

• Power = Intensity

• If one increases, so does the other

• If one decreases, so does the other

Power/Intensity α Amplitude2

Amplitude doubles, then what happens with power/intensity

• Amplitude halves, then what happens to the power/intensity

Power/Intensity α Amplitude2

• Amplitude doubles, then power/intensity increase by 4

• Amplitude halves, then power/intensity decreases by a quarter

what does Decibels (dB) compares? Ratio units are expressed as?

Compares intensities or amplitudes of two waves or wave points

• Ratio units are expressed as decibels

Decibels (dB), Rekate what? Express what values on a what scale?

Positive dB=

^this signal is what?

• Turning up gain – adding decibels – stronger echoes

• Will

• Relate two values to each other

• Express large range of values on a smaller scale

• Positive dB = increase in value

• Signal strength is increased

• Turning up gain – adding decibels – stronger echoes

Decibels (dB)

• Will

• Negative dB =

what happens to the signal

sound wave is what

(what may the sonographer need to do)

Decibels (dB)

• Will

• Negative dB = decrease in value

• Signal is weakened

• Sound wave is attenuated or weakened as it travels through tissue

• Sonographer may need to adjust gain to strengthen signal!

what are the positive dB and negative dB values?

The power control, which determines the amount of _____that goes to the

transducer, can be expressed as a ______or in ____. How it is expressed is

dependent upon the _____. Power is controlled by the _______!

The power control, which determines the amount of energy that goes to the

transducer, can be expressed as a percentage or in dB. How it is expressed is

dependent upon the vendor. Power is controlled by the sonographer!

100% is full power

0 dB is full power

The sound wave traveled through tissue and was attenuated by 6dB. The original intensity

of the wave was 16 mW/cm2. What is the ending intensity? Remember – attenuation is

weakening of the beam.

Look at the chart under negative dB (attenuation) and -6 dB equates to a decrease of 1⁄4 or

25%

16mW/cm2 x 1⁄4 = 4 mW/cm2

Ending intensity is 4mW/cm2

Define what we measure for the Wavelength (λ) and what are the unitts and ultrasound in soft tissue units…

determined by the? is it controlled by the sonographer?

•Distance / length of one complete cycle

• Units

• Millimeters, meters

• Ultrasound

• .1 - .8 mm in soft tissue

• Determined by the source and the medium

• Is not controlled by the sonographer

how is Wavelength (λ) related to frequency?

High f=

Low f=

• Inversely related to frequency (f)

• High f = short λ

• Low f = long λ

• Inversely related to frequency (f) - for Wavelength (λ)

what does the short wavelengths provide us with and what is the trade off?

Short wavelengths equate to higher quality images (detail)

• Trade off is poor penetration

Wavelength (λ) is directly related to what

•Directly related to propagation speed (c)

•Directly related to propagation speed (c) - Wavelength (λ)

C is dependent ?

• C changes so will the?

C is dependent upon the medium

• C changes so will the wavelength

why would the Sonographers will always use the highest frequency possible?

B/c it gives the most optimal penetration

Wavelength (λ)

•Defining

frequency, wavelength and propagation speed

what is the formula/ different formula for Wavelength (we can figure out different things)

• λ = c/f or c = f x λ or f = c/λ

Determine the wavelength produced by a 5.0 MHz

transducer traveling in soft tissue. c in soft tissue = 1.54 mm/μs

λ = c/f

λ = 1.54 mm/μs / 5MHz = .3 mm

Relating Frequency, Period and

Wavelength, what are the relationships?

what is Propagation Speed

what are the units

what is it dependent upon

all sound travels at the….

no matter the?

Rate that a sound wave travels through a medium

•Units

• m/s or mm/μs

• Ultrasound

• 500 to 4000 m/s

• Is dependent upon the medium through which it travels

• All sound travels at the same speed in any given medium

• No matter the frequency of transducer

is Propagation Speed dependent on the frequency of transducer?

No matter the frequency of transducer

Propagation Speed

• Medium =

what are the different types?

Medium = Tissue

• Stiffness

• Density

• Elasticity

• Compressibility

for Propagation Speed ultrasound machine accounts for what?

can it be changed by the sonographer?

•Ultrasound machine

• Accounts for speed of sound

• Can’t be changed by sonographer

Soft Tissue (average) =

1540

how does sound travel in solids vs liquids vs gases

Sound travels fastest in solids, slower in liquids and slowest in gases

Characteristics of the Medium

Stiffness, is ability to what?

what happens if the material is squeezed? does it retains its shape, what happens with non-stiff material shape?

Stiffness

• Ability to resist compression

• What happens if the material is squeezed?

• Stiff material

• Retains its shape

• Non-Stiff material

• Changes its shape

Characteristics of the Medium

• Stiffness

• Directly related to?

Two ______materials

• Stiffer of the two will have the?

Stiffness

• Directly related to speed

• Two identical materials

• Stiffer of the two will have the higher speed of sound

what are the other terms for stiffness?

Other terms for stiffness

• Bulk modulus

• Elasticity

• Compressibility

Characteristics of the Medium

•Density

• Relative to what?

Equal volume of material, the dense material will

is steel or aluminum dense

density has a what relationship to speeds

speed is determined by?

•Density

• Relative weight of the material

• Equal volume of material, the dense material will weigh more

• Steel is dense, aluminum is not

• Inversely related to speed

• Dense material = slower speeds

• Speed is determined by density and stiffness of the medium

Characteristics of the Medium

• Materials stiff, but not dense =

fastest speed

Materials not very stiff, but dense =

slowest speed

Stiffness has the greatest influence on?

Speed

Air has low stiffness =

sound travels slowly in air

• Why does this matter? Pathological conditions can and will

affect the sound wave

Period and frequency

• Together because they are?

reciprocals =1

Amplitude, power and intensity=

Magnitude of the sound wave

• Sonographer can control

Wavelength

• Determined by

sound source and medium

• Speed

• Determined by

the medium

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