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3) sound and ultrasound Flashcards

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1
Q

Acoustics

A

Section of physics that studies
-mechanical oscillations and waves

Physiological acoustics studies the work of organs for sound detection and production

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2
Q

Oscillations

A

-repeated movement or change of state

Periodic oscillations are repeated at regular time intervals

V=1/T

V= frequency of oscillations per unit of time (Hz)
T = the time after which the oscillation is repeated
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3
Q

Example

A

Example of periodic oscillations

The swinging of pendulum
The rhythmic contraction of the heart

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4
Q

Harmonic oscillations

A

Periodic oscillations are shown by a sine function
Y= Asin(Wt+@)

Y-displacement at time t
A- amplitude
W-angular frequency
@-initial phase

W=2piV = 2pi/T

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5
Q

Waves

A

If oscillating particles interact with its neighbors then it can make them oscillate

Wave-propagation of oscillation in space

Eg: waves on surface of water

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6
Q

Types of waves according to nature

A

Mechanical waves
-oscillations of material particles

Propagated in material media only
Eg:sound and water waves

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7
Q

Types of waves according to nature 2

A

Electromagnetic waves
Periodic oscillations of an electromagnetic field

Propagated in material media and in free space
Eg: light, X rays, radio waves

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8
Q

Types of waves according to oscillation direction

A

Longitudinal waves
The oscillations are parallels to the propagation of the wave

Eg:sound

DRAWING

||||||||||||||

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9
Q

Types of waves according to oscillation direction 2

A

Transverse
The oscillations are perpendicular to the propagated direction of the wave

Eg:electromagnetic waves and water

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10
Q

Main physical characteristics of waves

A

Period of wave T
-measured in seconds

Frequency of wave
-measured in hertz Hz

Propagation velocity
-measured in m/s

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11
Q

Basic physical characteristic of waves

A

Wavelength (lander)
Distance travelled by the wave for one period - lander=vt

Drawings

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12
Q

Basic physical characteristics of waves 2

A

Intensity I
-the energy fluency rate
The energy transferred by the wave through unit area normal to the propagation direction per unit of time

Units- w/m^2

I=dE/dsdt

DRAWING

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13
Q

The nature of sound

A

Sound-mechanical wave with frequency from 20-20,000Hz.

Other mechanical waves
Ultrasound- frequency above 20khz
Infrasound -frequency below 20hz

In liquids sound propagates as longitudinal waves and in solids it can be longitudinal or transverse

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14
Q

Velocity of sound

A

Gases : v alpha root T
T- absolute gas temp
In air V = 330m/s

Liquid: v= root(k/p)
K-bulk modulus is liquid
p- liquid density
In water V=1500m/s

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15
Q

Velocity of sound 2

A

In solids
-metals v=4000m/s

Longitudinal waves:
V=root(E/p)
E is Young’s modulus of elasticity

Transverse :
V=root(G/p)
G is the sheer modulus of the body

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16
Q

Acoustic impedance

A

Z_A=PV

The reflection and refraction of the sound wave at the boundary between two different media depends on the acoustic impedances of the media

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17
Q

Acoustic spectrum

A

Acoustic spectrum-the information about the frequencies and intensities of all harmonic oscillations.

The acoustic spectrum can be represented graphically or as a table

The various sounds have different acoustic spectra

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18
Q

Types of sound

A

Tone- the acoustic spectrum consists of a small number of frequencies

Pure tone-one frequency
Compound tone- several frequencies
-fundamental tone-with the lowest frequency
-overtones- all other components of the acoustic spectrum

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19
Q

Types of sound

A

Noise-has a continuous complex randomly varying acoustic spectrum

Sound strokes-a loud sound of short duration with a continuous acoustic spectrum

20
Q

Types of sound 2

A

DRAWING

21
Q

Acoustic spectra of the various types of sound

A

DRAWING

22
Q

The subjective characteristics of the human auditory perception

A

Sound is evaluated subjectively to different people due to

  • characteristics of the human ear
  • individual variation of these characteristics

The main subjective characteristics are

  • pitch
  • timbre
  • loudness
23
Q

Pitch

A

The pitch of the sound depends on its frequency

Higher frequency means higher pitch

If a sound has higher pitch than another sound then it is said to have s higher frequency aswell

If our sensation of pitch increases in arithmetic progression then frequency increases in a geometric progression

24
Q

Timbre

A

The changes of the overtones of a compound tone is sensed as variations in sound timbre

Eg:sounds with identical intensities and frequencies when played on different instrument are said to have different timbre

Human ears sense timbre difference between 2 tones if they have a 10% intensity difference

25
Q

Loudness

A

Sound loudness characterises the level of sound sensation above the threshold

Loudness L depends on sound intensity I as well as fundamental frequency

Loudness is complex and is determined by the sensitivity of the ear to sounds with different frequencies

26
Q

Hearing threshold

A

The sounds intensity for a given frequency that results in the minimum sound sensation

Normal herring threshold is 1khz

I_0=10^-12 w/m^2

27
Q

Spectral dependence of the hearing threshold

A

DRAWING

28
Q

Pain threshold

A

The sound intensity for a given frequency that results in a pain sensation

Normal pain threshold is 1KHz and is assumed to be

I_1= 10w/m^2

29
Q

Hearing area

A

The range limited by hearing and pain threshold for all audible frequencies

DRAWING

30
Q

The psychophysical law of Weber-fechner

A

The changes of the stimulus 🔺I resulting in a minimal change of the sensation 🔺L. Depends of initial value of the stimulus I.

🔺L=K 🔺I/I = L= klg I/I_0

For the sensation of hearing:
Loudness is proportional to the logarithm of the ratio of intensity I

31
Q

Measurements of sound

A

Sound measurements are based on the logarithmic dependence of loudness on sound intensity

This feature reflects the ability of the ear to adapt
-the sensitivity of the sensory organ changes depending on the strength of the stimulus

32
Q

Sound intensity level measurement scale

A

It is measured on a logarithmic scale

Zero sound intensity: I_0= 10^-12

33
Q

Loudness measurement scale

A

The loudness measurement scale divides the interval between hearing and the pain threshold for each frequency into 130 equal parts = loudness measurement unit is the phon

1kHz change in loudness = change of sound intensity by one decibel

34
Q

Sound loudness and area of speech

A

Whisper = 20-40 phons
Normal speech = 45-75 phons
Street traffic = 70-90

Normal speech area:
Loudness range 47-75
Frequency = 200-8000 Hz

35
Q

Audiometry

A

The investigation of the sharpness of hearing

Audiogram- graphical representation of hearing threshold versus frequency

audiometer- sound generator that that adjustable sound intensity and frequency

36
Q

Ultrasound

A

A mechanical wave with frequency above 20,000Hz

Main properties:

  • reflection and refraction
  • propagates as narrow sound beams
  • high intensity can destroy viruses, bacteria
37
Q

Detectors of ultrasound

A

Piezoelectric effect

-production of electric voltage when stress is applied by sound pressure

38
Q

Generators of ultrasound

A

Natural sources: dolphins, bags waterfalls

Artificial:
Converse piezoelectric effect

Production of electric field when stress is applied

39
Q

Ultrasound in medicine

A

Ultrasound diagnostics
Ultrasound therapy
Ultrasound surgery
Production of aerosols

40
Q

Principles of ultrasonic imaging

A

Diagnostic imaging of soft tissue

  • delay of echo is used to determine here depth of boundary
  • amplitude corresponds to the density of medium

DRAWING

41
Q

Ultrasonic Doppler technique

A

Measurements about the velocity of blood is blood vessels

  • emitted ultrasound js reflected using moving target
  • difference between frequency V1 and V2 is used to determine velocity
42
Q

Ultrasonic physical therapy

A

The commonly used ultrasound frequency is 800Hz and intensity is 1W/m^2 intensity

  • changes the permeability of the cell membranes
  • speeds up metabolic process inside the cells
  • speeds up healing process of bones
43
Q

Extracorporeal lithotripsy

A

The destruction the kidney and gall bladder stones

  • powerful ultrasonic wave is focused on the stone and high sound pressure shatters it only small pieces
  • soft tissue is not harmed as they have low density and low sound pressure
44
Q

Infrasound

A

Mechanical wave with frequency below 20Hz

Eg:
Explosions
Road traffic
Earthquakes

The absorption of infrasound by matter is small and it travels long distances.

45
Q

Effect of infrasound on the human body

A

Not sensed by human ear

  • harmful at high intensities
  • deteriorates vision
  • causes memory loss
46
Q

Vibrations

A

Mechanical oscillations and structures of machines

Effect on human body:
Harmful - vibration illness
Useful- vibrotherapy

Physics (11 decks)

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