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Physics > 3) sound and ultrasound > Flashcards

3) sound and ultrasound Flashcards

(46 cards)

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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

Study These Flashcards
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

21
Q

Acoustic spectra of the various types of sound

22
Q

The subjective characteristics of the human auditory perception

Study These Flashcards
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

Study These Flashcards
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

Study These Flashcards
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
Loudness
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
Hearing threshold
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
Spectral dependence of the hearing threshold
DRAWING
28
Pain threshold
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
Hearing area
The range limited by hearing and pain threshold for all audible frequencies DRAWING
30
The psychophysical law of Weber-fechner
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
Measurements of sound
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
Sound intensity level measurement scale
It is measured on a logarithmic scale Zero sound intensity: I_0= 10^-12
33
Loudness measurement scale
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
Sound loudness and area of speech
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
Audiometry
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
Ultrasound
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
Detectors of ultrasound
Piezoelectric effect | -production of electric voltage when stress is applied by sound pressure
38
Generators of ultrasound
Natural sources: dolphins, bags waterfalls Artificial: Converse piezoelectric effect Production of electric field when stress is applied
39
Ultrasound in medicine
Ultrasound diagnostics Ultrasound therapy Ultrasound surgery Production of aerosols
40
Principles of ultrasonic imaging
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
Ultrasonic Doppler technique
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
Ultrasonic physical therapy
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
Extracorporeal lithotripsy
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
Infrasound
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
Effect of infrasound on the human body
Not sensed by human ear - harmful at high intensities - deteriorates vision - causes memory loss
46
Vibrations
Mechanical oscillations and structures of machines Effect on human body: Harmful - vibration illness Useful- vibrotherapy

Physics (11 decks)

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