D1- SPI, Basic Math and Sound wave

speed of sound in tissue

1540 m/sec OR 1.54 mm/microsec

• ~ 1 mile per sec

Distance Formula

Sound

(1) is a mechanical wave (bc it has to travel through a medium)

(2) has to travel through a medium (tissue)

(3) travels in longitudinal waves/straight line

(4) is a pressure wave: when traveling through a medium, there are areas of compression and rarefaction

• compression- ↑ pressure and density (SQUEEZED)

• rarefactions- ↓ pressure and density (STRETCHED)

*can’t travel through a vacuum

Mechanical Waves

Longitudinal Wave- waves move ← to → and particles move PARALLEL to the direction of the wave

Transverse- waves move ← to → and particles move PERPENDICULAR to the direction of the wave (↑↓)

Sound Wave Interaction

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

• Out of Phase Waves- peaks and troughs occur at different times and locations

Huygen’s Principle

states that when waves interact, secondary spherical wavelets are created having the same freq. as original wavelets. these wavelets interfere with each other, combining to create the hourglass shape of the beam

Soundwave Interference

Constructive- interference of in-phase waves creates a single wave that has an amplitude greater than its components

Destructive- interference of out-of-phase waves creates a single wave with an amplitude lesser than one of its components

Complete Destructive Interference- when 2 out-of-phase waves have equal amplitude

Acoustic Variables

changes that occur IN THE MEDIUM as a result of sound traveling through the medium

• 4 forms of acoustic variables

(1) Pressure

(2) Density

(3) Distance (particle motion)

(4) Temperature

(1) Pressure

concentration of force in an area

• UNIT: Pascals (Pa)

• Pressure = Force/Unit Area

• varies cyclically as sound wave propagates through the medium

(2) Density

concentration of mass in volume

• UNIT: kg/cm³

• as mass ↑, density ↑

• Compression Phase- higher particle concentration (↑ density)

• Rarefaction Phase- lower particle concentration (↓ density)

(3) Distance (particle motion)

measure of particle motion

• UNIT: cm, ft, mile

(4) Temperature

sound wave vibrates particles in medium —> friction generates heat

• UNIT: degrees Celsius

• Compression Phase- ↑ temp

• Rarefaction Phase- ↓ density

Sound Wave Parameters

describes FEATURES of a sound wave

(1) Frequency

(2) Period

(3) Wavelength

(4) Propagation Velocity (speed of sound)

(5) Amplitude

• Intensity

• Power

(1) Frequency

(2) Period

(3) Wavelength

(4) Propagation Velocity (speed of sound)

(5) Amplitude