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Chapter 1: Basics
Acoustic Waves
What sound waves are and how they behave
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Sound Wave Properties
All sound waves (also called acoustic waves) share four key properties:
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Carry energy from one place to another
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Mechanical: need a medium (cannot travel through a vacuum)
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Longitudinal: particles move back and forth in the same direction the wave travels
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Straight line: sound travels in a straight, parallel path
Imagine a row of dominoes. You push the first one. Energy moves forward down the line, but each domino only rocks in place.
Energy Moves Forward
Each piece moves in place, but the wave travels across
The energy travels forward, but the particles (dominoes) only move back and forth in the same direction. That is what makes it longitudinal.
There are two main wave types. Sound is the top one.
Longitudinal: particles move in the same direction as the wave (back and forth). This is sound.
Transverse: particles move perpendicular to the wave (up and down). This is light, not sound.
Ultrasound Pulses Are Longitudinal
The transducer sends out pulses of sound that travel in a straight line into the body. The tissue particles vibrate back and forth along the same direction the pulse travels. This is why ultrasound is classified as a longitudinal, mechanical wave.
Energy Transfer, Not Particle Transfer
The sound energy moves from the transducer through the tissue and back, but the tissue particles themselves stay roughly in place. They vibrate, then return to their resting position. Only the energy travels.