Ultrasound Physics & Instrumentation - Waves

Flashcards covering basic definitions and classifications of sound waves and related physics concepts for Ultrasound Physics & Instrumentation.

Sound

Mechanical energy transmitted by pressure waves in a medium; a mechanical disturbance that progressively propagates through a medium at a fixed speed.

Energy

The capacity to do work, which can be electric, heat, or mechanical.

Mechanical Energy

A physical parameter that can be measured.

Wave

A coordinated disturbance moving through a medium at a fixed speed.

Mechanical Wave

A wave that transports energy (not matter) through a medium, utilizing the medium's molecules, and requires a medium to propagate.

Electromagnetic Wave

A wave that can propagate in a medium or a vacuum.

Sound Wave Production

Involves a vibrating object that pushes and pulls adjacent molecules, generating a 'traveling disturbance' through a series of compressions and rarefactions.

Transverse Wave (Shear Wave)

A wave that propagates by particle motion (oscillation) that is perpendicular or 'transverse' to the wave propagation direction. These do not travel through soft tissue very well.

Longitudinal Wave

A wave that propagates by particle compression and rarefaction (oscillation) that results in particle motion that is 'along' or in the same direction as the wave propagation direction.

Compression

Regions where the medium's molecules are squeezed together as a sound wave passes through, showing increased acoustic pressure.

Rarefaction

Regions where the medium's molecules are pulled apart as a sound wave passes through, showing decreased acoustic pressure.

Sound Wave Classification

Sound is classified as a longitudinal, mechanical wave.

Acoustic Variables

Four physical quantities (Pressure, Density, Temperature, Particle Motion) that undergo measurable changes in the medium as sound propagates.

Pressure

Defined as concentration of force, or force per area, and quantifies the strength of a sound wave. Common units include atmospheres and Pascals.

Acoustic Pressure

A quantification of the strength of a sound wave, with increased pressure in compression areas and decreased pressure in rarefaction areas.

Density

Defined as mass per volume (mass/volume), and changes in density affect the propagation of the sound wave.

Temperature

Acoustic variable referring to changes in temperature as a sound wave propagates through tissue, an important consideration for biological effects as ultrasound waves can heat tissue.

Particle Motion

An acoustic variable referring to the vibration of particles in their position as a wave passes, rather than the particles traveling with the wave itself. Can be measured as distance or velocity over time.