Ultrasound Physics & Instrumentation - Fundamentals

Comprehensive vocabulary flashcards covering the fundamental principles of ultrasound physics, including wave classifications, acoustic variables, parameters, and interference patterns.

Wave

A cyclical transfer of energy from one location to another.

Mechanical Wave

A wave that requires a medium to propagate, such as sound.

Electromagnetic Wave

A wave that can propagate through both a medium and a vacuum.

Transverse Wave

A wave where particle motion is perpendicular to the wave propagation direction.

Longitudinal Wave

A wave where particle motion is in the same direction as the wave propagation direction, occurring via compression and rarefaction.

Infrasound

Sound waves with frequencies below the range of human hearing ($< 20\,Hz$).

Audible Range

Sound frequencies that humans can hear, typically between $20\,Hz$ and $20\,kHz$.

Ultrasound

Sound waves with frequencies above the range of human hearing ($> 20\,kHz$).

Acoustic Variables

The four physical quantities that undergo mechanical changes as sound propagates: Pressure, Density, Distance (Particle Motion), and Temperature.

Pressure ($P$)

An acoustic variable defined as force per unit area ($P = F/A$). Units include Atmospheres, $mmHg$, Pascals, $kg/m^2$, $lbs/in^2$, and $dynes/cm^2$.

Density ($\rho$)

An acoustic variable defined as mass per unit volume ($\rho = \frac{\text{mass}}{\text{volume}}$). Expressed in units such as $kg/m^3$.

Frequency ($f$)

The number of cycles of compression and rarefaction that occur per second, measured in Hertz ($Hz$).

Period ($P$ or $T$)

The time required for one full cycle to occur; it is the reciprocal of frequency ($P = \frac{1}{f}$).

Propagation Velocity ($c$)

The distance sound travels per unit of time ($m/sec$), determined strictly by the physical properties of the medium.

Wavelength ($\lambda$)

The physical distance from one compression to the next compression ($\lambda = \frac{c}{f}$); it is determined by both the source and the medium.

Amplitude

The maximum variation of a variable from its mean; a measure of signal strength or volume, calculated as $\frac{\text{Max} - \text{Min}}{2}$.

Power

The rate of energy transfer, measured in Watts; it is proportional to intensity and proportional to $\text{amplitude}^2$.

Intensity

The concentration of energy in a sound beam, calculated as $\text{Intensity} = \frac{\text{Power}}{\text{Area}}$ ($Watts/cm^2$).

Constructive Interference

The addition of two in-phase waves resulting in a wave with a greater amplitude than either single wave.

Destructive Interference

The addition of waves that results in a wave with less amplitude than at least one of its components, potentially resulting in complete cancellation.

Bulk Modulus

A measure of a medium's resistance to compression (stiffness); high bulk modulus results in higher propagation speeds.

Stiffness

The quality of being incompressible or inelastic; materials that are stiff have high propagation speeds ($c \propto \text{stiffness}$).

Soft Tissue Velocity

The average propagation velocity of sound in human soft tissue, which is $1540\,m/sec$.