Unit 3: The Seven Parameters of Sound

Practice vocabulary flashcards defining key parameters, formulas, units, and acoustic relationships from Unit 3 on the Seven Parameters of Sound.

Parameters

Measurable characteristics of sound waves that define the specific sound wave from which they are obtained.

Seven Parameters of Sound

The seven measurable characteristics that describe sound waves: frequency, period, propagation speed, wavelength, amplitude, power, and intensity.

Cycle

One complete oscillation of a sound wave, moving from resting position through a complete compression, back through resting, through a complete rarefaction, and returning to the starting point.

Period

The time it takes to complete one single cycle of a sound wave, represented by the symbol $t$ and typically measured in microseconds ($\nu s$) in diagnostic ultrasound.

Frequency

The number of cycles that occur per second (or derivative unit of time), symbolized as $f$ and measured in hertz ($Hz$), kilohertz ($kHz$), or megahertz ($MHz$).

Reciprocal Relationship (Period and Frequency)

The special inverse relationship where period and frequency multiplied together equal $1$ ($\text{Period} \times \text{Frequency} = 1$); as frequency increases, period decreases.

Hertz ($Hz$)

The standard unit of measurement for frequency, meaning one cycle or event per second.

Infrasound

Sound waves with frequencies less than $20\,Hz$, which are below the range of human hearing.

Audible Sound

The range of sound frequencies that can be detected by the human ear, spanning from $20\,Hz$ to $20\,kHz$.

Ultrasound

Sound waves with frequencies greater than $20\,kHz$ ($20,000\,Hz$), which are above the limit of human hearing.

Propagation Speed

The rate at which a sound wave travels through a medium, symbolized as $c$ and determined solely by the characteristics of the medium.

Average Propagation Speed in Soft Tissue

The standard speed assumed by ultrasound systems for sound traveling through human soft tissue, defined as $1540\,m/s$ or $1.54\,mm/\nu s$.

Stiffness

A medium's ability to resist compression, which is directly related to propagation speed.

Bulk Modulus

A term synonymous with stiffness, describing a material's resistance to compression.

Density

The mass per unit volume of a medium, which is inversely related to propagation speed.

Wavelength

The distance or spatial length that a single cycle occupies, represented by the Greek letter lambda ($\lambda$) and measured in units of distance such as millimeters ($mm$).

Amplitude

The difference between the average value of an acoustic variable and its maximum or minimum value, describing the strength or loudness of the wave.

Power

The rate of work or energy transfer in a sound beam, symbolized as $P$ and measured in watts ($W$) or milliwatts ($mW$).

Intensity

The concentration of energy in a sound beam, calculated as power divided by beam area ($\text{Intensity} = \frac{\text{Power}}{\text{Area}}$) and expressed in $W/cm^2$.

Strength Parameters

The three parameters—amplitude, power, and intensity—that describe the size or bigness of a sound wave, are directly related to one another, and can be controlled by the sonographer using machine output power.