Describing Sound Waves Flashcards

Vocabulary and conceptual flashcards covering the seven parameters of sound waves, focusing on period, frequency, and their clinical applications in ultrasound physics.

Parameters

Features of a sound wave used to completely characterize it; there are seven parameters required for this description: period, frequency, amplitude, power, intensity, wavelength, and speed.

Sound Source

The ultrasound system and the transducer that establish the level or quantity of some parameters.

Medium

The tissue through which the sound wave is traveling.

Period

The time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle.

Units of Period

Reported in units of time, such as microseconds ($\mu s$), seconds, hours, or days.

Typical Values of Period

In diagnostic ultrasound, typically range from $0.06$ to $0.5\,\mu s$, which can also be written as $6 \times 10^{-8}$ to $5 \times 10^{-7}$ seconds.

Period Determined By

Determined by the sound source only, not by the medium.

Adjustability of Period and Frequency

No; the sonographer cannot change these parameters while using a basic ultrasound system with a particular transducer.

Frequency

The number of particular events (cycles) that occur in a specific duration of time; in diagnostic ultrasound, it is the number of cycles that occur in one second.

Units of Frequency

Reported in units of per second, $1/second$, hertz, or $Hz$. ($1\,kHz = 1,000\,Hz$; $1\,MHz = 1,000,000\,Hz$).

Typical Values of Frequency

In clinical imaging, frequency ranges from approximately $2\,MHz$ to $15\,MHz$. ($2$ million to $15$ million per second).

Frequency Determined By

Determined by the sound source only, not by the medium through which the sound is traveling.

Infrasound (Infrasonic)

Sound waves with a frequency less than $20\,Hz$, which is below the threshold of human hearing and considered inaudible.

Audible Sound

Sound with frequencies between $20\,Hz$ and $20,000\,Hz$ ($20\,kHz$), which humans can hear.

Ultrasound (Ultrasonic)

Sound with frequencies higher than $20,000\,Hz$ ($20\,kHz$), which is too high for humans to hear.

Relationship between Period and Frequency

They are inversely related; as frequency increases, period decreases, and as frequency decreases, period increases.

Reciprocal Relationship

A special relationship where two parameters multiplied together result in $1$; for example, $\text{Period} \times \text{Frequency} = 1$. ($Period = 1/Frequency$ and $Frequency = 1/Period$).

Complementary Units

Pairs of units used together for period and frequency: seconds and hertz, or milliseconds and kilohertz.

High Frequency Clinical Effects

Provides better resolution and greater image detail, but has low penetration because sound waves are absorbed quickly by tissues.

Low Frequency Clinical Effects

Allows for deeper penetration to image deep body structures like the heart or liver, but results in lower resolution and less image detail.