Describing Sound Waves: Bigness Parameters

Practice flashcards covering the definitions, units, and mathematical relationships of the three 'bigness' parameters of sound waves: amplitude, power, and intensity.

Amplitude

The difference between the maximum value and the average or undisturbed value of an acoustic variable, or the difference between the minimum and average value.

Peak-to-peak amplitude

The difference between maximum and minimum values of an acoustic variable, which is equal to twice the value of the amplitude.

Acoustic variable units for Amplitude

Pressure ($pascals$), density ($g/cm^3$), and particle motion ($cm$, inches, or any distance).

Typical values of pressure amplitude

In clinical imaging, it ranges from $1 \times 10^6 \text{ pascals}$ ($1 \text{ MPa}$) to $3 \times 10^6 \text{ pascals}$ ($3 \text{ MPa}$).

Power

The rate of energy transfer or the rate at which work is performed, measured in units of $watts$.

Typical values of power

In clinical imaging, typical powers range from $0.004$ to $0.090 \text{ watts}$ ($4$ to $90 \text{ milliwatts}$).

Mathematical relationship between power and amplitude

Power is proportional to the wave's amplitude squared ($ ext{power} ext{ ∝ } ext{amplitude}^2$).

Intensity

The concentration of energy in a sound beam, calculated by dividing the beam's power by its cross-sectional area.

Intensity formula

$$\text{intensity (W/cm}^2\text{)} = \frac{\text{power (W)}}{\text{area (cm}^2\text{)}}$$

Typical values of intensity

In clinical imaging, intensity ranges from $0.01$ to $300 \text{ W/cm}^2$.

Relationship between intensity and power

Intensity is proportional to power; if power is doubled, intensity is doubled.

Relationship between intensity and amplitude

Intensity is proportional to the wave's amplitude squared ($ ext{intensity} ext{ ∝ } ext{amplitude}^2$); if amplitude is doubled, intensity increases fourfold.

Determining factors for initial Bigness Parameters

Initial amplitude, power, and intensity are determined only by the sound source (the ultrasound system).

Adjustability of Bigness Parameters

Yes, the sonographer can alter the initial amplitude, power, and intensity using controls on the ultrasound system.