Page 18 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

wavelength
wavelength
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Chapter 1
An ultrasound wave travels through human tissue always at roughly the same speed of 1540 meters per second. Because this speed is more or less constant, the wavelength of the ultra- sound wave depends on the frequency of the oscillations in the wave as shown in Figure 1.5 and Figure 1.6. This relation between the wave speed (c), wavelength (λ) and frequency (f) is stated by the wave equation: c = λ × f or λ = c / f. When the frequency increases, the wave- length gets shorter and vice versa.
Why is this important? The depth of penetration of an ultrasound wave is determined by
its frequency and thus the number of oscillations/wavelengths for a certain distance the
sound waves have traveled. The higher these numbers are, the shallower tissue penetration is.
high frequency ultrasound wave
Figure 1.5 High-frequency ultrasound wave
The speed of the wave stays the same, a high frequency results in a shorter wavelength.
low frequency ultrasound wave
Figure 1.6 Low-frequency ultrasound wave
The speed of the wave stays the same, a low frequency results in a longer wavelength.