08 Ultrasound
Wavelength and period
λ = c/f and T = 1/f. Soft tissue c = 1540 m/s.
Listen
Listen · English
Simulation
Wavelength and period — Change the numbers; the scene follows.
Where it works
Ultrasound
Transducer
At the transducer face — wavelength, pulse length, and the near/far field of the beam.
Open this machineFormula
Variables
Results
λ
Wavelength
0.308mm
λ
Wavelength
308µm
T
Period
0.2µs
Explanation
What it means
Wavelength λ = c/f and period T = 1/f. At 1540 m/s, 5 MHz → λ = 0.31 mm. Resolution, speckle size and the onset of scattering vs reflection all scale with λ. This is a working relation in Ultrasound.
Where it is used
Clinically it sits on the Ultrasound — Transducer. At the transducer face — wavelength, pulse length, and the near/far field of the beam. Ultrasound equations sit on the probe face and along the beam: impedance, Snell, Doppler, MI and TI. They explain why gel matters, why aliasing appears, and why a mechanical index is on the screen.
Ultrasound · Open this machineHow to use it
Use λ as input to axial and lateral resolution calculators. 1–15 MHz covers most diagnostic probes; 20–50 MHz is intravascular / small-parts research. Change one input and watch the curve and the simulation follow.
Symbols
- fFrequency5 MHz
- cSpeed of sound1,540 m/s
Worked example
A typical case from the default values: f = 5 MHz (Frequency); c = 1,540 m/s (Speed of sound). Substituting into the relation gives λ = 0.308 mm; λ = 308 µm; T = 0.2 µs. These are teaching numbers — align them with your machine.
Typical values give
- λ = 0.308mm
- λ = 308µm
- T = 0.2µs
Where it comes from
The displayed formula is the working relation. λ = c/f and T = 1/f. Soft tissue c = 1540 m/s. Usual reference: Edelman / Bushberg. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: Edelman / Bushberg
Assumptions & limits
Constant c. Dispersion (c vs f) is small in tissue over diagnostic bands.
Pitfalls
Soft-tissue 1540 m/s is an assumption — not a measurement in that patient. Doppler angle 90° gives no shift. MI and TI are on-screen estimates, not absorbed dose. Constant c. Dispersion (c vs f) is small in tissue over diagnostic bands.
Keep this
Gel, angle, and assumed speed of sound — get those three right before you trust a centimetre. Constant c. Dispersion (c vs f) is small in tissue over diagnostic bands.
In this specialty