How does increasing transmitted frequency f0 affect the Doppler shift magnitude for fixed velocity and angle?

• A. fD increases linearly with f0
• B. fD decreases with f0
• C. fD is independent of f0
• D. fD increases with the square of f0

Answer: (A)

Doppler shift scales directly with the transmitted frequency when the target velocity and the beam angle are fixed. The reflected Doppler equation is fD = (2 f0 v cos θ) / c, where c is the speed of sound in tissue. Since v, cos θ, and c are constant in this scenario, fD is proportional to f0. Doubling f0 doubles the Doppler shift, you simply get a larger shift in proportion to how much you increase f0. This linear relationship is the key reason.