Davies Publishing SPI Practice Test 2026 – Your All-in-One Guide to Exam Success!

The key idea is that the Doppler frequency shift depends on the component of the target’s velocity along the ultrasound beam, captured by the cos of the incidence angle. The Doppler shift follows fD = (2 f0 v cos theta)/c, so as the angle theta increases, cos theta decreases. That means the frequency shift gets smaller, not larger, when you tilt the beam away from the direction of motion. Perpendicular incidence (theta = 90°) gives cos theta = 0, so no shift at all, which matches the statement about there being no frequency shift in that case. If you know the angle, you can solve for velocity from the measured shift, since v = (fD c)/(2 f0 cos theta). Because of this, the claim that increasing the interrogation angle increases the frequency shift is the one that isn’t true. The other statements align with the equation: higher transmitted frequency increases the shift, perpendicular incidence yields no shift, and velocity can be derived if the angle is known.