Ultrasonic Doppler Speedometer

Objective

(1) Understand the principles of the ultrasonic Doppler effect and its application in speed measurement.

(2) Design and build an ultrasonic Doppler speedometer to measure the velocity of a moving object.

(3) Analyze experimental data and improve measurement accuracy.

Principle

The ultrasonic Doppler effect states that when ultrasonic waves encounter a moving target (such as a small car or fluid), the frequency of the reflected wave shifts. The frequency shift Δf is related to the velocity v of the target as follows:

$\mathrm{\Delta }f=\frac{2f_{0}v\cos \theta }{c}$

where c is the speed of sound in air; θ is the angle between the wave propagation direction and the target's motion.