Experiment: Determination of Doppler DELTAF as a function of velocity

Topics covered:

- Propagation of ultrasound in the air

- Wavelength, propagation speed

- Doppler shift depending on speed

- Analogy with automotive radar

Principles and objectives:

The objective of the lab is to experimentally find the Doppler relation and its application to speed measurement.

1- Compare speed measurement using eff and Doppler to measurement by a reference system.

Put the cart in motion, and plan a speed measurement device (stopwatch, chronocine device, camera, etc). The speed can then be validated by a reference system.

2- Find the Doppler relation through the experiment:

- Vary the speed v of the cart using the potentiometer.

- Measure the Doppler frequency shift corresponding to the frequency

of the ouExperimentut signal from the Initio box (by reading the pointer, by modeling, or by Fourier transform: all these solutions are

integrated into the generalist Scientific Workshop Physics Chemistry software).

- Measure the speed v of the cart with a reference device.

- Represent Deltaf as a function of v.

- Deduce the slope of the corresponding line.

- Compare this value to the ratio c/fém.

- Deduce the Doppler equation

3- Analogy with automotive radar

The analogy with radar is made possible by positioning the Moduson® transmitter and receiver side by side and fixing the screen (provided) on the mobile cart

Comments:

The advantage of a motorized bench:

- Reproducible and repeatable experiments

- Controlled and secure device because of low speeds (cm.s-1) and controlled movements

- Speed is constant during movement

- Precise measurements

Roles of the Ultrasonic Doppler Box:

- Bench power supply

- Speed variation by changing the power supply voltage (Forward and reverse)

- Power supply for the simple Moduson® transmitter (not provided)

- Operations on emitted and received ultrasonic signals to have, as ouExperimentut, a signal with a frequency equal to the difference between the emitted and received frequencies.