Experiment: Determination of Doppler DELTAF as a function of velocity using an oscilloscope

Topics covered:

- Propagation of ultrasound in 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 relationship and its application to velocity measurement.

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

Set the cart in motion, and plan a velocity measurement device (stopwatch, chronocine device,

camera, etc.). The velocity can then be validated by a reference system.

2- Find the Doppler relationship through the experiment:

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

- Measure the Doppler frequency shift corresponding to the ouExperimentut signal frequency of the Initio box (by reading the pointer, or by modeling

or by Fourier transform: all these solutions are

integrated into the general Physics Chemistry Scientific Workshop software).

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

- Represent f as a function of v.

- Deduce the slope of the corresponding line.

- Compare this value to the ratio c/fem.

- 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:

- Repeatable and reproducible experiments

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

- Constant velocity 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 to the simple Moduson® transmitter (not provided)

- Operation on emitted and received ultrasonic signals in order to have, as ouExperimentut, a signal with a frequency equal to the

difference of the emitted and received frequencies.

- Pack eff and Doppler (ref 222138) - Moduson transmitter (ref 222076) - Moduson receiver (ref 222078) - Iniscope 2 oscilloscope (ref 297705)