scanning vibration with lissajous figures

Rectangular beam is driven into vibration by electromagnetic coil (far corner) and small NeFeB magnetic attached to beam. Small microphone is used to detect the nearfield sound radiation which is directly proportional to the beam's bending vibration. Lissajous figures on the oscilloscope compare the phase of the driving signal and the responding vibration. As the microphone scans along the length of the beam the slope of the Lissajous pattern on the oscilloscope changes sign (positive or negative) each time a nodal line is crossed. Using this technique, students can map out the various bending and torsional modes of a rectangular beam.

Category:

Education

Tags:

• physics
• vibration
• bending
• acoustics
• science