Gareth J. Bennett, Henry Rice, Nonlinear vibro-acoustic behaviour in a circular membrane oscillator, 7th EUROMECH Solid Mechanics Conference (ESMC2009), Mini-symposium on Nonlinear vibrations and acoustics, Lisbon, Portugal, 7-11 September 2009, 2009
Oscillating systems that produce noise at a frequency of excitation may have as an abatement
solution the increase of the frequency of excitation to above the audible frequency limit, viz.
20kHz. This approach may not be possible for systems subject to non-linear behavior as subharmonics
can be generated within the audible range. This paper describes the analysis of a
small metal annulus over which a thin membrane is stretched. The membrane is indirectly
excited via a piezoelectric transducer attached to the annulus and has an application as an
appliance in the electronics sector. The generation of noise is unwanted but found to occur occasionally.
The analysis confirms the non-linear behaviour of the system with sub-harmonics
resulting from a non-linear interaction with a low natural frequency. An experimental technique
using a 2-D Scanning Laser Vibrometer (Polytec PSV-400) allows the vibrational modes
of the annulus and membrane to be measured as a function of frequency and presented graphically
and demonstrates the membrane to be radiating the noise. The paper discusses with the
aid of both an analytical and numerical solution to the Duffing Equation how an increase in
damping will suppress the sub-harmonics. A practical damping solution is found for the design
which successfully eliminates the noise without negatively effecting its performance.
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