WAVES AND VIBRATIONS IN INHOMOGENEOUS STRUCTURES ...

2.3 Experimental demonstration 11
Figure 2.4 Experimental setup and part of the setup showing (from left to right) the
vibration exciter, force transducer, periodic bar system with supporting threads, and
accelerometer. From paper [2].
[dB/1.00 (m/s†)/N]
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FRF (Magnitude)
Working : PMMA-Alu-11-seg-7.5cm-200302-ref : Input : FFT Analyzer
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Figure2.5 Responsecurvesshowingtheacceleration responseattheendofthebarversus
the excitation frequency. Left: experimental data and right: corresponding theoretical
predictions. From paper [2].
2.3 Experimental demonstration
The theoretical predictions are based on simple mass-spring models. Thus, it is
here especially important to support observations and conclusions experimentally.
In this way it can be documented that the bandgap phenomenon manifests itself in
a realistic setup and is not merely the product of an overly simplified model.
Fig. 2.4 illustrates a schematic and experimental setup for measuring the forced
vibration response of an elastic rod composed of alternating sections of aluminum
and PMMA (a plastic material). The rod is subjected to periodic forcing imposed
by a shaker in one end and the acceleration is recorded in the other end using
an accelerometer. Fig. 2.5 shows plots of the measured response and the response
predicted by a mass-spring model fitted to the actual material parameters including
a single fitted viscous damping parameter.
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