Experimental modal analysis of three small-scale vibration isolator models

This paper discusses the experimentally measured free–free dynamics of three small-scale vibration isolator models: two single-stage isolators and one two-stage isolator. The first comprises two steel plates and one rubber element, the second two steel plates and four rubber elements, and the third three steel plates and eight rubber elements. The natural frequencies, mode shapes and associated modal damping derived from curve-fitting procedures applied to the measured frequency-response functions (FRFs) are presented. The modal behaviour of the isolators is more complicated than might at first be assumed, a major feature being significant coupling between different degrees of freedom. The modal properties can be used to reconstruct a complete set of FRFs for the isolator, including FRFs which were not measured directly. Vibration isolators are often characterised through the use of four-pole parameters or various transmissibilities, and so methods for calculating these parameters from the reconstructed FRFs are also given.