On the use of PZT-patches as exciters in modal analysis: Application to submerged structures

Modal analysis is an experimental technique widely used to determine the dynamic response of structures. One of the most critical part is the selection of the actuator that will excite the tested structure.In many cases traditional exciters, such as hammers and shakers, have been used for this purpose. Nevertheless, these exciters may have the disadvantage of modifying the modal parameters (as reported in some cases) and they are difficult to be used when the structure is not accessible (confined and/or submerged).For these cases PZT-patches, that are very light structures (compared to the tested structure), have been recently used as exciters. Although, in the analyzed studies the natural frequencies of the structure have been determined using PZTs, the rest of parameters that determine the FRF (Frequency response Function) are not obtained. This could be, because the calibration of PZTs as dynamic force transducers is a complicated task and is not an information given by the manufacturers, as in other exciters used for the same purpose.This paper analyzes experimentally and analytically the use of PZT-patches as exciters for modal analysis. For this purpose, a tested structure is excited in different ways with a PZT and its response compared with a reference case, obtained with a classical exciter. Analyses show how to obtain different modal parameters that determine the FRF of the structure, without previous calibration of the PZT. Finally, and in order to show the potential advantages of these exciters for inaccessible structures, the procedure is repeated for the same structure submerged, showing that PZT are much more appropriated exciters in these cases.