Instrumentation influence: a study about the intrusiveness level caused by a single PVDF in a flexible dynamic system

The interest in applying piezoelectric materials for modal analysis has been growing in the past few decades. In piezoelectric materials, both electrical and mechanical domains are coupled, i.e., these materials are able to convert electrical energy into mechanical energy and vice versa. Due to this key characteristic, they can be used in several applications as actuators or sensors. Furthermore, some piezoelectric materials exhibit a predominant coupling, which makes them more efficient when used for specific purposes/applications. This is the case of the polyvinylidene fluoride (PVDF) which is widely used as a sensor. An advantage associated with the PVDF is its small influence on the results, due to the low thickness and high flexibility; sometimes, its influence is completely neglected. The aim of this work is to evaluate the influence of a single PVDF film on a flexible beam model. For this purpose, an efficient methodology to verify and identify the intrusiveness level of the instrumentation is proposed, which consists in changing the sensor position (PVDF) and simultaneously acquiring the data by using a non-intrusive technique (laser vibrometer). The modal parameters (natural frequencies and damping factors) obtained by PVDF and laser vibrometer responses should be very close for each PVDF position. If this condition is satisfied, the variation of the modal parameters due to PVDF position will show the intrusiveness level imposed by the PVDF instrumentation. This research emphasizes the importance of verifying the influence of the instrumentation, even if it seems to cause merely a small intrusiveness on the dynamic system.