Visualisation of the Surface Vibration Using a PVDF Film Array

The ability to visualise the vibration of a structural surface is a big advantage when analysing the modal characteristics of the structure. This can be done using many accelerometers but can be a laborious, time consuming process. In addition, for small structures the accumulative effects of accelerometer mass can soon become a problem and adversely affect the measured natural frequencies. An alternative is to use a scanning laser doppler vibrometer (SLDV) where the surface can be scanned to passively obtain the surface velocity. These systems are very useful but can be expensive and difficult to use in confined spaces or within fluids. This paper investigates using Polyvinylidene fluoride (PVDF) polymer film as an alternative method for visualizing the surface vibration. PVDF film has been widely investigated as a sensor and transducer material due to its high piezo-, pyro- and ferro-electric properties. In can be easily fabricated into thin sheets (∼ few um) and as a result it is ideal for making small, very light piezoelectric sensors. An array of seventeen PVDF sensors was constructed and attached to a thinly clamped steel disk. The output of the array was recorded for the first six resonant frequencies of the disk and compared to simultaneous results obtained using a SLDV.