Development of a PVDF Sensor for the Measurement of the Acoustic Local Volume Displacement of Vibrating Beams

One method of reduction of radiated sound from vibrating structures is to reduce the surface volume velocity. At low frequencies, the volume velocity (or volume displacement) of a vibrating surface is directly related to the sound power emitted from that surface. Recent methods used for sensing surface volume displacement entail the use of a surface mounted strip of shaped polyvinylidene fluoride (PVDF) that spans the entire length of the structure. This paper shows that the volume displacement of a vibrating beam can be measured through the use of a set of localized PVDF sensors each spanning only an area of interest. Summation of the volume displacements measured by these sensors would yield the total beam volume displacement. In this application it was shown that two point sensors are required in addition to the distributed PVDF sensor to achieve such measurements. To examine the localized sensors developed, four beams with different end conditions (fixed-fixed, fixed-free, fixed-simply supported, and simply supported-simply supported) were constructed. In designing the localized surface sensors, the sensor shapes necessary to measure a localized area of interest were determined, these sensors were constructed, and subsequently tested using a fixture constructed for this specific purpose. Finally, a comparison between the measured values obtained using these combined PVDF/Accelerometer sensors were compared to those obtained using an array of accelerometers was performed to determine the accuracy of these sensors. It was discovered that the localized sensors developed were sufficiently accurate for sensing the volume displacement of the vibrating beam within a 0–1600 Hz frequency range. Possible sources of error are discussed in the text.