Elasticity investigation of thin cellular structure films for piezoelectric sensors

Purpose This paper aims to present the details of isotactic polypropylene (it-PP) films with a cellular structure (air-cavities) dedicated to pressure sensors. The polymer composites (thin films enriched with 5 and 10 wt% of mineral fillers as Sillikolloid P 87 and glass beads) should exhibit suitable structural elasticity within specific stress ranges. After the deformation force is removed, the sensor material must completely restore its original shape and size. Design/methodology/approach Estimating the stiffness tensor element ( C 33 ) for polymer films (nonpolar space-charge electrets) by broadband resonance ultrasound spectroscopy is a relatively simple method of determining the safe stress range generated in thin pressure sensors. Therefore, ultrasonic and piezoelectric studies were carried out on four composite it-PP films. First, the longitudinal velocity ( v L ) of ultrasonic waves passing through the it-PP film in the z-direction (thickness) was evaluated from the ω -position of mechanical resonance of the so-called insertion loss function. In turn, the d 33 coefficient was calculated from accumulated piezoelectric charge density response to mechanical stress. Findings Research is at an early stage; however, it can be seen that the mechanical orientation of the it-PP film improves its piezoelectric properties. Moreover, the three-year electric charge stability of the it-PP film seems promising. Originality/value Ultrasonic spectroscopy can be successfully handled as a validation method in the small-lot production of polymer films with the air-cavities structure intended for pressure sensors. The structural repeatability of polymer films is strongly related to a homogeneous distribution of the electric charge on the electret surface.