When exposed to sufficiently high electric fields, polymer-foam electret materials with closed cells exhibit ferroelectric-like behavior and may therefore be called ferroelectrets. In cellular ferroelectrets, the influence of the cell size and shape distributions on the application-relevant properties is not yet understood. Therefore, controlled inflation experiments were carried out on cellular polypropylene films, and the resulting elastical and electromechanical parameters were determined. The elastic modulus in the thickness direction shows a minimum with a corresponding maximum in the electromechanical transducer coefficient. The resonance frequency shifts as a function of the elastic modulus and the relative density of the inflated cellular films. Therefore, the transducer properties of cellular ferroelectrets can be optimized by means of controlled inflation.

Polymer foams are used in the automotive and construction industries for thermal insulation, vibration attenuation, and pressure absorption, due to their lightweight structure, thermal characteristics and low manufacturing costs. These foams have higher elasticity in their cross sections than bulk polymers, which makes them the preferred mount for capacitive sensor arrays. The authors describe a flexible pressure-sensitive surface mounted on packaging foam. The elastic properties of the foam are presented along with the sensor array’s weight sensitivity. The authors illustrate an inventory management application where objects on display can be detected through their weights.

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