ElectroMechanical Film (EMFi) - a new multipurpose electret material

The ElectroMechanical Film (EMFi) is a thin, cellular, biaxially oriented p olypropylene film that can be used as an electret. Having a special voided internal structure and high resistivity, it is capable of storing large per manent charge. The charge is injected by a corona method using similar to 1 0 kV cm(-1) fields, thus creating internal electrical discharges inside the cellular structure. Films of different thickness and elasticity can be man ufactured. The thickness in sensor and actuator applications is typically 3 0-70 mu m. When metallized on both sides, EMFi is capable of measuring pres sure and force changes offering large application potential in different fi elds of technology including microphones and also actuators. New loudspeake r panels based on EMFi are only a few millimeters thick. (C) 2000 Elsevier Science S.A. All rights reserved.