Piezoelectricity in cellular electret films

Permanently charged films with a cellular or porous structure represent a new family of polymer electrets. These materials show piezoelectric properties with high piezoelectric constants. The electromechanical response equations of such films are derived for their operation as sensors and as actuators. Experimental results are also presented for cellular polypropylene (pp). In particular, measurements of the direct and inverse piezoelectric constants in the frequency range 0 to 10 kHz and of the variation of these constants across the surface of the films are discussed. These measurements, performed by direct application of stress or by the use of a profilometer, an accelerometer and an interferometer yield a frequency-independent piezoelectric d/sub 33/ constant of /spl lsim/ 220 pC/N. Assuming reasonable charge distributions and charge densities, the calculated piezoelectric constants are in good agreement with the measured values. The theoretical model shows the reciprocity of the piezoelectric constants.

[1]  S. Bauer,et al.  Dielectric and electret properties of novel Teflon PTFE and PTFE-like polymers , 1999, 10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256).

[2]  Reimund Gerhard-Multhaupt,et al.  High surface-charge stability of porous polytetrafluoroethylene electret films at room and elevated temperatures , 1999 .

[3]  J. van Turnhout,et al.  Distribution and stability of charges in porous polypropylene films , 1999, 10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256).

[4]  K. Kirjavainen,et al.  Electrothermomechanical Film. Part I. Design and Characteristics , 1989 .

[5]  M. Paajanen,et al.  EMFi-New electret material for sensors and actuators , 1999, 10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256).

[6]  Don Berlincourt,et al.  3 – Piezoelectric and Piezomagnetic Materials and Their Function in Transducers , 1964 .

[7]  Z. Xia,et al.  Electret properties of silicon dioxide aerogels , 1996, 9th International Symposium on Electrets (ISE 9) Proceedings.

[8]  M. Paajanen,et al.  Modelling the sensor and actuator operations of the ElectroMechanical Film EMFi , 1999, 10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256).

[9]  S. Bauer,et al.  Large piezoelectric effects in charged, heterogeneous fluoropolymer electrets , 2000 .

[10]  Xia Zhongfu,et al.  The excellent charge storage stability of porous polytetrafluoroethylene (PTFE) film electrets , 1999, 10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256).

[11]  R. Gerhard-Multhaupt,et al.  Preliminary study of multi-layer space-charge electrets with piezoelectric properties from porous and non-porous Teflon films , 1999, 10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256).

[12]  Mechanical and electrical response of charged polymers with cellular structure , 1999, 1999 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (Cat. No.99CH36319).

[13]  Gerhard M. Sessler,et al.  Electromechanical response of cellular electret films , 1999 .

[14]  J. Gajewski,et al.  Double-layer electret transducer , 1997 .

[15]  R. Gerhard-Multhaupt,et al.  Piezoelectricity of porous polytetrafluoroethylene single- and multiple-film electrets containing high charge densities of both polarities , 2000 .