TY - JOUR A1 - Basso, Heitor Cury A1 - Altafim, Ruy Alberto Pisani A1 - Altafim, Ruy Alberto Pisani A1 - Mellinger, Axel A1 - Fang, Peng A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Three-layer ferroelectrets from perforated Teflon-PTFE films fused between two homogeneous Teflon-FEP films Y1 - 2007 SN - 978-1-4244-1482-6 ER - TY - JOUR A1 - Fang, Peng A1 - Hollaender, Lars A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Piezoelectric d(33) coefficients in foamed and layered polymer piezoelectrets from dynamic mechano-electrical experiments, electro-mechanical resonance spectroscopy and acoustic-transducer measurements JF - Measurement science and technology N2 - Piezoelectrets are novel transducer materials which can be widely applied in sensors and actuators. Here, three techniques for determining piezoelectric d(33) coefficients of piezoelectrets are reviewed and compared. Two types of piezoelectrets, polyethylene-naphthalate (PEN) polymer-foam piezoelectrets and fluorinated ethylene-propylene (FEP) copolymer-layer piezoelectrets, have been prepared and measured by means of dynamic, resonance, and acoustical methods. The dynamic measurements show that the d(33) coefficient of PEN-foam samples clearly decreases with increasing stress, but 80% of the initial d(33) can be retained after 1800 cycles of a continuous dynamic measurement in a mechanical fatigue test. The resonance measurements demonstrate that both PEN-foam and FEP-layer samples exhibit clear electro-mechanical resonances. PEN-foam samples show elastic moduli in the range from 1 to 12 MPa and d(33) values up to 500 pC N-1, while FEP-layer samples show homogeneous elastic moduli of about 0.3 MPa and d(33) values of about 280 pC N-1. The acoustical measurements reveal that both PEN-foam and FEP-layer samples exhibit stable frequency responses in the range from 5.7 to 20 kHz. In addition, d(33) coefficients obtained with different experimental methods are in good agreement with each other, which confirms the reliability of all three techniques. KW - piezoelectret KW - ferroelectret KW - dielectric resonance spectroscopy KW - piezoelectric measurements KW - acoustic-transducer materials KW - polyethylene naphthalate (PEN) KW - fluorinated ethylene-propylene copolymer (FEP) Y1 - 2012 U6 - https://doi.org/10.1088/0957-0233/23/3/035604 SN - 0957-0233 VL - 23 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Fang, Peng A1 - Ma, Xingchen A1 - Li, Xiangxin A1 - Qiu, Xunlin A1 - Gerhard, Reimund A1 - Zhang, Xiaoqing A1 - Li, Guanglin T1 - Fabrication, Structure Characterization, and Performance Testing of Piezoelectret-Film Sensors for Recording Body Motion JF - IEEE Sensors Journal N2 - During muscle contractions, radial-force distributions are generated on muscle surfaces due to muscle-volume changes, from which the corresponding body motions can be recorded by means of so-called force myography (FMG). Piezo- or ferroelectrets are flexible piezoelectric materials with attractive materials and sensing properties. In addition to several other applications, they are suitable for detecting force variations by means of wearable devices. In this paper, we prepared piezoelectrets from cellular polypropylene films by optimizing the fabrication procedures, and developed an FMG-recording system based on piezoelectret sensors. Different hand and wrist movements were successfully detected on able-bodied subjects with the FMG system. The FMG patterns were evaluated and identified by means of linear discriminant analysis and artificial neural network algorithms, and average motion-classification accuracies of 96.1% and 94.8%, respectively, were obtained. This paper demonstrates the feasibility of using piezoelectret-film sensors for FMG and may thus lead to alternative methods for detecting body motion and to related applications, e.g., in biomedical engineering or structural-health monitoring. KW - Forcemyography KW - motion registration KW - piezoelectret KW - film sensor KW - wearable Y1 - 2017 U6 - https://doi.org/10.1109/JSEN.2017.2766663 SN - 1530-437X SN - 1558-1748 VL - 18 IS - 1 SP - 401 EP - 412 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Fang, Peng A1 - Qiu, Xunlin A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Zirkel, Larissa T1 - Polyethylene-naphthalate (PEN) ferroelectrets : cellular structure, piezoelectricity and thermal stability N2 - Cellular polyethylene-naphthalate (PEN) ferroelectrets are useful as soft and flexible electromechanical transducer materials. Improved cellular PEN foams are prepared by means of a "voiding + inflation + stretching" process and investigated with respect to their structure and their applications-relevant properties. It is found that most of the cellular voids have heights below 8 mu m. The polymer walls do not allow sufficient gas exchange between the voids and the ambient atmosphere, when the cellular films are exposed to atmospheric pressures between a millibar and a few bars. As expected for ferroelectrets, a threshold voltage for charging is observed: A reasonable piezoelectric coefficient d(33) is only found when the charging voltage is higher than 4 kV. Furthermore, d(33) increases with charging voltage and reaches saturation at approximately 8 kV. Annealing after charging or charging at elevated temperatures may enhance the thermal stability of the PEN ferroelectrets. The d(33) of properly annealed samples is stable up to the respective annealing temperatures, but the annealing process reduces the piezoelectric activity of charged ferroelectret films to some extent. Samples charged at suitable elevated temperatures show much better thermal stability than those charged at room temperature, but the charging temperature should be limited to values below the material's glass-transition temperature T-g. Furthermore, the relevant elastic modulus c(33) of PEN ferroelectrets may decrease upon thermal treatment. Y1 - 2010 UR - http://ieeexplore.ieee.org/servlet/opac?punumber=94 U6 - https://doi.org/10.1109/TDEI.2010.5539678 SN - 1070-9878 ER - TY - JOUR A1 - Fang, Peng A1 - Wang, Feipeng A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Basso, Heitor Cury T1 - Three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films JF - Applied physics : A, Materials science & processing N2 - A process for preparing three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films is introduced. Samples are made from commercial FEP films by means of laser cutting, laser bonding, electrode evaporation, and high-field poling. The observed dielectric-resonance spectra demonstrate the piezoelectricity of the FEP sandwiches. Piezoelectric d (33) coefficients up to a few hundred pC/N are achieved. Charging at elevated temperatures can increase the thermal stability of the piezoelectrets. Isothermal experiments for approximately 15 min demonstrate that samples charged at 140A degrees C keep their piezoelectric activity up to at least 120A degrees C and retain 70% of their initial d (33) even at 130A degrees C. Acoustical measurements show a relatively flat frequency response in the range between 300 Hz and 20 kHz. Y1 - 2011 U6 - https://doi.org/10.1007/s00339-010-6008-2 SN - 0947-8396 SN - 1432-0630 VL - 103 IS - 2 SP - 455 EP - 461 PB - Springer CY - New York ER - TY - JOUR A1 - Fang, Peng A1 - Wegener, Michael A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Zirkel, Larissa T1 - Cellular polyethylene-naphthalate ferroelectrets : foaming in supercritical carbon dioxide, structural and electrical preparation, and resulting piezoelectricity N2 - Polymer foams with electrically charged cellular voids, the so-called ferroelectrets, are soft piezoelectric transducer materials. Several polymers such as polyethylene terephthalate or cyclo-olefin copolymers are under investigation with respect to their suitability as ferroelectrets. Here, the authors report an additional ferroelectret polymer, cellular polyethylene-naphthalate (PEN), which was prepared from commercial uniform polymer films by means of foaming in supercritical carbon dioxide, inflation, biaxial stretching, electrical charging, and metallization. Piezoelectric d(33) coefficients of up to 140 pC/N demonstrate the suitability of such cellular PEN films for transducer applications. Their piezoelectricity is partially stable at elevated temperatures as high as 100 degrees C. Y1 - 2007 UR - http://apl.aip.org/ U6 - https://doi.org/10.1063/1.2738365 SN - 0003-6951 ER -