@article{PhamPetreBerquezetal.2009, author = {Pham, Cong Duc and Petre, Anca and Berquez, Laurent and Flores Su{\´a}rez, Rosaura and Mellinger, Axel and Wirges, Werner and Gerhard, Reimund}, title = {3D high-resolution mapping of polarization profiles in thin poly(vinylidenefluoride-trifluoroethylene) (PVDF- TrFE) films using two thermal techniques}, issn = {1070-9878}, doi = {10.1109/TDEI.2009.5128505}, year = {2009}, abstract = {In this paper, two non-destructive thermal methods are used in order to determine, with a high degree of accuracy, three-dimensional polarization distributions in thin films (12 mu m) of poly(vinylidenefluoride- trifluoroethylene) (PVDF-TrFE). The techniques are the frequency-domain Focused Laser Intensity Modulation Method (FLIMM) and time-domain Thermal-Pulse Tomography (TPT). Samples were first metalized with grid-shaped electrode and poled. 3D polarization mapping yielded profiles which reproduce the electrode-grid shape. The polarization is not uniform across the sample thickness. Significant polarization values are found only at depths beyond 0.5 mu m from the sample surface. Both methods provide similar results, TPT method being faster, whereas the FLIMM technique has a better lateral resolution.}, language = {en} } @article{AssagraAltafimdoCarmoetal.2020, author = {Assagra, Yuri A.O. and Altafim, Ruy Alberto Pisani and do Carmo, Joao P. and Altafim, Ruy A.C. and Rychkov, Dmitry and Wirges, Werner and Gerhard, Reimund}, title = {A new route to piezo-polymer transducers: 3D printing of polypropylene ferroelectrets}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {27}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {5}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, doi = {10.1109/TDEI.2020.008461}, pages = {1668 -- 1674}, year = {2020}, abstract = {Here, a promising approach for producing piezo-polymer transducers in a one-step process is presented. Using 3D-printing technology and polypropylene (PP) filaments, we are able to print a two-layered film structure with regular cavities of precisely controlled size and shape. It is found that the 3D-printed samples exhibit piezoelectric coefficients up to 200 pC/N, similar to those of other PP ferroelectrets, and their temporal and thermal behavior is in good agreement with those known of PP ferroelectrets. The piezoelectric response strongly decreases for applied pressures above 20 kPa, as the pressure in the air-filled cavities strongly influences the overall elastic modulus of ferroelectrets.}, language = {en} } @article{BrinkerWirgesMolzowetal.1995, author = {Brinker, Walter and Wirges, Werner and Molzow, Wolf-Dietrich and Gerhard, Reimund and Melcher, R. and Budde, W. and Fiedler, H.}, title = {Active silicon CMOS addressing matrices for light-valve projection displays}, year = {1995}, language = {en} } @article{WertheimerStGeorgesRobillardLerougeetal.2012, author = {Wertheimer, Michael R. and St-Georges-Robillard, Amelie and Lerouge, Sophie and Mwale, Fackson and Elkin, Bentsian and Oehr, Christian and Wirges, Werner and Gerhard, Reimund}, title = {Amine-rich organic thin films for cell culture - possible electrostatic effects in cell-surface interactions}, series = {Japanese journal of applied physics}, volume = {51}, journal = {Japanese journal of applied physics}, number = {11}, publisher = {Japan Soc. of Applied Physics}, address = {Tokyo}, issn = {0021-4922}, doi = {10.1143/JJAP.51.11PJ04}, pages = {5}, year = {2012}, abstract = {In recent communications from these laboratories, we observed that amine-rich thin organic layers are very efficient surfaces for the adhesion of mammalian cells. We prepare such deposits by plasma polymerization at low pressure, atmospheric pressure, or by vacuum-ultraviolet photo-polymerization. More recently, we have also investigated a commercially available material, Parylene diX AM. In this article we first briefly introduce literature relating to electrostatic interactions between cells, proteins, and charged surfaces. We then present certain selected cell-response results that pertain to applications in orthopedic and cardiovascular medicine: we discuss the influence of surface properties on the observed behaviors of two particular cell lines, human U937 monocytes, and Chinese hamster ovary cells. Particular emphasis is placed on possible electrostatic attractive forces due to positively charged R-NH3+ groups and negatively charged proteins and cells, respectively. Experiments carried out with electrets, polymers with high positive or negative surface potentials are added for comparison.}, language = {en} } @article{QiuMellingerWegeneretal.2007, author = {Qiu, Xunlin and Mellinger, Axel and Wegener, Michael and Wirges, Werner and Gerhard, Reimund}, title = {Barrier discharges in cellular polypropylene ferroelectrets : how do they influence the electromechanical properties?}, year = {2007}, language = {en} } @article{QiuWirgesGerhard2011, author = {Qiu, Xunlin and Wirges, Werner and Gerhard, Reimund}, title = {Beneficial and detrimental fatigue effects of dielectric barrier discharges on the piezoelectricity of polypropylene ferroelectrets}, series = {Journal of applied physics}, volume = {110}, journal = {Journal of applied physics}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/1.3610507}, pages = {8}, year = {2011}, abstract = {Cellular polypropylene (PP) ferroelectrets combine a large piezoelectricity with mechanical flexibility and elastic compliance. Their charging process represents a series of dielectric barrier discharges (DBDs) that generate a cold plasma with numerous active species and thus modify the inner polymer surfaces of the foam cells. Both the threshold for the onset of DBDs and the piezoelectricity of ferroelectrets are sensitive to repeated DBDs in the voids. It is found that the threshold voltage is approximately halved and the charging efficiency is clearly improved after only 10(3) DBD cycles. However, plasma modification of the inner surfaces from repeated DBDs deteriorates the chargeability of the voids, leading to a significant reduction of the piezoelectricity in ferroelectrets. After a significant waiting period, the chargeability of previously fatigued voids shows a partial recovery. The plasma modification is, however, detrimental to the stability of the deposited charges and thus also of the macroscopic dipoles and of the piezoelectricity. Fatigue from only 10(3) DBD cycles already results in significantly less stable piezoelectricity in cellular PP ferroelectrets. The fatigue rate as a function of the number of voltage cycles follows a stretched exponential. Fatigue from repeated DBDs can be avoided if most of the gas molecules inside the voids are removed via a suitable evacuation process.}, language = {en} } @article{WegenerGerhardWirgesetal.2003, author = {Wegener, Michael and Gerhard, Reimund and Wirges, Werner and Bergner, Andr{\´e} and Bergweiler, Steffen}, title = {Breathing modes of organ-pipe bodies : experimental detection with ring-shaped piezoelectric-polymer sensors}, year = {2003}, language = {en} } @article{FangWegenerWirgesetal.2007, author = {Fang, Peng and Wegener, Michael and Wirges, Werner and Gerhard, Reimund and Zirkel, Larissa}, title = {Cellular polyethylene-naphthalate ferroelectrets : foaming in supercritical carbon dioxide, structural and electrical preparation, and resulting piezoelectricity}, issn = {0003-6951}, doi = {10.1063/1.2738365}, year = {2007}, abstract = {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.}, language = {en} } @article{QiuGrothWirgesetal.2018, author = {Qiu, Xunlin and Groth, Frederick and Wirges, Werner and Gerhard, Reimund}, title = {Cellular polypropylene foam films as DC voltage insulation and as piezoelectrets}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {25}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {3}, publisher = {Institut of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, doi = {10.1109/TDEI.2018.007192}, pages = {829 -- 834}, year = {2018}, abstract = {Polymer foams are in industrial use for several decades. More recently, non-polar polymer foams were found to be piezoelectric (so-called piezoelectrets) after internal electrical charging of the cavities. So far, few studies have been carried out on the electrical-insulation properties of polymer foams. Here, we compare the piezoelectric and the DC-voltage electrical-insulation properties of cellular polypropylene (PP) foams. Their cavity microstructure can be adjusted via inflation in high-pressure nitrogen gas in combination with a subsequent thermal treatment. While inflation is effective for improving the piezoelectricity, it is detrimental for the electrical-insulation properties. The original cellular PP foam shows a breakdown strength of approximately 230 MV/m, within the same range as that of solid PP. The breakdown strength decreases with increasing degree of inflation, and the dependence on the foam thickness follows an inverse power law with an exponent of 1.2. Nevertheless, up to a thickness of 140 mu m (3.5 times the original thickness), the breakdown strength of cellular-foam PP films is at least 7 times that of an air gap with the same thickness. In addition, the influence of high temperatures and high humidities on the piezoelectricity and the breakdown strength of cellular PP was studied. It was found that the piezoelectric d(33) coefficient decays rapidly already at 70 degrees C, while the breakdown strength slightly increases during storage at 70 or 90 degrees C. Under a relative humidity of 95\%, the breakdown strength increases with storage time, while the piezoelectric d(33) coefficient slightly decreases.}, language = {en} } @article{WegenerWirgesRichteretal.2001, author = {Wegener, Michael and Wirges, Werner and Richter, Kristin and K{\"u}nstler, Wolfgang and Gerhard, Reimund}, title = {Charge stability and piezoelectric properties of porous fluoro-polymer space-charge electrets in layer systems}, year = {2001}, language = {en} }