Browsing by Author "Sessler, Gerhard M."

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    Electric field profiles in electron-beam-charged polymer electrets
    (1983) Gerhard-Multhaupt, Reimund; Haardt, Martin; Eisenmenger, Wolfgang; Sessler, Gerhard M.
    A recently developed method, which uses piezoelectrically generated pressure steps for the determination of electric-field profiles in dielectrics, has been applied to electron-beam-charged polyfluoroethylenepropylene (FEP) and polyethyleneterephthalate (PETP) electrets. The results indicate that the technique can be employed to study volume charge effects in thin dielectrics. If properly calibrated, the method provides a quantitative measure of charge-integral functions or electric-field distributions in polymer foils.
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    Investigation of piezoelectricity distributions in poly(vinylidene fluoride) by means of quartz- or laser-generated pressure pulses
    (1984) Gerhard-Multhaupt, Reimund; Sessler, Gerhard M.; West, James E.; Holdik, Karl; Haardt, Martin; Eisenmenger, Wolfgang
    The direct determination of charge, polarization, or piezoelectricity profiles in thin dielectrics is now possible if piezoelectrically generated pressure steps or pulses and laser‐induced pressure pulses are employed. These recently developed high‐resolution methods were applied to the same piezoelectric poly(vinylidene fluoride) (PVDF) samples. Comparison of the respective results demonstrates the feasibility, the advantages, and the limitations of the new techniques for the study of piezoelectricity distributions. It is confirmed that, for relatively low poling fields, the piezoelectric activity of thermopoled PVDF foils is often confined to a layer near the positively biased surface. The same effect is found for poling with a positive corona discharge. For high‐field corona poling, the piezoelectric activity extends throughout the PVDF film.
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    Piezo and pyroelectricity in electrets : caused by charges, dipoles, or both?
    (1992) Sessler, Gerhard M.; Das-Gupta, Dilip K.; deReggi, Aimé S.; Eisenmenger, Wolfgang; Furukawa, Takeo; Giacometti, José A.; Gerhard-Multhaupt, Reimund
    In a homogeneous medium space charges cannot cause piezo or pyroeiectricity. If stressed, there will be affine geometrical changes throughout the medium, and therefore the induction charges on the electrodes will remain the same, and piezoelectricity cannot be generated. However, if dipoles are present in such a homogeneous dielectric, then piezoelectricity is possible. In an inhomogeneous medium such as a semicrystalline polymer, charges and dipoles can cause piezoelectricity. If you have, for instance, a semicrystalline polymer then the crystalline and the amorphous parts are, upon compression, subjected to different degrees of deformation; and for this reason, a piezoelectric effect can be generated.