Browsing by Author "Haardt, Martin"

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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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    High resolution technique for measuring charge and polarization distributions in dielectrics by piezoelectrically induced pressure step waves (PPS)
    (1982) Haardt, Martin; Eisenmenger, Wolfgang
    Our step wave technique, so far, has been discussed with respect to the investigation of already prepared samples. In some situations it is of interest to study the buildup of charge and polarization distributions during the poling procedure. This can be accomplished by inserting an additional insulating film, e.g. mylar between the conducting rubber electrode and the sample film. The insulating film acts as a series capacitor reducing the signal amplitude with no influence on the signal shape. Poling of the sample is possible by DC-current (voltage ) supply with a thin metal electrode at the insulating film evaporated on the face in sample contact. The same technique is used for measuring the electrostriction coefficient. In both cases quantitative evaluation additionally requires the measurement of the insulating film capacitance.
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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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    Observation of charge compensated polarization zones in polyvinylindenfluoride (PVDF) films by piezoelectric acoustic step wave response
    (1982) Eisenmenger, Wolfgang; Haardt, Martin
    A high resolution (2 μm) acoustic step-wave probing techniques has been developed to investigate the inhomogeneous distribution of the piezoelectric response of incompletely corona poled 85 μm thick PVDF films. We observe persistent polarization zones or layers of 20–40 μm width within the films which are electrostatically compensated by charge accumulation at the polarization zone boundaries. The zone development is explained by charge-trapping in proportion to polarization.