Cellular and porous polymers with internal bipolar space charge can exhibit large piezoelectric thickness coefficients and have therefore led to significant advances in the understanding and the application of piezoelectricity in polymer electrets. As possible alternatives to these cellular ferroelectrets, other potentially useful configurations of space-charge electrets, such as bi-layer or multi-layer stacks of at least one "soft" porous and one "hard" non-porous electret film have been suggested and investigated. Extending the concept of cellular or porous polymer electrets with microscopic voids, we propose and describe novel piezoelectret structures with regular arrays of millimeter-sized bubbles that are formed between fluoro-ethylene-propylene (Teflon®-FEP) films via a vacuum-assisted thermal process. After internal charging by means of high impulse voltages, the bubble structures exhibit rather large piezoelectric activities in their thickness direction, with phenomenological quasi-static d 33 coefficients of up to 500 pC/N (or pm/V) which quite strongly decrease with the amplitude of the applied force. The electromechanical behavior of the new piezoelectrets has been modeled in analogy to the operation of electret microphones. , he is a visiting professor at the Institute of Physics of the University of São Paulo in São Carlos, Brazil. The main research areas of Prof. Gerhard-Multhaupt are polymer electrets and ferroelectrets, in particular the mechanisms of space-charge storage and dipole polarization in dielectric polymers and polymer composites, their ferro-, pyro-and piezoelectrical properties, and their applications in sensors and actuators, as well as the nonlinear optical properties of polymers, and more recently also the physics of musical instruments. From 1974From until 1979 he was a fellow of the Studienstiftung des Deutschen Volkes. In 1988, he was awarded an ITG-Preis by the Informationstechnische Gesellschaft im VDE. In 1989, he received a Silver medal from the Stiftung Werner-von-Siemens-Ring. In 2001, he was awarded the first Technologietransfer-Preis by the Technologie-Stiftung Brandenburg and the Prof.-Adalbert-Seifriz-Preis by the Verein Technologie-Transfer Handwerk for his technological collaborations with small industrial companies. Reimund Gerhard-Multhaupt is a member of the American, European and German physical societies. Since 2002, he serves as Digest Editor of the IEEE Dielectrics and Electrical Insulation Society.
Multi-air voids space-charge electrets have been developed using two fluorethylenepropylene (Teflon-FEP) films. In this work, a new technique developed to assembler these films allows the control of the thickness and shapes of multi-air voids distributed on their surface. When an impulse voltage process charges these voids, it is possible to obtain samples with high piezoelectric coefficients. To explain this piezoelectric characteristic, a theoretical explanation based on the electret microphone mechanism is introduced. Measurements show the piezoelectric coefficients for different frequencies.
In the present work we report the first record of Chiroderma trinitatum Goodwin, 1958 for the state of Rondônia, northern Brazil. A map with all known records of C. trinitatum from Brazil is also presented. The record is based on a fluid preserved specimen with skull removed. The new record, though expected, fills a distributional gap in the Amazonic region of Brazil.
Multi-void space-charge electrets that have been formed by two fluoroethylenepropylene (Teflon®-FEP) films with internal surface charge layers of opposite polarity exhibit high piezoelectric coefficients. In these electrets, several charged bubbles are arranged in parallel. A significant voltage is generated between the electrodes when the arrangement is submitted to a mechanical force that acts perpendicular to the electrodes (direct piezoelectricity). The arrangement thus works in a similar manner as a large number of tiny electret microphones. In view of this mechanism, the size and the shape of the bubbles are important aspects for the design of sensor and actuator devices. In this paper, we therefore investigate the behavior of single air bubbles formed by two fluoroethylenepropylene (Teflon®-FEP) films theoretically and experimentally.
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