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    Design and testing of an efficient and compact piezoelectric energy harvester
    (ELSEVIER SCI LTD, 2011) Korla, S.; Leon, R. A.; Tansel, I. N.; Yenilmez, A.; Yapici, A.; Demetgul, M.
    Piezoelectric materials generate electricity when they are subjected to dynamic strain. In this paper compact size self contained energy harvesters were built by considering typical space available for AA size batteries. Each of the harvesters contains a rectifier circuit with four diodes and a capacitor. A series of piezoelectric energy harvesters with circular and square cross-sections were built and tested at different frequency and amplitude levels. On 1 M Omega impedance digital oscilloscope, it was observed that the voltages reached to 16 V (round cross-section) and 25 V (square cross-section) at 50 Hz frequency. The highest power output accomplished was 625 mu W. The outputs of both types of the harvesters were very similar at low amplitudes. However, the square cross-section facilitates better attachment of the piezoelectric elements with the harvester shell and worked efficiently at higher amplitudes without immediate failure. (C) 2010 Elsevier Ltd. All rights reserved.
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    Development of piezoelectric strain gages for structural health monitoring applications
    (AMER INST PHYSICS, 2007) Yenilmez, A.; Yapici, A.; Velez, C.; Tansel, I. N.
    The strain monitoring capability of piezoelectric materials was experimentally studied. Patches and fibers were considered for this purpose. A piezoelectric stripe actuator was used to obtain the typical signal of patches. Two designs were considered for the piezoelectric fibers. The first one was a commercial energy harvesting device with long fibers. The ends of the fibers were loose. In contrast, we designed a small piezoelectric strain gage with short fibers. Fibers were attached to wires at two ends with conductive resin. The piezoelectric strip actuator, and commercial energy harvesting device were connected to digital oscilloscope directly. A charge amplifier was used to condition the signals of the small piezoelectric strain gage with short fibers. All the units were attached to a beam and excited at different frequencies to evaluate the characteristics of their signals.
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    Representation of the characteristics of piezoelectric fiber composites with neural networks
    (AMER INST PHYSICS, 2007) Yapici, A.; Bickraj, K.; Yenilmez, A.; Li, M.; Tansel, I. N.; Martin, S. A.; Pereira, C. M.
    Ideal sensors for the future should be economical, efficient, highly intelligent and capable of obtaining their operation power from the environment. The use of piezoelectric fiber composites coupled with a low power microprocessor and backpropagation type neural networks is proposed for the development of a simple sensor to estimate the characteristics of harmonic forces. Three neural networks were used for the estimation of amplitude, gain and variation of the load in the time domain. The average estimation errors of the neural networks were less than 8% in all of the studied cases.
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    Resign of energy scavengers with the help of finite element packages
    (AMER INST PHYSICS, 2007) Yenilmez, A.; Yapici, A.; Tansel, I. N.; Martin, S. A.; Pereira, C. M.; Roth, L. E.
    Self-powering sensors have been desired for future platform sensor networks to minimize wiring and related problems. The selection of the proper area of piezoelectric patches at various operating conditions is an important challenge since the selection of a large patch area increases the complexity and weight. The small patch area could not provide enough energy to operate the electronics continuously. Many Finite Element Method (FEM) packages are capable of estimating the electricity after the stress or strain distribution is calculated. In this paper, the required energy for smart sensors is briefly discussed and the use of FEM is suggested for selection of the size and best location of the piezoelectric patch. The study indicated that the oscillation frequency affects the mode shape and the generated energy drastically. FEM is very useful to determine the mode shapes and the selection of patch locations with maximum dynamic strain.