Papers by Keyword: Frequency Dependence

Abstract: In this paper we present comparative study of frequency dependencies of an effective nonlinear elastic modulus of the three widely used glassy polymers, polystyrene, PMMA and polycarbonate. For measurements we use the methodology based on the acousto-elastic effect and analysis of variations in ultrasonic wave velocities under static stress applied to samples. The absolute values of the effective modulus γ = l − 2m, representing a combination of the Murnaghan moduli l and m, demonstrated pronounced nonlinear dependencies on the ultrasonic wave frequency for polystyrene and PMMA. At higher frequencies above ∼1 MHz no significant variations of the modulus occurred, while at lower frequencies down to 400 kHz its absolute value demonstrated a rapid rise of more than an order of magnitude. In polycarbonate the dependence was much less evident, the modulus γ also demonstrated some slight rise in the absolute value at lower frequencies, but the rise was not profound, less than two-fold and almost within the experimental error bars. The origin of the differences in nonlinear elastic properties of polystyrene/PMMA and polycarbonate requires further and more detailed investigation.

Abstract: We propose fabrication method of a planar quadrupole microelectrode for dielectrophoresis (DEP), which is fabricated by Au thin-film, ion coater and box cutter. This method is more cost effective and simpler than previous existing methods. We conducted two experiments for confirming usefulness of the Au DEP chip. Those are separation of yeast cells and trap force of DEP. To separate yeast cells, we used viable and non-viable cells. DEP force arises when an inhomogeneous AC electric field and sine wave frequency were applied to microelectrode. The Au DEP chip is able to distinguish between viable and non-viable cells and separate them by frequency dependence and the flow with Syringe pump. The chip can obtain viable cells which were trapped without contact to the microelectrode. The viable cells can use for fusion or cell culture. Furthermore, we carried out another experiment to investigate the trap force. The trap force of Negative-DEP becomes gradually weak when the frequency increases with 0.1, 0.5 and 1MHz. We were able to confirm relation between trap force and frequency by the Au DEP chip. The trap force has frequency dependence. Through the two experiments, we have established usefulness of the Au DEP chip.

Abstract: We propose fabrication method of a planar quadrupole microelectrode for dielectrophoresis (DEP), which is fabricated by Au thin-film, ion coater and box cutter. This method is more cost effective and simpler than previous existing methods. We conducted two experiments for confirming usefulness of the Au DEP chip. Those are separation of yeast cells and trap force of DEP. To separate yeast cells, we used viable and non-viable cells. DEP force arises when an inhomogeneous AC electric field and sine wave frequency were applied to microelectrode. The Au DEP chip is able to distinguish between viable and non-viable cells and separate them by frequency dependence and the flow with Syringe pump. The chip can obtain viable cells which were trapped without contact to the microelectrode. The viable cells can use for fusion or cell culture. Furthermore, we carried out another experiment to investigate the trap force. The trap force of Negative-DEP becomes gradually weak when the frequency increases with 0.1, 0.5 and 1MHz. We were able to confirm relation between trap force and frequency by the Au DEP chip. The trap force has frequency dependence. Through the two experiments, we have established usefulness of the Au DEP chip.

Abstract: Manganese doped cobalt nano ferrites were synthesized by co-precipitation method having general formula Co1-xMnxFe2O4 (x =0.0-1.0). These materials are studied to analyze the structural effects on the associated materials properties. The prepared samples were heat treated at 7500 C for two hours. Sintering effect on the structural properties was investigated. The lattice constants of samples were measured from X-rays diffraction data. The (311) peak was used to find crystallites size by the Scherrer formula. Structural morphology was observed by scanning electron microscopy. Variation with temperature in electrical resistivity (DC) and drift mobility were also investigated. The variations with frequency and composition in AC electrical properties of prepared samples were determined. The structural and electrical properties demonstrated firm association. Saturation magnetization, coercivity and remanence of the samples were discussed with the help of sharing of cations within crystals.

Abstract: Frequency dependence on image reconstruction for a buried conducting cylinder is investigated. A conducting cylinder of unknown shape scatters the incident wave in free space and measured the scattered field. By using measured fields, the imaging problem is reformulated into an optimization problem and solved by the steady-state genetic algorithm (SSGA). Numerical results show that the reconstruction is quite well in the resonant frequency range. This work provides both comparative and quantitative information

Abstract: In recent years, piezoelectric actuator is being widely used in vibration suppression and micro positioning applications for its fast response, nanometer resolution, no backlash, no friction and bigger driving force. However, its inherent hysteresis nonlinear characteristics between the input voltage and output displacement limit its control accuracy. To optimize the performance of piezoelectric actuator, it is essential to understand the hysteresis nonlinear behavior. In this work, the hysteresis nonlinear behavior was studied by experiment; the dependence of output characteristics on voltage under different electric field conditions in piezoelectric actuator was discussed. It was found that the input method and frequency of loading voltage has a great effect on the hysteresis nonlinearity of piezoelectric actuator. At last, some different hysteresis nonlinear models were introduced.