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Novakova K.,Technical University of Liberec | Mokry P.,Technical University of Liberec | Vaclavik J.,Research Center for Special Optics and Optoelectronic Systems
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

This paper analyzes the possibility of increasing the acoustic transmission loss of sound transmitted through planar or curved glass shells using attached piezoelectric macro fiber composite (MFC) actuators shunted by active circuits with a negative capacitance. The key features that control the sound transmission through the curved glass shells are analyzed using an analytical approximative model. A detailed analysis of the particular arrangement of MFC actuators on the glass shell is performed using a finite element method (FEM) model. The FEM model takes into account the effect of a flexible frame that clamps the glass shell at its edges. A method is presented for the active control of the Young-s modulus and the bending stiffness coefficient of the composite sandwich structure that consists of a glass plate and the attached piezoelectric MFC actuator. The predictions of the acoustic transmission loss frequency dependencies obtained by the FEM model are compared with experimental data. The results indicate that it is possible to increase the acoustic transmission loss by 20 and 25 dB at the frequencies of the first and second resonant modes of the planar and curved glass shells, respectively, using the effect of the shunt circuit with a negative capacitance. © 2012 IEEE. Source

Gureev M.Y.,Ecole Polytechnique Federale de Lausanne | Mokry P.,Research Center for Special Optics and Optoelectronic Systems | Tagantsev A.K.,Ecole Polytechnique Federale de Lausanne | Setter N.,Ecole Polytechnique Federale de Lausanne
Physical Review B - Condensed Matter and Materials Physics

The interaction of electric field with charged domain walls in ferroelectrics is theoretically addressed. A general expression for the force acting per unit area of a charged domain wall carrying free charge is derived. It is shown that, in proper ferroelectrics, the free charge carried by the wall is dependent on the size of the adjacent domains. As a result, the mobility of such domain wall (with respect to the applied field) is sensitive to the parameters of the domain pattern containing this wall. The problem of the force acting on a charged planar 180 ∞ domain wall normal to the polarization direction in a periodic domain pattern in a proper ferroelectric is analytically solved in terms of Landau theory. In small applied fields (in the linear regime), the force acting on the wall in such pattern increases with decreasing the wall spacing. It is shown that the domain pattern considered is unstable in a defect-free ferroelectric. The poling of a crystal containing such pattern, stabilized by the pinning pressure, is also considered. Except for a special situation, the presence of charge domain walls makes poling more difficult. The results obtained are also applicable to zigzag walls under the condition that the zigzag amplitude is much smaller than the sizes of the neighboring domains. © 2012 American Physical Society. Source

Kodejska M.,Technical University of Liberec | Mokry P.,Research Center for Special Optics and Optoelectronic Systems | Linhart V.,Technical University of Liberec | Vaclavik J.,Research Center for Special Optics and Optoelectronic Systems | Sluka T.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

An adaptive system for the suppression of vibration transmission using a single piezoelectric actuator shunted by a negative capacitance circuit is presented. It is known that by using a negative-capacitance shunt, the spring constant of a piezoelectric actuator can be controlled to extreme values of zero or infinity. Because the value of spring constant controls a force transmitted through an elastic element, it is possible to achieve a reduction of transmissibility of vibrations through the use of a piezoelectric actuator by reducing its effective spring constant. Narrow frequency range and broad frequency range vibration isolation systems are analyzed, modeled, and experimentally investigated. The problem of high sensitivity of the vibration control system to varying operational conditions is resolved by applying an adaptive control to the circuit parameters of the negative capacitor. A control law that is based on the estimation of the value of the effective spring constant of a shunted piezoelectric actuator is presented. An adaptive system which achieves a self-adjustment of the negative capacitor parameters is presented. It is shown that such an arrangement allows the design of a simple electronic system which offers a great vibration isolation efficiency under variable vibration conditions. © 2012 IEEE. Source

Psota P.,Technical University of Liberec | Psota P.,Research Center for Special Optics and Optoelectronic Systems | Ledl V.,Technical University of Liberec | Ledl V.,Research Center for Special Optics and Optoelectronic Systems | And 4 more authors.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

A method for the measurements of the out-ofplane displacement on the surface of vibrating object is presented herein. This method is based on frequency-shifted timeaveraged digital holographic interferometry, employing the principle of phase shifting. This approach allows for significant noise reduction, which results in high sensitivity of measurements. This method makes it possible to measure vibrations with amplitudes in the nanometer range over the whole measured surface. This method was applied to the visualization of the out-of-plane vibration modes of piezoelectric transformers. The amplitude and modal shapes were measured with a very high resolution. Furthermore, aspects influencing the measurement errors are discussed and the measurement results by holographic method were compared with the well-established single-point laser interferometry measurement method. © 2012 IEEE. Source

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