Pavel Mokry

Pressure on charged domain walls and additional imprint mechanism in ferroelectrics

Note: 1098-0121094110 Reference LC-ARTICLE-2007-020doi:10.1103/PhysRevB.75.094110View record in Web of Science Record created on 2007-10-18, modified on 2017-11-27

Adaptive vibration suppression system: an iterative control law for a piezoelectric actuator shunted by a negative capacitor

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.

Evidence for dielectric aging due to progressive 180 degrees domain wall pinning in polydomain Pb(Zr0.45Ti0.55)O-3 thin films

An evidence that the dielectric aging in the polydomain Pb(Zr0.45Ti0.55)O-3 thin films is controlled by progressive pinning of 180 degrees domain walls is presented. To provide such a conclusion, we use a general method, which is based on the study of the time evolution of the nonlinear but anhysteretic dielectric response of the ferroelectric to a weak electric field. A thermodynamic model of the ferroelectric system where the dielectric response is controlled by bending movements of pinned 180 degrees domain walls is developed. Within this model, the nonlinear permittivity of the ferroelectric is expressed as a function of the microstructural parameters of the domain pattern. It is shown that by using the analysis of the time evolution of the nonlinear permittivity, it is possible to estimate changes in the concentration of the pinning centers that block the movements of the 180 degrees domain walls during aging in polydomain perovskite ferroelectrics.

Sound shielding by a piezoelectric membrane and a negative capacitor with feedback control

The design and realization of an adaptive sound-shielding system based on a method to control the effective elastic stiffness of piezoelectric materials are presented in this paper. In this system, the sound-shielding effect is achieved by a sound reflection from the piezoelectric curved membrane fixed in rigid frame and connected to an active analog circuit that behaves as a negative capacitor. The acoustic transmission loss through the curved membrane was measured for the incident sound of frequency 1.6 kHz and of acoustic pressure level 80 dB. When the negative capacitor in the system was properly adjusted, the acoustic pressure level of the transmitted sound was reduced from the initial 60 dB to 15 dB by the action of the negative capacitor. Then the system was exposed to naturally changing operational conditions, and their effect on sound-shielding efficiency was studied. It is shown that the acoustic transmission loss of the system dropped by 35 dB within 30 min from the moment of negative capacitor adjustment. Therefore, a self-adjustment of the system has been implemented by appending an additional digital control circuit to the negative capacitor. It is shown that the aforementioned deteriorating effect has been eliminated by the adjusting action of the control circuit. The long-time sustainable value of 60 dB in the acoustic transmission loss of the adaptive sound shielding system has been achieved.

Application of piezoelectric macro-fiber-composite actuators for the suppression of noise transmission through curved glass plates

An investigation on the application of the piezoelectric Macro-Fiber-Composite (MFC) actuators for the suppression of the noise transmission through the curved glass plates is presented. It is known that when the incident sound wave in the air hits the glass plate or curved plate or shell, part of the acoustic wave is reflected, which makes the plate vibrate, and part of the wave is transmitted. It is easy to understand that the higher the flexural rigidity of the glass plate the bigger part of the acoustic sound wave is reflected than transmitted. This simple physical phenomenon can be profitably used for the suppression of the noise transmission through glass plates. The noise suppression effect is achieved using the MFC actuator, which is attached to the vibrating glass plate. When the piezoelectric MFC actuator is shunted by the active electronic circuit, which has a negative capacitance, it is possible to greatly suppress the vibration of the glass plate and also the noise transmission through the glass plate. The sound shielding efficiency of the glass plate is measured by the acoustic transmission loss (TL), which is expresed in decibel scale. If the amplitude of the window vibrations decreases, the value of TL increases. The effect of the glass plate geometry, and the electrical properties of the active shunt circuit on the enhancement of TL is analyzed using Finite Element Method numerical simulations. The comparison of the results of numerical simulations with acoustic measurements is presented. The possibility of the use of this method for the suppression of the noise transmission through the glass window plates is discussed.

Identification of defect distribution at ferroelectric domain walls from evolution of nonlinear dielectric response during the aging process

The motion of ferroelectric domain walls greatly contributes to the macroscopic dielectric and piezoelectric response of ferroelectric materials. The domain-wall motion through the ferroelectric material is, however, hindered by pinning on crystal defects, which substantially reduces these contributions. Here, using thermodynamic models based on the Landau-Ginzburg-Devonshire theory, we find a relation between the microscopic reversible motion of nonferroelastic 180 degrees domain walls interacting with a periodic array of pinning centers and the nonlinear macroscopic permittivity. We show that the reversible motion of domain walls can be split into two basic modes: first, the bending of a domain wall between pinning centers, and, second, the uniform movement of the domain-wall plane. We show that their respective contributions may change when the distribution of pinning centers is rearranged during the material aging. We demonstrate that it is possible to indicate which mechanism of the domain-wall motion is affected during material aging. This allows one to judge whether the defects only homogeneously accumulate at domain walls or prefer to align in certain directions inside the domain-wall plane. We suggest that this information can be obtained using simple macroscopic dielectric measurements and a proper analysis of the nonlinear response. Our results may therefore serve as a simple and useful tool to obtain details on domain-wall pinning in an aging process.

Numerical simulation of mechanical behavior of a Macro Fiber Composite piezoelectric actuator shunted by a negative capacitor

Numerical simulations of the elastic properties of Macro Fiber Composite (MFC) actuator shunted by an electric circuit with a negative capacitance are presented. If connected in parallel to the piezoelectric plate, the circuit with a negative capacitance has a significant influence on the elastic parameters of the piezoelectric actuator. Such an effect can be profitably used for a vibration and noise suppression, where the piezoelectric element works as an actuator and a sensor at the same time. The major advantages of the piezoelectric fiber composite actuators are their high performance, flexibility, and durability, when compared to the traditional piezoceramic (PZT) actuators. The recently developed MFC actuator provides these advantages and can be used in structural vibration applications. In this study, it is shown that the MFC can be controlled by the circuit with a negative capacitance. Finite Element Method (FEM) approach is used to obtaining frequency spectra of capacitance of MFC actuator and to show the ability to change the effective elastic parameters, when connected to the negative capacitance circuit.

A system for the vibration suppression in the broad frequency range using a single piezoelectric actuator shunted by a negative capacitor

A system for the vibration suppression using a single piezoelectric actuator is presented. The method is based on the fact that the transmission of vibrations between two objects can be reduced through an extremely soft element, which is placed between those objects. It is also known that by connecting a negative capacitor to the piezoelectric actuator it is possible to create an element whose elasticity can be arbitrarily tuned. Therefore, by combining these two principles, a new vibration control system, which consists of a piezoelectric actuator connected to a negative capacitor, has been realized. High efficiency of the vibration transmission suppression is achieved when the amplitude and phase of the piezoelectric actuator impedance matches (except the sign) the amplitude and phase of the negative capacitor impedance. The frequency, at which the both dependencies are intersecting, can be controlled by adjustable circuit elements of the negative capacitor. Every single setting of the negative capacitor parameters is optimal just for one corresponding frequency of the incident vibrations. In the case of vibration suppression in a broader frequency range, the frequency dependence of the negative capacitor capacitance has to match the frequency dependence of the piezoelectric element capacitance within the entire considered frequency range. By one single optimal setting of the negative capacitor parameters can be efficiently suppressed the transmission of vibrations with several harmonic components or with a random component. Two difficulties have been solved in the presented realization: first, the electronic arrangement that allows the extremely accurate adjustment of the negative capacitor circuit parameters and, second, the principle which allows achieving exactly the desired frequency impedance characteristics of the negative capacitor. It is shown that such an arrangement allows the realization of a simple and compact system, which, however, offers great vibration isolation efficiency in variable vibration conditions.

Planar acoustic metamaterials with the active control of acoustic impedance using a piezoelectric composite actuator

In the paper, there are presented methods for a precise active control of the acoustic impedance of large planar structures, e.g glass plates or shells, by means of distributed flexible piezoelectric composite actuators which are connected to passive or active electronic shunt circuits. Design of tunable acoustic metamaterials is realized using Finite Element Method simulations and their acoustic properties are evaluated using acoustic transmission loss measurements. Static and dynamic displacements of the metamaterials produced by electric voltage are measured using Digital Holographic Interferometry. We believe that deep understanding of presented systems should result in future applications that improve the quality of everyday life.

Analysis of noise transmission through the window glass plate and its control using the Macro Fiber Composite actuator

Glass windows are integral parts of buildings for several centuries. Unfortunately, they represent a major source of the interior noise, since they usually do not represent an effective sound barrier due to their low flexural rigidity. The aim of this work is to understand the sound transmission through the glass window and to analyze and demonstrate a new approach to reduce the noise transmission through the glass plate using a Macro Fiber Composite (MFC) piezoelectric actuator. The principle of Active Piezoelectric Shunt Damping (APSD) is used to achieve the required suppression of the noise transmission‥ The system is modeled by Finite Element Method (FEM) numerical simulations. The results are experimentally verified using Digital Holographic Interferometry (DHI).