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The energy conversion potential of ferroelectric materials originating from their phase transitions, in particular temperature ranges and electric field values, is very promising. Pyroelectric energy harvesting consists of directly converting thermal energy into electrical energy. Due to its high energy conversion potential, the Olsen cycle is the most favorable for pyroelectric energy harvesting. This cycle includes two isothermal and two constant electric field branches. In this study, the Olsen cycle was modeled, then varying temperatures and applied electric field directions for different crystal orientations were simulated. Polarization responses were obtained via the Landau–Devonshire theory. Then, an innovative way to model the electrocaloric effect was proposed; experimental results and first-principle calculations confirmed the simulation results. The resulting negative electrocaloric effect due to crystal orientation, previously reported in the literature, has been successfully simulated through a phenomenological approach. Finally, we identified which phase transitions are interesting for pyroelectric energy harvesting applications depending on crystal orientations while obtaining an energy density in the order of ≈ 10 2 mJ / cm 3. This value corresponds to previous results in the literature. [ABSTRACT FROM AUTHOR]

Magnetic losses in a laminated ferromagnetic core have been studied for years. However, magnetization mechanisms are complex, and the ideal model is still lacking. Classic resolution in the time domain combines a 1D magnetic diffusion equation with a viscosity-based magneto dynamic material law (first-order differential equation). This simultaneous resolution has already been solved by matrix inversion: the diffusion equation temporal term is replaced by its differential equation expression. It leads to a fast solution but overestimates the excess losses linked to the dynamic of the magnetic domains wall motions. Improved material laws using power operators have alternatively been tested. However, it is impossible to regroup the magnetic field terms on the same side of the final equation, and the resolution can only go through complex iterative methods (fixed point, Newton-Raphson). In this study, we propose to combine a fractional diffusion equation and a fractional viscosity-based magneto dynamic differential equation. Matrix resolution is possible, such as an accurate simulation of the dynamic behavior by adjusting the fractional order. The space term of the diffusion equation being solved by space discretization, the combined resolution leads to local information (excitation and induction fields). The number of dynamic parameters is limited but large enough for excellent simulation results. [ABSTRACT FROM AUTHOR]

Structural, dielectric, and ferroelectric properties, and electrocaloric effects of pure and Gd doped (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics prepared by the conventional solid-solid method have been carried out. The X-ray diffraction analysis confirms a pure perovskite structure with the coexistence of tetragonal and rhombohedra structures in both powders. The thermal and frequency dependences of the dielectric constants of both ceramics revealed relaxor behavior. The two compounds exhibited two phase transitions: ferroelectric/antiferroelectric (FE/AFE) transition followed by an antiferroelectric/paraelectric (AFE/PE) transition at higher temperatures. Remarkably, we noticed that the small amount of Gd doping (2%) highly enhanced the dielectric properties of the parent compound by about 71%. The phase diagram was as well influenced by the Gd doping, where the FE/AFE transition temperature rose from 90 in the parent compound to 115°C in the doped one whereas the AFE/PE transition temperature was decreased from 320 to 270°C, respectively. The direct electrocaloric measurements performed on both compounds showed that the ferroelectric/antiferroelectric phase transition was accompanied by a significant electrocaloric effect. The Gd3+ doping improved the electrocaloric properties of the parent compound, where a remarkable temperature variation of 1.4K was obtained in the doped ceramic. The results of the direct electrocaloric measurements will be compared and discussed with those derived from the indirect method. [ABSTRACT FROM AUTHOR]

We propose an approach to solve the coupled problem of the magnetic field penetration into soft ferromagnets and a frequency dependent magnetic hysteresis. The magnetic field diffusion is related to the macroscopic eddy currents. The hysteresis model is related to the microscopic eddy currents derived from the magnetic domain wall movements, and is responsible for the frequency dependence of hysteresis loops. In this paper, based on a lumped model and fractional derivative operators, we demonstrate that it is possible to replace the coupled diffusion/dynamic hysteresis in a simplest formulation using fractional operators. Such a formulation can be solved easily. Instead of solving a 1D problem of diffusion, we show here that a lumped model with appropriate fractional time derivative operator can be an exact formulation of the problem. In addition, we confirm that the model is using experimental available information, obtained by standard single sheet tester measuring bench (the tangential surface excitation field, and the cross section average induction). [ABSTRACT FROM AUTHOR]

This paper reviews the use of the fractional derivative operators for the dynamic magnetization of ferromagnetic specimens. Magnetic behaviors in ferromagnetic specimens are strongly nonlinear and frequency dependent. Magnetism has an atomic origin but the magnetic behavior as observed at the human scale is highly affected by phenomena occurring at larger scales. Under the influence of an external magnetic field, the homogeneity of a ferromagnetic sample magnetization is linked to the excitation dynamics. Models and simulations in this domain are strongly needed, as they provide theoretical explanations and allow us to anticipate complex phenomena, difficult to observe in a practical way. On the one hand, such multi-scale dynamical behaviors can hardly be taken into account with the usual mathematical operators. On the other hand, correct simulation results on large frequency bandwidths can be obtained using fractional derivative operators. The use of fractional derivatives can be envisaged through different approaches: Lump models based on time fractional differential equations is one option, and fractional anomalous diffusion equations is another. In this manuscript, these two methods are detailed and compared. Theoretical results are compared to experimental ones, and conclusions and perspectives are drawn such as possible improvements. [ABSTRACT FROM AUTHOR]

The present article proposes a dynamical model to obtain ferroelectric hysteresis dynamics based on fractional derivatives. The consideration of a fractional derivative term widely increases the frequency bandwidth of the accuracy of the traditional hysteresis models. As a consequence, the model is suited for successfully taking into account the well-known scaling relations of the ferroelectric hysteresis area, , versus the frequency, f, and field amplitude, E0. Under low frequency excitation, simulation tests provided good results regarding the comparison of the fractional model, experimental results and the well-known nonentire power law ∞f1/3E02/3 (where represents the hysteresis loop area). These results were followed by comparing the hysteresis area obtained from the fractional model with that from the well known scaling relations as f→∞, and the results were proposed as validation of the high frequency behavior. Next, the model was tested on large frequency bandwidths (>6 decades) and validated with success using the comparison between simulation tests and the only experimental results available in literature obtained in such conditions by Liu et al. [J. Phys.: Condens. Matter 16, 1189 (2004)] for BNT thin film samples. [ABSTRACT FROM AUTHOR]

This paper presents a model describing the hysteresis in ferroelectric materials at moderate to high driving levels. Hysteresis and nonlinearities are attributed to the irreversible displacement of domain walls. The model, based on a simple mechanism related to the dry-friction concept, is developed to describe the hysteresis of polarization and strain under electric field and stress. Besides coefficients such as [variant_greek_epsilon]33 and d33 also exhibit large hysteresis loops under high electric and/or mechanic level. In this paper it is shown that modeling macroscopic quantities such as P or S hysteresis lead to a reasonable estimate of the coefficients since their behavior depends mainly on polarization. The proposed approach is developed, discussed, and compared with experimental results from Navy II piezoelectric transducer ceramic. Comparisons on hysteresis loops are given and are in good agreement for the polarization and strain versus electric field and, to a less extent, for the coefficients [variant_greek_epsilon]33 and d33. The linear and Rayleigh regime are deduced from the proposed approach. [ABSTRACT FROM AUTHOR]

Synchronized switch damping (SSD) principle and derived techniques have been developed to address the problem of structural damping. Compared with standard passive piezoelectric damping, these new semi-passive techniques offer the advantage of self-adaptation with environmental variations. Unlike active damping systems, their implementation does not require any sophisticated signal processing nor any bulky power amplifier. This paper presents an enhancement of the SSD technique on voltage source (SSDV) which is the most effective of the SSD techniques. The former SSDV technique uses a constant continuous voltage sources whereas the proposed enhancement uses an adaptive continuous voltage source which permits fitting the mechanical braking force resulting from the SSDV process to the vibration level. A theoretical analysis of the SSDV techniques is proposed. Experimental results for structural damping under single frequency and for vibration control of a smart board under white noise excitation are presented and confirm the interest of the enhanced SSDV compared to other SSD techniques. Depending on the excitation type, a 4- to 10-dB damping gain can be achieved. [ABSTRACT FROM AUTHOR]