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Highlights: [•] The MPFs’ piezoelectric properties are lower than those of bulk ceramic counterpart. [•] The effect of geometrical shape is a main cause of the low-properties. [•] The effect of polarization also is the cause of the low-properties of the MPFs. [•] There is excellent agreement between the expected and experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract: (K, Na)NbO3-based lead free materials have been found to exhibit good piezoelectric properties due to the orthorhombic–tetragonal polymorphic phase transition (PPT) temperature compositionally shifted downward to near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties. In this work, new quaternary (1−x) (K0.4425Na0.52Li0.0375)(Nb0.8925Sb0.07Ta0.0375)O3 (KNLNST)–xSrTiO3 (ST) lead-free piezoelectric ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were also studied. The results of X-ray diffraction reveal that SrTiO3 diffuses into the KNLNST lattices to form a new solid solution with a perovskite structure. After the addition of SrTiO3, tetragonal–orthorhombic phase transition shifts to lower temperatures. The good piezoelectric properties of 0.995 KNLNST–0.005 ST material were found to be d 33∼295pC/N, k p∼42%, and ε r∼1902, with greatly improved temperature stability over the temperature range of 0–100°C, demonstrating practical potential for actuator and ultrasonic transducer applications. [Copyright &y& Elsevier]

Abstract: In a structural system with piezoelectric actuators, the damping effect can be achieved by properly switching the voltage on the actuators. Semi-active synchronized switch damping (SSD) approaches are typical switched-voltage control methods, which have recently been a topic of active research. In this study, the energy conversion of a SSD control system with an arbitrary switching frequency is investigated theoretically and validated numerically. First the general expression of the switched voltage on the piezoelectric actuator is derived. The results show that maximum voltage magnitude is obtained on the piezoelectric actuator when piezoelectric is switched at every odd number of displacement extrema. Next the average converted energy per vibration cycle is derived for an arbitrary switching frequency. The results show that the efficiency of energy conversion is reduced drastically even if the switching frequency is slightly deviated from the optimal frequency. Finally numerical simulation and experiments were carried out to validate the theoretical results. [Copyright &y& Elsevier]

The 0.55Pb(Ni1/3Nb2/3)O3–0.45Pb(Zr0.3Ti0.7)O3 (0.55PNN-0.45PZT) ceramics were prepared by conventional solid state reactions. The effects of calcining temperature on the particle size and piezoelectric properties of 0.55PNN-0.45PZT piezoelectric ceramics were investigated. The particle size and crystallinity of 0.55PNN-0.45PZT ceramic powders are influenced by calcining temperature, and therefore the microstructure and final piezoelectric properties of 0.55PNN-0.45PZT are different. The highest piezoelectric properties (d 33 = 720pC/N, k p = 0.55. ϵ r = 6255) were observed at the sample fabricated from the powder calcined at 1100°C, which was attributed to the improved crystallinity and the homogeneous distribution of the particles. [ABSTRACT FROM PUBLISHER]

Abstract: Considering the spillover and harmonic effect in real active vibration control, a novel composite controller based on disturbance observer (DOB) for the all-clamped panel is presented. The single-mode of the piezoelectric panel can be regarded as a second-order system. The unmodeled error of the current controlled mode, harmonic effects, uncontrolled mode effects, etc., are regarded as the lumped disturbances which can be estimated by the DOB, and the estimated value is used for the feed-forward compensation design. Then, an optimal linear quadratic regulator (LQR) strategy is employed for the feedback design. In order to solve the difficulty of determining the weight matrices of LQR, a chaos optimization method based on logistic map is proposed. So the weight matrices can be tuned automatically. Combining with a new transient performance function, the optimal weight matrices can be obtained. The composite controller can effectively suppress the lumped disturbances of the all-clamped panel. Experiment comparisons with conventional LQR are given to verify the effectiveness of the proposed method. [Copyright &y& Elsevier]

Abstract: In the paper, a vibration damping system powered by harvested energy with implementation of the so-called SSDV (synchronized switch damping on voltage source) technique is designed and investigated. In the semi-passive approach, the piezoelectric element is intermittently switched from open-circuit to specific impedance synchronously with the structural vibration. Due to this switching procedure, a phase difference appears between the strain induced by vibration and the resulting voltage, thus creating energy dissipation. By supplying the energy collected from the piezoelectric materials to the switching circuit, a new low-power device using the SSDV technique is proposed. Compared with the original self-powered SSDI (synchronized switch damping on inductor), such a device can significantly improve its performance of vibration control. Its effectiveness in the single-mode resonant damping of a composite beam is validated by the experimental results. [Copyright &y& Elsevier]

Abstract: BaTiO3 (BT) powders were synthesized by the hydrothermal method for fabricating lead-free barium titanate piezoelectric ceramics. The obtained powders were washed by distilled water and 0.01N acetic acid solutions separately, and utilized to obtain piezoelectric ceramics by traditional sintering. BT ceramics with the highest piezoelectric properties (d 33 value is over 190 pC/N) was obtained from the BT powder synthesized at 250°C and washed by acetic acid solution. The influence of washing method and sintering temperature on the piezoelectric properties of BT ceramics were studied. The reasons were investigated by comparing the properties of BT powders and their compacts sintered at different temperature. [Copyright &y& Elsevier]

Abstract: 0.55Pb(Ni1/3Nb2/3)O3–0.45Pb(Zr0.3Ti0.7)O3(PNN–PZT) ceramics with different concentration of xFe2O3 doping (where x =0.0, 0.8, 1.2, 1.6mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe2O3. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN–PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d 33 ~956 pC/N, the electromechanical coupling factor k p ~0.74, and the dielectric constant ε r ~6095 are achieved for the specimen with 1.2mol% Fe2O3 doping sintered at 1200°C for 2h. [Copyright &y& Elsevier]

This paper proposes a new energy harvesting architecture that optimizes the energy conversion under broadband vibrations, which is called adaptive synchronized switch harvesting (ASSH) technique. This technique is derived from the enhanced synchronized switch harvesting (ESSH) technique and based on a new and effective switch control law, which can prevent the switch in energy transferring circuit from over-frequent on-and-off and accordingly enhance the extracted power under multimode vibration. Compared with the ESSH technique, theoretical and experimental results demonstrate the new technique can improve electromechanical conversion efficiency when the piezoelectric energy harvester is excited under two-mode vibration, especially in the case of higher vibration amplitude of the second mode. The extracted power with the new technique is more than three times the ESSH technique in the case of the exciting signal of amplitude ratio (3:6). Furthermore, a self-powered circuit which implements the technique (ASSH) is proposed, which validates that the new technique can be truly self-powered, thus addressing the issue of harvesting environmental energy by autonomous devices. [ABSTRACT FROM AUTHOR]

Because of the good piezoelectric properties among polymers, poly(vinylidene fluoride) (PVDF) has been extensively applied in constructing flexible sensors and energy harvesters. Recent progress towards high performance sensors and energy harvesters has trigged significant interest in the fabrication of PVDF materials with superior piezoelectricity and good thermal piezoelectric stablility. Herein, we reported a flexible PVDF based nanocomposite that maintained high and stable piezoelectricity over a wide temperature range from 10 to 100 °C through the strong multi-interface effect. In this work, PVDF was firstly blended with poly(vinylidene fluoride- co -hexafluropropylene) (PVDF-HFP), and then dopamine modified BaTiO 3 hollow nanoparticles were introduced into the blend polymer matrix. Through optimizing the fabrication process and modulating the mass ratio of PVDF-HFP and BaTiO 3 , notably strenghthened ferroelectricity and piezoelectricity was achieved in the final composites, wherein the piezoelectric coefficient d 33 reached a peak of 40 pC/N and showed good retention with increasing temperatures up to 100 °C. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the synthesis and electromechanical characterization of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN–35PT) ceramics and fibers. To prevent the lead loss during the sintering of the fibers, lead-atmosphere was used during the sintering process. As a consequence, it was possible to ensure a good densification of the fiber and a pure perovskite phase. The electromechanical coupling factor and piezoelectric coefficient of the piezoelectric fiber were found to be k 31 =0.20 and d 31 =−130pC/N, respectively. These results are lower than ceramic sample properties (k 31 =0.32 and d 31 =−234pC/N). In order to determine reasons for these lower results in fiber shape sample, density and poling studies were performed. It is shown that fiber shape samples cannot be poled correctly because of the ratio between core and ceramic diameters. [Copyright &y& Elsevier]

To date, the fabrication of high-performance flexible energy harvesters/nanogenerators based on piezoelectric poly(vinyldene fluoride) (PVDF) is of great concern due to their huge potential to realize full-flexible self-powered electronics. Herein, in this work, we report a flexible piezoelectric nanogenerator (PNG) based on a textured hybrid film consisting of PVDF and manganese dioxide (MnO 2) nanorods. It is found that the combination of MnO 2 and PVDF can notably facilitate the formation of piezoelectric phase, increase the crystallinity and promote the polarization level, inducing dramatically strengthened piezoelectric and output activity for PVDF. Additionally, the addition of MnO 2 has the effect of significantly enhancing the mechanical property while slightly increasing dielectric constant of nanocomposites, which are advantageous to further harnessing the output enhancement. With an optimal loading of 1.0 wt% MnO 2 , the piezoelectric coefficient (d 33 ≈ 38 pC/N) and correspondingly output response of hybrid films reached the peak. For instance, under the d 33 working mode, an output voltage of 3.2 V can be achieved in hybrid films while that of PVDF is only 1.7 V. Image 1 • A novel piezoelectric PVDF based composite with highly aligned MnO2 rods was developed for energy harvesting application. • MnO2 rods can effectively promote interfacial polarization within PVDF and boosting piezoelectric and output responses. • The superior mechanical property while low dielectric constant of composites can further harness the output enhancement. [ABSTRACT FROM AUTHOR]

Transverse piezoelectric property of 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 (PZN-9%PT) single crystal poled along [011] direction under different fields have been investigated, the poling field giving the best property was between 350 and 650 V/mm at room temperature. Full tensorial elastic, dielectric, and piezoelectric properties of PZN-9%PT single crystal poled along the [011] direction under 500 V/mm have been determined by resonance and ultrasonic methods. It was found that the electromechanical coupling coefficients k32 and k33 can reach 0.90 and 0.89 and the piezoelectric coefficients d32 and d15 are –1705 and 2012 pC/N, respectively. This complete set of physical properties can provide convenience for piezoelectric device fabrication and domain engineering studies. [ABSTRACT FROM AUTHOR]