High Power Density Low-Lead-Piezoceramic-Polymer Composite Energy Harvester

Polymer-piezoceramic composites show mutual properties of piezoceramics and polymers that can be efficiently utilized in energy harvesting applications. Here we fabricated 0-3 composite films using high-performance low-lead piezoceramic (x)Bi(Ni1/2Zr1/2)0(3)-(1-x)PbTiOa (BNz-PT) as ceramic filler and polyvinylidene fluoride (PVDF) as polymer matrix. Unlike the conventional morphotropic phase boundary piezoelectrics such as the (1-x)PbTiO3-(x)PbZrO3, the large piezoelectric response of the BNZ-PT can be obtained by poling-induced cubic-like-totetragonal phase transformation. This leads to high piezoelectric coefficient of the PVDF-BNZ-PT composite films as well as highenergy harvesting performance. Composite films with different volume fractions of ceramic showed surface power density of 1.3-3.5 mu W/cm(2) , and volume power density of 72.2-175 mu W/cm(3) using simple bending and unbending movements. Energy harvester in the form of cantilever fixed at both ends showed surface power density of 56.97-163.63 mu W/cm(2) and volume power density of 3165-8165 mu W/cm(3) in response to impact pressure pulses. The generated power from the composite films is comparable to composite energy generators reported to date. The volume power density, however, is highest to the best of our knowledge among the reported 0-3 polymer-piezoceramic composite energy harvesters

Factors influencing the coupling between non-180 degrees domain switching and lattice strain in perovskite piezoceramics

Domain switching and lattice strain are known to be important processes contributing to the large electromechanical response observed in perovskite-based piezoelectrics. However, there is a lack of clarity regarding the coupling between the two phenomena, and the factors which influence this coupling. Here, we report a systematic investigation to understand the factors influencing the coupling between domain switching and lattice strain in perovskite piezoelectrics by x-ray diffraction in situ with electric field. In a slight departure from the conventional approach, we employ a strategy which enables x-ray diffraction study in situ with electric field on randomly oriented piezoelectric grains in their unclamped (free) state. Experiments were carried out on two different systems (1-x)PbTiO3-(x)BiScO3 and (1-x)PbTiO3-(x)PbZrO3 in their rhombohedral phase. We found that lattice strain along the nonpolar < 100 >(R) rhombohedral direction varies linearly with the non-180 degrees domain switching fraction (eta(111)). We introduce a parameter beta to characterize the strength of coupling between the two phenomena and show that the coupling is enhanced when the system approaches the morphotropic phase boundary. We also demonstrate that the grain-to-grain interaction nearly doubles this coupling in a dense piezoelectric ceramic

Response of cardiac pulse parameters in humans at various inclinations via 360° rotating platform for simulated microgravity perspective

Abstract On the Earth, the human body is designed and adapted to function under uniform gravitational acceleration. However, exposure to microgravity or weightlessness as experienced by astronauts in space causes significant alterations in the functioning of the human cardiovascular system. Due to limitations in using real microgravity platforms, researchers opted for various ground-based microgravity analogs including head-down tilt (HDT) at fixed inclination. However, in the present study, an investigation of response of various cardiac parameters and their circulatory adaptation in 18 healthy male subjects was undertaken by using an indigenously developed 360° rotating platform. Cardiac pulse was recorded from 0° to 360° in steps of 30° inclination using piezoelectric pulse sensor (MLT1010) and associated cardiac parameters were analyzed. The results showed significant changes in the pulse shape while an interesting oscillating pattern was observed in associated cardiac parameters when rotated from 0° to 360°. The response of cardiac parameters became normal after returning to supine posture indicating the ability of the cardiovascular system to reversibly adapt to the postural changes. The observed changes in cardiac parameters at an inclination of 270°, in particular, were found to be comparable with spaceflight studies. Based on the obtained results and the proposed extended version of fluid redistribution mechanism, we herewith hypothesize that the rotation of a subject to head down tilt inclination (270°) along with other inclinations could represent a better microgravity analog for understanding the cumulative cardiac response of astronauts in space, particularly for short duration space missions

Structural insights into electric field induced polarization and strain responses in K0.5_{0.5}Na0.5_{0.5}NbO3_3 modified morphotropic phase boundary compositions of Na0.5_{0.5}Bi0.5_{0.5}TiO3_3 -based lead-free piezoelectrics

K0.5Na0.5NbO3 (KNN)-modified morphotropic phase boundary (MPB) compositions of the two Na$_{0.5}$Bi$_{0.5}$TiO$_3$-based lead-free piezoelectrics, namely, 0.94Na$_{0.5}$Bi$_{0.5}$TiO$_3$−0.06BaTiO$_3$ (NBT-6BT) and 0.80Na$_{0.5}$Bi$_{0.5}$TiO$_3$−0.20K$_{0.5}$Bi$_{0.5}$TiO$_3$ (NBT-20KBT) are model systems exhibiting large (>0.4%) electric-field-driven strain. There is a general perception that (i) increasing KNN concentration monotonically weakens the direct piezoelectric response $(d_{33})$, and (ii) maximum electrostrain occurs when KNN pushes the system in the fully ergodic relaxor state. We have examined these issues using various complementary techniques involving electrostrain, piezoelectric coefficient $(d_{33})$, ferroelectric switching-current measurements, and field-driven structural studies on the global and local scales using laboratory and synchrotron x-ray diffraction, neutron powder diffraction, and Eu$^{+3}$ photoluminescence techniques. Our investigations revealed the following important features: (i) In the low-concentration regime, KNN induces a tetragonal ferroelectric distortion, which improves the weak signal piezoresponse. (ii) Beyond a threshold concentration, in-phase octahedral tilt sets in and weakens the long-range ferroelectric order to partially stabilize an ergodic state. (iii) The maximum electrostrain (∼0.6%) is achieved in the mixed (nonergodic + ergodic) state. (iv) The mixed state invariably exhibits a less-known phenomenon of field-driven ferroelectric-to-relaxor transformation during bipolar field cycling. (v) The enhanced electrostrain in the mixed state is associated with the electric field increasing the correlation lengths of the short-ranged tetragonal and rhombohedral ferroelectric regions without overall transformation of one phase to the other. We summarize the findings of this work in a comprehensive electric field composition (E-x) phase diagram. The findings reported here are likely to be true for other NBT-based MPB systems