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Generalized optimization method for energy conversion and storage efficiency of nanoscale flexible piezoelectric energy harvesters
摘要： The energy conversion and storage efficiency was commonly ignored in experimental studies on nanoscale flexible piezoelectric energy harvesters (PEHs). In this study, we develop a generalized theoretical method to optimize the energy conversion and storage efficiencies of nanoscale flexible PEHs. The results are validated by comparisons with experimental measurements for various ambient excitations. A simple scaling law is established to reveal the intrinsic correlation between the efficiency of energy conversion/storage and various system parameters of the PEHs. For either the energy conversion or storage circuit, the output power density may be maximized by properly designing an intrinsic normalized parameter. Furthermore, we demonstrate that an independent optimization criterion is indispensable for standard storage circuits since including a storage module into the conversion circuit redefines the electromechanical behavior of the PEH system. The results may be used as guidelines for optimizing the energy conversion and storage efficiencies of nanoscale flexible PEHs that have promising applications in harvesting biomechanical energies.
关键词： Scaling law,Optimization,Nanoscale flexible piezoelectric energy harvesters,Energy conversion,Energy storage
更新于2025-09-23 15:22:29
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Study on the thermal initiation of shelled PBXN-109 under laser irradiation
摘要： In order to investigate the thermal initiation mechanism of a warhead under laser irradiation, small scale experiments have been carried out with shelled PBXN-109 to obtain the initiation time and critical metal temperature. It was found that, as the laser power increases, the initiation time decreases exponentially; while the critical metal temperature increases linearly due to the effect of thermal conduct resistance. Based on theoretical analysis, a prediction model was built with a good accuracy for engineering application. In order to establish the relationship between the small-scale and the full-scale experiments, the scaling law of the thermal response process was approximated with that of the thermal conduct process, which was deduced through equation analysis to avoid the difficulty brought by the exponential nonlinearity from the equation of the thermal decomposition of the explosive.
关键词： laser,PBXN-109,metal,initiation,scaling law
更新于2025-09-23 15:19:57
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Thickness-dependent 109o domain evolution in multiferroic BiFeO3 thin films
摘要： Ferroelectric and ferroelastic 109o domain structure has great potentialities in ferroelectric and magnetoelectric devices. Understanding their structure is crucial to control the domain configurations for potential applications. In this work, a series of BiFeO3 (BFO) thin films with various thicknesses are investigated by piezoelectric force microscopy and transmission electron microscopy. Contrast analysis and electron diffractions reveal that the BFO films are mainly composed of 109o domains with small populations of charge domain walls and vortex structures. The domains are observed to be distributed periodically, and the sizes fall outside the validity range of the square root law, while a γ = 0.9 scaling exponent is revealed. These differences are discussed on the basis of ways of reducing the depolarization field energy by the coexistence of charge domain walls and vortex structures as well as bound charges near the surface.
关键词： 109o domains,BiFeO3,scaling law
更新于2025-09-19 17:15:36
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Partial Photoionization Cross Section of Collinear eZe Helium: Numerical Confirmation of Semiclassical Predictions
摘要： Based on the semiclassical theory of chaotic scattering, Tanner et al. [J. Phys. B 40, F157 (2007)] proposed the fluctuation in the partial photoionization cross section of helium below the double-ionization threshold would show the same characteristics as in the total cross section, predicting that the Fourier spectrum of the fluctuation reveals peaks at the classical actions of closed triple collision orbits and the amplitude of the fluctuation decreases algebraically as the energy approaches the double-ionization threshold. In that paper, however, the predictions were not clearly confirmed due to the lack of experimental data with sufficient accuracy. So instead, we calculate the partial photoionization cross sections of collinear eZe helium for the energy range from the single-ionization threshold I20 to I32 in order to numerically confirm the predictions. Analysis of the fluctuation in the partial cross section shows that the predictions are indeed valid. Our findings mean that the fluctuation in the partial photoionization cross section can be described by classical triple collision orbits in the semiclassical limit. Thus it explains in a natural way the mirroring and mimicking structures observed in cross section signals for different ionization channels.
关键词： Partial photoionization cross section,Collinear eZe helium,CTCO,Scaling law
更新于2025-09-10 09:29:36
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Equivalent electron correlations in nonsequential double ionization of noble atoms
摘要： Electron correlation is encoded directly in the distribution of the energetic electrons produced in a recollision-impact double ionization process, and varies with the laser ?eld and the target atoms. In order to get equivalent electron correlation effects, one should enlarge the laser intensity cubically and the laser frequency linearly in proportion to the second ionization potentials of the target atoms. The physical mechanism behind the transform is to keep the ponderomotive parameter unchanged when the laser frequency is enlarged.
关键词： double ionization,scaling law,electron correlation
更新于2025-09-09 09:28:46