A comparison between nonlinear cantilever and buckled beam for energy harvesting

Nonlinear dynamics has become one of the key aspect to improve the efficiency of kinetic energy harvesters working in the real environment. Different methods based on the exploitation of the dynamical features of stochastic nonlinear oscillators using bi-stable piezoelectric cantilevers or buckled beams have been proposed in the past years. Such methods are shown to outperform standard linear oscillators and to overcome some of the most severe limitations of present approaches once applied to ambient vibrations. This work presents simulation results comparing the two methods. The same piezoelectric element subjected to a fixed vibrating body in a cantilever or bridge configuration has been simulated. The kinetic excitation considered is a zero mean exponentially correlated gaussian noise with different amplitudes. The piezoelectric oscillator output response has been obtained as a function of a nonlinear parameter. This work is intended to help designing the most performing energy harvester for real world applications starting from the same piezoelectric element.     

Nonlinear optimization of acoustic energy harvesting using piezoelectric devices

In the first part of the paper, a single degree-of-freedom model of a vibrating membrane with piezoelectric inserts is introduced and is initially applied to the case when a plane wave is incident with frequency close to one of the resonance frequencies. The model is a prototype of a device which converts ambient acoustical energy to electrical energy with the use of piezoelectric devices. The paper then proposes an enhancement of the energy harvesting process using a nonlinear processing of the output voltage of piezoelectric actuators, and suggests that this improves the energy conversion and reduces the sensitivity to frequency drifts. A theoretical discussion is given for the electrical power that can be expected making use of various models. This and supporting experimental results suggest that a nonlinear optimization approach allows a gain of up to 10 in harvested energy and a doubling of the bandwidth. A model is introduced in the latter part of the paper for predicting the behavior of the energy-harvesting device with changes in acoustic frequency, this model taking into account the damping effect and the frequency changes introduced by the nonlinear processes in the device.     

蒙特卡罗法在高功率激光系统输出能量稳定性研究中的应用

以"四程 助推"放大系统为例,运用蒙特卡罗(Monte-Carlo)法计算分析了放大过程中注入能量、放大增益及损耗单独存在随机变化和以上因素共同作用时对系统输出能量稳定性的影响.计算结果表明,系统输出能量稳定性对四程小信号增益系数和腔内光学元件透过率的随机变化相当敏感;小信号增益随机变化明显大于注入能量对输出能量稳定性的影响.同时,也说明应用蒙特卡罗方法解决随机性问题的有效性和简洁性.     

椎弓根钉植入针道上骨组织光谱特性研究

运用光谱技术研究了椎骨组织不同位置的特征识别因子.光谱采集系统由双光纤手钻一体式探头(光纤芯径200 μm,中心距离0.5 mm)、卤素光源(波长360~2 000 nm)、光纤光谱仪(检测波长为200~1 100 nm)和计算机组成,可以同时获得生物组织的漫反射光谱和约化散射系数.以猪椎骨为实验对象,测量椎弓根螺钉植入针道上不同骨组织的漫反射光谱和约化散射系数,并对光谱进行特定波长的峰值、面积、斜率分析,获得特性识别因子.研究发现,椎弓根钉植入针道上不同骨组织的光谱表现出不同的变化特性.其中峰值的变化比约化散射系数的变化高1.88倍,面积的变化比约化散射系数的变化高2.05倍.在495~505 nm处,骨密质和骨疏质的光谱斜率都为正值;在520~535 nm处,骨密质光谱的斜率为正值,而骨疏质光谱的斜率为负值.结果表明,通过光谱特性分析获得的峰值、面积和斜率因子能够有效地区分针道上骨密质与骨疏质的差异.     

The time derivative of information gain as excess entropy production

An information gain depending on two nonequilibrium coarse-grained statistical operators is discussed. The relation between the time derivative of information gain and excess entropy production is derived. Prigogine's stability criterion is expressed by means of the information gain. It is shown in the domain of linear nonequilibrium thermodynamics that zero time derivative of information gain corresponds to a minimum of entropy production and K theorem can be formulated.     

高温压电材料、器件与应用

作为重要的功能材料,压电材料已经在国民经济的多个领域里有着重要应用.随着现代工业的快速发展,特别是新能源、交通和国防工业的高速发展,功能材料的应用已经从常规使用转向极端环境下的服役.本文综述了具有高居里点的压电材料,包括钙钛矿型压电陶瓷、铋层状结构氧化物压电陶瓷、钨青铜结构压电陶瓷以及非铁电压电单晶等;介绍了其晶体结构特征和高温压电性能、最新研究进展,并列举了一系列的高温压电器件和应用,包括高温压电探测器、传感器、换能器和驱动器等.另外,本文总结了高温压电材料的热点研究问题,并展望了今后的发展方向.     

Optimization and implementation of piezoelectric radiators using the genetic algorithm

Very thin and small (45 mm x 35 mm x 0.35 mm) piezoelectric radiators have been developed in this research. The system is modeled by using the energy method in conjunction with the assumed-modes method. Electrical system, mechanical system, and acoustic loading have all been accounted for during the modeling stage. On the basis of the simulation model, the genetic algorithm (GA) is employed to optimize the overall configurations for a low resonance frequency and a large gain. The resulting designs are then implemented and evaluated experimentally. Performance indices for the experimental evaluation include the frequency response, the directional response, the sensitivity, and the efficiency. It is found in the experimental results that the piezoelectric radiators are able to produce comparable acoustical output with significantly less electrical input than the voice-coil panel speakers.     

Output voltage regulation of a k15 mode piezoelectric transformer by an external L/C component

Smooth regulation of output voltage of piezoelectric transformers can significantly widen the application range of piezoelectric transformers. So far the driving frequency of piezoelectric transformers has been used to regulate the output voltage at a matching load. However, the regulation range of voltage gain achieved by the method is usually very narrow within the acceptable range of efficiency. In this work, we investigate the possibility to regulate the output voltage of a k₁₅ mode piezoelectric transformer by an external L/C component. The effects of an L/C component in series or parallel with the input and output ports on the voltage gain are investigated theoretically and experimentally. It is found that the voltage gain can be smoothly regulated in a relatively wide range by a tunable inductor that is in series with the input port. At a matching load of 80 Ω, the voltage gain can be regulated between 0.31 and 0.94 with efficiency larger than 90% and between 0.34 and 1.18 with efficiency about 80%. It is also found that a tunable capacitor in parallel or series with the output port can be used to regulate the voltage gain with efficiency higher than 90%.     

异面腔四频差动激光陀螺的色散平衡

为了减小异面腔四频差动激光陀螺(DLG)腔长变动导致的零漂,对DLG的色散平衡进行了研究.利用气体激光的经典理论,推导了DLG零偏与工作点和轴向磁场的函数关系,给出了色散平衡的理论证明.利用在DLG增益管上缠绕通电线圈,给增益介质施加大小可控的轴向磁场,通过驱动腔平移镜上的压电换能器调节腔长来改变工作点,做出了零偏随腔长和线圈电流的变化曲线.结果表明,零偏对腔长变化的灵敏度是轴向磁场的函数,当增益曲线的塞曼分裂量等于非互易分裂量时零偏对腔长变动不敏感.色散平衡技术减小了腔变动对DLG的影响,有利于提高DLG精度.     

四程放大激光系统输出能量稳定性研究

 根据原型装置主放大系统组合式四程放大结构的特点,计算分析了放大过程中注入能量、放大增益及损耗的微小起伏对系统输出能量稳定性的影响。根据原型装置集成实验结果,分析了目前原型装置单路输出能量稳定性水平。研究结果表明：注入能量越大,其变化对输出能量影响越小;小信号增益系数对输出能量的影响明显大于注入能量;系统输出能量稳定性对腔内光学元件的透过率变化要求高于腔外光学元件。在3 ns基频光输出达标点处要使输出能量不稳定性控制在5%以内,注入能量起伏要低于10%,腔内放大片小信号增益系数起伏要低于1%,腔内光学系统损耗起伏要低于2%。     

Properties of laser gain of Li:CdZnO/ZnMgO quantum well

The many-body optical gain in Li:CdZnO/MgZnO quantum well (QW) structures with spontaneous polarization and piezoelectric polarization, and ferroelectric dipole moment is investigated by using the non-Markovian gain model with many-body effects. The CdZnO/MgZnO QW structure with high Cd composition is found to have smaller optical gain because the strain-induced piezoelectric polarization and the spontaneous polarization in the well increase with the inclusion of Cd. The internal field is reduced due to the additional polarization by Li in the CdZnO/MgZnO QW structure. These results show that Li:CdZnO-based QW lasers are promising candidates for optoelectric applications in visible and UV regions.     

The Energy Transport, Including Emission and Absorption, in N2-Arcs of Different Radii

Steady, motionless cascaded N2-arcs with tube diameters of 2, 3, and 5 mm are investigated at atmospheric pressure to gain insight into the radiative energy transport for temperatures up to 27,000 K. From the electrical characteristics, the total emitted radiation, and the temperature distributions, the electrical conductivity and the transparent emission are evaluated. It is shown that transparent emission can be neglected in the energy transport of nitrogen. The thermal conductivity and the radiative balance as the difference between total emission and absorption per unit volume are determined by introducing the concept of a zero radius arc. Extrapolation to the zero radius arc also permits the determination of the total emission alone. The emission and reabsorption of radiation plays a decisive role in the energy transport for temperatures above 13,000 K.     

Effects of Screening and Finite Phonon Energy on the Transport in Quantized Layers in Compound Semiconductors

Analytical expressions for the momentum relaxation times of the conduction electrons in a non-degenerate two dimensional electron gas in the surface of a compound semiconductor have been obtained for interactions with the piezoelectric and deformation potential acoustic phonons taking due account of the screening of the perturbing potential under the the condition of low lattice temperature when the phonon energy cannot be neglected in comparison to the average thermal energy of the electrons and for that matter the equipartition approximation for the phonon distribution is hardly valid. The relaxation times calculated for inversion layers in GaAs and ZnO are found to depend upon the carrier energy, the lattice temperature and the impurity concentration in rather complex manners which are significantly different from what follows from the traditional approach of either neglecting the phonon energy or disregarding the process of screening. It is seen how the finite value of the phonon energy and the screening of the perturbing potential change the mobility characteristics significantly at the low lattice temperatures. The temperature dependence of the zero field mobility that one obtains using the relaxation times calculated here is quite different from the traditional laws.     

Design of a low-frequency miniaturized piezoelectric antenna based on acoustically actuated principle

An acoustically actuated piezoelectric antenna is proposed for low frequency (LF) band in this paper. The proposed antenna is theoretically calculated, numerically optimized by the finite element method (FEM), and experimentally analyzed. The measurement results show that the near-field radiation pattern of the piezoelectric antenna is similar to that of the electric dipole antenna. The radiation efficiency of the piezoelectric antenna is 3－4 orders of magnitude higher than that of electrically small antenna (ESA), with their sizes being the same size, and the maximum transmission distance obtained experimentally is 100 cm, which can be improved by increasing the input power. In addition, the gain, directivity, and quality factor of piezoelectric antenna are also analyzed. In this paper, traditional antenna parameters are creatively used to analyze the performance of piezoelectric antenna. The research conclusions can provide reliable theoretical basis for realizing LF antenna miniaturization.     

Pressure-induced reversal of the sign of the hydrostatic piezoelectric constant of lithium tantalate

Measurements of the piezoelectric polarization of lithium tantalate for hydrostatic pressures up to 26 kbar show that the hydrostatic piezoelectric constant decreases smoothly to zero at a pressure of 22 kbar. Above this pressure the piezoelectric constant smoothly changes sign. This is believed to be the first observation of such an effect.     

Effect of outer hair cell piezoelectricity on high-frequency receptor potentials

The low-pass voltage response of outer hair cells predicted by conventional equivalent circuit analysis would preclude the active force production at high frequencies. We have found that the band pass characteristics can be improved by introducing the piezoelectric properties of the cell wall. In contrast to the conventional analysis, the receptor potential does not tend to zero and at any frequency is greater than a limiting value. In addition, the phase shift between the transduction current and receptor potential tends to zero. The piezoelectric properties cause an additional, strain-dependent, displacement current in the cell wall. The wall strain is estimated on the basis of a model of the cell deformation in the organ of Corti. The limiting value of the receptor potential depends on the ratio of a parameter determined by the piezoelectric coefficients and the strain to the membrane capacitance. In short cells, we have found that for the low-frequency value of about 2-3 mV and the strain level of 0.1% the receptor potential can reach 0.4 mV throughout the whole frequency range. In long cells, we have found that the effect of the piezoelectric properties is much weaker. These results are consistent with major features of the cochlear amplifier.     

Spectral enhancement in optical parametric amplifiers in the saturated regime

We present numerical and experimental studies on a front-end laser system for seeding a sub-picosecond multi-terawatt/petawatt light source based on two highly saturated optical parametric amplifiers. Numerical results showing energy gain, spectral gain, and stability as saturation is approached are presented. An experimental realisation of the system has been constructed, and its performance has been found to be in good agreement with the numerical simulations. The total gain is in excess of 10⁵ over a few picosecond gain window, and the pulse energy is ～100 μJ with 4 % root mean square stability.     

Change of gain characters for short pulses with third order dispersion in a fiber amplifier

The effect of the third order dispersion (TOD) induced into pulses before entering an Yb-doped fiber amplifier on their power gain characters is investigated using a model of which the pulse amplification process is described by nonlinear time-dependent radiation transfer equations. Numerical results show that peak power gain for the pulse with positive TOD is larger than that with zero and without TOD while the improvement of the peak power gain varies as the obtained output pulse energy changes. The improvement also depends on the ratio of dispersion lengths for group velocity dispersion and TOD.     

太赫兹波段石墨烯等离子体的增益特性

基于麦克斯韦方程组和物质本构方程对石墨烯表面等离子体进行了研究.从理论上探索了石墨烯表面等离子体激元在太赫兹波段的增益特性曲线,并且讨论了石墨烯表面等离子体增益与石墨烯中载流子浓度、石墨烯所处温度以及载流子动量弛豫时间的关系.研究结果表明:在太赫兹波段增益峰值随着石墨烯载流子浓度的增加而发生蓝移,并且在所讨论的温度范围内,由于增益峰所对应的频率都大于1 THz,因此温度的变化对增益峰值以及相应频率的影响不大,即在不同的温度下,相同载流子浓度所对应的增益曲线上峰值的位置和强度几乎相同;增益与石墨烯载流子动量弛豫时间相关,随着载流子动量弛豫时间的增加,使得激发态激励的电子增加,从而导致石墨烯表面等离子体增益变得更大,但这种动量弛豫时间的增加却因弛豫时间对受激辐射频率影响较小而并未对增益峰值位置产生影响.     

压电网络复合板的波动特性与隔声性能分析

在压电网络复合板机电耦合波动方程基础上,首先对在其中传播的弯曲波的波动特性进行了分析,发现压电网络复合板中同时存在两种不同频散特性的弯曲波,电感电阻并联型压电网络复合板中存在的两种弯曲波的频散曲线具有频率转向现象;在频率转向区,弯曲波的衰减常数或达到最大或迅速增大这一结论为压电网络复合板的减振降噪设计提供了参考。对压电网络复合板中的能量分析给出了这一结论的机理:即在频率转向区板中的机械能与电能能够进行最大的能量交换;在波动分析的基础上对压电网络复合板的隔声特性进行了分析,发现压电网络复合板隔声曲线上的低谷随外界电感值的变化能够发生移动或者消失,最后结合压电网络复合板的波动频散特性对复合板的隔声机理进行了分析,为设计压电网络复合板的隔声性能提供了理论参考。