Master equation and conversion of environmental heat into coherent electromagnetic energy

We derive a non-Markovian master equation for the long-time dynamics of a system of Fermions interacting with a coherent electromagnetic field, in an environment of other Fermions, Bosons, and free electromagnetic field. This equation is applied to a superradiant p–i–n semiconductor heterostructure with quantum dots in a Fabry–Perot cavity, we recently proposed for converting environmental heat into coherent electromagnetic energy. While a current is injected in the device, a superradiant field is generated by quantum transitions in quantum dots, through the very thin i-layers. Dissipation is described by correlated transitions of the system and environment particles, transitions of the system particles induced by the thermal fluctuations of the self-consistent field of the environment particles, and non-local in time effects of these fluctuations. We show that, for a finite spectrum of states and a sufficiently weak dissipative coupling, this equation preserves the positivity of the density matrix during the whole evolution of the system. The preservation of the positivity is also guaranteed in the rotating-wave approximation. For a rather short fluctuation time on the scale of the system dynamics, these fluctuations tend to wash out the non-Markovian integral in a long-time evolution, this integral remaining significant only during a rather short memory time. We derive explicit expressions of the superradiant power for two possible configurations of the superradiant device: (1) a longitudinal device, with the superradiant mode propagating in the direction of the injected current, i.e. perpendicularly to the semiconductor structure, and (2) a transversal device, with the superradiant mode propagating perpendicularly to the injected current, i.e. in the plane of the semiconductor structure. The active electrons, tunneling through the i-zone between the two quantum dot arrays, are coupled to a coherent superradiant mode, and to a dissipative environment including four components, namely: (1) the quasi-free electrons of the conduction n-region, (2) the quasi-free holes of the conduction p-region, (3) the vibrations of the crystal lattice, and (4) the free electromagnetic field. To diminish the coupling of the active electrons to the quasi-free conduction electrons and holes, the quantum dot arrays are separated from the two n and p conduction regions by potential barriers, which bound the two-well potential corresponding to these arrays. We obtain analytical expressions of the dissipation coefficients, which include simple dependences on the parameters of the semiconductor device, and are transparent to physical interpretations. We describe the dynamics of the system by non-Markovian optical equations with additional terms for the current injection, the radiation of the field, and the dissipative processes. We study the dependence of the dissipative coefficients on the physical parameters of the system, and the operation performances as functions of these parameters. We show that the decay rate of the superradiant electrons due to the coupling to the conduction electrons and holes is lower than the decay rate due to the coupling to the crystal vibrations, while the decay due to the coupling to the free electromagnetic field is quite negligible. According to the non-Markovian term arising in the optical equations, the system dynamics is significantly influenced by the thermal fluctuations of the self-consistent field of the quasi-free electrons and holes in the conduction regions n and p, respectively. We study the dependence of the superradiant power on the injected current, and the effects of the non-Markovian fluctuations. In comparison with a longitudinal device, a transversal device has a lower increase of the superradiant power with the injected current, but also a lower threshold current and a lesser sensitivity to thermal fluctuations.     

Effects of resonance asymmetries on the conversion of laser phasenoise into amplitude noise in fiber optic ring-resonators

Fiber optic ring resonators constructed from a continuous strand of single-mode fiber and an evanescent wave directional coupler can show an asymmetric resonance characteristic due to coupler losses. The effects of this asymmetry on the conversion of laser phase noise into amplitude noise is discussed. A mathematical model, valid for highly coherent signals, is used to analyze even high-finesse ring resonators with a minimum of CPU time     

Economic optimization of energy conversion with storage

An experimental system being developed at Oklahoma State University represents the first phase of a research effort to formulate a model for optimizing an energy conversion and storage system. Some of the problems in providing energy storage as an alternative to added conversion capacity to meet peak demand are treated here. It is assumed that the conversion system is a steam or hydro plant with a controlled input as opposed to a solar or wind plant with a random input, although extension to the latter is possible.     

结构单元对双负材料电磁特性的影响

采用S参数提取法、结合HFSS仿真对双负材料电磁特性进行了分析研究,导出了S参数提取技术的相应计算公式。通过调节金属丝和金属谐振环单元的内外环间距、开口间距及覆铜厚度,分析结构单元的变化对双负材料谐振频率、介电常数及磁导率的影响。结果表明:双负材料的谐振频率随内外环间距的增大而迅速降低,随开口间距以及覆铜厚度的增大而缓慢增加。通过改变双负材料的结构单元可以实现对负介电常数和负磁导率频段的调控。     

基于FPGA的磁共振接收机数字下变频设计

介绍了变带宽数字下变频(Reconfigurable Digital Down Conversion,RDDC)的原理,针对磁共振成像接收机数字下变频的特点,提出了一种抽取率可在线编程的数字下变频器设计方法。对主要功能单元(变级数CIC滤波器、串并混合式FIR滤波器)的设计与FPGA实现进行了具体分析,同时针对ALTERA公司的5CGXFC9器件与1. 5T磁共振成像系统数字下变频需求,利用Verilog语言设计了输出量化位数为16bit、抽取率为180～11520的RDDC实例,基于ModelSim与MATLAB进行了功能仿真。通过仿真结果分析可知,该实例在给定器件资源约束下,实现了100MHz采样率、2kHz～200kHz带宽信号的RDDC功能,在单片FPGA内完成了对不同带宽信号的数字正交检波与抽取滤波操作,为磁共振成像接收系统提供了一种高通用性与高灵活性的变带宽DDC解决方案。     

基于电磁谐振式无线充电线圈实验研究

消费类电子产品传统的外接充电方式一般通过有线方式来实现。多电子设备充电装置之间往往并不通用,携带多个充电器也存在不便。目前,无线充电已成为广泛关注的替代方案。文中通过实验对电磁谐振式无线充电方法进行研究,在分别改变线圈半径、线圈匝数、线圈疏密程度以及谐振频率的情况下,得到并对比其在不同状态下的性能。首先,采用MOSFET对整个电路进行分析设计,其中发射电路和接收电路均采用电感与电容的并联匹配方式;其次,对发射线圈和接收线圈的不一致性进行分析。     

梯度掺杂对太阳能电池转换效率的影响

论述了梯度掺杂对太阳能电池光伏转换效率的影响。利用掺杂半导体导带中自由电子数目及静电场理论,计算出了单晶硅指数掺杂的电场,并给出了任意梯度掺杂电场强度所满足的微分方程。     

基于STM32的高效光伏能量转换系统设计

设计一种用于海岛上微传感器设备供电的光伏系统,以STM32作为主控制器,设计双轴跟踪平台实现太阳跟踪,研究了新的光照传感器布置方案;增加角度传感器SCA100T-D02测量太阳能板的方位角与高度角,控制器将其与GPS模块对比进行位置辅助校准,形成闭环控制。主控制器根据MPPT算法采用PWM控制方式对锂电池充电。实验结果表明,该系统能够精准实现太阳跟踪,大幅度提高光伏转化效率,拥有广阔的应用价值与前景。     

Transmission of electromagnetic pulse into the head

Characterstic of electromagnetic pulse transmission in homogeneous spherical models of human and animal heads are studied as a function of time and position. The incident pulse waveform is described by a triple exponential waveform which exhibits close agreement with measured pulse shapes. The transmitted pulse is shown to be proportional to the time rate of change of the incident pulse, with peak occuring at the leading surface of the spheres.     

Transmission of electromagnetic waves into time-varying media

Expressions are obtained for the electromagnetic fields transmitted into the time-varying medium when a plane wave is incident upon either a dielectric or dispersive half-space. Solutions are obtained for the case when the medium is changed in a stepwise fashion, and also for the case when the medium varies slowly and continuously.     

Doping of IV-VI semiconductors and the energy spectrum of holes with resonance states taken into account

Kinetic phenomena in the Pb_0.5Sn_0.5Te solid solution have been studied in wide ranges of concentrations and temperatures in the case of two types of acceptor doping: with overstoichiometric tellurium and with a combination of equal amounts of Na and Te atoms; in the latter case, two additives amounting to 1.0 and 1.5 at % of each element have been used. Hole densities attained in this case significantly exceeded the largest values corresponding to the Pb_0.5Sn_0.5 Te:Te samples. For both types of acceptors, the hole concentration in the solid solution is found to be a factor of 2 higher than in PbTe with the same level of doping. The specific features of behavior of the Hall coefficient, thermopower, and electrical conductivity are interpreted in the context of a model of a single-valence-band spe ctrum with a wide band of resonant levels. The mechanism of formation of resonant levels in PbTe and Pb_0.5Sn_0.5 Te solid solutions is discussed.     

机箱孔缝对电磁屏蔽效能的影响研究

近年来,随着电力电子技术与电气自动化技术的迅速发展,电磁环境日渐复杂,电子设备间的相互干扰日益严重,电磁兼容问题成为不容忽视的重要课题。为保证设备不受外界的电磁干扰,通常对设备外部加上金属屏蔽机箱,而由于需要散热、通风等因素的存在,不可避免需要在机箱上开孔开缝。外部的电磁干扰信号通过这些孔缝进入机箱内部,影响机箱正常工作。利用波导等效电路,计算了带有中心孔的矩形金属屏蔽体的屏蔽效能,并对孔的形状、矩形孔的长宽比以及入射波极化方向等参数对屏蔽效能的影响进行了讨论。另外,进一步研究了含有孔阵矩形金属机箱的屏蔽效能,并对电子机箱的电磁兼容性设计提出改进措施。最后利用Ansoft HFSS仿真软件验证模型的有效性和算法的正确性。     

电磁导波能量压缩式脉冲激励方法研究

电磁导波检测技术因其非接触耦合特性而被广泛应用于各种类型金属管道的损伤检测,但较低的激发效率却导致电磁导波信号能量传递范围有限,限制了其在长管道和结构复杂管道方面的应用。为提高电磁导波换能效率,本文摒弃了脉冲发生器和功率放大器相组合的激励源结构,提出了一种以能量压缩原理为核心的脉冲激发方法,在空间和时间上压缩存储于电容中的能量来提高激发信号强度,并确定了脉冲形成回路参数的选取规则。实验证明该方法可以有效增加电磁导波激发信号幅值。     

On the energy transport velocity of the electromagnetic field

A separation of the field energy into kinetic energy and rest energy is suggested. This implies an energy transport velocity which equals c in the limit of plane waves, and equals the point charge velocity in the limit of a slowly moving point charge. The old "4/3 paradox" is hereby avoided.     

Transference of electromagnetic energy to superficial human skin tissue

The way the energy is absorbed when skin surface is being exposed to an electromagnetic radiation, and the physical consequences involved, are essentially the purposes of this study. In particular, we are dealing with high frequency radiation. When it is directed toward the surface of the skin, energy is transmitted to its inner layers causing an increase of the temperature. This process has experimentally been proved to be beneficial in many cases. Yet theoretically there is still a slightly hollow basis about it. This study pretends to deal with that subject from its origin, and allows future study doors to tap in depth this theme. Skin tissue is actually a multilayer tissue with a different tissue in each layer. Each one of them is characterized by some parameters, such as permittivity, conductivity, density and specific heat. Two kinds of skin tissues will be analysed: a fibrous and a fatty one, each of both with different skin humidity. In a former study some parameters such a possible non-linear temporal evolution of tissue temperature and a redistribution of heat through the tissues had been neglected for simplicity.     

基于磁耦合谐振的无线电能传输装置

在基于耦合谐振技术上,设计一种无线电能传输装置,采用软件对所设计的耦合谐振电路进行了建模与仿真,在此基础上实际制作了无线电能传输装置,实测效果良好.该设计方法简洁实用,但从效率角度考虑,有进一步改进的空间.     

基于FDTD的环形孔缝电磁耦合规律研究

为提高电子设备及系统在复杂电磁环境下工作的稳定性,应用时域有限差分方法对不同脉宽电磁脉冲通过带有不同形状（方形环,圆环,矩形环）环形孔缝屏蔽腔体的耦合规律进行了分析.研究结果表明：电磁脉冲通过环形孔缝耦合现象明显,其通过圆环的耦合能量最小;对于矩形环,当入射波极化方向与环形孔缝的短边平行时,若矩形环孔缝纵横比越大,则耦合能量也越大,当极化方向与短边垂直时,则纵横比越大,耦合能量越小;入射电磁脉冲脉宽越短,电磁脉冲越容易耦合进入环形孔缝;腔体壁的反射及谐振会增强耦合效应.     

全息波带片用于太阳能转换

目前,在太阳电池发电中,迫切需要解决的问题是降低半导体材料的成本和提高能量转换效率。人们对此已经做了大量的研究工作。人们研究用全息光学元件聚集太阳能,并探讨基于这种全息光学元件组成集热器或光生伏打发生器。本文介绍一种适用于太阳电池聚光发电的全息方法。光电转换器的主要组成部分是体积位相全息波带片和半导体太阳电池。利用体积位相全息波带     

Influence of a sub-surface insulating layer on electromagnetic ground wave propagation

The exact formal solution for an electric dipole over a planar stratified medium is evaluated in the asymptotic limit. Special attention is given to the situation where one of the strata is an effective insulator. In this case, a waveguide type of propagation is possible which, in some cases, may be significant.     

瞬态电磁脉冲能量传输特性的物理实质

根据矢量位方程,在均匀电流模型下,分别给出了圆形和方形单元天线轴线上电磁场分量的时域表达式以及能量密度的解析计算公式;用等腰梯形电脉冲给天线馈电,采用数值计算的方法分别绘出了圆形和方形天线轴线能量密度随距离的衰减曲线,瞬态电磁脉冲能量传输呈现三段式传输规律和慢衰减特性;通过对能量密度解析计算公式物理意义的讨论,给出了瞬态电磁脉冲慢衰减传输特性的物理实质解释;采用亚纳秒电子源给抛物面天线馈电,对抛物面天线轴线辐射电磁脉冲波形及能量作实验测试,实验测试结果与数值计算结果相符合。