由散射系数反演电磁参量的一种改进算法

传输/反射法中存在的多值性问题多年来颇受关注。本文考察了两套由散射系数反演电磁参量的公式,表明在满足折射率虚部不小于零、阻抗实部大于零和折射率正切角取值范围受阻抗正切角限制关系三条件时,两套公式均可确定阻抗和折射率虚部,并给出数量有限的、可能的折射率实部。在此基础上,利用相邻频率点电磁参量的连续性,可分别求出数个差异显著的电磁响应谱。依据对材料电磁性能的初步认识,不难选出合适的介电常数和磁导率。最后,通过实例检验了上述方法的有效性。     

实虚部关联的量子噪声和抽运噪声对单模激光光强关联函数的影响

采用抽运噪声和实虚部之间关联的量子噪声驱动的单模激光损失模型，运用线性化近似方法计算了反映激光动力学性质的光强关联函数C(t)和光强相对涨落C(0)，讨沦了光强关联函数随时间t的演化，分析了量子噪声实虚部间关联系数λq，抽运噪声强度P和量子噪声强度Q对光强关联函数C(t)随时间t演化过程的影响。发现C(t)随时间t的演化是单调衰减过程，但噪声强度的减小和量子噪声实虚部间关联的减弱会使演化曲线整体下移，说明噪声强度和量子噪声实虚部间的关联对C(t)随时间t的演化过程有较大的影响。当时间t增加时，C(t)与量子噪声实虚部间关联系数λq的关系曲线出现了一个极值和三个极值两种不同的情况。最后分析了线性化近似方法适用的条件。     

退火温度对铁基纳米晶带材高频磁导率的影响

采用单线圈法,利用Agilent E4991A射频阻抗/材料分析仪,研究了退火温度对铁基纳米晶带材的高频磁导率的影响。结果表明:经550℃退火处理的30μm厚样品磁导率实部,随频率增加而减小,在1MHz下为1210,在20MHz下为234,磁导率虚部有类似的变化趋势;比较了30μm厚样品经不同温度退火处理后磁导率的测量结果,得出550℃是一个比较理想的退火温度。     

关于阿贝尔群上的希尔伯特和张—哈特莱变换(英文)

本文讨论了有限阿贝尔群上的希尔伯特变换和张—哈特莱变换的性质。由于引入了群元素排序的概念和定义了函数的奇偶性,从而能够将函数划分出真函数与虚函数两种类别。本文引述了作者和L.Salinas 1986年在国际多值逻辑学术会议论文集上发表文章的主要结果,即实偶函数的奎斯特恩逊谱是实的和偶的;实奇函数的谱是虚的和奇的;取实值的真函数和虚函数两大类型函数的希尔伯特变换同它们的奎斯特恩逊谱的实部与虚部有明确的关系。在这基础上本文详细论证了张—哈特莱变换的性质,并提出了一种快速算法。本文证明了一个函数的奎斯特恩逊功率谱可以直接用张—哈特莱变换计算。因为这种变换是实值的,因此复数运算是可以避免的。     

毫米波雪崩二极管振荡器

本文介绍一种稳定的毫米波雪崩二极管振荡器。如果从二极管位置所观察的振荡器的负载阻抗的实部和虚部能够容易独立地变化的话,那么振荡器便能在毫米波频段的任一频率产生最大的输出功率。振荡器的形伏和尺寸是根据一个放大五倍的比例模型测量确定的。这种振荡器能在40～60千兆赫的宽频率范围获到20分贝毫瓦或更大的功率,用相同的二极管在75千兆赫能获得15分贝毫瓦以上的输出功率。     

基于EIS-SVM的飞机复合材料健康监测研究

针对复合材料异常检测或健康监测的问题,对电阻抗谱法与支持向量机相结合应用于飞机复合材料构件健康监测进行了研究。制作了同面2电极传感器和两块碳纤维复合材料样板,设计实验电路测量了两个碳纤维被测样本的电阻抗谱,提取了不同类型的电阻抗特征参数;在Matlab软件平台上利用支持向量机对复合材料健康状态进行辨识,并比较分析了不同类型特征参数下的支持向量机辨识准确率。结果表明,相比于Cole-Cole曲线分段各段电阻抗实部或虚部幅值的平均值和频率——实部或虚部曲线分段线性拟合斜率,选取复合材料样板的Cole-Cole曲线分段线性拟合斜率作为特征参数时,支持向量机具有更高的健康状态辨识准确率。初步实验表明,支持向量机与电阻抗谱法结合起来进行飞机复合材料构件的健康监测是可行的。     

一种具有温度补偿的时钟振荡器设计

介绍了一种采用0.35μm CMOS工艺制作的具有温度补偿的时钟振荡器电路。从环形振荡器的基本原理出发,基于对CMOS工艺各种非理想性因素的分析,提出一种新型的工艺补偿电路,减小振荡器偏置电流随阈值电压的漂移;在延迟单元的设计中,引入NMOS交叉耦合对组成的交流负阻抗来进一步补偿PMOS迁移率随温度的变化,从而有效抑制输出频率随温度的变化。该振荡器电路用于MEMS加速度计读出电路芯片。样品电路测试结果表明,在-20~100℃温度范围内,时钟振荡器的频率仅变化38kHz。     

单模激光系统的光强相对涨落和功率谱

用线性化近似方法计算了单模激光损失模型在输入偏置调幅波信号后的稳态平均光强相对涨落C(0)和输出功率S(ω),得到稳态平均光强相对涨落C(0)与载波信号振幅B、高频载波信号频率ω以及量子噪声强度Q的变化规律,发现在低频调制信号频率增大、高频载波信号频率减小、量子噪声实虚部关联越强和远离阈值时,激光系统的统计涨落较小。通过对系统功率谱S(ω)与a0/A、低频调制信号频率Ω、高频载波信号频率ω以及量子噪声实虚部间的关联系数λq的研究,也发现了一些特殊的现象。     

信号调制噪声对单模激光光强关联函数的影响

采用受信号调制色泵噪声和实虚部关联量子噪声驱动的单模激光损失模型,用线性化近似方法研究反映单模激光统计性质的重要物理量光强关联函数C(t)随时间t的演化,发现当色泵噪声自关联时间τ变化时,C(t)随时间t的演化会出现单调衰减,单调上升,出现一个极大值,周期性振荡衰减等多种形式。当τ确定时,量子噪声实虚部间关联的加强会使C(t)的值减小;量子噪声强度Q的增大会使C(t)的值增大;泵噪声强度P的增大会延缓C(t)随时间t的衰减。     

m=0角向模表面波等离子体柱天线辐射特性

根据表面波在非磁化等离子体柱中的色散关系,理论计算得到存在电子-中性原子碰撞、径向与轴向等离子体密度非均匀分布条件下m=0角向模表面波波矢实部与虚部随信号频率、等离子体密度的变化关系.然后利用波矢的实部与虚部、等离子体柱天线表面指数分布电流模型、等离子体阻抗,推导得到等离子体柱天线的辐射方向图随信号频率、等离子体密度的变化关系;最大增益、天线辐射阻抗随信号频率的变化关系;天线径向能量辐射随等离子体密度的变化关系.理论计算结果表明等离子体柱天线辐射方向图随信号频率、等离子体密度的改变而变化非常明显,信号频率对最大增益、天线辐射阻抗的影响显著;同时,这些理论计算结果与他人实验实测结果吻合,这对于设计高精度要求的等离子体天线提供了重要的理论参考价值.     

2.45GHz微波频率下有机二元体系溶液等效介电系数新特性的实验研究

介质混合物的等效介电系数是微波化学研究中的一个重要内容.本文在微波频率下,利用微扰法测量了有机二元体系的等效介电系数.测试结果显示:在二元混合体系中,当两组元的等效介电系数实部接近而虚部相差较大或虚部接近而实部相差较大时,介质混合物的等效介电系数的实部(或虚部)随体积比变化过程中,会出现大于其中任何一种组份的介电系数实部(或虚部)的峰值.本文中,利用对称Bruggeman理论对这一与Clausius-Mossotti、 Onsager和Kirkwood等传统理论相悖的新特性进行了合理的解释与分析.     

基于FFT系数的正弦信号频率估计算法

针对基于FFT系数实部的频率插值算法在峰值谱线相位接近于±π/2时频率估计误差较大的问题,提出了一种改进的正弦信号频率估计算法。该算法首先利用FFT系数的实部和虚部序列索引出峰值谱线位置,然后根据峰值谱线的相位,选取实部与虚部序列中幅度较大的序列进行频率插值。仿真结果表明：在信噪比为3 dB、采样点为128的情况下,整个频段上归一化频率估计误差均方根小于0.02,接近Cramer Rao下限,整体性能优于基于FFT系数实部的频率插值算法和Rife算法。改进的算法频率估计精度高,计算量小,易于硬件实现。     

Impedance Spectroscopy of π‐Conjugated Organic Materials

AC electrical properties of organic light‐emitting diodes with poly(2‐methoxy‐5‐(2'‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV), poly[2,5‐bia(dimethyloctylsilyl)‐1,4‐phenylene‐vinylene] (BDMOS‐PPV), and tris‐(8‐hydroxyquinolate)‐aluminum (AlQ₃) as light‐emitting materials are studied. The frequency‐dependent real and imaginary parts of impedance were fitted using an equivalent circuit. We found that the conduction mechanism is a space‐charge limited current with exponential trap distribution.     

Impulses concealed by singularities: transmission line theory

The input admittance of a loss-free short-circuited transmission line is generally said to be a cotangent function of frequency, a function that is imaginary and odd. The symmetry implies that the impulse response, which has the admittance function of frequency as its Fourier transform, is also odd. However, there can be no response at negative times preceding the applied impulse. Therefore the cotangent formula for susceptance cannot be correct. A real, even function of frequency representing a conductance term must be added to the imaginary, odd susceptance. Likewise, the familiar formula Z=iZ₀ tan(2πL/λ) is deficient     

Electron transport in two dimensional electron gas formed at the heterojunction of AlxGa(1−x)N/GaN at microwave frequencies

Transport properties of the two dimensional electron gas (2DEG) formed at the interface of AlGaN/GaN heterostructure ranging from 20 K to 300 K has been investigated theoretically considering the various scattering mechanisms like the acoustic, the piezo, the surface roughness, the alloy, the polar optical phonon and the dislocation scattering. The dc mobility is found to remain constant up to 150 K and then it decrease sharply with further increase in temperature. The ac mobility is also found to decrease with increase in the temperature. The real part of ac mobility, i.e. μ_r decreases with the increase in the frequency very fast initially and then gradually attains a steady value. The imaginary part of the ac mobility μ_im initially increases with the increase in the frequency and then decreases after reaching the maximum value. The value of the ac mobility reduces quite reasonably as the 2D carrier concentration increases at lower range of the frequency. At the carrier concentration of 5 × 10¹⁷ m⁻², the ac mobility remains constant through a wide range of frequencies. With the increase in the dislocation densities, the values of the ac mobility are found to decrease at the lower range of frequencies. The thermo electric power is positive at the 2D carrier concentration of 5 × 10¹⁶ m⁻², the value of which increases with the increase in the temperature and gradually attains a steady value. But the thermoelectric power at n_2D of 10¹⁷ m⁻² is found to be negative in the value. The value of ZT is found to increase with the temperature and attains the maximum value of 0.007 at 150 K and the value of ZT then decreases with increase in the temperature.     

Fabrication of an AlAs/In0.53Ga0.47As/InAs Resonant Tunneling Diode on InP Substrate for High-Speed Circuit Applications

在InP衬底上采用感应耦合等离子体刻蚀技术制备了高性能的AlAs/In0.53Ga0.47As/InAs共振隧穿二极管.正向偏压下PVCR=7.57,Jp=39.08kA/cm2;反向偏压下PVCR=7.93,Jp=34.56kA/cm2.在未去除测试电极和引线等寄生参数影响下,面积为5μm×5μm的RTD的阻性截止频率为18.75GHz.最后对非对称的I-V特性进行了分析讨论.     

Influence of electrical parasitics and drive impedance on the laser modulation response

In this letter, we analyze the effects of electrical parasitics and drive impedance on the laser modulation response. It is found that for lasers with small active-region volume, e.g., vertical-cavity surface-emitting lasers, the finite drive impedance and/or the laser parasitic capacitance can significantly enhance the damping of the laser resonance peak at low bias. This is due to the voltage fluctuations across the laser diode active layer during modulation. It is also shown that the real pole of the small-signal response transfer function corresponding to the laser parasitic cutoff frequency is not fixed but decreases with the increased bias level.     

State-Space Analysis of General IMPATT Diode Small-Signal Lumped Models

The development of a lumped model for small-signal carrier-field interactions in an IMPATT diode results in a set of state equations. Using state-space analysis techniques, the equations are solved for the small-signal impedance of a general IMPATT diode as a function of dc bias current and frequency. Read, p-n, and p-i-n diodes are studied using realistic values for saturation carrier velocities and carrier-ionization rates. Curves indicating the influence of diode physical properties on the small-signal impedance are presented. By combining state equations describing the behavior of the external microwave circuit with the diode state equations, the small-signal oscillation frequency and threshold dc bias current of a coaxial IMPATT oscillator are determined.     

用于高速电路的InP基共振隧穿二极管制作

在InP衬底上采用感应耦合等离子体刻蚀技术制备了高性能的AlAs/In0.53Ga0.47As/InAs共振隧穿二极管.正向偏压下PVCR=7.57,Jp=39.08kA/cm2;反向偏压下PVCR=7.93,Jp=34.56kA/cm2.在未去除测试电极和引线等寄生参数影响下,面积为5μm×5μm的RTD的阻性截止频率为18.75GHz.最后对非对称的I-V特性进行了分析讨论.