基于改进EEMD与混沌振子的配电网故障选线

提出改进的集合经验模态分解(MEEMD)和混沌振子相结合的电网故障微弱信号检测方法。首先,建立神经网络预测模型,通过神经网络对配网各线路零序电流进行短时预测,滤除故障信号中的背景信号;其次,为了检测配网发生单相接地故障后微弱的5次谐波信号,提出结合多尺度排列熵和完备集合经验模态分解(CEEMD)改进的改进的集合经验模态分解算法;处理已经滤除背景信号的故障信号,提取其第一固有模态函数作为混沌振子的输入。混沌振子对和内驱动力信号同频的外策动力信号有较高的敏感性,通过混沌振子输出的相图完成电网故障选线。     

频率可调太赫兹回旋振荡管互作用电路的设计与研究

根据动态核极化核磁共振成像技术对回旋振荡管的要求,设计了130 GHz 回旋振荡管的注波互作用电路,基于线性理论对互作用电路进行了研究并选择了合适的工作点,分析了电路的频率调节特性。利用相对论电子回旋脉塞非线性理论对互作用系统进行了模拟和计算,优化了工作参数,计算了磁场及电子注参数对输出功率及效率的影响。最后,用粒子模拟方法进行了模拟并与非线性理论结果进行了比较,两者符合得很好。模拟结果显示,当电压为10 kV、电流为0.3 A、磁场强度由2.34 T 增加到2.41 T 时,输出功率由1310 W 减小到230 W,对应的效率分别为43.6%和7.7%,振荡管的频率可调范围约为2.7 GHz。     

Electrical oscillation generation with current-induced resistivity switching in VO2 micro-channel devices

We report large amplitude modulation waveforms as large as ~ 10 V using vanadium dioxide micro-channel devices operating under current-controlled conditions. The self-sustained electrical oscillations were generated by controlling the applied current in the negative differential resistance region of the investigated devices. An appropriate value of internal capacitance was achieved as parasitic capacitance in the device structure to stabilize the electrical oscillations. This eliminates the need of an external pulsed source or any external passive component connected to the micro-channel devices. Amplitude and frequency of the oscillation were tuned by illuminating the device micro-channel with an external laser. An equivalent circuit model was developed to simulate the waveforms. A good agreement between experiment and simulation was verified.     

Study on chaotic oscillator-based algorithm for weak GLONASS signal acquisition

According to the characteristics of the chaotic oscillator in detecting weak signals, an algorithm based on Duffing chaotic oscillator array was proposed for acquisition of weak GLONASS signals. By means of GLONASS intermediate frequency and Duffing chaotic oscillator models, Lyapunov exponent is adopted to judge the critical condition of phase track and decide whether GLONASS signals exist or not by the change of the critical condition, and numeric iteration procedure is used to calculate the exponent. Finally, the performance of algorithm is simulated using GLONASS intermediate frequency data. The results indicate that acquisition algorithm can satisfy the need of object positioning in low signal-to-noise ratio environment.     

Design and performance study of phase‐locked loop using fractional‐order loop filter

The present work reports the realization of an analog fractional‐order phase‐locked loop (FPLL) using a fractional capacitor. The expressions for bandwidth, capture range, and lock range of the FPLL have been derived analytically and then compared with the experimental observations using LM565 IC. It has been observed that bandwidth and capture range can be extended by using FPLL. It has also been found that FPLL can provide faster response and lower phase error at the time of switching compared to its integer‐order counterpart. Copyright © 2014 John Wiley & Sons, Ltd.     

应变纤锌矿ZnO/MgxZn1-xO量子点中离子施主束缚激子的光学性质

Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong built-in electric field(BEF) in strained wurtzite Zn O/Mg0:25Zn0:75O quantum dots(QDs), the optical properties of ionized donor-bound excitons(D+, X)are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of(D+, X) complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of(D+, X) complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth.     

New sinusoidal oscillator configurations using operational transresistance amplifier

The objective of this brief is to introduce four new structures of electronically tunable sinusoidal oscillators (SOs) designed using operational transresistance amplifier (OTRA). Each of the proposed SO consists of forward path derived from a generic structure along with one/two OTRA-based resistive gain stages or differentiator in its feedback path. All the proposed SOs enjoy independent tuning of the frequency of oscillation (FO) through resistors without affecting the condition of oscillation (CO). Further, all topologies are found to exhibit low f_o sensitivities at all frequencies with respect to circuit parameters, and the second topology is capable of achieving very low frequencies (VLFs) using less RC component spread and provides linear tuning too. The fourth circuit provides quadrature output. The proposed SOs have been successfully implemented and verified in 180-nm CMOS technology node using ADE (analog design environment) tool Cadence Virtuoso. Both prelayout and postlayout simulation results have been included. To assess the oscillator prefabrication performances, Monte Carlo and process-voltage-temperature (PVT) analyses have been performed. The total harmonic distortion (THD) is observed to be less than 3.5%.     

基于THz波的玻璃纤维复合材料无损检测方法研究

太赫兹具有透视性、安全性等特点,近年来在无损检测领域得到了较快的发展和应用,以返波振荡管连续太赫兹波成像系统对5mm厚的玻璃纤维复合材料进行无损检测实验,其中包括热损伤(dmin=0.5mm)、空气分层(smin=0.5mm2)等缺陷,获得样品的成像结果及数据。结果表明,返波振荡管连续太赫兹波成像技术对从背面对玻璃纤维复合材料样品中的两种缺陷有清晰成像,且结合成像数据,可排除样品中环氧树脂的影响,验证不同缺陷之间的特性,进一步确定损伤类型。     

基于光电混合双环的高边模抑制比振荡器

为了进一步有效提高光电振荡器的性能,提出了一种基于光电混合双环的高边模抑制比振荡器.利用两级电功分器构成电增益环腔,结合偏振分束器和偏振合束器形成的光纤双环结构,在没有引入外调制器和电滤波器的前提下,得到了高边模抑制比的小型化光电振荡器.实验中光纤长度取110m和2 km,获得了中心频率为11.4 GHz的微波信号,边模抑制比为60 dB,其相位噪声为-103.6 dBc/Hz@10 kHz.     

A 5-GHz LC VCO with digital AAC and AFBS for 2.4 GHz ZigBee transceiver applications

A 5 GHz LC VCO (voltage-controlled oscillator) with automatic amplitude control (AAC) and automatic frequency-band selection (AFBS) for 2.4 GHz ZigBee transceivers is presented. Instead of continuous feedback loop, an alternative amplitude calibration scheme is proposed in this paper to alleviate the deficiencies inherent in the conventional approach. It helps to keep the VCO at optimum amplitude to avoid saturation of the cross-coupled transistors and therefore stabilizes the phase noise performance over process, voltage and temperature variations. For the ZigBee application with 16 frequency channels, a coarse tuning loop is added in this work to implement the frequency-band selection using the AFBS mechanism. The VCO core and the digital AAC, AFBS modules have been fully integrated in a 2.4 GHz ZigBee transceiver which was fabricated in a 0.18 μm RF-CMOS technology. The current consumption is 4.7 mA at 4.85 GHz with 1.8 V power supply and a chip area of about 0.285 mm² is occupied. The VCO is capable of operating from 4.67 GHz to 5.18 GHz and the measured phase-noise level is –120 dBc/Hz at 1 MHz offset from a 4.85 GHz carrier. The tuning sensitivity K_VCO of the VCO is about 78 MHz/V with 0.9 V control voltage.