A single-magnet nonlinear piezoelectric converter for enhanced energy harvesting from random vibrations

Power harvesters from mechanical vibrations are commonly linear mechanical resonators that are most effective when excited at resonance. Differently, under wideband vibrations, linear converters are suboptimal. A nonlinear converter is here proposed that implements nonlinearity and bistability by employing a single external magnet, in order to improve conversion effectiveness while simplifying device fabrication. The converter is composed of a piezoelectric bimorph on a ferromagnetic cantilever. The fabrication technology is based on the screen printing of a PZT low-curing-temperature paste on harmonic steel substrate. The ferromagnetic cantilever converter, under proper coupling with the external magnet, bounces between two stable states when excited by random vibrations and generates an electric output via the piezoelectric effect. According to theoretical predictions, when bistable behaviour is present, experimental results demonstrate an improvement of about 400% of the rms voltage generated by the converter with respect to the linear case.     

Design of wideband hybrid silicon carbide single-stage power amplifier

RF wideband power amplifiers are desirable as they will reduce equipment, power consumption and operating cost for the RF communication infrastructure. For decades, the realization of single-stage broadband power amplifier has posed a significant challenge due to the electrical and thermal limitations of GaAs transistor technology. Silicon carbide (SiC) MESFET technology is a strong contender for such applications due to its superior properties. In particular, its high impedance reduces mismatch commonly encountered in such power amplifier.In this work, design of wideband hybrid single-stage power amplifier using a commercial 4H-SiC MESFET CRF24010 from Cree Inc is presented. The amplifier has been designed and fabricated for operating frequencies 650-1800 MHz, which is equivalent to more than 90% bandwidth, compared to only 3-4% bandwidth achievable using GaAs technology.     

宽带信号距离和速度分辨率的研究

本文中，首先分析了已有宽带模糊函数体积定义的不足之处，在此基础上给出了改进体积的定义其次在宽带信号分辨率的研究中采用了时间一尺度和频率．尺度变换[1]的概念并证明了宽带信号的距离和速度分辨率分别取决于信号的频谱结构和尺度谱结构最后用本文方法分析了几类信号的分辨率这为宽带信号处理提供了一个有力的理论分析工具。     

A low-complexity low-spurs digital architecture for wideband PLL applications

This paper presents a non-ideality analysis of the wideband frequency synthesizer, and proposes a new digital architecture for signal modulation and quantization. Using error masking strategy, this method can offer smaller routing area and less power consumption without sacrificing any system performance. Simulation results confirm the theoretical predictions. Finally, the design guidelines are derived to fulfill the customized synthesizer specifications.     

采用balun低噪声放大器的5GHz 7.2-dB NF低功耗直接转换接收机前端电路

A 5GHz low power direct conversion receiver radio frequency front-end with balun LNA is presented. A hybrid common gate and common source structure balun LNA is adopted, and the capacitive cross-coupling technique is used to reduce the noise contribution of the common source transistor. To obtain low 1/f noise and high linearity, a current mode passive mixer is preferred and realized. A current mode switching scheme can switch between high and low gain modes, and meanwhile it can not only perform good linearity but save power consumption at low gain mode. The front-end chip is manufactured on a 0.13-μm CMOS process and occupies an active chip area of 1.2 mm². It achieves 35 dB conversion gain across 4.9-5.1 GHz, a noise figure of 7.2 dB and an IIP3 of -16.8 dBm, while consuming 28.4 mA from a 1.2 V power supply at high gain mode. Its conversion gain is 13 dB with an IIP3 of 5.2 dBm and consumes 21.5 mA at low gain mode.     

Unfolding the frequency spectrum for undersampled wideband data

In this letter, we discuss the problem of unfolding the frequency spectrum for undersampled wideband data. The problem is of relevance to state-of-the-art radio frequency measurement systems, which capture repetitive waveform based on a sampling rate that violates the Nyquist constraint. The problem is presented in a compact form by the inclusion of a complex operator called the CN operator. The ease-of-use problem formulation eliminates the ambiguity caused by folded frequency spectra, in particular those with lines standing on multiples of the Nyquist frequency that are captured with erroneous amplitude and phase values.     

无线广播电视监测信号接收链路技术分析

通过对无线广播电视信号接收链路的分析研究,汇总整理了与接收性能有关的技术要点,提出改善接收效果、提高监测性能的具体措施。通过在监测前端的实践,极大提高监测数据的准确性,为广播电视发射台的安全播出提供了重要保障。     

欠采样下的多频带通信信号高精度载频估计

为根本解决当前主流的基于调制宽带转化器(MWC )的欠采样频率估计方法存在的3个问题,即采样通道数目多、载频估计精度低、信源频带分布稀疏度条件高,该文提出基于互素谱相位差校正的通信信号载频估计方法。通过将两路互素欠采样取代多路调制宽带转化器欠采样,克服了其耗费欠采样通道数目多的缺陷;基于此,既推导出全景谱谱峰位置与两路互素输出IDFT支路序号对的映射关系,又推导出相邻快拍下该序号对的IDFT相位差与载频值的解析关系,从而克服了主流方法的载频估计精度低的缺陷;通过将最小尺寸全相位滤波器对半分解方法融入原型滤波器设计,构造出两路并行互素谱分析器,还彻底克服了对信源频带分布稀疏度条件高的依赖。仿真表明,相比于主流方法,该文方法仅需耗费不足其1/2的样本数量,载频估计的相对误差降至其1/20以下。     

基于超表面的低雷达散射截面宽频贴片阵列天线设计

该文设计了一种基于超表面(MS)的低雷达散射截面(RCS)宽频贴片阵列天线。该天线由工作在不同频段的两种开缝贴片天线组成2×4的八元阵,以此实现天线小型化并扩展其带宽,根据相位相消原理,将两种人工磁导体(AMC)以棋盘布阵的方式组成超表面加载到天线阵周围,使其具有低RCS特性。实测和仿真结果表明：加载超表面后,天线工作带宽由5.7~6.2 GHz扩展为5.6~6.6 GHz,相对带宽增大1倍,辐射特性基本保持不变;当平面波垂直入射时,天线单站RCS减缩效果明显,其中,X极化波下3 dB减缩带宽为5.3~7.0 GHz,最大减缩量达31 dB,Y极化波下3 dB减缩带宽为5.8~6.9 GHz。     

短采样宽带信号方位估计快速算法

该文针对短采样宽带信号近似最大似然(AML)方位估计计算量大的问题,将马尔可夫蒙特卡罗方法与近似最大似然方位估计相结合,提出一种基于Gibbs抽样的近似最大似然方位估计新方法(Approximated Maximum Likelihood DOA estimator based on Gibbs Sampling, AMLGS)。研究结果表明,AMLGS方法不但保持了原近似最大似然方位估计方法的优良性能,而且显著减小了计算量。把原方法的计算复杂度从O(LK)减少到O(KJNs)。