A Thermo-Tunable Metamaterial as an Actively Controlled Broadband Absorber

Metamaterials have attracted increasing attention in recent years due to their powerful abilities in manipulating electromagnetic (EM) waves. However, most previously reported metamaterials are unable to actively control full-band EM waves. In this paper, we propose a thermo-tunable broadband metamaterial (T-TBM) using paraffin-based composites (PD-Cs) with different phase transition temperatures. Active control of the T-TBM reflection loss peaks from low to high frequency is realized by manipulating the solid–liquid state of the PD-Cs at different phase transition temperatures. The absorption peak bandwidth (where the reflection loss value is less than −30 dB) can be changed, while the broad bandwidth absorption (where the reflection loss value is less than −10 dB) is satisfied by adjusting the temperature of the T-TBM. It is shown that the stagnation of the phase transition temperature of the PD-Cs in the T-TBM provides a time window for actively controlling the EM wave absorption response under different thermal conditions. The device has a broad application prospect in the fields of EM absorption, intelligent metamaterials, multifunctional structural devices, and more.

Liquid crystal-integrated metasurfaces for an active photonic platform

Metasurfaces have opened the door to next-generation optical devices due to their ability to dramatically modulate electromagnetic waves at will using periodically arranged nanostructures.However,metasurfaces typically have static optical responses with fixed geometries of nanostructures,which poses challenges for implementing transition to technology by replacing conventional optical components.To solve this problem,liquid crystals(LCs)have been actively employed for designing tunable metasurfaces using their adjustable birefringent in real time.Here,we review recent studies on LCpowered tunable metasurfaces,which are categorized as wavefront tuning and spectral tuning.Compared to numerous reviews on tunable metasurfaces,this review intensively explores recent development of LC-integrated metasurfaces.At the end of this review,we briefly introduce the latest research trends on LC-powered metasurfaces and suggest further directions for improving LCs.We hope that this review will accelerate the development of new and innovative LC-powered devices.

Research of an Active Tunable Vibration Absorber for Helicopter Vibration Control

Significant structural vibration is an undesirable characteristic in helicopter flight that leads to structural fatigue, poor ride quality for passengers and high acoustic signature. Previous Individual Blade Control (IBC) techniques to reduce these effects have been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an active tunable vibration absorber using IBC approach to adaptively alter the 'structural impedance' at the blade root. In this paper, a mathematical model was developed to predict the response under harmonic excitations. An adaptive notch algorithm was designed and implemented on a TMS320c40 DSP platform. Reference signal synthesis techniques were used to automatically track the shifts in the fundamental vibratory frequency due to variations in flight conditions. Closed-loop tests performed on the proof-of-concept hardware achieved significant vibration suppression at harmonic peaks as well as the broadband reduction in vibration. The investigation verified the capability of the Smart Spring to suppress multiple harmonic components in blade vibration through active impedance control.

Tunable vacancy defect chemistry on free-standing carbon cathode for lithium-sulfur batteries

The defect chemistry is successfully modulated on free-standing and binder-free carbon cathodes for highly efficient Li-S redox reactions.Such rationally regulated defect engineering realizes the synchronization of ion/electron-conductive and defect-rich networks on the threedimension carbon cathode,leading to its tunable activity for both relieving the shuttle phenomenon and accelerating the sulfur redox reaction kinetics.As expected,the defective carbon cathode harvests a high rate capacity of 1217.8 mAh g^(-1)at 0.2 C and a superior capacity retention of61.7%at 2 C after 500 cycles.Even under the sulfur mass loading of 11.1 mg cm^(-2),the defective cathode still holds a remarkable areal capacity of 8.5 mAh cm^(-2).

Active tunable terahertz bandwidth absorber based on single layer graphene

In this paper,an active tunable terahertz bandwidth absorber based on single-layer graphene is proposed,which consists of a graphene layer,a photo crystal plate,and a gold substrate.When the Fermi energy(Ef)of graphene is 1.5 eV,the absorber shows high absorption in the range of 3.7 THz–8 THz,and the total absorption rate is 96.8%.By exploring the absorption mechanism of the absorber,the absorber shows excellent physical regulation.The absorber also shows good adjustability by changing the Efof graphene.This means that the absorber exhibits excellent tunability by adjusting the physical parameters and Efof the absorber.Meanwhile,the absorber is polarization independent and insensitive to the incident angle.The fine characteristics of the absorber mean that the absorber has superior application value in many fields such as biotechnology and space exploration.

A compact and reconfigurable low noise amplifier employing combinational active inductors and composite resistors feedback techniques

A compact and reconfigurable low noise amplifier(LNA)is proposed by combining an input transistor,composite transistors with Darlington configuration as the amplification and output transistor,T-type structure composite resistors instead of a simplex structure resistor,a shunt inductor feedback realized by a tunable active inductor(AI),a shunt inductor peaking technique realized by another tunable AI.The division and collaboration among different resistances in the T-type structure composite resistor realize simultaneously input impedance matching,output impedance matching and good noise performance;the shunt feedback and peaking technique using two tunable AIs not only extend frequency bandwidth and improve gain flatness,but also make the gain and frequency band can be tuned simultaneously by the external bias of tunable AIs;the Darlington configuration of composite transistors provides high gain;furthermore,the adoption of the small size AIs instead of large size passive spiral inductor,and the use of composite resistors make the LNA have a small size.The LNA is fabricated and verified by GaAs/InGaP hetero-junction bipolar transistor(HBT)process.The results show that at the frequency of 7 GHz,the gain S_(21)is maximum and up to 19 dB;the S_(21)can be tuned from 17 dB to 19 dB by tuning external bias of tunable AIs,that is,the tunable amount of S_(21)is 2 dB,and similarly at 8 GHz;the tunable range of 3 dB bandwidth is 1 GHz.In addition,the gain S_(21)flatness is better than 0.4 dB under frequency from 3.1 GHz to 10.6 GHz;the size of the LNA only has 760μm×1260μm(including PADs).Therefore,the proposed strategies in the paper provide a new solution to the design of small size and reconfigurable ultra-wideband(UWB)LNA and can be used further to adjust the variations of gain and bandwidth of radio frequency integrated circuits(RFICs)due to package,parasitic and the variation of fabrication process and temperature.

2μm可调谐全光纤脉冲激光器

本文采用光纤尾纤型马赫曾德型(MZ)结构的周期性铌酸锂(LiNbO 3)电光强度调制器进行主动调Q,设计了在环形腔结构中加入可调谐滤波器,实现了波长在1882 nm~1992 nm可调谐脉冲激光的稳定输出。调节施加在调制器上的信号频率,产生了激光器重复频率在15~70 kHz可调的脉冲激光。在重复频率为15 kHz时,泵浦功率为1 W时,获得最大单脉冲能量6.4μJ,峰值功率5.1 W。本研究具有全光纤化,波长大范围可调等优势,有助于进一步探索调Q脉冲激光的可调谐范围及其潜在应用。

High repetition rate actively mode-locked Er:fiber laser with tunable pulse duration

An actively mode-locked fiber laser with controllable pulse repetition rate and tunable pulse duration is presented,in which an optical delay line(ODL)is used to adjust the cavity length precisely for regulating the repetition rate,and a semiconductor optical amplifier(SOA)is introduced for enabling the pulse duration control.Experimentally,continuous tuning of the repetition rate from 2 GHz to 6 GHz is realized,which is limited by the availability of an even higher repetition rate radiofrequency(RF)source.Specifically,when the repetition rate is fixed at 2.5 GHz,the pulse duration can be tuned from 4 ps to30 ps,which is,to the best of our knowledge,the widest tuning range of pulse duration ever achieved in a gigahertz(GHz)repetition rate actively mode-locked 1.5μm fiber laser oscillator.

可调谐太赫兹超材料吸波器研究进展

太赫兹超材料吸波器具有吸收强、厚度薄、质量轻等优点,已被广泛应用于隐身材料、频率选择表面、太赫兹成像、通信传感等方面。但是,基于金属结构的传统太赫兹超材料吸波器一旦完成加工后,它的吸收性能是固定不变的。为解决这一问题,研究人员通过引入活性超材料设计了可调谐太赫兹超材料吸波器。结合可调谐太赫兹超材料吸波器的国内外研究现状,分类阐述了几类典型的可调谐太赫兹超材料吸波器,重点对单频带、多频带、宽频带以及可切换双功能太赫兹超材料吸波器的相关研究工作进行了梳理与总结,并对其未来发展趋势进行了分析。

基于VDTA的混合多模式双二阶滤波器的设计

针对各类核探测仪的供电电源系统和核能谱测量仪的前端电子线路广泛采用的滤波技术,提出了一种设计混合多模式双二阶滤波器的新方法。首先通过分析新的有源元件——电压差跨导放大器(VDTA)的一般工作原理,提出了一种采用CMOS晶体管实现VDTA的电路;然后基于实现的VDTA模块,设计了采用两级VDTA模块实现单输入、三输出或三输入、单输出电子可调混合多模式双二阶滤波器。通过选择输入端,该滤波器可以产生5种不同的电压和跨导纳模式滤波器功能,实现低通、带通、高通、带阻和全通5种不同的滤波信号。同时对滤波器的有限频率效应、稳定性条件和寄生元件效应进行了分析;仿真实验结果验证了所设计滤波器的性能,表明了理论设计的正确性和有效性。

节流口可调式减振器的性能分析与试验研究

设计了一种节流口可调式减振器,阐述了该减振器的结构形式和工作原理,对其外特性进行了理论分析 通过试验检验该减振器的性能,建立了阻尼力与步进电机转角之间的关系 试验结果表明,该减振器设计合理,性能稳定,满足设计要求;理论分析与试验结果相吻合 将该可调阻尼减振器应用于半主动悬架控制系统,可以获得良好的振动特性。

含时滞半主动悬架及其控制系统

建立了含时滞的半主动悬架的数学模型,提出了含时滞的半主动悬架临界时滞求取的理论分析及计算方法, 并设计了可调阻尼减振器及半主动悬架控制系统。在仿真计算基础上,进行了半主动悬架系统1／4模型台架试验, 分析了时滞对半主动悬架及其控制动态特性的影响,计算和试验结果基本吻合,为半主动悬架系统失稳机理及稳定性控制研究奠定了基础。

阻尼非线性半主动悬架的建模与控制

基于可调阻尼减振器的试验结果,拟合了可调阻尼减振器阻尼系数与步进电动机转角之间的非线性关系,建立了阻尼非线性半主动悬架数学模型,设计了模糊动态最优控制策略,研制了阻尼非线性半主动悬架系统控制器,在仿真的基础上,进行了实车道路试验。结果表明,阻尼非线性半主动悬架模型更接近实际模型,有效改善了车辆的乘坐舒适性、行驶安全性,协调了整车综合性能。

一种用于1/2汽车主动悬架的可调模糊控制器

本文对用于1/2汽车主动悬架系统的模糊控制器进行了研究。在设计模糊控制器时,引入模糊控制规则调整因子,使得控制策略灵活,适应性强,并以模拟路面时间历程为输入对汽车1/2主动悬架模型进行计算机仿真,结果表明用这种可调模糊控制器控制的主动悬架,汽车的适性和操纵稳定性都得到了明显改善。

可调减振器阻尼控制与半主动悬架的试验研究

建立车辆半主动悬架1/4模型,提出可调减振器阻尼控制的实现方法,设计半主动悬架台架试验系统。在可调减振器试验的基础上,建立了可调减振器阻尼与步进电机转角之间的关系。最后,对半主动悬架1/4物理模型进行了台架试验。结果表明,试验系统稳定可靠,阻尼控制易于实现,半主动悬架能较好地适应不同的路面输入,为半主动悬架及控制系统的进一步研究奠定了基础。

一款增益可调且平坦的超宽带低噪声放大器

设计了一款增益可调且平坦的超宽带低噪声放大器(FTG UWB-LNA)。输入级采用具有新型偏置电路和RLC反馈的共基-共射放大器;输出级采用电流镜偏置的共集放大器;放大级采用新型有源电感与达林顿结构构成的组合电路。实现了增益的可调且平坦以及宽带输入输出匹配。基于WIN 0.2μm GaAs HBT工艺库,对FTG UWB-LNA进行验证,结果表明:在1 GHz～6 GHz频带内,增益S_(21)可以在21.16 dB～23.9 dB之间调谐,最佳增益平坦度达到±0.65 dB;S_(11)小于-10 dB;S_(22)小于-12 dB;FN小于4.08 dB;在4 V的工作电压下,静态功耗小于33 mW。

有源频率选择表面研究进展及应用前景

有源频率选择表面(AFSS)是在传统频率选择表面(FSS)单元图形间加载一系列阻抗元件而构成的新型FSS,它具有可调的电磁特性。在分析了AFSS电磁特性调控机理的基础上,综述了AFSS在可调电磁屏蔽室、可调空间电磁滤波器、可调雷达天线等领域的研究进展,并重点阐述了AFSS在智能吸波结构上的应用,最后归纳了AFSS分析方法。

可电调谐超材料研究

超材料的谐振特性与其周期单元特性相关,周期单元的某一或是某几个参数的改变可以实现对超材料反射特性的调谐。利用有源集总元件的可变电阻特性,结合超材料设计,通过仿真优化和实验制备得到可电调谐超材料;分析对比了两种不同的布线方式所带来的不同的反射率特性和可调谐特性;并采用等效电路法对主动FSS层的阻抗特性进行了分析。

一种采用有源电感的可调增益小面积超宽带低噪声放大器

设计了一款采用可调谐有源电感(TAI)的可调增益的小面积超宽带低噪声放大器(LNA),输入级采用共基极结构,输出级采用射随器结构,分别实现了宽带输入和输出匹配;放大级采用带有反馈电阻的共射共基结构以取得宽的带宽,并采用TAI作负载,通过调节TAI的多个外部偏压使LNA的增益可调。结果表明,该LNA在2 GHz^9 GHz的频带内,通过组合调节有源电感调节端口的偏压可实现S21在16.5 d B^21.1 d B的连续可调;S_(11)小于-14.7 d B;S_(22)小于-19.3 d B;NF小于4.9 d B;芯片面积仅为0.049 mm^2。

基于AFSS的吸波性能可调的微波吸收体

从传统的Salisbury屏结构出发,设计了一种由半圆和三角图形组合而成的频率选择表面(FSS)单元,随后将PIN二极管与FSS图形相结合,制得了一种AFSS吸波结构体。利用电抗加载方式对该结构体进行了仿真,并在微波暗室下对实物进行了测试。结果表明:测试结果和仿真结果变化趋势相似。在2～8 GHz内,结构体吸收峰从–4 dB到–16 dB动态可调;而在8～18 GHz内,–8 dB以下的结构体吸波带宽从1 GHz到5 GHz动态可调。