Power transfer efficiency in an air-breathing radio frequency ion thruster

Due to a series of challenges such as low-orbit maintenance of satellites, the air-breathing electric propulsion has got widespread attention. Commonly, the radio frequency ion thruster is favored by low-orbit missions due to its high specific impulse and efficiency. In this paper, the power transfer efficiency of the radio frequency ion thruster with different gas compositions is studied experimentally, which is obtained by measuring the radio frequency power and current of the antenna coil with and without discharge operation. The results show that increasing the turns of antenna coils can effectively improve the radio frequency power transfer efficiency, which is due to the improvement of Q factor. In pure N_2 discharge,with the increase of radio frequency power, the radio frequency power transfer efficiency first rises rapidly and then exhibits a less steep increasing trend. The radio frequency power transfer efficiency increases with the increase of gas pressure at relatively high power, while declines rapidly at relatively low power. In N_(2)/O_(2) discharge, increasing the N_(2) content at high power can improve the radio frequency power transfer efficiency, but the opposite was observed at low power. In order to give a better understanding of these trends, an analytic solution in limit cases is utilized, and a Langmuir probe was employed to measure the electron density. It is found that the evolution of radio frequency power transfer efficiency can be well explained by the variation of plasma resistance, which is related to the electron density and the effective electron collision frequency.

Influence of anode temperature on ignition performance of the IRIT4-2D iodine-fueled radio frequency ion thruster

This paper reports the ignition performance of the iodine-fueled radio frequency(RF)ion thruster(IRIT)at different anode temperaturesT_(a0).The experimental results show that the anode temperature plays important role on the ignition process of the IRIT.There were two characteristic temperatures related to the anode:the minimum ignition temperatureT_(i0)and the stable ignition temperatureT_(is),which were much lower than the pipeline temperature and the storage tank temperature.AtT_(a0)<T_(i0),it failed to discharge.WhenT_(i0)≤T_(a0)<T_(is),it was ignited with dramatical oscillations.AtT_(a0)≥T_(is),the discharge was stable in a large anode temperature range.The analysis showed that the different discharge phenomena at different anode temperatures were attributed to the change of iodine flow rate during the process of the iodine deposition-clogging and sublimation-clearing inside the thruster.The research helps improve the preheating design of the iodine-fueled electric thruster.

Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source

The paper describes an experimental study of the characteristics of a pulse-modulated radiofrequency(RF)discharge sustained at low pressures,typical of the operating modes of RF gridded ion sources.The motivation for the study is the question of whether the RF pulsemodulated mode can increase the efficiency of the ion source.The ion current values extracted from an RF inductive ion source operating in continuous and pulse-modulated modes were compared.The experimental data were also compared with the parameter calculations based on a0D numerical model of the discharge.The measurements showed that the pulse-modulated operation mode of the RF ion source had a noticeable advantage when the power of the RF generator was 140 W or lower.However,as the generator power increased,the advantage was lost because the pulse-modulated operation mode,having a higher RF power instant value,entered the region of existence sooner than the continuous mode,where the ion production cost begins to grow with RF power.

Numerical research of a 2D axial symmetry hybrid model for the radio-frequency ion thruster

Since the high efficiency discharge is critical to the radio-frequency ion thruster(RIT), a 2D axial symmetry hybrid model has been developed to study the plasma evolution of RIT. The fluid method and the drift energy correction of the electron energy distribution function(EEDF) are applied to the analysis of the RIT discharge. In the meantime, the PIC-MCC method is used to investigate the ion beam current extraction character for the plasma plume region. The beam current simulation results, with the hybrid model, agree well with the experimental results, and the error is lower than 11%, which shows the validity of the model. The further study shows there is an optimal ratio for the radio-frequency(RF) power and the beam current extraction power under the fixed RIT configuration. And the beam extraction efficiency will decrease when the discharge efficiency beyond a certain threshold(about 87 W). As the input parameters of the hybrid model are all the design values, it can be directly used to the optimum design for other kinds of RITs and radio-frequency ion sources.

一种X波段三叉H型低电压RF MEMS开关设计

针对射频电路系统所需要的低电压,高隔离度,低插入损耗的应用需求,通过对开关正对面积对驱动电压产生的影响进行探究,设计了一款应用于X波段三叉H型的RF MEMS开关。开关具有六条悬臂梁作为支撑,通过增大上极板面积来降低开关的开启电压。分别使用HFSS和COMSOL对开关的射频性能和机械性能进行仿真,开关最终优化后,在8-12 GHz内,插入损耗为0.26~0.57 dB,隔离度大于31.30 dB。在10.1 GHz达到最优值,插入损耗为0.40 dB,隔离度为50.25 dB。开关电压在11V时就能够实现状态转换,开关的响应时间为18μs。此开关可与射频可重构器件结合,应用于新一代射频微波领域。

Progress of the RF negative hydrogen ion source for fusion at HUST

Huazhong University of Science and Technology has developed an experimental setup of a radio frequency(RF) driven negative hydrogen ion source,to investigate the physics of production and extraction of the H^(-)ions for neutral beam injection in nuclear fusion reactors.The main design parameters of the ion source are:RF power ≤40 kW;extraction voltage ≤10kV;accelerator voltage ≤20 kV.This paper gives an overview of the progress of the ion source with particular emphasis on some issues.The RF driver and source plasma are analyzed and optimized in terms of impedance matching,plasma characteristics and power coupling.In regard to the simulation analysis,a plasma model based on the particle-in-cell method and a beam trajectory model considering beam stripping loss are developed to investigate the plasma and negative ions transport inside the ion source.Furthermore,a collisional radiative model of H and H2is built for plasma optical diagnosis.

射频离子推力器研究进展

详细介绍了射频离子推力器的工作原理,以及近60年微牛级和毫牛级射频离子推力器的研究历程和成果。射频离子推进系统涉及多项关键技术难题,针对工质选取、射频电路阻抗匹配、气体流量控制、电中和控制和寿命问题提出了初步解决方案,结合射频离子推力器未来应用的需求,展望了射频离子推力器的发展趋势和研究方向。

静电式RF MEMS开关的可靠性

MEMS开关是最常见的RF MEMS控制元件,是RF结构中一个关键的MEMS器件。长期可靠性是目前制约MEMS开关商业化进程中的一个主要问题。主要综述了静电式RF MEMS开关可靠性的新进展。欧姆式开关通常由于黏附或接触电阻的增大而失效,电容式开关的主要失效机理则与电介质层的充电有关。接触材料的选择是决定欧姆开关可靠性最重要的一个因素,"主动断开/被动接触"MEMS开关适用于软金属材料欧姆接触的可靠性要求。改善电容式开关可靠性的途径是改善介电层、优化驱动电压波形等以减小介质层的充电。

基于RF MEMS开关的移相器设计

传统电子移相器由于损耗问题难以向更高频率发展,射频微机电系统(RF MEMS)技术的出现使其得以替代半导体开关来设计更高频率的移相器.利用具有优异RF性能的串联电阻式RFMEMS开关来进行开关线式移相器设计,通过开关切换不同的信号延迟通路,以实现从0°-180°步进22.5°的相移功能.仿真结果表明,该移相器在5.8 GHz时,插入损耗在-0.3--0.7 dB变化,输入回损低于-20 dB,相移功能正确.

碘工质射频离子推力器放电特性仿真研究

碘作为空间推进器中极具发展潜力的工质,近些年备受关注。与氙气不同,碘工质放电的产物较为复杂,主要是I^(+),同时还包含了少量的I^(-)、I_(2)^(+)、I_(2)^(+)和I_(3)^(+)。虽然多价离子的含量较少,但对推力器的工作性能存在着不小的影响。文章基于等离子体放电建立二维轴对称模型,分别研究了质量流量、射频功率以及背景压力对两种主要电离产物I^(+)、I_(2)^(+)的影响。质量流量为20~70 mL/min,随着质量流量的增加,I^(+)略微降低,I_(2)^(+)略微增加。射频功率为100~650 W,随着射频功率的增加,I^(+)迅速增加,I_(2)^(+)略微减小。背景压力在0.001~0.1 Torr时,随着背景压力的增加,I^(+)先是快速增加,在p0=0.015 Torr左右,开始减小;I_(2)^(+)一直维持缓慢增加。在忽略电离损耗的前提下,对三个影响因素进行全因子实验设计分析(DOE),得出质量流量在60 mL/min,射频功率在150 W,背压在0.015 Torr时,得出最优产物中I_(2)^(+):I^(+)=0.204094,与仿真结果 I_(2)^(+):I^(+)=0.205069,误差为0.48%。

用于钙离子全光囚禁的离子囚禁装置研究

随着离子光钟技术的飞速发展,由离子光钟中用来囚禁离子的射频场带来的微运动效应对其性能的影响也越来越不可忽略。为彻底消除这一效应,提出了全光囚禁离子光钟的实验方案。针对这一实验方案,设计并搭建了用于钙离子全光囚禁的离子囚禁装置。该装置是采用刀片型离子阱设计,能够实现剩余力仅有10^(-20) N量级的高精度的杂散电场补偿;具备6 mm的通关孔径,很好满足了全光囚禁实验中偶极囚禁激光的通过需求;基于改良的螺旋谐振器设计搭建的射频系统能够实现在9.33(1)MHz较低射频频率下的稳定耦合;结合高达10^(-9) Pa的真空制备和装配导电玻窗的真空腔体,可以实现长时间的离子囚禁。为全光囚禁钙离子提供了实验基础,对光学囚禁离子光钟的实现具有重大意义。

RF MEMS开关的研究进展及其应用

射频微电子机械系统（RF MEMS）开关是射频电子系统中的关键器件,首先简要介绍了RF MEMS开关的结构特点及分类方式,综述了RF MEMS开关的发展现状,列举了国内著名科研机构具有代表性的成果,并对比了其结构特点及性能参数,指出国内RF MEMS开关正向着小体积、宽频化、低驱动电压、高性能指标的方向发展。此外,还阐述了RF MEMS开关在多位移相器、可调滤波器、可重构天线等方面的应用,其在与多器件的集成和联合运用中潜力巨大。最后,分析了现有的RF MEMS开关的发展瓶颈,并展望了其以设计新结构、探寻新材料、探索新工艺、多种驱动方式相结合、多器件相集成为未来发展新方向。研发制作新的RF MEMS开关及其功能系统必将会对射频微波领域造成巨大影响。

基于谐振原理的RF MEMS滤波器的研制

采用与IC工艺兼容的硅表面MEMS加工技术,以碳化硅材料作为结构材料,研制出一种新型的基于谐振原理工作的RF MEMS滤波器。详细介绍了器件的工作原理、制备方法、测试技术和结果,并对测试结果做出分析。该RF MEMS滤波器由弹性耦合梁连接两个结构尺寸和谐振频率完全相同的MEMS双端固支梁谐振器构成,MEMS谐振器的结构决定了滤波器的中心频率,弹性耦合梁的刚度决定了滤波器的带宽。在大气环境下测试器件的频响特性,得到中心工作频率为41.5MHz,带宽为3.5MHz,品质因数Q为11.8。

一种基于Au-TiW触点的提高RF MEMS开关寿命的方法

针对基于Au-Au触点的射频微电子机械系统(RF MEMS)开关寿命低的问题,提出了一种高寿命RF MEMS开关的研制方法。对比Au与其他金属的硬度、杨氏模量以及方阻,最终选择性能优良的TiW金属作为新触点材料,其制备参数为溅射功率300 W,气压5 mTorr(1 mTorr=0.133 Pa),溅射时间1 568 s。设计了基于Au-TiW触点的RF MEMS开关工艺流程,给出了详细工艺参数,为进一步提高可靠性,设计了RF MEMS开关封装工艺流程并制作了封装样品。测试比较了基于Au-Au触点的RF MEMS开关与基于Au-TiW触点的RF MEMS开关的寿命与射频性能。结果表明,虽然基于Au-TiW触点的RF MEMS开关的射频性能有所降低,但开关寿命提高了两个数量级。该研究为提高RF MEMS开关的寿命提供了一种解决办法。

RF MEMS开关的静电斥力驱动研究

针对射频微机电系统(RF MEMS)开关工作时因介质充电而发生"粘连"失效的问题,提出了利用静电斥力驱动替代传统的静电引力驱动方式,使RF MEMS开关在工作时介质层不存在电势差,从根源上消除介质充电。通过COMSOL仿真软件,分析了静电斥力的产生机理,重点探究了静电斥力驱动结构中尺寸参数对可动极板位移的影响,并通过结构优化有效降低了驱动电压,为开关后续设计提供了参考。

基于改进PSO算法优化RF MEMS功分器设计

为了实现对射频微电子机械系统(MEMS)波段威尔金森功分器电路的精确设计和优化,使达到的设计目标满足性能要求,采用先进设计系统(ADS)软件对工作频带为32~36 GHz的RF MEMS功分器进行了建模仿真,并得到初始的电路设计参数。通过使用结合柯西变异的改进的粒子群优化(PSO)算法对RF MEMS功分器的初始电路设计参数进行优化,采用矩阵实验室(MATLAB)软件和高频结构仿真器(HFSS)软件进行联合仿真实现优化过程,最终得到满足设计目标的RF MEMS功分器的性能曲线,以及对应的功分器优化后的电路设计参数。结果表明,优化后的RF MEMS功分器回波损耗比设计目标优化了2.5 dB,插入损耗优化了0.3 dB,隔离度达到了-20 dB的设计要求。最终通过仿真验证了改进的PSO算法能够快速有效地对RF MEMS功分器的电路参数进行优化达到RF MEMS功分器设计的性能要求。

Sensitivity analysis of pull-in voltage for RF MEMS switch based on modified couple stress theory

An approximate analytical model for calculating the pull-in voltage of a stepped cantilever-type radio frequency （RF） micro electro-mechanical system （MEMS） switch is developed based on the Euler-Bernoulli beam and a modified couple stress theory, and is validated by comparison with the finite element results. The sensitivity functions of the pull-in voltage to the designed parameters are derived based on the proposed model. The sensitivity investigation shows that the pull-in voltage sensitivities increase/decrease nonlinearly with the increases in the designed parameters. For the stepped cantilever beam, there exists a nonzero optimal dimensionless length ratio, where the pull-in voltage is insensitive. The optimal value of the dimensionless length ratio only depends on the dimensionless width ratio, and can be obtained by solving a nonlinear equation. The determination of the designed parameters is discussed, and some recommendations are made for the RF MEMS switch optimization.

RF MEMS国内外现状及发展趋势

概述基于微电子机械系统MEMS(Micro-Electro-Mechanical System)技术的各类射频RF(Radio Frequency)无源器件及微小型单片集成系统的概念与内涵及其应用市场,重点介绍RF MEMS电容电感、开关、移相器、谐振器、滤波器、微型同轴结构、天线、片上集成微纳系统等的国内外研究现状、典型研究成果和产品、技术方案和微纳制造工艺及性能特点等,最后浅析RF MEMS领域的发展趋势。

Tokamak Plasma Flows Induced by Local RF Forces

The tokamak plasma flows induced by the local radio frequency （RF） forces in the core region are analyzed. The effective components of local RF forces are composed of the momentum absorption term and the resonant parallel momentum transport term （i.e. the parallel component of the resonant ponderomotive forces）. Different momentum balance relations are em- ployed to calculate the plasma flows depending on different assumptions of momentum transport. With the RF fields solved from RF simulation codes, the toroidal and poloidal flows by these forces under the lower hybrid current drive and the mode conversion ion cyclotron resonance heating on EAST-like plasmas are evaluated.

一种集成环行器的X波段三维异构集成T/R模组

微电子机械系统(MEMS)环行器被广泛应用于射频(RF)T/R微系统中,解决共用天线且收发隔离的问题。基于硅基三维(3D)异构集成工艺,设计了一种集成MEMS环行器的X波段T/R模组。该模组以高阻硅为介质基板,在硅基板上、下表面电镀金属图形,并堆叠多层硅基晶圆,在硅基模组上封装了集成无源器件(IPD)环行器,完成了多种微波芯片和MEMS环行器的系统级封装(SiP),将环行器紧凑集成在硅基T/R模组中。模组尺寸为12.0 mm×11.3 mm×2.0 mm。测试结果表明,在8~12 GHz频带内,模组接收通道增益为27 dB,接收通道噪声系数小于3.2 dB;发射通道增益为33 dB,饱和输出功率大于2 W。