Simulation of radio-frequency atmospheric pressure glow discharge in γ mode

The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.

Radio Frequency Environment Effect Algorithms and Implementation in Signal-level Radar System Simulation

In radar system simulation,the reliability of simulation results depends not only on radar and target models,but also on radio frequency (RF) environment models,including clutter,multipath,diffraction,atmosphere refraction and attenuation.In traditional radar function simulation,all of these factors are grouped into a single pattern-propagation factor and can only give limited information for radar models.In signal-level simulation,radar models require simulated echoes should include information such as delay,doppler frequency,polarization,etc.By discussing and analyzing the principles and algorithms of RF environment effects (clutter,multipath,diffraction,atmosphere refraction and attenuation),this paper is supposed to provide a general RF environment model in signal-level.Algorithms for the Weibull clutter with Gaussian power spectral density (PSD) is discussed;A standard multipath and diffraction algorithm is analyzed,and the spherical earth and knife edge(SEKE)diffraction algorithm is introduced;The ray-tracing algorithm and the effective earth model are discussed;Algorithms for the absorption of oxygen and vapor are introduced;For certain algorithms,some practical advice is given.Finally,an object-oriented RF environment effects model is implemented,which has been dedicatedly designed for signal-level simulations and can provide relatively authentic simulated RF environment for the signal-level simulation of radar systems.Two simulation examples including clutter model and multipath and diffraction model are carried out and analyzed.

A Simple Model for the Calculation of Plasma Impedance in Atmospheric Radio Frequency Discharges

In atmospheric radio-frequency （rf） discharges, the plasma parameters, such as electron density, sheath thickness and sheath voltage, are not easy to be probed experimentally, while the electrical characteristics, such as impedance, resistance and reactance, are relatively convenient to be measured. In this paper we presented a simple theoretical model derived from the fluid description of generated plasmas without considering the circuit model, to investigate the relationship between the plasma impedance and plasma parameters. By introducing a relaxation frequency, the plasma impedance could be predicted by formulas presented in this study, and the mean electron density and sheath thickness can also be calculated from the measured or simulated impedance and reactance, respectively.

Gas Breakdown of Radio Frequency Glow Discharges in Helium at near Atmospheric Pressure

A one-dimensional self-consistent fluid model was developed for radio frequency glow discharge in helium at near atmospheric pressure, and was employed to study the gas breakdown characteristics in terms of breakdown voltage. The effective secondary electron emission coefficient and the effective electric field for ions were demonstrated to be important for determining the breakdown voltage of radio frequency glow discharge at near atmospheric pressure. The constant of A was estimated to be 64：t=4 cm-lTorr-1, which was proportional to the first Townsend coefficient and could be employed to evaluate the gas breakdown voltage. The reduction in the breakdown voltage of radio frequency glow discharge with excitation frequency was studied and attributed to the electron trapping effect in the discharge gap.

Numerical study on characteristics of radio-frequency discharge at atmospheric pressure in argon with small admixtures of oxygen

In this paper, a 1D fluid model is developed to study the characteristics of a discharge in argon with small admixtures of oxygen at atmospheric pressure. This model consists of a series of equations, including continuity equations for electrons, positive ions, negative ions and neutral particles, the energy equation, and the Poisson equation for electric potential. Special attention has been paid to the electron energy dissipation and the mechanisms of electron heating, while the admixture of oxygen is in the range of 0.1%-0.6%. It is found that when the oxygen-to-argon ratio grows, the discharge is obviously divided into three stages： electron growth, electron reduction and the electron remaining unchanged. Furthermore, the cycle-averaged electric field, electron temperature, electron Ohmic heating, electron collisionless heating, electron energy dissipation and the net electron production are also studied in detail, and when the oxygen-to- argon ratio is relatively larger （R = 0.6%）, double value peaks of electron Ohmic heating appear in the sheath. According to the results of the numerical simulation, various oxygen-to-argon ratios result in different amounts of electron energy dissipation and electron heating.

Theoretical Study on the Characteristics of Atmospheric Radio Frequency Discharges by Altering Electrode Gap

In this paper, we present a theoretical study on the discharge characteristics of radio-frequency discharges at atmospheric pressure driven by a higher frequency of 40.68 MHz while the electrode gap is altered. Based on the analytical equations and simulation data from a one-dimensional fluid model, an optimal gap between electrodes, at which the largest electron density is obtained, can be observed under a constant power condition; however, as the electrode gap increases the time-averaged electron temperature decreases, and the underpinning physics is also discussed based on the simulation results. This study indicates that at a constant power by choosing an appropriate electrode spacing, the rf discharge can be effectively optimized at atmospheric pressure.

Radio Frequency Tank Circuit for Probing Planar Lipid Bilayers

We present first results from a hybrid coplanar waveguide microfluidic tank circuit for monitoring lipid bilayer formation and fluctuations of integrated proteins. The coplanar waveguide is a radio frequency resonator operating at ~250 MHz. Changes within the integrated microfluidic chamber, such as vesicle bursting and subsequent nanopore formation alter the reflected signal, and can be detected with nanosecond resolution. We show experimental evidence of such alterations when the microfluidic channel is filled with giant unilamellar vesicles (GUVs). Subsequent settling and bursting of the GUVs form planar lipid bilayers, yielding a detectable change in the resonant frequency of the device. Results from finite element simulations of our device correlate well with our experimental evidence. These simulations also indicate that nanopore formation within the bilayer is easily detectable. The simulated structure allows for incorporation of microfluidics as well as simultaneous RF and DC recordings. The technique holds promise for high throughput drug screening applications and could also be used as an in-plane probe for various other applications. It opens up possibilities of exploring ion channels and other nano scale pores in a whole new frequency band allowing for operating at bandwidths well above the traditional DC methods.

Effect of Duty Cycle on the Characteristics of Pulse-Modulhted Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge

Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are studied. The numerical results show that the dependence of discharge characteristics on the duty cycle is sensitive in the region of around 40% duty cycle under the given simulation parameters. In the case of a larger duty cycle, the plasma density is higher, the discharge becomes more intense, but the power consumption is higher. When the duty cycle is lower, one can get a weaker discharge, lower plasma density and higher electron temperature in the bulk plasma. In practical applications, in order to get a higher plasma density and a lower power consumption, it is more important to choose a suitable duty cycle to modulate the RF power supply.

射频隐身仿真分析和评估研究

当前对飞行器平台射频隐身的重视度越来越高,为了贴合实际地分析评估射频隐身性能,提出了一种用于多机协同传感器信号级联合仿真的评估方法。结合射频特征、低被截获性能表征指标以及作战场景、飞行器平台、雷达模型、截获接收机模型和低被截获性能分析算法模型,构建了可以用来对多机协同等作战样式下的射频隐身性能进行分析评估的仿真系统,为射频隐身设计提供支撑依据与评估验证环境。针对信息量大、复杂度高的表征参量计算模型,研究其近似快速算法,提高仿真系统的实用性。

高频雷达中射频干扰的RD图表现机理与建模仿真

射频干扰对于高频超视距雷达是一大威胁。本文研究射频干扰的距离-多普勒图表现机理和建模方法,分析了射频干扰频域特性与距离-多普勒图表现的关系,讨论了雷达信号处理中的射频干扰信号频谱变化。根据高斯白噪声通过线性滤波器的特性,设计滤波器响应函数来产生不同频谱和距离-多普勒图形态的射频干扰。基于以上研究,本文将射频干扰分为单频、窄带和宽带3类,归纳出射频干扰的距离-多普勒图表现机理,并提出了基于卷积的射频干扰新型建模方法。实测数据和仿真表明:本文对射频干扰距离-多普勒图表现机理分析合理,建模方法能很好地模拟多数实测干扰距离-多普勒图形态。

射频能量收集印刷天线仿真模型中长丝机织物结构简化方法及有效性

获得仿真精确度高且计算成本低的仿真模型是高效设计织物基丝网印刷射频能量收集天线的基础。本文构建了长丝机织物天线基底的几种不同简化结构特征的仿真模型,采用HFSS仿真软件模拟了织物仿真模型与电磁波的相互作用,且以孔隙率和粗糙度为变量参数化分析了具有不同仿真结构基底的天线性能差异,并实际制备了几种不同简化结构基底的天线。结果表明:通过对比反射率和透射率发现,细观交织结构可以等效为具有孔洞和/或凹凸结构模型,均匀结构模型基底的天线辐射性能、增益及效率都显著偏高。进一步以射频能量收集为场景的模型有效性及验证结果表明,仿真模拟结果与实际测试结果吻合良好,且不同简化结构基底的天线性能也无显著性差异。在超高频范围内,不同简化结构基底的天线最大传输距离达220 cm,在1 m处的单位面积接收信号强度在8.442 mW/cm^(2)以上,天线输出电压和能量转换效率可分别达135 mV、60%。因此,为节约计算成本,就孔隙率不超过30%且粗糙度在5.39μm以下的长丝平纹机织物基底,在丝网印刷超高频射频能量收集天线仿真模拟中可将其等效为均匀介质模型。

超声射频信号Nakagami参量与肌肉组织疲劳进程的相关性研究

肌肉疲劳、萎缩等肌肉功能状态的准确评估在人类健康、体育运动等领域非常重要。本课题研究肌肉组织超声射频信号所表征的肌肉微结构信息与肌肉疲劳进程之间的相关性,提出基于超声射频信号Nakagami参量的肌肉功能状态评价方法。通过有限元仿真软件进行肌肉组织模拟仿真,并对不同参量超声射频信号进行分析处理。发现Nakagami模型特征参数m值随着肌束半径的减小呈下降趋势,随着间质密度的增加呈上升趋势,随着肌束速度的增加呈下降趋势,Nakagami模型特征参数m值与肌束半径和间质密度呈正相关性,与肌束声速呈负相关性。树脂仿体与离体肌肉的实验结果表明,超声射频信号的统计特征随着树脂仿体半径增大而减小(从0.880单调下降至0.620),随着肌肉组织压缩距离的增大而增大(从0.540单调增加到1.220)。理论模拟、仿体实验和肌肉实验的结果都表明,超声射频信号的Nakagami模型特征参数m与肌肉组织不同参量间存在明显的相关性。该方法可为进一步评估肌肉功能状态提供理论参考与技术手段。

助剂辅助稠油射频加热模拟实验及稠油温度影响因素

为了解决原始稠油储层射频加热技术存在加热距离短的技术难题,提出助剂辅助稠油射频加热技术。在介绍加热机理和工艺的基础上,设计了模拟实验系统并开展了助剂辅助稠油射频加热模拟实验并对稠油温度分布的影响因素进行了研究。结果表明:稠油样品温度随着金属镍粉末和活性炭粉末注入量的增大而升高,但金属镍粉末对稠油样品温度的影响程度较活性炭粉末更大;在助剂使用总量相同的情况下,金属镍粉末和活性炭粉末协同作用比其单独运用时稠油样品的温度更高、射频加热效果更好。研究结果对于射频加热助剂优选和提高射频加热性能提供了指导。

多比特数字射频存储器的Simulink建模与仿真

数字射频存储器(DRFM)是相干干扰机的关键部件,主要用作干扰信号源;讨论了幅度量化DRFM的工作原理与流程,给出了幅度量化DRFM的Simulink仿真模型建立与仿真实验研究的一般方法;在此基础上研究了多比特幅度量化DRFM的寄生信号性能与量化电平的关系,建立了多比特幅度量化DRFM的采样量化编码以及恢复的Simulink模型,并对多比特幅度量化DRFM的采样率与量化电平的关系进行了仿真实验,分析了实验结果,给出了结论,分析结果同时也表明了理论研究的正确性。

基于数值模拟的射频加热技术在食品中的应用

射频加热技术是一种新型的食品加工处理技术,在食品加工领域具有巨大发展潜力。受耗时长、成本高等因素限制,基于实验方法的研究可行性较差。数值模拟研究可以建立射频加热处理食品过程的多物理场模型并对其进行分析计算,从而预测射频处理中食品材料的变化及可视化结果。本文介绍了射频加热技术的原理及其数值模拟的理论基础,综述了基于数值模拟的射频加热技术在解冻、干燥、杀虫和灭菌等领域的研究进展。总结了在食品加工过程中改善射频加热均匀性的方法和原理,并对射频数值模拟技术未来的研究方向进行展望,从而为射频加热的数值模拟技术进一步发展提供参考。

基于COMSOL Multiphysics的经皮心肌内室间隔射频消融仿真模型构建及应用

目的:构建一种经皮心肌内室间隔射频消融仿真模型,探究不同激励电压、不同消融时间对消融区域的影响。方法:以梗阻性肥厚型心肌病患者的术前CT数据为基础,利用Mimics软件实现心脏各区域组织的分割与三维表面重建,通过SolidWorks软件将重建后的各部分转化为三维实体模型,并将其与在COMSOL Multiphysics仿真软件中建立的电极针结构结合在一起,得到梗阻性肥厚型心肌病的经皮心肌内室间隔射频消融仿真模型。基于该模型设置电磁、热多物理场边界条件,并对组织温度分布以及消融时间、激励电压对消融区域的影响进行仿真分析。结果:利用该模型可以实现经皮心肌内室间隔射频消融的仿真分析,且不同的激励电压、不同的消融时间对有效消融区域具有明显的影响。结论:构建的经皮心肌内室间隔射频消融仿真模型为后续开展多种因素对消融结局的影响提供了模型基础,对进一步研究实际临床治疗中的参数优化具有重要意义。

面向物流工程的射频识别虚拟仿真实验的教学探索研究

随着电子通信的发展和物联网的推广,射频识别(RFID)技术在物流行业有着重要的用途。RFID利用射频信号的空间耦合传输,通过非接触的方式识别目标、读取数据,可以用于物流管理、仓储分拣、安全监测、信息传递等场景。读写器是RFID系统中的关键装置,负责对电子标签进行读取或写入信息。在面向物流工程专业的RFID课程教学中,由于阅读器系统架构复杂、理论性强,使得学生对RFID读写器机制的理解存在困难。在RFID教学中引入射频EDA仿真软件,通过虚拟仿真实验直观展示RFID读写器的工作机理,加强学生的实践和创新能力。文章探索了结合物流行业开展RFID教学活动,通过引入基于虚拟仿真的实践教学环节,提升教学质量,为物流工程专业培养复合型高素质人才。

红外/射频波束合成器设计及研究

多模复合制导技术在现代精确制导武器系统中扮演着重要角色。为提升制导性能,有必要开展半实物复合仿真试验研究制导系统的性能和功能。波束合成器作为复合制导半实物仿真系统的关键部件,通过反射红外信号、透射射频信号实现红外/射频信号复合,并将其通过共口径投射到被测设备入瞳处。文章设计薄膜式红外/射频波束合成器,并进行性能分析,结果表明薄膜式红外/射频波束合成器红外(中、长波)反射率不低于90%,射频(S、C、X、Ku、Ka、W波段)透过率不低于97%。

RFID系统的Matlab/Simulink建模及特性分析

首先介绍了射频识别(Rad io Frequency Identification,RFID)系统的工作原理,阐述了系统的结构和模块划分;在此基础上使用Matlab/Simulink对RFID系统进行了模型设计;最后,利用此模型对系统进行了实验仿真,并具体分析了码间干扰和调制深度对整个系统性能的影响。

针对时空统计特性的箔条云半实物射频仿真

本文针对箔条云半实物射频仿真(Radio Frequency Simulation System,RFSS)中的关键问题进行研究,给出了对箔条云进行半实物射频仿真时的三元组的馈电系数的计算公式.与对点目标的仿真不同,对箔条云的仿真更注重其散射场统计特性的复现.箔条云的空间随机分布和随机运动特性,表现为其回波的空间相关性和时间相关性.本文通过三元组馈电系数之间的相关性来仿真箔条云散射回波的空间相关性;通过差分重心公式的横向平移、径向相移以及时域滤波来仿真箔条云散射回波的时间相关性.数值模拟结果验证了所给出的箔条云射频仿真方法的有效性.这些工作为箔条云的半实物射频仿真提供了理论基础和分析框架.