宽带磁共振T/R开关的设计与实现

磁共振系统中的发射/接收（transmit/receive,T/R）开关用于收发通路的切换,要求在隔离大功率信号的同时具有较小的插入损耗;另外,在宽带磁共振谱仪中,一般的窄带T/R开关也不再适用.本文基于PIN（positive-intrinsic-negative）二极管设计了工作频率为10~100 MHz的宽带磁共振T/R开关.通过减小电平跳变、优化开关过冲和解决二极管被动导通等问题,获得了插入损耗小于1 dB、大功率信号隔离度大于75 dB、开关时间1 μs的整体性能.用本文设计的宽带T/R开关替代一般探头中的窄带T/R开关,在0.5 T核磁共振（NMR）波谱仪上测得了氢核和氟核两个不同频率的磁共振信号,验证了宽带T/R开关的宽带性能.     

低场核磁共振短死时间射频线圈与射频开关的设计

本文以核磁共振（NMR）射频线圈振铃信号产生原理为对象进行分析研究,提出了一种适用于低场环境下由环状间隙腔线圈与螺线管线圈构成的收发分离式短死时间射频线圈设计方案,采用优化调谐匹配网络提高发射效率;根据射频线圈方案需求设计了快速切换的射频开关及驱动．在此基础上依据仿真结果制作了短死时间射频线圈,并应用于自主研制的低场9.51 MHz便携式NMR谱仪系统,进行NMR实验,结果显示可将收发切换时间缩短至10 μs以内,验证了该设计方案的可行性．     

大电流窄脉宽LD脉冲驱动电源研究

基于三维激光成像雷达成像性能的需求,设计了一款应用于其发射系统的半导体激光器脉冲驱动电源。在对驱动电路模型理论分析的基础上,选取了RF高速功率开关,并运用PSPICE工具对驱动电路进行了仿真分析,设计出了一款峰值电流可达30A,上升沿小于2ns,脉宽小于6ns,重复频率15kHz的LD脉冲驱动电源。该设计满足激光成像雷达发射系统的技术指标要求。     

一种调节Marx电源脉冲边沿的驱动电路北大核心CSCD

为了调节固态Marx发生器输出脉冲的边沿,提出了一种新型的的驱动电路,该方案通过调整充放电管的驱动电压,结合驱动电路的硬件结构,调节米勒平台时间,进而调整充放电管开通速度,实现了对于高压输出脉冲的边沿调节,其结构简单,不需要每级独立的控制信号。对于该电路中驱动电压和开关管开通速度的关系建立了模型进行了推导。结合理论分析结果设计了驱动电路的参数,仿真结果表明该驱动电路能够调节输出脉冲边沿。搭建带有设计参数下驱动电路的固态Marx发生器在容性负载下和阻性负载下进行了实验验证。利用该方案实现了对于6级Marx电路的3.6 kV输出脉冲在55~7.7μs的边沿调节,验证了该方案的可行性,并对比分析了不同阻性负载对于脉冲边沿造成的影响。实验结果表明:该电路在提高固态脉冲电源的边沿调节性能方面有独特的优势。     

高频纳秒脉冲调制器的分立磁耦合驱动器设计

随着高压纳秒固态脉冲发生器在生物、工业和环境等领域的应用日益广泛和深入,脉冲波形、电压幅值、脉冲持续时间、脉冲重复频率等参数已成为特定脉冲功率应用所需的基本可控变量。为了进一步减小电源的体积、降低成本,提出一款以正极性Marx为主电路、多个脉冲变压器为核心驱动器、具有纳秒级前沿高重复频率的高压纳秒脉冲调制器。提出的驱动器结构紧凑,无需提供多路隔离供电的驱动电源,可以在高重复频率下实现两个金属氧化物半导体场效应晶体管（MOSFETs）的栅极电压快速同步上升和下降,获得百纳秒以内、幅值可控的栅极驱动电压。不仅最大脉宽不受磁芯饱和的限制,而且负偏置电压使开关管可控关断,同时在一定程度上避免了电流流过MOSFET米勒电容而引起的寄生导通,提高了电路工作的可靠性。此外,研究了不同匝数和磁芯材料对驱动波形的影响。搭建了一台14级脉冲调制器样机,测试结果表明,基于该驱动器下的调制器输出电压和脉宽都连续可调,具有改变脉冲轮廓的能力,最大输出电压可达5.5 kV,脉宽调节范围为100 ns～50 ms,最小上升时间约18 ns,重复频率为100 kHz。     

微型固态特斯拉线圈尖端放电演示仪

微型固态特斯拉线圈尖端放电演示仪以RLC串联谐振为基本原理实现高压放电.振荡信号由555输出,以Mosfet驱动芯片TC4420构建驱动电路,功率电路采用MOS管IRFP460,音频采用电源调制方式.该仪器可以演示尖端放电现象、音乐电弧、荧光灯隔空点亮以及无线传电现象.演示实验装置采用模块化设计,体积小、功率低,既达到了演示效果,又保障了演示实验的安全性.     

柔性悬臂电磁驱动光开关的仿真与制作

设计并制作了一种用于波长信道选择系统的新型柔性悬臂梁电磁驱动光开关,该光开关采用微光机电系统技术制作,由带有平面螺旋形线圈的聚酰亚胺悬臂梁、圆柱形永磁体、基座以及双面反射棱镜组成.通过改变线圈中激励电流的方向来控制开关动作.运用有限元的方法,模拟分析了线圈与永磁体之间电磁力的分布以及悬臂梁回复力、电磁力与挠度的关系.对该光开关的驱动性能进行了测试,实验结果表明：加载较小的工作电流（0.15A）,悬臂梁便可以产生较大的挠度（0.925mm）,满足波长信道选择系统光路偏转的要求. 关键词： 微光机电系统 光开关 柔性悬臂梁 电磁驱动     

全固态高重频高压脉冲电源

设计了一款全固态高重频高压脉冲电源,主电路采用以IGBT为主开关的半桥式固态Marx电路,驱动电路采用磁芯隔离带负压偏置的同步驱动方案,并由FPGA提供充放电控制信号和故障诊断、保护。该方案既可实现对多级电容的低阻抗的快速并联充电控制,又可实现截尾功能以加快脉冲后沿获得方波脉冲,且可实现百μs以上的宽脉冲输出,可用来产生高压脉冲电场。此外,该电源还可在突发模式下输出脉冲个数和频率均可调的多个高频脉冲系列。实验表明,该输出电压幅值可高达40 kV,输出峰值电流可达100 A,重频可达30 kHz,上升沿和下降沿均低于100 ns,突发模式下重频可高达200 kHz。所设计的脉冲电源输出参数连续可调,且体积小巧。     

一种紧凑型固态Marx发生器的研究

提出利用P型开关作为充电管、N型开关作为放电管串联形成半桥结构,将其门极也短接,以同一个信号同时驱动充电管和放电管。再利用共原边的串心磁环驱动方案,只需一个半桥电路就可以从原边同时传递驱动功率和信号,同步驱动所有充电管和放电管,大幅简化了脉冲电源结构和尺寸,降低了成本。以此搭建了24级固态Marx发生器,在10 kΩ阻性负载上,获得了10 kV、1 kHz、5μs的高压方波脉冲,验证了方案的可行性,该电源主电路的尺寸仅为20 cm（长）×13 cm（宽）×5.5 cm（高）。     

用同一个晶体管发射超声单脉冲和调制波的声速仪

一、工作原理用同一个晶体管发射超声单脉冲和调制波的声速仪的工作原理如图1所示.图1中脉冲回波重合法时序逻辑电路周期性地产生发射同步信号,信号经开关K1选通后,分别被送往单脉冲形成电路或调制波形成电路,然后再经过开关K2送在发射电路.当电源切换开关K3将高压直流电压VH送入发射电路时,该超声波声速仪处于发射超声单脉冲波的工作状态,发射电路输出幅度很高、边沿很陡的电脉冲,经过输出高频插座去激励压电晶片产生单脉冲的超声波,压电晶片与电感构成一个调谐回路路.当电源切换开关K3转向另一侧,将低压直流电压VL送入发射电路,该声速…     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.