基于Gate与Matlab的PET电子学仿真系统研究

正电子发射断层成像PET （Positron Emission Tomography）是一套庞大、复杂而又极其精密的大型医疗设备,由成千上万个探测单元及相应的信号采集通道组成,其复杂的采集逻辑直接导致系统前期研发迭代次数多、硬件调试困难,且时间与资金成本投入高。本文通过研究PET系统整体结构及前端电子采集模块的功能,设计出基于Gate仿真软件（Geant4 application for tomographic emission）和MATLAB （matrixlaboratory,Mathworks Inc.）数据处理包的PET电子学仿真架构,利用数字化单事件重建DiSER （digitalsingle-event-reconstruction）模型将Gate仿真得到的湮灭事件的能量、时间信息进行综合,转换为光子脉冲信号并由模数转换器ADC （analog-to-digital converter）进行量化,量化数据输入到现场可编程门阵列FPGA （field programmable gate array）和MATLAB协仿真模块中,验证FPGA硬件采集算法的可行性。待各模块的湮灭事件采集完毕,将多模块数据进一步综合输入到FPGA符合处理模块中,完成PET系统符合单元的功能验证。最后,将设计的算法在基于飞行时间技术的TOF （time-of flight）-PET样机上进行了测试,验证了设计的有效性和正确性。该系统仿真平台可应用于PET系统整个研发周期,其搭建思路也可灵活、有效地拓展到其他领域的系统建模与验证之中。     

基于FPGA与ARM的多路时序控制系统设计与实现

介绍了基于FPGA与ARM7的多通道、多时间范围的同步时序控制系统,采用FPGA实现20路高精度的信号延时输出控制,通过ARM7的数据总线接口实现了ARM与FPGA的数据交互;重点介绍了系统的硬件电路设计、ARM与FPGA总线的设计和FPGA内部程序模块的设计;各通道的输出信号类型与延时时间等参数均可以通过人机接口现场配置,也可以通过上位机软件来配置;该设计可以保证各通道信号通过外触发信号为基准来进行延时输出,系统的延时时间精度小于2μs;ARM7处理器芯片采用PHILIPS公司的LPC2214,FPGA采用Altera公司Cyclone系列的EP1C12Q240;采用硬件描述语言Verilog HDL来设计延时模块,延时精度达到1μs;该系统在靶场测试中验证了其正确性和有效性。     

基于国产FPGA及DAC的任意波形发生器的设计

任意波形发生器作为测试测量设备的一种重要仪器,在航空航天的测量与控制技术领域中得到了广泛应用。当前市场成熟任意波形发生器产品多为国外产品或者国内厂商基于国外FPGA和DAC研制的产品。为了打破技术垄断,提高国产任意波形发生器的自主技术保障能力,研制基于国产芯片的任意波形发生器愈发重要。随着国产芯片设计技术提升,国产FPGA和DAC的性能显著提高,并得到了广泛应用。PXI总线作为当前仪器领域的主要总线类型之一,可以满足大部分测试仪器的通讯要求。基于国产FPGA和DAC器件,从硬件设计和软件设计两个方面出发,成功研制了一款采样率为100MSa/s的 PXI总线任意波形发生器模块,实现了43MHz信号输出,通过实验测试了模块的功能和性能,完全满足模块指标要求,充分证明了国产芯片在工程设计中的性能特性。     

ADS注入器Ⅱ超导磁铁电源控制器的设计

针对加速器驱动次临界系统(ADS)注入器Ⅱ对超导磁铁电源系统的要求,设计了一款主要由光纤模块、数模转换器(DAC)和模数转换器(ADC)相关电路组成的高稳定度的超导磁铁电源控制器。提出了一种基于数字电位器(DCP)与现场可编程门阵列(FPGA)所组成的DAC,该DAC可以实现高稳定度的超导磁铁电源的控制,电源电流值通过该DAC给定,其电压给定输出稳定度优于2×10-5,完全满足超导磁铁电源系统5×10-5量级的稳定度要求。最后给出了系统的实际测试数据,验证了设计的合理性和使用的可靠性。     

一种用于高场MRI的多源射频发射机

介绍了高场磁共振成像（MRI）多源发射技术的原理,提出了一种用于高场MRI系统的多源射频信号发射机.它能并行输出多路频率、相位、幅度,可快速独立调节的射频脉冲信号.该射频发射机的实现基于单片现场可编程门阵列（FPGA）和多通道数模转换器（DAC）芯片,FPGA读取预存于双端口随机存取存储器（RAM）中的射频信号参数,并利用读取的参数分别实现每路信号的直接数字频率合成（DDS）和信号调制等核心功能,获得多路数字射频信号;FPGA输出的数字信号经过高性能DAC转化为模拟信号,即所需要的射频信号.该射频发射机在设计中大量采用软件无线电技术,即利用Xilinx提供的IP核实现DDS和信号调制等主要功能,具有集成度高、体积小、灵活度高的优点,同时,该设计可以大大缩短开发时间,有效降低实现的难度和成本,为高场MRI谱仪的多源射频发射机的设计研制提供了一种低成本、高效、高性价比的方案.     

基于PCIe总线的数据采集卡设计与实现

为了实现对多路高速光信号采集,利用FPGA设计基于PCIe总线的数据采集系统。对PCIe总线低速Slave通道与高速DMA通道的关键算法进行了研究。首先,介绍了数据采集卡的硬件构成及基本工作原理,提出了PCIe总线算法需要解决的数据传输问题;然后,分析数据采集卡PCIe总线低速Slave通道和高速DMA通道原理以及实现的关键算法。通过Modelsim和SignalTap工具分别对数据传输算法进行功能验证和在线仿真;最后,将设计数据采集卡互联PCIe上位机进行实际测试。实验结果表明,本设计PCIe总线采用X4接口模式,数据传输系统的数据上传峰值速率为615.38MB/s,可以满足稳定可靠、高带宽、模块化等要求。     

基于FPGA+DSP的数字化LCR设计与实现

以矢量化伏安法为研究背景,设计出一种基于软件无线电思想的高集成度、通用性强的数字化阻抗测量系统。该测量系统采用现场可编程门阵列FPGA及高速浮点数字处理芯片DSP为主要处理器,通过EMIF外部总线拓展接口及强大数据处理能力,结合时钟、电源、DAC数模转换和ADC模数转换模块,形成了并行与浮点计算优势互补的数字信号处理系统,解决了数字化矢量伏安法基带信号的并行处理及复杂的浮点模型解算问题,该系统能具有体积小、精度高等特点,经过实际试验测试,该系统性能稳定,具有广泛的运用前景。     

基于FPGA的QPSK信号干扰源设计

针对QPSK调制方式特点,设计了基于FPGA的信号干扰源,分析了系统干扰原理;利用m序列生成均匀白噪声,采用地址法完成高斯白噪声转换;以Logistic混沌映射电路作为信源,采用直接数字频率合成技术产生正弦信号作为载波,用VHDL语言设计FPGA与单片机的接口电路;在单片机控制下,用于FPGA生成干扰信号经AD9760实现数模转换;仿真和实验表明,该系统精度高,干扰参数易于控制修改,满足实际要求,并且稍加改动可生成多路同步干扰信号。     

基于FPGA 的超导动态电感探测器频梳读出信号产生

超导动态电感探测器(Kinetic Inductance Detectors, KIDs) 作为一种新型的超导探测器, 在天文学等领域得到了广泛应用, 具有高灵敏度、 高能量分辨率等优点, 并且可以通过频域复用直接扩展到大型阵列. 然而, 为了支持上千像素的探测,KIDs 阵列需要产生复杂的频梳信号, 占用较大的信号带宽. 因此, 数模转换器件(Digital-to Analog Converter, DAC) 的采样率对于 KIDs 阵列的读出电路实现至关重要. 基于JESD204B 传输协议的高速 DAC相较于传统低电压差分信号(Low-Voltage Differential Signaling, LVDS) 协议的转换器具有更高的采样率和传输速率, 可用于频梳信号波形的产生. 为此, 本文提出了一种基于现场可编程门阵列(Field Programmable Gate Array, FPGA) 的设计, 以 Xilinx 公司 Kintex-7 系列 FPGA 为主控芯片, 通过高速串行接口JESD204B 和高速 DAC 芯片AD9136 实现高速数据传输,DAC 采样率为2 GSPS, 能生成带宽为1 GHz 的基带信号. 实验结果表明, 该设计能够有效地生成复杂的频梳信号, 具有较高的信号质量和灵活性, 解决了传统 DAC 及直接数字频率合成(Direct Digital Synthesizer, DDS) 器件难以产生复杂多变波形的难题, 有助于拓展 KIDs 阵列的工程应用.     

基于SDRAM大容量缓存FIFO控制器的设计与实现

数据通过采集模块后需要进行缓存,然后再通过DMA写入上位机,SDRAM存储容量大,符合大批量数据的存储,FIFO可以在不同的速率下读写数据,根据两者的优势,本设计是基于SDRAM控制器实现的大容量缓存FIFO;系统中FPGA采用Altera公司的CycloneII:EP2C35F484I8,使用verilog语言实现,通过Quartus11.0编译、综合、布线后,时钟能够达到100 MHz;设计通过了仿真与验证,在仿真验证下,此大容量FIFO存储速率达到43.6 MByte/s;设计已经成功用于实际环境中,输入输出时钟完全不确定的情况下,SDRAM的最低利用率是43%,在时钟相差小的情况下,利用率可以达到100%,符合系统设计需要。     

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.     

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.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.