横流CO_2激光器SD放大实验研究

在充有CO_2-N_2-He混合气体的激光器SD放大实验装置内,用100～180KHz高频电源对长度为720 mm 的 SD 电极进行横向流动的无声放电(SD)放大实验,获得放电功率1.035 kw,SD 电极功率注入效率达96.5%。     

平板型臭氧发生器主要特性的实验研究

由于臭氧（O2）的独特性质使得它在社会发展中的应用得到越来越多的重视,但是由于臭氧合成效率低,人们一直在寻求高效的臭氧合成方法和装置．在众多臭氧合成方法中,介质阻挡放电法因其结构简单、成本低廉一直为大规模工业臭氧合成的主要方法．这篇论文对平板型介质阻挡放电臭氧发生器的实验过程及结果进行了陈述和理论分析,在本实验室的条件下对影响臭氧产量和浓度的主要因素,诸如气隙宽度、电源电压和频率以及介质层厚度,进行了实验研究,得出最佳的工作条件为;气隙宽度为1．7mm,电源电压为7．5kV,电源频率为38kHz,介质层厚度为1．5mm。     

对角线为4英寸的表面放电等离子体显示器

作者介绍了一种具有80×80个腔(象素)、腔距为1mm 的4英寸全色表面放电交流等流离子体显示器(SD—PDP)。实验结果表明三相驱动方式对提高器件的亮度和发光效率及改善存储系数有明显的效果。在4英寸和1英寸的全色 SD—PDP 屏中保     

屏蔽厚度对电路板充电防护仿真分析

卫星深层介质充放电是造成卫星异常的主要空间环境效应之一。本文基于地球同步轨道(GEO)为目标防护设计轨道,以NASA4002A上提出的GEO轨道最恶劣电子能谱作为环境输入参数,采用Geant4-RIC方法计算了不同屏蔽层厚度下,双面覆铜接地的厚度为2.0 mm的电路板介质的深层介质充电电场。计算结果表明,随着屏蔽层厚度的增加,介质内最大充电电场呈指数降低,当屏蔽层厚度大于1.4 mm等效Al时,充电电场小于106 V/m,没有深层介质放电风险。     

压电效应对多层陶瓷电容器放电性能的影响

为研究压电效应对多层陶瓷电容器放电性能的影响,搭建了放电周期可调的电路平台和基于光学多普勒效应的高精度振动测量平台。研究了陶瓷介质压电特性,电容在不同放电周期、不同加载电压下的振动状态和放电特性,以及失效放电周期和厚度的关系。结果表明,陶瓷介质具有压电效应,放电时,介质按交流电场频率规律振动,当振动频率与电容固有谐振频率一致时,激发机械共振,且振动幅度随电压增大而增大,当振动产生的应变超过介质承受极限时,介质开裂,导致击穿失效。失效放电周期随电容厚度增大而增大,呈线性关系。     

基于场路协同的手机静电放电仿真研究

随着电子产品集成度的提高,静电放电对手机等电子设备的危害愈来愈严重。本文建立了包含静电放电枪、手机外壳,内部PCB板及芯片模型的场路协同仿真模型,研究静电放电时手机内部的电磁干扰和信号传输情况。研究结果表明放电位置在同种介质上变化时,放电点与监测点距离因素占主导,同时手机外壳上的开孔及缝隙也会影响。不同介质上放电时,对金属铝壳放电时辐射干扰更大,而对玻璃介质放电时传导干扰更大。     

脉冲HF激光器预电离设计及效果评估

气体介质稳定体放电是放电激励气体激光器高效输出的基础和前提,预电离是实现高压气体介质稳定体放电的有效技术途径之一。基于放电激励脉冲HF激光器电气结构总体设计要求设计了结构紧凑的紫外光自动预电离装置, 并对其在气体介质中预电离产生的初始电子数密度进行了数值模拟。模拟结果表明:在整个放电区域内初始电子数密度均在109/cm3左右,满足介质体放电要求。通过激光器能量输出实验评估了预电离效果,对SF6和H2混合气体介质,在充电电压较低时,输出能量有数倍的提高;对SF6和C2H6混合气体介质,在充电电压20 kV时激光器输出能量由200 mJ提高至297 mJ,提高了近50%。实验结果表明:该预电离装置对改善激光器能量输出特性有明显效果。     

增加紫外预电离火花密度使XeCl激光输出能量提高

我们将紫外预电离火花由原来的30个增加至60个,有效地扩大了预电离火花辐照体积,放电均匀性明显变好,激光输出提高40％,效率也提高了40％。 实验装置 XeCl激光器结构截面示意图和激光电原理图示于图1。在主放电电极阴极两侧安装有作为预电离用的针状电极。直接与阴极充放电产生火花。针状电极在激光器气室外串联一个可拆卸的无感小电容,容量约200pF。预电离电极距主电极为～5mm,共60个,分布于40cm长的阴极两侧。在测量参数时,用拆去预电离电容来改变火花的数目。主放电电极材料为黄铜,面形为弧形。阴极为R=5mm,阳极为R=10mm,电极间距为20mm,腔长600mm。激光谐振腔一端为介质膜全反镜(R=∞),另     

脉冲参数对指纹放电成像质量的影响

利用介质阻挡放电照相的原理,成功实现了对人体指纹的提取。在静态法提取指纹过程中,记录了在3种脉冲宽度(2ns,3μs,1ms)下放电的指纹图像。放电空间电场分布的分析表明,随着脉冲宽度的增加,正离子在介质层上的累积使得放电空间的电场趋于均匀,导致指纹放电强度在空间的均匀化,从而使指纹成像的分辨率下降。采用较高幅度的ns脉冲放电时,发现了指纹放电中存在丝状放电的痕迹。进一步的实验表明,即使在放电空间不存在介质时,也能观测到良好质量的指纹放电图像。研究结果表明,采用较小幅度的ns脉冲放电技术,不仅提高了指纹图像的清晰度,而且也实现了大气中的辉光放电。     

纳秒脉冲宽度对介质阻挡放电图像对比度的影响

采用4．7、7．6和10．6ns 3种不同宽度的高压脉冲,对硬币进行了介质阻挡放电照相（DBDP）。结果表明,介质阻挡放电图像的对比度明显与脉冲宽度有关,脉冲宽度越窄,图像的对比度越高;反之,脉冲宽度越宽,图像对比度越差。对DBDP的分析表明,外电压施加在硬币上后,与放电电流脉冲对应的时间滞后与放电间隙有关。采用放电时间滞后的观点,就纳秒脉冲宽度对介质阻挡放电图像对比度的影响进行了合理的解释。     

Microwave noise performance of AlGaN-GaN HEMTs with small DC power dissipation

We report low microwave noise performance of discrete AlGaN-GaN HEMTs at DC power dissipation comparable to that of GaAs-based low-noise FETs. At 1-V source-drain (SD) bias and DC power dissipation of 97 mW/mm, minimum noise figures (NF/sub min/) of 0.75 dB at 10 GHz and 1.5 dB at 20 GHz were achieved, respectively. A device breakdown voltage of 40 V was observed. Both the low microwave noise performance at small DC power level and high breakdown voltage was obtained with a shorter SD spacing of 1.5 /spl mu/m in 0.15-/spl mu/m gate length GaN HEMTs. By comparison, NF/sub min/ with 2 /spl mu/m SD spacing was 0.2 dB greater at 10 GHz.     

Taser dart-to-heart distance that causes ventricular fibrillation in pigs

Electromuscular incapacitating devices (EMDs), such as Tasers, deliver high current, short duration pulses that cause muscular contractions and temporarily incapacitate the human subject. Some reports suggest that EMDs can kill. To help answer the question, "Can the EMD directly cause ventricular fibrillation (VF)?", ten tests were conducted to measure the dart-to-heart distance that causes VF in anesthetized pigs [mass = 64 kg +/- 6.67 standard deviation (SD)] for the most common X26 Taser. The dart-to-heart distance that caused VF was 17 mm +/- 6.48 (SD) for the first VF event and 13.7 mm +/- 6.79 (SD) for the average of the successive VF events. The result shows that when the stimulation dart is close enough to the heart, X26 Taser current will directly trigger VF in pigs. Echocardiography of erect humans shows skin-to-heart distances from 10 to 57 mm (dart-to-heart distances of 1-48 mm). These results suggest that the probability of a dart on the body landing in 1 cm2 over the ventricle and causing VF is 0.000172.     

Domino logic with variable threshold voltage keeper

A variable threshold voltage keeper circuit technique is proposed for simultaneous power reduction and speed enhancement of domino logic circuits. The threshold voltage of a keeper transistor is dynamically modified during circuit operation to reduce contention current without sacrificing noise immunity. The variable threshold voltage keeper circuit technique enhances circuit evaluation speed by up to 60% while reducing power dissipation by 35% as compared to a standard domino (SD) logic circuit. The keeper size can be increased with the proposed technique while preserving the same delay or power characteristics as compared to a SD circuit. The proposed domino logic circuit technique offers 14% higher noise immunity as compared to a SD circuit with the same evaluation delay characteristics. Forward body biasing the keeper transistor is also proposed for improved noise immunity as compared to a SD circuit with the same keeper size. It is shown that by applying forward and reverse body biased keeper circuit techniques, the noise immunity and evaluation speed of domino logic circuits are simultaneously enhanced.     

Ventricular volume measurement from a multiplanar transesophagealultrasonic imaging system: an in vitro study

We have developed a system to assess the feasibility of using multiple transesophageal ultrasonic images to measure left-ventricular volume, an important variable in patient management. The system includes a special transesophageal probe with a micromanipulator for acquiring cardiac images in multiple planes with known interplanar spatial relationship and an off-line processing system to compute the volume. In vitro studies with the probe demonstrated that the distance between two targets in space can be identified within 2 mm (SD = 0.4 mm) for points in the imaging plane 3.4 mm (SD = 0.5 mm) for points not lying in the imaging plane. This gives an average accuracy of +/- 6.5% for distances greater than 4.5 cm. Comparison of ultrasonic measurements of the volume of water-filled balloons and excised hearts to the volume required to fill them, revealed a correlation coefficient of 0.992, a regression line having a slope of 1.0 and an ordinate intercept at 0.2 mL, and a standard error of the estimate of 8 mL.     

A six-junction GaAs laser power converter with different sizes of active aperture

We investigate a novel GaAs-based laser power converters (LPCs) grown by metal-organic chemical vapor deposition (MOCVD), which uses a single monolithic structure with six junctions connected by tunnel junctions to obtain a high output voltage. The LPCs with diameters of active aperture of 2 mm and 4 mm were fabricated and tested. The test results show that under an 808 nm laser, two LPCs both show an open circuit voltage of above 6.5 V. A maximum power conversion efficiency of 50.2% is obtained by 2 mm sample with laser power of 0.256 W, and an output electric power of 1.9 W with laser power of 4.85 W is obtained by 4 mm sample. The performances of the LPCs are deteriorated under illumination of high flux, and the 4 mm sample shows a higher laser power tolerance.     

Advanced Dicing Technology for Semiconductor Wafer—Stealth Dicing

ldquoStealth dicing (SD)rdquo was developed to solve inherent problems of a dicing process such as debris contaminants and unnecessary thermal damages on a work wafer. A completely dry process is another big advantage over other dicing methods. In SD, the laser beam power of transmissible wavelength is absorbed only around focal point in the wafer by utilizing the temperature dependence of the absorption coefficient of the wafer. The absorbed power forms a modified layer in the wafer, which functions as the origin of separation in the separation process. In this paper, we applied this method for an ultra-thin wafer. The reliability of devices that is diced by SD was confirmed.     

蓝宝石衬底AlGaNöGaN 功率HEM Ts 研制

基于蓝宝石衬底的高微波特性 Al Ga N/Ga N HEMTs功率器件 ,器件采用了新的欧姆接触和新型空气桥方案。测试表明 ,器件电流密度 0 .784A/mm,跨导 1 97m S/mm,关态击穿电压 >80 V,截止态漏电很小 ,栅宽 1 mm的器件的单位截止频率 ( f T)达到 2 0 GHz,最大振荡频率 ( fmax) 2 8GHz,2 GHz脉冲测试下 ,栅宽 0 .75 mm器件 ,功率增益1 1 .8d B,输出功率 3 1 .2 d Bm,功率密度 1 .75 W/mm。     

A 77 GHz mHEMT MMIC Chip Set for Automotive Radar Systems

A monolithic microwave integrated circuit (MMIC) chip set consisting of a power amplifier, a driver amplifier, and a frequency doubler has been developed for automotive radar systems at 77 GHz. The chip set was fabricated using a 0.15 µm gate‐length InGaAs/InAlAs/GaAs metamorphic high electron mobility transistor (mHEMT) process based on a 4‐inch substrate. The power amplifier demonstrated a measured small signal gain of over 20 dB from 76 to 77 GHz with 15.5 dBm output power. The chip size is 2 mm × 2 mm. The driver amplifier exhibited a gain of 23 dB over a 76 to 77 GHz band with an output power of 13 dBm. The chip size is 2.1 mm × 2 mm. The frequency doubler achieved an output power of –6 dBm at 76.5 GHz with a conversion gain of ?16 dB for an input power of 10 dBm and a 38.25 GHz input frequency. The chip size is 1.2 mm × 1.2 mm. This MMIC chip set is suitable for the 77 GHz automotive radar systems and related applications in a W‐band.     

879 nm激光二极管抽运准三能级Nd:GdVO4激光器

利用879 nm新型激光二极管(LD)抽运Nd:GdVO4晶体,在室温下实现了4F3/2→4I9/2准三能级激光谱线跃迁。对掺杂原子数分数0.2%,3 mm×3 mm×3.8 mm的晶棒,在抽运功率为33 W时,获得912 nm最大输出2.5 W,斜率效率11%,相应的对吸收抽运功率的斜率效率达38%;对掺杂原子数分数0.2%,3 mm×3 mm×5 mm的晶棒,在抽运功率为33 W时,获得912 nm最大输出功率3.0 W,斜率效率16%,相应的对吸收抽运功率的斜率效率达45%。在腔内插入声光(AO)Q开关,当重复频率为10 kHz时, 获得了脉冲宽度为22 ns,平均功率为660 mW,峰值功率达3 kW。理论上分析了晶体的长度、浓度与准三能级激光器振荡阈值的关系,讨论了再吸收损耗对激光器的运转状态产生的影响,并通过实验观察了再吸收损耗的饱和效应。     

Ka频段PHEMT 1W功率单片放大器

设计制作了Ka频段高输出功率的单片功率放大器.基于河北半导体研究所的0.25μm栅长的75mm GaAsPHEMT工艺制作的三级功率放大器,芯片尺寸为19.25mm2(3.5mm×5.5mm).在32.5～35.5GHz的频率范围内,小信号线性增益大于16dB,带内平均1dB增益压缩点输出功率为29.8dBm,最大饱和输出功率为31dBm.