A multioctave (0.5–12.0 GHz) low-noise transistor amplifier

An effective method of computer calculation and optimization of characteristics of multioctave low-noise transistor amplifiers is presented. The method was used to design a three-stage amplifier built on the basis of microstrip technology using packaged transistors and chip resistors and capacitors. In a 0.5- to 12.0-GHz frequency band, the following characteristics are obtained: a noise ratio of 2.2–3.2 dB, a gain of >25.6 dB, a gain flatness of ±1.2 dB, a voltage standing wave ratio of <2.8 and <2.2 at the input and output, respectively.     

Note: cryogenic low-noise dc-coupled wideband differential amplifier based on SiGe heterojunction bipolar transistors

Silicon-germanium heterojunction bipolar transistors can be used to construct low-noise cryogenic amplifiers. We present a dc-coupled differential amplifier capable of operating down to 10 K. In this temperature regime it has bandwidth of 15 MHz and noise temperature as low as 1.3 K. When operated at liquid nitrogen temperature of 77 K, the measured noise temperature is lower than 3 K. The amplifier is based on the commercially available transistors NESG3031 and operational amplifier OPA836 and is capable of standalone operation without any additional stages at room temperature.     

Cryogenic tilt table

We describe the design and development of a cryogenic tilt table that will be used to test the flight hardware for NASA’s Satellite Test of the Equivalence Principle (STEP). Our table can tilt the hardware around two axes and is part of a test bed that has 6-degree-of-freedom controllability. The goal was to build a tilt table with a resolution better than ∼5 μrad (1 arcsec). Our table consists of three aluminum plates. The outermost plate is attached to the cryogenic probe and is fixed. The middle and inner plates rest on the outer and middle plates, respectively, using knife edges and knife edge holders made of silicon nitride that are glued to the aluminum plates. A cryogenic tilt sensor was also developed and integrated with the table. The sensor consists of an electrically grounded copper cube hanging from a support, and is placed between two pairs of capacitive electrodes. Any motion of the cube caused by tilting is measured differentially using a Wheatstone bridge circuit. The table is connected to the bottom of a cryogenic probe. A voice coil actuator, located on top of the probe at room temperature, is used to create the necessary tilt. A thin fiber is used to connect the actuator and the table. The system is controlled using a dSPACE control card. A test of the table at cryogenic temperatures (4.5 K) and low pressure (1 μTorr) showed a noise level of ∼0.7 μrad (150 marcsec), which is nearly an order of magnitude better than the required resolution.     

低温加工及其应用

从改善难加工材料的切削加工性入手 ,论述低温加工的优势、效益及分类 ,同时介绍低温加工刀具材料 ,切削用量的选择。     

用于液化天然气的低温球阀特性研究

介绍了低温阀门选材、结构设计、制造工艺以及低温试验的特殊要求及其注意事项。     

低温切削加工技术的研究进展

随着环保要求的愈发严格,低温切削加工技术作为一种绿色制造技术,受到越来越多的重视。低温切削使用低温流体作为冷却剂,切削过程中不会产生污染物,相对传统冷却液切削更加绿色环保。本文综述了低温切削加工技术的发展现状、分类和低温切削加工对工件加工表面质量的影响规律,并展望了低温切削加工技术的应用前景。     

凸轮铰杆增力夹具

介绍铰杆与偏心凸轮机构组成的夹紧装置的工作原理，给出相应的计算公式，并用实例证明，给手柄施加很小的力可以获得较大的输出力。该夹具结构简单，制造方便。     

往复式低温制冷机的气体润滑

对低温机械应用气体润滑技术的情况进行了综述及讨论,重点针对往复式低温机械活塞密封的气体润滑,分析了低温活塞膨胀机气体润滑活塞密封的结构特点、性能及使用,介绍了低温制冷机迷宫密封的应用概况,反映了微型制冷机中最新研发气体轴承活塞的结构特点及动态.     

球阀的低温试验

低温试验是对低温阀门性能验证的一个重要手段,现行标准规定的阀门低温试验方法与实际工况有一定的差异,不当的操作容易造成试验结果的失真,甚至对受试阀门的损害。本文主要针对低温球阀的特殊结构,分析了阀门低温试验中容易出现的问题,并结合实际操作经验,提出了一些应对措施。     

Note: Cryogenic microstripline-on-Kapton microwave interconnects

Simple broadband microwave interconnects are needed for increasing the size of focal plane heterodyne radiometer arrays. We have measured loss and crosstalk for arrays of microstrip transmission lines in flex circuit technology at 297 and 77 K, finding good performance to at least 20 GHz. The dielectric constant of Kapton substrates changes very little from 297 to 77 K, and the electrical loss drops. The small cross-sectional area of metal in a printed circuit structure yields overall thermal conductivities similar to stainless steel coaxial cable. Operationally, the main performance tradeoffs are between crosstalk and thermal conductivity. We tested a patterned ground plane to reduce heat flux.     

Thermal Failure of Multilayer SiGe/Si

In this report, we provide a comparison of the thermal transition and wear mechanisms of the interfaces of multilayered silicon–germanium (SiGe) on Si sublayers. From wear experiments, we determined the inherent deformation modes of samples, in particular, the wear sliding and thermal stability characteristics. The pile-up effect we observed on each side of the wear zone at room temperature was greater than that of the sample that had been subjected to thermal treatment. The distribution of the elements Si and Ge depended on the annealing conditions; decreases in element densities in secondary ion mass spectrometry depth profiles revealed interdiffusion within the films. We conclude that thermal analysis not only produced misfit dislocation defects but also significantly wavy sliding arising from interface adhesion failure. Annealing at RT, 800, 900, and 1,000 °C resulted in coefficients of friction of 0.125, 0.95, 0.85, and 0.11, respectively. We employed dynamic-mode ex situ wear tests to determine the applicability of the brittle and ductile transitions and adhesive wear effect of the multilayer SiGe/Si systems.     

浅谈难加工材料的低温切削

针对难加工材料的切削加工性,提出了改善其加工性能的方法.重点对低温切削加工方法进行了介绍,包括低温切削技术的特点及其制冷技术,最后阐述了机械制造领域中低温切削技术的研究成果.     

某三元材料锂离子电池低温性能研究

为研究三元材料锂离子电池的低温性能,以国内某公司生产的37Ah三元材料锂离子电池为研究对象,对不同环境温度下三元材料锂电池充放电电压、内阻及容量等性能进行研究。研究结果表明,当环境温度低于0 ℃时,三元材料锂离子电池端电压、内阻、容量等性能均会出现不同程度的下降;环境温度低于-10 ℃,充放电电压曲线均呈现非线性变化,内阻变化较剧烈,严重影响电池寿命;环境温度低于-20 ℃时,无法进行大倍率放电;环境温度低于-30 ℃,大小倍率放电无法进行,充电容量大幅度下降。     

低温阀门上密封结构的改进

分析了低温阀门上密封结构中存在的问题,提出了解决的方法。     

C波段制冷接收机充气系统

充气系统是给制冷接收机干空气腔体提供新鲜干燥空气、排出陈旧气体以防止水汽在真空窗表面遇冷凝结而影响观测的气动系统。某26 m射电望远镜C波段制冷接收机的馈源在杜瓦外部,故该接收机的充气系统将馈源设计为干空气腔体,通过充气机提供干燥空气,使用气体缓冲器作为辅助气源用于在充气机停止工作时补充提供干燥空气,以小的泄漏排出馈源腔体内的陈旧气体。该气动系统能很好地避免C 波段制冷接收机真空窗口表面结冰,在自动控制下的充气系统也可以很好地补偿腔体内压的变化,使得整个充、排气过程更加稳定,真空窗口表面保持干燥。     

单晶硅片的低温抛光技术

介绍了一种光学材料抛光新技术--低温抛光技术。首先把抛光液冷冻成低温抛光模层,并对单晶硅片做抛光实验,实验结果表明这是一种很好的光学材料抛光方法。     

Differential automatic zero-adjusting amplifier

A method is described for building a low-voltage-drift differential dc amplifier featuring automatic zero adjustment, a high input impedance, and a bandwidth of 10 kHz. This is achieved by an asymmetric two-step process between the input signal and ground. Bandwidth can be extended by the use of a second amplifier during the ground-sampling time. The amplifier can be made with standard electronic components. A major advantage of this method is that an existing amplifier can easily be converted into a low-voltage-drift amplifier by adding the essential elements of the described automatic zero-adjusting amplifier to its input stage. To illustrate the method a practical example is constructed featuring a drift of 0.2 microV/ degrees C.     

Control systems of high-voltage transistor switches

Control systems of high-voltage transistor switches are described. Possible ways to develop these systems are considered. A control system of the transistors of a high-voltage switch on the basis of a current loop is considered in detail. Signals for turning the transistors on and off arrive to their control boards from their common conductor with bipolar current pulses. A positive pulse turns the transistors on, while a negative pulse turns them off. The time interval between these pulses sets the time during which the switch is in the conducting state. The minimum duration of the conducting state is several microseconds, while the maximum duration is not limited. The results of tests of a switch prototype with an operating voltage of up to 4 kV are presented. The operation of the switch was demonstrated when obtaining rectangular pulses in the microsecond range across a resistive load. We also verified the possibility of forming pulses of damped oscillations at a frequency of 1 MHz by this device. The positive test results make it possible to develop switches for operating voltages of tens of kilovolts using the considered approach.     

A linearly variable high-voltage amplifier

A principle of operation and schematic diagram of a linearly variable (triangular pulses) high-voltage amplifier with a 300-gain and 1000-V maximum output voltage is described. The amplifier is intended for a system for prompt monitoring of voltage-capacitance characteristics and leakage currents of high-voltage semiconductor devices and products with dielectric layers.     

Pip amplifier for lightwave systems

A unidirectional-pulse amplifier is described that uses a base-bias voltage regulator to restore the dc component of the signal being amplified. The amplifier performance characteristics are the following: maximum output pulse current, 45 A; pulse rise time, 10 ns; pulse duration, 20–100 ns; and power gain, 19 dB.