半导体压阻传感器

早在本世纪三十年代初期Bridgman 和Alien等人就对晶体的压阻效应做了很多工作.1954年C.S.Smith 发现了锗和硅的压阻效应.不久,Herring和Vogt等人对半导体的压阻效应进行了理论研究,提出了半导体能带结构的多谷模型,为半导体压阻传感器的出现奠定了理论基础. 一、半导体压阻效应1.半导体压阻效应的描述 和一切物体一样,当半导体受到外力作用时,其内部就伴随产生了与外力大小相等方向相反的内力.通常,把单位面积上的内力叫做应力. 半导体的电阻率随其内部应力的变化而发生的变化叫做半导体压阻效应. (1)压阻系数π 在一维情况下,压阻系数…     

辐射压概念的研究

把辐射看成是一群光子,从粒子的观点介绍了辐射压的概念,阐明了辐射压的物理实质,给出了计算辐射压的一般公式。     

基于连续压导探针的水箱法测量爆压

为了使爆压测定方法更加方便并且更适合于野外大药量的测量,利用自行研制的压导式连续电阻丝探针,设计了一种改进水箱法,可在单次试验中连续记录炸药爆轰波和水中冲击波波阵面的运动轨迹。同时,为了进一步简化实验装置和操作过程,设计了基于连续压导探针的简化水箱法。利用以上两种实验装置,对不同组分的ANFO炸药进行爆压测量,获得了爆轰波-冲击波波阵面时程曲线。通过对爆轰波段数据拟合,得到了各待测炸药的爆速;利用贴近炸药区域介质中的冲击波数据,拟合得到初始冲击波速度,再结合水和有机玻璃的冲击Hugoniot曲线以及阻抗匹配原理,求解得到各待测炸药的CJ压力和绝热指数。实验结果表明,基于连续压导探针的改进水箱法可准确快捷地测量炸药的爆速、爆压等参数,可作为炸药性能测试技术的重要补充。     

系留气球差压数据的三余度设计

鉴于气囊差压数据对系留气球压力调节的至关重要性,提出了一种差压数据的余度设计方法。在分析差压传感器组成特点的基础上,采用硬件双余度差压传感器配置实现了气囊差压数据的三余度设计,并给出了基于互比监控的故障判定逻辑和故障处置方法,以较低的成本大幅提高了系留气球差压测量的容错能力。     

喷射器扩压室结构设计优化研究

扩压室对喷射器内混合流体的降速增压有着重要影响.本文基于真实流体物性,采用气体动力学方法建立改进的一维混合模型并提出扩压室结构设计优化方法.将模型计算结果与文献实验值对比验证了模型的准确性.分析了扩压室结构参数与喷射器膨胀比、喷嘴喉部直径和混合室直径之间的关系.结果表明,扩压室半锥角α随膨胀比Pg/Pe、扩压室出口直径...     

螺旋线型倍压器传输线损耗参数

 通过介绍螺旋线型倍压器的结构参数和工作原理,分析了影响螺旋线型倍压器输出特性的3个损耗参数：开关电阻损耗因子。螺旋线型倍压器传输线电阻损耗因子和传输线相邻同轴电容之间漏感损耗因子;螺旋线型倍压器的损耗参数主要由其结构参数所决定,通过实验研究,给出了各结构参数对螺旋线型倍压器输出特性的影响关系,并且给出了传输线电阻损耗因子和相邻同轴电容间漏感损耗因子与传输线结构参数间的经验公式,为螺旋线倍压器的电路模型构建提供参考数据。     

高温超导无绝缘线圈励磁电压特性研究

本文通过实验研究了焊锡浸渍、励磁电流PI控制、励磁速率以及励磁幅值对高温超导无绝缘线圈励磁电压特性的影响。实验结果表明:高温超导无绝缘线圈励磁电压具有时延特性,焊锡浸渍、励磁电流PI控制分别会增大和减小时延特性,而励磁速率和励磁幅值不会影响时延特性;励磁电压幅值随励磁速率增大而增大;焊锡浸渍可降低励磁电压幅值,而励磁电流控制对励磁电压幅值影响不明显。     

简易氧蒸气压温度计

本文介绍一种结构简单、价格便宜,适于商品生产的简易氧蒸气压温度计.测温精度可优于±0.05K.同时对这种结构的蒸气压温度计提供了一个零点修正公式.     

力学结构及末级压砧硬度对八面体压腔高压发生效率的影响

针对大腔体静高压装置中的多级八面体压腔,分析了两种不同加载结构的力的传递, 建立了高压发生效率的力学关系.室温下,采用定点标压法(Bi, ZnTe, ZnS, GaAs)分别标定了14/8, 12/6和10/4三种二级6-8型大腔体静高压组装的腔体压力, 定量地讨论了力学结构和末级压砧硬度对八面体压腔高压发生效率的影响. 实验结果表明,力学结构和末级压砧硬度都是影响高压发生效率的重要因素, 且力学结构对高压发生效率的影响更大.其中,腔体的几何结构越大,高压发生效率越高; 6-8型加载结构的高压发生效率高于2-6-8型加载结构;在八面体压腔内的压力接近末级压砧的维氏硬度时, 末级压砧硬度越大,高压发生效率越高,所能获得的腔体压力越大.     

多壁碳纳米管薄膜的压阻效应研究

对多壁碳纳米管薄膜的压阻效应进行了研究. 实验所用的多壁碳纳米管用热灯丝化学气相沉积法合成, 压阻效应用三点弯曲法测量. 研究发现: 在室温下与500微应变内, 原始的多壁碳纳米管薄膜无明显压阻效应, 而经化学修饰处理的碳纳米管膜的压阻因子最高可达120左右, 大大超过多晶硅(Si)在35°C时的压阻因子30, 并且压阻因子与制备方法密切相关. 重点讨论了多壁碳纳米管薄膜产生压阻效应的机制.     

六面顶压机立方压腔内压强的定量测量及受力分析

将六面顶压机立方压腔内置入电路,采用原位电阻测量确定Bi,Tl,Ba相变的方法,标定了压腔内不同位置的压力(强).通过标定立方压腔顶锤表面的压力并结合计算,分别得到了外部加载与压腔密封边受力以及合成腔体受力的对应关系.实验分析结果表明,随着外部加载的增加,当腔体压力达到5 GPa时,消耗在压腔密封边上的加载急剧上升,消耗在合成腔体的加载趋于不变,从而导致立方压腔压力达到上限.利用实验结果,分析了立方压腔在高压下的受力状态,解释了立方压腔的压力难以超过7 GPa的原因.结合立方压腔的几何结构,通过理论分析,提出了采用高体弹模量的物质作为传压介质,同时采用低体弹模量的物质作为密封边提高立方压腔压力上限的可行方案.通过定量标定叶腊石压腔轴向的压力梯度,给出了压腔内沿对称轴不同位置压力值的计算方法,此方法可为高压实验提供更精确的压力数据.     

高压电导研究

高压下物质结构和性质会发生很大的改变，电导对于认识压力的作用效应和寻找新的导电材料具有重要意义．高压电导研究所采用的设备主要有金刚石压腔、超高压大腔体装置(大压机)以及高压电导池三种．金刚石压腔可达550GPa压力；超高压大腔体装置压力一般在30GPa以下，可以提供较大体积的样品；高压电导池主要进行流体的电导研究，压力在400MPa以下，有静止和流动两种类型，流动式高压电导池是近年来才发展起来的，其准确方便．文章对目前高压电导的研究进行简单的介绍和分析．     

二级6—8型大腔体装置的高压发生效率机理研究

利用自行设计与集成的二级6—8型大腔体静高压装置,研究了影响八面体压腔高压发生效率的主要因素及机理,并提出了一种八面体压腔密封的简化力学模型.针对于10/4（八面体传压介质边长为10 mm,二级WC立方体增压块截角边长为4 mm）组装的实验结果发现：预密封边尺寸会显著影响八面体压腔的压力产生效率;在腔体压力为12 GPa左右时,高压发生效率随八面体MgO传压介质初始密度的增加而提高;在15 GPa以上时,影响压力产生效率的主要因素是WC增压立方块本身的强度以及加压过程中所形成密封边的尺寸及材料. 关键词： 6—8型大腔体静高压装置 压力产生效率     

Fiber ringdown pressure sensors

An exploratory study on a novel fiber ringdown pressure sensor is presented. With this technique, pressure measurements are achieved in a time domain by measurement of ringdown times. The proof-of-concept device consists of a diode laser light source, two 2 x 1 fiber couplers, a section of fused-silica single-mode fiber, a photodetector, and an electronic control. The sensor's performance in the areas of stability, repeatability, and dynamic range is explored. The results demonstrate the new concept of fiber pressure sensors and the technical feasibility of developing a new generation of fiber sensors for pressure measurements.     

Ruby under pressure

The ruby luminescence method is widely used for pressure measurement in the diamond anvil cell and other optically transparent pressure cells. With this application in mind, we briefly review the ground-state physical properties of corundum (α-Al₂O₃) with some emphasis on its behavior under high pressure, survey the effects of temperature and stress on the R-line luminescence of ruby (Cr-doped corundum), and address the recent efforts towards an improved calibration of the R-line shift under hydrostatic pressures beyond the 50 GPa mark.     

Radiation pressure

Formulae for the radiation pressure of electromagnetic and of sound waves are reviewed. The pressure on an obstacle in the path of the waves can be calculated from the momenta of the incident and scattered trains, and it is now well established that any train of waves of intensity J propagated with speed v has momentum J/v ² per unit volume. A general proof of this result is proposed, independent of the nature of the waves.     

Melting temperature of metals under pressure

In the present study, a thermodynamic model is formulated to determine the melting temperature of metals with increasing pressure using an equation of state (EoS). The model is applied to determine the melting temperature of Cu, Au, Ag, Zn, Cd, In and Pb at high pressure. The model formulation is based on Goyal and Gupta EoS which follows Stacey's criteria and is valid in high pressure conditions and also it does not involve any adjustable parameter. The volume compression, bulk modulus and its first order pressure derivative is determined using the EoS with an increase in pressure. It is observed that melting temperature show increase with the increase in pressure, however, variation is not linear. The comparison of present computed results of melting temperature under pressure is done with the theoretical and experimental results available and good consistency between the compared results is observed. This study helps in understanding the quantitative effect of pressure on the melting behavior of metals. The melting temperature at high pressures can also be predicted using the present formalism.     

Ruby-spheres as pressure gauge for optically transparent high pressure cells

Abstract

Ruby is widely used as an in siru pressure gauge for optically transparent pressure cells up to the megabar range. Usually ruby chips cut from bulk crystals are used which are ill-characterized and inconvenient to handle and to identify visually. Here we present a systematic study on corundum samples doped with Cr³⁺ ions with concentration from 60 to 23500 ppm to determine the optimal conditions for the use as an accurate pressure marker. The influence of the excitation wavelength on the luminescence spectra was investigated. These studies led to the synthesis of small (1–50 micrometer) ruby spheres with 3000 ppm chromium concentration. After annealing and a heat treatment to avoid internal strains we find reproducible values of the position and the width of the fluorescence lines. These ruby spheres are not only well suited for a reliable and accurate pressure determination in experiments using diamond anvil cells, but can also be used as an in sihr micro-thermometer in high pressure-low temperature studies.     

Measurement of pressure distribution from PIV experiments

In this study, a non-staggered grid SIMPLER pressure solution algorithm, which is able to produce correct pressure distribution directly if correct velocities are given, is proposed to solve the pressure distribution for PIV experiments. The cell face pseudo velocity required in the pressure equation is approximated by a simple linear average of the adjacent nodal pseudo velocities so that the velocity and pressure are collocated without causing the checkerboard pressure distribution problem. In addition, the proposed pressure solution algorithm has the features that upwind effects of the convective terms are considered, boundary conditions are not required, and the pressure distribution obtained can be used to correct the velocity field so that the continuity equation is satisfied. These features make the present algorithm a superior method to calculate the pressure distribution for PIV experiments. The pressure field solved is realistic and accurate. The proposed pressure equation solver is first calibrated with a two-dimensional cavity flow. It is found that the results are almost identical to the exact solution of the test flow. The algorithm is then applied to analyze a uniform flow past two side-by-side circular cylinders in a soap film channel. With the velocity and pressure distributions successfully measured, the structures of the complex shedding flow patterns are clearly manifested.     

High pressure equipment for food processing

Abstract

Processing food with pressure improves the quality and shelf life of the product. The pressure required is normally 600 to 900 MPa (approximately 6000 to 9000 atm). Equipment for high pressure food processing is available today from ABB Pressure Systems AB. The plant can have a through-put of 300 to 6000 litres per hour at 600 MPa pressure depending on the size of the press. The processing cost at 600 MPa is between 3 to 20 pence per litre depending on production capacity. Processing at 900 MPa instead of 600 MPa will increase the cost 50%, while prolonging the processing time from 3 minutes to 6 minutes at 600 MPa, i.e. introducing a hold time, increases the cost 100%. Pressure is thus cheaper than time. The food is prepacked in flexible material and loaded into the high pressure vessel. Pure water is used as pressure transmitting medium. The pressure is increased to the value required. After decompression the food is ready for distribution.