电阻应变式土压力传感器的设计方法(二)

<正> 三、弹性元件的计算 本文只简述比较常用的单弹性薄板式土压力传感器及单油腔土压力传感器的弹性元件厚度的计算方法。 (一)弹性敏感元件的计算 单弹性薄板式土压力传感器的弹性敏感元件为一圆形薄板,计算薄板厚度的控制条件有两种,一种由传感器对土介质的变形模量之比E_g/E_s值控制;一种由传感     

温度自补偿型光纤Bragg光栅土压力传感器设计

针对传统土压力传感器长期稳定性差、抗电磁干扰能力不强以及组网难度大等问题,根据传感器与土介质的匹配原则,设计了一种光纤Bragg光栅（FBG）温度自补偿土压力传感器,可实现温度和土压力2个参量的同时测量.对传感器灵敏度系数、匹配性等参数进行了理论分析计算.根据分析结果,加工封装传感器并对其进行了压力校准和温度自补偿性能实验.实验表明：传感器的输出波长分别与温度和土压力均呈线性关系,压力灵敏度系数为272.19 pm/MPa,输出分辨率为0.36％,线性相关度为99.989％;温度灵敏度系数为21.16 pm/℃,线性相关度99.998％,在0～40℃范围内具有良好的温度自补偿能力,其性能参数符合工程应用要求.     

焊接结构光纤Bragg光栅土压力传感器设计

针对传统土压力传感器长期稳定性差、抗电磁干扰能力不强以及组网难度大等问题,根据传感器与土介质的匹配原则,设计了一种焊接结构双膜片光纤Bragg光栅(FBG)温度自补偿土压力传感器,可实现温度和土压力2个参量的同时测量.传感器主要由2个膜片与基体组成,膜片与光栅固定柱一次成型,便于加工封装.对传感器灵敏度系数进行了计算分析.根据分析结果,加工封装传感器并对其进行了压力校准及温度自补偿性能实验.实验结果表明:传感器的输出波长分别与温度和压力呈线性关系,压力灵敏度系数为528.1 pm/MPa,输出分辨率为0.19%,线性相关度99.988%;在5~45℃内温度灵敏度系数为31.9 pm/℃,线性相关度99.998%,传感器在5~45℃范围内具有良好的温度自补偿能力,其性能参数符合工程应用要求.     

电阻应变式土压力传感器的设计方法(一)

<正> 众所周知,量测土压力是比较困难的,因为土介质和结构物材料的变形特性是变化的,所以要求土压力传惑器与土介质或结构材料的变形特性达到完全匹配是不可能的。一个设计得好的土压力传感器,就是在不完全匹配的情况下,使传感器在量测时的工作特性按一定的规律变化,所产生的误差是可知的。一、设计土压力传感器的理论依据 几十年来,国内外对土压力传感器进行了大量的理论和实验研究,如美国的泰     

基于PDMS海绵介质层的电容式柔性压力传感器

柔性压力传感器以其低成本和大的检测范围等优势广泛的应用于电子皮肤和可穿戴传感器领域。本文通过在PDMS中填充碳酸氢铵材料,制备了大面积高密度具有微观结构的PDMS海绵介质层,通过简易的方法完成了柔性压力传感器的制备。与以往的柔性压力传感器相比,制备的PDMS海绵介质层由于气孔的存在更容易在受到压力时发生形变,拥有高的灵敏度(0.23 kPa^-1)、大的检测范围(0～50 kPa)、稳定的重复性(>1 000循环)以及快的响应时间(<150 ms)。通过对不同厚度、不同大小的PDMS海绵介质层进行测试,利用厚度为1.5 mm,大小为8 mm×8 mm的PDMS海绵作为压力传感器的介质层实现了力的实时检测。     

基于黑磷烯/氧化石墨烯双介质层的柔性电容式压力传感器

设计并制备了由黑磷烯/氧化石墨烯双层材料为介质层的电容式柔性压力传感器,该传感器结构以ITO为电容上下极板,PET为柔性基底,并对该传感器进行了系统的性能测试与分析。着重研究了该传感器在不同压力量程内的灵敏度,进而分析了其温度漂移特性。测试结果表明,以黑磷烯/氧化石墨烯薄膜为双介质层的电容式柔性压力传感器在0～3.12 kPa压力量程内灵敏度可达到1.60 kPa^-1。同时,对该传感器和以氧化石墨烯薄膜为单介质层的传感器进行了弯曲应变性能的对照实验,可知具有双介质层的传感器结构能够显著提高传感器的输出特性。     

薄膜式土压力分布传感器研发及试验研究

在岩土力学与工程领域,随着对土压力荷载大小与分布研究的深入,新型土压力传感器的研发愈显重要.本文利用导电敏感复合材料研制了一种新型薄膜式土压力分布传感器,其总厚度小于0.2 mm.首先介绍了传感器的设计原理及结构,初步测试结果表明,双层结构传感器的灵敏度相对更高.然后,通过大型模型试验实测检验了研发的双层结构土压力分布传感器的基本性能.新型传感器具有测点面积小(可实现大密度测试)、T/D小(对土体扰动小)、引线方便以及弯曲挠度大(适合弯曲表面压力测试)等特点.综合来看,它用于土压力分布测试初步是可行的,具有进一步深入研究的价值.     

饱和土有效应力传感器的研制

饱和土有效应力传感器是岩土介质力学测试中所急需的一种传感器,通过对饱和土中孔隙水压力传感器的分析,建立了传感器滤水结构动态特性的数学模型,通过对该模型动态响应特性的分析,设计的传感器能有效应用于动态荷载作用下饱和土有效应力的测试,试验和实际应用效果良好。     

电容式土壤水分传感器的电导变异性试验研究

为评估电容式土壤水分传感器受土壤电导率的影响及其对农田土壤电导率变化范围的适用性,配制了一系列土壤等效含水率为40.6%、电导率为0~1.91dS/m的土壤等效介电溶液,分别对激励信号频率为40,50,60,70,80,90,100MHz的7种传感器进行了电导变异性试验,并且配制了相同含水率但电导率分别为0,0.31,0.46和0.61dS/m的4种土样进行了验证试验。试验结果表明:1)土样中的测试结果基本上与介电溶液吻合,可采用等效介电溶液评估传感器的电导变异性;2)传感器的电导变异率随待测介质电导率的升高而近似线性增大,相同电导率下,传感器激励信号频率越高其电导变异率越小;3)在农田土壤电导率基本变化区域0.239~0.650 dS/m内,当传感器激励信号频率从不低于80MHz时,其最大电导变异率为9.2%,能满足工程上的实际应用要求。     

土压力传感器的标定方法

<正> 一、概述 土压力测量中要求每个土压力传感器有一条供数据分析用的土中标定曲线,而目前大多数土压力传感器的制造厂家只提供一条经过处理的、在气压或水压作用下的标定曲线,这是不够的。因此,要求每个土压力传感器必须在一个专用的大型土压标定箱中,用现场的土介质,按预定的现场埋设方法安装,进行标定得到其土中标定曲线。     

叠加电桥检测的加速度传感器设计

基于压阻效应的叠加电桥检测法加速度传感器采用超对称"八悬臂梁—质量块"结构,构成惠斯通电桥的力敏电阻器布放在悬臂梁的两端,4个惠斯通电桥的输出电压叠加后作为传感器的最终输出,有效提高了加速度传感器的灵敏度。通过数学建模仿真分析验证了方案的可行性。性能测试结果表明:该加速度计的灵敏度为1.1381mV/gn,频响范围为0～1000Hz,灵敏度约为单电桥检测法和串联电桥检测法加速度传感器灵敏度的4倍。叠加电桥检测法为压阻式传感器提高灵敏度提供了一种新思路。     

温度对聚偏氟乙烯压力传感器灵敏度的影响

聚偏氟乙烯(PVDF)压电薄膜的热电效应对PVDF压力传感器的输出灵敏度影响较大。通过对研制的PVDF压力传感器灵敏度受温度影响的试验研究得出:传感器的灵敏度随温度增加而增大,两者关系是一条曲线;在-20～60℃范围内其热灵敏度漂移系数是个常数,其值为0.007619℃;利用室温时传感器校准得出的输出灵敏度,用公式可以计算出-20～60℃范围内任何温度时的灵敏度,从而实现了传感器灵敏度受热电效应影响的修正。     

Tribocharge build-up and decay at a slider-disk interface

As the gap between the head and disk decreases and the sensitivity of recording transducers increases, the head and disk are more likely to come in contact, which may damage the recording transducer during start/stop and flying cases. One important effect associated with the intermittent head-disk contacts is the tribocharge/tribocurrent phenomenon. In this study, tribocharge and tribocurrent generation during a pico-slider/disk interaction were measured by using an electrometer. These triboelectrical properties were compared with friction force and acoustic emission signals. The electrical potential difference between the slider and the disk was caused by mechanical interactions between them. The tribocharge was generated during the slider-disk interaction and its saturation charge level was about 1 V. The tribocharge build-up level was independent of the slider-disk interaction time. However, the tribocharge decayed when there was no interaction between the slider and the disk. The decay of tribocharge was inversely proportional to the square root of time. Tribocurrent generation coincided with tribocharge generation. The tribocurrent was also independent of the slider-disk interaction time. The current level measured in this study may not reach the electrostatic discharge (ESD) damage level, but it can induce the dissociation of lubricant.This work was supported by KOSEF (Korea Science and Engineering Foundation; Grant No. R01-2003-000-10142-0) and CISD (Center for Information and Storage Device; Grant No. R11-1997-042-12001-0).     

基于声异常透射效应的高强度聚焦超声换能器

高强度聚焦超声（High intensity focused ultrasound,HIFU）作为一种新型无创的外科技术已在临床上应用于各种良恶性实体肿瘤治疗。为了实现安全高效的肿瘤治疗,HIFU换能器的聚焦效率仍然有待提高。本文综述了声异常透射效应的基本原理,以及近期利用声异常透射效应的HIFU聚焦超声换能器的研究。主要涉及两个方面的工作：（1）将声人工结构引入凹面型声透镜的设计,设计并制作了声超常透镜,对声透镜式聚焦换能器进行改进,达到了降低旁瓣的效果,从而提高了HIFU治疗的安全性;（2）基于球弧周期槽阵列设计并制作了超构聚焦换能器,以增强HIFU换能器聚焦效率。从理论及实验两方面研究了超构聚焦换能器与传统凹面换能器的声压分布和在组织中产生的温升。本文研究结果可进一步促进HIFU在临床治疗的广泛应用。     

A novel Terfenol-D transducer for guided-wave inspection of a rotating shaft

The purpose of this study is to develop a new ultrasonic transducer capable of transmitting and receiving guided-waves in a rotating shaft. The key idea in this development is the use of wireless capability of the magnetostrictive effect. In this investigation, relatively low-frequency longitudinal waves are generated by Terfenol-D, a giant magnetostrictive alloy (GMA). After an underlying magnetostrictive transducer configuration is presented, the effects of various design parameters on the transducer performances are studied experimentally. The material behavior of Terfenol-D is also briefly discussed. To show the effectiveness of the developed transducer, the transducer is used for guided-wave damage inspection in a rotating shaft having an artificial crack.     

苯并[1,2-b:4,5-b']二噻吩的共轭聚合物光伏材料的能隙的理论研究

共轭聚合物材料的吸收谱带和能隙是影响太阳能电池(PSCs)能景转换效率(PCE)的主要因素,为了预测吸收谱带和能隙提高新型共轭聚合物的光伏性能,用量子化学方法计算了具有不同共轭单体的苯并[1,2-b:4,5-b']二噻吩(BDT)的吸收光谱和能隙.基态分子结构优化用密度泛函理论(DFT)B3LYP方法及6-31G(d)基组,吸收光谱和最低激发能(Eg)用含时密度泛函理论(TD-DFT)计算.聚合物的△H-L和Eg值用外推法计算,而且提出了相关参数用以调控共轭聚合物能隙和吸收谱带.计算结果与实验结果相符.     

On the Minimization of Finite State Transducers over Semigroups

Finite state transducers over semigroups are regarded as a formal model of sequential reactive programs that operate in the interaction with the environment. At receiving a piece of data a program performs a sequence of actions and displays the current result. Such programs usually arise at implementation of computer drivers, on-line algorithms, control procedures. In many cases verification of such programs can be reduced to minimization and equivalence checking problems for finite state transducers. Minimization of a transducer over a semigroup is performed in three stages. At first the greatest common left-divisors are computed for all states of a transducer, next a transducer is brought to a reduced form by pulling all such divisors “upstream,” and finally a minimization algorithm for finite state automata is applied to the reduced transducer.     

Fe-Ga合金换能器动态输出特性分析

Fe-Ga合金具有应变大、响应时间短、能量密度高、磁机耦合系数高、驱动方式简单等优点.Fe-Ga合金换能器在高频驱动电流下会产生涡流损耗.驱动电流频率越大,集肤效应越明显,涡流损耗越大,磁场分布越不均匀,从而影响换能器的输出位移和输出功率.首先基于麦克斯韦方程组分析了不同频率下Fe-Ga棒内的磁场分布,结合结构动力学模块分析了Fe-Ga合金换能器棒内的磁场分布,进而得到Fe-Ga合金换能器的输出位移和频率的关系.结果表明,所使用的Fe-Ga合金换能器共振频率为700 Hz,最大输出位移为6μm.     

Soil-structure interaction and effect of axial force on the dynamics of offshore structures

The offshore structures are flexible systems subjected to various types of loadings. The heavy gravitational loads on the top decks, wind and water wave pressures acting on the platforms are transferred to the soil through the piles or mat foundations. Under the vibration, the variation in the pore pressures induces additional effects on the embedded part of the piles. The effect of the soil-structure interaction on the dynamics of the structure is taken into account as the deformations of the soil caused by the motion of the structure which in turn modify the response of the structure. The effect of the axial forces, within the individual members, on the vibration of the structure is included in the formulation. The dynamic stiffness matrix of the members are developed by considering the actual mass distribution and the effect of the axial force of the members. For the members embedded into soil, the soil reactions and the skin frictions are also considered as continuously varying over the members. Therefore, the equations of motion are satisfied along any infinitesimal element of the members. The new formulation is introduced in the general purpose computer code STDYNL, then the sensitivity of the overall dynamic response of the deep water platforms to the variation of the soil characteristics and to the effect of the axial forces of the members are investigated.