水银柱活塞差动式光纤布拉格光栅倾角传感器

为了适应公路边坡倾斜监测的需要,提出了一种新型的水银柱活塞差动式光纤布拉格光栅(FBG)倾角传感器。传感器所测对象的倾角发生变化时,水银柱在金属壳内的有效长度发生改变,对传压活塞的压力也相应改变。传压活塞通过传力杆将水银的压力传递给等强度悬臂梁自由端,使得粘贴在等强度悬臂梁左右两侧的FBG中心波长变化。利用有限元方法在不同倾斜角度下运用两点粘贴法分析等强度悬臂梁与FBG的应力特性,根据仿真参数研制了倾角传感器,并对该传感器进行了角度标定实验和温度敏感实验。实验结果表明,FBG倾角传感器量程范围为0°~40°,灵敏度为21.8pm/(°),拟合度R2为0.998,重复性为1.12%。     

高精度低成本多路自动测压系统

文章从压力传感器的基本原理出发,对测压系统所能出现的种种误差进行详细分析后,总结出一套较完整的消除和控制诸系统误差的办法。在充分利用计算机这一近代工具、并创新地设计和制成了一种名叫“多路夹板式伐门”以后,这一合理的设想得以顺利地实现了。系统采用国产普通压力传感器,尽管它们原来的综合误差高达百分之几,但通过本技术途径以后,能使大部分传感器获得了优于0.1％满量程的测压精度。这些传感器的环境温度仍可允许缓慢地变化,传感器的激励电源,可采用最廉价的直流稳压电源。     

水平管道段塞流特征参数的压差波动分析

分析了压力波动信号互相关求液塞速度存在的不足，引入了压差波动分析法；明确了液塞到达和离开上、下游测压点的时刻与压差波动信号起峰点与落峰点位置的关系；指出了压差信弓脉冲宽度为液塞义到达上游测压点和液塞尾离开下游测压点的时间间隔，脉冲宽度与液塞速度的乘积为液塞长度与差压传感器间距之和．把空气－水、柴油和机械油的试验结果与文献中经验关系式进行了对比，验证了该测量方法的正确性．     

超稳定TO-8型压力传感器在气体导热系数测定实验中的应用

介绍了TO-8型压力传感器的性能及电源电路.以气体导热系数测定实验为例,用TO-8型压力传感器制成的测压装置代替旋转式麦氏真空计,利用可调针孔式放气阀对真空气压进行连续调节,实现了对测试系统真空度的实时监测.     

活塞式菱形结构光纤布喇格光栅渗压传感器

为了适应矿井、大坝对渗压监测的需要,提出一种活塞和菱形传压结构相结合的光纤布喇格光栅渗压传感器,活塞把测试压力传递到菱形传压结构,菱形传压结构拉动其上下对称连接的弹性钢片,导致粘贴在弹性钢片上的光纤布喇格光栅中心波长产生变化.利用有限元方法在500kPa的测试环境中对顶角分别为90°、110°、130°、150°情况下菱形传压结构的应力特性进行分析,根据仿真参量研制了渗压传感器,并对该传感器进行了压力标定试验和温度补偿试验.实验结果表明:传感器对渗压的灵敏度为2.04nm/MPa,拟合度为0.997,重复性为0.9%,两个测压光栅温度灵敏度分别为0.023 33nm/℃、0.021 68nm/℃,温补光栅为0.009 916nm/℃.     

强烈段塞流特征参数测量方法试验研究

通过对单个液塞经过管道上某一测压点时的压力信号进行理论分析,指出了压力波动曲线上的特征点与液塞相对于测压点位置之间的对应关系。根据分析结果,采用单压力信号判断法,求得了强烈段塞流的液塞运动速度、液塞长度等特征参数。与利用双平行电导探针相关法求得的结果比较发现,单压力信号判断法具有测量结果准确、不受流动介质物性限制、不干扰流场、简便实用等优点。     

炮管非定常边界层的研究

本文的主要目的是通过求解炮管内的非定常边界层问题,求得内膛最大壁温和高温气体对壁面的传热量,为研究炮管烧蚀问题提供理论依据。 1、实验研究 如图1所示,1—6为测压孔,4′为测温孔。压力-时间曲线用压电传感器测定;内壁温度由热电偶测定。而弹丸炮口速度则通过测定弹丸飞过两个一定间距的线圈的时间来换算。     

基于PCI8602的压力传感器测试系统设计

为了便于压力传感器生产商对产品质量进行检测,设计了一种压力传感器性能测试系统,该系统由工业计算机、数据采集卡、标准压力变送器、信号处理电路以及多通道被测传感器组成,系统测试时使用工业计算机端VB应用程序控制整个测试过程;通过将4~20 mA标准压力变送器和被测多通道压力传感器置于同一被测环境,由VB应用程序实时采集两者的输出值并进行计算,软件通过分析处理可判断被测传感器性能好坏;测试系统可借助VB语言灵活地调整软件功能及测试界面,广泛应用于企业压力传感器的实验室检测;实际应用表明,该系统可节省人工,降低工人劳动强度,提高检测质量。     

新型应变式高膛压测试系统研制

 根据电子测压器的特点,以测压器的端盖作为弹性敏感元件,研制出了一种新型的集测压器壳体与传感器于一体的应变式高膛压测试系统。利用厚板变形理论,对电子测压器壳体的力学特性进行了理论分析,并利用ANSYS对壳体的应力、应变分布及弹性敏感元件的模态进行了仿真模拟。50～550 MPa静压标定实验结果表明,该测试系统的线性误差为0.62%,基本误差为4.6%,灵敏度为2.231 3×10^-12 Pa^-1,压力测量范围可涵盖0～600 MPa;动态实验结果表明利用该应变式测试系统测量高膛压是准确可行的。     

柔性压阻式压力传感器的研究进展

柔性压阻式压力传感器作为柔性压力传感器的重要分支,具有结构简单、灵敏度高、工作范围大、响应速度快及稳定性高等特点,在人类运动行为探测、健康监测、仿生电子皮肤开发及人机交互等领域均具有潜在发展需求.但是截至目前,如何同时实现低成本、高性能、低能耗和自驱动仍旧是柔性压阻式压力传感器未来所面临的挑战,而新型传感机制的开发、新型功能化纳米材料的融合及柔性器件的新型制备工艺将是未来发展的方向.本文综述了近年来柔性压阻式压力传感器的研究进展,从传感机制出发,对柔性压阻式压力传感器的活性层材料种类和微结构设计类型进行了总结,最后对其未来的潜在应用进行了展望.     

黏弹材料动力学参数的宽频测试

利用改进的波速法,对黏弹性材料连续宽频范围的动力学参数进行测试。利用有限元方法,对波速法的测试过程进行了仿真,验证了利用长短棒波速法测量宽频动力学参数的有效性。采用可控脉冲生成技术,在激振器上产生了用于宽频测试的短脉冲信号。黏弹性长短棒在上述宽带短脉冲激励下作纵向强迫振动,利用激光测振仪测量长短两棒自由端的纵向振动速度,从而可得两振动信号在连续宽频范围的幅值比和相位差,进而可根据波速法原理计算得到材料在连续宽频范围的储能模量和损耗因子。测试结果表明,该系统通过较少次数测试,可直接计算得到1~5 kHz连续宽频范围的动力学参数,测试结果与黏弹仪数据吻合。通过对幅值比和相位差进行线性最小二乘拟合,可以进一步拓展测量的频率范围。该方法准确可靠、简便快速,具有实际应用价值。      

Design of an ultrasonic sensor for measuring distance and detecting obstacles

This paper introduces a novel method for designing the transducer of a highly directional ultrasonic range sensor for detecting obstacles in mobile robot applications. The transducer consists of wave generation, amplification, and radiation sections, and a countermass. The operating principle of this design is based on the parametric array method where the frequency difference between two ultrasonic waves is used to generate a highly directional low-frequency wave with a small aperture. The aim of this study was to design an optimal transducer to generate the two simultaneous longitudinal modes efficiently. We first derived an appropriate mathematical model by combining the continuum model of a bar and countermass with the compatibility condition between a piezoelectric actuator and a linear horn. Then we determined the optimal length of the aluminum horn and the piezoelectric actuator using a finite element method. The proposed sensor exhibited a half-power bandwidth of less than ±1.3° at 44.8 kHz, a much higher directivity than existing conventional ultrasonic range sensors.     

Theory and experiment of Fourier-Bessel field calculation and tuning of a pulsed wave annular array

A one-dimensional (1D) Fourier-Bessel series method for computing and tuning (beamforming) the linear lossless field of flat pulsed wave annular arrays is developed and supported with both numerical simulation and experimental verification. The technique represents a new method for modeling and tuning the propagated field by linking the quantized surface pressure profile to a known set of limited diffraction Bessel beams propagating into the medium. This enables derivation of an analytic expression for the field at any point in space and time in terms of the transducer surface pressure profile. Tuning of the field then also follows by formulating a least-squares design for the transducer surface pressure with respect to a given desired field in space and time. Simulated and experimental results for both field computation and tuning are presented in the context of a 10-ring annular array operating at a central frequency of 2.5 MHz in water.     

磁致伸缩换能器辐射板形状对声场分布的影响

磁致伸缩换能器可作为热声制冷机的声源装置,辐射板的形状直接影响声压输出效率,从而影响制冷效果。为提高换能器工作效率、减小换能器体积,辐射板需在Terfenol-D棒的激励下产生大振幅、高频率的活塞振型。针对这一问题,应用ATILA软件分析了磁致伸缩换能器辐射板形状对谐振腔振动幅频特性的影响以及对谐振腔内声场分布的影响。结果表明:相同激励条件下,凹球面辐射板出现活塞振型时振幅最大,对应谐振腔中声压幅值最高;谐振腔端面形状为凹球面时,具有聚焦声压幅值的作用;端面形状为凹发射端-凸反射端组合的谐振腔内声压幅值最高。以上结论为合理设计辐射板、谐振腔两端面组合形状提供了参考。     

Mode analysis of trilaminar bender bar transducers using an approximation method

Based on the vibration theory of a thin plate, an analytical treatment of the trilaminar bender bar with piezoelectric elements and inert substrate of various lengths is presented for mode analysis. Resonance frequency and effective electromechanical coupling coefficient are calculated by this method. The impacts of the geometries of the bender bar on the performance of its fundamental and third-order flexural mode are investigated in detail under rigid boundary conditions. It is shown that resonance frequency is extremely sensitive to the thickness of inert substrate. Moreover, the effective electromechanical coupling coefficient has peaks as the length of piezoelectric elements varies. The peaks are achieved when the length of piezoelectric elements equals the length between two nodes having zero strains in the x-direction. The trilaminar bender bar will be effectively excited when the strains on the piezoelectric element are in the same phase, which is important to disclose the vibration mechanisms of this kind of transducer. Also, analytical results are compared with the ones of numerical simulation. The results suggest that effective electromechanical coupling coefficient shares similar patterns with electrical conductance, which can be used to characterize transducer performance to a certain extent. It also demonstrates that the analytical treatment provides an efficient alternative way for optimizing the bender bar transducer design.     

ESTIMATION OF 3D FIELD QUANTITIES AND ENERGY FLUX ASSOCIATED WITH ELASTIC WAVES IN A BAR

A method to estimate dispersion relations and warping associated with elastic wave propagation in a bar is presented. The method is based on Hamilton's principle. It is shown how the theoretical model together with strain measurements can be used to evaluate three dimensional (3D) field quantities like displacements and stresses at an arbitrary position in the bar, as well as energy flux through an arbitrary cross-section of the bar. It is also shown how redundant measurements can be used to increase the accuracy. The method is general and can be applied to any mode of wave propagation, isotropic or anisotropic linearly elastic material, and any cross-sectional geometry. Here, it is applied to longitudinal waves in a split Hopkinson pressure bar with linear elastic isotropic material behaviour and square cross-section. In particular, axial displacement, axial stress and energy flux are evaluated at a free end of the bar in order to test the method. The method is also used to estimate the Poisson ratio of the bar material, by measuring axial and transverse strains at the same axial position.     

Measurements of velocity and attenuation of leaky waves using an ultrasonic array

A new method of measuring velocity and attenuation of leaky surface waves is presented. A single focused transmitting transducer and linear receiving array in a pitch-catch arrangement are used in the proposed system. The spatial distribution of the acoustic field in the leaky wave is recorded by the array, and the parameters of the leaky wave can be obtained by processing the output waveforms. In comparison with existing material characterization systems, the mechanical scanning of the transducers is not used any more, and the measurement time is only limited by the time of the wave propagation and speed of the electronic data acquisition system.     

Pulsating one-dimensional detonations in hydrogen–air mixtures

The propagation of one-dimensional detonations in hydrogen–air mixtures is investigated numerically by solving the one-dimensional Euler equations with detailed finite-rate chemistry. The numerical method is based on a second-order spatially accurate total-variation-diminishing scheme and a point implicit time marching algorithm. The hydrogen–air combustion is modelled with a 9-species, 19-step reaction mechanism. A multi-level, dynamically adaptive grid is utilized, in order to resolve the structure of the detonation. Parametric studies for an equivalence ratio range of 0.4–2.0, initial pressure range of 0.2–0.8 bar and different degrees of detonation overdrive demonstrate that the detonation is unstable for low degrees of overdrive, but the dynamics of wave propagation varies with fuel–air equivalence ratio and pressure. For equivalence ratios less than approximately 1.2 and for all pressures, the detonation exhibits a short-period oscillatory mode, characterized by high-frequency, low-amplitude waves. Richer mixtures exhibit a period-doubled bifurcation that depends on the initial pressure. Parametric studies over a degree of overdrive range of 1.0–1.2 for stoichiometric mixtures at 0.42 bar initial pressure indicate that stable detonation wave propagation is obtained at the high end of this range. For degrees of overdrive close to one, the detonation wave exhibits a low-frequency mode characterized by large fluctuations in the detonation wave speed. The McVey–Toong short-period wave-interaction theory is in qualitative agreement with the numerical simulations; however, the frequencies obtained from their theory are much higher, especially for near-stoichiometric mixtures at high pressure. Modification of this theory to account for the finite heat-release time significantly improves agreement with the numerically computed frequency over the entire equivalence ratio and pressure ranges.     

具有单相单向换能器的水平剪切声表面波压力传感器插入损耗特性

为实现水平剪切声表面波压力传感器低损耗设计,系统研究了均匀叉指换能器(IDT)和单相单向换能器(SPUDT)器件的声波能量损耗性能.在确定最优反射系数的SPUDT结构的基础上,建立3D周期性有限元仿真模型,计算器件表面振动位移和双向输出电压瞬态响应.通过对电压信号进行傅里叶变换获得器件模型的插入损耗,并制备两种不同换能...     

Spatial filtering of wall pressure fluctuations beneath a turbulent boundary layer

Methods of experimental spatial filtering of wall pressure fluctuations beneath a turbulent boundary layer are developed with the aim of obtaining information on the wave number-frequency spectrum. The spatial filtering of the pressure field components by wave-vector filters is studied. The method of spatial filtering of pressure fluctuations by an acoustic array, i.e., a periodic structure with a finite number of elementary transducers, is analyzed. The relation between the wave number characteristic of the acoustic array and the wave number spectrum of the amplitude distribution of transducer’s local sensitivity is determined. Quantitative estimates are obtained for the sensitivity of the array to the wave number spectrum of turbulent boundary-layer pressures, which is necessary for measuring the wall pressure fluctuations in a turbulent boundary layer by wave-vector filters.