Shock isolation using an isolator with switchable stiffness

A semi-active control strategy is presented for the shock isolation of resiliently mounted equipment where the isolator has light damping. This is achieved by switching the stiffness of the isolator between a high-state and a low-state. The control strategy involves two stages: the first stage involves the displacement control of the equipment during the shock, and the second stage involves suppression of the subsequent residual vibrations. The performance of the switchable isolation system is illustrated using a base-excited single degree-of-freedom system. It is characterized in terms of the maximum absolute acceleration and displacement of the isolated mass, the relative displacement between the base and the mass, and the effective damping ratio of the system. Provided that the damping in the isolator is light, it is found that the semi-active system can outperform a linear passive system during both stages of control.     

一种光电载荷非线性隔振装置的研究

针对光电载荷对隔振性能的需求,提出一种采用菱形连杆机构作为负刚度组件,具有高静、低动刚度特点的非线性隔振器（简称菱形HSLDS隔振器）。采用静力学分析方法,建立了隔振器数学模型,研究了刚度参数设定以及非线性调节方法;利用谐波平衡法（HBM）求解动力学方程,分析了各参数对隔振性能的影响关系;采用动力学仿真软件ADAMS及实物样机对理论模型与结论进行了验证。测试结果表明:菱形HSLDS隔振器具有较方便的参数调整能力,零位刚度及刚度非线性可通过拉簧参数与连杆参数进行设定、优化,隔振的刚度非线性优化程度受主隔振器阻尼以及零位刚度参数影响。相比于传统线性隔振器,菱形HSLDS具有显著的非线性隔振优势,可较好地满足光电载荷隔振需求。     

Dynamic isolation systems using tunable nonlinear stiffness beams

Vibration isolation devices are required to reduce the forcing into the supporting structure or to protect sensitive equipment from base excitation. A suspension system with a low natural frequency is required to improve isolation, but with linear supports the minimum stiffness is bounded by the static stiffness required to support the equipment. However, nonlinear high-static-low-dynamic-stiffness (HSLDS) mounts may be designed, for example by combining elastic springs in particular geometries, to give the required nonlinear force-displacement characteristics. Current approaches to realise the required nonlinear characteristics are often inconvenient. Furthermore, the weight of the supported equipment, the environment, or the structural stiffness may change. This paper investigates the design of HSLDS isolation mounts using beams of tunable geometric nonlinear stiffness. In order to obtain the nonlinear response required, we first study the case of generic beams subject to static loads that are able to tune their nonlinear force-displacement characteristics to ensure that the isolators have very low dynamic stiffness. Tuning is achieved by actuators at the ends of the beams that prescribe the axial displacement and rotation. Secondly, we study a composite beam with an initial thermal pre-stress, resulting in internal stresses that give the required nonlinear response.     

冲击环境下MEMS器件的弹性限位块设计（英）

采用限位块可以提高MEMS器件的抗冲击性能,但由于冲击环境中MEMS结构与限位块的碰撞过程可能产生较大的瞬间冲击以致器件失效,用弹性限位块可以有效解决上述问题,但是其防护效果会受到限位参数的影响。为了得到限位块最佳设计参数,首先建立了MEMS器件的冲击动力学模型,提取了影响MEMS器件冲击响应的因素,进而分析了限位块弹性系数、限位距对冲击响应的影响;最后提出了限位块的设计方法并给出了最终设计结果。结果表明：设计弹性限位块需要兼顾限位效果和缓冲性能,同时减小限位距也可显著提高微器件抗冲击性能。     

冲击环境下MEMS器件的弹性限位块设计（英文）北大核心CSCD

采用限位块可以提高MEMS器件的抗冲击性能,但由于冲击环境中MEMS结构与限位块的碰撞过程可能产生较大的瞬间冲击以致器件失效,用弹性限位块可以有效解决上述问题,但是其防护效果会受到限位参数的影响。为了得到限位块最佳设计参数,首先建立了MEMS器件的冲击动力学模型,提取了影响MEMS器件冲击响应的因素,进而分析了限位块弹性系数、限位距对冲击响应的影响;最后提出了限位块的设计方法并给出了最终设计结果。结果表明:设计弹性限位块需要兼顾限位效果和缓冲性能,同时减小限位距也可显著提高微器件抗冲击性能。     

Active pneumatic vibration isolation system using negative stiffness structures for a vehicle seat

In this paper, an active pneumatic vibration isolation system using negative stiffness structures (NSS) for a vehicle seat in low excitation frequencies is proposed, which is named as an active system with NSS. Here, the negative stiffness structures (NSS) are used to minimize the vibratory attraction of a vehicle seat. Owing to the time-varying and nonlinear behavior of the proposed system, it is not easy to build an accurate dynamic for model-based controller design. Thus, an adaptive intelligent backstepping controller (AIBC) is designed to manage the system operation for high-isolation effectiveness. In addition, an auxiliary control effort is also introduced to eliminate the effect of the unpredictable perturbations. Moreover, a radial basis function neural network (RBFNN) model is utilized to estimate the optimal gain of the auxiliary control effort. Final control input and the adaptive law for updating coefficients of the approximate series can be obtained step by step using a suitable Lyapunov function. Afterward, the isolation performance of the proposed system is assessed experimentally. In addition, the effectiveness of the designed controller for the proposed system is also compared with that of the traditional backstepping controller (BC). The experimental results show that the isolation effectiveness of the proposed system is better than that of the active system without NSS. Furthermore, the undesirable chattering phenomenon in control effort is quite reduced by the estimation mechanism. Finally, some concluding remarks are given at the end of the paper.     

High-throughput concept for tailoring switchable mirrors

The optical properties, the switching kinetics and the lifetime of hydrogen switchable mirrors based on Mg-Ni alloys are determined with particular regard to the composition of the optically active metal-hydride layer in combination with the thickness of the catalytic capping layer. For this, a high-throughput experiment is introduced. The switching kinetics and the reversibility of switchable mirrors are strongly thickness dependent, though the details hinge on the fine structure of the clustered capping layer. Therefore, the kinetics is correlated with the surface structures of Pd on Mg_yNi_1−y as investigated by scanning tunneling microscopy. The results are explained by the so-called strong metal-support interaction (SMSI) state, characterized by a complete encapsulation of the capping layer clusters by oxidized species originating from the support. The SMSI-effect is less important with increasing Pd-layer thickness, and is suppressed by a good wetting of the Pd-clusters on the optically active film. This explains the critical thickness for the catalyzed hydrogen uptake observed in many switchable mirror systems. Moreover, the degradation of the kinetics during cycling is found to depend on the Pd-layer thickness and on the gas environment. Only films, covered with at least 15 nm Pd, show small degradation caused by the SMSI-effect. The SMSI-effect is partly reversible: after changing the gas environment from hydrogen to oxygen, the oxide on the Pd-clusters can be partly removed.     

Microstructured switchable mirror for polar molecules

By miniaturizing electrode geometries high electric fields can be produced using modest voltages. A planar array of 20 microm wide gold electrodes, spaced 20 microm apart, is made on a sapphire substrate. A voltage difference of up to 350 V is applied to adjacent electrodes, generating an electric field that decreases exponentially with distance from the substrate. This microstructured array can be used as a mirror for polar molecules and can be rapidly switched on and off. This is demonstrated by retro-reflecting a beam of state-selected ammonia molecules with a forward velocity of about 30 m/s.     

Vibration isolation characteristics of a nonlinear isolator using Euler buckled beam as negative stiffness corrector: A theoretical and experimental study

This paper concerns the vibration isolation characteristics of a nonlinear isolator using Euler buckled beams as negative stiffness corrector. Both analytical and experimental studies are carried out. The Harmonic Balance Method (HBM) is used to determine the primary resonance response for the single degree of freedom (SDOF) nonlinear system composed by a loaded mass and the nonlinear isolator. The distuning of the loaded mass is taken into consideration, resulting in a Helmoholtz–Duffing equation. The performance of the nonlinear isolator is evaluated by the defined two kinds of transmissibility and compared with that of the linear isolator without the stiffness corrector. The study shows that the asymmetric SDOF nonlinear system can behave like a purely softening, a softening–hardening or a purely hardening system, depending on the magnitude of the excitation level. An experimental apparatus is set up to validate the analytical results. The transmissibility results of the SDOF nonlinear system under base excitation with both discrete sinusoidal frequencies and slowly forward and backward sweeps are given and discussed. The complex jump phenomena under different excitation levels are identified. By introducing the stiffness corrector, the starting frequency of isolation of the nonlinear isolator is found to be lower than that of the linear one with the same support capacity. The proposed nonlinear isolator performs well in applications where the excitation amplitude is not too large.     

An atomic device for trapping energy

An atomic device which “traps” energy from a continuous radiation, is proposed. A possible use of the device as a solar energy trap is discussed.     

平行板电容器演示实验装置的改进

介绍一种具有干燥、照明和充电系统的演示实验装置，该装置使平行板电容器在演示时能保持所带电荷基本不变。     

射流冲击泡沫金属强化电子器件冷却的实验研究

实验研究射流冲击泡沫金属的强化传热在电子器件冷却中的作用,分析热流密度、传热面与喷射气流温度差、喷射速度和喷嘴距泡沫金属上表面的高度等因素对传热特性的影响。在泡沫金属材质为铜,孔隙率为0.96,喷嘴宽度为0.5cm的情况下,喷嘴距泡沫金属上表面高度越低和喷射速度越大,泡沫金属的传热效果越明显,冷却效果越显著,并对实验数据,进行最小二乘法拟合,得到相应的拟合方程式。该文的分析结果,可为射流冲击泡沫金属强化传热技术的应用提供一定指导和借鉴。     

An experimental and computational study of methyl ester decomposition pathways using shock tubes

The high-temperature decomposition of three simple methyl esters: methyl acetate, methyl propionate and methyl butanoate, were studied behind reflected shock waves using tunable diode laser absorption of CO₂ near 2.7 μm. CO₂ yield measurements were made over the range of temperatures 1260-1653 K, pressures of 1.4-1.7 atm and reactant concentrations of 2-3%, with the balance Ar. The CO₂ absorption strengths near 2.7 μm are approximately 50 to 1000 times stronger than the bands near 2.0 and 1.55 μm, respectively, and offer opportunities for significantly more sensitive and accurate combustion measurements than previous absorption work using CO₂ bands at shorter wavelength. The experiments provide the first laser-based time-history measurements of the CO₂ yields during pyrolysis of these bio-diesel surrogate fuels in a shock tube. Model predictions for CO₂ yields during methyl butanoate pyrolysis at high temperatures, using the detailed reaction mechanisms of [E. M. Fisher, W. J. Pitz, H. J. Curran, C. K. Westbrook, Proc. Combust. Inst. 28 (2000) 1579-1586.] and others, are significantly lower than those measured in this study. However, an improved methyl butanoate model which extends the recent theoretical work of [L.K. Huynh, A. Violi, J. Org. Chem. 73 (2008) 94-101.] provides substantially improved predictions of CO₂ yields during methyl butanoate pyrolysis. As earlier mechanisms predicted low yields of CO₂ from methyl butanoate decomposition, these new findings imply that existing bio-diesel fuel models, which rely on the rapid formation of two oxygenate radicals from methyl esters (rather than a single non-reactive CO₂ molecule) to account for the tendency for soot reduction, may have to be revisited.     

LWIR/SWIR switchable two color device based on InP/InGaAs integrated HBT/QWIP

A novel two color infrared (IR) device that allows fast electrical switching between the short wavelength IR (SWIR) band (0.9–1.6 μm) and the long wavelength IR (LWIR) band (8–12 μm) is presented. The integrated sensor is based on MOCVD grown, lattice matched (to InP substrate) epilayers of InGaAs/InP and consists of two, monolithically integrated sections of heterojunction bipolar transistor (HBT) and quantum well infrared photodetector (QWIP).     

基于离子注入隔离的微缩化发光二极管阵列性能

基于F离子注入隔离技术实现一种新型微缩化发光二极管(micromicro-LED)阵列器件,并系统研究注入能量及发光孔径对micro-LED阵列器光电性能的影响.研究结果表明:相比于F离子50 ke V单次注入器件, 50/100 ke V两次注入器件具有更好的光电性能,器件反向漏电降低8.4倍,光输出功率密度提升1.3倍.同时,在不同的发光孔径(6, 8, 10μm)条件下,器件反向漏电流均为3.4×10–8 A,但正向工作电压随孔径增大而减小,分别为3.3, 3.1, 2.9 V.此外,器件不同发光孔径的有效发光面积比(实际发光面积与器件面积之比)分别为85%, 87%, 92%.与传统台面刻蚀micro-LED器件相比,离子注入隔离技术实现的micro-LED器件具有较低反的向漏电流密度、较高的光输出密度及有效发光面积比.     

Metrics for diagnosing negative mass and stiffness when uncoupling experimental and analytical substructures

When testing to identify an experimental model of a substructure, it is often beneficial to exercise the interface by attaching a fixture such as a rigid mass. An analytical representation of the fixture must then be used to subtract its effects from the assembly. However, this can cause the mass and stiffness matrices to become indefinite in some situations. This paper presents two new metrics that can be used by the analyst to determine the cause of indefinite mass or stiffness matrices after substructure uncoupling. The metrics rank the experimental and fixture modes based upon their contribution to offending negative eigenvalues. Once the troublesome modes have been identified, they can be inspected and often reveal why the mass has become negative. Two examples are presented to demonstrate the metrics and to illustrate the physical phenomena that they reveal.     

A vibration isolation system in low frequency excitation region using negative stiffness structure for vehicle seat

This paper designs and fabricates a vibration isolation model for improving vibration isolation effectiveness of the vehicle seat under low excitation frequencies. The feature of the proposed system is to use two symmetric negative stiffness structures (NSS) in parallel to a positive stiffness structure. Here, theoretical analysis of the proposed system is clearly presented. Then, the design procedure is derived so that the resonance peak of frequency-response curve drifts to the left, the load support capacity of the system is maintained, the total size of the system is reduced for easy practical application and especially, the bending of the frequency-response curve is minimized. Next the dynamic equation of the proposed system is set up. Then, the harmonic balance (HB) method is employed to seek the characteristic of the motion transmissibility of the proposed system at the steady state for each of the excitation frequency. From this characteristic, the curves of the motion transmission are predicted according to the various values of the configurative parameters of the system. Then, the time responses to the sinusoidal, multi frequency and random excitations are also investigated by simulation and experiment. In addition, the isolation performance comparison between the system with NSS and system without NSS is realized. The simulation results reveal that the proposed system has larger frequency region of isolation than that of the system without NSS. The experimental results confirm also that with a random excitation mainly spreading from 0.1 to 10 Hz, the isolation performance of the system with NSS is greatly improved, where the RMS values of the mass displacement may be reduced to 67.2%, whereas the isolation performance of the system without NSS is bad. Besides, the stability of the steady-state response is also studied. Finally, some conclusions are given.     

Numerical and experimental investigation of burner device for anode gas reburning

A complex numerical and experimental investigation of burner devices for a reburning of the anode gas of aluminum production was carried out. The chosen mathematical model of the processes of aerodynamics, heat exchange, and gas burning was identified and adapted on the basis of data of real-scale measurements. Basing on computational experiments the optimization of the design of elements of the system for anode gas detoxication and transport was carried out. A new system was proposed and tested for reburning the anode gases of electrolysis production, which consists of an improved burner device and a dust-sedimenting chamber with a possibility of regulating the amount of gas suction.     

An eye behavior measuring device for VR system

This work presents an eye-tracking and pupil size-measuring device that interfaces with a computer for applications useful in psychometry, ophthalmology, physiology and virtual reality (VR) systems. This system utilizes a change-coupled device (CCD) camera, appropriate lenses, PC with frame grabber and a DSP unit with various types of VR equipment, i.e., HMD, simulator or LCD projection device. The digital signal processing unit is used to calculate the average brightness and contrast of the VR video image. A CCD camera with various attachments can be mounted on various VR systems to capture the human eye image for testing. An image capture card and a personal computer are used to analyze the test image. From the eye digital image, the computer obtains data on the pupil size and a trace of the tested eye. A pattern recognition computer program and five measurement parameters are used to distinguish the position of the pupil, calculate the pupil location coordinate and analyze the physical conditions of the user. These data can be plotted against the average brightness and contrast of the VR video image in real time. This information is shown on the screen of a personal computer and used for cross-link analysis. This eye-tracking interface can determine the position of a subject's pupil and map that position into a display point on a computer screen. The pupil size and location data versus the average brightness and contrast of a VR video image are computed in real time.