大型客车车身振动和声学特性分析

为了解决客车车身振动导致乘员室产生低频噪声的问题,在对车身骨架结构、车室腔体进行模态特性分析和对车身结构进行频响分析的基础上,运用边界元法对车室进行声场分析和车身板块贡献度分析,进而找出车内噪声声压峰值处所对应的振动频率及该峰值下的“噪声源”板块,提出对车身结构的修改建议。     

Two-dimensional manipulation of micro particles by acoustic radiation pressure in a heptagon cell

An acoustic particle manipulation system is presented, using a flexible printed circuit board formed into a regular heptagon. It is operated at 4 MHz and has a side dimension of 10 mm. The heptagonal geometry was selected for its asymmetry, which tends to reduce standing wave behavior. This leads to the possibility of having fine control over the acoustic field by varying the output phases of the transducer elements. Configurations with two and three active transducers are demonstrated experimentally. It is shown that with two transducers, the particles align along straight lines, the position of which can be moved by varying the relative excitation phases of the two transducers. With three active transducers, hexagonal-shaped patterns are obtained that can also be moved, again according to the phase of the excitation signals. Huygens' principle-based simulations were used to investigate the resultant pressure distributions. Good agreement was achieved between these simulations and both Schlieren imaging and particle manipulation observations.     

Array-controlled ultrasonic manipulation of particles in planar acoustic resonator

Ultrasonic particle manipulation tools have many promising applications in life sciences, expanding on the capabilities of current manipulation technologies. In this paper, the ultrasonic manipulation of particles and cells along a microfluidic channel with a piezoelectric array is demonstrated. An array integrated into a planar multilayer resonator structure drives particles toward the pressure nodal plane along the centerline of the channel, then toward the acoustic velocity maximum centered above the subset of elements that are active. Switching the active elements along the array moves trapped particles along the microfluidic channel. A 12-element 1-D array coupled to a rectangular capillary has been modeled and fabricated for experimental testing. The device has a 300-μm-thick channel for a half-wavelength resonance near 2.5 MHz, with 500 μm element pitch. Simulation and experiment confirm the expected trapping of particles at the center of the channel and above the set of active elements. Experiments demonstrated the feasibility of controlling the position of particles along the length of the channel by switching the active array elements.     

Computation of a spectrum from a single-beam fourier-transform infrared interferogram

A new high-accuracy method has been developed to transform asymmetric single-sided interferograms into spectra. We used a fraction (short, double-sided) of the recorded interferogram and applied an iterative correction to the complete recorded interferogram for the linear part of the phase induced by the various optical elements. Iterative phase correction enhanced the symmetry in the recorded interferogram. We constructed a symmetric double-sided interferogram and followed the Mertz procedure [Infrared Phys. 7,17 (1967)] but with symmetric apodization windows and with a nonlinear phase correction deduced from this double-sided interferogram. In comparing the solution spectrum with the source spectrum we applied the Rayleigh resolution criterion with a Gaussian instrument line shape. The accuracy of the solution is excellent, ranging from better than 0.1% for a blackbody spectrum to a few percent for a complicated atmospheric radiance spectrum.     

Electrophoretic cell manipulation and electrochemical gene-function analysis based on a yeast two-hybrid system in a microfluidic device

A novel microfluidic device with an array of analytical chambers was developed in order to perform single-cell-based gene-function analysis. A series of analytical processes was carried out using the device, including electrophoretic manipulation of single cells and electrochemical measurement of gene function. A poly(dimethylsiloxane) microstructure with a microfluidic channel (150 microm in width, 10 microm in height) and an analytical chamber (100 x 20 x 10 microm (3)) were fabricated and aligned on a glass substrate with an array of Au microelectrodes. Two microelectrodes positioned in the analytical chamber were employed as a working electrode for the electrophoretic manipulation of cells and electrochemical measurements. A yeast strain ( Saccharomyces cerevisiae Y190) carrying the beta-galactosidase reporter gene was used to demonstrate that the device could detect the enzyme. Target cells flowing through the main channel were introduced into the chamber by electrophoresis using the ground electrode laid on the main channel. When the cell was treated with 17beta-estradiol, gene expression was triggered to produce beta-galactosidase, catalyzing the hydrolysis of p-aminophenyl-beta- D-galactopyranoside to form p-aminophenol (PAP). The enzymatically generated PAP was detected by cyclic voltammetry and amperometry at the single-cell level in the chamber of the device. Generator-collector mode amperometry was also applied to amplify the current response originating from gene expression in the trapped single cells. After electrochemical measurement, the trapped cells were easily released from the chamber using electrophoretic force.     

Distortion of acoustic emission signals by a change of gain in the sensing device

A semi-theoretical model of an acoustic emission (AE) signal is used to predict the effects of changes of amplification and threshold level in the recording device. Predictions are confirmed by experiments on simulated AE signals. The progress of real AE tests on cracks in welds is analysed statistically to predict the effect of the same variations in the sensitivity of the recording device. Once again the predictions are confirmed by experiment and it is shown how to convert an AE/time curve from one set of recording conditions to another.It is concluded that compensation for distortion of AE signals by changes of sensitivity of the recording device presents no great difficulty.     

Dynamics of multiple trapping by a single-beam laser tweezer

A multiple-trap single-beam scanning laser tweezer system was developed and characterized. Different stationary and mobile multiple-trap modes were generated for polystyrene beads in a water environment. Trapping efficiency and stability were investigated for several dynamic parameters such as transition time between the sites, waiting time on a single site, number of trapping sites, and IR laser power. Optimal parameters for efficient generation of complex arrays and matrices were determined. We demonstrate an example of a single laser beam multiple-trap application by measuring the trap's stiffness in water for our laser tweezer setup.     

绿色建筑楼板声学性能优化研究

绿色建筑对建筑健康性、舒适性和环境性提出了更高要求,满足楼板隔声性能要求是其基本的功能要求,但现实设计中却往往不被重视。建筑楼板作为分隔空间的构件,工程中应重视去解决楼板撞击声的隔声问题。以钢筋混凝土住宅楼板为基准,考虑了弹性材料类型、厚度、质量密度、动态刚度以及浮板质量和厚度等因素,给出了不同系列浮筑楼板做法,通过理论分析和试验,研究了其隔声性能的变化。研究结果对于建筑楼板的隔声降噪设计提供了技术支撑和案例经验,对于优化改善建筑隔声性能有积极意义。     

OTFTs结构与器件性能

在重掺杂的Si衬底上分别制备了底电极（Bottom—contact organic thin—film transistors，BCOTFYs）和顶电极（Top—contact organic thin—film transistors，TC—OTFYs）有机薄膜场效应晶体管，探讨了源、漏电极位置对器件性能的影响。结果表明，顶电极可以形成良好的欧姆接触，其器件的迁移率和开关电流比均高出BC—OTFYs器件三个数量级。研究了栅绝缘层的薄膜厚度对器件的电性能的影响。结果表明，在相同电压下，薄的绝缘层增大了沟道区域的电场，可积累更多的电荷，以填充更多的陷阱，使器件的场效应迁移率和工作电流得到了明显的提高。     

声学放大器对热声发动机性能的影响

对声学放大器的声功传输能力以及其对热声发动机性能的影响进行了实验研究,发现声学发大器只有在一定条件下才能提高热声发动机的输出压比,当末端阻抗减小时其放大能力也减小.声学放大器本身也是一个声学阻力部件,如果仅以负载引出功计算热声发动机的效率,声学放大器在输出端负载阻抗较大时能够提高系统热效率,当负载阻抗减小后,它将使发动机的热效率急剧降低.     

Impact of SAW device passivation on RF performance

Passivation layers consisting of sputtered Al₂O₃ have been deposited onto SAW devices for the purpose of reducing the incidence of shorts. A coupling-of-modes model was used with one-port resonators, coupled resonator filters (CRF), and test structures. The passivation layer stiffens the surface with a velocity increase proportional to t/λ, where t is the passivation layer thickness. Attenuation is increased slightly, producing a 0.25-dB increase in the loss of a one-port resonator at 314 MHz. The effect on reflectivity is minimal and of much lesser importance to the designer     

带凹槽平板型声透镜聚焦性能的理论分析与数值模拟

基于相位补偿和惠更斯-菲涅尔原理,利用理论分析和数值模拟的方法,研究了一种带凹槽的平板型声透镜,讨论了凹槽个数、声透镜材料等参数对声透镜聚焦性能的影响。结果表明:优化后的菲涅尔声透镜聚声效率理论上可达40%,放大倍数约为7倍,是一种较为高效、成本低廉的新型声透镜。     

水声通信系统性能评估方法研究

水声通信系统性能主要受水声信道和通信体制影响,通常采取海洋水声试验的手段进行性能测试,但这需要进行多次不同信道条件下的试验才能得出正确的评估结论,难度较大且成本较高。因此,建立准确的水声通信系统性能评估模型和评估方法,对于通信系统设计及性能预测显得尤为重要。从水声信道模型开始分析,结合水声通信特点,讨论了典型水声通信接收机结构,提出了一种通用水声通信系统性能评估模型和方法,并针对采用QPSK调制的通信系统性能进行了评估,结果与海试数据较为接近。     

多孔性水泥-聚苯颗粒材料的吸声性能研究

水泥-聚苯颗粒材料被广泛用作外墙外保温材料,通过特殊制备工艺可形成多孔性结构,从而同时具备吸声功能,改善建筑环境.以水泥为胶凝材料,以聚苯颗粒为骨料,以聚丙烯纤维和可再分散乳胶粉为增韧材料,采用半干料压缩工艺成型制备吸声材料,分析了水泥用量和蒸汽养护对材料吸声性能的影响.结果表明:水泥掺量越高,在高频段的吸声系数越低,但水泥掺量过低对低频声的吸收不利;蒸汽养护使材料表面形成了空腔共振吸声结构,对提高一定频率下的吸声性有利,根据理论计算了空腔共振吸声结构提高吸声性的频率范围,结果与实测结果一致,分析认为通过调整聚苯颗粒粒径可实现在相对较宽频率范围的高效吸声;纤维提高了抗折强度,可在保障强度的前提下降低水泥用量以提高吸声性.     

Effects of a static magnetic field on sub-Doppler molasses:manipulation of cesium atoms

An experimental investigation of the effects of magnetic field on cooling and trapping of neutral atoms is presented. Applied to optical molasses, a static magnetic field often produces spectacular effects. It can either induce a sub-Doppler cooling effect or shift a sub-Doppler-cooled atomic sample away from its zero-velocity position. Some of the effects have potential applications in the manipulation of cesium atoms (deflecting an atomic beam or launching an optical molasses into an atomic fountain) and can probably be used in the development of a future cesium atomic frequency standard. The observed experimental effects are interpreted by simple physical models and calculations     

基于形状记忆合金的新型消能减震装置抗震性能研究

本文首先通过形状记忆合金的材性试验研究了形状记忆合金的超弹性变形性能,并将其等效拟合为多线性模型,得到其设计参数,并详细介绍了分析计算时所采用的形状记忆合金的本构模型。然后,针对框架结构的变形特点,提出了一种基于形状记忆合金的消能减震装置,即在底层框架柱的反弯点附近设置锚固装置,形状记忆合金索的上端固定在锚固装置上,将其下端锚固在地下,在震时通过其来回反复变形耗散地震能量。然后通过有限元程序对设置形状记忆合金索的新型框架与普通框架进行静力推覆分析和低周反复分析,研究表明新型框架不仅屈服承载力和极限承载力高于普通框架,而且其滞回环更加饱满,累积塑性滞回耗能能力提高了41.4%,形状记忆合金索的滞回环也很饱满,具有优良的耗能能力,最后,还比较了对角设置形状记忆合金索的框架的耗能能力与本消能减震装置的耗能能力。因此该消能减震装置在减轻框架柱震害方面具有一定的工程应用价值和前景。     

Implementation of single-beam multiplexing encoding with a dually modulated spatial light modulator

We propose a novel method for signal storage and encryption, called single-beam multiplexing encoding. The single beam is composed of an inside signal beam and an outside reference beam. The signal beam is amplitude modulated, and the reference beam is phase modulated. The dual modulation is implemented by a spatial light modulator (SLM). Multiplexing holography with different reference beams from different directions, called directional multiplexing, is analyzed in detail. With an SLM based on a twisted nematic liquid crystal display, we demonstrate a single-beam directional multiplexing method using a holographic encoding technique, and the retrieved signals are presented. This encoding system is more stable, miniaturized, and flexible. It should be of great interest for applications in signal encryption as well as for high-capacity data storage.