纳机电矢量水听器耐压结构设计

纳机电矢量水听器具有低频性能好,灵敏度高等性能优点,在深海探测领域具有巨大的应用潜力,为满足超深水工作的要求提出了绝缘托盘式新型封装结构,解决了纳机电矢量水听器的耐高静水压技术难题。首先,进行聚氨酯透声帽外围封装承压分析,理论论证聚氨酯基体树脂材料的极限耐静水压强度为42.3 MPa。然后,对MEMS芯片输出电压进行理论计算以及对其进行模态仿真,得出在高达20 MPa的静水压作用下,传感器的输出灵敏度基本无变化,而且工作频带有所拓宽。测试结果表明:改进封装的纳机电矢量水听器在高压20 MPa时,可以实时获得敲击信号;加压前后,该水听器在20 Hz~1 000 Hz工作频带内水听器的灵敏度和指向性基本一致。     

Modeling and characterization of a micromachined artificial hair cell vector hydrophone

In the paper, a micromachined artificial vector hydrophone arises from a biological inspiration, the fish hair cell is presented. It is desirable that the application of piezoresistive effects combined with ingenious bionic structure and MEMS technology may improve the low-frequency sensitivity of the vector hydrophone as well as its miniaturization. Modeling processes for realizing the artificial hair cell hydrophone, along with preliminary characterization results in terms of sensitivity, frequency response and directivity patterns are also introduced. The microstructure of the sensor consists of four vertical cantilever beams with attached rigid plastic cylinder in the center of the structure. By locating eight piezoresistors logically formed the Wheatstone bridges; they can detect two components of underwater acoustic signal simultaneously. The prepared vector hydrophone has been measured in the standing wave field finally. The experiment results show that the vector hydrophone has good low-frequency characteristic, the free-field voltage sensitivity is −197.2 dB (0 dB = 1 V/μPa) at 400 Hz with a about 2 dB one-third octave positive slope over the 40–400 Hz bandwidth. The depth of pits of the directivity pattern is about 34.6 dB.     

新型三维MEMS矢量水听器的设计

根据国内对高灵敏度、低频小体积三维矢量水听器的需求,提出了一种仿鱼侧线纤毛的MEMS三维矢量水听器。该水听器采用多纤毛结构分别用来接收X、Y与Z方向的声信息,采用ANSYS进行仿真,静力分析得出了布放压阻的合理位置,谐响应分析得出该结构的固有频率在1.5 kHz左右;驻波桶校准测试结果表明:该水听器的灵敏度范围在-200 dB到-180 dB左右;在25 Hz～2 000 Hz频段内具有良好的频响特性;指向性分辨率大于等于30 dB,具有良好的"8"字形指向性。     

Do moods affect programmers’ debug performance?

There is much research that shows people’s mood can affect their activities. This paper argues that this also applies to programmers, especially their debugging. Literature-based framework is presented linking programming with various cognitive activities as well as linking cognitive activities with moods. Further, the effect of mood on debugging was tested in two experiments. In the first experiment, programmers (n = 72) saw short movie clips selected for their ability to provoke specific moods. Afterward, they completed a debugging test. Results showed the video clips had a significant effect on programmers’ debugging performance; especially, there was a significant difference after watching low- and high-arousal-evoking video clips. In the second experiment, programmers’ mood was manipulated by asking participants (n = 19) to dry run algorithms for at least 16 min. They performed some physical exercises before continuing dry running algorithms again. The results showed a significant increase in arousal and valence that coincided with an improvement in programmers’ task performance after the physical exercises. Together, this suggests that programmers’ moods influence some programming tasks such as debugging.     

MEMS矢量水听器及其方位估计研究

水下目标被动侦测对高灵敏、低频检测矢量水听器提出了越来越高的要求,传统的矢量水听器已不能满足需求。基于新原理的矢量水听器的大量研究,提出了一种新的MEMS矢量水听器,介绍了该水听器方位检测原理;设计了方位估计实验方案,完成了实际的方位估计实验。测试结果表明：该水听器角度测试值与真实值基本相符,误差约为2°。     

MEMS矢量水听器减振结构的设计与研究

在MEMS矢量水听器现有结构的基础上,设计出一种新型减振结构,期望利用该封装结构衰减水听器工作时安装平台的振动噪声,削弱安装平台振动对水听器测量精度的影响,提高水听器的抗噪能力。结合理论分析确定减振材料并采用有限元软件进行仿真,对矢量水听器先后采用原有封装结构和减振封装结构进行封装,并通过振动台实验和驻波桶灵敏度测试。测试结果表明：该结构可有效实现对MEMS矢量水听器干扰信号的衰减,同时基本不影响水听器的接收灵敏度。     

纤毛式矢量水听器新型封装结构的研究

针对仿鱼侧线的敏感单元提出了一种新型的封装,即采用与透声帽相同材料的聚氨酯代替蓖麻油进行灌封,且聚氨酯仅淹没到纤毛的一半,该封装结构能够提高矢量水听器的灵敏度.建立了水听器封装结构的声学理论模型,并由此推导出新型封装结构的透声系数.采用ANSYS对矢量水听器敏感单元封装结构进行仿真,得出传感器的灵敏度为0.259mV/...     

磁方位修正MEMS矢量水声传感器研制

介绍了一种磁方位补偿微机电系统(MEMS)矢量水声传感器.采用电容原理MEMS技术构造内部振子,并与信号处理电路紧靠方式设计,可减小噪声干扰并抑制信号衰减.利用磁方位修正技术,对MEMS矢量水声传感器判定的方位进行修正,解决了单个矢量水声传感器定向精度不高问题.传感器完成了国家一级计量站标定和磁方位误差修正测试,测试结果验证了定向方法的可行性,矢量水声传感器可实现水下目标探测、定位及导航等任务.     

The Neural Network Approach to Input–Output Analysis for Economic Systems

Economic practitioners in China are giving up the classical Leontief’s Input–Output analysis methods. This paper offers an alternative method of input–output analysis. The proposed method is based on the layered neural network model. It shows that neural networks method can be useful for input–output analysis for a dynamic economic system.       

基于丁腈橡胶帽封装的MEMS仿生水听器的设计

针对现有封装结构会对灵敏度造成一定程度的损失,使现有水听器的灵敏度小于水听器芯片裸测灵敏度的问题,改用了透声性能好、耐腐蚀的丁腈橡胶(NBR)制作的透声帽,并对现有的矢量水听器的封装外壳进行相应的优化设计。该封装结构的水听器的共振频率降低到50 Hz以下,水听器所感兴趣的频段(50 Hz~4 kHz)不会受到封装谐振的干扰,拓宽了水听器的工作频段。该封装的灵敏度提高到几乎与裸片的灵敏度一致,达到(-170±2)dB,并优化金属管壳的圆盘的尺寸,即水听器最大径,由36 mm缩小至28 mm,使水听器的封装进一步小型化。     

Optical flow approximation based motion object extraction for MPEG-2 video stream

This paper presents a compressed-domain motion object extraction algorithm based on optical flow approximation for MPEG-2 video stream. The discrete cosine transform (DCT) coefficients of P and B frames are estimated to reconstruct DC + 2AC image using their motion vectors and the DCT coefficients in I frames, which can be directly extracted from MPEG-2 compressed domain. Initial optical flow is estimated with Black’s optical flow estimation framework, in which DC image is substituted by DC + 2AC image to provide more intensity information. A high confidence measure is exploited to generate dense and accurate motion vector field by removing noisy and false motion vectors. Global motion estimation and iterative rejection are further utilized to separate foreground and background motion vectors. Region growing with automatic seed selection is performed to extract accurate object boundary by motion consistency model. The object boundary is further refined by partially decoding the boundary blocks to improve the accuracy. Experimental results on several test sequences demonstrate that the proposed approach can achieve compressed-domain video object extraction for MPEG-2 video stream in CIF format with real-time performance.     

Benchmarking quality measurement

This paper gives a simple benchmarking procedure for companies wishing to develop measures for software quality attributes of software artefacts. The procedure does not require that a proposed measure is a consistent measure of a quality attribute. It requires only that the measure shows agreement most of the time. The procedure provides summary statistics for measures of quality attributes of a software artefact. These statistics can be used to benchmark subjective direct measurement of a quality attribute by a company’s software developers. Each proposed measure is expressed as a set of error rates for measurement on an ordinal scale and these error rates enable simple benchmarking statistics to be derived. The statistics can also be derived for any proposed objective indirect measure or prediction system for the quality attribute. For an objective measure or prediction system to be of value to the company it must be ‘better’ or ‘more objective’ than the organisation’s current measurement or prediction capability; and thus confidence that the benchmark’s objectivity has been surpassed must be demonstrated. By using Bayesian statistical inference, the paper shows how to decide whether a new measure should be considered ‘more objective’ or whether a prediction system’s predictive capability can be considered ‘better’ than the current benchmark. Furthermore, the Bayesian inferential approach is easy to use and provides clear advantages for quantifying and inferring differences in objectivity.

A cross-modal approach for karaoke artifacts correction

Karaoke singing is a popular form of entertainment in several parts of the world. Since this genre of performance attracts amateurs, the singing often has artifacts related to scale, tempo, and synchrony. We have developed an approach to correct these artifacts using cross-modal multimedia streams information. We first perform adaptive sampling on the user’s rendition and then use the original singer’s rendition as well as the video caption highlighting information in order to correct the pitch, tempo and the loudness. A method of analogies has been employed to perform this correction. The basic idea is to manipulate the user’s rendition in a manner to make it as similar as possible to the original singing. A pre-processing step of noise removal due to feedback and huffing also helps improve the quality of the user’s audio. The results are described in the paper which shows the effectiveness of this multimedia approach.

Roll-to-roll hot embossing of microstructures

In this paper we present a new roll-to-roll embossing process allowing the replication of micro patterns with feature sizes down to 0.5 μm. The embossing process can be run in ‘continuous mode’ as well as in ‘discontinuous mode’. Continuous hot embossing is suitable for the continuous output of micro patterned structures. Discontinuous hot embossing has the advantage that it is not accompanied by waste produced during the initial hot embossing phase. This is because in ‘discontinuous mode’, embossing does not start before the foil has reached the target temperature. The foil rests between two parallel heating plates and foil movement and embossing starts only after the part of the foil resting between the heating plates has reached a thermal steady state. A new type of embossing master is used which is based on flexible silicon substrates. The embossing pattern with sub-μm topographic resolution is prepared on silicon wafers by state of the art lithography and dry etching techniques. The wafers are thinned down to a thickness of 40 μm, which guarantees the mechanical flexibility of the embossing masters. Up to 20 individual chips with a size of 20 × 20 mm2 were assembled on a roller. Embossing experiments with COC foils showed a good replication of the silicon master structures in the foil. The maximum depth of the embossed holes was about 70% of the master height.     

Modeling of the intrinsic stress effect on the resonant frequency of NEMS resonators integrated by beams with variable cross-section

Nano-electro-mechanical systems (NEMS) resonators integrated by a double clamped beam with variable cross-section are used in several applications such as chemical and biological detectors, high-frequency filters, and signal processing. The structure of these resonators can experience intrinsic stresses produced during their fabrication process. We present an analytical model to estimate the first bending resonant frequency of NEMS resonators based on a double clamped beam with three cross-sections, which considers the intrinsic stress effect on the resonant structure. This model is obtained using the Rayleigh and Macaulay methods, as well as the Euler–Bernoulli beam theory. We applied the analytical model to a silicon carbide (SiC) resonator of 186 nm thickness reported in the literature. This resonator has a total length ranking from 80 to 258 μm and is subjected to a tensile intrinsic stress close to 110 MPa. Results from this model show good agreement with experimental results. The analytic frequencies have a maximum relative difference less than 6.3% respect to the measured frequencies. The tensile intrinsic stress on the resonant structure causes a significantly increase on its bending resonant frequency. The proposed model provides an insight into the study of the intrinsic stress influence on the resonant frequency of this nanostructure. In addition, this model can estimate the frequency shift due to the variations of the resonator geometrical parameters.     

流体对MEMS矢量水听器共振频率的影响

由中北大学研制的MEMS仿生矢量水听器具有低频、灵敏度高等性能特点,但是由于流体的影响,水听器微结构在空气中的共振频率与液体中不同,为此研究了流体对MEMS矢量水听器共振频率的影响。首先,理论上分析了流体对共振频率的影响。然后,采用ANSYS对空气中和液体中MEMS矢量水听器的共振频率进行仿真。最后分别采用振动台和矢量水听器校准系统进行了测试。结果表明MEMS矢量水听器在水中的共振频率较空气中下降了约31.2%。     

A constructive approach to constrained hexahedral mesh generation

Mitchell proved that a necessary and sufficient condition for the existence of a topological hexahedral mesh constrained to a quadrilateral mesh on the sphere is that the constraining quadrilateral mesh contains an even number of elements. Mitchell’s proof depends on Smale’s theorem on the regularity of curves on compact manifolds. Although the question of the existence of constrained hexahedral meshes has been solved, the known solution is not easily programmable; indeed, there are cases, such as Schneider’s Pyramid, that are not easily solved. Eppstein later utilized portions of Mitchell’s existence proof to demonstrate that hexahedral mesh generation has linear complexity. In this paper, we demonstrate a constructive proof to the existence theorem for the sphere, as well as assign an upper-bound to the constant of the linear term in the asymptotic complexity measure provided by Eppstein. Our construction generates 76 × n hexahedra elements within the solid where n is the number of quadrilaterals on the boundary. The construction presented is used to solve some problems posed by Schneiders and Eppstein. We will also use the results provided in this paper, in conjunction with Mitchell’s Geode-Template, to create an alternative way of creating a constrained hexahedral mesh. The construction utilizing the Geode-Template requires 130 × n hexahedra, but will have fewer topological irregularities in the final mesh.     

Testing Planarity of Geometric Automorphisms in Linear Time

It is a well-known result that testing a graph for planarity and, in the affirmative case, computing a planar embedding can be done in linear time. In this paper, we show that the same holds if additionally we require that the produced drawing be symmetric with respect to a given automorphism of the graph. This problem arises naturally in the area of automatic graph drawing, where symmetric and planar drawings are desired whenever possible. An extended abstract of this paper has been published in the proceedings of ISAAC 2002 (Lecture Notes in Computer Science, vol. 2518, pp. 563–574, 2002). The first author is supported by the Marie Curie Research Training Network ADONET 504438 funded by the EU. This paper was partially written when he was visiting the University of Sydney. The second author was supported by a grant from the Australian Research Council. National ICT Australia is funded by the Australian Government’s Backing Australia’s Ability initiative, in part through the Australian Research Council.     

On the determination of Poisson’s ratio of stressed monolayer and bilayer submicron thick films

In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (σ₀) and biaxial Young’s modulus (E/(1 − υ)). Associating square and rectangular membranes with different length to width ratios, the Poisson’s ratio (υ) can also be determined. LPCVD Si₃N₄ monolayer and Si₃N₄/SiO₂ bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si₃N₄, E = 212 ± 14 GPa, σ₀ = 420 ± 8 MPa and υ = 0.29.     

Dynamic simulation of a contact-enhanced MEMS inertial switch in Simulink?

A novel contact-enhanced design of MEMS (micro-electro-mechanical system) inertial switch was proposed and modeled in Simulink^?. The contact effect is improved by an easily realized modification on the traditional design, i.e. introducing a movable contact point between the movable electrode (proof mass) and the stationary electrode, therefore forming a dual mass-spring system. The focus of this paper is limited to a vertically driven unidirectional one for the purposes of demonstration, but this design concept and Simulink^? model is universal for various kinds of inertial micro-switches. The dynamic simulation confirmed the contact-enhancing mechanism, showing that the switch-on time can be prolonged for the dynamic shock acceleration and the bouncing effect can be reduced for the quasi-static acceleration. The threshold acceleration of the inertial switch is determined by the proof mass-spring system’s natural frequency. Since the inertial switches were fabricated by the multilayer electroplating technology, the proof mass thickness were assigned two values, 100 and 50 μm, in order to get threshold levels of 56 and 133 g respectively for the dynamic acceleration of half-sine wave with 1 ms duration. Other factors that influence the dynamic response, such as the squeeze film damping and the contact point-spring system’s natural frequency were also discussed. The fabricated devices were characterized by the drop hammer experiment, and the results were in agreement with the simulation predictions. The switch-on time was prolonged to over 50 μs from the traditional design’s 10 μs, and could reach as long as 120 μs. Finally, alternative device configurations of the contact-enhancing mechanism were presented, including a laterally driven bidirectional inertial switch and a multidirectional one.