400MHZ带宽声表面波RAC器件

一、引言 声表面波线性调频脉冲压缩滤波器以其卓越的性能在雷达与微波辐射测量系统中得到了广泛应用,随着此类系统对观测目标成像分辨率、清晰度和稳定性要求的提高,宽频带高性能的声表面波线性调频脉冲压缩滤波器的研究工作就显得更为重要.本文介绍我们最新研制可用于雷达、微波辐射测量设备的宽频带声表面波沟槽反射栅脉冲压缩滤波器(简称声表面波RAC器件),其线性调频带宽可作到400MHz.     

声学测量技术20年

文章扼要评述近20年来在声频范围内声学测量技术的重要进展。对若干 涉及诸如声强测量，传递函数法及膺噪声等方面测量技术的主题分别作了讨论。     

一种微波源调频噪声测量系统

分析了一种微波源调频噪声测量方法的原理，根据需要研制了一套微波源调频噪声测量系统，详细给出了为保证系统测量结果准确可靠所必需的调试步骤，并结合实际设计出一种独特的定标方法，使用该系统实测了一个２２．６８ＧＨｚ锁相稳频信号的调频噪声，并对测量结果进行了讨论。     

激光发声及其发声的机理

宽带调制的相关光声检测技术是兼有单频和脉冲光声检测特点的一种新的光声检测技术。在时域,它可以获得不同深度的信息,在频域,它可以得到很宽频率范围内的响应。 目前宽带调制技术主要有伪随机编码调制和线性调频两种。我们在实现了Lagrange序列伪随机编码调制的光声检测后,又进行线性调频技术的研究。理论和实验上均已证明线性调频信号的自相关函数比伪随机编码调制信号的自相关函数更逼近δ函数。本文将简要地介绍线性调频技术的原理及在薄膜热扩散率测定中的一些实验结果。线性调频技术在光声检测薄膜热扩散率中的应用@钱梦騄$同济大学…     

声学测量技术20年

文章扼要评述近20年来在声频范围内声学测量技术的重要进展.对若干涉及诸如声强测量,传递函数法及膺噪声等方面测量技术的主题分别作了讨论.     

基于H∞滤波器的多分量线性调频信号参数估计

针对多分量线性调频信号数据长度较短的情况，利用多分量线性调频信号的时空域信息，将其分解成多个单分量线性调频信号。针对未知噪声的情况，利用有限长H∞滤波器的良好瞬时特性和鲁棒特性，对每个单分量线性调频信号的参数进行估计，进而实现多分量线性调频信号参数估计。由于采用H∞平方根估计算法，此方法能够抑制递推计算的发散。计算机仿真表明了此方法的有效性。     

调频源调频解调失真的测量

本文介绍了用测量调频线性来达到测量调频源调频解调失真的方法和它的估算公式及实验数据。     

原子钟相位与频率估计的误差特性

本文讨论了原子钟内部的3种噪声即白色调相噪声，白色调频噪声和随机游走调频噪声对相位和频率估计的影响，分析表明，这3种噪声对相位估计和频率估计的影响完全不同，在相位估计中，选择适当的平滑长度和取样间隔可以控制估计误差，而在频率估计中，估计精度不能通过[估计器或测量设备的改进而任意提高，存在一个极限，这个极限由原子钟的内部噪声来决定。     

一种声发射系统的设计

设计了一种声传输的发射系统,为探测油层参数选择通信声信号的频带。利用MATLAB作出了线性调频的采样点,通过PIC单片机控制DAC输出线性调频波形。通过功率模块放大后控制变压器为换能器提供驱动信号。同时还对变压器的高压电源部分做了介绍。     

声表面波付里叶变换信息处理机

线性调频变换是一种新的处理技术,这种技术能够用时间域表示频率域的方法来提供信号的实时付里叶变换。这种技术已经能用有效而高质量的大时间—带宽乘积的声表面波(SAW)线性调频滤波器来实现。声表面波线性调频变换信息处理机为信号处理提供了一种强有力的工具。这种处理机能完成大量各种各样的信号处理功能,如:谱分析、网络分析、信号的产生和过滤等。     

Shape similarity assessment of polyhedral parts based on boundary models

Shape similarity evaluation is the core technology for many intelligent CAD/CAM applications. In this work a method to evaluate the shape similarity of polyhedral objects based on their boundary models is presented. The proposed method takes the unique boundary models of a query part and a reference part as its input and returns the match coefficient between these two parts. The match coefficient is calculated based on the 'feasible match' of the boundary faces, which is a set of matched faces that preserve the face adjacency relationships. While directly searching for the optimal feasible match in two boundary models could be computationally intractable, a divide-and-conquer method is proposed in this work to find a near-optimal match in a reasonable time. The divide stage corresponds to the extraction and matching of 'sweep features'. A sweep feature of a polyhedral object is a set of parallel faces that are sorted along their common normal vector. The sorted faces in sweep features are matched through an efficient constraint-directed tree search to generate intermediate matches. The intermediate matches that are orientation consistent are merged to form the final feasible matches. A prototype system based on the proposed methodology has been implemented and shape similarity comparison results between various mechanical parts with complicated intersecting features are presented.     

Digital generation of coherent sweep signals

The authors describe a digitally implemented coherent sweep generator, i.e. a sweep generator in which sweep rate, start frequency, and start phase can be specified. By carrying out a digital integration twice, using a counter and an accumulator as integrators, a quadratic phase function of a linear sweep is produced. The desired start frequency and start phase are introduced by presetting the counter and accumulator. The mod (2π) of the quadratic phase function is extracted and used as an address for a sine look-up table whose output is applied to a digital-to-analog converter. The system is capable of producing sweep signals from DC up to the lower megahertz range, and the sweep rate can be verified over several orders of magnitude. By operating several digital sweep generators from the same clock, multiple coherent sweep signals may be produced, or quadrature signals can be produced with two modules. The digital sweep generator has been implemented with transistor-transistor logic (TTL). Generated waveforms are presented     

Sweep signal time-delay estimation with time-frequency cross-correlation algorithm

Sweep signal is usually employed as a source signal in active detection such as radar and sonar. Since the frequency spectrum of the sweep signal varies against time, a novel algorithm, namely a time-frequency cross-correlation (TFCC) algorithm based on wavelet packet transform (WPT), is proposed to estimate the time delay of sweep signal. In this algorithm, the source sweep and the received signals are decomposed with WPT to obtain their time-frequency representations and the TFCC between the source sweep and the received signals is performed. Each reflected sweep in the received signal is converted into a time-frequency correlation peak whose position can indicate its time delay. The TFCC algorithm can suppress ambient noise effectively and improve the performance of sweep extraction and can match more precisely the source and the reflected sweeps to their known time-frequency characters. Numerical experiments were performed to compare the performance of the TFCC algorithm with that of the conventional cross- correlation and phase-data algorithms. The results proved that the TFCC algorithm can extract the reflected sweeps effectively and its performance is better than that of the conventional algorithms.     

线性调频连续波雷达发射信号的动态测试

本文提出了一种利用点目标差拍信号对线性调频连续波雷达的发射信号进行动态测试的方法，可以实现扫频线性度、扫频斜率、扫频带宽以及瞬时频率偏离的动态测试。文中给出了该方法的原理、误差分析实验结果。     

高浓度无机盐乳化基质的触变性研究

该文采用剪切速率扫描、时间扫描方法研究了高浓度无机盐乳化基质的剪切应力、剪切粘度、测定了基质的触变性大小和弹性大小，说明了乳化基质是触变性粘弹体系，从乳化基质的微观结构解释了这些变性机理。     

新型BTG塑料合金关于温度-频率-振幅的动态阻尼性能模型

建立了描述一种新型BTG塑料合金的温度-频率-振幅的动态阻尼性能数学模型。通过动态热分析仪DMA242, 获取了BTG塑料合金的频率扫描、温度扫描和幅值扫描的动态阻尼损耗因子实验数据。通过分析实验数据, 将温度扫描的阻尼损耗因子量分离为仅与频率相关以及与频率、温度均相关的两个分量, 并分别用Kelvin分数导数的阻尼损耗因子模型和高斯函数模型来表达这两个分量, 再以此为基准, 考虑振幅对阻尼损耗的影响, 由此建立了综合考虑温度-频率-振幅的阻尼损耗数学模型。结果表明, 所建立的综合考虑温度-频率-振幅的阻尼损耗数学模型能准确描述实验数据。      

Fin sweep angle does not determine flapping propulsive performance

The importance of the leading-edge sweep angle of propulsive surfaces used by unsteady swimming and flying animals has been an issue of debate for many years, spurring studies in biology, engineering, and robotics with mixed conclusions. In this work, we provide results from three-dimensional simulations on single-planform finite foils undergoing tail-like (pitch-heave) and flipper-like (twist-roll) kinematics for a range of sweep angles covering a substantial portion of animals while carefully controlling all other parameters. Our primary finding is the negligible 0.043 maximum correlation between the sweep angle and the propulsive force and power for both tail-like and flipper-like motions. This indicates that fish tails and mammal flukes with similar range and size can have a large range of potential sweep angles without significant negative propulsive impact. Although there is a slight benefit to avoiding large sweep angles, this is easily compensated by adjusting the fin’s motion parameters such as flapping frequency, amplitude and maximum angle of attack to gain higher thrust and efficiency.     

Magnetothermal properties of Nb-W,Nb-Ti,and Nb-Mo alloys in the mixed state

Flux jumps and magnetothermal effects in single crystals of niobium and niobium doped with tungsten, titanium, and molybdenum have been studied in the mixed state in a vacuum calorimeter. It is observed that (a) the field at which the first flux jump occurs is independent of the sweep rate at low sweep rates (1–10 Oe sec) but increases sharply at higher sweep rates (～100 Oe/sec) of the magnetic field, (b) the heat evolved during the flux jump becomes larger as the sample's temperature is reduced, (c) the temperature fluctuations of the type observed by Zebouni et al. and Levy et al. are evidently due to the imperfect adiabatic conditions of experiments, and (d) the interval between the successive flux jumps is in good agreement with that expected from the critical state model of Swartz and Bean.     

Magnetic scan head for high-frequency recording

A stationary magnetic head scans the width of a record magnetically, enabling successive lines of video information to be recorded on a slowly moving tape. The head contains a large number of laminations. All except one of these are blocked from transducing action with the tape by currents through sweep windings. As the sweep currents are changed, every lamination becomes active in succession. For playback, such a head operates on a magnetic-modulator principle which is sensitive to flux rather than to its rate-of-change.     

基于模糊图像合成技术的MEMS平面微运动测试技术

随着微电子机械系统(MEMS)研究的深入和产业化的需求，捡测技术在其中的重要性越来越大．基于机器微视觉的MEMS动态测试系统．利用模糊图像合成技术对MEMS的平面微运动特性参数进行提取和分析．利用图像处理方法对MEMS谐振器做扫频和扫压测量，获得了MEMS器件的平面微运动特性，并对测量结果进行了分析和讨论．由实验结果可以看出，这种方法有较高的测量精度，测量重复性误差为100nm．