Surface-acoustic-wave oscillator tuned by magnetoelastic effect

A new technique for achieving frequency modulation with a surface-acoustic-wave delay-line oscillator is reported. A 339MHz s.a.w. delay line has been fabricated on an epitaxial garnet film. A significant phase-velocity shift has been measured as a function of an inplane magnetic field. An s.a.w. oscillator has been implemented with this delay line and its frequency has been controlled by the magnetoelastic effect. A frequency shift of 600kHz (a relative variation of 1.75 × 10-3) has been obtained by changing the biasing magnetic field.     

分布式光纤应力、应变传感技术

文章较详细地介绍了分布式光纤应力、应变传感器的各种结构和检测方法,分析讨论了它们的特点和性能。     

基于压缩感知的线性调频雷达信号截获方法

低采样率截获宽带线性调频信号(LFM)是电子侦察的难点。基于压缩感知理论,提出了分数阶变换(FrFT)域LFM信号截获方法。采用随机序列与低通滤波器实现信号的压缩,基于LFM在FrFT域的稀疏性,实现LFM信号的精确重构,得到重构精确度与减采样因子、信噪比(SNR)的关系,当减采样因子在20倍以内时,信号频域重构的归一化均方根误差(NRMSE)在2.2%以内,信噪比大于12 dB时,重构精确度优于90%。仿真表明该方案具有有效性和可行性。     

CMOS RF switched capacitor bandpass filter tuned by ring VCO

A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with ‘XOR’ gates are proposed. Implemented in a standard CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications [380–520 MHz]. Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240–500 MHz], with a quality factor that can be as high as 300.     

Tunability limitations of microwave resonators tuned by several capacitances and inductances

Tunability limitations of resonators that consist of transmission line sections and are tuned by several capacitances and inductances are established. The limitations are common for lossy and lossless resonators. It is shown that an increase in the number of tuning elements does not lead to increasing frequency ratio. It is proved that combined tuning is more effective that tuning by one-type elements. This tuning makes possible continuous variation of the resonance frequency in a wide range exceeding a decade.     

光电流稳频复合腔调谐CO_2波导激光器的研究

研究了CO_2波导激光器光电流效应及光电流稳频、复合腔调频的CO_2波导激光器系统。获得60条谱线连续分立输出。单线最大输出功率为8W,长时间稳定度优于1％。     

Effects of thermal noise on dynamic stress sensing of nanoelectromechanical resonators

Nanoelectromechanical resonators are promising high-sensitivity sensors for force, charge and mass detection. Presented is a dynamic stress-sensing technique using nano-scale suspended beams. Using magnetomotive transduction, the effective dynamic stress was measured on the beam from the resonance frequency at room temperature under a moderate vacuum. The sensitivity of the nano-scale resonator varied less than 1%, while its signal-to-noise ratio was reduced by about 30% in a muW electrothermal power range.     

量子阱态对Pb薄膜局域功函数的调制

理想的厚度均一的薄膜中，由于电子的运动在垂直于膜面方向受到限制，其能级会发生量子化，形成分立的能量本征态，即量子阱态。Pb／Si系统作为典型的量子阱态体系，由于Pb在[111]方向的层间距约为电子费米波长的1／4，所以Pb薄膜的厚度每变化一个单原子层都会引起费米面附近态密度的很大变化，从而导致其物理性质的变化。对此体系的研究表明Pb薄膜的许多物理性质，例如，超导转变温度、热膨胀系数及薄膜稳定性等均受到量子阱态的影响。     

Determination of ocular torsion by means of automatic patternrecognition

A new, automatic method for determination of human ocular torsion (OT) was developed based on the tracking of iris patterns in digitized video images. Instead of quantifying OT by means of cross-correlation of circular iris samples, a procedure commonly applied, this new method automatically selects and recovers a set of 36 significant patterns in the iris by the technique of template matching as described by In den Haak et al. (1992). Each relocated landmark results in a single estimate of the torsion angle. A robust algorithm estimates OT from this total set of individually determined torsion angles, thereby largely correcting for errors which may arise due to misjudgement of the rotation center. The new method reproduced OT in a prepared set of images of an artificial eye with an accuracy of 0.1°. In a sample of 256 images of human eyes, a practical reliability of 0.25° was achieved. To illustrate the method's usefulness, an experiment is described in which ocular torsion was measured during two dynamic conditions of whole-body roll, namely during sinusoidally pendular motion about either an Earth horizontal or Earth vertical aids (that is “with” and “without” otolith stimulation, respectively)     

应用决策树的航天测控干扰识别方法

针对航天测控链路面临的无先验知识的干扰信号的识别问题,应用决策树的分类方法,提出了一种干扰信号识别方法。基于从属性到结论的方式,选取辨识能力强的特征因子,并将特征因子值作为每个树结点的属性值,与预设的门限进行比较判决形成类别集,并据此方式再对下一级的类别集进行判决,多次循环,反复比较,最终识别出干扰信号的类型及其调制方式。仿真结果表明,设计的决策树流程能够有效识别航天测控干扰信号。     

用激光调阻法提高线列光导PbS焦平面探测器性能

首次在国内报道了用激光调阻法提高线列1×128光导PbS红外焦平面探测器性能的研究成果.针对PbS探测器芯片的特点,用激光调阻法对采用负载电阻分流型电路的焦平面探测器的背景输出电平进行平坦化研究.实验结果表明,用激光调阻使背景电平平坦化之后,通过优化器件的工作参数,探测器平均黑体响应率由4.45×106V/W提高到8.82×106V/W;平均黑体探测率由6.52×109cm·Hz1/2·W-1提高到1×1010cm·Hz1/2·W-1;动态范围由46 dB提高到52 dB.研究结果为今后的薄膜型焦平面探测器实用化提供了参考.     

Open-loop control of a stepping motor using oscillation-suppressiveexciting sequence tuned by genetic algorithm

A new method for suppression of rotor oscillation in open-loop drive of a stepping motor is proposed. In this method, the torque equilibrium position of the motor is manipulated so as to guarantee insensitiveness to the variation of rotor inertia; the motion of the equilibrium position is made to be nonoscillatory, and the frequency of the motion is bound within the region limited by the maximum frequency determined by considering the performance on the condition with the largest inertial load. The exciting sequence used for a single-step drive is tuned by using the technique of genetic algorithm. It is shown by the experimental results that rotor oscillation can be well suppressed on the load conditions with different inertial loads     

复合腔可调谐CO_2波导激光器的研究

研究了用光栅复合腔调谐的CO_2波导激光器,在63条激光谱线上获得了激光输出,单支谱线最大功率为1W。分析了复合腔理论,理论与实验结果是一致的。     

Observation of saturation peaks in a He-Ne laser by tuned laser differential spectrometry

Light-field-induced saturation peaks in the Ne2p_{4}velocity distribution inside a 0.63-μ He-Ne gas laser are investigated by measuring the resultant frequency-dependent single-pass gain reduction of an additional 1.15-μ He-Ne laser beam.     

Broadband damping of non-rigid-body resonances of planar positioning stages by tuned mass dampers

In high tech motion systems, the finite stiffness of mechanical components often limits the bandwidth of the control system. This is usually counteracted by increasing the controller complexity, for instance by adding notch filters. The height of the resonance frequencies of the non-rigid body dynamics and the amount of damping significantly affect the achievable bandwidth. This paper describes a method to add damping to the flexible behavior of a motion stage, by using tuned mass-dampers with an over-critical damping value in contrast to a regular TMD with 10–20% damping. This over-critical damping results in a robust damper mechanism which is insensitive for parameter variations in terms of stiffness and damping. The main result is a significant modal damping increase over a broad band of resonant frequencies, with only four dampers added. This results in a bandwidth improvement of over 150% in z-direction, which leads to a disturbance suppression of over 10 times for both force and displacement disturbances. A damper test setup has been realized and tested to validate the possibility to create dampers with this over-critical damping behavior.     

Remote sensing by nuclear quadrupole resonance

Detection of explosives has the flavor of those mathematical problems that are not invertible. It is easier to hide explosives than to find them. Many approaches have been proposed and executed for the remote detection of explosives, contraband materials, weapons of mass destruction, currency, etc. Most detection technologies suffer from a common problem: the features they look for, such as discontinuities in electrical conductivity, are not unique properties of the target but are contained, to some degree, in the more benign surroundings. Such a degeneracy leads to “clutter” in the response. For example, resolving the false alarms generated by this clutter can determine the rate of advance of a conventional electromagnetic metal detector employed as a landmine detector. One approach that provides a “unique” signature is nuclear quadrupole resonance (NQR) (the technique is also called QR, to avoid confusion with strictly nuclear techniques). This paper outlines the important physical principles behind the use of NQR for remote detection, indicates areas of applicability, and presents results of field trials of a prototype landmine detection system     

Dynamic contact sensing by flexible beam

This paper discusses a new dynamic sensing system capable of detecting the contact point between a flexible beam and an object. The proposed sensing system, named dynamic antenna, is simply composed of an insensitive flexible beam, a torque sensor, a joint position sensor, an actuator, and a payload at the tip end of the beam. The contact point can be detected through estimation of the oscillation frequencies of the beam in contact with the object. First, a dynamic model of the sensor is derived. Next, it is shown that information of the fundamental and the second natural frequencies is sufficient for unique determining of the contact point if the beam has uniform mass and stiffness distribution. In practical realization, the fundamental and the second natural frequencies of the beam in contact with the object are extracted from the torque sensor measurements with the use of the maximum entropy method. Then, the frequencies are mapped into the contact-point coordinate. Extraction of the frequencies and mapping them into the contact point constitute a sensing strategy which is tested under experiment     

保偏光纤偏振耦合应力传感器的研究

作用在保偏光纤上的横向应力可以引起偏振耦合现象,通过测量耦合强度可以检测应力的位置和大小,实现应力传感.设计了应力施加装置,包括底座、手动微位移台、数显测力计、施力探头、旋转台、光纤夹持机构和受力支架.在1根直径125μm,拍长2.1 mm的保偏光纤上进行了应力大小和作用长度对偏振耦合强度影响的实验研究.结果表明作用长度为拍长一半的奇数倍时,耦合强度最大.在部分区域耦合强度和应力大小成线性关系,可应用于应力传感器中.