Achromatic fourier transforming properties of a separated diffractive lens doublet: theory and experiment

The strong chromatic distortion associated with diffractive optical elements is fully exploited to achieve an achromatic optical Fourier transformation under broadband point-source illumination by means of an air-spaced diffractive lens doublet. An analysis of the system is carried out by use of the Fresnel diffraction theory, and the residual secondary spectrum (both axial and transversal) is evaluated. We recognize that the proposed optical architecture allows us to tune the scale factor of the achromatic Fraunhofer diffraction pattern of the input by simply moving the diffracting screen along the optical axis of the system. The performance of our proposed optical setup is verified by several laboratory results.     

Stability analysis of a new class of MEMS gyroscopes with parametric resonance

In this paper, a parametrically resonated MEMS gyroscope is considered, and the effect of its parameters on the system stability is studied. Unlike the general case of MEMS gyroscopes with harmonic excitation, in this new class of gyroscopes with parametric excitation, the origin is one stationary point of the system. The study starts with the stability analysis of the origin, and then it goes on to analyze the effect of each parameter on the stability of periodic orbits. Stabilities are studied by means of Floquet theory. As the results indicate, presence of a non-trivial response for the system is closely interconnected to the stabilities (and instabilities) of the system. It is demonstrated that the stability of the origin always contributes to a zero response for the sensor, and hence the instability of origin is required for the occurrence of parametric resonance. In contrast, stability of a periodic orbit does not necessarily guarantee a resonant response for the gyroscope, and again it is the instability of the origin which is required for this purpose. Because in the case of linear stiffness—linear parametric excitation the instability of the origin results in instability of the system, it is concluded that nonlinearities are required for a parametrically actuated gyroscope.     

单片三轴硅微机械振动陀螺仪研究

设计、制造了一种单片集成三轴硅微机械振动陀螺仪.该器件由两个结构完全相同的单轴水平陀螺仪和一个单轴垂直陀螺仪组合而成,三只单轴陀螺仪均采用静电驱动、电容检测的结构形式.采用体硅溶解薄片法制造了该三轴陀螺仪芯片,并对其在空气中的驱动性能进行了初步测试.测试结果表明,该单片三轴硅微机械振动陀螺仪驱动模态的实际谐振频率与理论值之间的最大误差小于5%,满足设计要求.     

Micromachined Vibratory Gyroscopes Controlled by a High-Order Bandpass Sigma-Delta Modulator

This work reports on the design of novel closed-loop control systems for the sense mode of a vibratory-rate gyroscope based on a high-order sigma-delta modulator (SigmaDeltaM). A low-pass and two distinctive bandpass topologies are derived, and their advantages discussed. So far, most closed-loop force-feedback control systems for these sensors were based on low-pass SigmaDeltaM's. Usually, the sensing element of a vibratory gyroscope is designed with a high quality factor Q to increase the sensitivity and, hence, can be treated as a mechanical resonator. Furthermore, the output characteristic of vibratory rate gyroscopes is narrowband amplitude-modulated signal. Therefore, a bandpass SigmaDeltaM is a more appropriate control strategy for a vibratory gyroscope than a low-pass SigmaDeltaM. Using a high-order bandpass SigmaDeltaM, the control system can adopt a much lower sampling frequency compared with a low-pass SigmaDeltaM while achieving a similar noise floor for a given oversampling ratio (OSR). In addition, a control system based on a high-order bandpass SigmaDeltaM is superior as it not only greatly shapes the quantization noise, but also alleviates tonal behavior, as is often seen in low-order SigmaDeltaM control systems, and has good immunities to fabrication tolerances and parameter mismatch. These properties are investigated in this study at system level     

Optical Angular Encoder Installation Error Measurement and Calibration by Ring Laser Gyroscope

This paper deals with the installation errors of an optical angular encoder (OAE). A harmonic model is proposed to describe the installation errors, including the effects of eccentricity, swash, and distortion. Moreover, a method of OAE calibration with the ring laser gyroscope (RLG) is introduced. The calibration method can potentially reach the accuracy of 0.1$^{primeprime}$. The calibration method is proved to be experimentally effective. With the harmonic model obtained from the experiment, the calibration of the OAE can be carried out in real time.      

Digital signal processing for an open-loop fiber-optic gyroscope

Open-loop fiber-optic gyroscopes (FOG's) are generally less stable than closed-loop FOG's, yet they offer simpler implementation. We propose a modification of the harmonic division algorithm for an open-loop FOG, which is more stable and also simpler for implementation than the original one. It is shown that when the analog signal is properly sampled and quantized, the performance of our algorithm reaches that of closed-loop FOG's. Our algorithm may be implemented by the use of off-the-shelf component, and does not require an integrated optics circuit.     

机床直行部件运动误差测量的精度分析与对策

分析了经典频域三点法测量直行部件运动误差时所存在的谐波抑制，直线度误差的非周期性、非封闭性以及端点不连续而引起的高阶谐波分量失真等方法误差。为了减少上述方法误差，提出了一种新的时域两点法误差分离技术。首先对传感器拾取的数据做对称延拓，这样可以减小由于所采信号的非封闭性所引起的高阶谐波失真。利用频域三点法得到时域两点法所需要的叠代初值。采用现代控制理论研究了谐波抑制的产生机理。通过合理地配置传感器的安装位置可以优化测量系统的传递特性，减少谐波抑制的发生。该方法既可以得到机床直行部件的运动误差，又可以得到在该机床上加工零件的直线度形状误差，这些测量信息都有助于诊断机床的误差源。通过试验验证了该方法的有效性和精确性。     

基于最小二乘平滑滤波与CEEMDAN的光纤陀螺信号处理研究

针对光纤陀螺在面板堆石坝面板挠度监测中易受到噪声干扰,难以准确提取反映结构变形特征信号的实际问题,提出一种基于最小二乘平滑滤波与CEEMDAN混合降噪的方法。该方法运用CEEMDAN将光纤陀螺实测信号进行分解,得到一系列IMF分量。分别对每一阶IMF分量进行傅里叶频谱分析得到幅值谱图和幅值的方差,根据幅值方差的大小判断噪声IMF分量与有用信号IMF分量的分界,结合最小二乘平滑滤波对噪声IMF分量进行降噪。最后将降噪后的IMF分量与有用信号IMF分量进行重构,得到降噪后的光纤陀螺信号。通过对仿真信号和水布垭面板堆石坝面板挠度监测的实测数据进行分析,该方法能有效滤除噪声信号,准确提取反映结构变形的特征信号,验证了该方法对实际工程中光纤陀螺测量信号降噪的可行性和适用性。     

Testing an ADC linearized with pseudorandom dither

When a pure sinewave is digitized by an analog-to-digital converter (ADC), the errors are determined by the input voltage and, hence, the phase of the sinewave. The errors generate signal harmonics coherently. One technique used to reduce the harmonic distortion is dithering by combining a pseudorandom wide bandwidth dither signal with the input signal. When pseudorandom dither is added to a sinusoidal signal, it randomizes the ADC errors with respect to the sinewave so that the errors cannot add coherently. The dominant effect of the dither component is to reduce large spurious harmonic distortion components by spreading them into many smaller ones. This paper presents a test method for testing an ADC linearized with pseudorandom dither. We present results of testing a 12-bit, 5 MHz converter and a state-of-the-art, 14-15-bit, 10 MHz converter     

光纤陀螺技术的军事应用及前景

介绍了光纤陀螺的原理及种类,通过将光纤陀螺与其它陀螺进行比较,总结出了光纤陀螺的优点.最后,综述了光纤陀螺在武器装备上的应用,并对光纤陀螺的应用前景作了预测.     

Design and operation of a very large ring laser gyroscope

The design and initial operation of a vertical square He-Ne ring laser G0 with a perimeter of 14 m is discussed. This builds on earlier demonstrations of the feasibility of large ring lasers (perimeter approximately 4 m) for single-mode gyroscope operation and with lesser pulling than navigation gyroscopes. With servoing of the rf excitation to yield single-mode operation, G0 gave a quality factor 1 x 10(12) and a Sagnac line with a frequency of 287.8 +/- 1.0 Hz induced by Earth rotation Omega(E). This has confirmed some vital questions over the feasibility of very large gyroscopes for geodetic measurements at the level of 10(-9) Omega(E).     

利用虚拟仪器实现角速度波动率的采集和处理

利用NI 的PXI-6281高速数据采集卡来完成角速度波动信号的采集,借鉴信号失真度的概念,分析角速度反馈信号的基波和高次谐波大小,求取高次谐波与基波幅值比,作为角速度波动率.     

Optical encoder based on a nondiffractive beam

Optical encoders are used in industrial and laboratory motion equipment to measure rotations and linear displacements. We introduce a design of an optical encoder based on a nondiffractive beam. We expect that the invariant profile and radial symmetry of the nondiffractive beam provide the design with remarkable tolerance to mechanical perturbations. We experimentally demonstrate that the proposed design generates a suitable output sinusoidal signal with low harmonic distortion. Moreover, we present a numerical model of the system based on the angular spectrum approximation whose predictions are in excellent agreement with the experimental results.     

Numerical studies on time-domain responses of on-off-keyed modulated optical signals through a dense fog

We present a numerical technique to simulate the propagation characteristics of an on-off-keyed modulated optical signal through fog. The on-off-keyed modulated light (a square wave) is decomposed into a finite number of harmonic components, and a numerical solution for the vector radiative transfer equation is obtained for each harmonic that corresponds to the modulation frequency. With this method we study the distortion and the pulse spread in the received signal due to attenuation and scattering. We investigate the propagation characteristic of the modulated signal with different communication system parameters. This information can be used to study communication channel reliability.     

残周期正弦波形总失真度的测量评价

针对残周期正弦信号波形总失真度的评价校准,提出了一种技术方案,包括:直接使用残周期正弦曲线拟合方法进行参数估计和残差估计,然后按照测量系统量程以及动态有效位数进行失真度的修正,最终给出残周期正弦波形曲线的总失真度评价结果。讨论了残周期情况下谐波失真的测量评价问题,获得了残周期波形谐波分析误差较大、谐波失真评价结果远大于总失真度的结论,残周期正弦波形的谐波分析尚无法进行实际应用。在一组超低频振动实验数据的基础上,对残周期和多周期正弦波形总失真度的评价结果进行了比较,验证了本文方法的有效性和可行性。     

Third harmonic transmit phasing for tissue harmonic generation

Generation of tissue harmonic signals during acoustic propagation is based on the combined effect of two different spectral interactions of the transmit signal. One produces harmonic whose frequency is the sum of transmit frequencies. The other results in harmonic at difference frequency of the transmit signals. Both the frequency-sum component and the frequency-difference component are sensitive to the phase of their constitutive spectral signals. In this study, a novel approach for modifying the amplitude of tissue harmonic signal is proposed based on phasing these two components to achieve either harmonic enhancement or suppression. Both experiments and simulations were performed to investigate the effects of 3f0 transmit phasing on tissue harmonic generation. Results indicate that the relative phasing between the frequency-sum component and the frequency-difference component markedly changes the amplitude of the second harmonic signal. For harmonic enhancement, approximate 6 dB increase of second harmonic amplitude can be achieved while the lateral harmonic beam pattern also is improved as compared to conventional situations in which only the frequency-sum component is considered. For harmonic suppression, the second harmonic signal also could be significantly reduced by about 11 dB when the frequency-difference component is out of phase with the frequency-sum component. Hence, the method of 3f0 transmit phasing has potentials for both improving signal-to-noise ratio in tissue harmonic imaging and enhancing image contrast in contrast-agent imaging by suppression of tissue harmonic background.     

The influence of the intermolecular surface forces on the static deflection and pull-in instability of the micro/nano cantilever gyroscopes

In this paper, the effects of van der Waals and Casimir forces on the static deflection and pull-in instability of a micro/nano cantilever gyroscope with proof mass at its end are investigated. The micro/nano gyroscope is subjected to coupled bending motions which are related by base rotation and nonlinearities due to the geometry and the inertial terms. It is actuated and detected by capacitance plates which are placed on the proof mass. The extended Hamilton principle is used to find the equations governing the static behavior of the clamp-free micro/nano gyroscopes under electrostatic, Casimir and van der Waals forces. The equations of static motion are discritized by Galerkin’s decomposition method. The nonlinear equilibrium equations are solved analytically using homotopy perturbation method (HPM). The static response of the micro/nano gyroscopes to variations in the DC voltage across the drive and sense electrodes is obtained and the effects of different parameters on pull-in instability are investigated. The presented results can be used for accurate estimations of the instability and performance of the micro/nano gyroscopes.     

Three-dimensional finite element simulation of a piezoelectric vibrator under gyration

A three-dimensional finite element modeling is applied to the characteristic evaluation of the piezoelectric gyroscopes. The Coriolis' effect is incorporated with the three-dimensional finite element code that we have already developed. There is no limitation for the vibrational modes and the direction of the gyratory axis. The piezoelectric thin plate gyroscope in plane vibration is again considered for the demonstration. The solution characteristics are compared with those of the two-dimensional modeling and also with the experimental results. Reasonable agreement is achieved. The application is then extended to a bimorph-type gyroscope vibrating out of plane, which is only numerically considered for another example of demonstration. The examination shows that, with this configuration, not only the rotation but also the gyratory axis can be detected in the three-dimensional space     

参量扬声器DSB法的互调失真研究

参量扬声器足近年来出现的一种新的声源。根据宽带参量阵理论的“Berktay远场解”,对参量扬声器的一种信号处理方法——DSB（Double Side Band）法的互调失真问题进行了理论与实验研究。研究发现,DSB法除了存在幅值失真、谐波失真外,还存在互调失真,且实测互调失真较理论预测的复杂。在此基础上指出,“Berktay远场解”只能在一定程度上作为参量扬声器信号处理的理论依据,寻找更为精确的自解调理论模型是解决参量扬声器信号处理问题的根本途径。