基于小波降噪和短时傅里叶变换的主轴突加不平衡非平稳信号分析

针对主轴运行过程中突加不平衡而产生的非平稳信号无法采用传统的傅里叶变换对信号进行分析处理的问题,提出一种采用小波降噪与短时傅里叶变换相结合对主轴振动特征信息进行准确提取的方法,该方法利用小波降噪技术对非平稳信号进行滤波处理,再对滤波处理后的信号进行重构,最后通过短时傅里叶变换精确获取主轴振动幅值,通过仿真和实验验证了该方法的有效性。     

基于正交复小波变换和小波去噪的改进系统De-OCWDM

用近似线性相位正交复小波变换(ALOCWT)取代了正交频分复用(OFDM)系统中的离散傅立叶变换(DFT),形成了正交复小波波分复用(OCWDM)系统.ALOCWT具有时频特性、正交特性、重构特性等特性,能够很好地取代DFT,同时ALOCWT能够保留复信号的相位信息,使得信号重构精度更高,从而提高了信号传输的准确性和系...     

Simultaneous measurement of out-of-plane displacement and slope using a multiaperture DSPI system and fast Fourier transform

The simultaneous quantitative measurement of out-of-plane displacement and slope using the fast Fourier transform method with a single three-aperture digital speckle pattern interferometry (DSPI) arrangement is demonstrated. The method coherently combines two sheared object waves with a smooth reference wave at the CCD placed at the image plane of an imaging lens with a three-aperture mask placed in front of it. The apertures also introduce multiple spatial carrier fringes within the speckle. A fast Fourier transform of the image generates seven distinct diffraction halos in the spectrum. By selecting the appropriate halos, one can directly obtain two independent out-of-plane displacement phase maps and a slope phase map from the two speckle images, one before and the second after loading the object. It is also demonstrated that by subtracting the out-of-plane displacement phase maps one can generate the same slope phase map. Experimental results are presented for a circular diaphragm clamped along the edges and loaded at the center.     

Velocity measurement of particles flowing in a microfluidic chip using Shah convolution Fourier transform detection

A noninvasive radiative technique, based on Shah convolution Fourier transform detection, for velocity measurement of particles in fluid flows in a microfluidic chip, is presented. It boasts a simpler instrumental setup and optical alignment than existing measurement methods and a wide dynamic range of velocities measurable. A glass-PDMS microchip with a layer of patterned Cr to provide multiple detection windows which are 40 microns wide and 70 microns apart is employed. The velocities of fluorescent microspheres, which were electrokinetically driven in the channel of the microfluidic chip, were determined. The effects of increasing the number of detection windows and sampling period were investigated. This technique could have wide applications, ranging from the determination of the velocity of particles in pressure-driven flow to the measurement of electrophoretic mobilities of single biological cells.     

改进经验小波变换与最小熵解卷积在铁路轴承故障诊断中的应用

经验小波变换是一种小波框架下的自适应信号分解方法,对旋转机械的非线性、非平稳振动信号有很好的分解作用。针对传统经验小波变换过程中频谱划分过多的问题,提出根据互信息值对频谱进行重新划分与合并的方法,能有效减少频带数量;选择峭度值最大的分量进行信号重构,再使用最小熵解卷积对重构信号进行降噪;对降噪后的信号进行包络分析,能够有效地诊断出滚动轴承的微弱故障。通过仿真信号与铁路货车轮对轴承实验信号验证了该方法的有效性,为下一步工程应用奠定了基础。     

Sensitivity of the fractional Fourier transform to parameters and its application in optical measurement

The fractional Fourier transform (FRT) is becoming important in optics and can be used as a new tool to analyze many optical problems. However, we point out that the FRT might be much more sensitive to parameters than the conventional Fourier transform. This sensitivity leads to higher requirements on the optical implementation. On the other hand, high parametric sensitivity can be used in optical diffraction measurements. We give the first proposal, to our knowledge, of the FRT's applications in optical measurement.     

Fourier transform infrared measurement of solid-, liquid-, and gas-phase samples with a single photoacoustic cell

A photoacoustic detector based on the optical cantilever microphone has been built. The detector is capable of measuring solid-, liquid-, and gas-phase samples. Photoacoustic Fourier transform infrared (FT-IR) measurement with three samples in different phases was demonstrated. Example samples were polyethene, sunflower oil, and methane. The sensitivity of the cell was compared to a commercial photoacoustic FT-IR detector. With the standard carbon black sample the cantilever detector gave approximately five times higher signal-to-noise ratio than the reference detector. The sensitivity with methane was also compared to the DTGS detector of the FT-IR instrument corresponding to an absorption path of 6.3 cm. Simulation of the photoacoustic signal showed that a compromise has to be made in the cell design between sensitivity for solid- and gas-phase samples but it is possible to highly enhance the sensitivity for all types of samples by reducing cantilever dimensions.     

激光跟踪测量系统校验及在三维测量中的应用

介绍了激光跟踪仪（LTS）原理，提供了一种校验激光跟踪测量系统的方法。通过与高精度三坐标测量机（CMM）比对测量，检验其精度，实验结果表明角向误差是影响LTS精度的主要因素。利用激光跟踪仪对汽车外形进行扫描，建立其三维模型，发现测量中存在的问题，并提出解决方法，结果表明，激光跟踪仪应用于汽车车身扫描有操作简单、精度较高等优点。     

Phase measurement in temporal speckle pattern interferometry: comparison between the phase-shifting and the Fourier transform methods

The measurement of dynamic displacements by use of speckle pattern interferometry and temporal phase unwrapping allows for the evaluation of large-object displacement fields without the propagation of spatial unwrapping errors. If a temporal carrier is introduced in one of the beams of the interferometer, phase data for whole-object displacement can be retrieved by use of a temporal phase-shifting method or a temporal Fourier transformation approach. We present a comparison between both methods of temporal phase measurement in terms of precision and execution speed. We performed the analysis by using computer-simulated speckle interferograms, an approach that allowed us to know precisely the original phase distribution and also to determine the spatial rms phase error as a function of the phase change introduced between two consecutive speckle interferograms. The performance of both methods to process experimental data is also illustrated by use of the results from a high-speed speckle interferometry study of a carbon fiber panel.     

Assessment of random and systematic errors in millimeter-wave dielectric measurement using open resonator and Fourier transform spectroscopy systems

Assessment of random and systematic errors is performed for the first time on the real part of permittivity (/spl epsiv/') and loss tangent (tan/spl delta/) of ceramics and polymers using two different measurement systems. Data measured from the full cavity length and the frequency variation techniques using the 60 GHz open resonator system and the millimeter-wave dispersive Fourier transform spectroscopy system (DFTS) are compared and analyzed. Data measured by the frequency variation technique were seen to be more accurate than those measured by the full cavity length variation technique with lower random errors for the specimens measured. The /spl epsiv/' of the specimens measured by the frequency variation technique followed closely with those measured by the millimeter-wave DFTS system with a slight difference of about 0.02%. Finally, for all the specimens measured in this paper, the DFTS system was seen to provide much better accuracy for /spl epsiv/' values. The frequency variation technique from the open resonator system generated the best tan/spl delta/.     

直角坐标系下的水下被动目标跟踪自适应卡尔曼滤波算法

针对纯方位被动目标跟踪中，直角坐标系下的扩展卡尔曼滤波器容易发散，导致滤波精度很差的情况，文章中提出了一种直角坐标系下自适应卡尔曼滤波算法，对虚拟噪声进行了估计，动态补偿观测模型的线性化误差，削减系统的观测误差，并对其滤波理论及其算法进行了研究和仿真，结果表明，该算法提高了滤波的稳定性、快速性和精确性，优于一般的扩展卡尔曼滤波算法。     

Parasitic diffuse reflection in a Fourier transform spectrometer yielding subharmonic ghosts and line-shape distortion

When using a high-resolution Fourier transform spectrometer (FTS) in a cube-corner configuration, subharmonic ghosts are observed in the spectrum. These ghosts are attributable to parasitic diffuse reflections on the mirrors of the FTS arm. The reflected beams skip a part of the interferometer and travel a different path from the main beam thus experiencing a smaller optomechanical gain. These reflections are present in the reference laser channel as well as on the measurement channel, and each affect the estimated spectrum differently. The sampling grid generated by the reference laser has periodic errors that are synchronized with the fringe signal. The measured spectrum can therefore exhibit sampling jitter ghosts at submultiples of the reference laser wavenumber in addition to its own additive subharmonics. The diffuse reflection experiencing the nominal optomechanical gain, such as in a plane-mirror configuration, will impact directly on the instrument line shape and on the radiometric accuracy of the spectrometer since some radiation is not propagating at the expected angles in the instrument.     

Measurements of (12)CH4 nu4 band halfwidths using a tunable diode laser system and a Fourier transform spectrometer

Air-broadened and N2-broadened halfwidths at room temperature for twenty-five transitions in the 4 fundamental band of '2CH4 have been determined from IR absorption spectra recorded with a tunable diode laser spectrometer. Two tunable diode lasers operating in the 1250-1380-cm(-1) region were used to obtain these data. Air-broadened halfwidths for twenty of these lines were also determined from additional spectra recorded at 0.01-cm(-1) resolution with the Fourier transform spectrometer in the McMath solar telescope complex on Kitt Peak. The air-broadened halfwidths obtained from these two techniques are very consistent with agreement better than 3% in most cases.     

Parts-per-billion mass measurement accuracy achieved through the combination of multiple linear regression and automatic gain control in a Fourier transform ion cyclotron resonance mass spectrometer

Fourier transform ion cyclotron resonance mass spectrometry has the ability to achieve unprecedented mass measurement accuracy (MMA); MMA is one of the most significant attributes of mass spectrometric measurements as it affords extraordinary molecular specificity. However, due to space-charge effects, the achievable MMA significantly depends on the total number of ions trapped in the ion cyclotron resonance (ICR) cell for a particular measurement. Even through the use of automatic gain control (AGC), the total ion population is not constant between spectra. Multiple linear regression calibration in conjunction with AGC is utilized in these experiments to formally account for the differences in total ion population in the ICR cell between the external calibration spectra and experimental spectra. This ability allows for the extension of dynamic range of the instrument and for the mean MMA values to remain less than 1 part-per-million (ppm). In addition, multiple linear regression calibration is used to account for both differences in total ion population in the ICR cell as well as relative ion abundance of a given species, which also affords mean MMA values at the parts-per-billion (ppb) level.     

Surface-induced dissociation in a Fourier transform ion cyclotron resonance mass spectrometer: instrument design and evaluation

A new Fourier transform ion cyclotron resonance mass spectrometer (FTICR MS) has been constructed in our laboratory. The instrument employs surface-induced dissociation (SID) as an activation method for obtaining structural information on biomolecules in the gas phase. Tandem SID mass spectra can be acquired using either a continuous or a pulsed mode of operation. Collision energy of precursor ion is controlled by a dc offset of the ICR cell. This approach eliminates defocusing of the ion beam by the ion-transfer optics as a function of ion kinetic energy and constitutes a significant improvement over our previous experimental setup. Furthermore, it can be easily implemented on any FTICR mass spectrometer. Very high signal-to-noise ratios of 200-500 were obtained in single-scan SID mass spectra of model peptides with acquisition time less than 1.1 s. Reasonable SID signal was detected in single-scan spectra with total acquisition time of only 0.3 s. The high signal-to-noise ratio and the fast acquisition time point on a potential application of SID for high-throughput studies in FTICR MS.     

Fourier transform infrared (FT-IR) spectroscopy and improved principal component regression (PCR) for quantification of solid analytes in microalgae and bacteria

In bioanalytical chemistry, a detailed chemical understanding of biomaterials is often difficult to obtain due to the sheer number of analytes contained in a sample along with the samples' generally low reproducibility. This study presents a Fourier transform infrared (FT-IR) spectroscopic technique in conjunction with innovations in sample preparation and chemometric data preprocessing to overcome these limitations. These methodologies were applied to quantitative analyses of 31 representative compounds commonly found in biomaterial, which have been incorporated into a spectroscopic calibration database, that is, albumin (protein); D-alanine, glycine, histidine, valine, arginine, cysteine, phenylalanine, tyrosine, methionine, L-glutamine, and glutamic acid, (amino acids); glucose, fructose, galactose, mannose, sucrose, lactose, glycogen, agarose, and starch (carbohydrates); DNA (salmon sperm), sulphonoquinovosyl diglyceride ( sulpho-lipid ), and 1,2-diacyl-sn-glycero-3-phospho-L-serine ( phospho-lipid ); succinic acid and malic acid ( carboxylic acids ); glycolic acid (a -hydroxy acid), sodium pyruvate, b -carotene, frustules (microalgae silica-shells), and ammonium formate. Two proof-of-principle applications were based on calibration models incorporating these solids, i.e., characterization of E. coli and microalgae. The former aims for detection of bacterial contamination and the latter to enable investigations of changes in chemical composition of microalgae cells in response to shifting environmental conditions. Chemometric preprocessing steps have been developed for handling sample-to-sample fluctuations of absorption path lengths and baselines; the former incorporated mass normalization while the latter utilized a novel baseline correction method that requires no a priori information. Data preprocessing, chemometric calibration, and evaluation algorithms have been combined, together with an extensive spectral database of the aforementioned compounds (～1500 samples), for quantitative calibration purposes through the remotely accessible Virtual Chemometrics Lab , which can be utilized for a multitude of applications through a graphical user interface.     

Extrasampling and thermal behavior of diode lasers used as a reference source in a Fourier transform IR spectrometer

The diode laser is often used as a reference source in an interferometer because its interferogram zero crossings allow for precise intervals to be used for sampling the measured interferogram. The diode laser side modes, the features of which depend on the laser's temperature and power, may generate extra sampling points. The number of extra sampling points is analytically evaluated, and the synthetic spectra are compared with those obtained experimentally using the Planetary Fourier Spectrometer. The conclusion is that the theoretical resolution is guaranteed in practice only when no more than one extra sampling point is generated. This is the case when either the diode laser side mode amplitudes are less than one half of the main mode amplitude or the distance in wave numbers between the side modes and the main mode times the maximum optical path difference is less than 1. Finally, once an appropriate diode laser has been chosen, the actual spectral resolution might be degraded by poor device-operating conditions.     

Nonlinear filtering in object and Fourier space in a joint transform optical correlator: comparison and experimental realization

The use of different kinds of nonlinear filtering in a joint transform correlator are studied and compared. The study is divided into two parts, one corresponding to object space and the second to the Fourier domain of the joint power spectrum. In the first part, phase and inverse filters are computed; their inverse Fourier transforms are also computed, thereby becoming the reference in the object space. In the Fourier space, the binarization of the power spectrum is realized and compared with a new procedure for removing the spatial envelope. All cases are simulated and experimentally implemented by a compact joint transform correlator.     

多频海底声学原位测试系统在海水中的声源响应及子波分析

多频海底声学原位测试系统是国家海洋局第二海洋研究所自行研制的海底声学原位测试系统。利用声源换能器的等效电路,分析了声源换能器输入终端输入脉冲与输出接收脉冲之间的关系。将系统的低频声源等效为一定半径的球形声源,确定了系统在15kHz时在试验海域海水中的声源换能器的角频率响应和输出回路品质因子。计算了系统理论接收脉冲,结果表明输出接收脉冲并非输入脉冲的简单复制。并与实测接收脉冲进行了比对,理论接受脉冲与实测脉冲在细节上达到了很好的匹配,说明本文确定的各响应参数很好的代表了本系统在海水中的声源响应。     

Preparation and in situ characterization of surfaces using soft landing in a Fourier transform ion cyclotron resonance mass spectrometer

Mass-selected peptide ions produced by electrospray ionization were deposited onto fluorinated self-assembled monolayer surfaces (FSAM) surfaces by soft landing using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially designed for studying interactions of large ions with surfaces. Analysis of the modified surface was performed in situ by combining 2-keV Cs+ secondary ion mass spectrometry with FT-ICR detection of the sputtered ions (FT-ICR-SIMS). Regardless of the initial charge state of the precursor ion, the SIMS mass spectra included singly protonated peptide ion, peptide fragment ions, and peaks characteristic of the surface in all cases. In some experiments, multiply protonated peptide ions and [M + Au]+ ions were also observed upon SIMS analysis of modified surfaces. For comparison with the in situ analysis of the modified surfaces, ex situ analysis of some of the modified surfaces was performed by 25-keV Ga+ time-of-flight-secondary ion mass spectrometry (TOF-SIMS). The ex situ analysis demonstrated that a significant number of soft-landed peptide ions remain charged on the surface even when exposed to air for several hours after deposition. Charge retention of soft-landed ions dramatically increases the ion yields obtained during SIMS analysis and enables very sensitive detection of deposited material at less than 1% of monolayer coverage. Accumulation of charged species on the surface undergoes saturation due to coulomb repulsion between charges at close to 30% coverage. We estimated that close to 1 ng of peptide could be deposited on the spot area of 4 mm2 of the FSAM surface without reaching saturation.