共查询到19条相似文献,搜索用时 125 毫秒
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脉象采集方法及功率谱分析研究 总被引:2,自引:0,他引:2
在对压力脉搏波的分析及中医理论研究基础上,提出了一种多点三维动态压力脉搏波的采集方案,以获得有效的脉象数据用于模拟传统中医诊脉.根据信号功率谱的特点,在数据采集过程中结合了功率谱分析手段动态提取脉象的位置及力度特征,同时通过实验得出脉象变化与压力脉搏波功率谱变化的内在相关性,从而得到一种简单有效的脉象特征分析和提取的实验和研究方法. 相似文献
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为解决转子碰摩损伤声发射信号分类及解释难题,应用PCI-2声发射系统和WS-ZHT1型多功能转子实验台组成转子碰摩声发射检测系统,采集转子局部碰摩声发射信号,通过理论分析声发射信号特征和小波基函数性质,dB8小波适合提取声发射信号特征;碰摩产生大量声发射信号,大量声发射信号的统计特性蕴涵较多碰摩信息。对不同转速条件下不同检测位置碰摩声发射信号的统计分析表明,声发射信号的功率谱密度集中在100~400 kHz。声发射信号平均幅值、平均能量可作为区分转子碰摩程度特征参数;功率谱主频可作为区分声发射相对位置特征参数,结论与碰摩类型无关。 相似文献
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对于一些机械设备,经过长期的使用后,在其应力集中处、危险截面处容易形成疲劳裂纹。裂纹形成后会迅速扩展,从而导致灾难性的事故,是一种非常危险的缺陷。本文通过对带有缺陷的钢板进行加载得到裂纹声发射信号。通过对功率谱因子进行分析,得到裂纹扩展的不同阶段的功率谱主频带的变化规律和信号功率随频率轴的分布规律。从而说明利用功率谱因子对裂纹声发射信号进行分析是可行的。 相似文献
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传统检测扩频信号的声光技术,是将扩频信号建模为随机平稳过程,而扩频信号是被伪随机码调制的周期信号,应建模为循环平稳随机过程。基于声光技术与循环谱相关技术,提出了扩频信号的声光谱相关检测方法。建立了基于声光时间积分的声光谱相关检测模型,分析了当干扰瞄准扩频接收机时,扩频信号在循环频率α=1/Tc的循环谱,给出了循环谱峰的检测公式TcRs1/。仿真实验结果表明,与传统的声光技术检测扩频信号的功率谱相比,在光电检测阵列上检测的循环谱峰,谱峰旁瓣几乎为零,并可多获得约3dB的增益,表明声光谱相关检测方法具有更优异的检测和抗干扰性能。 相似文献
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基于焊接过程声信号的声学检测技术是一种实时采集和检测缺陷的有效方法,对材料内部结构变化反映明显。概述了常规焊接缺陷无损检测方法的优缺点,对焊接过程声信号的分类和声信号采集系统进行了论述,分析总结了声发射信号和可听声信号的发声机理、检测原理和信号处理方法,并阐述其在焊接质量在线检测领域的研究现状及应用,特别是焊接缺陷、熔滴过渡形式和熔透状态的识别与预测。为了满足在线检测要求,包含声学检测在内的多传感信息融合焊接系统研究是关键,智能传感、信号处理、自动控制与人工智能技术的进一步研究能促进焊接产业的长足发展。 相似文献
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煤粉粒径的测量是燃煤电站一项重要的工作。针对目前筛分法存在的缺点,提出了一种结合声发射信号与BP神经网络在线识别煤粉粒径的方法。在频域中对噪声信号与煤粉声发射信号进行比较,确定了信号中反映煤粉粒径的频率区间,并利用小波包置零方法对信号进行去噪,在信噪比与信号平滑度方面比较了几种常用小波函数的去噪效果。通过功率谱分析发现了信号能量随煤粉粒径的变化特征。最后提取信号能量特征,利用BP神经网络对煤粉粒径进行识别。研究结果表明,结合声发射信号与BP神经网络识别煤粉粒径,可以获得良好的效果。 相似文献
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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。 相似文献
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外置式非标准视频同步信号发生器的设计 总被引:6,自引:0,他引:6
采用TMS320F206作为USB接口芯片PDIUSBD12的控制器,实现对高速数据采集卡的同步控制。主机从荻得的非标准视频数据中提取同步信号参数,通过USB接口及时传输给DSP,DSP对分频系数实行模糊控制,产生精度可达7ps的视频同步信号,实现非标准视频信号的采集和稳定显示。分别对行频为15.625kHz、场频为50Hz的CCD视频信号,及行频为48.656kHz、场频为60Hz的计算机显示器视频泄漏信号进行了采集与显示,证实了此方案的可行性。 相似文献
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Peter Schoderböck Hermann Klocker Lorenz S. Sigl Gernot Seeber 《International Journal of Thermophysics》2009,30(2):599-607
Thermal-diffusivity data obtained by a pulse technique are substantially in error if the sample thickness becomes too small.
In this case the inevitable spike caused by the trigger pulse for the laser and the thermogram of the specimen are interacting,
and a superposition of both signals is recorded, whose evaluation with standard algorithms systematically underestimates the
thermal diffusivity of materials. Therefore, this incorrect calculation corresponding to the spike-thermogram overlay was
investigated for general tendencies, and a calculation method transferring the experimental data obtained for small thicknesses
into representative thermal diffusivity values for the investigated material will be introduced. 相似文献
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Dong-Lai Liu Waag R.C. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1995,42(4):590-601
The specific circumstances under which the van Cittert-Zernike theorem applies in ultrasonic imaging systems are examined through analysis and computations. Expressions are obtained for the mutual coherence function of an incoherent source when the signals are discrete in time and space and have finite lengths. Expressions are also obtained for statistics and effective signal-to-noise ratios that describe the error in the assumption of an incoherent source with finite signal lengths. Images of a one-dimensional source are reconstructed for different signal lengths and different pulse windows. The results show that ultrasonic signals with a relatively long effective length are needed to satisfy the incoherence requirement for image reconstruction based on the van Cittert-Zernike theorem. Consequently, although the van Cittert-Zernike theorem may be used to estimate the coherence length of ultrasonic signals in the aperture of an imaging system, special data acquisition techniques are needed for satisfactory reconstruction of ultrasonic images when depth resolution like that in current b-scans is required 相似文献
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We have developed a new data acquisition approach followed by a suitable data analysis for Laser-induced breakdown spectroscopy. It provides absolute concentrations of elements in particulate materials (e.g., industrial dusts and soils). In contrast to the known calibration procedures (based on the ratio of spectral lines), which are applicable only when one component is constant, this approach requires no constant constituent and results in absolute (rather than relative) concentrations. Thus, the major drawback of this analytical method, namely, the signals' instability (especially when particulate materials are concerned) is partially solved. Unlike the commonly used integrated data acquisition, we use a sequence of signals from single breakdown events. We compensate for pulse to pulse fluctuations in an intrinsic way, and the final results do not depend on the presence of any constant component. Extended linear calibration curves are obtained, and limits of detection are improved by 1 order of magnitude relative to previous methods applied to the same samples (e.g., detection limit of 10(-12) g of Zn in aerosol samples). The proposed compensation for pulse variations is based on the assumption that they can be described as a multiplicative effect for both the spectral peaks and a component of the baseline. In other words, we assume that the same fluctuation pattern observed in the spectral peaks is present in the baseline as well. This assumption is shown to hold and is utilized in the proposed method. In addition, a proper data-filtering process, which eliminates ill-conditioned spectra, is shown to partially compensate for problems due to the nature of analysis of particulate materials. 相似文献
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Two-dimensional 1H-13C HSQC (heteronuclear single quantum correlation) and fast-HMQC (heteronuclear multiple quantum correlation) pulse sequences were implemented using a sensitivity-enhanced, cryogenic probehead for detecting compounds relevant to the Chemical Weapons Convention present in complex mixtures. The resulting methods demonstrated exceptional sensitivity for detecting the analytes at trace level concentrations. 1H-13C correlations of target analytes at < or = 25 microg/mL were easily detected in a sample where the 1H solvent signal was approximately 58,000-fold more intense than the analyte 1H signals. The problem of overlapping signals typically observed in conventional 1H spectroscopy was essentially eliminated, while 1H and 13C chemical shift information could be derived quickly and simultaneously from the resulting spectra. The fast-HMQC pulse sequences generated magnitude mode spectra suitable for detailed analysis in approximately 4.5 h and can be used in experiments to efficiently screen a large number of samples. The HSQC pulse sequences, on the other hand, required roughly twice the data acquisition time to produce suitable spectra. These spectra, however, were phase-sensitive, contained considerably more resolution in both dimensions, and proved to be superior for detecting analyte 1H-13C correlations. Furthermore, a HSQC spectrum collected with a multiplicity-edited pulse sequence provided additional structural information valuable for identifying target analytes. The HSQC pulse sequences are ideal for collecting high-quality data sets with overnight acquisitions and logically follow the use of fast-HMQC pulse sequences to rapidly screen samples for potential target analytes. Use of the pulse sequences considerably improves the performance of NMR spectroscopy as a complimentary technique for the screening, identification, and validation of chemical warfare agents and other small-molecule analytes present in complex mixtures and environmental samples. 相似文献
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Miralles R Vergara L Salazar A Igual J 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(3):637-647
In this paper, we propose and analyze by means of simulations the use of surrogate data algorithms for blind detection of nonlinearities in multiple-echo ultrasonic signals.We assume a blind scheme so that no information about the input (emitted ultrasonic pulse) can be used. The metrics and equations that model some nonlinear situations are carefully reviewed. Also, closed form equations of the third-order metrics from a simplified second-order Volterra kernel are derived. Computer simulations show that the surrogate data technique is a potentially powerful tool for blind detection of nonlinearities in multiple-echo ultrasonic signals if adequate metrics are chosen. They also reveal interesting trade-offs among parameters that model ultrasonic systems and detection percentages. 相似文献
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Le Drogoff B Chaker M Margot J Sabsabi M Barthélemy O Johnston TW Laville S Vidal F 《Applied spectroscopy》2004,58(1):122-129
Quantitative analysis of aluminum and copper alloys by means of laser-induced plasma spectroscopy (LIPS) has been investigated for three representative laser pulse durations (80 fs, 2 ps, and 270 ps). The experiments were carried out in air at atmospheric pressure with a constant energy density of 20 J/cm2. Because the decay rate of the spectral emission depends on the laser pulse duration, the optimum detection requires an optimization of the temporal gating acquisition parameters. LIPS calibration (sensitivity and nonlinearity) and the limit of detection (LOD) are discussed in detail. While the LOD of minor elements embedded in alloy samples obtained by sub-picosecond or sub-nanosecond laser pulses are both time and element dependent, provided an appropriate temporal window is chosen, the optimum LODs (several parts per million (ppm)) prove to be independent of the laser pulse duration. Finally, it is found that for elements such as those detected here, gated LIPS spectra using picosecond or sub-picosecond laser pulses provide much better LOD values than non-gated spectra. 相似文献