基于Hilbert谱的心率变异信号时频分析方法

心率变异性(heart rate variability,HRV)信号的频域分析方法是用来表征自主神经调控信息的基本方法。为了评估自主神经系统功能及对心血管活动的影响,提出一种基于Hilbert时频谱的HRV信号的时频特征提取和分析的新方法。对HRV信号进行希尔伯特-黄变换(Hilbert-Huang transform,HHT)以获得HRV信号Hilbert时频谱,依据短时程HRV信号的线性频域分析指标,得到不同生理频带的Hilbert能量棒形图,提取总能量、各生理频带的能量和其归一化能量以及生理频段的能量比值作为评价心率变异性的时频特征。对MIT-BIH数据库的年轻人、老年人样本和健康人、心衰病人样本的HRV信号分析表明,基于Hilbert谱的时频特征的区分性能好,有较清晰的生理意义,能反映人的生理病理变化,为短时程HRV信号分析提供了一种有效方法。     

Measurement of distorted exponential signal components using maximum likelihood estimation

Exponential signal is a suitable stimulus for dynamic ADC testing because of the simplicity of the generating RC circuit. A potential distortion source of the ideal exponential shape is the dielectric absorption of the capacitor, whose effect can be represented by additional superimposed exponential components with longer time constant and smaller peak value. Measurement of the distortion of the exponential signal by using a reference waveform recorder with known nonlinearity is the initial step in the calibration of an ADC testing stand with exponential stimulus, along with the assessment of its uncertainty. Lack of the orthogonality of stimulus signal components makes classical analysis methods difficult to apply.This paper presents a method for measurement of multiexponential signal components as an example of the more general task of signal decomposition where signal components are non-orthogonal. The proper optimization procedure based on the ML method will be presented, which usually reaches the global minimum of the cost function. Effectiveness will be shown by simulation, and by application to measurement of a multiexponential signal acquired by a reference waveform recorder with known error parameters.     

基于AFM的纳米梁杨氏模量和残余应力测量

针对同一工艺流程下相同杨氏模量和残余应力的双端固支梁阵列,建立了简化的杨氏模量和残余拉应力的弯曲测试模型,并将应力刚化理论应用到几何非线性有限元分析中用于上述模型的理论误差评价.提出将拉曼频移测试与原子力显微镜(AFM)弯曲测试相结合的实验方案,首先利用拉曼频移判断结构中的应力拉压性质,随后利用AFM测量梁阵列的弹性系数,最终利用MATLAB求解超定方程组的方法解得梁阵列的杨氏模量和残余应力,测试结果证明了该实验方案的可行性.     

Measurement of human response to tactile temperature sensing using stochastic system identification

Tactile response is limited for many operations that are preformed in extreme environments due to bulky equipment or the limitations of the human body. In order to allow a user in extreme environments to regain some of their temperature-tactile response, a glove was developed that converts temperature into a vibration felt by the user. An RTD was attached to the glove and connected to a microcontroller. This microcontroller converted temperature into a voltage and transmitted it to a micromotor that controlled the vibration felt by the user. Through this scheme, the user was able to identify a temperature increase with a 4 s delay. This paper also presents the system response of the glove to a temperature impulse. Using this system transfer function, it is possible to make improvements to the glove to reduce the overall delay between the glove sensing a temperature and the user recognizing the temperature change.     

Measurement of fluid flow rate using nanocomposite silicone rubber sensor

This paper describes the use of an elastic nanocomposite sensor to measure the water flow rate in open and closed hydraulic circuits. A sensor was constructed of multiwalled carbon nanotubes (MWCNTs) dispersed in silicone rubber (SR) and subsequently tested to verify its ability to measure water flow rate. The results reveal that the correlation between the fluid flow rate and the pressure variation across the sensor entails that its electrical resistance can be correlated to the flow rate. The sensor constructed of 2 and 3 wt,% of MWCNTs in SR-based nanocomposite sensors exhibited a low percolation threshold. An electron microscope (HRSEM) was used to characterize the manufactured nanocomposite sensors and confirm the conductive networks. The variation in the electrical resistance of the sensor in terms of both water pressure and flow rate is described. The elastic sensor was calibrated to measure the water flow rate in the range of 0–35 l/min. The results show that an elastic sensor fabricated from MWCNTs dispersed in silicone rubber does exhibit sensitivity to the slight strain levels produced by dynamic water pressure and, as such, can be used to measure flow rate. In addition, the sensor's response to water flow in the presence of bubbles enables pump cavitation monitoring. This paper also investigates the reduction of sensor electrical conductivity in response to water immersion. The findings reveal that the elastic nanocomposite sensor could potentially be used as a liquid sensor to detect water leakage in hydraulic circuits.     

Measurement of particle migration in micro-channel by multi-capacitance sensing method

Study of particle migration is important to enhance and increase the efficiency of the positioning and sorting process in order to produce the high yield of desired product especially in microfluidic applications. In this study, in order to study particle migration, normalized particle concentration in a micro-channel has been calculated for high initial particle concentrations (ξ=3.0, 5.0 and 10.0%) and the small particle diameters (d_p=1.3, 1.5 and 2.1 μm) by using capacitance data measured by a multi-capacitance sensing method. From the calculations, it has been observed that the particle concentration at the wall vicinity area is increased as ξ and d_p are increased while the particle concentration at the center area is decreased. To analyze the tendency of the particle migration, two quantitative indicators are introduced, viz., streamwise migration ratio (Ψ) which is the ratio of particle concentration at the downstream to the upstream cross-section position, and the cross-sectional migration ratio (Φ) which is the ratio of the particle concentration at the wall to the center area at the same cross-sectional position. The result shows that the Ψ at the center area is decreased as the particles move along the channel irrespective of ξ and d_p while the Ψ at the wall vicinity area is increased. Based on Ψ and Φ, it has been observed that the particle migrate from the center area towards the wall vicinity area in the case of low ξ and small d_p while the particles tend to concentrate on the center area in the case of high ξ and the large d_p. As a result, the particle concentration at center is higher in the case of the lower ξ and the smaller d_p than that in the case of higher ξ and the larger d_p.     

Measurement of optical-beat frequency in a photoconductive terahertz-wave generator using microwave higher harmonics

A new method for measuring optical-beat frequencies in the terahertz (THz) region using microwave higher harmonics is presented. A microwave signal was applied to the antenna gap of a photoconductive (PC) device emitting a continuous electromagnetic wave at about 1 THz by the photomixing technique. The microwave higher harmonics with THz frequencies are generated in the PC device owing to the nonlinearity of the biased photoconductance, which is briefly described in this article. Thirteen nearly periodic peaks in the photocurrent were observed when the microwave was swept from 16 to 20 GHz at a power of -48 dBm. The nearly periodic peaks are generated by the homodyne detection of the optical beat with the microwave higher harmonics when the frequency of the harmonics coincides with the optical-beat frequency. Each peak frequency and its peak width were determined by fitting a Gaussian function, and the order of microwave harmonics was determined using a coarse (i.e., lower resolution) measurement of the optical-beat frequency. By applying the Kalman algorithm to the peak frequencies of the higher harmonics and their standard deviations, the optical-beat frequency near 1 THz was estimated to be 1029.81 GHz with the standard deviation of 0.82 GHz. The proposed method is applicable to a conventional THz-wave generator with a photomixer.     

Measurement of residual stress using linearly integrated GMR sensor arrays

Tubular-type transmission towers have several advantages, but could be compromised if welding defects from the construction process are not found during deployment. This research derived an equation that illustrates how a change in stress accompanied with mechanical deformation triggered a change in distribution of magnetic flux density. Furthermore, it verified experimentally that a change in distribution of magnetic flux density occurred due to a change in stress at the welding zone. Using this principle, this research proposes a system to measure residual stress occurred in the welding zone of tubular-type transmission tower. The ultrasound examination results were compared and the result showed that ultrasound signals revealed defects in a place where sudden distribution of magnetic flux density was presented. However, when a number of welding defects occurred across the large area, the distribution of magnetic flux density may not change due to the alleviating effect of the stress concentration.     

A three-lead, programmable, and microcontroller-based electrocardiogram generator with frequency domain characteristics of heart rate variability

The objective of this study is to design and develop a programmable electrocardiogram (ECG) generator with frequency domain characteristics of heart rate variability (HRV) which can be used to test the efficiency of ECG algorithms and to calibrate and maintain ECG equipment. We simplified and modified the three coupled ordinary differential equations in McSharry's model to a single differential equation to obtain the ECG signal. This system not only allows the signal amplitude, heart rate, QRS-complex slopes, and P- and T-wave position parameters to be adjusted, but can also be used to adjust the very low frequency, low frequency, and high frequency components of HRV frequency domain characteristics. The system can be tuned to function with HRV or not. When the HRV function is on, the average heart rate can be set to a value ranging from 20 to 122 beats per minute (BPM) with an adjustable variation of 1 BPM. When the HRV function is off, the heart rate can be set to a value ranging from 20 to 139 BPM with an adjustable variation of 1 BPM. The amplitude of the ECG signal can be set from 0.0 to 330 mV at a resolution of 0.005 mV. These parameters can be adjusted either via input through a keyboard or through a graphical user interface (GUI) control panel that was developed using LABVIEW. The GUI control panel depicts a preview of the ECG signal such that the user can adjust the parameters to establish a desired ECG morphology. A complete set of parameters can be stored in the flash memory of the system via a USB 2.0 interface. Our system can generate three different types of synthetic ECG signals for testing the efficiency of an ECG algorithm or calibrating and maintaining ECG equipment.     

Measurement of active power by time domain digital signal processing

This paper compares DSP time domain algorithms of one-phase active power measurement by non-coherent sampling that are superior to some frequency domain algorithms in active power estimation of non-sinusoidal signals. The measurement bias, uncertainty and sampling time necessary for the required accuracy are compared for various data windows with the use of simulations and measurements. Both monofrequency and multifrequency signals are dealt with. Analytical formulas are presented for the active power bias for rectangular and general cosine windows and for standard uncertainty of active power measurement. A simple method is described for correction of the multiplexing delay in power measurement using multiplexing DAQ boards. The information from this paper can also be used for measuring energy consumption and three-phase power.     

基于小波熵的低误报率人体热释电红外信号识别

提出一种基于双密度双树复小波变换小波熵特征的热释电红外(PIR)信号人体识别方法.首先对人体和狗的PIR探测器输出信号进行去噪预处理,然后提取信号的双密度双树复小波变换的小波熵作为特征,最后采用最小二乘支持向量机对特征进行分类.实验结果表明:所提取的特征及分类方法对人体与狗的热释电红外信号的识别率可达93.6%.因此该识别方法能大大降低PIR探测器的误报率,并可进一步提升PIR探测器在安防和智能家居系统中应用.     

测试系统中非平稳信号的时频优化小波包检测算法

非平稳信号为测试系统所测试分析的主要目标之一.对于这些信号传统的检测方法(例如:傅里叶变换)不能起到有效的分析作用.小波包变换是非平稳信号分析的常用工具.Shannon小波函数是现有的单小波家族中唯一能够对信号频域进行严格划分的小波函数,但是由于其时域的非紧支性限制了其应用.本文通过对Shannon小波函数的时频联合优化,改善了其在非平稳信号检测过程中的性能;首先在时域上,改写其时域表达式,并保留其频域的紧支性,提升了其时域的紧支性;其次在频域上,提出了对Shannon小波函数频域滤波器的插值算法,改善其频域的滤波性能;再次,通过牛顿插值法给出了算法的快速实现;最后,做出了仿真实例.结果表明,通过本文的算法,改善了Shannon小波包变换的性能,使其成为测试系统关于非平稳信号检测的有效手段.     

空间差分干涉的光纤分布式水下声波测量

为了实现大范围的水下微弱声波探测,提出了一种基于后向瑞利散射空间差分干涉的光纤分布式声波检测(DAS)技术。声波振动引起单模传感光纤中后向瑞利散射光的变化,将含有声波信息的后向瑞利散射光注入到非平衡迈克尔逊干涉仪,调节干涉仪的臂长差实现不同长度的相邻空间段的后向瑞利散射光干涉,然后采用3×3耦合器解调技术解调出相位信息,实现声波信号的测量。实验搭建了一套基于DAS技术的水下声波测量系统,该系统不仅能够实时准确定位两个声波位置,还能还原声波的幅值、频率、相位等信息,并且实现了1kHz情况下的-148.8dB(re rad/μPa)水下声压相位灵敏度,100~1 500Hz频率的频响平坦度在1.2dB之内。实验结果证实DAS技术能够实时快速地实现多个声波信息的定量测量。     

荧光免疫分析仪对沙门氏菌的检测

为探讨一起食物中毒的病原菌,按照GB/T4789-2003及WS/T9-1996中食源性致病菌的检验方法,应用mini-VIDAS全自动荧光免疫分析仪等对所采集的食物中毒标本进行检验。结果25件标本中检出的5株菌均为都柏林沙门氏菌,说明本次食物中毒的病原菌为都柏林沙门氏菌。     

Measurement of residual stress in thick section composite laminates using the deep-hole method

The deep-hole method is a method of measuring residual stress in large metallic components. In this paper, an extension to the deep-hole method is described to allow the residual stresses in thick section composite laminated plates to be evaluated. The method involves first drilling a small hole through the laminate perpendicular to the surface. The material around the hole is then machined away, resulting in a change in diameter of the hole due to the release of residual stress. This change in diameter is measured and used to calculate the residual stress. The calculation requires the evaluation of coefficients that depend on the properties of the composite. In this work, the finite element method is used to evaluate these coefficients. Using this method, the residual stresses in a 22 mm thick carbon/epoxy composite plate are measured and reported.     

电力系统信号与数据的压缩传感技术综述

随着智能电网建设及电力系统自动化、智能化水平的不断提高,电力系统信号分析与数据处理方法在电力系统中的重要作用进一步凸显。压缩传感(CS)是一种基于信号的稀疏特性,将利用奈奎斯特采样定理的信号采样过程转化为基于优化计算恢复信号的观测过程的新兴信号处理方式,并广泛应用于信号/图像处理、医疗成像与无线通信等领域。基于压缩传感的电力系统信号分析与数据处理方法具有采样速率低、高压缩比,以及便于提取信号特征等优点,因而,在电力系统中具有广泛的应用前景。描述了压缩传感理论框架,并对该理论在电力系统信号分析与数据处理中的应用进行详细综述,其中主要围绕电能质量分析、故障分析、电力系统模态识别、电力系统预测、数据传输,以及智能电网等方面进行评述,并结合压缩传感在电力系统信号分析与数据处理领域的发展状况,对其发展前景进行展望。     

Measurement and processing of vibro-acoustic signal from the process of rock disintegration by rotary drilling

The paper is focused on methods aimed at processing of vibro-acoustic signal from the process of rock disintegration by rotary drilling. The idea is to use the measured accompanying vibro-acoustic signal emerging in the process of drilling as an integrating information resource. The process of rock disintegration by rotary drilling is among those technological processes which mathematical modeling based on the known laws of physics does not lead to satisfactory results. Here can be applied an empirical approaches that lead to a model applicable to some limited space. An important feature of the rock disintegration process is its relatively strong stochastic component of the signal. From the above, it is necessary to rise from the selection of suitable processing of measured signal. Measured accompanying vibro-acoustic signal is integrating information sources, containing some information on the nature and mode of the current rock drilling. This signal is explicitly represented in the time domain by its behavior of amplitudes or in the frequency domain by its spectrum. The information contained in this signal may be in the form of defined characteristics of signals in time or frequency domain.     

微波消解-电感耦合等离子体-原子发射光谱法测定剩余污泥中的全硫

采用微波消解技术,用HNO3-HCl-HF-H3BO3作为消解溶液,在110～100 ℃下将剩余污泥样品加热约40min,样品溶解后,用电感耦合等离子体-原子发射光谱法(ICP-AES)测定其中的全硫含量.方法的检出限为O.0084μg/mL,回收率为96.9%～105.3%,精密度为0.81%～2.39%.将本方法用于污泥中全硫的日常检测,有利于对剩余污泥作出科学的处理,防止对环境造成污染.     

采用马赫-曾德尔干涉法测量单晶硅在线应力损伤

开展了毫秒脉冲激光辐照单晶硅的实验研究,基于马赫-曾德尔干涉技术测量了毫秒脉冲激光与单晶硅相互作用过程中的在线应力损伤。用COMSOL Multiphysics有限元仿真软件建立了毫秒脉冲激光辐照单晶硅的数值仿真模型。从理论和实验两方面探讨了毫秒脉冲激光与单晶硅作用时,相同脉宽不同能量密度下应力场随时间的演变规律。进一步研究了干涉条纹的处理方法,基于传统x轴投影法提出了用45°投影法来计算材料各方向上的应变,并对两种处理方法得到的实验结果进行了对比。结果显示:与仿真结果相比,x轴投影法实验结果的误差为9.5%~29.3%,而45°投影法实验结果的误差为0.1%~22.6%,表明用马赫-曾德尔干涉法测量激光辐照单晶硅产生的在线应力损伤时,采用45°投影法计算材料各方向上的应变结果更为准确。该实验和计算方法为单晶硅在线应力损伤的研究提供了理论和实验上的指导。     

Comparison of heart rate variability (HRV) and nasal pressure in obstructive sleep apnea (OSA) patients during sleep apnea

In this study, a novel R wave detection algorithm was developed and used to analyze the heart rate variability (HRV) of obstructive sleep apnea patients with obstructive sleep apnea (OSA). The purpose of our study was to investigate the biosignal changes in the synchronization between HRV, nasal pressure, and the effect of OSA. HRV, nasal pressure, and sleep electroencephalogram (EEG) signals recorded in control and OSA patients with sleep apnea who were matched according to EEG arousal in OSA during sleep apnea. Experiment steps were completed for R–R interval calculation and to estimate its power spectral density (PSD) over several frequency ranges of apnea states (severe, moderate and mild). Patients with severe OSA had persistently longer R–R intervals compared to patients with mild OSA. As a measure of apnea classification accuracy, the algorithm correctly classified 99.7% of the evaluation database. An advantage of the proposed method is the combination of R wave detection techniques to enhance the accuracy of wave detection that is easily implemented with HRV verified by accurate classification and quantification.