An efficient cardiac signal enhancement using time–frequency realization of leaky adaptive noise cancelers for remote health monitoring systems

Nowadays telecardiology is an important tool in cardiac diagnosis from a remote location. During Electrocardiogram (ECG) or Cardiac Signal acquisition several artifacts strongly affect the ST segment, degrade the signal quality, frequency resolution, produce large amplitude signals in ECG that can resemble PQRST waveforms and mask the tiny features that are important for clinical monitoring and diagnosis. So the extraction of high-resolution cardiac signals from recordings contaminated with artifacts is an important issue to investigate. In this paper, various novel block based time–frequency domain adaptive filter structures for cardiac signal enhancement are presented. These filters estimate the deterministic components of the cardiac signal and remove the noise component. The Block Leaky Least Mean Square (BLLMS) algorithm, being the solution of the steepest descent strategy for minimizing the mean squared error in a complete signal occurrence, is shown to be steady-state unbiased and with a lower variance than the LMS algorithm. To improve the filtering capability some variants of BLLMS, Block Normalized LLMS (BNLLMS) and Block Error Normalized LLMS (BENLLMS) algorithms are implemented in both time domain (TD) and frequency domains (FD). Finally, we have applied these algorithms on real cardiac signals obtained from the MIT-BIH data base and compared their performance with the conventional LLMS algorithm. The results show that the performance of the block based algorithms is superior to the LLMS counterparts in terms of signal to noise ratio improvement (SNRI), excess mean square error (EMSE) and misadjustment (M). Among all the algorithms FDBENLLMS achieves higher SNRI than other techniques. These values are 25.8713 dB, 20.1548 dB, 21.6718 dB and 20.7131 dBs for power line interference (PLI), baseline wander (BW), muscle artifacts (MA) and electrode motion artifacts (EM) removal.     

Development of an embedded system and MATLAB-based GUI for online acquisition and analysis of ECG signal

This paper illustrates a low-cost method for online acquisition of ECG signal for storage and processing using a MATLAB-based Graphical User Interface (GUI). The single lead ECG is sampled at a rate of 1 kHz and after digitization, fed to a microcontroller-based embedded system to convert the ECG data to a RS232 formatted serial bit-stream. This serial data stream is then transmitted to a desktop Personal Computer at a rate of 19.2 kbps and a state-of-the art developed software stores it automatically in a temporary data file. The original ECG data is reconstructed from the digital data set by a conversion formula. The MATLAB-based GUI is designed to perform online analysis on the ECG data to compute the different time-plane features and display the same on the GUI along with the ECG signal plot.     

A system for gas sensing employing correlation spectroscopy and wavelength modulation techniques with a multimode diode laser

A tunable multi-mode diode laser system based on correlation spectroscopy and wavelength modulation spectroscopy (TMDL–COSPEC–WMS) is designed and demonstrated for the concentration measurements of oxygen using A-band absorption lines of oxygen around 760 nm. The O₂ concentrations are conversed from the relation between the normalized WMS-2f signal peak heights of the measurement and reference signals which selected based on high signal to noise ratio and correlation coefficient. The correlation and the fitted slope between the measured and actual O₂ concentration are 0.9987 and of 1.025 ± 0.012 respectively over the tested range, which indicate the high linearity and accuracy of the system. A sensitivity of 350 ppm m is approved using 30 successive measurements with each measurement time taking ∼20 s during 30 min. A continuous measurement for oxygen in ambient air during approximately 200 min confirms the stability and the capability of the system.     

A novel approach for realization of primary vibration calibration standard by homodyne laser interferometer in frequency range of 0.1 Hz to 20 kHz

The paper discusses the primary vibration calibration standard of NPL, India capable of calibrating the reference accelerometers in frequency range from 0.1 Hz to 20 kHz as per ISO 16063-11. The excitation subsystem produces constant vibration at a specified amplitude and frequency, while the measurement system uses NI interface for measuring the quadrature output. The acceleration level and voltage level at the calibration frequency f is determined by applying a Discrete Fourier Transform to the voltage and displacement signals, and then examining the spectral component at frequency f. A PC-based data acquisition system acquires the accelerometer voltage signal and analog quadrature interferometer photodetector signal pair as well as a digital quadrature pair whereby the software processes the demodulated photodetector signals to reconstruct the armature displacement. The validation of the calibration results for standard reference accelerometers with manufacturer results and uncertainty in calibration in entire frequency range 0.1 Hz to 20 kHz is reported in the present work.     

用于心电信号的能量最大化模拟信息转换系统

现有便携式心电采集系统需要低功耗高分辨率的模拟数字转换模块,虽然基于脉冲宽度调制的模拟信息转换器(AIC)可以有效降低系统的采样速率,但是该系统量化部分的转化时钟与量化精度成正比,因此存在功耗过高的问题.依据心电信号的能量不均衡特性,提出一种基于功率熵的精度可调时间-数字转换模块(TDC)设计方法.以能量最大化作为设计...     

A microcontroller-based variable voltage variable frequency sinusoidal power source with a novel PWM generation strategy

The present paper describes the development of a low cost, microcontroller-based variable voltage variable frequency sinusoidal power source, which is the demand of the day for various applications. The power source is developed using MOSFET H-bridge inverter and with a stand alone LCD display system. The design methodology proposes to utilize a novel concept of generating sinusoidal pulse width modulation signals for the driver circuit of the inverter. The system proposes to incorporate a ROM-based LUT within the power source itself for the sinusoidal signal generation with enhanced stability. This low cost, yet accurate power source has been successfully developed for wide range of voltage commands (30-80 V rms) and frequency commands (40-70 Hz), and their real-life performances in voltage wave generation were also found to be quite satisfactory.     

Miniature low-power IR monitor for methane detection

A portable methane gas monitor based on an infrared spectrum absorption principle has been developed using a dual-channel and dual-wavelength pyroelectric infrared detector, active filters around the overtone absorption lines of methane at 3.31 μm, reference filters around the non-absorption lines of methane at 3.93 μm, mid-IR LEDs, a miniature gold-filled cell structure, temperature sensors for gas concentration calibration and compensation, an electrical modulation source, and a highly integrated intelligent controller. A detailed investigation has been carried out to design a low-cost portable IR optical sensor for methane detection that can operate in harsh environments with temperature variations between −10 °C and 40 °C. The infrared detection optics principle used in developing this system is mainly analyzed. A prototype based on this design showed an accuracy of ±0.05%, which meets the technology requirements of lower-power consumption, reduced volume, and wide measurement range.     

电容耦合非接触电极及心电信号获取

电极与皮肤间接触所导致的不适感,是穿戴式心电信号测量系统实际应用中的常见问题。设计了一种非接触心电信号测量系统。采用印刷电路板制作的测量电极,借助电容耦合测量位移电流的方式获取心电信号。采用反接二极管提供测量所需的高阻值偏置电阻,结合高输入阻抗仪表放大器,制作了测量电极信号提取电路。测量系统由两个测量电极与一个直接与测量电路地相连的参考电极组成。选择金属铝板、导电纤维和导电橡胶作为参考电极,实验研究了共模干扰抑制性能与参考电极接触阻抗之间的量化关系。将主元分析与奇异谱分析相结合,提出了一种心电信号处理算法。实验结果表明,该系统可在棉质线衣外侧有效获得满意的心电信号。     

Thrust bearing groove race defect measurement by wavelet decomposition of pre-processed vibration signal

Nature of vibration signal from a ball bearing system reveals location of fault and its severity. A proper signal processing technique is required to extract relevant information from a vibration signal. In this work measurement of groove race defect width in thrust bearing is presented by processing vibration signal using wavelet based technique. In the first step, pre-processing of vibration signal is done by multiplying the signal amplitude with its own absolute values. It helps to overcome the problem of detection of weak burst in normal vibration signal retaining sign of the original signal. In the second step, Symlet5 wavelet based decomposition is applied to the pre-processed signal to measure the size of seeded defect in outer groove race of thrust bearing. The decomposition based on Symlet wavelet is preferred because it reduces the ambiguity in detecting the entry point and exit point of the defect as it is having linear phase in nature. Measurement has been done for the groove defect width over the range of 0.4399–1.4854 mm. Measurement of defect has been also verified using image examination. Maximum deviation in result has been found in the cases which have minimum axial load (48 N) for every size of defect. With increase in axial load to 73 N and further to 98 N the bearing system gets properly stressed, which increases the accuracy of measurement. With further increase in axial load to 126 N and above, it has been observed that the burst disappears due to prevailing over-stressed condition of the loading disk and additional stiffness and damping of the flexible shaft at increased load.     

低功耗便携式加速度信号记录仪的研制

在详细介绍了Freescale高集成度三轴加速度传感器芯片MMA7260工作原理的基础上,提出了一种以MMA7260为传感器,以TI公司低功耗处理器MSP430F149为控制核心,以SD卡为大容量存储设备的低功耗便携式加速度信号记录仪的软硬件设计方案,实现了人体日常活动时加速度信号的动态采集和实时记录,并且将加速度信号以文件的形式存储在SD卡中,便于上位机的读取和进一步分析。最后对该系统进行了实验分析,分析结果表明,所设计的便携式加速度信号记录仪可以准确地捕获人体行走时产生的三维加速度信号。     

A Two-Channel Recorder of Single Signals with a 400-MHz-Sampling Frequency

A two-channel signal recorder with a 200-MHz-sampling frequency (with two channels) or 400-MHz-sampling frequency (with one channel) is described. The number of bits is eight, the total storage size is 256 Kbyte, the input signal is 1 V, and the input is matched to a 50- line. The recorder is made in the form of a computer PCI card and is intended to record fast processes in the interaction of laser pulses and gases. Block diagrams of the recorder and test results are given.     

Design of a Three-Lead Synthetic ECG Generator Using the Simplified McSharry's Model

Abstract

Recently, due to the dramatic improvement in computing capabilities and processing speed of microcontrollers and digital signal processors, many analytic algorithms for electrocardiograms (ECGs) have been developed and applied to a variety of portable electronic devices. In order to test whether the algorithms can analyze the various morphologies of electrocardiogram well, it is necessary to expend much effort collecting various ECG samples to establish an ECG database. Therefore, this paper simplifies and adopts a synthetic electrocardiogram model composed of three coupled differential equations proposed by Dr. McSharry et al. (2003), as well as utilizes an improved fourth-order Taylor series to quickly approximate the exponential function within the differential equation of a simplified synthetic ECG model so that, when studying ECG analytic algorithms, the graphical user interface (GUI) application “Synthetic Waveforms Control Panel,” developed by the author using LabVIEW, can be used to attain the desirable morphology of electrocardiogram as well as the time intervals between peaks (P, Q, R, S, T) and heart rate. The parameters of the adjusted synthetic ECG model are then sent to the memory of a synthetic ECG generator through a USB interface, and the ECG generator will generate three synthetic electrocardiograms of Einthoven's triangle for testing the electrocardiogram analytic algorithms.     

A portable wireless biometric multi-channel system

This article presents an 8-channel system for capturing bioelectric signals and transmitting them by the ZigBee protocol. It is a small, portable system with optimised power supply so that it can be battery fed. One of its main advantages is its versatility, since it enables each channel to be configured, in a dynamic and individualised way. This makes it possible to capture diverse bioelectric signals simultaneously, such as electrocardiogram (ECG), electroencephalogram (EEG), electrooculogram (EOG), etc. The developed system can be easily integrated into a Wireless Sensor Network based on ZigBee technology.     

基于分布计算的心电特征波检测算法研究

体外反搏装置依据心电信号对下肢进行加压及释放,需要识别率高、实时性强的心电特征波检测方法。 借鉴传统医学 信号处理方法,本文提出一种基于改进差分阈值和分布计算的心电特征信号检测算法,采用低通滤波和移动平均滤波等预处理 方法对心电信号进行平滑预处理,借助自适应差分双阈值法和分布计算法,识别和确定 R 波、P 波及 T 波的位置。 基于 MITBIH 数据库及心电采样模块进行仿真分析和实验验证。 结果表明:该算法对心电信号 R 波的综合识别准确率为 99. 9% ,识别 P 波和 T 波准确率为 99. 87% ,算法平均耗时仅为 0. 65 s,可识别常见类型心电信号特征波,能很好地满足体外反搏等装置快速识 别心电特征波的需求。     

Method, algorithm and device for estimation of components above the harmonic frequency range up to 9 kHz

The paper presents a method of estimation of frequency groups with 200 Hz bandwidth in the frequency range from the 50th harmonic up to 9 kHz. The method consists of the application of a fast Fourier transform (FFT) for wavelet coefficients after input signal decomposition and partial synthesis for chosen frequency bands. It enables the computational complexity of the algorithm to be reduced and also attenuates influence of the fundamental component and low-frequency harmonics, as required by IEC Standard 61000-4-7. The particulars of this method are shown and analysis for a chosen wavelet family is provided. Further, the algorithm and its implementation in real device for power quality monitoring is presented. Finally, the results of measurements of two testing signals are shown. The required attenuation of fundamental component and required accuracy was obtained.     

An experimental study on the concrete hydration process using Fabry–Perot fiber optic temperature sensors

This paper describes the contribution of Fabry–Perot (FP) fiber optic temperature sensor to investigate the effects of concrete hydration process. The FP temperature sensor was easily fabricated by controllable chemical etching and adjustable fusion splicing. Detailed optical properties of the sensor were theoretically analyzed and temperature calibration experiments were performed. A sensor with a 90 μm cavity length was demonstrated to have a temperature sensitivity of 0.01 nm/°C and the linearity coefficient of 0.99. Furthermore, the FP sensor was embedded in the concrete structure for sensing the temperature change during the early age of hydration. During the concrete hydration experiments, the measured peak temperatures of the concrete specimens with different water-to-cement (w/c) ratios of 0.4, 0.5 and 0.6 were 51.42 °C, 52.88 °C, and 55.08 °C, respectively, corresponding to final setting times of 13.52 h (w/c = 0.4), 14.16 h (w/c = 0.5) and 15.2 h (w/c = 0.6) after concrete casting. Temperature profiles will be used for concrete hydration heat study, which will help us to have a better understanding of cement hydration behavior.     

Measurements of dimensional standards and etalons with feature size from tens of micrometres to millimetres by using sensor strengthened nanomeasuring machine

A laser focus sensor and a contact inductive sensor have been coupled to an ultra high precision positioning stage, referred to as a nanomeasuring machine (NMM), for measurements of dimensional standards with a large measurement volume of 25 mm × 25 mm × 5 mm. Control and measurement software have been designed and complemented. The measurement uncertainty of strengthened NMM has been analyzed and discussed. Groove depth and step height standards with feature heights of tens of micrometres to millimetres as well as aspherical surface etalons are calibrated by nanomeasuring machine. The paper also introduces a method for characterising the measured aspheric surface by least square fitting the measured data to a quadratic paraboloid function. The obtained quadratic coefficients are compared to that measured by a conventional coordinate measuring machine (CMM) and a stylus profiler, showing a good agreement.     

Design of product polar quantizers for A/D conversion of measurement signals with Gaussian distribution

In this paper, a design of product polar quantizers for A/D (analog-to-digital) conversion of measurement signals and an analysis of their performances in the wide range of variances are considered, in a general manner, i.e. for any compression function. Special attention is devoted to the design of robust product polar quantizers, applying the developed theory on μ-law logarithmic compression function, which is very important since a lot of measurement signals are nonstationary. The proposed quantizers achieve much better performances than scalar quantizers (they have higher the maximal SQNR (signal-to-quantization noise ratio) for about 2.5 dB and they are more robust), without increasing of complexity. Theory is proved by simulation. These quantizers can be applied for many different types of measurement signals and can be used in many measurement systems (telemetry, telemedicine, wireless sensor networks, etc.).     

Development of high-precision micro-coordinate measuring machine: Multi-probe measurement system for measuring yaw and straightness motion error of XY linear stage

Today, with the development of microsystem technologies, demands for three-dimensional (3D) metrologies for microsystem components have increased. High-accuracy micro-coordinate measuring machines (micro-CMMs) have been developed to satisfy these demands. A high-precision micro-CMM (M-CMM) is currently under development at the National Metrology Institute of Japan in the National Institute of Advanced Industrial Science and Technology (AIST), in collaboration with the University of Tokyo. The moving volume of the M-CMM is 160 mm × 160 mm × 100 mm (XYZ), and our aim is to achieve 50-nm measurement uncertainty with a measuring volume of 30 mm × 30 mm × 10 mm (XYZ). The M-CMM configuration comprises three main parts: a cross XY-axis, a separate Z-axis, and a changeable probe unit. We have designed a multi-probe measurement system to evaluate the motion accuracy of each stage of the M-CMM. In the measurement system, one autocollimator measures the yaw error of the moving stage, while two laser interferometers simultaneously probe the surface of a reference bar mirror that is fixed on top of an XY linear stage. The straightness motion error and the reference bar mirror profile are reconstructed by the application of simultaneous linear equations and least-squares methods. In this paper, we have discussed the simulation results of the uncertainty value of the multi-probe measurement method using different intervals and standard deviations of the laser interferometers. We also conducted pre-experiments of the multi-probe measurement method for evaluating the motion errors of the XY linear stage based on a stepper motor system. The results from the pre-experiment verify that the multi-probe measurement method performs the yaw and straightness motion error measurement extremely well. Comparisons with the simulation results demonstrate that the multi-probe measurement method can also measure the reference bar mirror profile with a small standard deviation of 10 nm.