Real time microprocessor-based 50 Hz notch filter for ECG

High performance analogue notch filters are difficult to realize in practice. Their real time digital counterparts, when implemented on an inexpensive microprocessor with no additional hardware, also have limitations of their own. To overcome these limitations, we have developed a new type of 50 Hz notch filter with its poles close to the zeros of the transfer function 1 + Z^−N. This new type of digital notch filter can be used for suppression of 50 Hz noise in the ECG. The filter is simple to design and easy to implement on most 8-bit microprocessors. It has a high execution speed, low analogue to digital noise, low recursive noise and good frequency response with no overshoot or ringing. It is capable of suppressing 50 Hz noise by at least 40 db. Its finite bandwidth of 4 Hz causes about 2% attenuation on the QRS peak, which is acceptable for almost all practical applications. One possible drawback is that multiple notches occur at higher frequencies. However, this has hardly any effect on the ECG because of the limited notch bandwidth.     

A simple program for a phaseless recursive digital filter

A brief comparison of several types of digital filters is made and a simple subroutine implementing a recursive digital phaseless low and high pass filter is described. The subroutine, written in standard Fortran, is suitable for any computer with a Fortran IV compiler.     

Short latency somatosensory and spinal evoked potentials: Power spectra and comparison between high pass analog and digital filter

Medium nerve somatosensory evoked potentials (SSEPs) and intraoperative spinal evoked potentials were analyzed using different analog and zero phase shift digital high pass filter and by power spectrum. Additionally, high pass analog and digital filtering was performed on various sine, triangular and rectangular waves manufactured by a wave form generator. Recordings were also transformed to the 1st and 2nd time derivatives.The great abundance of spectral energy for scalp recorded median nerve SSEPs was below 125 c/sec but lower energy fast frequency components consistently extended to 500 c/sec. Power spectrum of the Erb's point compound nerve action potential revealed a wide band of spectral energy commencing at about 50–100 c/sec, peaking at about 250–270 c/sec and extending to nearly 1000 c/sec. This suggests that synchronous axonal activity generates predominantly faster frequencies above 100 c/sec.High pass analog filter confers phase non-linearity which results in various distortions including latency shift and a morphological change which may be visually similar to the 1st or 2nd time derivatives. High pass zero phase shift digital filter removes selected low frequencies without accompanying phase distortion. This accentuates fast peaks seen at open bandpass as well as transition points between baseline and component ascent or descent. Zero phase shift digital filter may also generate peaks that are not visualized at open pass but which reflect the sum of frequencies which were not removed by filtering. These peaks do not necessarily correspond to discrete singular neuroanatomical structures.Although peaks observed in high pass analog and digital filter appear similar and comparable, their underlying activity may be of different origin. This is because high pass analog filter projects a considerable amount of overlap from earlier onto later waves.For clinical correlation it is important that restricted bandpass analog or digitally filtered recordings be compared with open pass data. Only those peaks visualized in both open and restricted bandpass can be considered authentic. Examples of spinal and scalp SSEPs indicate that selective filtering may, under certain circumstances, distinguish axonal or lemniscal from synaptic generators.     

基于FPGA 超声信号数字动态滤波器的实现

目的:本文研究了基于现场可编程门阵列(Field Programmable Gate Array,FPGA)超声成像系统中数字动态滤波器的实现方法和过程。方法:动态滤波器中FIR滤波器采用分布式算法(Distributed Arithmetic,DA)实现结构,并在应用中对DA算法进行了改进,包括数据并行处理结构的设计、对查找表(Look Up Table,LUT)输入字长N大小的控制和具有对称系数的FIR滤波器的采用。改进后的DA实现在FPGA资源占用和处理速度之间达到了平衡。同时,结合多级流水线结构,动态滤波器实现了数字超声信号并行处理。结果:采用常值滤波器(远场匹配参数)进行滤波后,超声回波图像远场分辨率达到了要求,但越靠近近场效果越差。相比之下,本文设计的基于FPGA超声信号动态数字滤波器达到了很好的滤波效果,使回声图像近场和远场都有最佳分辨率。结论:利用FPGA实现超声系统中动态滤波器是完全可行的,并且有助于提高系统的稳定性和可靠性,并大大减低系统成本。     

A general solution for the time delay introduced by a low-pass Butterworth digital filter: An application to musculoskeletal modeling

Low-pass Butterworth digital filters are commonly used in biomechanics-related research. In general, the input signal is filtered in the forward and reverse directions so that a temporal shift in the output signal does not occur. There are times, however, when introducing a specific time delay is an important consideration when modeling a physiological event. Filtering the data in the forward direction only can be used as an efficient method to account for a specific time delay. Specific delays are possible by carefully selecting the filter order and cut-off frequency. The purpose of this paper is to present the analytical formulation of a general solution for the time delay introduced by a low-pass Butterworth digital filter.     

The influence of digital filter type,amplitude normalisation method,and co-contraction algorithm on clinically relevant surface electromyography data during clinical movement assessments

There is a large and growing body of surface electromyography (sEMG) research using laboratory-specific signal processing procedures (i.e., digital filter type and amplitude normalisation protocols) and data analyses methods (i.e., co-contraction algorithms) to acquire practically meaningful information from these data. As a result, the ability to compare sEMG results between studies is, and continues to be challenging. The aim of this study was to determine if digital filter type, amplitude normalisation method, and co-contraction algorithm could influence the practical or clinical interpretation of processed sEMG data. Sixteen elite female athletes were recruited. During data collection, sEMG data was recorded from nine lower limb muscles while completing a series of calibration and clinical movement assessment trials (running and sidestepping). Three analyses were conducted: (1) signal processing with two different digital filter types (Butterworth or critically damped), (2) three amplitude normalisation methods, and (3) three co-contraction ratio algorithms. Results showed the choice of digital filter did not influence the clinical interpretation of sEMG; however, choice of amplitude normalisation method and co-contraction algorithm did influence the clinical interpretation of the running and sidestepping task. Care is recommended when choosing amplitude normalisation method and co-contraction algorithms if researchers/clinicians are interested in comparing sEMG data between studies.     

耳蜗滤波器设计

提出了一种非线性耳蜗滤波器组的设计方法,设计的耳蜗滤波器组结构简单,易于实现,能模拟因输入信号电平的不同而引起的耳蜗滤波器的非线性特性,而且其特征参数能随着更新实验结果的出现灵活地加以修正。文中给出了设计细节以及具体的数字实现方法。     

Digital IIR filters design using differential evolution algorithm with a controllable probabilistic population size

Design of a digital infinite-impulse-response (IIR) filter is the process of synthesizing and implementing a recursive filter network so that a set of prescribed excitations results a set of desired responses. However, the error surface of IIR filters is usually non-linear and multi-modal. In order to find the global minimum indeed, an improved differential evolution (DE) is proposed for digital IIR filter design in this paper. The suggested algorithm is a kind of DE variants with a controllable probabilistic (CPDE) population size. It considers the convergence speed and the computational cost simultaneously by nonperiodic partial increasing or declining individuals according to fitness diversities. In addition, we discuss as well some important aspects for IIR filter design, such as the cost function value, the influence of (noise) perturbations, the convergence rate and successful percentage, the parameter measurement, etc. As to the simulation result, it shows that the presented algorithm is viable and comparable. Compared with six existing State-of-the-Art algorithms-based digital IIR filter design methods obtained by numerical experiments, CPDE is relatively more promising and competitive.     

The design of digital filters for biomedical signal processing Part 2: Design techniques using the z-plane

Design methods for digital filters using z-plane techniques are developed out of the basic concepts described in part 1. The relationship between impulse response shape and side lobe generation in the frequency response is investigated by means of rectangular, triangular and cosine window filters. The limited choice of cut-off frequencies available for simple linear phase digital filters is explained. Design direct from the frequency domain is summarized. z-plane techniques for the design of high- and band-pass digital filters and the digital equivalents of analogue filters are described. s-plane to z-plane mapping by means of the Bilinear transformation is compared to the direct z-transform method of filter design.     

Abundance estimation of rocky shore invertebrates at small spatial scale by high-resolution digital photography and digital image analysis

We have tested both the usefulness of high-resolution digital photography for data acquisition and digital image analysis, by non-supervised classification and high pass filter, for recognition and abundance estimation of benthic intertidal organisms. These digital tools were compared with visual scan and photo quadrat conventional methods. The comparison was done using 40 quadrats (10×5 cm) randomly selected along a 5-m transect on the rocky shore of the Pemaquid Point, Maine, USA. ANOVA for repeated measures was used to test differences among methods. Monte Carlo simulation analysis was used to explore differences among methods over a large set of data (n=100, 500, 1000 quadrats). Differences among methods were observed when 40 quadrats were used. Tukey multiple comparison test showed that abundance estimation from visual scan, photo quadrat and digital image analysis by high pass filter do not differ significantly among them but differ from non-supervised classification results. Due to its accurate estimation, high pass filter (Prewitt) method was chosen as the most reliable digital method to estimate species abundance. Monte Carlo simulation of visual scan, photo quadrat and high pass filter results showed significant differences when the number of quadrats was larger. These results showed that the combined use of digital photography and digital image analysis techniques for the acquisition and analysis of recorded data is a powerful method for the study of intertidal benthic organisms. Results produced using these techniques were similar than those produced by conventional methods but were obtained in a much-reduced time.     

基于PC声卡的生物医学电信号采集方法

把生物医学电信号以线性调幅的方法调制在音频载波信号之上,用PC声卡采集该已调波信号,用软件实现调幅波的解调,经数字低通滤波器的滤波,恢复出生物医学电信号,达到采集和显示生物医学电信号的的目的。实践证明,该方法具有成本低、多通道工作实时性好的特点,具有实用价值。     

CMOS microelectrode array for the monitoring of electrogenic cells

Signal degradation and an array size dictated by the number of available interconnects are the two main limitations inherent to standalone microelectrode arrays (MEAs). A new biochip consisting of an array of microelectrodes with fully-integrated analog and digital circuitry realized in an industrial CMOS process addresses these issues. The device is capable of on-chip signal filtering for improved signal-to-noise ratio (SNR), on-chip analog and digital conversion, and multiplexing, thereby facilitating simultaneous stimulation and recording of electrogenic cell activity. The designed electrode pitch of 250 microm significantly limits the space available for circuitry: a repeated unit of circuitry associated with each electrode comprises a stimulation buffer and a bandpass filter for readout. The bandpass filter has corner frequencies of 100 Hz and 50 kHz, and a gain of 1000. Stimulation voltages are generated from an 8-bit digital signal and converted to an analog signal at a frequency of 120 kHz. Functionality of the read-out circuitry is demonstrated by the measurement of cardiomyocyte activity. The microelectrode is realized in a shifted design for flexibility and biocompatibility. Several microelectrode materials (platinum, platinum black and titanium nitride) have been electrically characterized. An equivalent circuit model, where each parameter represents a macroscopic physical quantity contributing to the interface impedance, has been successfully fitted to experimental results.     

便携式心电监护中实时信号处理方法研究

针对心电信号处理过程中的心电信号数字滤波、心电波形的动态显示、心电数据存储等问题,阐述了3个可用于心电信号实时处理的方法：一是运用滤波器频谱的周期性减少了滤波器系数个数,提高了运算速度,并根据卷积公式特点实现了数字滤波的实时性;二是运用基于内存虚拟屏幕技术实现心电波形动态显示,解决了屏幕闪烁和绘图不连续问题;三是采用嵌入式数据库SQLITE实现了心电数据存储。所有方法均考虑实时性要求,并已成功用于课题组开发的便携式心电监护仪,效果较为理想,具有很强的实用价值。     

A model-free method for mass spectrometer response correction

A new method for correction of mass spectrometer output signals is described. Response-time distortion is reduced independently of any model of mass spectrometer behavior. The delay of the system is found first from the cross-correlation function of a step change and its response. A two-sided time-domain digital correction filter (deconvolution filter) is generated next from the same step response data using a regression procedure. Other data are corrected using the filter and delay. The mean squared error between a step response and a step is reduced considerably more after the use of a deconvolution filter than after the application of a second-order model correction. O2 consumption and CO2 production values calculated from data corrupted by a simulated dynamic process return to near the uncorrupted values after correction. Although a clean step response or the ensemble average of several responses contaminated with noise is needed for the generation of the filter, random noise of magnitude less than or equal to 0.5% added to the response to be corrected does not impair the correction severely.     

A sterile, regulated, pulsation-dampened precision dosing system for biomedical technics

For sterile continuous metering of small and very small flow rates delivered by peristaltic pump, a gravimetric control system which permits a high accuracy of mass flow is described. This is achieved by a digital PI controller and a digital filter with which the very accurate signal from a high precision electronic scale is filtered. In addition proposals are made for solving the problem of refilling the reservoir and for compensating the pulsations caused by the peristaltic pump.     

Improving surface EMG burst detection in infrahyoid muscles during swallowing using digital filters and discrete wavelet analysis

The visual inspection is a widely used method for evaluating the surface electromyographic signal (sEMG) during deglutition, a process highly dependent of the examiners expertise. It is desirable to have a less subjective and automated technique to improve the onset detection in swallowing related muscles, which have a low signal-to-noise ratio. In this work, we acquired sEMG measured in infrahyoid muscles with high baseline noise of ten healthy adults during water swallowing tasks. Two methods were applied to find the combination of cutoff frequencies that achieve the most accurate onset detection: discrete wavelet decomposition based method and fixed steps variations of low and high cutoff frequencies of a digital bandpass filter. Teager-Kaiser Energy operator, root mean square and simple threshold method were applied for both techniques. Results show a narrowing of the effective bandwidth vs. the literature recommended parameters for sEMG acquisition. Both level 3 decomposition with mother wavelet db4 and bandpass filter with cutoff frequencies between 130 and 180 Hz were optimal for onset detection in infrahyoid muscles. The proposed methodologies recognized the onset time with predictive power above 0.95, that is similar to previous findings but in larger and more superficial muscles in limbs.     

A rapid algorithm for processing digital physiologic signals: Application to skeletal muscle contractions

Quantifying mechanical output is fundamental to understanding metabolism that fuels muscle contraction and more recent attempts to understand signal transduction and gene regulation. The latter requires long-term application of exercise protocols that result in large amounts of data on muscle performance. The purpose of this study was to develop software for automated quantification of skeletal muscle contractions. An in situ mouse sciatic nerve stimulation model was used to produce contractions over a broad range of frequencies and recorded as both digital and analog signals using a PC analog to digital converter board and chart recorder, respectively. Spectral analysis of the noise components formed the basis for designing a smoothing Chebyshev filter. Algorithms implemented in custom software identified twitches and estimated baseline levels from the smoothed signal. The time to peak force, peak force, tension-time integral, and half-relaxation time were determined for each twitch after baseline correction. The automated results were compared to those obtained from manual measurements of the analog signal. Bland–Altman analysis of the parameters computed from digital signals compared with the corresponding measurements by manual planometry demonstrates the agreement of the digital processing algorithm with planometry over a wide range of twitch characteristics. This program may also be used to study the mechanics of other preparations from isolated muscles, human proximal limb performance, and other digital physiologic signals. Adaptation of the filter function is required to apply the analysis to another experimental apparatus with differing noise characteristics. A full version of the program and instructions for its use are available for download at www.rad.msu.edu.     

AUDIO COMPUTERS—THEORY OF OPERATION AND GUIDELINES FOR SELECTION OF SYSTEMS AND COMPONENTS

ABSTRACT

Computers are available that can store, synthesize and replay sounds using digital technology. I describe the major components of audio computers, the principles of digital sound acquisition and playback, and information and caveats for scientists interested in acquiring an audio computer system for their own use. A tutorial on analog filter application is also included as well as a diagnostic procedure and a buyer's check list.     

Compact digital storage of ECG's.

The technique of predictive coding is applied to the problem of reversible compression of digitized electrocardiograms. Integer-based predictors and MMSE predictors are studied as regards performance at varying sampling rates and digital resolutions for both long-term ECGs and ECGs recorded at rest. It is concluded that MMSE predictors are to be preferred only in the case when the ECG is oversampled (i.e., the sampling rate is much higher than twice the cut-off frequency of the presampling filter). In other cases the integer predictor which yields the so-called 2nd differences is superior. The problem of encoding the resulting residuals with a variable-length code is studied for long-term ECGs digitized at 100 Hz and using 8 bits digital resolution. The code has a simple struture leading to speed of execution while the efficiency loss is small.