Comparative analysis of power-line interference between two- or three-electrode biopotential amplifiers

Teaching Essential EMG Theory to Kinesiologists and Physical Therapists Using Analogies Visual Descriptions, and Qualitative Analysis of Biophysical Concepts

Electromyography (EMG) is a multidisciplinary field that brings together allied health (kinesiology and physical therapy) and the engineering sciences (biomedical and electrical). Since the physical sciences are used in the measurement of a biological process, the presentation of the theoretical foundations of EMG is most conveniently conducted using math and physics. However, given the multidisciplinary nature of EMG, a course will most likely include students from diverse backgrounds, with varying levels of math and physics. This is a pedagogical paper that outlines an approach for teaching foundational concepts in EMG to kinesiologists and physical therapists that uses a combination of analogies, visual descriptions, and qualitative analysis of biophysical concepts to develop an intuitive understanding for those who are new to surface EMG. The approach focuses on muscle fiber action potentials (MFAPs), motor unit action potentials (MUAPs), and compound muscle action potentials (CMAPs) because changes in these waveforms are much easier to identify and describe in comparison to the surface EMG interference pattern (IP).

Design of Smart Steering Wheel for Unobtrusive Health and Drowsiness Monitoring

This article describes the design of a smart steering wheel intended for use in unobtrusive health and drowsiness monitoring. The aging population, cardiovascular disease, personalized medicine, and driver fatigue were significant motivations for developing a monitoring platform in cars because people spent much time in cars. The purpose was to create a unique, comprehensive monitoring system for the driver. The crucial parameters in health or drowsiness monitoring, such as heart rate, heart rate variability, and blood oxygenation, are measured by an electrocardiograph and oximeter integrated into the steering wheel. In addition, an inertial unit was integrated into the steering wheel to record and analyze the movement patterns performed by the driver while driving. The developed steering wheel was tested under laboratory and real-life conditions. The measured signals were verified by commercial devices to confirm data correctness and accuracy. The resulting signals show the applicability of the developed platform in further detecting specific cardiovascular diseases (especially atrial fibrillation) and drowsiness.

Two-Electrode ECG for Ambulatory Monitoring with Minimal Hardware Complexity

This article introduces a two-electrode ground-free electrocardiogram (ECG) with minimal hardware complexity, which is ideal for wearable battery-powered devices. The main issue of ground-free measurements is the presence of noise. Therefore, noise suppression methods that can be employed for a two-electrode ECG acquisition system are discussed in detail. Experimental measurements of a living subject and patient simulator are used to investigate and compare the performance of the three proposed methods utilizing the ADS1191 analogue front-end for biopotential measurements. The resulting signals recorded for the simulator indicate that all three methods should be suitable for suppressing power-line noise. The Power Spectral Density (PSD) of the signals measured for a subject exhibits differences across methods; the signal power at 50 Hz is −28, −24.8, and −26 dB for the first, second, and third method, respectively. The digital postprocessing of measured signals acquired a high-quality ECG signal comparable to that of three-electrode sensing. The current consumption measurements demonstrate that all proposed two-electrode ECG solutions are appropriate as a battery-powered device (current consumption < 1.5 mA; sampling rate of 500 SPS). The first method, according to the results, is considered the most effective method in the suppression of power-line noise, current consumption, and hardware complexity.

IMPLEMENTATION OF MULTIPLE-CHANNEL CAPACITIVE ECG MEASUREMENT BASED ON CONDUCTIVE FABRIC

Capacitive electrocardiogram (cECG) measurement is an attractive approach for long-term health monitoring. However, there is little literature available for the implementation of multiple-channel cECG system in standard limb leads. The circuit diagram for such a system is also rarely available in literature. This paper presents a multiple-channel limb-lead cECG system that utilized conductive fabrics as the capacitive sensors. The design criteria and the corresponding circuit diagram are described in detail. The proposed system also incorporates the capacitive driven-body (CDB) circuit to reduce the common-mode power-line interference (PLI). The presented system is verified to be stable by theoretic analysis and long-term experiments. The signals acquired by the presented system are competitive with those by commercially available electrocardiogram (ECG) machines. The feasible size and distance to the subject for the sensor made by conductive fabric have also been evaluated by a series of tests. From the test results, the sensor is suggested to be of greater than 60 cm2 in area and not more than 3 mm in distance for cECG measurement.

Estimation of stray coupling capacitances in biopotential measurements

Biopotential measurements are very sensitive to electromagnetic interference (EMI) from power-lines. Interference conditions are mainly imposed by electric-field coupling, whose effects can be described by coupling capacitances. The main of them are the patient-to-ground and the patient-to-power-line capacitances, usually denoted as C(B) and C(P), respectively. A technique to estimate these elements and experimental data obtained in different environmental conditions are presented. It was found that C(B) ranges from hundreds of pF to nF, and C(P) from hundredths of pF to few pF. The presented technique also lets it know the small amplifier-to-ground and amplifier-to-power-line capacitances. The knowledge of all these capacitances allows estimating the EMI conditions that biopotential amplifiers can be subject to, thus, resulting useful data for specifying their design requirements and constraints in real working conditions.

Getting rid of the wires and connectors in physiological monitoring

One of the main limitations towards an easy-touse, comfortable, and reliable product for physiological monitoring comes from wires and associated connectors. Wireless solutions for data transmission are more and more common in every domain, but for biopotential and impedance measurements, at least one galvanic line will always be needed. This paper describes a new technology that can make possible the measurement of biopotentials and body impedances with high quality standard using only one wire. As this wire requires neither shield nor isolation, one can imagine a conductive garment that simply connects several sensors distributed over the body. From the user point of view, the product would be 'cableless'.

Two-Electrode Biopotential Measurements: Power Line Interference Analysis

In this paper, an analysis of power line interference in two-electrode biopotential measurement amplifiers is presented. A model of the amplifier that includes its input stage and takes into account the effects of the common mode input impedance Z(C) is proposed. This approach is valid for high Z(C) values, and also for some recently proposed low-Z(C) strategies. It is shown that power line interference rejection becomes minimal for extreme Z(C) values (null or infinite), depending on the electrode-skin impedance's unbalance deltaZ(E). For low deltaZ(E) values, minimal interference is achieved by a low Z(C) strategy (Z(C) = 0), while for high deltaZ(E) values a very high Z(C) is required. A critical deltaZ(E) is defined to select the best choice, as a function of the amplifier's Common Mode Rejection Ratio (CMRR) and stray coupling capacitances. Conclusions are verified experimentally using a biopotential amplifier specially designed for this test.

Real-time recording of neuropsychophysiological parameters during 50 Hz magnetic field exposure

In order to assess the possible effects of occupational levels of 50 Hz magnetic fields (MF) on human performance it is preferable to monitor performance during rather than subsequent to MF exposure. We previously reported studies of heart rate and cognitive behaviour where the issue of contamination was not a serious one. Our present study involves electrophysiological measures, which have a greater capacity to identify the effects and assist in localising them. The contamination of EEG signal by the MF exposure is clearly a problem in this type of study. Previous investigators have not reported these types of measurement concurrent with MF exposure due to the contamination difficulty; but this paper reports means of accomplishing this. Overall a combination of 12 methods for reducing pickup were employed. These were: 1) Distancing recording instruments from the MF source; 2) Shielding the devices and wiring; 3) Appropriate choice of cables; 4) Grounding the instrumentation; 5) Orientation of conduits; 6) Isolation of electrical mains power supplies; 7) Balancing the input impedances; 8) Applying a driven shield technique; 9) Improved electronics design incorporating pre-amplification and circuit impedance level control; 10) Analogue filtering; 11) Signal Averaging; and 12) Post acquisition digital filtering using frequency and time domain techniques.

A simple and effective process for noise reduction of multichannel cortical field potential recordings in freely moving rats

Simple and useful steps, i.e. placing a grounded plate under the recording chamber as well as using multiple reference electrodes, are introduced here for obtaining reliable low-noise recordings of brain activity in freely moving rats. A general circuit model was built to analyze the electrical interference of both single-grounded and two-reference ground-free recording configurations. In both simulated and realistic conditions under two recording states, 60-Hz magnitude was in the microvolt range. Moreover, the noise was significantly reduced by shortening the distance between the subject and the grounded plate under the recording chamber. Furthermore, in chronically implanted rats, average 60-Hz interference of multichannel electroencephalograms of two-reference ground-free recordings (3.74 +/- 0.18 microV) was significantly smaller than that of the single-grounded condition (9.03 +/- 1.98 microV). Thus, we demonstrated that a lower-noise recording can be achieved by a two-reference configuration and a closely-placed metal grounded plate in an open-field circumstance. As compared to the use of a Faraday cage, this simple procedure is of benefit for long-term behavioral tracking with a video camera and for pharmacological experiments.

Two-electrode biopotential amplifier with current-driven inputs

A circuit was developed for a differential two-electrode biopotential amplifier. Current sources at the amplifier inputs were controlled by the common-mode voltage. This principle is well known in telephony for interfacing the telephone line with analogue-type phones. A low impedance of about 1 k(ohm) was obtained between each input and the common point of the circuit. The differential input impedance of 60 M(ohm) was obtained with the use of precision resistors. Considerable reduction in the common-mode voltages of more than 200 times resulted. The circuit can be useful for biosignal acquisition from subjects in areas of very high electromagnetic fields, where high common-mode voltages could saturate the input amplifier stages.

Biopotential amplifier for simultaneous operation with biomagnetic instruments

A multichannel biopotential amplifier for simultaneous use with biomagnetic measurements in a magnetically shielded room is designed and evaluated. Particular care is taken to make the amplifier electromagnetically compatible with the biomagnetic instruments over the whole frequency spectrum, from DC to RF. The electromagnetically quiet environment allows the use of high electrode impedances; the preamplifier has been designed accordingly. Special care is taken to analyse the coupling mechanisms of mains interference to the amplifier. Over 170 simultaneous electric and magnetic recordings have been performed using the system in a hospital environment.