Electrode-skin Contact Research Articles

Development and Evaluation of 3D‐Printed Dry Microneedle Electrodes for Surface Electromyography

AbstractSurface electromyography (sEMG) allows for direct measurement of electrical muscle activity with use in fundamental research and many applications in health and sport. However, conventional surface electrode technology can suffer from poor signal quality, requires careful skin preparation, and is commonly not suited for long‐term recording. These drawbacks have challenged translation of sEMG to clinical applications. In this paper, dry 3D‐printed microneedle electrodes (MNEs) are proposed to overcome some of the limitations of conventional electrodes. Employing a direct‐metal‐laser‐sintering (DMLS) 3D printing process, a two‐step fabrication method is developed to produce sharp medical‐grade stainless steel MNEs. The developed MNEs are compared to needle‐free versions and to standard wet Ag/AgCl electrodes. Functional testing is conducted to analyze the electrode–skin impedance in healthy human volunteers and sEMG data are recorded from the biceps brachii muscle. Results show that microneedle electrodes display a greatly reduced (≈63%) electrode–skin contact impedance with respect to needle‐free electrodes and record sEMG at a signal‐to‐noise ratio comparable to clinical‐grade wet Ag/AgCl electrodes over a period of up to 6 h. Overall, a fabrication method and electrode type are presented which yield high‐quality sEMG signals when evaluated in humans, highlighting the potential of MNEs as a platform for biosignal recording.

Electrode Placement Strategies for the Measurement of Radial Artery Bioimpedance: Simulations and Experiments

Continuous cardiac output is a significant matter that must be considered in monitoring the functioning of cardiovascular system. A noninvasive sensing system that is based on measuring electrical bioimpedance variations of radial artery is proposed to evaluate the physical condition of a patient. To optimize the signal acquisition, different electrode placement strategies are compared with the goal of finding the most suitable ones. The finite-element method (FEM) simulation of sensitivity distribution and experimental measurements on radial artery are performed for experimenting circular and distal electrode placements. Importantly, also the modified electrode placement strategies, guided by the idea of focused impedance method (FIM), are investigated. To reduce the number of electrodes in measurement setup, its novel version is proposed: a five-electrode FIM strategy. The efficiency of the proposed strategy can be seen in the reduced amount of required number of electrodes: the smaller area of electrode-skin contact interface results in smaller influence of uncertainties. Moreover, the reduced number of electrodes contributes to benefit through developing simpler instrumentation having lower energy consumption and cheaper manufacturing costs. The results show the advances of the proposed novel five-electrode FIM strategy for measuring the pulsating volume of blood in radial artery with the goal of determining the central aortic pressure (CAP) of blood.

Adaptive Spatial Filtering of High-Density EMG for Reducing the Influence of Noise and Artefacts in Myoelectric Control.

Electromyography (EMG) is a source of neural information for controlling neuroprosthetic devices. To enhance the information content of conventional bipolar EMG, high-density EMG systems include tens to hundreds of closely spaced electrodes that non-invasively record the electrical activity of muscles with high spatial resolution. Despite the advantages of relying on multiple signal sources, however, variations in electrode-skin contact impedance and noise remain challenging for multichannel myocontrol systems. These spatial and temporal non-stationarities negatively impact the control accuracy and therefore substantially limit the clinical viability of high-density EMG techniques. Here, we propose an adaptive algorithm for automatic artefact/noise detection and attenuation for high-density EMG control. The method infers the presence of noise in each EMG channel by spectro-temporal measures of signal similarity. These measures are then used for establishing a scoring system based on an adaptive weighting and reinforcement formulation. The method was experimentally tested as a pre-processing step for a multi-class discrimination problem of 4-digit activation. The approach was proven to enhance the discriminative information content of high-density EMG signals, as well as to attenuate non-stationary artefacts, with improvements in accuracy and robustness of the classification.

Development of medical capacitive coupling electrodes using the skin-electrode contact control

PurposeThe purpose of this paper is the development and study of capacitive coupling electrodes with the ability to monitor the quality of the skin–electrode contact in the process of electrocardiogram (ECG) diagnostics. The study’s scope embraces experimental identification of distortions contributed into the recorded ECG signal at various degrees of disturbance of the skin–electrode contact.Design/methodology/approachA capacitive coupling electrode is designed and manufactured. A large number of experiments was carried out to record ECG signals with different quality of the skin–electrode contact. Using spectral analysis, the characteristic distortions of the ECG signals in the event of contact disturbance are revealed.FindingsIt was found that the violation of the skin–electrode contact leads to significant deterioration in the recorded signal. In this case, the most severe distortions appear with various violations of the skin–electrode contact of two sensors in one lead. It has been experimentally shown that the developed sensor allows monitoring the quality of the contact, and therefore, improvement of the quality of signal registration, enabled by the use of bespoke processing algorithms.Practical implicationsThese sensors will be used in personalized medicine devices and tele-ECG devices.Originality/valueIn this work, authors studied the effect of the skin–electrode contact of a capacitive electrode with the body on the quality of the recorded ECG signal. Based on the studies, the necessity of monitoring contact was shown to improve the quality of diagnostics provided by personalized medicine devices; the capacitive sensor with contact feedback was developed.

Sacrificial layer-assisted one-step transfer printing for fabricating a three-layer dry electrode

A sacrificial-layer assisted one-step transfer printing method is presented to fabricate a three-layer dry electrode for detecting electrophysiological signals. First, an Au electrode layer was deposited on a silicon wafer covered by a Cu sacrificial layer. Then, a polyimide (PI) intermediate layer was patterned on the Au layer by a standard photolithography process, and subsequently the Au layer was patterned by wet etching, using the patterned PI layer as the etching mask. Finally, both the patterned Au layer and PI layer were transferred onto a stretchable film in one step to make a three-layer dry electrode by etching away the Cu sacrificial layer. This three-layer dry electrode exhibited excellent conformability and stretchability and low electrode-skin contact impedance. The performance of the three-layer dry electrode for long-term and dynamic electrocardiogram (ECG) monitoring was also examined. The quality of ECG signals was well maintained for 48 h, during which period the signal to noise ratio was kept at 40 dB. It was also found that the physical exercises had only slight effects on the ECG signal, where all features of the signal were clearly distinguishable when the volunteer ran at 5 km/h.

Fabrication and Analysis of Wearable Bioimpedance Analyzers on Paper and Plastic Substrates

Wearable flexible sensors have recently gained much attention as they have the potential to revolutionize the way we monitor activities of the human body. Electronic sensors fabricated on flexible substrates provide compactness, comfort, and flexibility. In this letter, we report a novel design of wearable and mechanically flexible bioimpedance analyzers. We fabricate the analyzers by printing electronic circuits on paper and plastic substrates. The sensor module is lightweight, comfortable, and can be worn on the wrist to measure the body impedance continuously. Failure analysis is performed by bending the flexible sensor modules with the circuit breaking angles at 53° ± 4° and 42° ± 3° for paper and plastic substrates, respectively. The performance of the flexible sensors is compared with an analyzer developed on a conventional rigid printed circuit board. In an active mode, the paper-based sensor consumes more power (83.3 mW) than the plastic (65.7 mW) and rigid (53.42 mW) sensors. The flexible sensor modules are integrated with dry electrodes, while gel-based Ag/AgCl electrodes are attached to the rigid sensor module for bioimpedance measurements. The experiments are conducted on 12 healthy human subjects by using all three sensor modules. The integrated dry electrodes of the flexible sensor modules provide lower skin-electrode contact impedance along with enhanced convenience, durability, and reusability, as compared to commercial Ag/AgCl electrodes.

A Novel Passive Method for the Assessment of Skin-Electrode Contact Impedance in Intraoperative Neurophysiological Monitoring Systems

Intraoperative Neurophysiological Monitoring is a set of monitoring techniques consisting of reading electrical activity generated by the nervous system structures during surgeries. In order to guarantee signal quality, contact impedance between the sensing electrodes and the patient’s skin needs to be as low as possible. Hence, monitoring this impedance while signals are measured is an important feature of current medical devices. The most commonly used technique involves injection of a known current and measurement of the voltage drop in the contact interface. This method poses several problems, such as power consumption (critical in battery-powered systems), frequency dependency and regulation issues, which are overcome by using a passive method. The fundamentals of the method proposed in this paper are based on the utilization of the variation suffered by the input random signal when a known resistance is connected in parallel to the input terminals of the low-noise amplifier (LNA) of the analog front-end of the acquisition system. Controlling the connection of the resistors and computing the root mean square of the LNA output voltage has been proved to be a useful tool to assess that the contact impedance is suitably low, allowing the user to know if the neural measurements obtained are valid.

Performance Evaluation of Woven Conductive Dry Textile Electrodes for Continuous ECG Signals Acquisition

Electrocardiogram (ECG) signal monitoring is one of the essential techniques for determining the physiological state of human beings. Long-term ECG monitoring is very much essential for the diagnosis and treatment of infrequent arrhythmic episodes. Although, most of the wearable microelectronic ECG implementations employ the well-established surface electrodes technology for bio-potential recordings; they are found to be susceptible to skin irritation and influence the skin-contact impedance to larger extent in long-term monitoring applications. Integration of such sensors into wearable intelligent biomedical clothing is not feasible. This specific research study determines the application of two different conductive textile fabric materials, namely, the woven conductive silver and conductive knitted jersey as dry textile electrodes for ECG biopotential acquisition. The skin-electrode contact impedance measurements for both electrodes presented reduced skin-contact impedance of less than 1 $\text{M}\Omega $ /cm2 compared to 1–5 $\text{M}\Omega $ /cm2 as reported in literature. The performance of the proposed textile sensors is evaluated qualitatively through visual inspection and quantitatively using metrics such as power spectral density, kurtosis, baseline wander analysis, and signal-to-noise ratio (SNR). The obtained quantitative measures were compared with standard clinical grade conductive-gel based disposable Ag/AgCl surface electrodes. The simulation and comparison studies showed that, the proposed textile electrodes exhibit acceptable performance for ECG acquisition and in some instances improved performance than the traditional commercial disposable gel-based surface electrodes.

Effect of Sweating on Electrode-Skin Contact Impedances and Artifacts in EEG Recordings With Various Screen-Printed Ag/Agcl Electrodes

In response to the growing clinico-economic need for comprehensive home-based sleep testing, we recently developed a self-applicable facial electrode set with screen-printed Ag/AgCl electrodes. Our previous studies revealed that nocturnal sweating is a common problem, causing low-frequency artifacts in the measured electroencephalography (EEG) signals. As the electrode set is designed to be used without skin abrasion, not surprisingly this leads to relatively high electrode-skin impedances, significant impedance changes due to sweating and an increased risk of sweat artifacts. However, our recent electrochemical in vitro investigations revealed that the sweat artifact tolerance of an EEG electrode can be improved by utilizing an appropriate Ag/AgCl ink. Here we have investigated in vivo electrode-skin impedances and the quality of EEG signals and interference due to sweating in the population of 11 healthy volunteers. Commercial Ag and Ag/AgCl inks (Engineered Conductive Materials ECM LLC and PPG Industries Inc.) were used to test electrode sets with differently constructed ink layers. Electrode-skin impedances and EEG signals were recorded before and after exercise-induced sweating. There was extensive variation in the electrode-skin impedances between the volunteers and the electrode positions: 14.6–200 $\text{k}\Omega $ (PPG electrodes) and 7.7–200 $\text{k}\Omega $ (ECM electrodes). Sweating significantly decreased ( $p ) the impedances in most cases. The EEG signal quality was assessed by comparing average band powers from 0.5 to 2 Hz before and after sweating. Only slight differences existed between the ECM and PPG electrodes; however, the lowest band power ratio ( i.e . the smallest increase in the band power due to sweating) was achieved with ECM electrodes.

Mechanisms of Sporadic Control Failure Related to the Skin-Electrode Interface in Myoelectric Hand Prostheses

ABSTRACT Introduction This study is concerned with the control of hand prostheses based on electromyograms. As the prosthesis is moved in space, the socket and electrodes can shift on the residual limb, causing changes in the observed electromyograms. These changes can be misinterpreted by the electronic controller and cause the hand to move unintentionally or fail to execute solicited movements. The goal of this study was to explore the mechanisms related to these myoelectric control failures. Materials and Methods To study these phenomena, conventional prosthetic EMG electrodes were augmented with force sensors to record the forces through the devices. These multimodal sensors were then used to control prosthetic hands by 15 users with losses below the elbow. The subjects performed four tasks resembling activities of daily living while the electromyogram signals, force signals, and the performance of the hands (including video images) were recorded. Eight subjects reported a total of 38 control errors, each of which was assigned to one of four failure classes and analyzed. Results The article shows examples of the electromyogram and force signals recorded during the control failures and discusses possible causes of the failures. Involuntary opening of the hand was identified as the most common failure, and these failures seemed to be associated with changes in the electrode-skin contact forces. It was not possible to attribute clear causes for 26.2% of the failures. Conclusions Knowledge of common failure mechanisms can guide improved design of sockets and electrodes and signal processing to reduce the errors experienced by prosthesis users.

Denoising and Analysis of ECG Signal using Wavelet Transform for Detection of Arrhythmia

Electrocardiography is fundamental in the observation of heart function and diagnosis of diseases related to it. It involves measurement of very small bioelectric signals (in millivolts) produced by the human heart during its opening and closing of valves in atria and ventricle and is represented on a scaled paper. P, QRS, and T wave annotations by cardiologists then help in the diagnosis of the patient. Due to the electrical activity of muscles (EMG), instability of electrode-skin contact and patient movement, the noise gets induced during the plotting of the electrocardiogram (ECG). It is important to remove the noise from this signal as it is a signal having very small amplitude and different frequencies repeated almost every second. For such nonstationary biosignals, Wavelet Transform (WT) can be used. In this study, Continuous Wavelet Transform (CWT) and Discrete Wavelet Transform (DWT) are used to denoise and extract features from the ECG, respectively. The features extracted from DWT are used as input to Artificial Neural Network (ANN) for the classification of normal and abnormal ECG. Abnormal ECGs are further classified into tachycardia and bradycardia. The results show that ANN can classify ECGs with high accuracy. The data used for this study is from the MIT-BIH Arrhythmia Database Directory.

Noninvasive measurement of stroke volume changes in critically ill patients by means of electrical impedance tomography

Previous animal experiments have suggested that electrical impedance tomography (EIT) has the ability to noninvasively track changes in cardiac stroke volume (SV). The present study intended to reproduce these findings in patients during a fluid challenge. In a prospective observational study including critically ill patients on mechanical ventilation, SV was estimated via ECG-gated EIT before and after a fluid challenge and compared to transpulmonary thermodilution reference measurements. Relative changes in EIT-derived cardiosynchronous impedance changes in the heart ([Formula: see text]) and lung region ([Formula: see text]) were compared to changes in reference SV by assessing the concordance rate (CR) and Pearson's correlation coefficient (R). We compared 39 measurements of 20 patients. [Formula: see text] did not show to be a reliable estimate for tracking changes of SV (CR = 52.6% and R = 0.13 with P = 0.44). In contrast, [Formula: see text] showed an acceptable trending performance (CR = 94.4% and R = 0.72 with P < 0.0001). Our results indicate that ECG-gated EIT measurements of [Formula: see text] are able to noninvasively monitor changes in SV during a fluid challenge in critically ill patients. However, this was not possible using [Formula: see text]. The present approach is limited by the influences induced by ventilation, posture or changes in electrode-skin contact and requires further validation.

A novel active AC coupled input stage of instrumentation amplifier for bioelectrical applications

For recording bioelectrical signals using Instrumentation Amplifiers (INA), capacitive AC coupling of the differential inputs is necessary for two major reasons, providing DC electrical isolation of the subject to avoid hazards of tissue burn, and to block DC or very low frequency skin-electrode contact potentials. The latter, when met, allows high admissible differential gain of the INA, which in turn, is expected to give a desirable high Common Mode Rejection Ratio (CMRR). However, the use of conventional passive RC high pass filters at the input greatly reduces CMRR. This work intends to design an improved AC coupled input circuitry for INA giving high CMRR and high input impedance. A differential RC high-pass input circuit has been developed using an active element. It creates an effective high resistance for the common mode current but provides a low resistance path to input bias currents for normal operation of the INA. Between 1 Hz and 100 Hz, CMRR of the DC coupled INA (LT1167) was 115 dB, using a well matched traditional RC coupling, 55 to 95 dB, while it was 110 dB using the improved active AC coupled circuit. This improvement was practically demonstrated through Electrocardiogram measurements from a human subject. A novel active AC coupling circuitry has been proposed and developed giving high CMRR, very close to the maximum of an INA, which is non-varying within the frequency band of interest of Bioelectrical amplifiers. The developed input circuit will improve all bioelectrical measurements in the future.

Development of a Wearable Electrical Impedance Tomographic Sensor for Gesture Recognition With Machine Learning.

A wearable electrical impedance tomographic (wEIT) sensor with 8 electrodes is developed to realize gesture recognition with machine learning algorithms. To optimize the wEIT sensor, gesture recognition rates are compared by using a series of electrodes with different materials and shapes. To improve the gesture recognition rates, several Machine Learning algorithms are used to recognize three different gestures with the obtained voltage data. To clarify the gesture recognition mechanism, an electrical model of the electrode-skin contact impedance is established. Experimental results show that: rectangular copper electrodes realize the highest recognition rate; the existence of the electrode-skin contact impedance could improve the gesture recognition rate; Medium Gaussian SVM (Support Vector Machine) algorithm is the optimal algorithm with an average recognition rate of 95%.

The research of the quality of ECG recording by capacitive electrodes in violation of the skin-electrode contact

This paper presents actual development in the field of personal telemedicine. For personal cardiographs most suitable dry electrodes that do not require a conductive gel. This article describes experiments with capacitive electrodes from Plessey Semiconductors. On the basis of the obtained experimental data, it is planned to create own capacitive electrodes with the possibility of detuning from the skin-electrode contact.

Magnetic field assisted laser fabrication and electrical characterizations of metal dry Biolectrode with surface microstructures

Magnetic field assisted laser fabrication is proposed to process metal dry bioelectrode with surface microstructures. The effects of magnetic flux density on the geometrical dimension of surface microstructures of bioelectrode is investigated. The electrode-skin contact impedance is then studied using the two-electrode measurement method. Finally, electromyography (EMG) signal is recorded using bioelectrodes processed in different magnetic flux density. Our results show that the magnetic field has obvious influences on the height and bottom width of microstructure of bioelectrode. When a magnetic field of 100 mT is selected, larger height-width ratio of microstructures is obtained, which provides a stronger ability to penetrate stratum corneum. Consequently, much lower contact impedance is obtained. Signal-noise ratio (SNR) of EMG signal shows a correlation coefficient of 0.9836 with height-width ratio of microstructures on the surface of metal dry bioelectrodes. Raw EMG signals recorded by metal dry bioelectrodes in 100 mT magnetic field show a high SNR up to 27.350, which is slightly higher than that of traditional Ag/AgCl wet bioelectrodes (26.689). By stationary wavelet transform (SWT) de-noising, noise interfused in raw EMG signals is suppressed effectively. Moreover, the de-noised EMG signal recorded using metal dry bioelectrodes processed in 100 mT magnetic field still remains a fairly high SNR.

Inexpensive and flexible nanographene-based electrodes for ubiquitous electrocardiogram monitoring

Flexible electronics is one of the fundamental technologies for the development of electronic skin, implant wearables, or ubiquitous biosensing. In this context, graphene-derived materials have attracted great interest due to their unique properties to fulfill the demands of these applications. Here we report a simple one-step method for the fabrication of electrophysical electrodes based on the photothermal production of porous nanographene structures on the surface of flexible polyimide substrates. This approach constitutes an inexpensive alternative to the commercial medical electrodes, leading to a lower and much more stable skin–electrode contact resistance and providing comparable signal transduction. This technology has been framed inside the IoT paradigm through the development of a denoising and signal classification clustering algorithm suitable for its implementation in wearable devices. The experiments have shown promising achievements regarding noise reduction, increasing the crest factor ~3.7 dB, as well as for the over 90% heart rate-monitoring accuracy.

A Novel Bristle-Shaped Semi-Dry Electrode With Low Contact Impedance and Ease of Use Features for EEG Signal Measurements.

In this paper, we present a novel soft bristle-shaped semi-dry electrode for electroencephalography (EEG) recording. Because the bristle-shaped structure with electric conductivity could overcome the obstacle of hair and enable direct connection to scalp, the semi-dry electrode could work with drinking water instead of saline water that was widely used in previous semi-dry or water electrodes to improve its convenience. The electrode consisted of conductive bristles and a 3D-printed casing. Carbon-coated nylon conductive bristles could achieve low impedance and soft properties of the semi-dry electrode. The bristles could spread on skin and realize a larger contact area. The carbon-coated conductive bristles could also continuously penetrate water into the corneum of skin to reduce contact impedance. The contact impedance of the bristle-shaped semi-dry electrode was similar to the traditional wet electrode, but much lower than dry electrode. Although the saline water had much lower impedance than drinking water, our electrode still achieved even lower skin-electrode contact impedance than previous semi-dry or water electrode with saline water. The alpha rhythms, P300 visual evoked potential, and steady-state visual evoked potential were, respectively, measured to evaluate the electrode performance for EEG recording.

An Online Spectral Information-Enhanced Approach for Artifact Detection and Fault Attentuation in Myoelectric Control.

In myocontrol of neuroprosthetic devices, multichannel electromyography (EMG) can be used to decode the intended motor command, based on distributed activation patterns of stump muscles. In this regard, the high density EMG (HD-EMG) approach allows for enhancement of the spatiotemporal resolution for motor intention detection. Despite the advantages of relying on several EMG channels, the challenge of high-density electrode systems is the dynamically changing electrode-skin contact impedance, which can affect a considerable number of electrodes over the time of data acquisition. This can result in obtaining unreliable, low-quality EMG recording with a distributed artifact pattern over the grid of EMG sensors. To address this issue, we propose a novel online approach for adaptive information extraction and enhancement for automatic artifact detection and attenuation in HD-EMG-based myocontrol of prosthetic devices. The method is based on an adaptive weighting scheme that modifies the contribution of each HD-EMG channel considering the spectral information content relative to artifacts. The technique (named IE-HD-EMG) was tested as an online pre-conditioning step for a challenging multiclass classification problem of 4-finger activation, using linear discriminant analysis. It is shown that for this application, the proposed IE-HD-EMG technique led to a superior performance in finger activation recognition (79.25% accuracy, 89% sensitivity, 89.15% specificity) in comparison to the conventional HD-EMG recording under the same condition without the proposed approach (56.25% accuracy, 61.3% sensitivity, 67% specificity). Therefore, the proposed technique can have a significant potential to expand the clinical viability of HD-EMG systems.

The influence of skin-electrode contact on the quality of ECG recording for personal telemedicine systems

In this article are presented the results of the study of the Tele-ECG system. Presented system automatically records the ECG signal and transmits it to the server, where occurs process of the decryption (automatic detection of R-waves and ST-segments on the ECG). A distinctive feature of the system is the use of it includes devices with capacitive sensors. The results quality research of the signal received through different dielectrics. The necessity of revision of sensors that will allow to avoid the interference caused by man and external factors. As a result, this refinement will allow to receive a signal for automatic diagnostics with the least loss of information due to the presence of interference in the signal.