Electrode Contact Impedance Research Articles

Fabric-based lamina emergent MXene-based electrode for electrophysiological monitoring

Commercial wearable biosignal sensing technologies encounter challenges associated with irritation or discomfort caused by unwanted objects in direct contact with the skin, which can discourage the widespread adoption of wearable devices. To address this issue, we propose a fabric-based lamina emergent MXene-based electrode, a lightweight and flexible shape-morphing wearable bioelectrode. This work offers an innovative approach to biosignal sensing by harnessing the high electrical conductivity and low skin-to-electrode contact impedance of MXene-based dry electrodes. Its design, inspired by Nesler’s pneumatic interference actuator, ensures stable skin-to-electrode contact, enabling robust biosignal detection in diverse situations. Extensive research is conducted on key design parameters, such as the width and number of multiple semicircular legs, the radius of the anchoring frame, and pneumatic pressure, to accommodate a wide range of applications. Furthermore, a real-time wireless electrophysiological monitoring system has been developed, with a signal-to-noise ratio and accuracy comparable to those of commercial bioelectrodes. This work excels in recognizing various hand gestures through a convolutional neural network, ultimately introducing a shape-morphing electrode that provides reliable, high-performance biosignal sensing for dynamic users.

Novel dry EEG electrode with composite filler of PEDOT:PSS and carbon particles.

We have developed a novel composite filler with Poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonic acid) (PEDOT:PSS), a biocompatible organic conductive polymer, adsorbed on carbon particles for biological electrodes. This composite filler enables to fabricate high-performance biological electrodes simply by adding it to resin in the same way as conventional conductive fillers. The fabricated electrodes achieve ion exchange properties similar to those of PEDOT:PSS polymers and therefore low skin and electrode contact impedance. Electroencephalogram (EEG) measurements show that these electrodes capture various brain activities and exhibit high correlation (≥ 0.9) to commercially available wet and AgCl electrodes. Additionally, each electrode can be molded into various shapes and structures while retaining its electrode characteristics. Therefore, the proposed electrode is promising for EEG measurement, which requires high comfort and signal quality.

Electrode-Skin Impedance Model Parameter Estimation in the Frequency-Domain.

This paper presents a method for identifying parameter values for a double parallel resistor/constant-phase-element model of the electrode-skin interface for individual silver and silver/silver chloride electrodes. The impedance of each electrode was measured in five from 1 Hz-10 kHz. Phase features of these data were used to guide initial estimates for parameter values which were refined using a least squares algorithm. Resultant model impedances were compared with experimental data across a typical biosignal bandwidth (1 Hz-500 Hz). The method was effective in estimating component values in most datasets, and resulted in a mean relative RMS error of 7 % (σ = 8.3%) across the biosignal bandwidth.Clinical relevance- This work establishes a feature-based method for finding component parameter estimates for an electrode contact impedance model.

Estimation of electrode contact impedance and conductivity of single-layer graphene using electrical impedance tomography

The paper describes a novel method of detecting defects in the fabrication of graphene films which have many important applications due to their unique mechanical and electronic properties. The illustrative method is based upon electrical impedance tomography and is demonstrated using a testbed to obtain the conductivity profile across the entire graphene surface. Sensed data are processed using a described reconstruction procedure that estimates electrode contact impedances and spatial conductivity. The results are presented of numerical simulations and experiments with graphene wafers of size 2.5 cm. The results show that the proposed method can jointly estimate contact impedance at each electrode and conductivity distribution.

A Bioinspired Sweat‐Drainable Janus Electrophysiological Electrode for Scientific Sports Training

AbstractRecent technological innovations in wearable electronics offer possibilities to perform real‐time monitoring of electrophysiological parameters, such as ECG, EMG, and EEG. To achieve accurate and long‐term electrophysiological measurement, great signs of progress have been made in the skin–electrode interfacial problems; nevertheless, the challenges related to sweat have not been fully resolved. Excessive sweat between human skin and the electrode usually fails to achieve a conformal and intact contact, and the nonconductive barriers will lead to a high skin–electrode impedance. Inspired by the structure of liquid directional movement in nature, a Janus gold nanowires/nitrocellulose (AuNWs/NC) electrophysiological electrode with conical micropores is developed to solve interfacial problems caused by sweat. The Janus AuNWs/NC electrodes spontaneously wick sweat from the AuNW side to the NC side, thus keeping intimate skin–electrode contact and low interfacial impedance to ensure a high‐fidelity signal during the long‐term monitoring. By integrating Janus AuNWs/NC electrode with circuit modules and advanced algorithms, a real‐time visualization system is developed for muscle activity intensity. This system is applied to precisely evaluate the muscle controllability and assess the muscle balance ability, which presents great potentials for health monitoring, sports training, and the areas of human–computer interaction.

Improvement of performance and sensitivity of 2D and 3D image reconstruction in EIT using EFG forward model

This paper presents a pure element-free Galerkin method (EFGM) forward model for image reconstruction in 2D and 3D electrical impedance tomography (EIT) using an adaptive current injection method. In EIT systems with the adapting current injection method, both static and dynamic images can be reconstructed; however, determination of electrode contact impedances in the complete electrode model is difficult and the Gap model is used. In this paper, in the EIT forward problem a weak form functional based on the Gap model and a pure EFGM approach are developed, and in the EIT inverse problem, Jacobian matrix is computed by the EFGM, and a fast integration technique is introduced to calculate the entries of the Jacobian matrix within an adequate computation time. The influence of increasing the density of nodes at and near the electrodes with steep electric potential gradients on the accuracy of FEM and EFGM forward solutions is investigated, and the performance of the image reconstruction algorithm with the proposed fast integration technique is examined. The numerical results reveal that the proposed EFGM forward model with the fast integration technique has an efficient performance both in terms of mean relative imaging errors and computational time.

Ionic liquid regenerated cellulose membrane electroless plated by silver layer for ECG signal monitoring

Nowadays, more and more attention has been paid to flexible electrodes, which can be used to make wearable devices so as to monitor health signals, such as those in ECG, EMG and EEG. However, the contact impedance of many membrane electrodes is high due to the bad fit between the sensors and the skin, or the poor sensitivity caused by low conductivity. Therefore, we fabricated a skin-like conductive electrode via electroless silver plating on the surface of regenerated cellulose membrane, which was prepared from the cellulose dissolved in ionic liquid [Bmim]Cl. The as-prepared biocompatible electrodes with low skin-electrode contact impedance can be used as a dry electrode for a long time. Its impedance at 700 Hz is only 8 kΩ/cm2 and the conductivity reaches 252 s/cm. After 5 h of wearing, the electrode-skin contact impedance at 700 Hz is only 10 kΩ/cm2 when 0.20 mol/L AgNO3 is used. In short, the prepared electrode can not only ensure stable and clear ECG signals but also can greatly reduce electrode–skin contact impedance when used for long-term health monitoring.

Low Voltage and Low Power Front Panel Design for 12 Lead ECG

The use of portable devices is increasing day by day. Mainly these devices play a vital role in medical field when the doctors are unavailable. In that one of the important emergency medical portable systems is Electro Cardiogram (ECG). ECGs are used to measure the abnormalities of the heart by performing electrical activities. It can be done by attaching electrodes on the body for few minutes. To collect the information from electrodes data acquisition system is used in ECGs or in any biomedical systems. The major challenge in implementing data acquisition system is the increase in power dissipation due to the excessive contact impedance of electrodes. As a solution to this, A CMOS 12 lead ECG data acquisition circuit is designed by using analog multiplexers is proposed in this paper. The proposed system is designed by using improved DTMOS based analog multiplexers and these works with a power supply of ±0.2 V with a dynamic voltage range from 1uv to 200mv with the Power dissipation of 140 nW.

Wearable Smart Textiles for Long-Term Electrocardiography Monitoring-A Review.

The continuous and long-term measurement and monitoring of physiological signals such as electrocardiography (ECG) are very important for the early detection and treatment of heart disorders at an early stage prior to a serious condition occurring. The increasing demand for the continuous monitoring of the ECG signal needs the rapid development of wearable electronic technology. During wearable ECG monitoring, the electrodes are the main components that affect the signal quality and comfort of the user. This review assesses the application of textile electrodes for ECG monitoring from the fundamentals to the latest developments and prospects for their future fate. The fabrication techniques of textile electrodes and their performance in terms of skin–electrode contact impedance, motion artifacts and signal quality are also reviewed and discussed. Textile electrodes can be fabricated by integrating thin metal fiber during the manufacturing stage of textile products or by coating textiles with conductive materials like metal inks, carbon materials, or conductive polymers. The review also discusses how textile electrodes for ECG function via direct skin contact or via a non-contact capacitive coupling. Finally, the current intensive and promising research towards finding textile-based ECG electrodes with better comfort and signal quality in the fields of textile, material, medical and electrical engineering are presented as a perspective.

Performance of a flexible electrode based on natural leather

A novel electrode is developed to detect electrocardiogram (ECG) signals using the top grain leather and split leather of pig as the substrate due to their mechanical strength, flexibility, permeability, long-term durability and visual acceptance. The natural leather is pre-treated with Ar plasma and a thin silver paste coating is brush-painted on the surface to gain electrical conductivity. The sheet resistance of the electrodes is approximately 120 mΩ sq−1. The electrodes based on leather can reliably transmit low-frequency and low-voltage signals, which benefit the acquisition of cardiac signals. Although the electrode-skin contact impedance of the dry leather-based electrodes is higher than the silver/silver chloride (Ag/AgCl) electrodes, the contact impedance decreases at least 57.74% after wetting the skin. All cardiac waves obtained by the leather-based electrodes are clear and visible, and the signal-to-noise ratio (SNR) of electrodes are higher than the Ag/AgCl electrodes. The electrodes based on leather have great potential for smart wearable devices.

Sensitivity analysis of the complete electrode model for electrical impedance tomography

Electrical impedance tomography (EIT) is an imaging technique that reconstructs the conductivity distribution in the interior of an object using electrical measurements from the electrodes that are attached around the boundary. The Complete Electrode Model (CEM) accurately incorporates the electrode size, shape, and effective contact impedance into the forward problem for EIT. In this work, the effect of the conductivity distribution and the electrode contact impedance on the solution of the forward problem is addressed. In particular, the sensitivity of the electric potential with respect to a small-amplitude perturbation in the conductivity, and with respect to some defective electrodes is studied. The Gâteaux derivative is introduced as a tool for the sensitivity analysis and the Gâteaux differentiability of the electric potential with respect to the conductivity and to the contact impedance of the electrodes is proved. The derivative is then expressed as the unique solution to a variational problem and the discretization is performed with Finite Elements of type P1. Numerical simulations for different 2D and 3D configurations are presented. This study illustrates the impact of the presence of perturbations in the parameters of CEM on EIT measurements. Finally, the 2D inverse conductivity problem for EIT is numerically solved for some configurations and the results confirm the conclusions of the numerical sensitivity analysis.

Electrochemical Characteristics Based on Skin‐Electrode Contact Pressure for Dry Biomedical Electrodes and the Application to Wearable ECG Signal Acquisition

Based on one simulated skin‐electrode electrochemical interface, some electrochemical characteristics based on skin‐electrode contact pressure (SECP) for dry biomedical electrodes were analysed and applied in this research. First, 14 electrochemical characteristics including 2 static impedance (SI) characteristics, 11 alternating current impedance (ACI) characteristics and one polarization voltage (PV), and 4 SECP characteristics were extracted in one electrochemical evaluation platform, and their correlation trends were statistically analysed. Second, dry biomedical electrode samples developed by the company and the laboratory, including textile electrodes, Apple watch, AMAZFIT rice health bracelet 1S, and stainless steel electrodes, were placed horizontally and vertically on the “skin” surface of the electrochemical evaluation platform, whose polarization voltages were quantitatively analysed. Third, electrocardiogram (ECG) collection circuits based on an impedance transformation (IT) circuit for textile electrodes were designed, and a wearable ECG acquisition device was designed, which could obtain complete ECG signals. Experimental results showed SECP characteristics for dry electrodes had good correlations with static impedance and ACI characteristics and the better correlation values among 2‐10 Hz. In addition, polarization voltages in vertical state were smaller in horizontal state for dry biomedical electrodes, and polarization voltage of electrode pair (PVEP) values for Apple watch bottom was always smaller than ones for Apple watch crown and LMF‐2 textile electrode. And the skin‐electrode contact impedance of IT textile electrodes was less than the traditional textile electrodes.

Imaging Conductivity Changes in Monolayer Graphene Using Electrical Impedance Tomography.

Recently, graphene has gained a lot of attention in the electronic industry due to its unique properties and has paved the way for realizing novel devices in the field of electronics. For the development of new device applications, it is necessary to grow large wafer-sized monolayer graphene samples. Among the methods to synthesize large graphene films, chemical vapor deposition (CVD) is one of the promising and common techniques. However, during the growth and transfer of the CVD graphene monolayer, defects such as wrinkles, cracks, and holes appear on the graphene surface. These defects can influence the electrical properties and it is of interest to know the quality of graphene samples non-destructively. Electrical impedance tomography (EIT) can be applied as an alternate method to determine conductivity distribution non-destructively. The EIT inverse problem of reconstructing conductivity is highly non-linear and is heavily dependent on measurement accuracy and modeling errors related to an accurate knowledge of electrode location, contact resistances, the exact outer boundary of the graphene wafer, etc. In practical situations, it is difficult to eliminate these modeling errors as complete knowledge of the electrode contact impedance and outer domain boundary is not fully available, and this leads to an undesirable solution. In this paper, a difference imaging approach is proposed to estimate the conductivity change of graphene with respect to the reference distribution from the data sets collected before and after the change. The estimated conductivity change can be used to locate the defects on the graphene surface caused due to the CVD transfer process or environment interaction. Numerical and experimental results with graphene sample of size 2.5 × 2.5 cm are performed to determine the change in conductivity distribution and the results show that the proposed difference imaging approach handles the modeling errors and estimates the conductivity distribution with good accuracy.

Prediction of Behavioral T/C Levels in Cochlear Implant Patients Based Upon Analysis of Electrode Impedances

Fitting cochlear implants in babies and noncooperative patients is cumbersome and time consuming. Therefore, objective parameters have been sought in order to predict the subjective threshold (T) and maximum comfort (C) levels. Measurements of the electrically evoked compound action potentials (ECAPs) have been widely used for this purpose, yet the correlation between these objective measures and the subjective T/C levels is weak to moderate. This article aims (1) to evaluate correlations between the subjective parameters of the fitting maps such as thresholds (T level) and maximum comfort levels (C level), the impedance of the electrode contacts, and the ECAP thresholds, and (2) to compare the value of the electrode impedances and the ECAP measures for prediction of the T/C levels. Case review study in a quaternary otologic referral center. Ninety-eight consecutive CI patients were enrolled. The average age of the patients was 49 years. All patients were users of the Nucleus 24RECA (Freedom, Contour Advance-of-Stylet electrode) cochlear implant. Data on impedance of the electrode contacts and the behavioral T/C levels at the first fitting session (2-5 weeks after surgery) and at the 5th fitting session (4-6 months after surgery) have been retrospectively collected in 98 consecutive CI patients. Additionally, the intraoperative impedance values and the ECAP thresholds (tNRT) have been recorded. Impedances of electrode contacts show significant strong negative correlations with the stabilized T/C levels at 4 to 6 months after implantation and are an important predictor for the behavioral T/C levels. They can explain R 2 = 28 to 41% of the variability of the behavioral T/C levels. In multiple regression analysis electrode contact impedances can explain twice as much of the variability of the stabilized T/C levels than the tNRT values. The electrode impedances together with the tNRT values are able to explain R 2 = 37 to 40% of the global variability of the T/C levels while the tNRT thresholds solely are able to explain only R 2 = 5 to 14% of the T/C levels variability. Impedances of electrode contacts correlate strongly with the stabilized behavioral T/C levels and may be used as an objective measure for fitting of cochlear implants.

A Comparison of Front-End Amplifiers for Tetrapolar Bioimpedance Measurements

Many commercial benchtop impedance analyzers are incapable of acquiring accurate tetrapolar measurements, when large electrode contact impedances are present, as in bioimpedance measurements using electrodes with micrometer-sized features. External front-end amplifiers can help overcome this issue and provide high common-mode rejection ratio (CMRR) and input impedance. Several discrete component-based topologies are proposed in the literature. In this article, these are compared with new alternatives with regard to their performance in measuring known loads in the presence of electrode contact impedance models, to emulate tetrapolar bioimpedance measurements. These models are derived from bipolar impedance measurements taken from the electrodes of a tetrapolar bioimpedance sensor. Comparison with other electrode models used in the literature established that this is a good and challenging model for bioimpedance front-end amplifier evaluation. Among the examined amplifiers, one of the best performances is achieved with one of the proposed topologies based on a custom front-end with no external resistors (AD8066/AD8130). Under the specific testing conditions, it achieved an uncalibrated worst-case absolute measurement deviation of 4.4% magnitude and 4° at 20 Hz, and 2.2% and 7° at 1 MHz accordingly with loads between $10~\Omega $ and 10 $\text{k}\Omega $ . Finally, the practical use of the front-end with the impedance analyzer is demonstrated in the characterization of the bioimpedance sensor, in saline solutions of varying conductivities (2.5–20 mS/cm) to obtain its cell constant. This article serves as a guide for evaluating and choosing front-end amplifiers for tetrapolar bioimpedance measurements both with and without impedance analyzers for practical/clinical applications and material/sensor characterization.

Screen‐Printed Dry Electrodes: Basic Characterization and Benchmarking

The electrical performance of screen‐printed dry electrodes on thermoplastic polyurethane substrates are evaluated according to their conformance to international standards, skin–electrode impedance, and ability to gather high quality electrocardiograms. The electrical behavior of seven screen‐printed electrodes (Ag, Ag/PEDOT:PSS, Ag/AgCl, Ag/AgCl/PEDOT:PSS, C, C/AgCl, and PEDOT:PSS) is compared to two commercially available gel electrodes (3M RedDot 50 and Philips NeoLead) which represent the state‐of‐the‐art. After basic standard electrical characterization (electrode–electrode impedance, direct current [DC] offset voltage, defibrillation recovery, bias stress, and noise), it is shown that layers such as AgCl or PEDOT:PSS help to reduce the contact impedance of dry electrodes. However, the quality of the electrical signal is primarily governed by the skin impedance, which, without physical disruption or preparation, maintains a high impedance. For this reason, the impedance of all screen‐printed dry electrodes allows the collection of electrocardiograms with a quality equal to that of gel electrodes. Dry electrodes, while capable of obtaining similar electrical signal quality also bring the advantages of reusability, comfort, and the capability for long‐term measurements.

Model-Guided Design of Microelectrodes for HFO Recording.

High Frequency Oscillations (HFOs, 200-600 Hz) are recognized as a biomarker of epileptogenic brain areas. This work aims at designing novel microelectrodes in order to optimize the recording and further detection of HFOs in brain (intracerebral electroencephalography, iEEG). The quality of the recorded iEEG signals is highly dependent on the electrode contact impedance, which is determined by the characteristics of the recording electrode (geometry, position, material). These properties are essential for the observability of HFOs. In this study, a previously published hippocampal neural network model is used for the simulation of interictal HFOs. An additional microelectrode model layer is implemented in order to simulate the impact of using different types and characteristics of microelectrodes on the recorded HFOs. Results indicate that a small layer PEDOT/PSS and PEDOT/CNT on microelectrodes can effectively decrease their impedance resulting in the increase of HFOs observability. This model-based study can lead to the actual design of new electrodes that will ultimately contribute to improved diagnosis prior to invasive therapies.

Electrical properties of calcia-stabilised zirconia ceramics

The electrical properties of cubic, calcia-stabilised zirconia ceramics, CaxZr1-xO2-x: 0.12 ≤ x ≤ 0.18 have been investigated using impedance spectroscopy to separate bulk, grain boundary and electrode contact impedances. The most appropriate equivalent circuit to characterise the bulk response required inclusion of a dielectric component, represented by a series RC element, in parallel with the oxide ion conductivity represented by a parallel combination of a resistance, capacitance and constant phase element. The dielectric component may be attributed to defect complexes involving immobile oxygen vacancy pairs whereas long range conduction involves single oxygen vacancies.

Comparison of electrophysiological parameters between perimodiolar and lateral wall electrodes in paediatric cochlear implant users.

(1) To compare the in vivo impedances of electrical contacts of the Nucleus Contour Advance (CA) perimodiolar electrodes and the Nucleus Slim Straight (SS) lateral wall electrodes. (2) To compare the relation between the electrode contact impedances and the behavioural T-/C-levels for both types of electrodes. Retrospective case review in two quaternary otologic referral centres was performed. Data on the impedance of the electrode contacts and the T-/C-levels have been collected from 70 consecutive paediatric CI patients. (1) SS electrodes show significantly higher impedance values of the contacts compared to the CA electrodes. This can be explained by differences in the active surface of the electrode contacts and is true for the whole electrode arrays. (2) There are significant negative correlations observed between the impedances of the electrode contacts and the behaviourally measured T-/C-levels. (3) The strength correlation between the electrode impedances and the behavioural T-/C-levels is significantly higher and the T-/C-level variability is lower for the perimodiolar CA electrodes than for the lateral wall SS electrodes. There exist significant differences in the contact impedance between different cochlear implant electrode arrays. These differences could influence the implant programming parameters and should be considered in any protocols related to automatic implant programming based on objective measures. The predictive value of the electrode impedances for the behavioural T-/C-levels is higher for the perimodiolar CA electrodes than for the lateral wall SS electrodes.

Influence of the pre- or postlingual status of cochlear implant recipients on behavioural T/C-levels

IntroductionPrevious auditory experience modifies the sensitivity of the auditory cortex to the afferent activity of the auditory pathways and may influence the threshold (T) and comfort (C) levels in patients receiving a cochlear implant (CI). Literature data on this particular topic is very scarce. ObjectiveThis study aimed to evaluate the differences in T/C-levels between pre- and postlingually implanted cochlear implant patients. MethodsRetrospective case review in a quaternary otologic referral centre was performed. Data on the T/C-levels have been collected in 90 consecutive CI patients divided into 2 groups. Group 1 comprised 16 prelingually deaf children implanted between 8 months and 10 years of age. Group 2 comprised 74 postlingually deaf adults (average age of 62 years). All patients were users of the Nucleus 24RECA (Freedom, Contour Advance-of-Stylet electrode) cochlear implant. All measurements were performed at the fifth implant programming session at 4–6 months after surgery, when stable T/C thresholds have already been obtained. ResultsThe behavioural C-levels present important and statistically significant differences between the pre- and postlingually implanted patients for all electrode contacts that could reach 30 CL. For the T-levels the observed differences were smaller and statistically insignificant for most electrode contacts. ConclusionsThe previous auditory experience (pre- or postlingual deafness) seems to be an independent parameter influencing the T/C-levels in patients receiving a CI. Together with the electrode contact impedance and the contact position in the electrode array it can explain up to 37% of the variability in the definition of the C-levels. The fact that the stabilised C-levels measured 4–6 months postoperatively can be up to 30 CL higher in the prelingually deaf patients than in the postlingual ones results also in a much higher dynamic range observed in prelingual subjects. Therefore implant programming of the prelingual patients should be very cautious in order to avoid the risk of overstimulation.