Wearable FES Electrodes

Artificial Organs, 2008

Abstract: Discomfort experienced during surface functional electrical stimulation (FES) is thought to be partly a result of localized high current density in the skin underneath the stimulating electrode. This article describes a finite element (FE) model to predict skin current density distribution in the region of the electrode during stimulation and its application to the identification of electrode properties that may act to reduce sensation. The FE model results show that the peak current density was located in an area immediately under the stratum corneum, adjacent to a sweat duct. A simulation of surface FES via a high-resistivity electrode showed a reduction in this peak current density, when compared to that with a low-resistivity electrode.

Physiological Measurement, 2010

Physiol. Meas. 35(2) 231-252. doi:10.1088/0967-3334/35/2/231

Particular neuromuscular electrical stimulation (NMES) applications require the use of the same electrodes over a long duration (>1 day) without having access to them. Under such circumstance the quality of the electrode-skin contact cannot be assessed. We used the NMES signal itself to assess the quality of the electrode-skin contact and the electrical properties of the underlying tissues over a week. A 14% decrease in the skin’s stratum corneum resistance (from 20kΩ to 17kΩ) and a 15% decrease in the resistance of the electrodes and underlying tissues (from 550Ω to 460Ω) were observed in the 14 healthy subjects investigated. A follow-on investigation of the effect of exercise-induced sweating on the electrical properties of the electrode-skin-underlying tissue composite during NMES indicated a correlation between the decrease in the resistance values observed over the course of the week and the accumulation of sweat at the electrode-skin interface. The value of the capacitance representing the dielectric properties of the skin’s stratum corneum increased after exercise-induced sweating but did not change significantly over the course of the week. We conclude that valuable information about the electrode-skin-underlying tissue composite can be gathered using the NMES signal itself, and suggest that this is a practical, safe and relatively simple method for monitoring these electrical properties during long-term stimulation.

Physiological Measurement, 2010

Medical Engineering and Physics, 2009

Array electrodes are a promising technology that is likely to bring transcutaneous electrical stimulation (TES) a step forward. The dynamic adaptation of electrode size and position helps to simplify the use of electrical stimulation systems and to increase their clinical efficacy. However, up to now array electrodes were built by trial and error and it is unclear how, for example, the gaps between the array elements or the resistivity of the electrode-skin interface material influence the current distribution. A TES model that comprises a finite element model and a nerve model has been used to analyze the influence of array electrode gaps and gel resistivities on nerve activation. Simulation results indicate that the resistivity of the electrode-skin interface layer should be adapted depending on the size of the gaps between the array elements. Furthermore, the gap sizes should be smaller than 3 mm in order to keep losses small.

arXiv (Cornell University), 2017

Direct and alternating current iontophoresis and electro-osmosis methodologies have provided new methods of transcutaneous drug delivery. A byproduct of such methods is lowering the electrical impedance of the electrode to skin contact, as conductive ions permeate the stratum corneum, the primary resistive layer of the skin. We developed a method for adapting iontophoresis to condition the electrode to skin contact, both for electrophysiological recording and electrical stimulation of body tissues. By utilizing direct current to treat electrodes with high impedance we show the effectiveness of iontopheresis as a driving force for permeation of ionic electrolyte into the skin barrier. We applied direct current (DC) levels of 50 µA to electrodes on the human head for 30 seconds with paste (Nihon Kohden Elefix) electrolyte. Typically immediately after DC treatment conditioning there was an impedance drop of 10-30%. The effect was lasting over several hours, with the paste electrolyte. These results demonstrate the feasibility of DC conditioning to reduce the set time of electrolytic solutions and to maintain good skin contact during extended recording or stimulation sessions.

International Journal of Biomedical and Clinical Engineering, 2017

The electrical impedance between skin-electrodes placed at the intact skin can be a source of artefacts when small electrical voltages such as ECG- and EEG-signals are recorded. This is mainly due to random variations of the electrical properties of the electrode-skin interface. To reduce the effect of these shortcomings, the skin is prepared with conductive paste and sometimes stripped to remove the outer corneous layer of the skin at the sites where the electrodes are placed. That reduces the impedance between the electrode and the skin and subdues disturbing electrical signals emanating from external sources. Numerous electrical models have been presented in the literature in order to relate electrical parameters to physiological and anatomical properties of the skin and to counteract the distortion of electrical signals recorded from the skin surface. To meet these requirements flexible electrodes combined with biochemical sensors have been developed which seem to prepare the wa...

Bulletin of Electrical Engineering and Informatics, 2021

For more than 50 years, transcutaneous electrical stimulation method has been used to cure the spinal cord injury, stroke or cerebral palsy. This method works by activating the excitable nerves, muscle fibers by electrical current stimulation through electrode interface to skin. Electrode to skin interface requires equivalent circuit to overcome the inability of measuring the skin resistivity directly. Therefore, equivalent circuit inside the E-textile must be modelled properly for it to represents the skin nature, which is resistive and capacitive. We have been learned several models after the skin from previous works, which are from Lawler, Moineau and Keller & Kuhn. Unfortunately, Moineau model neglects the capacitance effect (we then neglected this model in our simulation analysis), while Lawler and Keller and Kuhn include capacitive and resistive nature of skin in their equivalent circuits. Both models consisted of only one parallel RC block. This paper presents the simulation ...

Characterization of the Electrode-Skin Impedance of Textile Electrodes, 2014

Wearable systems are expected to contribute for improving traditional biopotential signals monitoring devices due to higher freedom and unobtrusiveness provided to the wearer. Textile electrodes present advantages compared with the conventional Ag/AgCl electrodes for the capturing of biopoten-tials, namely in terms of skin irritation due to the hydrogel and the need of a technician to place the electrodes on the correct positions. Due to the lack of hydrogel, textile electrodes present different electrical contact characteristics. The skin-electrode impedance is an important feature since it affects the captured signal quality. Although a low impedance is desired, a comfortable wearable system should not require the electrodes to be covered by the hydrogel or be moistened. A forearm sleeve provided with textile electrodes was used to study the electrode-skin impedance and the signal-to-noise ratio (SNR) of surface electromyographic (EMG) signals on a long-term use basis. The sleeve can be adjusted for different levels of tightening to control the pressure applied on the electrodes. The obtained results provide valuable information on the pressure that the textile garments of a sleeve or vest should apply on the recording electrodes, in order to assure a good electrical and mechanical contact between the electrodes and the skin and decrease the noise due to motion. It was observed that the electrode-skin impedance measurement alone is not sufficient to establish a relation with the SNR. The extraction of parameters from an electrical equivalent model of the electrode-skin interface allows to determine a relation with the model parameters and the SNR. The evaluation of these parameters during long-term monitoring will allow assessing the quality of biopotential measurements in textile electrodes.