Assessment of Carbon/Salt/Adhesive Electrodes for Surface Electromyography Measurements

Abstract

This paper presents the evaluation of novel electrodes for surface electromyography (sEMG) measurements. The electrodes are based on the mixture of carbon powder, quaternary salt, and viscoelastic polymeric adhesive (carbon/salt/adhesive or simply CSA), which when combined, provide the unique advantages of having longer (theoretically infinite) shelf life and potentially lower cost than Ag/AgCl hydrogel electrodes, consistent with FLEXcon’s Patent #8 673 184. The 20 subjects were recruited to collect simultaneous recordings of sEMG signals using Ag/AgCl and CSA electrodes, side-by-side on triceps brachii, tibial anterior muscles, biceps brachii, and quadriceps femoris. Although CSA sEMG electrodes showed higher electrode-skin contact impedance for the frequency range of 4 Hz–2 kHz, no significant differences were found in the signals’ amplitude between the two electrodes either during relaxation or contraction stages. Furthermore, correlations of the computed linear envelopes (>0.91), rms value envelopes (>0.91), and power spectral densities (>0.95) of the signals were found to be high between the two media. Detected ON- and OFF-times of contraction were also highly correlated (>0.9) and interchangeable (ON-time: bias = −0.02, variance = 0.11; OFF-time: bias = −0.04, variance = 0.23) between the two media. However, CSA sEMG electrodes exhibited a significantly better response to noise (38.3 ± 10.6 dB versus 32.7 ± 15.6 dB) and motion artifacts (24.1 ± 12.1 dB versus 16.6 ± 8.52 dB), and a significantly lower spectral deformation (1.32 ± 0.2 versus 1.46 ± 0.4). Ag/AgCl electrodes showed a significantly more peaked and sensitive response to EMG amplitude (67.9 ± 13.9 dB versus 65.4 ± 14.6 dB). Given no significant differences in many of the measures described earlier and the fact that CSA electrodes have an infinite shelf-life are potentially lower cost, and are more resistant to motion artifacts, the new electrodes provide an attractive alternative to Ag/AgCl electrodes for sEMG measurements.

Assessment of Dry Epidermal Electrodes for Long-Term Electromyography Measurements

“…SNR for the ESS electrode was greater than 25 dB across all tests, and there was no apparent trend in signal quality with an SNR > 30 dB over four days, and the average CV was below 10% for all muscles types and tests conducted. This is much higher than the suggested 15 dB for sEMG data with noise artifacts, and higher than or comparable to SNR reported in previous literature [ 18 , 24 ]. In fact, the average SNR of both the six-hour trial and the four-day trial were close to 50 dB, the SNR of an sEMG signal under ideal conditions [ 31 ], and the ESS SNR was significantly higher than the Delsys SNR for the ECR, FCU, and TRI during the six-hour test.…”

“…To help address these concerns, a variety of dry electrodes have been developed with flexible polymers and textiles that allow the electrode to adhere and move with the skin. For electrodes with a polymer adhesive, thin sheets of metal [ 10 , 18 , 19 , 20 , 21 , 22 , 23 ], carbon ink [ 24 ] and powders [ 25 ], as well as atomically thin sheets such as graphene [ 26 ] have been used as a conductive material. Textile-based electrodes with silver-plated conductive thread have also been reported [ 27 ].…”

“…The most common are electrode-skin contact impedance and signal-to-noise ratio (SNR). While lower impedance is desirable for better conduction [ 28 ], dry electrodes tend to have a much higher impedance than wet electrodes, on the order of high kΩ-high MΩ [ 7 , 10 , 22 , 29 ], whereas wet electrodes have an impedance on the order of low kΩ-low MΩ [ 24 , 30 ]. For long-term sEMG data measurements, constant impedance over time is desirable to ensure detected changes reflect true changes in muscle activity and not changes in the sensing environment.…”

Evaluation of Swallowing Related Muscle Activity by Means of Concentric Ring Electrodes

“… Signal-to-motion ratio (SMR) gives information about the level of the motion artifacts in the signal. It was computed using the whole recorded signal according to the description given by [ 42 ] where is the power to the frequency in the power spectral density (PSD) and is a straight line between cero and the highest mean power density, is the sampling frequency: 5 kHz. Zero-crossing (ZC) provides indirect information about the time domain of the signal frequency.…”

Characterization of capacitive electromyography biomedical sensor insulated with porous medical bandages

“…Informed consent was obtained from each subject prior to their participation in the experiment. A wet contact electrode (Ag-AgCl) is the gold standard of a surface EMG measurement 16 . It was used to benchmark the performance of these porous medical bandage insulated cEMG biomedical sensors 17 .…”