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

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Assessment of Carbon/Salt/Adhesive Electrodes for Surface Electromyography Measurements
This work presents the evaluation of novel electrodes for surface electromyography (sEMG) measurements. The electrodes are based on a 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. Twenty 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 to 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 vs. 32.7 ± 15.6 dB) and motion artifacts (24.1 ± 12.1 dB vs. 16.6 ± 8.52 dB), and a significantly lower spectral deformation (1.32 ± 0.2 vs. 1.46 ± 0.4). Ag/AgCl electrodes showed a significantly more peaked and sensitive response to EMG amplitude (67.9 ± 13.9 dB vs. 65.4 ± 14.6). Given no significant differences in many of the measures described above 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.

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