Abstract
To achieve robust sEMG measurements in an EMG prosthetic system, this study proposes a surface electromyogram (sEMG) sensor with a novel electrode structure composed of two-layered conductive silicone with different carbon concentrations. We hypothesized there is an optimal carbon concentration for achieving a large sEMG amplitude with robustness to external perturbation, and we empirically determined this optimal concentration. We produced fourteen sets of electrodes, with the weight ratio of carbon to silicone ranging from 1.7% to 4.0%. Using these electrodes, the user sEMG and electrical properties of the electrodes were measured. An external perturbation was applied on one side of the electrode to introduce a condition of unbalanced contact to the sEMG sensor. We defined an index of robustness for the sEMG sensor based on the signal-to-noise ratio in the balanced and unbalanced contact conditions. Based on the results of the robustness index, two optimal carbon concentrations, at weight ratios of 2.0%–2.1% and 2.6%–2.7%, were observed. Moreover, the double-peak property was correlated to the capacitance. Our results clearly demonstrate an optimal carbon concentration for robust sEMG measurements, and suggest that the robust measurement of sEMG is supported by the capacitance component of the sensor system.
Highlights
Electromyography (EMG) is often used as an input signal to intuitively control a powered prosthetic hand[1,2,3]
We developed surface electromyogram (sEMG) sensors using electrodes composed of a conductive fabric[25] and conductive silicone[26]; these sensors were applied to control numerous types of powered prosthetic hands and arms[27,28,29,30]
We developed an sEMG sensor with two-layered electrodes, as shown in Fig. 1
Summary
Electromyography (EMG) is often used as an input signal to intuitively control a powered prosthetic hand[1,2,3]. A dry-type sEMG sensor without contact between the metal and the skin is required. To achieve stable sEMG measurement in the EMG prosthetic hand system, the problem of unbalanced contact in the electrodes must be resolved. For the electrode of the sEMG sensor to be suitable for an EMG prosthetic hand system, (1) the sEMG must be robustly measured when the contacts of both electrodes are stable, and (2) the measurement ability of the sEMG cannot undergo substantial changes, even for an unbalanced contact in the electrodes. The aim of this study is to design an sEMG sensor structure with two-layered electrodes and to find the optimal carbon concentration of the conductive silicone in contact with the skin. We measured the electrical properties of the electrode with skin contact and evaluated the relationship between the electrical properties and the robustness index
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