Influences of stitch types on performance of embroidered fabric electrodes for surface electromyography
Objective The aim of this study is to develop high-performance embroidered fabric electrodes for surface electromyography(sEMG)and optimize their process parameters.Four embroidered fabric electrodes with different stitch types were designed and produced to investigate the influence of stitch types on their conductivity properties and sEMG signal fitting performance,ultimately determining the optimal stitch type.Method Fabric electrodes were produced using embroidery techniques by virture of the advantage of tailored fiber placement in embroidery.Silver-plated yarn,known for its high conductivity,served as the conductive embroidery thread,and elastic knitted structure were used as the substrate to improve the fit of the electrodes to the skin.Four embroidered fabric electrodes with different stitch types,i.e.,tabby-stitch,box-stitch,annular-stitch and radial-stitch,were designed and produced.Skin-electrode impedance testing was conducted for each embroidered fabric electrode.In the states of walking and jogging,embroidered fabric electrodes and Ag/AgCl electrodes were aolopted to synchronously collect sEMG signal of the medial side of calf gastrocnemius muscle,and sEMG signal fitting performance of embroidered fabric electrodes and Ag/AgCl electrodes was evaluated in time-domain,frequency-domain and by correlation function analysis.Results 1)Through skin-electrode impedance testing,it was found that direct embroidery on elastic knitted fabric tends to cause wrinkling in the fabric,resulting in deformation of the embroidered fabric electrodes.Placing non-adhesive interlinings such as paper interlining or cloth interlining on the bottom layer of elastic knitted fabrics cannot effectively solve this problem.However,using hydrosol double-sided fuse interlinings to synthesize elastic knitted fabrics and paper interlinings into fabric substrate for embroidery can effectively prevent fabric wrinkling and electrodes deformation.2)Through skin-electrode impedance testing,it was found that stitch types significantly affect the skin-electrode impedance of embroidered fabric electrodes.During the test,the order of skin-electrode impedance was found to be annular-stitch electrode＞box-stitch electrode＞tabby-stitch electrode＞radial-stitch electrode.The conductivity performance of embroidered fabric electrode with radial stitch is optimal.3)In the time-domain comparison diagram,sEMG signal of each embroidered fabric electrode was basically consistent with that of Ag/AgCl electrodes.The time-domain indices extracted include root mean square(RMS)and average rectifying value(ARV),while frequency-domain indices encompassed mean power frequency(MPF)and median frequency(MF).RMS,ARV,MPF and MF of each embroidered fabric electrode were close to those of Ag/AgCl electrodes.Therefore,the sEMG acquisition effect of embroidered fabric electrodes were similar to that of Ag/AgCl electrodes.4)The time-domain and frequency-domain characteristics of the sEMG signals collected by embroidered fabric electrode with radial stitch and Ag/AgCl electrodes were similar.Moreover,the ratio of information entropy of sEMG signal collected by embroidered fabric electrode with radial stitch and Ag/AgCl electrodes was the closest to 1,and the correlation coefficient between them was higher than 0.455 in the jogging state.So,it is believed that the sEMG signal fitting performance of the embroidered fabric electrode with radial stitch was better,and it was more suitable for sEMG monitoring.This result was related to the smaller skin-electrode impedance of embroidered fabric electrode with radial stitch,as generally speaking,the smaller the skin-electrode impedance of the electrode,the weaker the attenuation of the sEMG signal.Conclusion The sEMG signal acquisition effect of four embroidered fabric electrodes with different stitch types are similar to that of Ag/AgCl electrodes,which verifies the feasibility of embroidered fabric electrodes.The type of stitch affects the skin-electrode impedance and sEMG signal fitting performance of embroidered fabric electrodes.The embroidered fabric electrode with radial stitch has the smallest skin-electrode impedance and demonstrated optimal sEMG signal fitting performance,indicating that optimizing stitch can improve the performance of embroidered fabric electrodes.
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