Abstract:

Objective Embroidery electrode is known to have numerous merits including personalized customization function, good reproducibility, fast and flexible production and reliable electrical performance, and much research attention has been attracted to the development of smart electrocardiograms (ECG). In order to improve the sensitivity and stability of embroidered ECG electrodes and standardize the design and application of electrodes, this paper carries out the design of electrode size, pattern and embroidery type, and analyzes its influence on the physical characteristics and electrical properties of the electrodes.

Method Embroidery electrodes were fabricated by embroidering conductive yarns on textile substrates. The upper and lower surfaces were both covered by the conductive yarn. The embroidery parameters were shown to affect its physical characteristics and appearance, which in turn affected its electrical properties. In this paper,electrode thickness, flatness, skin-electrode interface impedance, signal-to-noise ratio, baseline stability time, and baseline offset amplitude were taken as performance indicators, performances of individual electrodes were tested and analyzed so as to identify and understand the influencing factors.

Results The area, pattern and stitch of the embroidered electrode were found to affect its performance in every aspects. Too large or too small an area would negatively affect its sensing sensitivity and the quality of the captured signal. The diameter of the electrode has a significant impact on the arrangement of machine-embroidered stitches, influencing whether they overlap or are placed side by side; consequently, the electrode's size directly affects its thickness. When the electrode diameter was smaller than 23 mm, the signal-to-noise ratio was found negatively correlated with the thickness of the embroidery electrode. When the diameter increased to 26 mm, the signal-to-noise ratio was increased significantly, and the baseline stabilization time appeared smaller. However, when the diameter was more than 26 mm, the surface deformation of the embroidery electrode became larger when it touched the skin This resulted in decreased signal-to-noise ratio, and increased baseline stabilization time. However, the sensing stability of the embroidered electrode was shown to decrease with the increase of the signal capture pathway, indicating that the larger the area, the greater the amplitude of the ECG baseline shift. For embroidery electrodes with the same surface area, when the pattern of the electrode is closer to a circular pattern, the current in the electrode is distributed more uniformly, so the skin-electrode interface impedance of the electrode is smaller, the signal-to-noise ratio is larger, the baseline stabilization time is shorter, and the magnitude of the baseline shift is smaller. When the electrode area and pattern are the same, embroidery electrodes prepared using embroidery stitches with uniform thickness and flat surface of the finished product have smaller skin-electrode interface impedance, larger signal-to-noise ratio, and smaller baseline shift, in which the baseline stabilization time of the softer samples is shorter. In summary, the final optimized solution was derived as 5.3 cm² area, circular pattern and satin stitch for embroidery. The preferred embroidered electrode reduced the skin-electrode interface impedance value by 1.064 MΩ, improved the signal-to-noise ratio by 3.161 dB, shortened the baseline stabilization time by 3 s, and reduced the baseline offset amplitude by 0.07 mV when compared with the commercial 3M gel electrode.

Conclusion As a new type of electrode material, the design and performance study of the embroidery electrode area, pattern and embroidery type was studied, the factors influencing the electrode performance were analyzed in detail. By establishing the performance evaluation system of embroidery electrodes, different embroidery electrodes were compared and evaluated. Compared with the commercial 3M gel electrodes, the embroidery electrode prepared by adopting the optimized design demonstrated better electrical properties, with better sensitivity and stability. In addition, the embroidery electrode itself showed improved comfort and better fit to the skin when used. This work provides a useful information for the subsequent research of embroidery electrodes.

Key words: embroidery electrode, smart electrocardiogram, electrocardiogram signal, impedance, signal-to-noise ratio, electrocardiogram baseline, silver coated nylon yarn