Magnetic field assisted laser fabrication is proposed to process metal dry bioelectrode with surface microstructures. The effects of magnetic flux density on the geometrical dimension of surface microstructures of bioelectrode is investigated. The electrode-skin contact impedance is then studied using the two-electrode measurement method. Finally, electromyography (EMG) signal is recorded using bioelectrodes processed in different magnetic flux density. Our results show that the magnetic field has obvious influences on the height and bottom width of microstructure of bioelectrode. When a magnetic field of 100 mT is selected, larger height-width ratio of microstructures is obtained, which provides a stronger ability to penetrate stratum corneum. Consequently, much lower contact impedance is obtained. Signal-noise ratio (SNR) of EMG signal shows a correlation coefficient of 0.9836 with height-width ratio of microstructures on the surface of metal dry bioelectrodes. Raw EMG signals recorded by metal dry bioelectrodes in 100 mT magnetic field show a high SNR up to 27.350, which is slightly higher than that of traditional Ag/AgCl wet bioelectrodes (26.689). By stationary wavelet transform (SWT) de-noising, noise interfused in raw EMG signals is suppressed effectively. Moreover, the de-noised EMG signal recorded using metal dry bioelectrodes processed in 100 mT magnetic field still remains a fairly high SNR.
Keywords: Contact impedance; De-noising; Dry bioelectrode; EMG signal; Laser processing; Magnetic field; Surface microstructures.