Fabrication and testing of a novel biopotential electrode array

This paper focuses on the fabrication and testing of a novel biopotential electrode array for detecting human brainwaves activity signals. A hybrid micro electro-machining process that combines spark erosion with silver deposition to create suitable taper-shaped micropillar and special discharge craters for holding the biopotential electrode in position on the human scalp is proposed. By means of controlling the secondary-electrode wear rate, the required taper-rate (T = 1/7) and special surface roughness (Ra = 2.9 μm) on the designed biopotential electrode are successfully achieved. The trend curves of bottom wear and carbon deposition in the secondary-electrode reveal near linear increases while the residual hole-depth declines with increased machinings. This indicates that the work energy used allows a steady-state wear rate in the secondary-electrode. Silver deposition is conducted to enhance the safety, electrical conductivity of the microprobe array and being antibacterial. Clinical and experimental results demonstrate that the formed biopotential skin electrode with an array of short-tapered pillars realizes quasi-invasive light contact between cerebral cortex and the microprobe. Four brainwave activity frequency signals are confirmed with superior intensity and repeatability to those realized by present-day commercial planar electrodes. Approaches to secondary-electrode formation, traction force testing, novel microprobe formation in batch mode, work capacitance, and pulse current effects, insertion durability tests, and life expectancy tests of the secondary-electrode are all evaluated in detail.