Study Of Dry Electrode For Electroencephalogram Recording

Biopotential recordings are indispensable and vital tools for both medical and research use, especially in the form of electroencephalogram (EEG), which plays an important role in the study of brain function and diseases. Generally, a wet electrode is used in EEG recording and its use is quite complicated and limited by the environment. However, novel dry electrode is more convenient to use and can be portable, which is in line with modern personalized health care needs of the society.MEMS technology is a kind of micro manufacture technology which develops along with silicon micro manufacture technology. By fabrication process such as photolithography, we can manufacture device in micro or nano dimension. In recent years, flexible MEMS and Bio-MEMS have emerged. Based on flexible substrate, device in micrometer dimension can be fabricated by MEMS technology, and these devices can bear impact and can be curved. In vitro diagnostic device and vivo implanted device, Bio-MEMS technology can provide edges as well.Based on MEMS technology and the requirement of EEG recording, we first design the configuration of three various types of dry electrodes with microneedles, including 3D electrode, plane electrode based on Polyimide (PI) substrate and plane metal electrode. The fabricated 3D electrode has an array of 10×10 grid, with the diameters of microneedles being 50μm, 60μm and 80μm. There are two groups of plane electrodes based on PI substrate, the first of which has microneedle sizes of 250μm(l)×50μm(w), 300μm(l)×60μm(w) and 350μm(l)×80μm(w), with height of 40μm, the second of which has microneedle sizes of 300μm(l)×150μm(w) and 500μm(l)×200μm(w), with height of 60μm. There are also two groups of plane metal electrodes, one with straight needles and another with tilted needles. Those with straight needles have the same sizes of needles as the second plane electrodes based on PI substrate while those with tilted needles, the size of which is 350μm(l)×150μm(w), with height of 60μm, also include a base with side length of 500μm beneath the needle. The angle between needle/base and electrode is 60°.In our study, we used standard MEMS fabrication technology which involves sputtering, photolithography, etching, and electroplating. We also realized three different fabrication processes, analyzed and optimized the process. The general impedance of a single plane electrode tested in 0.9% saline solution is 100 k? ~ 100 ?, at the frequency from 0.1Hz to 1000 Hz. In the following vivo human experiment, the effects of the plane electrode and conventional wet electrode have been compared. The comparison among various types of plane electrodes has also been made. It has been proved that EEG signals can be recorded by every type of electrodes, of which the second batch of plane electrodes based on PI substrate as well as plane metal electrodes can achieve better recordings, especially those assembled by 6-10 pieces.