Development Of Convenient Ear Electrode And Its Application In BCI

Brain-machine interface devices are one of the key technologies in the development of human-computer interaction as an important component to realize the interaction between the brain and external devices.Non-invasive brain-machine interfaces do not require invasive surgery and can collect neural signals directly from outside the brain.Among them,EEG is one of the most widely used brain-machine interface technologies as a non-invasive acquisition method for recording electrical potential changes on the scalp surface of the brain,which has relatively simple recording equipment and high temporal resolution.Most EEG is currently performed in a laboratory setting,and the preparation of wearable recording electrodes by combining EEG acquisition with wireless signal transmission shows great promise in order to enable real practical applications of EEG.However,conventional scalp acquisition electrodes are affected by the hair on the scalp surface and require conductive paste to reduce the impedance,which limits the convenient operation of the electrodes.Previous studies have shown that EEG signals comparable to those of the scalp can be acquired by placing EEG electrodes on hairless areas such as the forehead,ear and face.In particular,the ear can be placed with the help of headphones and other forms of electrodes for concealment and convenience,and is one of the best alternatives to the scalp as an acquisition area.The following aspects are accomplished in this thesis:Ⅰ.Study of dry ear electrodes based on conductive silver cloth and semi-dry ear electrodes based on conductive gelTwo types of molds were prepared using a simple mold-flipping technique: a personalized custom in-ear mold and a universal behind-the-ear patch.A dry in-ear electrode was prepared by fixing the conductive silver cloth to the pre-set site bumps of the in-ear mold by means of adhesion;a disposable disposable gel probe was prepared by using conductive gel,which was installed in the recesses of the in-ear mold and the posterior ear patch to prepare a semi-dry in-ear electrode and a posterior ear electrode.Ⅱ.Electrochemical performance and brain-machine interface performance tests of dry and semi-dry ear electrodesIn order to verify the performance of the two types of prepared ear electrodes,the electrochemical impedance and open-circuit voltage of the ear electrodes were tested separately using an electrochemical workstation.By comparison,it was verified that the gel ear electrode exhibited superior electrochemical performance and long-term stability.Using steady-state visual evoked potentials(SSVEP)with good time-and phase-locking characteristics,subjects aged 22 to 32 years were randomly selected to perform multiple SSVEP experiments to test the performance of the two prepared ear electrodes in BCI,with conventional EEG electrodes placed in the occipital region for comparison.The test results showed that the gel ear electrode exhibited more BCI performance.Ⅲ.Optimization of brain-computer interface performance of semi-dry ear electrodesIn order to further improve the performance of the ear electrode in SSVEP-based experiments,the number of channels,stimulation frequency,and algorithm of data processing of the ear electrode were experimentally compared and optimized respectively,and the optimized ear electrode could achieve the best information transmission rate(ITR:37.56 ± 18.88 bit/min).The results showed that the prepared semi-dry ear electrodes could obtain SSVEP signals comparable to those of the occipital area electrodes,and the subjects were more willing to accept the semi-dry postauricular electrodes for SSVEP acquisition.