Smart Mouthguard With Fabric Electrodes for Wireless Intraoral Electrooculogram Monitoring

In recent years, electrooculography (EOG) has become a well-established method used in studies related to neuroscience, cognition analysis, psychological behavior, assistive technology, and sleep. The traditional placement of the EOG electrodes around the eyes tends to cause discomfort and is prone to displacement during sleep. This article presents a more comfortable and reliable way to measure the sleep EOG signals: a wireless smart mouthguard with integrated EOG sensors. The smart mouthguard is made of two ethylene-vinyl acetate (EVA) submouthguards, five conductive fabric electrodes, a flexible EOG measuring board, and a small LiPo battery, which is encapsulated in the Ecoflex for waterproofing. The device can transfer the EOG data through Bluetooth Low Energy (BLE) 5.0 to an Android app or computer terminal and can be charged wirelessly. The magnitude of skin-electrode impedance of the fabric electrodes on the mouthguard is less than 14 k $\Omega $ , which is comparable to that of the standard gold EOG electrodes. The EOG measurement board has the differential gain over 19 (or 25.6 dB) and common-mode rejection ratio (CMRR) over 98.6 dB in the EOG bandwidth. The smart EOG mouthguard is validated on eight subjects for detecting EOG signal patterns of different eye activities. Results show that different eye activities can be detected from the acquired EOG signal with an accuracy of 100% for horizontal eye movements and at least 94% for vertical eye movements. As the smart mouthguard fits well and do not get displaced during sleep, the proposed smart mouthguard has potential for comfortable long-term sleep EOG monitoring.