Sensing the human alpha rhythm using a non-contact electroencephalographic (EEG) electrode

The electroencephalogram is the recording of bioelectrical potentials on the scalp due to neural current sources in the brain and are typically recorded using wet surface electrodes that make ohmic contact with the scalp surface using an electrolyte gel. Unfortunately, wet electrodes are intrusive to the user, problematic for EEG studies requiring high spatial resolution, and are unsuitable for long-duration EEG recordings. Wet electrodes ultimately limit spatial resolution since the gel can short neighboring electrodes. They also do not meet long-duration recording demands since the gel can dry out over time. This dissertation explores the feasibility of measuring the EEG at room temperature, through hair, without scalp contact using two capacitive probe techniques. This is achieved by focusing on measurement of the alpha rhythm, an oscillatory EEG signal that is common among the population and is easily elicited with eye closure. Research results suggest that it is possible to sense the alpha rhythm within 4.0mm of scalp-probe spacing and that the ultra-high impedance fieldmeter probe technique is the most promising. Non-contact recordings are compared to wet electrode recordings and issues related to hair and motion artifact are discussed. Areas critical to the development of this technology are suggested

High-Performance Accelerometer Based On Asymmetric Gapped Cantilevers For Physiological Acoustic Sensing

Continuous or mobile monitoring of physiological sounds is expected to play important role in the emerging mobile healthcare field. Because of the miniature size, low cost, and easy installation, accelerometer is an excellent choice for continuous physiological acoustic signal monitoring. However, in order to capture the detailed information in the physiological signals for clinical diagnostic purpose, there are more demanding requirements on the sensitivity/noise performance of accelerometers. In this thesis, a unique piezoelectric accelerometer based on the asymmetric gapped cantilever which exhibits significantly improved sensitivity is extensively studied. A meso-scale prototype is developed for capturing the high quality cardio and respiratory sounds on healthy people as well as on heart failure patients. A cascaded gapped cantilever based accelerometer is also explored for low frequency vibration sensing applications such as ballistocardiogram monitoring. Finally, to address the power issues of wireless sensors such as wireless wearable health monitors, a wide band vibration energy harvester based on a folded gapped cantilever is developed and demonstrated on a ceiling air condition unit

Ballistocardiographic Coupling of Triboelectric Charges into Capacitive ECG

© 2019 IEEE.Capacitive ECG (cECG), a technique older than 50, is able to replace the gold standard ECG only in certain applications where unobtrusiveness and conformity are aimed at the expense of reduced signal quality. Triboelectric surface charges, motion artifacts, and resulting time-variant coupling capacitances are among the reasons for the signal deformations in cECG. In this paper, the mechanical vibrations of the human body are proposed as the source of time-variant coupling capacitances causing motion artifacts, which questions the applicability of adaptive filtering approaches to the problem of time-variant coupling capacitance. Ballistocardiogram (BCG) measurements on cECG electrodes are recorded and analyzed to investigate how these mechanical vibrations reflect on a differential biopotential measurement. Furthermore, using measured signals in a human experiment, numerical and test bench simulations were conducted to replicate how triboelectric surface charges might cause deformation on cECG signals