Abstract

To reduce the burden on the health system and democratize access to health care, current research is aimed at embedding medical devices in daily-life objects with autonomous diagnostic algorithms. In the case of popular tools such as the electrocardiogram (ECG), electroencephalogram (EEG), and electromyography (EMG), one of the scientific challenges is replacing the standard wet Ag/AgCl electrode. A strong candidate is the capacitive electrode, which can be seamlessly integrated into chairs, beds, car seats and wearable devices. This is a dry and active kind of electrode, fabricated on a rigid or flexible printed circuit board. Although in ideal conditions capacitive electrodes can provide high-quality biopotential measurements, they are prone to motion artifacts (MAs) because they do not stick to the patient's body. A MA is a large interference that can render the ExG analysis impossible. Often, it is much larger than the targeted signal and it can even saturate the analog front-end's input. MAs are often described as random or unpredictable events, however, in this dissertation they were modeled based on triboelectric nanogenerator theory. The proposed model uses information on displacement and speed to mimic the MA behavior. It also supports existing bibliography that MA comprises two main phenomena, a change in electrode capacitance (capacitance between electrode and patient) and generation of triboelectricity. The electrode capacitance variation can cause voltage division with the input capacitance (reduce signal to noise ratio), low cut-off frequency fluctuation (common-mode signals converted into differential artifacts) and modulation of DC voltages across the electrode capacitance (voltage spikes). To attenuate the effects of electrode capacitance variation, three topologies of capacitive electrode are proposed: i) a through-body negative feedback is applied to stabilize the electrode's gain; ii) the input resistance is boosted with a positive feedback so a series capacitance can be inserted; iii) a control system detects the electrode capacitance change and modifies the input resistance.