| Abstract [eng] |
Vital signs‘ monitoring is an indispensable part of modern medicine. In contrary to most contemporary clinical methods, sensors based on electromagnetic coupling work without electrical contact, and they have a possibility to be implemented without connecting cables. Also, they can easily be integrated in chairs, vehicle seats, wheel-chairs and mattresses. Despite that, this field is hardly developed – there are only several publications, in which heart activity is detected using electromagnetic sensors. The aim of this work is to research the electrodes of capacitive sensors and to propose an optimal electrode configuration for heart activity monitoring. By performing experiments and using a model of finite elements, a total of 10 different active capacitive electrodes are analyzed and compared. A novel capacitive sensor was proposed, that was the most suitable for heart activity monitoring. It has active fractal electrode and both electrodes overlapping on one plate. Sensor of this structure is smaller, solid, and it avoids the deviations from movements between electrodes. To compliment the research, signal processing and heart beat detecting algorithm was created. Validity of the method was confirmed by comparing capacitive signals with reference ECG signal. To test the system in realistic conditions, a test with four subjects in two physical activation states was executed. The results of the test were creditable, even though the algorithm was often mislead by movement–induced artifacts. Also, heart beats located on the slopes of breathing curve, are left with very low amplitudes after the high-pass filtering. After analyzing sixteen (60 sec.) signals, a maximum inaccuracy of 3 beats per minute (bpm) (from the real heart rate) was observed. The main accomplishment of this work is that a new, effective, sensitive and penetrative fractal capacitive sensor was created. That could be used and improved in future capacitance - based biomedical research. There is a potential for these sensors to be applied in capacitive biomedical vital signs‘ monitoring devices. |
