Non-contact ECG employing signal compensation

Non-contact ECG monitoring is an attractive option in a number of applications such as long-term health monitoring where traditional adhesive ECG sensors would cause skin irritation and require frequent replacement. Also, integrating ECG sensors into furniture, automobile seats and elsewhere in the environment will enable non-invasive sensing of cardiac signals. Subject-electrode relative motion causes spurious signals and significant signal distortion. The ECG signal of interest as well as static charge and electromagnetic interference are modulated by changes in the coupling capacitance between the electrodes and subject, which leads to significant distortions. The focus of this paper is the development of a non-contacting ECG sensing system including the electrodes, interface electronics and a signal-processing unit that work together to address this issue. The subject-to-electrode distance is continuously monitored by a secondary sensing circuit that uses the ECG electrodes themselves which serve as both the primary ECG readout and the secondary subject-to-electrode distance readout. Finally, the experimental results show the secondary readout signal can be used to compensate the motion-related gain variations of the primary ECG monitoring circuit as well as the additive interference by motion events.