Simulation study of a contactless, capacitive ECG system

The electrocardiogram (ECG) is one of the primary sources of information for assessing cardiovascular function. Conventional ECG systems are not suitable for continuous, long-term monitoring. Contactless measurement of ECG using capacitive sensors is emerging as an attractive alternative. One of the disadvantages of a contactless system is that the signal quality is poor as far as the clinical acceptance of the system is concerned. The contactless ECG signal typically contains a relatively large amount of dc, due to electrode offset or artifacts, which would drive the front end of the high-gain amplifier into saturation. Hence, what is required is a circuit that would effectively block dc while coupling the differential ac signal. A circuit developed for conventional ECG systems has been made use of, for this purpose. This paper describes the simulation and analysis of a contactless ECG monitoring system, using capacitive electrodes, with an ac-coupled front end for effective dc decoupling. The performance of the circuit is studied for different material and thicknesses of clothing.