Proposal of Measuring DC Biomedical Signals using a New Modulation Type of Capacitive Electrode with Capacitive Coupling

Difference of contact voltages between the electrodes and the human body causes a measurement error in measuring DC biomedical signals. It was unable to measure DC signals using the capacitive electrode because lower cut-off characteristics are formed by the capacitance of the electrode. The authors reported a modulation type of capacitive electrode using variable capacitance modulation to measure DC biomedical signals in the previous paper. However, the AC current for exciting the modulation capacitances on the electrode must be fed into the body, when the electrode is used.  We propose a new modulation type of capacitive electrode that does not need to apply the AC current to the body. The signal voltage is applied on the modulation capacitances of the electrode through the input coupling capacitance of the electrode. Since the modulation capacitances have a nonlinear relationship between the applied voltage and the electric charge, modulated output voltage due to the signal voltage is produced by the modulation capacitances. This paper describes behavior of the new modulation type of capacitive electrode, and some experiments on the electrode. As a result, it is suggested that the electrode can measure DC biomedical signals of more than 1mV.