Modulation-type capacitive electrode driven by small AC current for measuring DC biological signals

In the measurement of DC biological signals, it is inevitable that errors occur due to the offset difference between the electrodes, which is generated by the contract voltage between the biological object and the electrode. When a conventional insulator electrode is used, lower cutoff characteristics are produced in the measurement system in order to eliminate the effect of the contact voltage, which makes DC measurement difficult. Consequently, this paper investigates a new electrode. A capacitance (ferroectric) electrode is attached, and the biological object is treated as a part of the electrode system. By applying a small AC current through the electrodes and the biological object, the capacitance of the capacitive electrode is varied. Then, the electric charge stored in the capacitive electrode is modulated by the biological signal so that the DC biological signal is converted to an AC signal and is output. The modulation characteristics of the electrode, as well as the noise characteristics, are investigated. Measurements are made of the potential generated on the skin near the eye due to the cornea–retina potential. The results show that the proposed electrode can be used in the measurement of DC biological potentials such as the DC brain potential and the sympathetic skin response. © 2005 Wiley Periodicals, Inc. Syst Comp Jpn, 36(13): 69–80, 2005; Published online in Wiley InterScience (). DOI 10.1002sscj.20238