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Metal microelectrodes used in physiological studies exhibit large noise due to their high impedance. In this paper we present measured noise spectra over the frequency range of 0.05 Hz to 1 kHz for platinum, tungsten, and stainless steel microelectrodes.<BR>The noise of metal microelectrodes shows a <I>f</I><SUP>-0.2</SUP> to <I>f</I><SUP>-2.3</SUP> frequency dependence when measured in 0.9% NaCl solution. By comparing the measured noise with thermal noise as given by Nyquist theorem from the resistive part of electrode impedance, the following properties are understood.<BR>In the high frequency range (<I>f</I> >1-100 Hz) thermal noise dominates at rest potential and also under the condition of direct current application (less than a few 100, μA/cm<SUP>2</SUP>). At low frequencies, electrode noise exceeds thermal noise even at rest potential. Usually, the ratio of power spectrum density of measured noise to that of thermal noise for W electrodes at 10 Hz falls in the 10 to 100 range. W electrodes show the largest ratios followed by Pt and stainless steel electrodes. The ratios tend to increase with unit area polarization resistance.<BR>When direct current passes through the Pt electrode, the low frequency noise greatly increases. Particularly, at about 10, uA/cm<SUP>2</SUP> anodic current a large noise peak is observed. For extremely small tip microelectrodes, this current density is often caused by a leak current of usual J-FET input amplifier.<BR>The measurement resolution of bioelectric signals is determined by electrode noise, since noise of metal microelectrodes having impedance above several 100 kΩ at 100 Hz is comparable to or larger than J-FET input amplifier noise.
- 一般社団法人 日本生体医工学会の論文
一般社団法人 日本生体医工学会 | 論文
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