On one hand, it is good news, on the other hand, it is not. I found a paragrah on the ACamp website on how DC bias currents cause double layers to form.
AC-coupled amplifiers with true AC-coupled inputs have capacitors on the inputs that form high pass filters. In addition to rejecting DC and low frequency signals, the input capacitors also block all DC bias currents from flowing across the amplifier inputs. One advantage is that blocking input DC bias currents eliminates double layer charging across the electrode surface of an input transducer, which significantly increases the transfer of analog biomedical signals across the tissue/transducer interface. Input capacitors also create added patient safety during clinical measurements. Similar advantages also apply to other analog amplifier systems including audio amplifier.I've been saying this for a long time! The inventor is Dr. Michael F. Suesserman, from Seattle, WA (Patent 5,300,896). I wonder how many people have licensed his technology... a search on Suesserman on flashpoint reveals that he wrote a number of articles with Francis Spelman, who in turn did a substantial amount of research on EEG. Posted by torque at January 8, 2004 5:41 PM | TrackBack