US Patent 6961601 Sensor system for measuring biopotentials

A system for measuring a biopotential signal produced by a body in free space at a location adjacent to the body, and if desired, through clothing, includes a probe that can be positioned adjacent to the body. The probe includes a conductive electrode to receive the biopotential signal and a conductor that is maintained at a fixed distance from the electrode. The potential of the conductor can be maintained substantially equal to the potential of the electrode to shield the electrode from stray electrical noise. The system further includes a high impedance first stage amplifier that is incorporated into the probe and electrically connected to the electrode using a relatively short connector to minimize connector noise. Functionally, the first stage amplifier compares the electrical potential of the electrode to a second potential (e.g. a local ground) and generates a signal that is indicative of the biopotential.