  The paper describes highly-sensitive passive electric potential sensors (EPS)
for non-contact detection of multiple biophysical signals, including
electrocardiogram (ECG), respiration cycle (RC), and electroencephalogram
(EEG). The proposed EPS uses an optimized transimpedance amplifier (TIA), a
single guarded sensing electrode, and an adaptive cancellation loop (ACL) to
maximize sensitivity (DC transimpedance $=150$~G$\Omega$) in the presence of
power line interference (PLI) and motion artifacts. Tests were performed on
healthy adult volunteers in noisy and unshielded indoor environments. Useful
sensing ranges for ECG, RC, and EEG measurements, as validated against
reference contact sensors, were observed to be approximately 50~cm, 100~cm, and
5~cm, respectively. ECG and RC signals were also successfully measured through
wooden tables for subjects in sleep-like postures. The EPS were integrated with
a wireless microcontroller to realize wireless sensor nodes capable of
streaming acquired data to a remote base station in real-time.
