Radio-Frequency Near-Field Sensor Design for Minuscule Internal Motion

We present the improved design of a radio-frequency (RF) near-field sensor for minuscule internal motion inside structures and small animals. The design tradeoffs of the antenna placement and transceiver configuration are explored experimentally by a structural setup of the fluid stirrer. The sensor performance is benchmarked in various antenna configurations and quadrature baseband sampling settings. An optimized antenna pair holder design is then applied to a continuous touchless recording for the respiration and heartbeat of nestling and adult tree swallows noninvasively. Furthermore, we also built a low-power portable all-in-one RF sensor printed circuit board (PCB) using the system parameters from previous experiments. A 40-min experiment on a conscious and free-to-move 13-day-old nestling tree swallow for respiration monitoring was successfully conducted.