Focused Near-Field Meta-Surface Sensors of Internal Tissue Motion with Low Interference

Accurate monitoring of internal tissue dynamics can be applied to various disorder diagnostics. However, conventional sensors encounter challenges such as shallow body penetration, low signal specificity due to limited control of the capture volume, and vulnerability to ambient interferences. The sensing signal can suffer from data loss and limited spatial resolution when the interference is strong. Here we introduce a compact meta-surface sensor featuring a 2×2 planar inverted-F antenna (PIFA) array, integrated with an artificial magnetic conductor (AMC) structure for operation around 4.85 GHz. The meta-surface design was compared against the conventional monopole antenna for vital signs and muscle actuation. We conducted ambulatory vital-sign monitoring with robustness against large motion interference and wrist tissue actuation detection with high waveform stability. The proposed PIFA-AMC element provides a low-interference and high-precision solution compared to previous radio sensors.