Metamaterial-Integrated Space–Time Coding Array With Direct Antenna Modulation for Multiperson Vital Sign Monitoring

This work introduces a metamaterial (MTM)-integrated space-time coding (STC) transmitting array to detect the multitarget vital sign signals including respiration and heart rates (HR). A zeroth-order MTM resonator serves as a series power divider, evenly distributing the carrier signal across each antenna element of the proposed STC array. Each antenna element employs direct antenna modulation (DAM) to achieve a binary phase shift of 0° and 180° in the far-field, while the amplitude and polarization are maintained. This phase difference represents the states of the 1-bit STC. In addition, a digitally switched microstrip line provides a 90°-phase delay, used with DAM to establish the 2-bit STC states. The STC coding matrix sequences are controlled digitally via a field programmable gate array (FPGA), with optimization of the coding matrix for different scenarios through a genetic algorithm (GA). The harmonic beam steering patterns are measured to confirm the effectiveness of the matrix-optimized algorithm. Experimental results confirm the proposed system’s capability to monitor up to four human targets simultaneously. The optimized matrix’s effectiveness is verified through the measured harmonic beam patterns, which efficiently utilize spectrum due to the narrow modulation bandwidth in the kilohertz range. The detected respiration and HRs align closely with ground-truth data from commercial wearable devices. Compared to traditional multitarget radar systems with multiple RF channels, the proposed STC array significantly reduces complexity and cost, making it ideal for indoor medical IoT applications.