Optimization of a Compact Wearable LoRa Patch Antenna for Vital Sign Monitoring in WBAN Medical Applications Using Machine Learning

This study introduces an innovative and compact wearable Long-Range (LoRa) patch antenna developed for monitoring vital signs, with a focus on heart rate and body temperature, in medical applications of Wireless Body Area Networks (WBAN). The antenna functions within the 868 MHz and 915 MHz LoRa bands, filling a notable gap in current literature regarding compact, wearable antennas operating below 1 GHz. Fabricated on a Rogers Duroid RO3003 substrate, the antenna incorporates a U-slot on a conventional rectangular patch, a matching stub, and a partial ground plane to enhance impedance matching and performance efficiency. Furthermore, the antenna displays a bidirectional radiation pattern in the E-plane and an omnidirectional pattern in the H-plane at both frequencies, achieving a peak gain of 2.12 dBi and a radiation efficiency of 99.8% at 868 MHz. The antenna, measuring
$80 \times 60 \text {mm}^{2}$
(
$0.23~\lambda _{0} \times 0.17~\lambda _{0}$
), was designed, simulated, and optimized using CST Microwave Studio (MWS) software. The performance under bending conditions was also assessed, revealing a bending an excellent efficiency with minimal impact on bandwidth and gain. Specific Absorption Rate (SAR) analysis indicated that all values were within the safety limits set by FCC and ICNIRP standards. Supervised regression machine learning models, specifically the ensemble regression model, were employed to predict resonance frequencies based on various antenna parameters, resulting in an R-squared score of 87.68%. This approach significantly reduced the computational time required for full-wave simulations, streamlining the design process. Real-world experimental validation involved open-field testing of the fabricated prototype for WBAN LoRa applications. The performance, evaluated on a LoRa transceiver system utilizing the LoRa SX1276, demonstrated the superior capabilities of the proposed antenna in heart rate and temperature monitoring, with an average RSSI improvement of -5 dBm at various points within a range of up to 1 km. This confirmed its improved signal transmission and reception capabilities in vital sign monitoring. The proposed antenna shows strong performance metrics and significant potential for WBAN in long-range applications, as evidenced by thorough experimental validations.