Characterization and Analysis of Planar Inverted‑F Antennas for Fat-Intrabody Communication Systems

Intrabody communication between implantable medical devices and external receivers relies on small antennas that operate in the human tissues. However, the complex structure of the body causes problems of frequency detuning, signal attenuation, and SAR. Modern research has focused on miniaturization, broadband techniques, and circular polarization to reduce distortion, but knowledge of how PIFA in the dual band acts in fat tissues is limited. This study investigates the performance of dual‑band PIFA antennas designed for 2.4 GHz and 5.8 GHz ISM bands when implanted in adipose tissue. The work aims to characterize return loss, transmission efficiency, and the influence of fat thickness and multilayer structures. The antenna was simulated in three environments: free space, homogenous fat, and a three-layer model (skin-fat-muscle). Results were obtained for different implant depths and separation distances. Within the adipose tissue, the resonance frequency shifted downward, and S21 decreased by approximately 10 dB due to dielectric coupling. Increasing fat thickness from 5 mm to 25 mm lowered S21 by 8–12 dB at 5.8 GHz. The proposed PIFA is larger in size (≈19 × 13 × 1.2 mm³) but offers a simpler structure and acceptable transmission through adipose tissue. The dual-band PIFA enables effective intrabody coupling through fat while maintaining low transmission losses. Although miniaturized designs achieve smaller volumes and wider bandwidths, this study highlights the importance of characterizing antennas with realistic fat layers and quantifies the effect of thickness on the connection bandwidth. Future research should integrate circular polarization, miniaturization, and experimental validation of heterogeneous tissue phantoms.