Miniaturized Dual-Resonant Helix/Spiral Antenna System at MHz-Band for FSK Impulse Radio Intrabody Communications

Abstract

In this article, a miniaturized dual-resonant antenna system at MHz-band operating at around 20 and 50 MHz is proposed for frequency-shift keying impulse radio (FSK-IR) intrabody communications. This antenna system comprises a swallowable helix-coil in-body antenna with a hollow cylindrical shape of 10 mm diameter and 30 mm length, and two single band on-body matched planar spiral-coil antennas with a compact size of 79 mm $\times\,\,72$ mm $\times\,\,2.8$ mm. For in-body antenna design, a nonuniform helical pitch structure is utilized to produce dual-resonant frequencies. The soft ferrite magnetic sheet with high relative permeability and low dissipation factor is used as a flexible conformal substrate to realize antenna miniaturization without lumped element loading. Simulation results for antenna performance, electromagnetic field distribution, and specific absorption rate are presented with different tissue-type phantoms, as well as an anatomical numerical human model. In addition, experimental verification of antenna performance and implant transmission characteristics is also conducted in a liquid phantom. At an implant depth of 50 mm, the measured maximum transmission coefficients are −33 and −45 dB at the dual-resonant frequency bands, respectively. Simulation and measurement results demonstrate that the proposed dual-resonant antenna is suitable for the FSK-IR system and can be expected to realize a data rate as high as 10 Mb/s for biomedical implant applications at MHz-band.