Design of a dual-band capsule antenna based on effective relative permittivity for realistic implantable medical devices

The effective relative permittivity (eeff) of planar capsule antennas differs significantly from that of antennas implanted directly into biological tissue. However, this distinction has been largely overlooked in most planar capsule antenna designs reported in the recent literature for implantable medical devices (IMDs), where it is commonly assumed that antenna performance in direct tissue implantation is equally valid within a capsule environment. In this article, the eeff of a microstrip antenna is first calculated using an efficient analytical model for both implantation scenarios. Based on these insights, a dual-band planar capsule antenna with a novel configuration is proposed for implantable and ingestible applications, carefully designed with consideration of the effective relative permittivity to ensure robust performance. The proposed antenna features a compact footprint of 14 mm x 14 mm x 0.634 mm3 and operates in both the 402 MHz MICS and 2.4 GHz ISM bands. The miniaturized dual-band antenna configuration is achieved by combining an efficient radiator, a shorting pin, and a slotted ground plane. A prototype of the proposed antenna, whose numerical design and analysis were conducted on both homogeneous muscle tissue and realistic human models, was encapsulated, and its performance was measured using minced meat.