A Conformal Differentially Fed Antenna for Ingestible Capsule System

Abstract

A conformal differentially fed antenna at 915 MHz industrial, scientific, and medical (902–928 MHz) band for monitoring in body core temperature is presented in this paper. In virtue of its characteristics of ultrathin and flexible substrate, the peculiarity that proposed antenna can be wrapped around the capsule inner wall demonstrates the satisfactory performance of occupying a little space. The volume of the conformal patch antenna only measures 30 mm3 by notching meandering slots to achieve miniaturization. The simulated impedance bandwidth ( $\vert S_{11}\vert dB) covers from 861 to 942 MHz. The integrated capsule system, inserted in a cubic homogeneous muscle phantom for initial parametric studies and optimization, occupies the dimensions of 22 mm (length) $\times11$ mm (diameter). Meanwhile, the performance on the sensitivity to surrounding environment and specific absorption rate distribution are studied. In the measurements, the conformal antenna is rolled around a 3-D-printed capsule inside minced pork. The pork temperature data are monitored in time and transferred wirelessly. To confirm the system reliability, hardware circuits are designed with differential concept and a data logger is also realized to record in-time temperature data. Finally, the feasibility of system function demonstrates the suitability of the conformal differentially fed antenna in biomedical applications.