Suitability of Common Ingestible Antennas for Multiplexed Gastrointestinal Biosensing

TL;DR

This study compares dipole, patch, and loop ingestible antennas in gastrointestinal tissues to evaluate their sensing, robustness, and radiation performance for biosensing applications, aiding design decisions for internal health monitoring devices.

Contribution

It provides a comprehensive comparison of common ingestible antennas as biosensors, focusing on their electromagnetic properties in gastrointestinal tissues, which was previously lacking.

Findings

Dipole antennas show high sensing capability based on phase changes.

Shell thickness affects gain and radiation efficiency significantly.

All antenna types exhibit different robustness levels across tissues.

Abstract

Ingestible sensor devices, which are increasingly used for internal health monitoring, rely on antennas to perform sensing functions and simultaneously to communicate with external devices. Despite the development of various ingestible antennas, there has been no comprehensive comparison of their performance as biosensors. This paper addresses this gap by examining and comparing the suitability of three common types of ingestible antennas -- dipole, patch, and loop -- as biosensors for distinguishing gastrointestinal tissues (stomach, small intestine, and large intestine) based on their electromagnetic properties. The antennas studied in this work conform to the inner surface of biocompatible polylactic acid capsules with varying shell thicknesses and operate in the 433 MHz Industrial, Scientific, and Medical band. The comparison is performed in gastrointestinal tissues using several antenna parameters: 1) Sensing Capability: Changes in the phase of the reflection coefficient in the tissues are selected as the sensing parameter. 2) Robustness: The frequency interval (f_i) in which the antennas are matched (|S11| < -10 dB) in all the tissues and the maximum change in the center frequency (f_c) in different tissues are examined. 3) Radiation Performance: The gain and radiation efficiency of the antennas are examined. The effect of shell thickness on gain and radiation efficiency at 434 MHz is presented. Additionally, the radiation efficiency at various frequencies allocated for medical communications is compared with the theoretical maximum achievable efficiencies. These comprehensive data provide valuable information for making engineering decisions when designing multiplexed biosensor antennas for ingestible applications.