Gastrointestinal Segment Tracking of Ingestible Capsules Using Biodegradable Superstrates

Miniaturized wireless capsule endoscopes offer minimally invasive real-time monitoring of vital parameters of the gastrointestinal tract. Although various ingestible capsules are commercially available for wireless endoscopy, the precise real-time localization of these capsules within the tract remains a challenge. This work proposes the utilization of a pH -sensitive biodegradable superstrate for gastrointestinal segment tracking in the 433 MHz Industrial, Scientific, and Medical (ISM) band. The superstrate consists of three rings engineered to degrade at specific pH levels that correspond to the distinct environments of the GI tissues - stomach, small intestine, and large intestine. This superstrate covers the outer surface of a capsule which features an integrated conformal dipole antenna. Hence, biodegradation of each ring of the superstrate in its respective GI segment leads to the alteration of the near-field of the antenna, changing its center frequency and reflection coefficient at 434 MHz in each segment. In this way, biodegradation process links the location data to the input parameters of the antenna, enabling segment tracking within the tract. Simulation results show that a shift of at least 5 MHz can be created in the center frequency as the capsule advances along each segment while the antenna is kept operational over the 433 MHz ISM band throughout the entire tract. Finally, preliminary tests using liquid gastrointestinal phantoms are conducted to validate the proposed technique.