Modeling the Surface Field From an Ingested Radio Transmitter With an Approximate Attenuation Model for Gastroenterology Investigations

Objective: The precise location of an ingested radio transmitter/sensor is of importance in gastroenterology studies. Given the complex geometry of the gut and the very large variations in human size and electromagnetic characteristics, inverse modeling from surface-based measurements is very complex, and a unique location solution is not possible. This paper proposes a simple method based on far-field approximation of the attenuated field from the ingested transmitter. Methods: The validation experiments for an ellipsoid cylinder using averaged electromagnetic properties of the human gastrointestinal tract (conductivity 0.87 S/m, relative permittivity 62) and a Hertzian dipole radiator inside the body with a frequency of 433 MHz were conducted assuming a receiver dynamic range of less than 100 dB. Results: The surface field intensity distribution patterns and the amplitude ranges were established for different positions and orientation of the dipole in every segment of the tract. The reliability of the method was verified by comparison with finite-difference time-domain modeling. Conclusion: The method provides an analytical solution to estimate the surface field intensity depending on the dipole location and orientation with a negligible computational cost. Significance: This efficient algorithm can be incorporated into an inversion algorithm for localization of wireless endoscopy sensors to allow precise targeted treatment.