NUMERICAL MODELLING OF BODY-ANTENNA INTERACTION EFFECTS IN INTRACORPOREAL UHF RADIO TELEMETERS

W G Scanlon and N E Evans
N Ireland Bioengineering Centre & School of Electrical and Electronic Engineering
University of Ulster, Shore Road, Newtownabbey, Co Antrim, N Ireland, UK, BT37 0QB

INTRODUCTION Intracorporeal UHF radio telemeters are used for human and animal physiological monitoring in both clinical and research settings. In-body placement governs the resultant output power and polar pattern shape of the radiating system. Both parameters are frequency dependent, and are strongly influenced by body structure and the electrical properties of the surrounding tissue.

Practical determination of body influences is not always feasible since extensive antenna test range facilities are required to implement near and far field electric field strength measurements. Finite-Difference Time-Domain (FDTD) numerical modelling methods, however, allow the accurate determination of all critical parameters affecting in-body antenna performance provided a suitable body model is available.

METHOD Body models were constructed by segmenting the NIH Visible Human data for the regions directly surrounding the implanted telemeter. A FDTD program was developed using ‘C’; the advantage of this technique is the direct calculation of near-field electromagnetic data and the relatively straightforward generation of radiation patterns.

RESULTS Representative results are presented below. An electrically small 418 MHz source was placed in the abdomen of an adult male body model. The plot shows the vertical component of the electric field across a transaxial plane.

Software generated body-model                     Isoelectric field plot

DISCUSSION The calculated anterior radiation is dominant as the posterior near-fields are non-uniform resulting in a 15 dB power reduction in this direction.