The radiation from an electrically small circular wire loop implanted in a dissipative homogeneous spherical medium

Abstract

Radio-frequency rediation properties of the implanted transmitter were studied. Two models using spheres representing the biological body were studied theoretically; one is for current loop without insulation, and the other, a loop housed in a small spherical insulation embedded in the lossy sphere. The observed anomalous phenomenon, that received rf field is increased after transmitter is embedded in a biological body, has been explained theoretically. Increase of rf field occurs when effective wavelength approaches diameter of sphere and loss tangent of medium is less than or near 1. When loop is at center of spherical body, the radiation pattern is closely the same as that of loop in free space. When loss tangent is less than 1, maximum field strength occurs if effective wavelength is equal to diameter of sphere. When loop is off-centered, orientation of the loop is found to be important in determining field strength and radiation pattern. If the magnetic dipole moment direction of loop is perpendicular to radial axis of the sphere, rf field is 5≈10 times stronger than when the dipole direction is parallel. These results will be useful in the design of implant telemetry systems.