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.
Similar content being viewed by others
References
Abramowitz, M., andStegun, I. A. Handbook of mathematical functions with formulas, graphs and mathematical tables. Washington, D.C.: U. S. Department of Commerce, National Bureau of Standards, Applied Mathematics Series 55, 7th Printing, May, 1968.
Cruzan, O. R. Radiation properties of a thin wire loop antenna embedded in a spherical medium. InInstitute of Radio Engineers Transactions on Antennas and Propagation AP-7, 1959, 345–352.
Harrington, R. F.,Field computation by moment methods. New York: MacMillan, 1968.
Kang, S. R. The radiation from an electrically small circular wire loop implanted in a dissipative homogeneous spherical medium. Master of Science Thesis, Case Western Reserve University, Cleveland, OH, 1970.
Ko, W. H., andNeuman, M. R. Implant biotelemetry and microelectronics.Science,56, 1967, 351–360.
Mackay, R. S. Bio-Medical telemetry, 2nd ed. New York: John Wiley, 1970.
Rush, S., Abildskov, J. A., andMcFee, R. Resistivity of body tissue at low frequency, Circulation Research 12, 40–50, 1963.
Schwan, H. P., Electric characteristics of tissues—A survey.Biophysik 1, 1963, 198–208.
Schwan, H. P., and Kay, C. F., The conductivity of living tissues.Annals New York Academy of Sciences, 1965, 1007–1013.
Stratton, J. A. Electromagnetic theory, New York: McGraw-Hill, 1941.
Wilkinson, J. H. The solution of ill-conditioned linear equations InMathematical methods for digital computers, New York: John Wiley, 1967 Vol. 2.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Ko, W.H., Plonsey, R. & Kang, S.R. The radiation from an electrically small circular wire loop implanted in a dissipative homogeneous spherical medium. Ann Biomed Eng 1, 135–145 (1972). https://doi.org/10.1007/BF02584203
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF02584203