Theory and simulation of an orthogonal-coil directional beam antenna for biomedical applications

Many biomedical applications, including in-body localization, in vivo sensor data acquisition, and measurement of the electrical properties of human tissues require or may greatly benefit from a highly concentrated and directional beam emanating from a transmitting antenna. While many beam focusing efforts have utilized large aperture antennas or large antenna arrays, these methods are not always convenient for biomedical use. Furthermore, sensing modalities operating in the far-field susceptive to multi-path issues related to the many diverse material property interfaces within the human body. This work presents the theoretical background related to the construction and operation of a very small and easily located antenna that generates a highly directive signal ideal for biomedical use. The antenna, constructed from a pair of orthogonally oriented magnetic dipoles excited in quadrature, utilizes the advantages associated with operating in the Fresnel region, directing most of its emitted energy 45 degrees from broadside. Numerical simulations support this operation and have led to a number of applications as identified herein prompting the development of a Finite Element Method compatible human body model based on the Visible Human Project data maintained by the National Institute of Health.