Design of Spiral Circular Coils in Wet and Dry Tissue for Bio-Implanted Micro-System Applications
This paper deals with the design of small-sized bio-implanted spiral circular coils (pancake) with an operating frequency of 13.56 MHz. The external and internal coils' geometric dimensions are dout = 56 mm, din = 10 mm and dout = 11.6 mm, din = 5 mm, respectively, in which the electrical performance is verified through the commercial field solver High Frequency Structural Simulator (HFSS 13.0), which employs the finite-element method (FEM) technique. Mathematical models for the proposed coils are developed. The simulation is performed-based on the developmental model in the air and at depths 6\,mm in a human biological tissue of dry and wet-skin. The results demonstrate that the external and internal coils have maximum near-field gains of 54.15 dB and 53.30 dB in air. The maximum gains of the external coil contacted the wet and dry skin are 49.80 dB and 48.95 dB, respectively. The maximum gains of the internal coil at depths of 6 mm in the wet and dry tissue are 41.80 dB and 41.40 dB, respectively. However, the external coil radiation efficiencies on wet- and dry-skin are 92% and 90%, respectively, compared with that on air. The internal coil radiation efficiencies on wet- and dry-skin are 78.4% and 77.6%, respectively, compared with that on air. In this study, the specific absorption rate (SAR) and radiated power results of the internal coil are investigated using SEMCAD 16.4 software. The SAR and power loss studies show that the designed implanted coil has a negligible effect on the wet and dry skin and can be ignored.