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Rectangular coils modeling for inductive links in implantable biomedical devices

Wirelessly coupled coils are crucial for efficient power transmission in implantable biomedical devices. Previous design methods are only eligible for improving the efficiency of circular or square coils. This paper presents a method of characterizing and optimizing rectangular coils frequently used in inductively coupled systems. After a lumped component model is set up for inductive coils, the efficiency can be expressed in terms of geometrical parameters of the coils. Subsequently, the power efficiency can be plotted versus these parameters in Matlab, thus the desired coils for optimum power transfer can be obtained. With this design procedure from mathematical optimization, we eventually designed two rectangular coils spaced 10 mm apart, which achieves a power transmission efficiency of 46.4 % at a frequency of 3 MHz. The design methodology is verified by simulation and measurement.