A finite element/superposition technique for the design of electromagnetically coupled coils

The authors present a numerical technique for the design of electromagnetically coupled coils. The technique is applicable to coil systems (transmitter and receiver coils) located in the same medium and separated by variable communication distances as well as to coils in different media. Coil geometries, and optimum data communication distances can be obtained with the technique presented here. The design method developed is based on a general solution of the electromagnetic field problem associated with these coil systems, using constrained finite-element field solutions obtained by an optimization technique. Since the electromagnetic energy transfer between the coil systems is established bidirectionally, superposition of the fields from the coils was required to determine forward and reflected field data. This information is then used to determine reflected voltages or phase differences which can be utilized by the system electronics. Two separate coil systems were implemented as examples in order to compare the numerical design results with those obtained by conventional empirical formulas and with the results of laboratory performance tests. The validity of the method wa confirmed by the comparison