Significant Improvement of Magnetic Field Focusing Ability in Actively-Tuned Resonant Loop Array

When a metallic loop array is properly designed, the incoming magnetic field is redistributed to enhance the transmitted magnetic field in the vicinity of the array, and such loops are, in general, electrically small in the kilohertz and megahertz ranges. We experimentally demonstrate that, at 13 MHz, a variable-capacitor-loaded resonant loop array provides a 31-fold increase of the magnetic field at a distance of 2 mm away from the array. Moreover, the resonant frequency of the loop array can be tuned electrically. Experimental results agree with numerical results obtained by the method-of-moment-based simulator FEKO.