Synthesis and Design of Programmable Subwavelength Coil Array for Near-Field Manipulation

We present the design and experimental demonstration of a programmable subwavelength coil array, which can manipulate the evanescent magnetic field leading to a precisely controlled electric-field pattern at an image plane in the near-field zone. A synthesis methodology is outlined for 2-D near-field manipulations. Simulation based on a full-wave electromagnetic solver clearly demonstrates the focused electric-field pattern, and its implementation is discussed. An example of a three-layer subwavelength coil array with 48 units is fabricated and measured. The consensus of the measured results with the simulated and synthesized results verified the presented synthesis method. Such a device, capable of producing a programmable magnetic field and electric field, respectively, in orthogonal planes, will find applications in biomedical devices such as neural stimulation, and potentially other areas such as noncontact charging.