Near-Field Focusing With a Corrugated Surface

In this letter, we present a theoretical device that can produce electromagnetic near-field patterns with deep subwavelength resolution. The device consists of a single slit in a corrugated metallic surface. The surface exhibits a nonperiodic series of grooves symmetrically positioned about a waveguide-fed slit. A procedure for designing such a device is described in detail. The electromagnetic response of the corrugated surface is shown to be as theoretically predicted, producing a subwavelength focal pattern with a null-to-null beamwidth of lambda/10. In addition, the effect of losses on the performance of the device is studied. Finally, it is shown that the device can be impedance-matched to its waveguide feed. Such devices will find use in noncontact sensing and near-field probing applications.