We designed a periodic structure by using metallic split-ring-resonator (SRR) arrays as effective mu-negative (NING) materials and metal fork arrays as effective epsilon-negative (ENG) materials. The finite-difference-time-domain (FDTD) simulations confirmed that such structure possesses a locally resonant gap that depends on the ratio of the thicknesses of the two media. (c) 2006 Elsevier B.V. All rights reserved.