Figure 1. Principle in coiling up the acoustic and the electromagnetic space.
(a) Waves confined along a curled channel have an equivalent refractive index n1D≫1 comparing to propagation along a straight line. (b) (photograph) A unit of the acoustic space-coiling metamaterial fabricated using aluminum with a = 2.33 cm. (c) Simulated pressure field in a single unit being excited by a plane wave propagating to the right at 2.7 kHz, with red/blue color denoting high/low values. (d) (photograph) A unit of the electromagnetic space-coiling metamaterial by stacking copper-wire patterns printed on circuit boards, with a = 0.76 cm and foam spacers in the vertical direction. (e) Simulated H-field pattern at the copper wire layer being excited by a plane wave propagating to the right at 6.54 GHz. White lines represent the aluminum walls or the copper wires.