Ultrathin Perfect Absorbing Metamaterial Stacked with Solid and Inverse Antenna Above Metal Ground

Metamaterials have proven to be effective electromagnetic (EM) wave absorbers with unprecedented control over the properties of the wave.(<i>1-3</i>) To achieve ultracompact, flexible, and lightweight EM absorbers, the ability to perfectly absorb an EM wave with a material much thinner than the wavelength is required. Herein, we demonstrate a metamaterial with extreme subwavelength thickness by introducing a cross-shaped aperture into the bottom metal plane of a conventional three-layer metal patch/dielectric/metal stack.(<i>4</i>) With the stack placed above a metal ground for perfect absorption, a total thickness of only 1/1250 of the working wavelength is achieved. The aperture increases the resonance wavelengths by up to 10-folds by enlarging the inductance of the stack. More specifically, the induced current in the aperture plane must flow around the aperture, creating a magnetic flux that increases with aperture area. Using this approach, we experimentally demonstrate perfect absorption using the appropriate dielectric thickness and loss tangent needed to achieve critical coupling. To the best of our knowledge, our EM absorbers provide the largest wavelength-to-thickness ratios to date. The principles outlined here are general and can be extended to other frequencies.<br/><br/><br/>Reference<br/>1. C. M. Watts, X. Liu, W. J. Padilla, “Metamaterial Electromagnetic Wave Absorbers. <i>Adv. Mater.”</i> <b>24</b>, OP98-OP120 (2012).<br/>2. N. I. Landy, S. Sajuyigbe, J. J. Mock, D. R. Smith, W. J. Padilla, “Perfect Metamaterial Absorber. <i>Phys. Rev. Lett.”</i> <b>100</b>, 207402 (2008).<br/>3. Y. Ra’di, C. R. Simovski, S. A. Tretyakov, “Thin Perfect Absorbers for Electromagnetic Waves: Theory, Design, and Realizations. <i>Phys. Rev. Appl.”</i> <b>3</b>, 037001 (2015).<br/>4. M. Kim, K. Jung, Y. Choi, S. S. Hwang, J. K. Hyun, “Coupled Solid and Inverse Antenna Stacks Above Metal Ground as Metamaterial Perfect Electromagnetic Wave Absorbers with Extreme Subwavelength Thicknesses. <i>Advanced Optical Materials”</i>, 2101672 (2022).