Split-ring resonator (SRR) based metamaterials have been studied for the development of highly sensitive, small-sized, low-power chemical and biomolecular sensors. However, the anisotropic behavior arising from their two-dimensional (2D) structure presents substantial challenges leading to ambiguity in their transmission spectra. In this paper, we present the design of a three-dimensional (3D) isotropic octagram split-ring resonator (OSRR) demonstrating a three-dimensionally coupled resonance behavior that overcomes the anisotropic response of conventional 2D SRRs, leading to a strong, distortion-free, and polarization-invariant transmission response. The OSRR undergoes 3D coupling through the splits at the corners of the 3D structure (cube), which remains invariant under any polarization along the coordinate axes. The strong coupling between resonant segments provides the OSRR with 25 times higher sensitivity than the corresponding 2D structure, allowing the resonant frequency to be reliably monitored for small changes in concentration of a targeted substance. The isotropic frequency response of the 3D OSRR, without ambiguity in the amplitude caused by the polarization dependence, also allows monitoring the amplitude for minute changes in concentration that are too small to cause any shift in resonant frequency. Thus, the detection range for the presented 3D OSRR stretches from large to minute variations of targeted substance.
Bibliographical noteFunding Information:
This research was supported by the National Science Foundation under Grant No. CMMI-1454293 and a start-up fund at the University of Minnesota, Twin Cities. The authors also acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing computing resources that contributed to the simulation results reported within this paper. A portion of this work was also carried out in the Minnesota Nano Center, which receives partial support from the NSF through the NNCI program. H. P., J. J., and D. K. were supported in part by the National Research Foundation of Korea (NRF) under MSIP: NRF-2015R1A3A2031768, NRF-2016R1D1A1A02937152, and MOE: BK21 Plus Program-21A20131111123.
- isotropic metamaterials
- octagram SRRs
- optical sensors
- split-ring resonators