Vol.:(0123456789) 1 3 Applied Physics A ( 2020) 126:110 https://doi.org/10.1007/s00339-019-3274-5 Actively tunable terahertz metamaterial with single‑band anddual‑band switching characteristic Xingzhuo Hu 1  · Daoye Zheng 1  · Yu‑Sheng Lin 1 Received: 10 November 2019 / Accepted: 30 December 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract We present a design of tunable terahertz (THz) metamaterial (TTM) with single-band and dual-band fltering and switch- ing characteristics. The proposed device is composed of face-to-face split-ring resonator (SRR) and a central bar. By mov- ing the SRRs to change the gap between SRRs and central bar, the free spectrum ranges (FSR) could be bi-directionally broadened 0.14 THz and narrowed 0.19 THz at TE and TM modes, respectively. To control the coplanar moving central bar, the electromagnetic response of TTM device exhibits polarization-dependent characteristic. TTM shows the switching characteristic between single-band to dual-band resonance at TE mode and exhibits resonance-insensitive to the displace- ment of central bar at TM mode. These results open an avenue to be potentially used for detector, sensor, and switch in the THz-wave applications. Keywords Metamaterial · Terahertz · Resonator · Switch 1 Introduction In the entire electromagnetic (EM) spectra, terahertz (THz) metamaterials are artifcial EM composites allowing peo- ple to control their optical properties, including amplitude, phase, frequency, and polarization of incident light. They have been attracting more and more attentions owing to their exotic optical characteristics that natural materials do not have [1]. It can be enabled by the manipulation of EM wave by strongly localized resonances within the devices [2]. Such unique EM characteristics make many concepts theoretically feasible including negative refractive index [3, 4], super- lens [5], cloaking [6] and perfect absorber [7, 8]. Among these metamaterials, the confguration of split-ring resonator (SRR) is a classical design of metamaterials with negative permeability and negative refractive index proposed by J. B. Pendry in 1999 [9]. The EM resonance of SRR is a function of refraction index of EM wave, according to the quasi-static formulas for a parallel plate capacitor and a solenoid. Such concept was established by D. R. Smith et al. in 2000 [10]. After that, a plenty of researches for metamaterials based on SRR structure were presented and demonstrated to opti- mize the EM characteristics in the terahertz (THz) frequency range [11-16]. Recently, there are various types of metama- terials presented and demonstrated, including I-shape [17], V-shape [18], complementary shape [19], and so on. Among these metamaterials, the corresponding resonant frequency could not be tuned to possess large tuning range and multi- functional applications. Recently, many metamaterials with tunable EM charac- teristics come up such as metamaterial absorber with vana- dium dioxide [20], graphene-based tunable absorber [21], and metamaterial with tunable negative refractive [22]. To date, the tuning approaches of metamaterial resonant fre- quency are included but not limited to the uses of semicon- ductor diode [23-25], thermal tuning [26, 27], ferroelectric material [28] and reconfigurable tuning [29- 31]. These methods are usually nonlinear and highly dependent on the material characteristics. The reconfgurable tuning method is more practical and feasible since the transmission property can be tuned linearly by reshaping the structural size pro- portionally which includes the reconfgurable metamaterial [32, 33], reshaping the structural element [34], bending the substrate or lattice [35] or rotating the metamaterial [36, 37]. * Yu-Sheng Lin linyoush@mail.sysu.edu.cn 1 State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Sun Yat-Sen University, Guangzhou 510275, China