Displacement Current Mediated Resonances in Terahertz Metamaterials

Abstract

devices, their relatively low Q-factors (typically below 20 of single-ring resonator MMs) [ 11,13 ] compared to micro-and nanoscale mechanical resonators (typically between 10 4 and 10 7 ) [ 14 ] impose a limitation on their sensitivities.One of the approaches to increase the Q-factor of MMs is to reduce the energy losses of MMs and substrates by optimizing the material properties and structures of the MMs. [ 15 ] There are typically three main energy loss mechanisms: Ohmic loss of MMs, [ 16 ] dielectric loss of the substrate, [ 17 ] and radiation loss of MMs. [ 18 ] The most common method to increase Q-factor of MMs without changing material properties is to design asymmetric split resonators (ASRs) by breaking the symmetry of the MMs. [ 19,20 ] The asymmetric design reduces the radiation loss of the resonator and increases Q-factor up to 30. [21][22][23][24] Another method uses coupling between MMs in a super unit to excite both odd and even modes of the MMs. This approach improves Q-factor by a factor of 5 compared to typical fi lm-based MMs. [ 25 ] The Q-factor of THz MMs needs to be further enhanced (10-20 times) to meet the requirement of ultrasensitive sensors with high selectivity. In the present study, we introduce novel nanopillar-based THz split ring resonator (SRR) MMs, utilizing displacement current in the dielectric medium between nanopillars that signifi cantly increases energy storage in the MMs, leading to enhanced Q-factor up to about 450 (about 30 times higher than that of typical thin-fi lm-based MMs). A metallic nanopillar array is designed in the form of a single gap (C-shape) SRR. Vacuum or dielectric materials of different permittivities are fi lled between the nanopillars to form nanoscale dielectric gaps. The size of the dielectric gaps varies from a few nanometers up to tens of nanometers. Since the use of nanopillars offers large surface area, the total electric charge separation (+ q and − q ) on the collective surfaces increases, resulting in the increase in electrostatic energy stored in the MMs, which leads to signifi cantly enhanced Q-factor. In addition, dielectric nanogaps reduce the Ohmic loss generated by the current circulating in the metal conductor, thus the total energy loss of MMs is reduced, which further enhances the Q-factor of the MMs. Hence, high Q-factor up to about 450 can be observed in the nanopillar-based SRR MMs, which means that they are much more sensitive than typical thin-fi lm-based MMs.Terahertz metamaterials (THz MMs) have been proven to be good candidates for chemical, biological, temperature, strain, and position sensing. However, currently developed thin-metal-fi lm-based split ring resonator (SRR) MMs have relatively low quality factor (Q-factors), leading to a poor sensitivity, which is one of the obstacles for development of sensors. In order to enhance the Q-factor, novel THz MMs, nanopillar-based MMs, are designed, fabricated, and characterized. The nanopillar-based MMs excite the inductivecapacitive resonance via desplacement currents, showing a...

Small‐Scale Biological and Artificial Multidimensional Sensors for 3D Sensing

“…Other viable applications of the 3D cubic nanosensor include high sensitivity detection and analysis of biological molecules and chemical species through shift in conventional LC or plasmonic resonances. However, 2D micro‐ and nanoscale biological sensors possess a major disadvantage for performing measurements under in vivo conditions as a result of the highly directional response . Attempts to fabricate polarization invariant (isotropic) SRR have been primarily limited due to the use of planar substrates which can achieve only partial isotropy .…”

“…The 0D, 1D, 2D, and 3D objects are represented by morphological features of the point, line, plane, and multifaced polyhedron, respectively as illustrated in Figure . The 0D to 3D sensors are found to have point‐like (e.g., nanoparticles, quantum dots), linear (e.g., nanowire, carbon nanotubes), planar (e.g., thin film structures), and multifaceted sensing elements (e.g., cube, pyramids), respectively . It is worth noting that 3D sensors equip a unique sensing capability which cannot be realized with 0D, 1D, and 2D sensing systems.…”

Enhancement and Switching of Fano Resonance in Metamaterial

“…Recently, Fano‐type spectral response in plasmonic nanostructures and metamaterials have attracted considerable attention due to its superior capability to manipulate various characteristics of the Fano resonance in a broad frequency range, which is applicable for practical applications including chemical or biosensing, nonlinear optics, slow light device, and spectroscopy . Numerous metallic or dielectric metamateirals have been designed to demonstrate Fano resonances using a common method of breaking the structural symmetry of nanostructures, such as split‐ring resonators, asymmetric double bars, nanoparticle clusters, dolmen structures, and hybridized structures …”

Three-Dimensional Anisotropic Metamaterials as Triaxial Optical Inclinometers

“…A major limiting factor in the further implementation and commercialization of these devices have been disadvantages arising from their low quality factor leading to a low sensitivity. However, research into design of the conventional C-shaped SRR using nanopillar 45 , asymmetry of the split 46 , and modification of coupling within SRR arrays 47 have led to an increase in the quality factor by a factor of 30 and a corresponding 10 fold increase in sensitivity.

Figure 1Illustration of two- and three-dimensional split-ring resonators (SRRs) and their simulated transmission response. ( a ) A conventional, two-dimensional SRR with L = 36 µm, g = 4 µm, and a = 48 µm, that can be rotated along the X-, Y-, and Z-axis at angles θ x , θ y , θ z degrees, respectively.

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