Enhanced FANO Structure Based on Tip-Field-Enhancement Theory

Tianchi Zhou,Kaijun Song,Shixiong Liang,Lan Wang,Bo Zhang,Chao Shu,Yaxin Zhang

doi:10.3390/app9235009

Abstract

High-Q metasurfaces have attracted much interest owing to their potential application in biological sensors. FANO is a type of high-Q factor metasurface. However, it is difficult to achieve large resonant intensity and a high-Q factor at the same time. In this paper, by sharpening the tips of the asymmetrical split-ring FANO structure and letting more charges stack at the tips to enhance tip coupling, the Q factor was significantly improved without sacrificing too much resonant intensity. Simulation results showed that the Q factor increased up to 2.4 times, while the resonant intensity stayed higher than 20 dB, and the experiment results agreed with the simulations. This indicated that the tip-field-enhancement theory can be applied in time-harmonic electromagnetic-fields, and the method proposed here can be used to increase the sensitivity and accuracy of microfluidic sensors. Additionally, other types of research, such as on antenna design, could benefit from this theory.

Highlights

Metasurfaces are 2D arrays that consist of a series of elements that can be used, for example as filters, modulators, sensors, and vortex-beam generators [1,2,3,4,5,6,7,8,9,10,11,12,13]
Materials other than metal that can be used in FANO structures are proposed, including a nanoscale subwavelength dielectric resonator array[24], an asymmetric ferroelectric wire pair [25] in order to achieve a high-Q factor that can expend the slope of application for all-dielectric meta resonators
An enhanced FANO resonance structure was proposed in this paper

Summary

Introduction

Metasurfaces are 2D arrays that consist of a series of elements that can be used, for example as filters, modulators, sensors, and vortex-beam generators [1,2,3,4,5,6,7,8,9,10,11,12,13]. Unlike dipole structures and LC resonant structures that have low-Q factors, FANO is a group of metasurfaces that can reach high-Q resonances, usually based on asymmetric structures [14,15,16]. Stronger coupling will cause the current phase shift in a narrower band, which means strong coupling forms high Q resonance. The asymmetric structures lead to asymmetric charge distribution and excite unbalanced current mode, causing strong destructive interference with input THz wave, resulting in FANO resonances [19,20]. Materials other than metal that can be used in FANO structures are proposed, including a nanoscale subwavelength dielectric resonator array[24], an asymmetric ferroelectric wire pair [25] in order to achieve a high-Q factor that can expend the slope of application for all-dielectric meta resonators. This can be applied to microfluidic chips to increase its sensitivity on particle detection

Simulations

Experiments and Discussion

Conclusions