Encoded-Enhancement of THz Metasurface Figure of Merit for Label-Free Sensing.

Gian Paolo Papari,Antonello Andreone,Can Koral

doi:10.3390/s19112544

Gian Paolo Papari, Antonello Andreone + Show 1 more

Open Access

https://doi.org/10.3390/s19112544

Copy DOI

Abstract

We describe an experimental strategy for the use of Terahertz (THz) metasurfaces as a platform for label-free wide range detection of the dielectric function in biological fluids. Specifically, we propose a metagrid (MG), opportunely infiltrated with a fluid and then capped, as the reference structure for sensing experiments with a high reproducibility character. By combining experiments and full-wave simulations of the transmission T of such a structure, we introduce a reliable set up where the volume of the involved analyte in each unit cell is precisely determined. The unavoidable decrease in the quality factor of the intrinsic resonances due to the lossy fluid and cap layer is circumvented using an appropriate transformation of T that amplifies the change in the MG intrinsic resonances, improving in such a way the sensor sensitivity to values close to the experimental limits. The transformed signal features delta-like peaks enabling an easy readout of frequency positions at resonances.

Highlights

Metasurfaces (MS) are artificial 2D-structures typically realized by patterning a metallic layer in an array of resonators distributed over a dielectric substrate [1,2,3,4,5]
The frequency position of each resonance f0 ∼ 1/ L0 C0, where C0 and L0 describe the effective capacitive and inductive coupling respectively between the impinging radiation and the metallo-dielectric structures, is potentially sensitive to any change of the electromagnetic environment [6,7,8]. This effect is stimulating an extensive application of MS in the THz band, where sensing experiments enjoy a series of advantages with respect to other portions of the electromagnetic spectrum
In this frequency region the geometrical features needed for the MS design are achieved by standard UV lithography, in contrast with optical/infrared band operating structures, where nanoscale fabrication demands more working time and higher costs since they are based on electron/ion lithography (EBL/FIB) [9,10,11]

Summary

Introduction

Metasurfaces (MS) are artificial 2D-structures typically realized by patterning a metallic layer in an array of resonators distributed over a dielectric substrate [1,2,3,4,5]. Frequency position of each resonance f0 ∼ 1/ L0 C0 , where C0 and L0 describe the effective capacitive and inductive coupling respectively between the impinging radiation and the metallo-dielectric structures, is potentially sensitive to any change of the electromagnetic environment [6,7,8] This effect is stimulating an extensive application of MS in the THz band, where sensing experiments enjoy a series of advantages with respect to other portions of the electromagnetic spectrum. In this frequency region the geometrical features needed for the MS design are achieved by standard UV lithography, in contrast with optical/infrared band operating structures, where nanoscale fabrication demands more working time and higher costs since they are based on electron/ion lithography (EBL/FIB) [9,10,11]. Computational efforts are drastically reduced since in this case the sensing experiment is based on the frequency shift induced in just a few resonances [14]

Methods

Results

Discussion

Conclusion