Surface Wave Enhanced Sensing in the Terahertz Spectral Range: Modalities, Materials, and Perspectives

Abstract

The terahertz spectral range (frequencies of 0.1-10 THz) has recently emerged as the next frontier in non-destructive imaging and sensing. Here, we review amplitude-based and phase-based sensing modalities in the context of the surface wave enhanced sensing in the terahertz frequency band. A variety of surface waves are considered including surface plasmon polaritons on metals, semiconductors, and zero gap materials, surface phonon polaritons on polaritonic materials, Zenneck waves on high-k dielectrics, as well as spoof surface plasmons and spoof Zenneck waves on structured interfaces. Special attention is paid to the trade-off between surface wave localization and sensor sensitivity. Furthermore, a detailed theoretical analysis of the surface wave optical properties as well as the sensitivity of sensors based on such waves is supplemented with many examples related to naturally occurring and artificial materials. We believe our review can be of interest to scientists pursuing research in novel high-performance sensor designs operating at frequencies beyond the visible/IR band. Keywords: terahertz band; surface waves; amplitude sensing modality; phase sensing modality; surface plasmon polaritons; surface phonon polaritons; Zenneck waves; spoof plasmons Recently, the THz spectral range (frequencies of 0.1-10 THz, wavelengths of 3 mm-30 µm) has emerged as the next frontier in non-destructive imaging and sensing. Key advantages when operating in the THz band are the ability to detect the complex electric field of THz waves (phase and amplitude), availability of both pulsed (sub-1 ps) and continuous wave (CW) THz systems, as well as ability of conducting dynamic measurements with sub-1 ms temporal resolution [6]. Additionally, relative transparency of dry dielectrics to THz radiation, strong absorption of THz waves by water and other polar solutions, as well as the non-ionizing nature of THz light enable many and more graphical than analytical, which is the main reason why we chose a more theoretically elegant approach for the characterization of sensor sensitivity with respect to changes in the analyte refractive index complemented by the study of the surface wave probing depth. Amplitude Sensing ModalityAmplitude sensing modality offers the simplest sensor implementation as it only requires monitoring of the sensor transmission amplitude. A simplified schematic of an amplitude-based sensor is presented in Figure 1. The amplitude sensing detection modality is mostly used to detect variations in the imaginary part of the analyte refractive index.Sensors 2020, 20, x FOR PEER REVIEW 3 of 24 theoretically elegant approach for the characterization of sensor sensitivity with respect to changes in the analyte refractive index complemented by the study of the surface wave probing depth. Amplitude Sensing ModalityAmplitude sensing modality offers the simplest sensor implementation as it only requires monitoring of the sensor transmission amplitude. A simplified schematic of an amplitude-based sensor is presented in Figure 1...

Additive manufacturing of highly reconfigurable plasmonic circuits for terahertz communications

“…In the case of silver layers deposited using wet chemistry (as used in our work), their metal conductivity can be significantly smaller than that of a fine silver sheet because of the nano/microcrystallization and oxidation effects. While it was demonstrated that for such nanostructured surfaces Drude-Smith model of metal permittivity could provide more accurate numerical results for THz surface waves, this model is experiment-specific and lacks universality [14,56]. To make comparison between experimental and numerical work more realistic, and considering that operational frequency range of our devices is relatively narrow (~110-170 GHz), we retain the simple Drude-Lorentz model of silver for our simulations, while simply fitting the damping factor to achieve the best fit of our numerical simulations with the experiment (black and red curves in .…”

“…Galva mirror scanners), a more reliable and robust solution would ideally forgo the use of moving parts and rather employ integrated solutions such as passive and active leaky waveguides and leaky wave antennas [5][6][7][8]. In the microwave and THz range such structures often employ metallic waveguides [10,11] as well as modes propagating along conductive surfaces [12][13][14] (which in THz range are also known as Sommerfeld waves or Zenneck waves depending on the material of a surface). In this respect, development of integrated metallic waveguides supporting various types of plasmonic modes is of great interest.…”

Additive manufacturing of highly reconfigurable plasmonic circuits for terahertz communications

“…In the case of silver layers deposited using wet chemistry (as used in our work), their metal conductivity can be significantly smaller than that of a fine silver sheet because of the nano/microcrystallization and oxidation effects. While it was demonstrated that for such nanostructured surfaces Drude-Smith model of metal permittivity could provide more accurate numerical results for THz surface waves, this model is experiment-specific and lacks universality [14,56]. To make comparison between experimental and numerical work more realistic, and considering that operational frequency range of our devices is relatively narrow (~110-170 GHz), we retain the simple Drude-Lorentz model of silver for our simulations, while simply fitting the damping factor to achieve the best fit of our numerical simulations with the experiment (black and red curves in Fig.…”

Continuous Fabrication of Microstructured Fibers for THz Communications Using Infinite 3D Printing

“…A standard "Rectilinear" infill pattern is used in the optimization process as it usually results in mechanically isotropic prints in the build plane. Optimal extrusion temperature for the Polypropylene is reported in the 190 -250 ℃ range [2], and in our experiments is chosen to be 240 ℃ according to the filament manufacturer recommendations…”

“…The terahertz (THz) spectral range (0.1 THz-10 THz) has recently attracted much attention because of many potential applications in sensing [1,2], imaging [3,4], security [5,6] and communications [7,8]. In communications industry, in particular, the global IP traffic is increasing exponentially and is expected to reach 396 exabytes per month by 2022 [9].…”