Enhanced Terahertz Spectral‐Fingerprint Detection of α‐Lactose Using Sub‐Micrometer‐Gap On‐Chip Waveguides

Sae June Park,Rowan S Parker‐Jervis,John E Cunningham

doi:10.1002/adts.202100428

Sae June Park, Rowan S Parker‐Jervis + Show 1 more

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https://doi.org/10.1002/adts.202100428

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Abstract

AbstractWe investigate using finite element methods how sub‐micrometer to micrometer‐scale coplanar waveguide (CPW) can be used for the detection of fingerprint spectra of very small (of order 10−14 mL) volumes of analytes in the terahertz (THz) frequency range. The electric field distribution is investigated near the waveguide for various gap widths between the center conductor and ground plane using a finite element simulation (ANSYS High Frequency Structure Simulator, HFSS). Taking lactose monohydrate as an exemplar material, a Drude–Lorentz model is combined for its real and imaginary permittivities with this numerical simulation, finding a significant enhancement in fingerprint detection as the gap width is reduced; the electric field in the CPW is found to increase by a factor ≈14 times moving from a 20 to 0.5‐µm‐wide gap between center conductor and ground plane, while the on‐resonance THz absorption increases ≈14 times. The effective absorption coefficient of the lactose at 530 GHz is investigated as a function of the slot width for various lactose block thicknesses to understand how change in the field confinement and in the effective overlap between the lactose block and incident THz waves affect the effective absorption coefficient.

Highlights

IntroductionIntroduction tion of the lactose spectraIn both of these studies, plasmonicA wide range of polycrystalline materials including lactose,[1] the common explosives RDX,[2] SX2,[2] and C–4,[3] as well as pharmaceutical drugs such as Alprazolam,[4] and Ibuprofen[4]exhibit spectral fingerprints in THz frequency range; and have been intensively investigated by free-space THz time-domain structures were predesigned to make them resonate at the target material’s absorption frequency in order to detect the spectral fingerprint of the target material with enhanced sensitivity.On the other hand, we previously showed that on-chip THz waveguides such as microstrip-line,[11] and Goubau-line[12] can be used to recover the absorption spectra of polycrystalline materials in a broadband range (up to 2 THz) even without such resonant structures.[12]
We previously showed that on-chip THz waveguides such as microstrip-line,[11] and Goubau-line[12] can be used to recover the absorption spectra of polycrystalline materials in a broadband range even without such resonant structures.[12]
We suggest a novel method for the enhanced detection of the fingerprint of target material in the THz frequency range using submicrometer-gapped CPW structures. α-lactose was chosen as an example target material and permittivities of α-lactose were modelled using the Drude–Lorentz function

Summary

Introduction

Introduction tion of the lactose spectraIn both of these studies, plasmonicA wide range of polycrystalline materials including lactose,[1] the common explosives RDX,[2] SX2,[2] and C–4,[3] as well as pharmaceutical drugs such as Alprazolam,[4] and Ibuprofen[4]exhibit spectral fingerprints in THz frequency range; and have been intensively investigated by free-space THz time-domain structures were predesigned to make them resonate at the target material’s absorption frequency in order to detect the spectral fingerprint of the target material with enhanced sensitivity.On the other hand, we previously showed that on-chip THz waveguides such as microstrip-line,[11] and Goubau-line[12] can be used to recover the absorption spectra of polycrystalline materials in a broadband range (up to 2 THz) even without such resonant structures.[12]. A wide range of polycrystalline materials including lactose,[1] the common explosives RDX,[2] SX2,[2] and C–4,[3] as well as pharmaceutical drugs such as Alprazolam,[4] and Ibuprofen[4]. We previously showed that on-chip THz waveguides such as microstrip-line,[11] and Goubau-line[12] can be used to recover the absorption spectra of polycrystalline materials in a broadband range (up to 2 THz) even without such resonant structures.[12] It is noteworthy that on-chip THz systems.

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