Optical Gas Sensors Using Terahertz Waves in the Layered Media

Abstract

Terahertz (THz) wave propagation in the layered media is presented based on the waveguide and artificial-material configurations to sense the gas molecules. The single dielectric layer with a cylindrical conformation works as a pipe waveguide in the wave frequency of 0.1-1 THz. For a long-distance propagation over 10 cm of the pipe, resonant modes are characterized from the transmission power dips. The pipe-waveguide resonator works for a THz refractive-index sensor when the resonance frequency is monitored to sense vapor molecules inside the pipe core. Besides of the waveguide configuration, a multilayer microporous polymer structure (MPS) is considered an artificial material to transmit THz waves for sensing gaseous molecules. The MPS is not only transparent to THz waves but also enhances the detection resolution of THz absorption for the vapor molecules. The porous structure provides a large hydrophilic surface area and numerous micropores to adsorb or fill vapors, thereby leading to greatly enhanced wave-analyte interaction with an apparent THz signal change. Different concentrations of toxic methanol adulterated in alcoholic aqueous solutions are thus identified in their vapor phases by using the MPS-based THz sensor.

Analytical Gas Sensing in the Terahertz Spectral Range

“…This plasmon effect was significantly modified when the graphene layer was placed under a magnetic field of appropriate strength, which can be exploited to achieve higher-sensitivity gas detection [77]. Microfluidics is used for more precise manipulation of the gases [78]. By integrating different components of a THz system on a single chip, a compact and portable system could be possible for use in field applications [79].…”