Highly sensitive optical sensing can use the resonant responses of engineered structures to detect the refractive index of the surrounding medium. There has been much research in this area focused on the terahertz (THz) range of frequencies for applications such as DNA hybridization, biochemical sensing, and thin film characterization. Unfortunately many of these uses are limited to planar or open geometry and cannot be used with flow monitoring or in line process applications. Resolutions are also limited by the intrinsic linewidth of the resonant line.
This technology consists of a THz resonator integrated with a parallel-plate waveguide with a thin dielectric cover. The cover acts to contain the fluid as well as to accurately define the sensing volume. The system exhibits very narrow linewidths which translate to a refractive index-sensitivity of 3.7 x 10^5 nm / refractive index unit (RIU), among the highest reported. Rather than using the transverse electromagnetic mode of the waveguide, this technique uses the transverse electric mode enabling a device with a highly effective resonant cavity integrated into a parallel-plate waveguide.
The easy integration into microfluidic devices lends this technology to applications of in-line process monitoring and microfluidic sensing. The high refractive index sensitivity offers great accuracy while the design geometries offer improvements over other THz frequency sensors.
US patent 8,309,925; this invention is available for licensing from Rice University.
Daniel Mittleman is a Professor of Electrical and Computer Engineering at Rice University.
“Terahertz microfluidic sensor based on a parallel-plate-waveguide resonant cavity,” Rajind Mendis, Victoria Astley, Jingbo Liu, and Daniel M. Mittleman, Applied Physics Letters, 95, 171113 (2009).
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