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A Volatile Molecular Sensor Using Terahertz Resonators on Porous Substrates

Volatile sensing in the terahertz (THz) spectrum is attractive since many volatile molecules exhibit unique spectral signatures with higher absorption strength. In this paper, a practical approach for volatile molecular sensing at atmospheric pressure and room temperature in the THz spectrum is investigated. A metamaterial-based periodic split ring resonator is designed on a porous flexible substrate and is placed in the optical beam path of a THz signal enclosed inside a sealed chamber. Different volumes of volatiles are introduced into the chamber and the resonance frequency is monitored over time. The substrate porosity naturally allows condensing of volatile molecules into the pores through capillary condensation and surface adsorption. This changes the effective substrate dielectric constant leading to a shift in resonance frequency. The frequency shift dynamics can be monitored for identifying different volatiles and enables profiling. The proposed sensing technique is non-destructive in nature and can be easily adapted for monitoring volatiles emitted inside packaged food along a supply chain. The developed sensor tag is flexible and can be easily integrated with existing microsystems packaging technology.