An ultra-sensitive Lorentz microwave sensor for detection of low-permittivity gaseous water states and sub-wavelength biosamples

Abstract

The high sensitivity of Lorentz sensors comes from its narrowband resonant characteristics marked by rapid slope change of slope of its phase spectrum, a phenomenon known as Anomalous dispersion. Unlike conventional microwave resonant sensors which have a resonant amplitude, the Lorentz sensors also have unique signature in its phase spectra which adds a second degrees of freedom in detection and removes ambiguity in the identification of the resonant frequency. We demonstrate two sensing applications in which ultra-high sensitivity is required. In particular, we show that by exploiting the high electric field regions in Lorentz resonators detection of low density gaseous water states (steam) and sub-wavelength sized biomaterials is possible. The material sensing is performed by characterizing the resonant shifts in the frequency range of 1 to 2 GHz. Depending on the gaseous state concentrations, the dielectric constant of the detected steam lies between 1.04 and 1.6 GHz. The Lorentz resonator is shown to distinguish accurately between different sub-wavelength samples derived from different parts of chicken. We anticipate that the proposed sensor can be used in biosensing of cancerous cells and in detecting low-permittivity poisonous gaseous matter such as clear smoke, carbon mono oxide, methane and nitrogen.