Multi-frequency RF sensor for non-contact monitoring of organic matter

The non-invasive evaluation of organic matter is a major challenge in many fields such as agriculture, food engineering and healthcare. Among the low-cost sensing techniques, bio-impedance, capacitive or inductive measurements are good candidates to assess such complex matter through the sensing of their dielectric properties. Indeed, the complex permittivity is determined by and informative about the nature, the composition and the state of organic materials. It is considered as relevant indicator of physicochemical or physiopathological changes within the organic matter. In this presentation, we will focus on transmission-line based LC resonators, used as passive and inductive sensors for non-contact monitoring applications. More specifically, an original wireless multifrequency transmission-line resonator (WMFR) sensor will be presented. Associated with a multi-frequency equivalent electrical model, the WMFR allows to distantly monitor the changes of the complex permittivity of the investigated matter on a given set of frequencies, and thus to produce a multiscale analysis, spatially and / or over time. Experimental validations of the approach are carried out using different study supports, such as dairy products, ripening fruits, tissue decomposition, and localization of local dielectric contrasts. Such sensors opens the way to the development of noninvasive and low cost devices for 3D or 4D multiscale monitoring of organic matter.