A system for monitoring dielectric constant of a substrate includes a resonator structure formed on a surface of the substrate. A distal end of a waveguide is coupled to the resonator structure and spaced apart from the resonator structure such that a gap is provided between the distal end of the waveguide and the resonator structure. An excitation energy is coupled to the resonator structure out of the waveguide, and a response energy from the resonator structure is coupled into the waveguide and is detected at a proximal end of the waveguide. A detector detects the response energy received at the proximal end of the waveguide and generates a signal indicative of the detected response energy. A processor is coupled to the detector for receiving the signal indicative of the detected response energy and processing the signal to determine dielectric constant of the substrate.