Chipless RF liquid sensor

A method for the wireless evaluation of the dielectric permittivity of liquids is presented. The use of a thin-film, slotted waveguide sleeve around a standard unplasticised polyvinyl chloride pipe is proposed. Wireless interrogation of the slot with a plane wave excites a resonant mode whose frequency is dependent on the dielectric permittivity within the pipe. The proposed method allows for measurements to be taken in situ with no need for samples. The device has good potential for very low-cost monitoring applications, which may require real-time, continuous assessment.