A waveguide with central frequency 868 MHz is used in transmission/reflection operation regime to accurately measure the behaviour of the complex permittivity of high complex permittivity granular materials and it has been frequencyextended up to 3 GHz using the Debye fitted relaxation model. It is shown that for highly granular high permittivity materials a waveguide based transmission/reflection technique is necessary to reduce the uncertainty of the extracted permittivity values. The technique is first described and validated with isopropyl alcohol and then applied to the characterization of cement based materials. This paper provides accurate data on the evolution of the complex permittivity of concrete and mortar from the moment of pouring until air dried condition is achieved.
This paper presents the design, manufacture and characterization of a novel 3D passive UHF-RFID tag for embedded applications. The prototype is fabricated using additive manufacturing techniques: 3D printing and copper electroplating. The design, manufacturing process and measurement setup are presented and discussed in detail. We propose a biconical antenna design with spiral strips embedded in the cones to provide compactness without breaking the symmetry of the component and to improve bandwidth. The antenna is matched to a commercial UHF-RFID integrated circuit. We incorporate a packaging design that consists of a dielectric coating, to provide proper operation in different media or surrounding environments with changing electromagnetic properties. The good agreement between experimental results and Finite Element Method simulations allows us to validate the whole process. Finally, a compact capsuletype RFID tag is proposed and its performance in different media is reported.
A cylindrical mode expansion of the fields produced by an embedded antenna is used to determine the dimensions of the antenna packaging in order to minimize antenna impedance changes when the antenna is immersed in a varying dielectric medium.
An RFID-based wireless system to measure the evolution of the setting process of cement-based materials is presented in this paper. The system consists of a wireless RFID temperature sensor that works embedded in concrete, and an external RFID reader that communicates with the embedded sensor to extract the temperature measurement conducted by the embedded sensor. Temperature time evolution is a well known proxy to monitor the setting process of concrete. The RFID sensor consisting of an UWB Bow Tie antenna with central frequency 868 MHz, matched to the EM4325 temperature chip through a T-match structure for embedded operation inside concrete is fully characterized. Results for measurements of the full set up conducted in a real-scenario are provided.
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