Debye Frequency-Extended Waveguide Permittivity Extraction for High Complex Permittivity Materials: Concrete Setting Process Characterization

Abstract

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.

Wireless Sensing of Concrete Setting Process

“…Once validated, the feasibility of the proposed RFID system for wireless monitoring of the setting reaction produced in concrete over time at 0.868 GHz, it could be of interest for potential designers to compare the attenuation parameter (see Table 3 ) obtained from the results presented in [ 1 ], at 0.43 GHz, 0.868 GHz (this paper), and 2.45 GHz. These are typical frequencies in the ISM band employed in sensing applications.…”

“…It is known from [ 1 ] that the real part of the relative permittivity of concrete throughout the setting reaction varies exhibiting maximum values around at the beginning of the reaction and lowering to by the eighth day of the process. With this phenomenon in mind, the Impedance Coupling Factor between the wrapped T-match bow-tie antenna and the RFID-IC has been evaluated for real part relative permittivities ranging between 4 and 18 ( Figure 4 ).…”

“…We have extracted from [ 1 ] the relative permittivity values measured at 868 MHz for a concrete sample at days 0.5, 1, 2, 4, and 8 of the setting reaction. Table 2 and Table 3 summarize all communication link parameters, while Figure 7 represents the propagation loss in the considered scenario over distance computed through Equation ( 2 ).…”

“…In [ 1 ], it is shown that the exothermic hydration process associated to the concrete setting causes temperature and also dielectric constant variations of the concrete mixture in the UHF (Ultra High Frequency) band. Monitoring the changes in the dielectric constant of the concrete mixtures has been proposed in [ 2 ] in a wired experimental set-up as a way to monitor the setting process.…”

“…Its data logging features allow an asynchronous reading of the sensors. As shown in [ 1 ], in the initial stages of the concrete setting large changes in its dielectric constant and high losses are expected. In consequence, one of major challenges is designing a sensor that is able to properly operate and transmit the measured data embedded in a heavily lossy changing medium.…”