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The formula describing the relationship between the dielectric constant of a composite and the dielectric constants or volume rates of its components is called a dielectric model. The establishment of a cement concrete dielectric model is the basic and key technique for applying electromagnetic wave technology to concrete structure quality testing and internal damage detection. To construct the dielectric model of carbon nanofiber reinforced concrete, the carbon nanofiber reinforced concrete was measured by the transmission and reflection method for dielectric constant ε, and ε,, in the frequency range of 1.7~2.6 GHz as the fiber content was 0, 0.1%, 0.2%, 0.3% and 0.5%. Meanwhile, concrete was considered as a composite material composed of three phases, matrix (mortar), coarse aggregate (limestone gravel) and air, and the dielectric constants and volume rates of each component phase were tested. The Brown model, CRIM (Complex Refractive Index Model) model and Looyenga model commonly used in composite materials were modified based on the experimental data, suitable dielectric models of carbon nanofiber reinforced concrete were constructed, and a reliability check and error analysis of the modified models were carried out. The results showed that the goodness of fit between the calculated curves based on the three modified models and the measured curves was very high, the accuracy and applicability were very strong and the variation rule for the dielectric constant of carbon nanofiber concrete with the frequency of electromagnetic wave could be described accurately. For ε, and ε,,, the error between the dielectric constant calculated by the three modified models and the corresponding measured values was very small. For the dielectric constant ε,, the average error was maintained below 1.2%, and the minimum error was only 0.35%; for the dielectric constant ε,,, the average error was maintained below 3.55%.

In this paper, we demonstrate an active switching of extremely high Q-factor Fano resonances using vanadium oxide (VO2)-implanted THz asymmetric double C-shaped metamaterial (MM) structures. The simulation results indicate the highly temperature-sensitive nature of the double Fano resonances that can be switched at very low external thermal pumping (68 °C), which is only slightly higher than room temperature. We employ the surface current and electric field distributions of the structure to analyze the physical mechanism of the observed switching behavior in the thermally excited Fano MMs. More importantly, by optimizing the asymmetric parameter (offset length), the linewidth of the Fano resonance can reach only 0.015 THz and the Q-factor is as high as 98, which is one order of magnitude higher than that of the traditional MMs. The findings of this work would enable a thermally-induced high-Q Fano resonance MMs for ultra-sensitive sensors, modulators, low threshold switching in metadevices.