Electromagnetic Properties of Bearing Cement-Based Materials

For studying absorption/bearing integration of building materials, high-strength cement-based materials were prepared by using active fly ash, silica fume and quartz, etc. Electromagnetic parameters of the cement-based materials were measured through coaxial method, and then by means of these parameters, the reflectivity of electromagnetic waves of the cement-based materials were simulated under variable electromagnetic wave incident angle (θ), frequency (f) and thickness of the material(d).The reflectivity of electromagnetic waves with 8~18GHz frequency range vertically transmitting into the cement-based materials was obtained through far field radar scattered cross-section measurement, and was compared with simulated reflectance under the same incident conditions. The results show that the high-strength cement-based materials with imaginary part of dielectric constant can consume energy of the incident electromagnetic wave. Incident angle less than 15° has little effect on the reflectivity of the cement-based materials in 2~18GHz frequency range. While the thickness of the cement-based materials is 15mm or 25mm, simulation results of the reflectivity are in good agreement with measured ones. Measured absorption peak and -10dB bandwidth increase with the increasing of thickness of the cement-based materials with compressive strength of 120.7MPa. This suggests that the cement-based materials studied in this paper have the characteristics of absorption/bearing integration.

Decay Instability of an Electromagnetic Wave Incident on a Weakly-Inhomogeneous Magnetised Plasma

This paper considers the parametric decay of an electromagnetic wave incident on a weakly-inhomogeneous magnetised plasma into a Langmuir wave and an ion-acoustic wave. The Vlasov model is used in order to calculate the low-frequency electron-density perturbation produced by the beating of the side-band modes with the pump wave. The results show that the threshold value of the pump wave to undergo a decay instability drops in the presence of an inhomogeneity in the plasma.