Effect of Incident Area Size on Estimation of EMI Shielding Effectiveness for Ultra-High Performance Concrete With Carbon Nanotubes

The electromagnetic interference (EMI) shielding effectiveness (SE) of Ultra-High Performance Concrete (UHPC) mixed with carbon nanotubes (CNTs) (UHPC/CNT composites) having a thickness of 200 mm in the frequency range of 10 kHz to 18 GHz was investigated according to IEEE-STD-299 for the first time. In addition, the effect of the size of the incident area on the SE was analyzed by comparing the SE results for two different incident areas: a small incident area of 300 x 300 mm(2) and a large incident area of 1200 x 1200 mm(2). A significant improvement in the SE of the UHPC/CNT composite was achieved by increasing the CNT content up to the percolation threshold. Experimental observations indicated that the small incident area caused a distortion of the SE in the magnetic field owing to the aperture effect, whereas it had little effect on the SE for a plane wave. Thus, to eliminate the effect of the aperture on the measurement of the SE for UHPC/CNT composites in a magnetic field, an incident area larger than 1200 x 1200 mm2 is recommended. According to a statistical analysis of the experimental results, a practical model was proposed to estimate the SE of cementitious material for different frequency ranges.