The transmission characteristics of metallic like smartphone case made of resin and small metallic particles

The smartphone designers prefer using metallic material to make smartphone case because it gives the consumer the impression of luxuriousness and toughness. It raises a hard task for antenna engineers that they can not arrang the antennas inside such metallic smartphone case. Although it is possible to use metallic case as a part of an antenna, there are still the requirements of mounting the antennas inside the case because it is convenience to arrange several antennas that are necessary in a smartphone. The material made of resin mixed with metallic particles is thought promising to satisfy the above requirements. In this paper, the propagation property of electromagnetic waves in such material is studied carefully for the different size, the different volume density and the different arrangement of metallic particles. The transmission and reflection coefficients of a plane wave incident on a 1mm thick plate of the material are calculated by using FDTD method. To obtain the propagation loss of the material, the metallic particle is assumed as a good conductor such as the copper, and the spatial division is chosen as 0.5 micrometer of the order of the skin depth. The particles of the size of several micrometers are arranged in the direction of the propagation, and the transverse directions are terminated by the perfect electric and magnetic walls. The result shows that the material is a low-pass property, and transmission coefficient decreases with the frequency. The transmission coefficient also decrease with the volume density of metallic particles. When the copper is used as metallic particles, the transmission coefficient is about 0.96, 0.92, 0.8 with a volume density of particles of 1.6%, 12.5%, 42.2%, respectively at frequency 5 GHz.