Convoluted I-Shaped Metamaterial on Rigid and Flexible Substrates for Electromagnetic Cloaking

For cloaked objects larger than the optical wavelength, we present two types of microwave cloaks which offer a low scattering cross-section. In the first design, an I-shaped metamaterial with convoluted curved ends is designed using a rigid substrate. The metamaterial exhibits negative permittivity near its resonance. A cuboidal cloak is constructed using four walls made of copper-printed FR4 substrate with thickness of 1.6 mm. A cylindrical metallic object becomes electromagnetically invisible when it is placed inside the cloak at 3.55 GHz. Using the same copper pattern and lateral dimensions of the unit cell of the cuboidal cloak, another unit cell is designed using a flexible substrate with thickness of 0.1 mm for constructing a cylindrical cloak with radius 9.6 mm. The cylindrical cloak is wrapped around the metallic cylinder to make it electromagnetically invisible at 7.5 GHz. The function of the metamaterial unit cells is explained by proposing their equivalent circuit models. Since backscattering is prevented by the metamaterial unit cells, the incident waves bend around the object and travel in the forward direction. This results in lowering of the radar cross-section (RCS) of the cloaked object. Maximum RCS reduction of 8 dB is obtained using the cuboidal cloak, while maximum RCS reduction of 16 dB is obtained using the cylindrical cloak during measurements at the cloaking frequencies.