The increasing requirements for electromagnetic (EM) shielding technology that arises from rapid maturity of wireless technology motivate the development of EM absorbing materials with higher efficiency, smaller size, lighter weight and lower cost. The metamaterial-based EM absorbers (MMAs) are widely recognized as promising candidates to fulfill these requirements. For MMAs, the EM absorption performance can be artificially designed by means of adjusting the geometrical parameters, while the conventional absorbing materials are constrained by the inherent properties of constitutive materials. However, prototyping MMAs are falling behind the modeling investigations and envisaged applications because there are still several critical issues limiting their practical performances, i...[ Read more ]

The increasing requirements for electromagnetic (EM) shielding technology that arises from rapid maturity of wireless technology motivate the development of EM absorbing materials with higher efficiency, smaller size, lighter weight and lower cost. The metamaterial-based EM absorbers (MMAs) are widely recognized as promising candidates to fulfill these requirements. For MMAs, the EM absorption performance can be artificially designed by means of adjusting the geometrical parameters, while the conventional absorbing materials are constrained by the inherent properties of constitutive materials. However, prototyping MMAs are falling behind the modeling investigations and envisaged applications because there are still several critical issues limiting their practical performances, including the restriction of the dielectric substrate, polarization sensitivity, narrow frequency bandwidth and incident angle sensitivity. To implement the advantages of MMAs in practical applications, this research is dedicated to addressing the above issues by proposing a new MMA design based on 3D all-metal metamaterials. And a general algorithm is constructed for guiding structural design in a fast and cheap way.

A new complementary split ring resonator (CSRR) structure is introduced into MMA design instead of using the conventional SRR structure. Different from the isolated SRR structure, the CSRR array is designed to be continuous so that it can be self-stand without support from dielectric substrate. And the design principle of four-fold rotational symmetric is followed, which can guarantee the polarization independent property of the CSRR-based MMA. The electric field and current distribution on the designed CSRR array surface analyzed by simulation in HFSS indicate that although the CSRR array is made of a continuous metal, the skin effect at high frequency limits the induced current to concentrate around the elements, so it can achieve excellent EM absorbing performance that comparable to the conventional isolated SRR structure. For further verifying the absorption property of the CSRR-based MMAs, the samples with the new designed CSRR arrays are fabricated with photolithography method. The experiments conducted on the experimental platform built in shield room prove the feasibility of CSRR-based MMA designs.

Based on the continuous CSRR arrays, the all-metal MMA is designed and constructed. To compare the performance of all-metal design and conventional structure, both simulation and experiments are processed. The results show that the all-metal structure has the same response frequency as the single CSRR arrays, while the existing of dielectric in conventional structure reduces the frequency by 9 GHz. All-metal MMA design can keep the inherited frequency selective feature of the designed element arrays, which brings great convenience in frequency design of MMAs. Moreover, the use of all-metal structures makes the structure design more flexible. Two methods are utilized to expand the response frequency band of the all-metal MMA based on CSRR arrays, including distribute elements with different scales on element array layer and cascade two or more element layers together. Both methods are proved to be efficient by simulation and experiments. Furthermore, a 3D CSRR array structure is constructed, which can achieve a stable response to the EM waves with incident angle as large as 70° at both TE and TM modes. Thus, the 3D all-metal structure proposed in this research has potential to overcome the drawbacks of conventional MMAs introduced before.

At last, to study the frequency selective property of the CSRR arrays and more efficiently and conveniently guide the MMA design, the equivalent circuit model for the CSRR structure is constructed and analyzed, with which the corresponding geometrical parameters on the target frequency can be quickly determined. The overall CSRR structure is equivalent to a series of distributed inductances and capacitances. A series of differential equations are delivered to express the equivalent circuits based on Kirchhoff’s law. And the values of the distributed electrical parameters (L, M and C) in the equations are calculated according to the geometrical scales of the element structure. Thus, the relations between the EM response behavior of the CSRRs and their geometrical scales are established. With the results achieved by the above equivalent circuit approaches, a geometrical scale algorithm based on target frequency as parameters is developed to guide the structure design of CSRRs, which is the function that commercial software cannot reach. And this analysis method is quite general and can be expanded to different element structures.