## 1 Introduction  
Electromagnetic meta-atoms are composed of artificial atoms, whose electric and magnetic response could be flexibly tailored to meet desired exotic EM properties. Benefiting from these novel properties, meta-atoms have produced many exotic effects in several applications, such as negative permeability, sub-wavelength imaging super-lens, electromagnetic absorbers [1], negative refraction [2], filter design [3], antenna performance enhancing, SAR reduction [4] and invisible cloaking [5]. The development of the meta-atoms utilizes the intrinsic loss of the system, with the help of structural design, to obtain a wide bandwidth or sharp resonance at a certain frequency. Material that exhibits either negative permittivity or negative permeability is called a single-negative meta-atom. When the values of permittivity and permeability are near zero over a specific frequency range, the material is specified as a near-zero refractive index meta-atom. Moreover, a material exhibiting negative permeability and negative permittivity simultaneously can be characterized as a double-negative or left-handed meta-atom. Although negative permittivity can be found in a few metals, negative penetrability is hard to discover. Therefore, the presence of both negative permeability and permittivity is exceptionally hard to acquire as the characteristic for left-handed materials. Recently, various composites based on metallic and dielectric structures that act as left-handed meta-atoms have been developed (Figure 1) [6; 7; 8; 9; 10; 11; 12]. In 1968, [PERSON] first discussed the negative index material. He demonstrated that a negative index material refraction would occur at negative angles, energy would flow in a direction opposite to the direction of the phase velocity and the Doppler effect would be reversed at a certain frequency [13]. In 1996, [PERSON] et al. projected their summary of a thin wire configuration, which exhibited a negative permittivity (\(\varepsilon\)), and in 1999, they presented the split ring resonator with a negative permeability (\(\mu\)) [14]. Owing to the absence of such properties in natural materials, the topic was not particularly interesting to researchers until [PERSON] and his colleagues invented the first successful metamaterial in the laboratory. In 2000, [PERSON] et al. exhibited a material that displayed negative permittivity and permeability at the same time with unusual natural properties [15]. In the last few years, multi-band meta-atom arrays at different rotation angles with a compact size, left-handed properties and a wide bandwidth have become a promising research field for specialists because very few studies are concentrated on this sector. In 2017, [PERSON] et al. suggested that a tri-band metamaterial absorber was developed by the square shape resonators with a circular ring in the middle of the square resonators. The designed metamaterial absorber illustrates a 4.71 GHz-wide bandwidth and applicable for tri-(C-, X- and Ku-) band applications. The effective medium ratio was 5.83, and the absorptions were  
Figure 1: Examples of several meta-atom based metamaterial (MTM) structures through periodic repetition of metallic and dielectric elements: (**a**) double-fishnet negative-index metamaterial with several layers. Reproduced with permission from [[PERSON], [PERSON] et al. ], [Opt. Lett. ]; published by [The Optical Society], [2009] [6]; (**b**) chiral metamaterial fabricated through stacked electron-beam lithography. From [[PERSON] et al. Optical Metamaterials—More Bulky and Less Lossy. Science 2010, 330, 1633–1634]. Reprinted with permission from [PERSON] [7]; (**c**) chiral metamaterial made using direct-laser writing and electroplating. From [[PERSON] et al. Gold Helix Photonic Metamaterial as Broadband Circular Polarizer. Science 2009, 325, 1513–1515]. Reprinted with permission from AAAS [8]; (**d**) hyperbolic metamaterial made by electroplating hexagonal-hole-array templates. From [[PERSON] et al. Gold Helix Photonic Metamaterial as Broadband Circular Polarizer.