# A Polarization Independent Quasi-TEM Metamaterial Absorber for X and Ku Band Sensing Applications
## 1 Introduction  
Periodic arrangement of metallic patterns in the microwave frequency range using thin wires and certain design characteristics show unconventional properties of materials like negative values of permittivity, permeability, refractive index, etc. These characteristics-based materials are known as metamaterials and cannot be found in Nature. A significant number of researchers have been comprehensively studying these phenomena during the last few years observing such characteristics of metamaterials. Due to a wide range of application scope from cloaking to radar systems [1; 2; 3; 4] the research interest of scholars is increasing day by day. For instance, a detailed review on photonic, terahertz and microwave applications was provided in [5], where the authors cited numerous mechanisms as well as materials regarding metamaterial and metadevice research. Robust analysis and sophisticated design for sensing based on the metamaterial concept was described in [6; 7; 8], such as nanoparticles-inspired structural properties analysis in terms of Maxwell's equation and their application in sensing, structures with near-zero parameters (like permittivity, permeability or refractive index) working principle with application potentiality, the substantial role of graphene in the inhomogeneous spatiality, and non-uniform conductivity pattern in transformation optics, etc. Remote sensing techniques using metamaterial absorbers is one of the promising research fields in recent years. Conventional remote sensors have performance issues in certain critical application environments whereas an absorber with metamaterial properties can overcome those issues [1]. Typically, a perfect metamaterial absorber consists of three different structures like two metallic layers namely one ground plane and an electric split ring resonator (SRR), where in between these there exists a dielectric layer. The resonator is intended to couple a strong uniform electric field with dielectric layer but a weak magnetic field is observed [2; 3; 4]. In this way, the electric field becomes dependent on the frequency range. Regarding the incident waves, the magnetic field propagates between the resonator and the metallic ground plane and incurs a frequency-dependent magnetic response. To get absorption properly, various measures can be taken like dimension variation of the resonator and ground plane or changes to the gap. As a result, a matching of impedance between the absorber and free space happens at that instant and simultaneously the reflection coefficient tries to reach almost zero. Typical absorbers are physically thick in size and their frequency response is very much hampered by their complex permittivity and permeability [2; 3; 4]. However, MM absorbers are frequently used in terahertz (THz), visible frequency spectrum, infrared range applications, etc. [9; 10; 11; 12]. Common applications of MM absorbers in radar technology are to reduce the radar signature in stealth techniques and to overcome electromagnetic interference (EMI). This application requires a lowest possible thickness of material with a wider bandwidth for flexible operation and system integrity [13]. In the widespread application prospects, thickness and bandwidth are crucial parameters [14; 15; 16]. Other critical parameters are the magnetic loss spectrum and bandwidth optimization to minimize reflections. Structure-based analysis for making absorbers focused on cost optimization and light weight have been presented for microwave broadband electromagnetic absorption [17; 18]. Other researchers have focused on the design of MM absorbers in the microwave scale. Such scholars designed and fabricated their unit cells in a millimeter range where some of them used SRR with a lumped resistor and got above 90% absorption [19; 20; 21]. Double negative (DNG) metamaterial-based, different permeability, and permittivity-based absorbers were also proposed by a few researchers.