A Polarization-Insensitive Dual-Band Metamaterial Absorber for High-Performance Microwave Liquid Sensing

Abstract

A compact dual-band metamaterial absorber (MTM-A) for microwave sensing is proposed and numerically analyzed over 4–14 GHz. The unit cell consists of a metallic resonator and a continuous metallic ground plane, separated by an FR-4 epoxy substrate with a relative permittivity of 4.3. The optimized design exhibits near-unity absorption at 5.57 and 11.09 GHz, with stable performance under variation of polarization angle and oblique incidence under both polarization modes. The sensing performance is evaluated using a sample layer (SL) whose dielectric constant is varied from 1.8 to 3.6, resulting in a clear frequency shift. The sensor achieves sensitivities of 0.57 GHz/RIU and 1.4 GHz/RIU along with corresponding figure of merit (FOM) values as <inline-formula> <tex-math notation="LaTeX">$14.98~{\mathbf {RIU}}^{-\mathbf {1}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$37.61~{\mathbf {RIU}}^{-\mathbf {1}}$ </tex-math></inline-formula> at the respective resonance frequencies. Furthermore, the enhanced quality factors for both the resonance bands indicate sharp resonance characteristics and enhanced detection accuracy. These results confirm the suitability of the proposed metamaterial (MTM)-A for microwave liquid sensing applications, including vegetable oil and petroleum-based hydrocarbon liquids.