In this paper, a terahertz (THz) metamaterial absorber (MTMA), incorporating surface Pythagorean tree fractal resonators, was designed and experimentally fabricated on the flexible substrate of polyethylene terephthalate. The design presented two peaks with strong absorption of more than 97% at 0.49 and 0.69 THz. The dual-band absorption peaks were seen to be shifted with the change in the refractive index of the surrounding medium, with a corresponding sensitivity of 0.0968 and 0.1182 THz/RIU. The spectral shift of the reflection resonance dip was utilized as an assessment index to evaluate the sensing performance of the new structure, and it was found to be 2.08 and 2.98 for the two resonance peaks, respectively. It was observed that the proposed structure acted as an epsilon negative material at the first resonance and as a mu negative material at the second resonance. Further investigations on the electric field, magnetic field, and surface current distributions were carried out to elaborate on the absorption characteristics at various resonance frequencies. The proposed sensor is a highly sensitive MTMA which can be used to investigate the interaction of matter with THz waves.

In this paper, a new metamaterials-based hypersensitized liquid sensor integrating omega-shaped resonator with microstrip transmission line is proposed. Microwave transmission responses to industrial energy-based liquids are investigated intensively from both numerical and experimental point of view. Simulation results concerning three-dimensional electromagnetic fields have shown that the transmission coefficient of the resonator could be monitored by the magnetic coupling between the transmission line and omega resonator. This sensor structure has been examined by methanol–water and ethanol–water mixtures. Moreover, the designed sensor is demonstrated to be very sensitive for identifying clean and waste transformer oils. A linear response characteristic of shifting the resonance frequency upon the increment of chemical contents/concentrations or changing the oil condition is observed. In addition to the high agreement of transmission coefficients (S21) between simulations and experiments, obvious resonant-frequency shift of transmission spectrum is recognized for typical pure chemical liquids (i.e., PEG 300, isopropyl alcohol, PEG1500, ammonia, and water), giving rise to identify the type and concentration of the chemical liquids. The novelty of the work is to utilize Q factor and minimum value of S21 as sensing agent in the proposed structure, which are seen to be well compatible at different frequencies ranging from 1–20 GHz. This metamaterial integrated transmission line-based sensor is considered to be promising candidate for precise detection of fluidics and for applications in the field of medicine and chemistry.

A triple band metamaterial absorber in the terahertz range, incorporating a three closed circle ring resonator, was designed and fabricated on flexible polyethylene terephthalate “PET” substrate. The proposed design was investigated theoretically and experimentally. Computer simulation technology “CST” was used to study the designed structure, while lithography technique was used to fabricate the absorber and terahertz time-domain spectroscopy was utilized to measure the reflectivity. Results showed the presence of three intensive peaks at the resonance frequencies of ‘0.43, 0.61, and 0.88 THz’, which correspond to the absorptivity of 98%, 91%, and 98%, respectively. The sensitivity of the three peaks was found to be ‘70.5, 133, and 149.5 GHz/RIU’, respectively. The parametric studies and field distributions were analysed. Furthermore, the proposed design exhibited polarization insensitivity for both transverse electric “TE” and transverse magnetic “TM” modes from 00 to 900. It was concluded that the proposed design can be specifically viable for some important applications such as ‘THz’ images, filtering, biological sensing, and optical communications.