The operation of the metasurface based on silicon cylindrical rings coated by a gold as a terahertz (THz) bandpass filter/antireflection structure is studied. The decrease in the reflectance is conditioned by the destructive interference of electromagnetic waves reflected from structural layers of the metasurface. An efficient antireflection band with the reflectance below 10% is formed in the frequency spectrum of 0.71–0.92 THz with a relative bandwidth of 26%. It is shown that the operating spectrum of the suggested metasurface can be varied by changing the total radius of cylindrical rings, whereas the filter’s performance is rather insensitive to the variations in cylinder height and inner radius. The dependence of the antireflection band on the polarization and incidence angle of the THz waves is also analyzed. The antireflection band is sensitive to changes in the surrounding medium, hence enabling control of the transmittance band by exploiting refractive-index-changing materials.

A simplified kinetic model for the quantitative analysis of a potentiometric, pH-based urea biosensor is presented. The device was an electrolyte–insulator–semiconductor capacitor (EISCAP) with a pH-sensitive Ta₂O₅ gate functionalized by a polyallylamine hydrochloride (PAH)/urease bilayer. Within the steady-state approximation, the kinetic equations yielded an implicit algebraic relation linking the bulk urea concentration to the local pH at the sensor surface. Numerical solution of this equation, combined with a fitting routine, provides the apparent Michaelis–Menten constant ($K_M$) and the normalized maximum reaction rate (${\overline{k}}_V$). Validation against the literature data confirmed the reliability of the approach. Experimental results were then analyzed in both phosphate buffer (PBS) and artificial urine (AU), covering urea concentrations of 0.1–50 mM. The fitted parameters showed comparable $K_M$ values of 10.9 mM (PBS) and 32.4 mM (AU), but strongly different ${\overline{k}}_V$ values: $2.2\times {10}^{-4}$ (PBS) versus $8.6\times {10}^{-7}$ (AU). The three-order reduction in AU was attributed to the inhibitory effects inherent to complex biological fluids. These findings highlight the importance of the model-based quantitative analysis of EISCAP biosensors, enabling the accurate characterization of immobilized enzyme layers and guiding optimization for applications in realistic sample matrices.