Dual-band infrared metamaterial absorbers that combine high spectral selectivity with tolerance to geometrical variation are of considerable interest for multispectral detection, thermal management, sensing, and selective infrared emission. In this work, a periodic metal-dielectric-metal absorber comprising L-shaped gold (Au) resonators, a silicon dioxide (SiO₂) spacer, and an optically thick Au ground plane is numerically investigated and optimized using the finite-difference time-domain (FDTD) method combined with particle swarm optimization (PSO). The nine geometrical parameters of the unit cell are optimized simultaneously so as to place two absorption bands at the mid-infrared wavelengths of 4.5 and 6.2 μm, which are selected for their relevance to mid-wave infrared detection and to the molecular fingerprint region. The optimized structure exhibits absorption efficiencies of 99.7% and 99.4% at the two resonance wavelengths. The physical origin of the dual-band response is examined through electric-field, surface-current, and induced-charge distributions, which indicate that the two bands arise from dipolar responses supported by two unequal effective current pathways of the asymmetric L-shaped resonator rather than from a fundamental-quadrupolar mode pair. A retrieved effective-impedance analysis and an equivalent LC-circuit description are used to quantify the impedance-matching condition responsible for the suppression of reflection, and a control simulation of the unpatterned Au/SiO₂/Au multilayer isolates the contribution of the patterned resonator. The dependence of the optical response on spacer thickness, spacer permittivity, resonator dimensions, polarization azimuth, incidence angle, and layer-thickness deviation is systematically assessed. The present study is entirely numerical; experimental fabrication and characterization are identified as necessary subsequent steps. The combined PSO-FDTD framework and the accompanying electromagnetic analysis provide a systematic route for designing compact dual-band infrared absorbers and for assessing their robustness prior to experimental realization.
A highly sensitive surface plasmon resonance (SPR) sensor is proposed and numerically investigated for blood cancer detection. The presented sensor is based on photonic crystal fiber (PCF) and employs a silver plasmonic grating. In the proposed structure, the D-shaped geometry has been utilized, which enhances the evanescent field interaction and improves the core and surface plasmon polariton (SPP) mode coupling. The refractive index (RI) of the analyte is varied from 1.362 to 1.390 to investigate the RI dependent sensing response of the proposed structure. The selected RI range is considered for RI based biomedical sensing relevant to blood cancer related applications. The simulations are performed on COMSOL Multiphysics software using Full-vector finite-element-method (FEM) to analyze the performance parameters. Local optimization of structural parameters is carried out to improve the sensing response, and the Taguchi method is further employed to study the impact of geometrical parameters on the sensing performance of the sensor. The proposed sensor achieves a wavelength sensitivity of 35,000nm/RIU with a maximum amplitude sensitivity (AS) of 499.26RIU−1, and minimum resolution of 2.86×10−6RIU indicating that the suggested sensor is highly sensitive and offers very good resolution. Furthermore, the evaluated resonance linewidths give FWHM values in the range of 128–182 nm, with a maximum figure of merit (FOM) of 192.31RIU−1 at na=1.380 making it a promising sensor for blood cancer sensing and other biomedical sensing applications based on RI sensing.
