Maurício Duarte Almeida

This work investigates the electromagnetic absorption performance of a compact, symmetric, planar Ni–PTFE metamaterial absorber operating over the 300–3000 nm optical range. The structure comprises a nickel resonator disk on a polytetrafluoroethylene substrate backed by a continuous nickel ground plane. Nickel was selected for its thermal stability and optical properties, while PTFE provides low dielectric loss and chemical stability. A computational domain analysis demonstrates that a single unit cell with periodic boundary conditions accurately reproduces the response of larger arrays while reducing simulation time by up to 43 times. Full-wave simulations predict an average absorption of 97.96%, with peaks reaching 99.72%. The absorber maintains high performance under transverse electric, transverse magnetic (TM), and transverse electromagnetic excitations for incidence angles up to 60°. Electric and magnetic energy density analyses further reveal the physical mechanisms responsible for efficient broadband electromagnetic energy confinement and absorption.

This letter presents the design and experimental evaluation of a magnetic-resonant wireless power transfer (WPT) system for brain implants. A circuit-based model is proposed to predict the behavior of multicoil structures and to accurately estimate self- and mutual inductances under lateral and angular misalignment. A method is introduced to identify the spatial regions of approximately uniform mutual inductance, improving robustness relative to conventional repeater-assisted configurations. The influence of biological media is evaluated using an equivalent homogeneous head model representing the averaged dielectric properties of the underlying tissues. The proposed system was evaluated through the proposed modeling, full-wave CST simulations, and experimental measurements in air and in the equivalent biological medium. Results show close agreement among all approaches and confirm that tissue heterogeneity has negligible impact on coupling, resonance, and delivered power. The system operates stably across different implant positions, delivering the required power for neural devices implants.

This study presents a high-performance, ultra-thin metamaterial absorber consisting of nickel resonator disks arranged in a 4 × 4 matrix on a polytetrafluoroethylene (PTFE) substrate. The novelty of the design lies in the integration of nickel—a cost-effective alternative to noble metals—and PTFE, whose excellent thermal stability enhances the overall performance of the metamaterial. Additionally, the simplified unit cell structure enables scalability and offers a practical alternative to conventional absorbers. The proposed metamaterial absorber achieves broadband absorption across the ultraviolet, visible, and infrared spectra. A systematic parametric analysis was conducted to optimize the structural parameters, maximizing absorption efficiency while maintaining minimal thickness. Numerical simulations performed in CST Studio Suite^® validated the optimized design, demonstrating an average absorption of 99.00% and a peak absorption of 99.36% within the 375–850 nm range. Given the elevated absorption rates achieved, the analysis range was extended to 300–3000 nm, and a genetic algorithm was employed to refine the geometric parameters. This optimization resulted in a stable absorption profile with an average efficiency of 98.98%, and a peak of 99.96%. This structurally simple design offers an advantage by combining cost-effective material selection with high broadband absorption performance.