Metasurfaces for Far-Field Radiation Pattern Correction of Antennas under Dielectric Seamed-Radomes

A high-index dielectric radome seam is camouflaged with respect to a low-index dielectric radome panel by tuning the seam with carefully engineered metasurfaces. A transmission-line approach is used to model the metasurface-tuned seam and analytically retrieve the corresponding surface impedance, from which the unit-cell design is then tailored. Full-wave simulations and microwave antenna measurements performed on a proof-of-concept prototype validate the undesired scattering suppression effect in the case of normally and obliquely incident transverse electric and transverse magnetic wave illuminations. Robustness of the proposed solution to fabrication tolerances is also reported. The study presents metasurface-tuning as an easily implementable, frequency adjustable, and polarization insensitive solution to reduce the scattering of dielectric mechanical seams and improve the overall transparency performance of radome structures.

Design of a large-range rotary microgripper with freeform geometries using a genetic algorithm

This paper describes a novel electrostatically actuated microgripper with freeform geometries designed by a genetic algorithm. This new semiautomated design methodology is capable of designing near-optimal MEMS devices that are robust to fabrication tolerances. The use of freeform geometries designed by a genetic algorithm significantly improves the performance of the microgripper. An experiment shows that the designed microgripper has a large displacement (91.5 μm) with a low actuation voltage (47.5 V), which agrees well with the theory. The microgripper has a large actuation displacement and can handle micro-objects with a size from 10 to 100 μm. A grasping experiment on human hair with a diameter of 77 μm was performed to prove the functionality of the gripper. The result confirmed the superior performance of the new design methodology enabling freeform geometries. This design method can also be extended to the design of many other MEMS devices.

A wideband metamaterial cross polarizer conversion for C and X band applications

This article present wideband Metamaterial Cross Polarizer (MCP) structure for C and X band applications. The proposed structure consists of wheel shaped associated with meander line and triangular shaped patches having overall dimension of 18 × 18 mm. The anisotropic design patchis a single metallic layer (Cu) placed at the top of dielectric substrate FR-4 and backed by a ground also consists of metal layer (Cu). A wideband Polarization Conversion Ratio (PCR) above 0.8 magnitudes is achieved having bandwidth of 8.1 GHz ranging from 3.43 to 11.53 GHz and it works for C (4–8 GHz) and X (8–12 GHz) band approximately. The bandwidth of PCR at Full Width Half Maxima (FWHM) achieved is 8.24 GHz (3.60–11.84 GHz). Three distinct PCR peaks are observed at 4.2, 5.98, and 9.46 GHz with PCR magnitudes at 91.07, 96.39, and 99.76% respectively. Analysis of polarization conversion phenomena at these three frequencies is described with the help of current and electric field distribution. The proposed anisotropic structure is examined at different angles under normal and oblique incident. The simulation is performed through ANSYS HFSS (19.1), fabrication is done on substrate FR-4 using printed circuit board (PCB). The simulated and measured curves obtained for reflection coefficient and PCR are similar to one another with minute difference due to fabrication tolerances.

High-Efficiency, Wide Working Bandwidth Antenna Based on SOI Platform for Optical Phased Array

A novel structure of a subwavelength surface optical antenna for optical phased array is proposed in this paper. An asymmetric vertical grating structure is applied to achieve high emission efficiency (73% at 1550 nm). Optical antennas with large fabrication tolerances can also maintain a wide working bandwidth of 1 dB between 1350 and 1850 nm. The far-field scanning characteristics of 16-channel optical phased array are investigated in this study by employing the proposed antenna. The results show that the background suppression without considering side lobes caused by the antenna arrangement is −24.5 dB when the phase difference is 0 and when the scan range is as large as ±14.8° × 73.6°.

Broadband sound absorbers of multilayered micro-slit panels using Bayesian probabilistic inference

Micro-perforated panel absorbers can typically achieve either visual transparency or broadband absorption, but not both. This paper assesses the potential of Multilayer Micro-Slit panels to maintain both of these characteristics simultaneously. Micro-slit panels are similar to micro-perforated panels, and can similarly achieve high absorption coefficients without fibrous backing materials. The arrangement of slits are better suited to visual transparency than perforated holes because it provides more unobstructed panel per perforated area. However, these types of absorbers are limited to a narrow frequency bandwidth of effective absorption. By combining several panels into a multilayer assembly, broadband absorption becomes possible. The inherent complexity stemming from optimizing the parameters for multiple layers to meet a given design criteria necessitates the use of the Bayesian framework. This probabilistic method rapidly hones in on the best parameters of each individual layer so that the overall composite meets the design goal. Furthermore, Bayesian inference implemented cyclically alongside panel fabrication and testing allows for corrections of fabrication tolerances while assessing visual transparency.

Global optimization of an encapsulated Si/SiO$$_2$$ L3 cavity with a 43 million quality factor

We optimize a silica-encapsulated silicon L3 photonic crystal cavity for ultra-high quality factor by means of a global optimization strategy, where the closest holes surrounding the cavity are varied to minimize out-of-plane losses. We find an optimal value of $$Q_c=4.33\times 10^7$$ Q c = 4.33 × 10 7 , which is predicted to be in the 2 million regime in presence of structural imperfections compatible with state-of-the-art silicon fabrication tolerances.

Optimization of Optical Filters based on Integrated Coupled Sagnac Loop Reflectors

We theoretically investigate integrated photonic resonators formed by two mutually coupled Sagnac loop reflectors (MC-SLRs). Mode interference in the MC-SLR resonators is tailored to achieve versatile filter shapes with high performance, which enable flexible spectral engineering for diverse applications. By adjusting the reflectivity of the Sagnac loop reflectors (SLRs) as well as the coupling strength between different SLRs, we achieve optical analogues of Fano resonance with ultrahigh spectral slope rates, wavelength interleaving / non-blocking switching functions with significantly enhanced filtering flatness, and compact bandpass filters with improved roll-off. In our designs the requirements for practical applications are considered, together with detailed analyses of the impact of structural parameters and fabrication tolerances. These results highlight the strong potential of MC-SLR resonators as advanced multi-functional integrated photonic filters for flexible spectral engineering in optical communications systems.

Advanced Classical Optical Filters with Three Waveguide Coupled Sagnac Loop Reflectors

We theoretically investigate advanced multi-functional integrated photonic filters formed by three waveguide coupled Sagnac loop reflectors (3WC-SLRs). By tailoring the coherent mode interference, the spectral response of the 3WC-SLR resonators is engineered to achieve diverse filtering functions with high performance. These include optical analogues of Fano resonances that yield ultrahigh spectral extinction ratios (ERs) and slope rates, resonance mode splitting with high ERs and low free spectral ranges, and classical Butterworth, Bessel, Chebyshev, and elliptic filters. A detailed analysis of the impact of the structural parameters and fabrication tolerances is provided to facilitate device design and optimization. The requirements for practical applications are also considered. These results theoretically verify the effectiveness of using 3WC-SLR resonators as multi-functional integrated photonic filters for flexible spectral engineering in diverse applications.

Global optimization of an encapsulated Si/SiO2 L3 cavity with a 43 million quality factor

We optimize a silica-encapsulated silicon L3 photonic crystal cavity for ultra-high quality factor by means of a global optimization strategy, where the closest holes surrounding the cavity are varied to minimize out-of-plane losses. We find an optimal value of Qc = 4.33 × 107 , which is predicted to be in the 2 million regime in presence of structural imperfections compatible with state-of-the-art silicon fabrication tolerances.

Advanced Three Waveguide Sagnac Loop Reflectors for High Performance Optical Filters

We theoretically investigate advanced multi-functionalintegrated photonic filters formed by three waveguide coupledSagnac loop reflectors (3WC-SLRs). By tailoring the coherentmode interference, the spectral response of the 3WC-SLRresonators is engineered to achieve diverse filtering functionswith high performance. These include optical analogues of Fanoresonances that yield ultrahigh spectral extinction ratios (ERs)and slope rates, resonance mode splitting with high ERs and lowfree spectral ranges, and classical Butterworth, Bessel,Chebyshev, and elliptic filters. A detailed analysis of the impactof the structural parameters and fabrication tolerances isprovided to facilitate device design and optimization. Therequirements for practical applications are also considered.These results theoretically verify the effectiveness of using 3WCSLRresonators as multi-functional integrated photonic filters forflexible spectral engineering in diverse applications.