Search Results (59)

Although the elitist genetic algorithm (EGA) is an approach for the optimal design of pixelated metasurfaces, it is necessary to convert a two-dimensional (2D) metasurface to a one-dimensional array. This ignores the effects of the mutation on neighboring data in 2D metasurfaces, and hinders the rapid convergence of the algorithms. Therefore, we propose the 2D mutation-based EGA (2DM-EGA) to optimally design the linear-to-circular (LTC) polarization conversion metasurface (PCM). Compared with EGA, 2DM-EGA can significantly improve the convergence rate. Furthermore, combined with the proposed intuitive reward-based fitness function and circular polarization discrimination pertaining to an ellipticity angle β, 2DM-EGA, programmed in Python (2023 version), is used to accomplish optimal targets. Finally, the simulated operating band of the optimized metasurface varies from 8.16 GHz to 11.5 GHz with a reduced ellipticity angle β/π ≥ 0.15 and a relative bandwidth of 33.5%, which suggests that the optimized metasurface realizes the broadband LTC polarization conversion. The measured results are in excellent accord with the simulations validating 2DM-EGA for the optimal design of transmission-type wideband LTC PCMs. Additionally, the physical mechanism of the design is expounded. Full article

The agro-industry is among the largest methane emitters, posing a critical challenge for sustainability. In rural areas, producers lack effective technologies to manage daily organic waste. Anaerobic digestion (AD) offers a circular pathway by converting waste into biogas and biofertilizers; however, its adoption is limited by inappropriate designs and insufficient operational control. Theoretical-applied research addresses these barriers by improving the design and operation of small-scale biodigesters, elevating pH and Electrical Conductivity (EC) from passive indicators to first-order control variables. Based on the design of a compact biodigester previously validated in the Chillón Valley and replicated in Huaycán under a utility model patent process (INDECOPI, Exp. 001087-2025/DIN), a stoichiometric NaHCO${}_3$ strategy with joint pH–EC monitoring was formalized, defining operational windows (pH 6.92–6.97; EC 6200–6300 μS/cm and dose–response curves (0.3–0.4 kg/day for 3–4 day) to buffer VFA shocks and preserve methanogenic ionic strength. The system achieved stable productions of 370–462 L/day, surpassing the theoretical potential of 352.88 L/day calculated by Buswell’s equation. A multivariable predictive model (linear, quadratic, interaction terms pH × EC, temperature, and loading rate) was developed and validated with field data: R² = 0.78; MAPE = 2.7%; MAE = 11.2 L/day; RMSE = 13.8 L/day; r = 0.89; residuals normally distributed (Shapiro–Wilk p = 0.79). The proposed approach enables daily decision-making in low-instrumentation environments and provides a replicable and scalable pathway for the safe valorization of organic waste in rural areas. The design consolidates the shift from reactive to proactive and co-optimized pH–EC control, laying the foundation not only for standardized protocols and training in rural systems but also for improved environmental sustainability. Full article

We present a single-slab metasurface that converts a normally incidental linearly polarized wave into either right- or left-handed circular polarization (RHCP/LHCP) through a simple ${90}^{\circ }$ mechanical rotation. Each unit cell comprises two L-shaped metallic resonators placed on the opposite faces of a low-permittivity substrate. Operating in transmission mode, the linear-to-circular (LTC) converter does not require any active electronic components. The geometry is optimized by using full-wave simulations to maximize the conversion up to 26% relative bandwidth with polarization conversion efficiency up to 65%, and insertion loss below 1.3 dB. Power balance analysis confirms low-loss, impedance-matched behavior. A scaled prototype fabricated from AWG-25 steel wires validates the model: experimental measurements closely reproduce the simulated bandwidth and demonstrate robust handedness switching. Because the resonance frequency depends primarily on resonator length and unit-cell pitch and thickness, the design can be retuned across the microwave spectrum through straightforward geometrical scaling. These results suggest that mechanical rotation could provide a simple and reliable alternative to electronic tuning in reconfigurable circular polarizers. Full article

This paper investigates the performance of a spacecraft equipped with a diffractive sail in a heliocentric mission scenario that requires phasing along a prescribed elliptical orbit. The diffractive sail represents an evolution of the more traditional reflective solar sail, which converts solar radiation pressure into thrust using a large reflective surface typically coated with a thin metallic film. In contrast, the diffractive sail proposed by Swartzlander leverages the properties of an advanced metamaterial-based film to generate a net transverse thrust even when the sail is Sun-facing, i.e., in a configuration that can be passively maintained by a suitably designed spacecraft. Specifically, this study considers a sail membrane covered with a set of electro-optically controlled diffractive panels. These panels employ a (controlled) binary metamaterial arrayed grating to steer the direction of photons exiting the diffractive film. This control technique has recently been applied to achieve a circle-to-circle interplanetary transfer using a Sun-facing diffractive sail. In this work, an optimal control law is employed to execute a rapid phasing maneuver along an elliptical heliocentric orbit with specified characteristics, such as those of Earth and Mercury. The analysis also includes a limiting case involving a circular heliocentric orbit. For this latter scenario, a simplified and elegant control law is proposed based on a linearized form of the equations of motion to describe the heliocentric dynamics of the diffractive sail-based spacecraft during the phasing maneuver. Full article

Although linear overproduction and overconsumption have benefited businesses, they have created an unsustainable society. Converting wood waste into construction material can support the transition to a circular economy. The mechanical properties of beams constructed from wood waste were measured. Squares with 50, 60, and 70 mm side lengths were glued to create beams, to which the three-point test method was applied parallel to the fibres. The stiffness and moduli of elasticity and rupture were analysed with standard industrial statistical techniques. Specifically, a two-stage analysis was performed using the normal distribution and Shewhart control charts. Changes of 100 mm in width and height and 200 mm in length caused a change of 200–400 N/mm² in elasticity and 500–1300 MNmm² in stiffness. Modulus of rupture values were relatively comparable, as they were determined by the properties of oak wood, from which the beams were made. The observed differences in the tested mechanical parameters will be useful in the optimisation of furniture construction, with our research suggesting that it is possible to predict mechanical properties from the dimensions of the waste-wood pieces. Ultimately, this should help to design sustainable furniture that is aesthetic, functional, and safe. Full article

In this paper, a wideband circularly polarized folded reflectarray antenna (CPFRA) based on a transmissive linear-to-circular polarization converter is proposed. The CPFRA consists of a primary reflector and a sub-reflector. To achieve broadband performance, a metasurface-based RA element on the primary reflector surface and a transmissive linear-to-circular polarization converter on the sub-reflector surface are applied. Moreover, the transmissive linear-to-circular polarization converter on the sub-reflector surface helps convert linear polarization to circular polarization. To verify the proposed CPFRA, a prototype is designed, fabricated, and tested. The measured results exhibit that the proposed CPFRA presents a 3 dB gain bandwidth of 27.4% and a 3 dB axial ratio bandwidth of 23%. The CPFRA achieves a peak gain of 21.2 dBi with an aperture efficiency of 27.2%. The proposed CPFRA is a promising candidate for millimeter-wave (mm-W) satellite communication applications because of its advantages of high gain, low cost, low profile, and broad bandwidth. Full article

This academic paper proposes a terahertz (THz) device featuring dynamic adjustability. This device relies on composite metamaterials made of graphene and vanadium dioxide (VO₂). By integrating the electrically adjustable traits of graphene with the phase transition attributes of VO₂, the suggested metamaterial device can achieve both broadband absorption and dual-band linear-to-circular polarization conversion (LCPC) in the terahertz frequency range. When VO₂ is in its metallic state and the Fermi level of graphene is set to zero electron volts (eV), the device shows remarkable broadband absorption. Specifically, it attains an absorption rate exceeding 90% within the frequency span of 2.28–3.73 terahertz (THz). Moreover, the device displays notable polarization insensitivity and high resistance to changes in the incident angle. Conversely, when VO₂ shifts to its insulating state and the Fermi level of graphene stays at 0 eV, the device operates as a highly effective polarization converter. It attains the best dual-band linear-to-circular polarization conversion within the frequency ranges of 4.31–5.82 THz and 6.77–7.93 THz. Following the alteration of the Fermi level of graphene, the device demonstrated outstanding adjustability. The designed multi-functional device features a simple structure and holds significant application potential in terahertz technologies, including cloaking technology, reflectors, and spatial modulators. Full article

This paper proposes a mechanically reconfigurable multi-polarization antenna based on a 3D-printed anisotropic dielectric polarizer, offering wide bandwidth, high gain, and extremely low cost. The working mechanism of the dielectric polarizer is analyzed, demonstrating its ability to efficiently convert linear polarization (LP) to circular polarization (CP) over a wide frequency range. Furthermore, the polarizer exhibits subwavelength characteristics. For a given duty cycle, its phase response depends only on the height and is independent of the aperture size. This property enables miniaturized and customized designs of the polarizer’s aperture size. Subsequently, the polarizer is placed above a Ku band waveguide and standard horn antennas. The results show that by rotating the dielectric polarizer and adjusting the positions of the antennas, right-handed CP (RHCP), left-handed CP (LHCP), and dual LP radiation switching can be achieved in the 12.4–18.0 GHz band, verifying the quad-polarization reconfigurability. Additionally, the polarizer significantly enhances the gain of the waveguide antenna by approximately 9.5 dB. Furthermore, due to the low-cost 3D printing material, the manufacturing cost of the polarizer is exceptionally low, making it suitable for applications such as anechoic chamber measurements and wireless communications. Finally, the measurement results further validate the accuracy of the simulations. Full article

The development of polarization converters is crucial for various applications, such as communication and sensing technologies. However, traditional polarization converters often encounter challenges in optimizing performance due to the complexity of multiparameter structures. In this study, we propose a novel multiparameter linear-to-circular polarization (LCP) converter design that addresses the difficulties of comprehensive optimization, where balancing multiple structural parameters is key to maximizing device performance. To solve this issue, we employ a machine learning (ML)-guided approach that effectively navigates the complexities of parameter interactions and optimizes the design. By utilizing the XGBoost model, we analyze a dataset of over 1.3 million parameter combinations and successfully predict high-performing designs. The results highlight that key parameters, such as the graphene Fermi level, square frame size, and VO₂ conductivity, play a dominant role in determining the performance of the LCP converter. This approach not only provides new insights into the design of LCP converters but also offers a practical solution to the complex challenge of multiparameter optimization in device engineering. Full article

In this study, we present a novel ultra-wideband passive polarization conversion metasurface (PCM) that integrates double V-shaped patterns with circular split-ring resonators. Operating without any external power supply or active components, this design effectively manipulates the polarization state of incident electromagnetic waves. Numerical and experimental results demonstrate that the proposed PCM can convert incident linear polarization into orthogonal states across a wide frequency range of 7.1–22.3 GHz, encompassing the C-, X-, Ku-, and K-bands. A fabricated prototype confirms that the polarization conversion ratio (PCR) exceeds 90% throughout the specified band. Furthermore, we explore an additional application of this passive metasurface for electromagnetic stealth, wherein it achieves over 10 dB of monostatic radar cross-section (RCS) reduction from 7.6 to 21.5 GHz. This broad effectiveness is attributed to strong electromagnetic resonances between the top and bottom layers, as well as the Fabry–Pérot cavity effect, as evidenced by detailed analyses of the underlying physical mechanisms and induced surface currents. These findings confirm the effectiveness of the proposed design and highlight its potential for future technological applications, including 6G communications, radar imaging, anti-interference measures, and electromagnetic stealth. Full article

Aquaculture wastewater treatment not only assists in alleviating the scarcity of clean water for daily usage and environmental pollution, but also generates valuable byproducts. This paper aims to review the generation of wastewater from the aquaculture sector, its characteristics, and available treatment technologies, while comprehensively discussing the adoption of a biocircular economy approach through waste valorization. With rich nutrients, such as nitrogenous compounds, and the presence of phosphorus in the aquaculture effluent, these aspects could be explored and valorized into biofertilizers, broadening their application in aquaponics and hydroponics, as well as in algae and daphnid cultivation. Biofertilizer can also be used in agriculture because it contains essential elements needed by plants. Thus, methods of converting nutrients into biofertilizers in terms of sludge recovery can be accomplished via anaerobic and aerobic digestion, drying, composting, and vermicomposting. Moving forward, aquaculture effluent recovery is addressed under the biocircular economy by re-engaging aquaculture wastewater effluents into the production cycle. The enhancement of aquaculture effluents and biomass for uses such as aquaponics, hydroponics, algae cultivation, daphnid co-cultivation, and biofertilizers presents valuable opportunities for nutrient recovery while ensuring that non-toxic wastewater can be safely discharged into external water bodies. This approach has the potential to revolutionize wastewater treatment in aquaculture, shifting the economic model of wastewater management from a linear system to a circular, more sustainable one. Full article

The technologically advanced learning ocean system—wave energy converter (TALOS-WEC) project addresses the urgent need for sustainable and efficient energy solutions by leveraging the vast potential of wave energy. This project presents a pioneering approach to wave energy capture through its unique multi-axis and omnidirectional point absorber design. Featuring a fully enclosed power take-off (PTO) system, the TALOS-WEC harnesses energy across six degrees of freedom (DoFs) using an innovative internal reaction mass (IRM) mechanism. This configuration enables efficient energy extraction from the relative motion between the IRM and the hull, aiming for energy conversion efficiencies ranging between 75–80% under optimal conditions, while ensuring enhanced durability in harsh marine environments. The system’s adaptability is reflected in its versatile geometric configurations, including triangular, octagonal, and circular designs, customised for diverse marine conditions. Developed at Lancaster University, UK, and supported by international collaborations, the TALOS-WEC project emphasises cutting-edge advancements in hydrodynamic modelling, geometric optimisation, and control systems. Computational methodologies leverage hybrid frequency-time domain models and advanced panel codes (WAMIT, HAMS, and NEMOH) to address non-linearities in the PTO system, ensuring precise simulations and optimal performance. Structured work packages (WPs) guide the project, addressing critical aspects such as energy capture optimisation, reliability enhancement, and cost-effectiveness through innovative monitoring and control strategies. This paper provides a comprehensive overview of the TALOS-WEC, detailing its conceptual design, development, and validation. Findings demonstrate TALOS’s potential to achieve scalable, efficient, and robust wave energy conversion, contributing to the broader advancement of renewable energy technologies. The results underscore the TALOS-WEC’s role as a cutting-edge solution for harnessing oceanic energy resources, offering perspectives into its commercial viability and future scalability. Full article

This study investigates the potential of converting waste biosolids from industrial sources, focusing on economic viability and heavy metal removal efficiency. Traditional management methods like landfilling and incineration are increasingly impractical due to land constraints and environmental concerns, prompting a shift towards thermal and biological conversion technologies including anaerobic digestion, pyrolysis, gasification, and hydrothermal liquefaction. Incorporating a pretreatment for heavy metal removal is essential, as industrial wastes are highly subjected to metal contamination. The study screens a range of metal removal processes, including precipitation, adsorption, ion exchange, and microwave induction. Although a techno-economic analysis can help give a perspective on the economic viability and environmental impact of each technology, it does not account for technical limitations and variations in the treated waste stream. A mixed integer linear programming (MILP) optimization model is developed to fill in this gap and assist in waste stream allocation to the most appropriate technology, taking into account both technology capacities and feed characteristics. This study looked into the optimal treatment route at different feed moisture contents and varying flow rates. The results demonstrate that the model distributes the feed across the different technologies on the basis of maximizing the capacity of the optimal technology while ensuring the moisture and heavy metal content limits are satisfied. Thus, it maximizes profitability and ensures heavy metal removal efficiency. By optimizing industrial biosolids treatment pathways, this study promotes sustainable resource recovery aligning with circular economy principles in waste management. The developed model facilitates informed decision-making in biosolids management and industrial waste treatment practices. Full article

Focusing water surface waves is a promising approach for enhancing wave power in clean energy harvesting. This study presents a novel method that simplifies the wave-scattering problems of large-scale three-dimensional (3D) focusing blocks by decomposing them into scattering problems of two-dimensional (2D) phase regulators. The phase lags of transmitted waves over such 2D structures of various heights and thicknesses are investigated using both linear potential flow theory and numerical simulations based on smoothed-particle hydrodynamics (SPH). Due to propagation path differences of a converging wave, our approach compensates for circular phase differences within a maximal collection angle by optimizing the geometries of 2D phase regulators. Based on this concept, we designed three types of submerged structures and tested them in a 3D numerical water tank. All three structures successfully converted monochromatic plane waves into circular waves, which then converged at the designated focal point. This study offers a potential method to enhance the collection efficiency of monochromatic and regular waves for wave energy converters. Full article

The angle of incidence of the compact polarization conversion device is crucial for practical use in integrated miniaturized optical systems. However, this index is often ignored in the design of quarter-wave plate based on metasurface. Herein, it is shown that a thick metallic cross-shaped hole array supports extraordinary optical transmission peaks controlled by a Fabry–Pérot (FP) resonator mode. The positions of these peaks have been proven to be independent over a large range of incidence angles. We numerically design a miniatured quarter-wave plate (QWP) with an 80 nm bandwidth (840~920 nm) and approximately 80% average efficiency capable of effectively functioning as a linear-to-circular (LTC) polarization converter at an incidence inclination angle of less than 30°. This angle-insensitive compact polarization conversion device may be significant in a new generation of integrated metasurface-based photonics devices. Full article