Skip to main content

Dual‐Spectral Design of Porous Anodic Alumina for Tunable Colored Passive Radiative Cooling

Research Abstract

Passive radiative cooling requires materials that combine high mid-infrared (MIR) emissivity within the atmospheric transparency window (8–13 µm) with minimal solar absorption, while maintaining scalability and long-term stability. Porous anodic alumina (PAA) is an attractive dielectric platform due to its intrinsic phonon-polariton infrared emission and electrochemically tunable nanostructure. However, achieving independent control of visible photonic properties and MIR emissivity within a single architecture remains challenging. Here, we demonstrate dual-spectral control of PAA photonic structures integrated with aluminum (Al) substrates using charge density-controlled sinusoidal pulse anodization. Periodic voltage modulation generates well-defined photonic stop bands (PSBs) in the visible range, enabling tunable structural coloration while preserving high MIR emissivity. Systematic pore widening produces a progressive blue shift of the PSB accompanied by non-monotonic reflectance changes, revealing distinct mechanisms governing spectral position and optical coherence. In contrast, MIR emissivity remains robust against variations in the visible photonic response, as confirmed by a constant-voltage reference sample. The PAA architecture provides intrinsic optical impedance matching through a gradual refractive-index transition, while the Al substrate acts independently as a back reflector that suppresses transmission losses. These findings establish PAA as a versatile platform for color-designed radiative cooling surfaces with independently engineered optical and thermal functionalities.

Research Authors
Zeinelabedin A. Mohamed, Maksymilian Włodarski, Małgorzata Norek
Research Date
Research Department
Research Journal
Small
Research Member
Research Year
2026

Simulation study on optimizing spectral selectivity of thick PAA/Al bilayers for passive daytime radiative cooling

Research Abstract

Passive radiative cooling offers energy-free sub-ambient cooling; however, its main challenge is achieving low solar absorption (visible − NIR) while maintaining strong thermal emission in the mid-infrared atmospheric window. In this work, we numerically investigate a planar porous anodic alumina (PAA)/Al bilayer as a spectrally selective emitter for daytime radiative cooling. The optical response of the PAA layer is modeled using an effective-medium approach based on the Maxwell–Garnett (MG) formalism, allowing systematic tuning of porosity. The simulations are conducted using COMSOL software with a highly refined mesh to ensure accuracy. The study demonstrates the influence of PAA thickness, Al thickness, and porosity on thermal emissivity in the mid-infrared range. Furthermore, field intensity, power dissipation, and penetration-depth analyses are consistent with mid-infrared spectral selectivity originating primarily from intrinsic phonon absorption within the Reststrahlen band of alumina, modulated by wavelength-dependent interference effects. At an incident angle of 35◦, where the simulated angular emissivity profile exhibits a local maximum for TM polarization, the PAA/Al bilayer achieves an average emissivity of 0.982 within the atmospheric window (8 − 13 μm) for a porosity of 30%. Moreover, the designed structure shows high PRC performance under normal atmospheric conditions, achieving a maximum temperature reduction of up to 8.3◦C below ambient temperature. Also, at thermal equilibrium, it delivers an anticipated net cooling power of 77.36W/m2. The PAA-based approach proposed here provides a promising route for producing low-cost, efficient radiative coolers at large scales for practical energy conservation

Research Authors
Zeinelabedin A. Mohamed, Małgorzata Norek
Research Date
Research Department
Research Journal
Solar Energy Materials and Solar Cells
Research Member
Research Year
2026

Enhanced mid-infrared emissivity in metal dielectric multilayer grating structures for passive radiative cooling

Research Abstract

Elevated operating temperatures significantly reduce the efficiency and lifetime of Si photovoltaic (PV) modules, motivating the development of spectrally selective passive radiative cooling (PRC) coatings that dissipate heat without compromising solar energy harvesting. Here, we propose and numerically investigate a multilayer metal–dielectric metasurface composed of a staircase-shaped silica () grating integrated onto a Si/Al platform, where the Al layer acts as a reflective back mirror and the Si layer represents the PV absorber. The design addresses the limited emissivity and impedance mismatch of conventional planar dielectric coatings in the  atmospheric transparency window. The structure is engineered by systematically optimizing the grating step heights, lateral widths, and periodicity to promote synergistic excitation of surface phonon-polariton resonances (SPhPs) and guided-mode resonances. Electromagnetic (EM) simulations under TM polarization, using experimentally measured complex refractive indices for , Si, and Al, were performed to evaluate spectral emissivity, angular response, and solar absorptance. The optimized  metasurface achieves an average emissivity of 0.92 within the  window while maintaining low solar absorptance across  and preserving absorption near the Si bandgap . Thermal performance was assessed using a coupled radiative–convective energy balance model under AM1.5G solar irradiation. The proposed structure reduces the equilibrium temperature of the structure by more than  relative to bare Si, corresponding to a projected PV efficiency improvement approaching . Although sub-ambient daytime cooling is not achieved due to residual solar absorption inherent to PV integration, the metasurface functions effectively as a radiative heat-rejection coating compatible with real-world Si solar modules. These results demonstrate that engineered dielectric micro-gratings can overcome the emissivity limitations of planar films and provide scalable, all-inorganic solutions for PV thermal management.

Research Authors
Zeinelabedin A. Mohamed, Małgorzata Norek
Research Date
Research Department
Research Journal
Solar Energy Materials and Solar Cells
Research Member
Research Year
2026

One-Dimensional Photonic Crystal Mirror Heterostructure for Ultra-high-Q Optical Refractive Index Sensing

Research Abstract

Refractive index sensing based on photonic crystal structures has emerged as a powerful platform for label-free and highly precision detection in chemical and biological applications. Here, we present a high-performance one-dimensional photonic crystal (1D PC) heterostructure tailored for ultra-sensitive refractive index sensing. The design leverages a symmetric, reverse-stacked cavity configuration to achieve an exceptionally high-quality factor (Q−factors) and near-unity transmission in the telecom band. The structure comprises two mirror-symmetric 1D PCs arranged in reverse order to generates a localized interface state at their junction, giving rise to a sharp resonance within the photonic bandgap (PBG). Impedance-matching layers composed of silicon and air are added at both input and output interfaces to enhance light–matter interaction and transmission efficiency. We employ finite-element-method (FEM) simulations with lossless materials to realize a sharply defined resonance, yielding a Q−factor of 1.32 × 10⁸, sensitivity of 1197.2 nm/RIU, figure of merit (FOM) of 9.04×104, and detection limit (DL) of ∼1.1×10−8 RIU. The structure exhibits near-unity transmission, polarization insensitivity, and operates in the telecom band (𝜆≈1512𝑛𝑚). Despite their idealized nature, these findings lay a high-performance foundation for the design of practical 1D PCs sensors targeting trace gas or low-concentration biochemical detection

Research Authors
Zeinelabedin A. Mohamed, Małgorzata Norek
Research Date
Research Department
Research Journal
Optical and Quantum Electronics
Research Member
Research Year
2026

Design and investigation of a plasmonic metamaterial terahertz sensor for refractive index sensing

Research Abstract

Significant research interest has been directed toward terahertz (THz) metamaterials, motivated by their prospective applications in the domains of biosensing and environmental detection. Among their most beneficial properties are the capabilities for speedy and non-destructive analysis. This study demonstrates a terahertz plasmonic sensor for monitoring environmental refractive index. The structure is designed with three key layers: a top gold film etched with two elliptical cross-shaped resonators, a middle silica insulator, and a continuous gold base layer. The novelty of this architecture lies in the specific symmetry of the crossed elliptical resonators, which suppresses radiative losses to achieve an exceptionally high-Q resonance—approximately eight times superior to traditional THz metamaterial sensors. We employed a 3D finite element model in COMSOL Multiphysics® to simulate the absorption spectra and analyze the field distribution. Notably, the model demonstrates high-performance resonance, with a peak absorption of 88\% occurring at 3.684 THz. The resonance condition, which is critical for sensing, is facilitated by the coexistence of electric and magnetic dipole responses, and the performance is subsequently determined by the associated localized field distribution. To verify the underlying physical mechanism, the geometrical parameters of the sensor were systematically varied, and the corresponding absorption performance was analyzed. The design also achieves high-performance refractive index sensing with a sensitivity of 2.02\text{T}\text{H}\text{z}/\text{R}\text{I}\text{U}, a \text{Q}-\text{f}\text{a}\text{c}\text{t}\text{o}\text{r} of 584.01, and a \text{F}\text{O}\text{M} of 321.14. These findings indicate that the presented sensor holds considerable promise for future deployment in biomedical detection and the monitoring of essential metrics within environmental applications.


 

Research Authors
Zeinelabedin A. Mohamed
Research Date
Research Department
Research Journal
Optical and Quantum Electronics
Research Member
Research Year
2026

High performance terahertz sensor structure based on coupled mim waveguide–disk resonator structure

Research Abstract

Hybrid plasmonic configurations provide an efficient and straightforward framework for achieving high-sensitivity and miniaturized optical sensing. Electromagnetic fields at terahertz frequencies open the window to multiple optical applications such as optical sensing, wireless communication, and medical imaging. The present research explores the performance of a terahertz refractive index (RI) sensor employing the finite element method (FEM) for numerical analysis. The proposed sensor is investigated based on coupling mechanism between a metal–insulator–metal (MIM) waveguide and a porous silicon (pSi) disk resonator. The coupling mechanism induces a sharp and asymmetric Fano resonance profile with significant enhancement in transmission value. The maximum sensing performance can be achieved by manipulating structure parameters and disk porosity. Simulation results reveal that the resulting Fano resonance exhibits an approximately linear dependence on the index of the surrounding index environment. Through optimization, the design exhibited outstanding sensing capabilities, with sensitivity reaching 1433 nm/RIU, a figure of merit of 392.06 RIU⁻¹, and quality factor of 5706.35. The study demonstrates that this design approach can effectively generate compact sensor architectures with high performance for microscale RI detection.


 

Research Authors
Zeinelabedin A. Mohamed
Research Date
Research Department
Research Journal
Sensing and Imaging
Research Member
Research Year
2026

Sensory systems underlying sociality in the naked mole-rat

Research Abstract

Social interactions rely on the integration of information across multiple sensory modalities. In many species, individuals recognize conspecifics through combinations of auditory, olfactory, tactile, and visual cues, reflecting the capacity of neural systems to integrate diverse streams of sensory input. The naked mole-rat (Heterocephalus glaber) provides a powerful model system for understanding how social living shapes the evolution of such communication systems, particularly under conditions where visual information is largely absent. Naked mole-rats represent a rare example of mammalian eusociality, living in large multigenerational colonies organized around a strict reproductive hierarchy and cooperative care of offspring [1]. Here, we review evidence that naked mole-rats integrate multiple sensory modalities, focusing on audition, olfaction, and somatosensation to encode social identity.

Research Authors
Mohammed A. Khallaf, Wenhan Luo, Firdevs Murad, Gary R. Lewin, Alison J. Barker
Research Department
Research File
Research Journal
Current Opinion in Neurobiology
Research Member
Research Publisher
Current Opinion in Neurobiology
Research Year
2026

Advancing sustainable groundwater mapping and management in arid quaternary aquifers using machine learning and geospatial analytics integrating remote sensing and field hydrogeological data

Research Abstract

Groundwater (GW) represents a critical resource for sustaining agriculture and rural communities across the arid regions of many developing countries. This study assesses three predictive approaches boosted classification tree (BCT), the bivariate frequency ratio (FR), and a hybrid BCT–FR ensemble for mapping Potential Zones (GWPZ) in arid environments. The modelling framework integrates satellite-derived variables with pumping-test measurements (specific capacity (SPC) and transmissivity (T)) and incorporates topographic, geological, hydrogeological, and anthropogenic factors using an inventory of forty-two wells divided into calibration (70%) and validation (30%) datasets across the West El-Minia region of Upper Egypt. Change-detection analysis over the study period (2000–2025) indicated a substantial increase in agricultural activity, with cultivated lands expanding by more than 560 km². This expansion was accompanied by an observed level decline of approximately five meters over the same period, based on field measurements from 42 wells and calculated using observed water table differences. Based on SPC predictions, the BCT and hybrid FR–BCT models achieved relatively high area under the curve (AUC) values. For transmissivity, the corresponding accuracy values were 83.38% for BCT and 92.58% for FR–BCT. Model outputs were assessing their reliability by comparing the GW potential map generated with available borehole information and daily GWproductivity data from the aquifer system. The study area was classified into four GW potential categories: very high (8%), high (26%), moderate (54%), and low (12%), with the northeastern sector exhibiting the highest recharge and storage potential. Overall, the applied machine-learning techniques demonstrated good performance for GW potential assessment in data-limited environments. The results provide important guidance for GW resource management by identifying zones with substantial recharge and development potential.

Research Date
Research Department
Research Journal
Environmental Earth Sciences
Research Pages
346
Research Publisher
Springer Berlin Heidelberg
Research Vol
85
Research Website
https://link.springer.com/article/10.1007/s12665-026-13021-0
Research Year
2026
Subscribe to