Impedance Mismatch Research Articles

Realization of tunable non-Hermitian zero-index photonic crystals

In this work, we present a novel method for designing non-Hermitian zero-index photonic crystals using dielectric materials with tunable parameters. By adding non-Hermitian elements, either gain or loss, Dirac dispersion in the complex frequency domain can be achieved onto the original double-zero-index photonic crystals with accidental degeneracy. Our effective medium theory shows that the composite structure can maintain the near-zero value of the real parts of the effective permittivity ε and permeability μ while their imaginary parts can be designed. Multiple geometrical parameters in the added components can provide a large range of tunability of the imaginary parts of our proposal of non-Hermitian zero-index photonic crystals, which makes it a perfect platform for future non-Hermitian optics applications. With the adjustability of the imaginary part of the effective parameters, we achieve a wide tunability of the surface impedance of the non-Hermitian zero-index photonic crystals designed, and two applications are thus demonstrated. An arbitrary impedance matching is realized by both numerical simulations and microwave experiments so that the impedance mismatch between any two materials can be mitigated by our design. The emergence of a Zak phase will induce interface states between two non-Hermitian zero-index photonic crystals with different surface impedances, which also verifies our successful strategy to engineer material surface impedance. The research offers a general approach to constructing non-Hermitian zero-index materials, paving the road for material realization of non-Hermitian optics devices.

MXene Nanoribbon Aerogel-Based Gradient Conductivity Electromagnetic Interference Shields with Unprecedented Combination of High Green Index and Shielding Effectiveness.

The desire to reduce secondary pollution from shielded electronics devices demands electromagnetic interference (EMI) shields with high green index (GI), which is the ratio of absorbance over reflectance. Achieving high GI values simultaneously with high shielding effectiveness (SE) over 50dB is a serious unresolved challenge. Reducing the impedance mismatch between the shield and free space is the key to reducing the reflection of incoming radiation and enabling more penetration into the body of the shield for absorption. Here a sandwich structure with gradient conductivity is introduced that achieves a combination of high GI (≈2) and SE (70dB). The top layer deliberately uses an aerogel of low conductivity MXene nanoribbon in PEDOT:PSS polymer to boost the GI. The aerogel also reduces the permittivity of the shield, as another way to reduce the impedance mismatch for a nonmagnetic material. The bottom layer consists of a MXene nanosheet-polymer with its high metal-like conductivity to provide high SE. This successful demonstration is expected to lead to other novel ways to create conductivity gradient EMI shields.

An Electric‐Magnetic Dual‐Gradient Composite Film Comprising MXene, Hollow Fe3O4, and Bacterial Cellulose for High‐Performance EMI Shielding and Infrared Camouflage

AbstractIt is crucial to develop electromagnetic interference (EMI) shielding materials with high shielding efficiency (SE) and reduced reflection to mitigate the secondary pollution caused by electromagnetic waves (EMWs). Herein, a novel multilayer assembly strategy inspired by the structure of “Turkish dessert—Baklava” is proposed to introduce magnetic hollow Fe3O4 nanospheres (HFO) and conductive MXene nanosheets into a bacterial cellulose (BC) network. Through a layer‐by‐layer vacuum filtration approach, a composite BC/MXene/HFO film with a controllable electric‐magnetic dual‐gradient structure is achieved. The construction of electric‐magnetic dual gradients alleviates the impedance mismatch at the air‐film interface, resulting in reduced reflectivity toward EMWs, while the unique hollow structure of HFO facilitates the “absorption–reflection–reabsorption” process of EMWs. Consequently, the as‐prepared composite film (0.35 mm thickness) exhibits an extraordinary EMI SE of 67.6 dB and a reflection SE as low as 5.1 dB. Furthermore, it also demonstrates exceptional mechanical properties, efficient thermal management, and Joule heating capabilities, as well as remarkable passive and active infrared camouflage performances. This study offers an innovative approach to achieve less reflection and more absorption of EMWs, and expands the application scope of EMI shielding materials in precision electronics, aerospace, and military equipment fields.

A Dual‐Band Dual‐Polarized Rectenna for Efficient RF Energy Harvesting in Battery‐Less IoT Devices With Broad Power Range

ABSTRACTThe demand for maintenance‐free, battery‐less IoT devices, driven by sustainable Industry 4.0 practices, necessitates efficient RF energy harvesting solutions. Addressing the limitations of single‐frequency harvesting, a novel dual‐band, dual‐polarized rectenna operating at 3.6 GHz and 5.8 GHz is proposed. The antenna resonates at 3.6 GHz with linearly polarized (LP) characteristics and 5.8 GHz with circularly polarized (CP) characteristics with impedance bandwidth (IBW) of 2.2% and 5.63%, respectively, achieving a gain of 4.85 dBi and 6.75 dBic, respectively. A rectenna consists of an antenna at the front end and an RF‐DC rectifier at the backend. This approach maximizes power conversion efficiency by minimizing impedance mismatches and reflection losses and mitigates interference between the dual bands within the rectifier circuitry. The rectifier achieves peak efficiencies of 65.5% at 3.6 GHz with a 3 dBm input and 44% at 5.8 GHz with a −1 dBm input, both with 2KΩ load. Efficiency exceeds 30% at 3.6 GHz for an input range from −10 to 6.5 dBm and exceeds 20% at 5.8 GHz for an input range from −13 to 3 dBm. These design considerations enable reliable harvesting of ambient RF energy across a range of −20 to 20 dBm, enabling continuous IoT device operation. Our measurements confirm the design's effectiveness in converting low‐power RF signals into usable energy, supporting sustainable and autonomous IoT deployments at 3.6 and 5.8 GHz.

A Highly Efficient Electrolysis System Enabled by Direct Impedance Matching Between Charge Migration Triboelectric Nanogenerator and Series Connected Electrolysers

As an electromechanical conversion technology, triboelectric nanogenerators (TENGs) are widely used in water electrolysis for hydrogen production. Nevertheless, the impedance mismatch between TENGs and conventional electrolysers significantly reduces energy utilization...

Large-scale acoustic single cell trapping and selective releasing.

Recent advancements in single-cell analysis have underscored the need for precise isolation and manipulation of individual cells. Traditional techniques for single-cell manipulation are often limited by the number of cells that can be parallel trapped and processed and usually require complex devices or instruments to operate. Here, we introduce an acoustic microfluidic platform that efficiently traps and selectively releases individual cells using spherical air cavities embedded in a polydimethylsiloxane (PDMS) substrate for large scale manipulation. Our device utilizes the principle of acoustic impedance mismatches to generate near-field acoustic potential gradients that create trapping sites for single cells. These single cell traps can be selectively disabled by illuminating a near-infrared laser pulse, allowing targeted release of trapped cells. This method ensures minimal impact on cell viability and proliferation, making it ideal for downstream single-cell analysis. Experimental results demonstrate our platform's capability to trap and release synthetic microparticles and biological cells with high efficiency and biocompatibility. Our device can handle a wide range of cell sizes (8-30 μm) across a large active manipulation area of 1 cm2 with 20 000 single-cell traps, providing a versatile and robust platform for single-cell applications. This acoustic microfluidic platform offers a cost-effective and practical method for large scale single-cell trapping and selective releasing with potential applications in genomics, proteomics, and other fields requiring precise single-cell manipulation.

Development of a Fire-Retardant and Sound-Insulating Composite Functional Sealant.

The use of traditional sealing materials in buildings poses a significant risk of fire and noise pollution. To address these issues, we propose a novel composite functional sealant designed to enhance fire safety and sound insulation. The sealant incorporates a unique four-component filler system consisting of carbon nanotubes (CNTs) decorated with layered double hydroxides (LDHs), ammonium dihydrogen phosphate (ADP), and artificial marble waste powder (AMWP), namely CLAA. The CNTs/LDHs framework provides structural support and enhances thermal stability, while the ADP layer acts as a protective barrier and releases non-combustible gases during combustion. AMWP particles contribute to sound insulation by creating impedance mismatches. The resulting composite functional sealant exhibits improved mechanical properties. In terms of flame retardancy, it boasts the lowest peak heat release rate (PHRR) of 224.83 kW/m2 and total smoke release (TSR) of 981.14 m2/m2, achieving the V-0 classification. Furthermore, its thermal degradation characteristics reveal a notably higher carbon residue rate. Additionally, the sound insulation capability has been significantly enhanced, with an average sound insulation level of 43.48 dB. This study provides a promising solution for enhancing the fire safety and acoustic properties of building sealing materials.

Improved singular spectrum decomposition method for resonance recognition of air-coupled ultrasonic signals in through-transmission steel plate detection

Abstract Air-coupled ultrasonic resonance detection is an emerging technique that eliminates the need for coupling agents in conventional ultrasonic testing and has a wide range of applications. However, this technique faces challenges, such as weak signal strength and susceptibility to noise, primarily due to the mismatch of acoustic impedance at the air–solid interface and sound attenuation in the air. This study proposed an improved signal processing method based on singular spectrum decomposition (SSD), optimizing the frequency components of each iteration using singular spectrum analysis. Additionally, a weighted Hurst exponent was introduced as a selection criterion to identify useful components and reconstruct the signal. Simulation results demonstrated the effectiveness of this method in denoising components and extracting weak resonance frequency features, especially in low signal-to-noise ratios (SNRs). Compared with conventional SSD and empirical mode decomposition, the proposed method improved the SNR by 39.4% and 301.33%. Furthermore, repeated experimental studies on steel plates with varying air lift-off distances and thicknesses confirmed that the proposed method could effectively reduce noise, thereby enabling accurate measurement of steel plate thickness.

Shock Response Characteristics and Unreacted Equation of State Calibration of GAP/RDX/TEGDN propellant

Abstract Understanding the shock response characteristics of propellants is crucial for studying the safety of the shock wave dominating shock initiation. To study shock response characteristics of high-energy solid propellant (GAP/RDX/TEGDN propellant, GRT propellant) and obtain its unreacted equation of state (EOS) parameters, a shock response experiment (plate impact experiment) was conducted using a caliber 57 mm single stage light-gas gun device. The propellant/window interface particle velocity is measured by using a velocity interferometer system for any reflector (VISAR), and the corresponding mechanical parameters of GRT propellant are obtained by the impedance matching method. The Hugoniot parameters of GRT propellant further were obtained by the parameter inversion method based on Abaqus/explicit, calibrated the unreacted EOS. The experiment results show that: At an impact velocity of 212 m·s−1 and 282 m·s−1, the propellant/window interface particle velocity time-history curve shows a double wave composed of elasticity and viscoplasticity. The shock front rise time in the viscoplasticity wave stage is relatively slow and shows shock viscosity characteristics. The shock viscosity is attributed to the viscous dissipation of each constituent and the wave scattering caused by a wave impedance mismatch between each constituent. Its duration decreases with impact velocity increasing. In addition, the unreacted EOS fitting curve is consistent with the experimental result inversion value and the calibrated parameters are valid.

Ratcheting fluid pumps: Using generalized polynomial chaos expansions to assess pumping performance and sensitivity

A large diversity of fluid pumps is found throughout nature. The study of these pumps has provided insights into fundamental fluid dynamic processes and inspiration for the development of micro-fluid devices. Recent work by Thiria and Zhang [Appl. Phys. Lett. 106, 054106 (2015)] demonstrated how a reciprocal, valveless pump with a geometric asymmetry could drive net fluid flow due to an impedance mismatch when the fluid moves in different directions. Their pump's geometry is reminiscent of the asymmetries seen in the chains of contractile chambers that form the insect heart and mammalian lymphangions. Inspired by these similarities, we further explored the role of such geometric asymmetry in driving bulk flow in a preferred direction. We used an open-source implementation of the immersed boundary method to solve the fluid-structure interaction problem of a viscous fluid moving through a sawtooth channel whose walls move up and down with a reciprocal motion. Using a machine learning approach based on generalized polynomial chaos expansions, we fully described the model's behavior over the target 3-dimensional design space, composed of input Reynolds numbers (Rein), pumping frequencies, and duty cycles. Scaling studies showed that the pump is more effective at higher intermediate Rein. Moreover, greater volumetric flow rates were observed for near extremal duty cycles, with higher duty cycles (longer contraction and shorter expansion phases) resulting in the highest bulk flow rates.

Facile fabrication of lightweight and three-dimensional porous Dy2O3 decorated single-walled carbon nanotubes/reduced graphene oxide composite aerogels for broadband microwave absorption

Reduced graphene oxide aerogel (GA) has emerged as a promising microwave absorbing (MA) material. However, it remains a challenge for pure GA to achieve excellent MA performance owing to the limitation of loss model and impedance mismatching. Herein, a 0D@1D/2D construction of Dy2O3 decorated single-walled carbon nanotubes/reduced graphene oxide (Dy2O3@SWCNT/rGO) composite aerogel (DCGA) with high-performance electromagnetic wave (EMW) absorption was successfully obtained using a simple reduction self-assembly process. The DCGA features a distinctive 3D porous network formed by the stacking of lamellar rGO and has a low bulk density. As expected, the microwave attenuation performance of the DCGA exhibits a level of tunability that can be achieved by varying the mass ratio of GO along with Dy2O3@SWCNT. Benefiting from synergistic effect, the resulted ultralight DCGA-3 (4.6 mg/cm−3) exhibits a strong reflection loss (RL) of −57.6 dB (3 mm) at 13 GHz and a low filler loading ratio of ca. 1.4 wt%. Further, the maximal effective absorption bandwidth (EAB) (RL < −10 dB) of DCGA-1 can reach 7.8 GHz (10.2–18 GHz) with a thickness of 2.8 mm. Notably, the EAB of DCGA can completely cover X band and Ku band by adjusting the thickness. The excellent EMW absorbing ability was originated from the combined influence of optimized impedance matching, a distinctive multidimensional porous structure, a leaf-like conductive network and the presence of numerous defects and interfaces. Consequently, this research may aid in the development of graphene-infused hybrid composites featuring a 3D porous architecture, serving as lightweight and efficient absorbers of EMWs.

Pressure waves induced by the bcc-hcp phase transition in dynamically loaded single crystal iron

Molecular Dynamics simulations have been used to investigate the dynamic response of single crystal iron to ramp compression along the [001] crystallographic direction, with a focus on the coupling between the propagation and interaction of pressure waves and the phase transformation process. In particular, we report an original observation at the atomic level of release and recompression waves specifically induced by the phase transition. We provide a straightforward, physically-based explanation of the origin of these waves based on impedance mismatch between the parent, daughter, and mixed-phase region, and show how they depend directly on the kinetics of the transformation. This analysis may be generalized to other time-dependent phase transformations in other materials subjected to dynamic loading, and it is probably still valid at the much larger space and time scales encountered in experiments, which could have practical implications.

Enhanced Electromagnetic Wave Absorption Properties of Layer-By-Layer Films Comprising MXene@Fe3O4/Thermoplastic Polyurethane Fabricated via Spray Coating

Electromagnetic interference (EMI) poses significant challenges in various fields, including automotive, military, and maritime applications, as well as concerns regarding its impact on human health. Consequently, research efforts have been directed towards developing effective electromagnetic shielding materials. While metals have traditionally been utilized for their excellent conductivity, recent focus has shifted towards 2D materials due to their lightweight and deformability. Among these materials, MXene has emerged as a promising candidate owing to its remarkable electrical conductivity. However, its application in absorption-based shielding, crucial for stealth operations, is hindered by reflection-based characteristics stemming from impedance mismatching.In this study, we synthesized iron oxide (Fe3O4) nanoparticles, known for their magnetic properties, in conjunction with MXene via a hydrothermal synthesis method to enhance absorption properties and mitigate impedance mismatching. We employed a simple spray-coating technique to fabricate layer-by-layer films comprising Thermoplastic polyurethane (TPU) and MXene@Fe3O4 composites. This facilitated the creation of interlayer spacing, promoting multiple reflections and thereby augmenting absorption shielding properties. Our study presents a synergistic approach to enhancing electromagnetic absorption shielding through the integration of MXene and Fe3O4 nanoparticles, offering potential applications in diverse electromagnetic interference mitigation scenarios.

Oscillation Mechanism and Suppression of Variable-Speed Pumped Storage Unit with Full-Size Converter Based on the Measured Single-Input and Single-Output Impedances

As the penetration rate of clean energy gradually increases, the demand for flexible regulation resources in the power grid is increasing accordingly. The variable-speed pumped storage unit with a full-size converter (FSC-VSPSU) can provide fast and flexible regulation resources for the power grid, which assists in the stable operation of the clean-energy-dominated power systems. Thus, its application is gradually becoming widespread. FSC-VSPSU relies on the power electronic converter for grid connection. When the impedance mismatch between FSC-VSPSU and the power grid occurs, the grid-connected system will experience oscillations, which seriously threatens its safe and stable operation. Aiming at this, this article firstly relies on the SISO impedance measurement and an equivalent impedance analysis to obtain the stability analysis criterion. Furthermore, applying the impedance matching analysis with the Bode diagram, the influence rules of the parameters of the grid-connected FSC-VSPSU on oscillation are obtained. In addition, with the summarized oscillation analysis results, this study delves into an exploration of pertinent strategies for oscillation suppression. Finally, a grid-connected FSC-VSPSU simulation model is built in MATLAB/SIMULINK, and the simulation results verify the correctness of the oscillation analysis results and the effectiveness of the proposed oscillation suppression strategy.

Enhanced microwave absorption properties of Ti3AlC2 particles modified by a facile preoxidation strategy

MAX phases are considered to be promising microwave absorbing materials in fifth-generation (5G) communications, but their high electrical conductivity causes impedance mismatching, weakening their ability to absorb microwaves. Here, we present a universal preoxidation strategy to improve the impedance matching and the microwave absorption performance of a Ti3AlC2 MAX phase absorbing material. The microwave absorption properties of Ti3AlC2 particles were enhanced after preoxidation at temperatures of 500–700 °C for only 30 min in air, as compared with unoxidized Ti3AlC2 particles. More interestingly, the 600 °C-preoxidized Ti3AlC2 material reached a minimum reflection loss (RLmin) value of −50.56 dB at 8.87 GHz, superior to −12.36 dB at 12.82 GHz for the original Ti3AlC2 material. The preoxidized Ti3AlC2 particles were covered by a thin oxidation layer comprising both amorphous TiO2 (a-TiO2) and rutile TiO2 (R-TiO2). The oxidation layer endows the preoxidized Ti3AlC2 particles with good impedance matching, and a large number of nano-interfaces of a-TiO2/R-TiO2 and micro-interfaces of a-TiO2/Ti3AlC2 also contribute to the dielectric loss mechanism, thus improving its microwave absorption ability. This work provides a practical strategy for the fundamental study and the optimal design of MAX microwave absorbing materials.

Synthesis of (TiyVzCr1-y-z)3C2Tx MXene for excellent electromagnetic wave absorption properties

MXenes are remarkable 2D materials for microwave absorption applications, with respect to physical and chemical properties. However, their elevated electrical conductivity and impedance mismatch results in a diminished microwave absorption rate. To overcome these issues, we have prepared TiVCrC2Tx and Ti0.5V2Cr0.5C2Tx MXenes using an element doping strategy. Thanks to their suitable dielectric constant, lattice distortion, and a large amount of defects caused by multiple transition metal atoms, results in an increase in polarization loss, enhanced impedance matching, and increased electromagnetic (EM) wave absorption capability. The experimental results showed that few-layer TiVCrC2Tx with a thickness of 3.19 mm and operating frequency as 6.88 GHz can achieve a minimum reflection loss (RLmin) of −57.8 dB. Additionally, it has an effective absorption bandwidth (EAB) of 2.88 GHz. On the other hand, few-layer Ti0.5V2Cr0.5C2Tx with a thickness of 1.95 mm and operating at a frequency of 10.72 GHz has an RLmin of −52.75 dB and an EAB of 1.44 GHz. The advantages of the element doping strategy in enhancing the microwave absorption performance of MXene are demonstrated by its excellent EM wave absorption capability, thin matching thickness, and low filling amounts of only 30 wt percent. These results suggest that doped MXene showed highly promising application in the field of EM wave absorption.

A frequency reconfigurable antireflection metasurface for GPR

Abstract The antireflection metasurface (AM) is employed in ground penetrating radar (GPR) to mitigate the strong reflection of electromagnetic waves at the air-ground interface due to impedance mismatch. However, due to constraints imposed by the relative bandwidth (RBW) and manufacturing processes, these layers tend to exhibit excessive thickness and bulky shape, narrow RBW, and fixed functionality in a passive configuration. This paper presents a novel, dual-band, independent wideband tuning, frequency reconfigurable AM based on varactor diodes with center frequencies of 1.35 GHz and 2.60 GHz. This metasurface possesses positive properties such as a single layer, the ultrathin thickness (0.03 &amp; 0.06λ), the wide RBW (43.3% &amp; 27.4%) and remarkable antireflection. The aforementioned metasurface achieves the described mechanisms and features through the destructive interference theory and the combine element technique. Numerical simulation results of surface currents and electric field energy power demonstrate the antireflection property. The equivalent electromagnetic parameter retrieval results also provide equivalent impedance conditions for non-perfect antireflection. The proposed AM samples demonstrate notable stepwise frequency reconfigurable properties in free-space experiments. The imaging effect after loading this AM is significantly improved in real-world GPR ballast roadbed anomaly detection experiments. This approach provides significant research value and promising prospects across various disciplines, including the stepped-frequency GPR, microwave imaging, and interdisciplinary fields.

Spatial Confinement Growth Enabling MoS2@Hollow Mesoporous Carbon Spheres Microspheres with Enhanced Microwave Absorption and Corrosion Resistance.

The complex electromagnetic applications in harsh corrosive environments urgently require research into multifunctional microwave absorption (MA) materials. The core-shell structure is an effective strategy to prepare multifunctional MA materials by efficiently combining the advantages of each component. Nevertheless, it remains a tough challenge to elucidate the effect of the binding positions of each component in MA materials on the comprehensive electromagnetic performance. Herein, two types of core-shell structured composites based on hollow mesoporous carbon spheres (HMCS), HMCS@MoS2 and MoS2@HMCS, were prepared via synergistic etch growth and spatial confinement growth strategies, respectively. Compared with HMCS, HMCS@MoS2 severely destroys the connection of HMCS, therefore resulting in impedance mismatching. Comparatively, the growth of MoS2 within the HMCS reduces the disruption of the HMCS connection, enabling MoS2@HMCS with enhanced dielectric loss while optimizing the impedance matching, and therefore, it yields an optimal reflection loss of -46.91 dB at 2 mm and an effective bandwidth of 5.78 GHz at 2.4 mm mixed with polydimethylsiloxane (PDMS). In addition, the combinations of the spatial confinement effect of HMCS, corrosion resistance of MoS2, and chemical stability of PDMS resulted in minimal changes in the MA performance of MoS2@HMCS/PDMS after soaking in acidic and alkaline solutions for 14 days, proving an excellent corrosion resistance property. This inspiring work proposes an effective spatial confinement growth strategy to optimize the impedance matching and further tailor the multifunction for dielectric loss dominated MA materials.

An Energy Management System for Distributed Energy Storage System Considering Time-Varying Linear Resistance

As the proportion of renewable energy in energy use continues to increase, to solve the problem of line impedance mismatch leading to the difference in the state of charge (SOC) of each distributed energy storage unit (DESU) and the DC bus voltage drop, a distributed energy storage system control strategy considering the time-varying line impedance is proposed in this paper. By analyzing the fundamental frequency harmonic components of the pulse width modulation (PWM) signal carrier of the converter output voltage and output current, we can obtain the impedance information and, thus, compensate for the bus voltage drop. Then, a novel, droop-free cooperative controller is constructed to achieve SOC equalization, current sharing, and voltage regulation. Finally, the validity of the system is verified by a hardware-in-the-loop experimental platform.

Structurally Colored Photonic Crystal Biomimetic Microstructures for Daytime Radiative Cooling.

Daytime radiative cooling offers a novel solution to the energy crisis, enabling green and efficient thermal management in space. High reflectance in the solar spectrum is essential for passive radiative cooling, rendering dye coloring and similar methods unsuitable for colored coolers. This paper presents a structurally colored photonic crystal biomimetic microstructured radiative cooler. Inspired by natural biological systems, this cooler features a dual-layered microtruncated-cone array structure on the surface and bottom membrane layers. The silver reflector and 3D micrograting surface structure produce continuous iridescent colors through multiple interference effects. Optimized lithographic process enable the fabrication of the ordered dual-layer surface microstructure arrays with precise angular combinations. The dual-layered microtruncated-cone introduces a gradient refractive index, reducing impedance mismatch at the interface. As a result, the radiative cooler achieves high solar spectral reflectance (0.95) and high mid-infrared emissivity (0.95). Notably, the net theoretical cooling power and the subambient temperature drop are 106.9 W m-2 and 7.4 °C, respectively, at an ambient temperature of 40 °C, with a measured average temperature reduction of 6.1 °C under direct sunlight. This performance matches that of advanced radiative coolers, striking a balance between aesthetics and radiative cooling capability.