Micropatterned architectures for directional control of thermal emission and enhanced radiative cooling

Background

Radiative cooling is a passive thermal management strategy that enables surfaces to shed heat by emitting infrared radiation to the cold sky, especially during clear nights. This approach is particularly valuable for building roofs in urban environments, where air conditioning and active cooling systems contribute significantly to energy consumption and urban heat islands. As cities grow denser and the demand for sustainable, energy-efficient cooling solutions increases, the need for advanced radiative cooling technologies becomes more urgent. Effective radiative cooling can reduce reliance on electricity, lower greenhouse gas emissions, and improve occupant comfort, making it a critical component of future urban infrastructure.

However, current radiative cooling approaches face significant limitations that hinder their widespread adoption and effectiveness. Traditional solutions, such as epsilon-near-zero (ENZ) thin films and metasurfaces, typically offer limited control over the directionality and spectral range of thermal emission. These materials often emit radiation in all directions, which means that in dense urban environments, a substantial portion of the emitted heat can be reabsorbed by surrounding buildings or reflected back from the warm cityscape, reducing cooling efficiency. Furthermore, many of these technologies are challenging to manufacture at scale, lack tunability for specific applications, and may not be compatible with existing building materials or retrofitting processes. As a result, there is a pressing need for scalable, tunable, and angle-selective radiative cooling solutions that can overcome these shortcomings and provide reliable performance in real-world urban settings.

Technology

This technology introduces advanced micropatterned surface architectures—specifically, tapered hole arrays and spheroidal microlens arrays—engineered to control the angular direction of thermal emission for radiative cooling applications. The tapered hole array consists of a reflective substrate, such as aluminum, patterned with holes that are wider at the top and narrower at the bottom. This geometry directs thermal radiation from the surface upward toward the zenith, while reflecting incoming heat from the horizon, thereby maximizing cooling efficiency. The spheroidal microlens array, fabricated from transparent materials like polyethylene or zinc compounds, uses hemispherical or ellipsoidal lenses to achieve total internal reflection: radiation within a defined critical angle passes through, while higher-angle radiation is reflected. Both designs are highly tunable through adjustments to geometry, spacing, refractive index, and encapsulation, and can be manufactured at scale using methods such as laser micromachining, embossing, or roll-to-roll processing.

What differentiates this technology is its unprecedented combination of broadband, angle-selective thermal emission with scalable and retrofittable design. Unlike conventional radiative cooling solutions—such as ENZ thin films or metasurfaces—which are limited by narrow spectral or angular control and challenging fabrication, these micropatterned structures offer precise, customizable control over both the direction and spectrum of emitted radiation. This enables efficient cooling even in dense urban environments, where surrounding buildings and surfaces typically hinder radiative heat loss. The technology’s versatility extends to a wide range of applications, including passive building cooling, photovoltaic efficiency enhancement, photochemical processes, and thermal camouflage for defense. Its compatibility with existing building materials and large-scale, low-cost manufacturing further sets it apart, making it a practical and impactful solution for next-generation thermal management.

Benefits

• Enables directional (polar) thermal emission to enhance passive radiative cooling by emitting heat toward the sky while minimizing heat gain from surrounding warm environments.
• Provides broadband and angle-selective emission control, overcoming limitations of existing technologies in spectral and angular management.
• Highly tunable through geometric parameters (hole/lens size, spacing, angles) and material selection to optimize performance for specific applications and environments.
• Compatible with scalable, low-cost manufacturing methods such as laser micromachining, embossing, imprinting, and roll-to-roll processing, facilitating large-scale deployment and retrofitting.
• Offers versatility for multiple applications including building cooling, photovoltaics, photochemistry, defense (thermal camouflage), and targeted heating/cooling of various surfaces.
• Includes encapsulation options with infrared-transparent, sunlight-opaque films for protection, durability, and aesthetic integration.
• Demonstrated feasibility and effectiveness through fabricated prototypes with confirmed directional control of thermal radiation.

Applications

• Passive radiative cooling for buildings
• Thermal camouflage for defense
• Photovoltaic system efficiency enhancement
• Targeted cooling for vehicles
• Photochemical process optimization

Additional info

These micropatterned architectures utilize tapered hole arrays and spheroidal microlens arrays to achieve directional thermal emission for radiative cooling. Tapered holes in reflective substrates direct radiation toward the zenith while reflecting incident heat from the horizon. Microlens arrays leverage total internal reflection to transmit radiation within specific angles. Fabricated from materials like aluminum or polyethylene, these tunable structures optimize thermal management for urban rooftops through geometric and refractive index control.