Research Progress on Infrared and Radar-Compatible Stealth Materials Based on Metamaterials

Modern information warfare relies heavily on reconnaissance technologies, making battlefield transparency a key challenge. Infrared (IR) and radar detection are widely used, driving research into materials that are simultaneously stealthy in both infrared and radar domains. Compared to traditional stealth materials, metamaterial-based IR and radar-compatible materials show significantly superior performance.

Infrared stealth aims to reduce an object's detectability by IR sensors by minimizing the temperature and emissivity of its surface. High-emission equipment or personnel contrast strongly with their environment, so controlling surface temperature and material emissivity is essential.

Radar stealth focuses on reducing the radar cross-section (RCS), the measure of how much electromagnetic energy a target reflects back to radar. RCS can be minimized by shaping the object to scatter radar waves or by using radar-absorbing materials (RAM).

Creating materials that are stealthy in both IR and radar is challenging because these requirements conflict: IR stealth requires low absorption/emission, while radar stealth needs high absorption. Researchers use two main strategies:

Single-material solutions that combine low IR emission with high radar absorption.

Composite solutions that layer separate IR- and radar-stealth materials while retaining their respective properties.

Traditional single-material approaches include conductive polymers, nanomaterials, and doped oxide semiconductors. However, metamaterials offer a new paradigm.

Metamaterials are engineered materials composed of subwavelength unit structures. Their properties depend on the structure, not chemical composition, enabling extraordinary control over electromagnetic waves. Key types include:

Electromagnetic metamaterials: Allow tailored control over wave phase, amplitude, and polarization.

Photonic crystals: Periodic dielectric structures that create photonic bandgaps, useful for IR stealth.

Absorbing metamaterials: Composite structures that achieve near-perfect absorption through impedance matching and electromagnetic resonance, offering radar stealth with minimal thickness and weight.

Coded metamaterials: Use digital design principles to control reflection phase, enabling precise electromagnetic manipulation.

(a) SEM image of the cross-section of the CPC sample; (b) Transmittance comparison curves of glass-based CPC and glass substrate at 2–18 GHz; (c) Microstructure of the doped one-dimensional photonic crystal.

Photonic Crystal-Based Materials
Photonic crystals consist of periodic dielectric materials that can block or transmit specific electromagnetic wavelengths. By tuning the bandgap to the IR spectrum, these structures suppress IR emission. Combining photonic crystals with radar-transparent layers allows simultaneous IR and radar stealth. Multi-layer films, flexible cloaks, and combined plasma-photonic designs have been demonstrated, with applications extending to multispectral stealth, including visible and laser ranges.

Absorbing Metamaterials
Absorbing metamaterials achieve near-total radar absorption. Layered designs with selective IR radiation control allow IR stealth while maintaining radar absorption. Examples include hierarchical metamaterial structures (HMMs) and water-based tunable materials that enable adjustable IR emissivity, showing promise for broadband stealth.

Coded Metamaterials
Coded metamaterials reduce RCS through engineered phase cancellation. Designs integrating random metallic grids and encoded surfaces enable flexible control of microwaves while maintaining high IR transparency. Advanced structures combine IR-shielding layers with microwave-absorbing layers for dual stealth capabilities.

Metamaterial-based IR and radar-compatible stealth materials are evolving toward:

Improved dual stealth performance through selective IR radiation and wider radar absorption bands.

Compatibility with additional spectral ranges, including visible light and lasers.

Integrated designs to reduce structural complexity.

Challenges remain in material stability, fabrication cost, and manufacturing processes. Current techniques, such as lithography, etching, 3D printing, and screen printing, are costly and complex. Developing high-precision, low-cost, and durable metamaterials is critical for practical deployment.

Dynamic, spectrum-tunable stealth materials are a future direction, enabling real-time adaptability against AI-driven detection systems. Phase-change materials and electro-optical devices offer opportunities for multi-spectral, tunable stealth applications.

(a) Schematic diagram of the heat-resistant metallic metasurface; (b) High-temperature RCS reduction measurement results of the prepared sample; (c) Infrared emission characteristics of the metasurface at room temperature.

Metamaterial-based IR and radar-compatible stealth materials outperform traditional materials in dual-band performance and design flexibility. However, challenges in stability, cost, and fabrication limit real-world application. Future research will focus on dynamic, spectrum-tunable designs to address advanced detection technologies and broaden practical applications.

Sources: Materials Reports, MEMS, Mechanical Engineering Materials
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