The review, led by Jie Zuo and Jinghua Ye of Guangdong University of Technology together with colleagues at Chongqing University of Technology and Sichuan University, systematically surveys how artificially structured electromagnetic materials can be integrated into miniaturized antennas for targeted microwave hyperthermia. The authors contend that these materials, whose properties arise from sub-wavelength periodic structures rather than their chemical composition, offer a degree of electromagnetic control that conventional antenna designs simply cannot match. Their conclusion is cautiously optimistic: metamaterial-assisted designs are already alleviating the miniaturization-versus-efficiency dilemma, and emerging techniques could soon make adaptive, clinically translatable hyperthermia systems a practical reality for solid tumors.

The physics of the problem is unforgiving. In microwave hyperthermia, the quantity that matters most is the specific absorption rate, or SAR—the rate at which electromagnetic energy is converted into heat per unit mass of tissue. For a treatment to be effective and safe, the SAR distribution must peak within the tumor volume while sparing surrounding healthy structures, including skin, fat layers, and critical organs. Yet the human body is an extraordinarily hostile medium for microwave energy: high water content means strong absorption, and tissue heterogeneity means that fields scatter, reflect, and refract unpredictably as they propagate. Traditional antennas operating at established medical frequencies, such as 434 MHz or 2.4 GHz, face a fundamental scaling constraint—antenna size is tied to wavelength, so achieving efficient radiation typically demands an applicator that is large, rigid, and difficult to position conformally against the body. Reducing antenna size through conventional loading techniques almost inevitably increases energy lost as heat within the antenna itself rather than within the tumor, and shallow penetration depths leave deep-seated tumors effectively unreachable.

Metamaterials attack this constraint from an entirely different direction. Because their effective permittivity and permeability are engineered through geometry—split-ring resonators, complementary split-ring resonators, epsilon-negative structures, high-impedance surfaces, and Huygens metasurfaces among them—they can exhibit electromagnetic responses that no natural material provides, including negative refractive indices, near-zero permittivity, and engineered phase gradients. Loaded onto or integrated into an antenna, these structures decouple the antenna’s electrical size from its physical footprint. A patch antenna loaded with epsilon-negative metamaterial elements can resonate at a fraction of the wavelength of its conventional equivalent, shrinking the applicator without the punishing efficiency penalty. Metasurface superstrates, meanwhile, act as near-field lenses and beam shapers, concentrating energy into localized hotspots and reshaping SAR distributions in ways that would otherwise require elaborate multi-antenna arrays and heavy signal processing.

The review highlights several concrete mechanisms by which metamaterials improve hyperthermia outcomes. Near-field control is perhaps the most transformative: by structuring the surface through which the radiated field passes, designers can focus microwave energy deep into tissue, achieving heating at depths that conventional applicators cannot safely reach. Studies of near-field focused metasurfaces and metamaterial lens applicators demonstrate precisely this capability, with graded-index and left-handed lens designs steering and concentrating fields toward tumor volumes. SAR shaping follows naturally from near-field control—by manipulating phase and amplitude across the aperture, a metasurface can sculpt the absorption pattern so that hotspots align with the tumor while cool zones protect healthy tissue. Time-reversal focusing techniques combined with metasurfaces have even been explored for brain tumor hyperthermia, one of the most demanding targeting challenges in the field. Energy optimization rounds out the picture: by improving impedance matching and reducing backward radiation, metamaterial coatings raise the fraction of source power that actually reaches the target, meaning shorter treatment times and lower risk of unintended thermal damage.

The review organizes current applications into two core system categories, each with its own engineering logic. Implantable and interstitial antennas—miniaturized devices inserted into or near the tumor, often through catheters—benefit enormously from metamaterial loading because their size constraints are the most severe. Reactive-loaded monopoles and dual-slot antennas integrated with engineered structures can operate efficiently at dimensions that would render conventional designs impractical. Wearable and external applicators, by contrast, must conform to the body’s contours and maintain stable performance across the wide range of tissue geometries presented by different patients. Here, conformal metasurface antennas and compact cavity-backed designs enhanced by metamaterial superstrates show promise for applications such as breast cancer hyperthermia, where sustained, comfortable, precisely targeted heating over treatment sessions lasting tens of minutes is essential. Epidermal sensor grids based on RFID technology have even been explored to monitor skin temperature in real time during treatment, feeding back into the energy-delivery system.

Safety and regulatory considerations loom over all of this, and the review does not shy away from them. International guidelines for limiting human exposure to electromagnetic fields, along with time-temperature thresholds for thermal hazards, define the envelope within which hyperthermia systems must operate. Precise SAR control is not merely a performance metric but a safety obligation, and the review identifies current inadequacies in SAR management as a key bottleneck. Treatment planning tools that model electromagnetic and thermal fields in patient-specific anatomies are advancing rapidly, and real-time three-dimensional temperature reconstruction from sparse measurements—a capability recently demonstrated using advanced computational methods—points toward closed-loop systems that adjust delivered energy on the fly. Yet the feedback mechanisms integrated into today’s metamaterial-assisted antennas remain immature, a gap the authors flag as critical for clinical translation.

Manufacturing is the other stubborn obstacle. Metamaterial structures derive their properties from fine geometric features, and fabricating them reliably—particularly in biocompatible, flexible, or implantable formats—remains complex and costly. Additive manufacturing is beginning to change that calculus, with printed metasurfaces spanning frequencies from microwaves to photonics, but the transition from laboratory prototype to sterilizable, patient-ready device involves tolerances, materials, and regulatory scrutiny that go well beyond electromagnetic performance. The review also notes that programmable and digital metamaterials, in which tunable elements allow the electromagnetic response to be reconfigured electronically, are an emerging frontier: a single applicator that could reshape its field dynamically would be invaluable for tracking tumors that move with respiration, one of the classic challenges shared with radiation therapy.

Looking forward, the authors identify three converging trends. Artificial intelligence-driven design is accelerating the exploration of vast metamaterial configuration spaces that are intractable by hand optimization, promising antenna structures tailored to individual patient anatomies. Reconfigurable metamaterials will imbue applicators with adaptability, allowing frequency, beam direction, and SAR patterns to be adjusted during treatment. And integration with millimeter-wave frequencies opens new therapeutic regimes, where shorter wavelengths enable finer spatial control of heating, alongside growing interest in the distinct biological effects of millimeter-wave exposure. Combined with synergistic approaches such as microwave-sensitive nanomaterials that heat preferentially within tumors, the roadmap sketched in the review points toward hyperthermia systems that are simultaneously smaller, smarter, and safer.

What emerges from this comprehensive survey is a field in transition. Microwave hyperthermia has spent decades fighting the physics of its own delivery mechanisms; metamaterials offer a principled way out, converting the problem of antenna miniaturization from a lossy compromise into an exercise in engineered field control. The trade-off between shrinking an applicator and conserving its energy has not disappeared, but the review makes a compelling case that it is no longer fundamental. If fabrication matured, feedback loops closed, and AI-driven customization reached the clinic, metamaterial-assisted antennas could transform hyperthermia from a supportive adjunct into a precise, adaptive, stand-alone modality for treating solid tumors—delivering heat exactly where it is needed, and nowhere else.