Space-Time-Modulated Metasurface Enabled High-Performance Near-Field Focusing with Enhanced Phase Modulation

Near-field focusing (NFF) holds significant importance for applications such as communication, wireless power transfer, and sensing. Reconfigurable metasurfaces enable real-time NFF, but current methods relying on 1-bit or finite quantization limit performance and efficiency. Here, a space-time-modulated (STM) metasurface is proposed to overcome these limitations, enabling high-quality NFF performance with low cost and reduced spatial requirements. By introducing a new phase term at harmonic frequencies (ƒ_c + kƒ_o), where ƒ_c = 24.5 GHz is the carrier, and ƒ_o = 100 kHz is the modulation frequency and k is the harmonic order (k = ±1, ±2, ±3…). The STM method provides nearly continuous phase compensation at the +1^st harmonic, resulting in superior NFF performance compared to the fundamental frequency. Furthermore, as the number of meta-atoms reduces, the STM metasurface maintains a stable focusing performance, whereas traditional 1-bit transmission metasurface exhibits elevated sidelobe levels. Consequently, the STM approach provides enhanced NFF performance with fewer meta-atoms, resulting in fewer active components, reduced hardware complexity, and smaller spatial footprints. An 8 × 8 prototype is fabricated and experimentally validated to assess its NFF characteristics. The findings of this research substantiate the proposed technology and lay the groundwork for future applications in compact, high-performance imaging and detection systems. © 2025 The Author(s). Laser & Photonics Reviews published by Wiley-VCH GmbH.