Microstructure-based terahertz sensing technology: from electromagnetic response enhancement to multi-scale detection

Terahertz (THz) waves exhibit distinctive properties, such as high transmittance, pronounced absorption, and minimal photon energy, enabling a wide range of applications in biomedical diagnosis, non-destructive testing, and quality/safety monitoring of food and agricultural products. Consequently, THz-based sensors have garnered increasing attention. However, the design of traditional coupling structures fails to effectively match the high-frequency oscillation of THz waves, resulting in low signal energy transmission efficiency and limiting the performance of THz sensors, while microstructure technology can offer a solution by achieving localized enhancement of the electromagnetic field energy through precise matching of sub-wavelength resonance units with the high-frequency oscillation of THz waves, which significantly improves the sensitivity of THz sensors. This review summarizes the basic principles and research status of various THz sensors based on different microstructures, such as split-ring resonators (SRRs), photonic crystals, waveguide resonators, and surface plasmon resonance. Notably, the rapid development of artificial intelligence, especially deep learning, is increasingly influencing THz sensing technologies with its strengths in signal processing, pattern recognition accuracy, and inverse design. Integrating deep learning with THz sensor design enhances feature extraction from complex signals, improves target identification, and enables intelligent optimization of microstructure parameters for high-performance sensor design and performance prediction. This interdisciplinary approach provides a new pathway to overcome traditional design limitations and advance THz sensor performance.