Spoof Localized Surface Plasmons for Sensing Applications

Abstract Localized surface plasmons (LSPs) are localized oscillations of free electrons in metal nanoparticles at optical frequencies. Confined mode profiles and near‐field enhancements make LSPs ultrasensitive to the dielectric environment, making them good candidates as sensors. The concept and applications have been generalized to spoof LSPs in microwave and terahertz frequencies, via plasmonic metamaterials composed of subwavelength corrugations. Herein, the basic physics, sensing prototypes, detection schemes, and state‐of‐the‐art progress are broadly reviewed from optical LSP sensing to microwave spoof LSP sensing. While optical LSPs exhibit localized sensitivity enhancement with high attenuation, spoof LSPs in microwave and terahertz frequencies combine the characteristics of deep‐subwavelength confinement and sensitivity enhancement of optical LSPs with low loss, high quality factor, multipole modes, and on‐chip detection of optical microcavities. Meanwhile, advances in printed circuits, integrated circuits, wireless communications, wearable devices, and Internet of things have endowed microwave sensing with a solid technical foundation and promising prospects. Applications in liquid sensing, gas sensing, and wearable sensing are demonstrated. Discussions are extended to electromagnetic sensing throughout the wave spectra, with concerns about key supporting technologies. The prospect of microwave sensing is emphatically investigated, specifically on leveraging the advantages of plasmonic enhancement.