subwavelength

Subwavelength describes a regime in which the characteristic dimensions of a structure or the features of a phenomenon are smaller than the wavelength of the interacting wave. When a feature is subwavelength, it cannot support propagating waves at that wavelength in the bulk medium, and its interaction is dominated by near-field, evanescent components. The concept is widely used in optics, acoustics, and electromagnetism. In optics, subwavelength structures—such as nanostructured screens, antennas, and metamaterials with features well below visible wavelengths—can modify transmission, reflection, and phase in ways that surpass conventional diffraction limits. This underpins technologies such as subwavelength imaging, sensing, and cloaking approaches, as well as subwavelength waveguides and resonators. Subwavelength phenomena include plasmonic resonances in metals and the guidance of light by metamaterials that achieve effective parameters not found in natural materials. In acoustics, subwavelength structures control sound with features smaller than the sound wavelength, enabling acoustic metamaterials that slow, bend, or trap sound. Practical challenges include fabrication limits, losses, and bandwidth constraints, since effects relying on subwavelength features often operate over narrow frequency ranges. The term is often contrasted with the diffraction limit, a fundamental constraint that relates resolution and wavelength in conventional imaging. Researchers continue to explore subwavelength concepts to enable higher-resolution sensing, compact devices, and novel wave manipulation.