Deep-Subwavelength-Scale Directional Sensing Based on Highly Localized Dipolar Mie Resonances

This paper reports the formation of highly localized Mie resonances on a closed metasurface encapsulating a rigid core and the realization of directional sensing at deep-subwavelength scale (diameter similar to lambda/8) with the proposed physical model. Based on modal-expansion and mode-matching methods, it is theoretically shown that the extremely anisotropic metasurface shell can support varied orders of Mie resonances around the rigid core. We further experimentally demonstrate that the Mie resonance with a dipolelike profile is strongly excited under the illumination of a plane wave at low frequencies, enabling the sensitive directional sensing due to the intensified and azimuthally dependent pressure field.