Theory of spoof magnetic localized surface plasmons beyond effective medium approximations

A homogeneous negative permeability sphere can support magnetic localized surface plasmons (MLSPs). Generally, negative permeability materials are metamaterial (MM) structures exhibiting very deep subwavelength spatial scales, whose effects may be detrimental in the near-field for those applications based on effective medium approximations. We suggest to overcome this fundamental limitation by demonstrating analytically that the electromagnetic spatial distribution, associated to a MLSP resonance and excited by a near-field source, can be accurately reproduced outside the sphere by substituting the negative permeability sphere with a homogeneous high-index dielectric one having the same radius. Considering that a large class of ferroelectric materials shows ultra-high dielectric constant and low-losses at low frequency (up to GHz), our spoof MLSPs theory could be a key tool for realizing high performance subwavelength magnetic photonic devices in the radiofrequency and microwave regions.