Your question is a bit vague. What do you mean by miniaturized, and by ultra-miniaturized? Presumably you have a specific length-scale in mind, either in (eg) microns, or in terms of wavelengths? And wavelengths of what? There are acoustic, electromagnetic, water-wave, and mechanical metamaterials, and no doubt other types as well.

@paul kinsler, I am talking about EM spectrum in sub 6 GHz range.