Two types of flexible terahertz metamaterials were fabricated on polyethylene naphthalate (PEN) substrates. The unit cell of one type consists of two identical split-ring resonators (SRRs) that are arranged face-to-face (i.e., FlexMetaF); the unit cell of the other type has nothing different but is arranged back-to-back (i.e., FlexMetaB). FlexMetaF and FlexMetaB illustrate the similar transmission dips under zero strain because the excitation of fundamental inductive-capacitive (LC) resonance is mainly dependent on the geometric structure of individual SRR. However, if a gradually variant strain is applied to bend FlexMetaF and FlexMetaB, the new resonant peaks appear: in the case of FlexMetaF, the peaks are located at the lower frequencies; in the case of FlexMetaB, the peaks appear at the frequencies adjacent to the LC resonance. The origin and evolution of strain-induced resonances are studied. The origin is ascribed to the detuning effect and the different responses to strain from FlexMetaF and FlexMetaB are associated with the coupling effect. These findings may improve the understanding on flexible terahertz metamaterials and benefit their applications in flexible or curved devices.
(Ba0.96Nd0.04) (Ti0.96Ho0.04) O3 (BNTH4) ceramic with a cubic perovskite structure was prepared using the coldpressing ceramic technique of solid-state reaction. Under 638-nm excitation, the photoluminescence (PL) monitoring provided the evidence of a small number of Ho 3+ ions at Ba-sites. BNTH4 exhibits the multiplicity of PL signals of Nd 3+ and Ho 3+. Ho 3+ in BNTH4 exhibits an asymmetric amphoteric behavior, i.e., 3.82 at. % Ho 3+ ions dominantly occupy Tisites and 0.18 at.% Ho 3+ ions occupy Ba-sites.
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