We experimentally demonstrate multiple resonances in split-ring resonators (SRRs) from direct electric excitations in midinfrared and near infrared regions. The ratio of the entire length of SRRs to the resonance modes and wavelengths presents a clear linear relationship. Such expression validates in both cases of electric and magnetic responses in SRRs excited by electric field and is further confirmed by examining the SRRs with different lengths. Therefore, our quantitative observations indicate that the multiple resonances can be interpreted by the standing-wave plasmonic resonances and further facilitate to design the desired operation frequencies and responses of SRRs for practical applications.
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