Magnetic and electric excitations in split ring resonators.

We studied the electric and magnetic resonances of U-shaped SRRs. We showed that higher order excitation modes exist in both of the electric and magnetic resonances. The nodes in the current distribution were found for all the resonance modes. It turns out that the magnetic resonances are the modes with odd-number of half-wavelength of the current wave, i.e. lambda/2, 3lambda/2 and 5lambda/2 modes, and the electric resonances are modes with integer number of whole-wavelength of current wave, i.e. lambda, 2lambda and 3lambda modes. We discussed the electric moment and magnetic moment of the electric and magnetic resonances, and their dependence to the length of two parallel side arms. We show that the magnetic moment of magnetic resonance vanishes as the length of side arms of the SRR reduces to zero, i.e. a rod does not give any magnetic moment or magnetic resonance.