Effects of the surface elastic modulus parameter Es in conjunction with the eccentricity ε on the fundamental frequency of the eccentric annular DLGSs for both CeC and CeF boundary conditions are presented in Figs. 3 and 4 for IPM and APM, respectively. The eccentricity parameter is taken in the range of 0e8 nm, while the surface elastic modulus is considered as 0 and 6 N/m. From Figs. 3 and 4, it can be observed that for CeF boundary condition, the first frequencies corresponding to IPM and APM increase with increasing eccentricity slowly, whereas for CeC boundary condition, they decrease significantly. In other words, it can be concluded that for a CeF DLGS, the first frequency of IPM does not depend on the eccentricity. Results show that the surface elastic modulus parameter Es and the eccentricity ε have more significant effects on the in-phase vibration modes than the anti-phase ones.