The ultra-high field (UHF) small-animal MRI (sa-MRI) device provides a powerful platform for translational imaging. To achieve a high signal-to-noise ratio, as well as sufficient signal homogeneity in abdominal imaging, the RF coil has to be precisely tuned. A novel geometry for a high-permittivity material (HPM) was designed and integrated into an enlarged (90 mm) birdcage (BC) RF coil. The geometrical design of the HPM attachment was based on a computational calculation, and was compared with the commonly used 72 mm bandpass filter BC coil without any HPM attachments. The resulting RF transmission (|B ₁ ⁺|) map clearly shows that the increased coil diameter led to a decreased |B ₁ ⁺| intensity. However, this loss in field intensity was mitigated by optimally integrating the HPM attachment with the coil. As a result of this attachment, the proposed design exhibits superior |B ₁ ⁺| intensity and uniformity along the main magnetic field z-direction.