Ultra-high dielectric constant (uHDC) materials can effectively manipulate and enhance the RF field. The effects of uHDC materials on RF field is closely related to the geometry of the material in relation to RF coils. The uHDC ceramics with a given geometry can possess intrinsic resonance modes which also depends on its mutual coupling with the coil. In this study, we compared the B1+ field enhancement of rectangular uHDC blocks with different thickness, resonance condition and sizes of coupling coils. Computer modeling and phantom experiments are performed in this study.