A proposed folded dipole tag antenna for a radio frequency identification (RFID) sensor system is employed to determine qualities of a material under test (MUT). In this paper, a study on the characteristics of specifically designed tags (SDTs) placed on a dielectric material with a gap is presented. The CST Microwave Studio is used to study characteristics of these SDTs in the presence of an MUT near or contact with SDTs. Simulated results show that different SDTs provide different characteristics depending on MUTs.