4408AF Transponder Coils Fastron 4408AF Transponder Coils offer an SMD package that is optimized for low-frequency RFID applications. These wirewound coils cover a wide range of electrical performances. The inductors' length and cross-section area are optimized for best sensitivity in the coil axis. Fastron 4408AF Transponder Coils are used for wireless data transmission in low-frequency RFID products, such as immobilizers, TPMS, and keyless entry. Other industrial applications include access control and tracking devices.