Texas Instruments is a company well known for their semiconductor integrated circuits.

For application in RFID (radio frequency identification) they also manufacture transponders, readers and antennas, see their website www.ti.com/rfid.

Some technical documents feature ring cores in 4C65 NiZn ferrite, which is chosen as a reference material for matching transformers, baluns and common-mode chokes in RFID systems operating at 13.56 MHz.



Fig : Matching transformer (right) and balun (left), from HF Antenna design notes.

See the below links to technical application reports :

HF Antenna Design Notes (matching transformer and balun in chapter 7)
HF Antenna Cookbook (common-mode choke in chapter 3 and balun in chapter 5)
Constructing a 1000 x 600 HF Antenna (common-mode choke in chapter 6)