1. Postrel RD, Haven KR, Empson EH, Fang CC (2017) Point of sale device. United States Patent, Postrel at al. Patent Number: 6,003,008. 19
2. Breed DS, Johnson WC, DuVall WE (2019) Smartcard. United States Patent, Intelligent Technologies International, Inc. Patent Number: US10,438,106B2
3. Dory JR, Hanes DH, Dowdy JG (2018) Near field communication (NFC) data transfer. United States Patent, Dory et al. Patent No.: US10,021,727B2
4. Smart Card Alliance The what, who and why of contactless payments. A Smart Card Alliance Contactless Payments Council White Paper, Publication Number: CPC-06002
5. Spencer CA (2019) RFID /NFC functionality for portable electronic devices. United States Patent, Spencer, II. Patent No.: US10, 387870B2