This paper presents the design of low cost, conformal UHF antennas and RFID tags on two types of cork substrates: natural cork and agglomerate cork. Such RFID tags find application in wine bottle and barrel identification and additionally they are suitable for numerous antenna-based sensing applications. This work includes the high frequency characterization of the selected cork substrates considering the anisotropic behavior of such materials. Plus, the variation of their permittivity value as a function of the humidity is also verified.
As a proof-of-concept demonstration, three conformal RFID tags have been implemented on cork and their performance has been evaluated using both a commercial Alien ALR8800 reader and an in-house measurement setup. The reading of all tags has been checked and a satisfactory performance has been verified, with reading ranges spanning from 0.3 m to 6 m. Also, this paper discusses how inkjet printing can be applied to cork surfaces and an RFID tag printed on cork is used as humidity sensor. Its performance is tested under different humidity conditions and a good range in excess of 3 m has been achieved, allied to a good sensitivity obtained with a shift of more than 5 dB in threshold power of the tag for different humid conditions.