A Miniaturized UHF RFID Tag Antenna Attached to a Container of Filled Liquid

A miniaturized novel antenna design for a UHF RFID tag placed on a container of filled liquid is described in this study. A perfect match between the input impedance of the antenna, equivalent circuit model, and complex impedance of a Monza-6 chip (10.5-j134 Ohm at 915 MHz), can be achieved by changing the size of the gaps or controlling the capacitance of Cg. To optimize the dimension of the antenna and minimize the effects of the tag antenna on a container of full liquid with high conductivity and permittivity, the design technique based on the excitation of the same direction surface current paths is introduced to lengthen the effective electrical length of the tag. Consequently, the tag not only becomes smaller in size but also yields a stable reading distance (> 5.0 m). The simulated and measured results confirm the presence of the liquid, which does not affect the performance of the tag.