This paper presents a novel UHF RFID tag antenna for mass-retailed products. The tag is realized on low-cost material. The antenna is composed of two elements: a planar dipole-based antenna, matched with a small inductive coil. In particular, it is able to work when directly mounted on different materials. When the permittivity or the thickness of the material on which it is mounted changes, the antenna's impedance varies around a fixed impedance on the Smith chart. This impedance is close to the conjugate of the RFID chip's input impedance. The different mounting materials tested were cardboard, a paper block, plastic, wood, a bottle of tap water, and a glass bottle. The measurement results indicated a maximum range of eight meters for materials with a low permittivity, and a maximum range close to two meters for denser materials or materials with a higher permittivity.
This paper presents a Radio Frequency measurement method that allows to determine electrical characteristics like scattering parameters or impedance of contactless passive chips, using common measurement devices as oscilloscope, personal computer and directional coupler. The measurements obtained using this method are as accurate as those obtained with vector network analyzer (VNA) measurements, while providing several improvements. First, the method makes it possible to measure a chip's impedance in activation state, which requires large input power, not compatible with VNA measurements. Secondly, this method realizes a real time measurement, which consists in impedance measurement as a function of time. Therefore, this real-time measurement makes possible to detect and measure the impedance changes of an actual contactless smart card's integrated circuit during a load modulation communication at different powers. Finally, this real time impedance measurement gives important information on chips electrical characteristics that can be used to optimize NFC (Near Field Communication) devices design in order to reduce the power losses within an RFID (Radio Frequency Identification) tag.
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