Optimized antennas for enhanced RFID sensor tags

The RFID-based sensor networks are becoming increasingly appealing because of the perspective of applicability at a reasonable cost. Nevertheless, they require the integration of passive RFID tags and sensors. Even if technically possible, this integration is still limited both in type and cost. In fact, the embedding implies strict constraints in terms of size and energy consumption of the sensor. Moreover, the extra microwave and digital circuitry cause the sharp increase of the intrinsic value of the tag. This last aspect is crucial because the most attractive feature of a passive RFID tag is its cost-effectiveness other than its ease of use. In this work we propose a new version of our previously published label-type Sensor Tag, an RFID device that accepts as an input a generic sensor and allows the transmission of the measured data. The new enhanced sensor tag is based on four optimized antennas designed by taking into account the size constrains and the mutual coupling effects. The size reduction, compared with the old version, is appreciable, and the working distance is now as good as a long range passive UHF tag.