Electromagnetic Design of UHF RFID Tags Enabling a Novel Method to Retrieve Sensor Data

The addition of sensing capabilities to UHF RFID tags has been a hot topic during the last few years, with plenty of interesting results in the literature. Among other solutions the direct integration in the RFID chip has been also proved, and a number of chips are already on the market. Nevertheless, although all of them allow for the passive identification, to retrieve sensed data it is necessary to perform a specific writing-reading sequence during which the chip must be kept powered. This is not guaranteed by standard RFID readers, so that sensing functionalities are generally exploited only when the tag works in battery-assisted passive (BAP) mode. A mean to avoid the use of batteries thus maintaining compactness and cost-effectiveness of the sensor tag is proposed in this paper and consists in implementing a novel so-called pseudo-BAP mode. In particular, after the introduction of the design strategy and the some considerations about the antenna matching, a passive testing board composed of a circuitry implementing the pseudo-BAP mode and a tag mounting a sensor-provided UHF RFID chip is designed, realized, and tested so to verify its appropriateness to guarantee RFID sensing, other than identification, even when using universally standardized reader commands.