Passive Distributed Sensor Array Using Multiple RF Sensing Tags

Radio-frequency (RF) sensing tags are emerging as the next-generation paradigm toward gathering context-awareness information related to all objects' physical phenomena for the future Internet of Things (IoT). However, the most attention has been given to realize the sensing functions of a single tag rather than the mutual influences among adjacent tags. It has been found that when multiple RF sensing tags are deployed adjacently, these tags may fail to function properly. Therefore, motivated by the common requirements of deploying multiple RF sensing tags in the IoT, the mutual influences among tags are analyzed. We believe that the mutual impedance of tag antennas, which changes with the antenna separations among adjacent RF sensing tags, affects the wireless links between the tags and reader. The mutual impedance is analyzed using the method of moments and is substituted into forward and backward links. The calculation results show that the influence of the antenna mutual impedance on the RF sensing tag takes the wavelength of RF waves as the period, fluctuates, and gradually diminishes as the separations between antennas increase. To validate the analysis, a sensor array is formed using multiple RF sensing tags integrated with magnetic sensors. The experimental results show that once the antenna separations between the tags exceed 1.5 wavelengths, the backscattering sensing data can be decoded, and the interrogation success rates reach 100%. Numerous sensor arrays can be deployed ubiquitously with convenience, providing a clustered solution toward distributed sensing for the IoT.