Localization of passive UHF RFID tags on assembly line based on phase difference

As a key technology of internet of things (IOT), RFID technology is widely used in object identification and tracing. In some manufacturing applications, such as the assembly line, the localization of the specific product is very important for the customized production. In recent years, although localization technology based on UHF RFID has gained great attention and development, the accuracy of the existing systems still can not meet the demand of different production applications. To improve the performance of the UHF RFID localization system, a method of using the phase of the passive RFID tag's reflected signals is proposed. Note that the phase reflected by the tags is distance sensitive, which is conductive to locate the tags accurately. Moreover, a set of geometry equations is derived to estimate the position of the tag on an assembly line. The phase difference between two antennas is utilized to overcome the periodicity of the phase. The analysis of models and experimental results on a motorized stage show that the phase reflected by the passive UHF RFID tags can be used to locate RFID tags on the assembly line accurately.