Accurate and Automatic Detection of Oblique RFID-Enabled Objects in Mobile Manner

In the scenarios of warehousing or industrial manufacturing, the objects usually should be placed vertically, box containing bottles of wine cannot be inverted, and the books should be vertically placed on the shelves. RFID has many attractive advantages, no requirement on line-of-sight and battery-free for long-term monitoring. Hence, an RFID-based solution was proposed to detect whether tagged objects are oblique. However, the existing solution has two major limitations: (i) it requires that both RFID reader and tagged objects should be static; (ii) it can only deal with the case of upside down but fails when objects are oblique with angle less than 180^∘. To overcome these limitations, this paper proposes an RFID approach called Mobile Detection of Oblique objects (MDO). In MDO, the tagged objects move relatively in a straight line at a uniform velocity with respect to the reader antenna, RFID reader antenna is fixed and the objects move on conveyor belt. MDO compares the collected phase profile and the theoretical phase profile to determine whether the concerned object is oblique or not. We use Commercial-Off-The-Shelf (COTS) RFID devices to implement the MDO approach. Extensive experimental results prove that MDO can precisely detect the oblique objects with an accuracy larger than 90% under various conditions.