Improvement of Moving RFID Microtag Detection in Different Angular Orientations Using Multiple Tubular Coils

Directionality problem caused by the rolling of microtag with flowing fluid seriously affects the reliability of an oilwell downhole radio frequency identification (RFID) system. In this article, we propose a novel RFID reader antenna structure using multiple tubular coils for reduced orientation sensitivity. The conventional solenoid coil and saddle-coil pairs are combined to overcome the respective defects of the two coils and develop their advantages to form a complementary structure at the same time. Then, a series of coil parameters are designed in detail to provide strong magnetic field distribution both in the
$x$
-axis,
$y$
-axis, and
$z$
-axis directions. To verify the design, the proposed multiple tubular coils have been fabricated and measured. Experimental results demonstrate more potential than the conventional solenoid coil for microtag detection in different angular orientations, which is very important to improve the reliability and applicability of the current oilwell downhole RFID system.