Analysis and Computational Methods for a Reader Solenoid Coil Used in Industrial Environments

This paper proposes a new reader solenoid coil with a metal tube for the use in high-temperature water, mud, and other impurities in an oil well downhole. The coil can read commands transmitted from the ground surface via inactive microtags and write the sensor data collected in the downhole into the microtags for transmission to the ground. By combining transformer theory and electromagnetic field theory, the main parameters of the reader solenoid coil in the harsh industrial environment in a downhole are calculated, and the main factors responsible for radio-frequency identification communication failure at 125 ± 10 kHz of the reader solenoid coil are analyzed. Then, a mathematical model is developed to describe the relationship among the electromagnetic field density, the ac resistance of complex permittivity, and the complex permeability with water and the metal tube of the reader solenoid coil. Methods to reduce the changes in the inductance and resistance are presented. The minimum flux density of the reader solenoid coil is designed to provide a continuous energy supply to inactive microtags, and the identification rate by the reader is 100% at 125 ± 10 kHz. Furthermore, the reader solenoid coil was tested in an industrial environment in the downholes of six oil well drilling systems for two years.