Detection of Oil-Water Emulsions in Oil Samples Using Low-Cost UHF RFID Sensors

A low-cost sensor integrating chipped ultrahigh-frequency radio frequency identification (UHF RFID) and paper flow channels is designed to characterize water content (WC) in oil. We first introduce the sensor design consisting of tag antenna, tag integrated circuit (IC), and probe with integrated paper flow channel. We then discuss the fabrication of sensor prototypes and conduct measurements of pure water, pure SAE oil, and SAE/water 70%/30% emulsion (S/W 70/30). The sensor is seeded with the fluid under test (FUT) and the sensor signal is recorded using an UHF RFID reader while the FUT propagates in the flow channel. We show that our sensor can perfectly differentiate between water, oil, and S/W 70/30 using the RSSI at discrete times as well as the slope of the RSSI-over-time signal in two distinct areas. Finally, we show that linear discriminant analysis (LDA) and affinity propagation (AP) on data transformed with principal component analysis (PCA) are effective methods for automated FUT classification in supervised and unsupervised scenarios, respectively.