An On-Chip Inductive-Capacitive Sensor for the Detection of Wear Debris and Air Bubbles in Hydraulic Oil **This work was supported by the Natural Science Foundation of China (Grant No. 51679022), the Dalian Science and Technology Innovation Fund (Grant No. 2019J12GX023).

An on-chip inductive-capacitive sensor is proposed to detect metal debris and air bubbles in hydraulic oil. The sensor includes inductance and capacitance detection units. The inductance detection unit detects and distinguishes the properties of metal debris by monitoring the inductance change of the solenoid coil. The capacitance detection unit detects air bubbles by monitoring the capacitance change of the cylindrical capacitor. Inductance tests are conducted using iron and copper debris with different sizes. The test results showed that the inductance pulse amplitude increases nonlinearly with debris size. Capacitance tests are conducted using air bubbles with different sizes. The test results showed that the cylindrical capacitor can detect and count air bubbles with high sensitivity. The design concept presented in this paper can be extended to oil conditioning sensors for multi-contaminants detection and differentiation.