Pan Dou is an Assistant Professor in the School of Mechanical Engineering, Xi’an Jiaotong University, China. His research interests include ultrasonic measurement of lubrication film thickness, tribology, signal processing, and engineering applications of lubrication monitoring. Tonghai Wu is a Professor in the School of Mechanical Engineering, Xi’an Jiaotong University, China. His research interests include online machinery health monitoring and prognostics, embedded oil/liquid sensing systems, multi-physical signal processing (vibration, ultrasonic, acoustic emission), and oil-data-driven diagnosis and life prediction methods. Yaguo Lei is a Professor in the School of Mechanical Engineering at Xi’an Jiaotong University, China. His research interests include dynamic modeling of mechanical systems, vibration and multi-physical signal processing, intelligent diagnosis and prognostics, and big-data-driven condition monitoring and predictive maintenance. He has pioneered many signal processing techniques, intelligent fault diagnosis methods, and remaining useful life prediction models for machines. Thomas Reddyhoff is a Reader in Tribology in the Department of Mechanical Engineering, Imperial College London, UK. His research focuses on experimental and numerical tribology, lubrication and friction behavior of sliding contacts, in-situ measurement of lubrication film thickness, acoustic emission and friction-state analysis, as well as surface texturing and lubricant performance optimization. Min Yu is a Research Fellow in the Department of Mechanical Engineering, Imperial College London, UK, where he conducts research on intelligent sensing, instrumentation and control for mechanical interfaces. His work focuses on sensing and control methods for lubricated contacts, condition sensing of lubrication, and mechatronic interface design.