Accurate in-situ sensing and condition monitoring of bearings using embedded conformal piezoelectric sensors

Rolling bearings are critical components that carry loads in rotating machinery. However, conventional sensors mounted outside the bearing are susceptible to signal attenuation along complex transmission paths, variations in mounting conditions, and environmental interference. To enable in situ perception close to the excitation source, this study develops an intelligent bearing that integrates a thin, flexible, and conformal PVDF-TrFE piezoelectric sensor into a local recess in the bearing outer ring. The sensor is fabricated by depositing a functional PVDF-TrFE layer onto a patterned copper clad polyimide substrate using a flexible electronics spray coating system developed in house. A systematic design strategy was adopted to integrate sensor geometry, electrode patterning, conformal installation on the outer ring, mechanical compatibility, and fault sensing evaluation within a unified framework. Finite element analysis demonstrated that adapting the recess geometry to the sensor profile markedly reduces the local structural disturbance caused by sensor integration. Under the conservative static loading condition considered, the optimized numerical configuration shallow recess retained approximately 82.5 % of the apparent local radial stiffness of the intact outer ring. Bearing experiments conducted at rotational speeds from 1800 to 3000 r/min demonstrated that the embedded sensor simultaneously captured high frequency impacts induced by faults and low frequency responses associated with rolling element passage. The relative phase between these components varied with the circumferential position of the outer race defect, providing preliminary information about the fault location. Under identical experimental conditions, the embedded sensor also exhibited consistently higher signal to noise ratios for fault related components and higher normalized fault amplitudes than the external acoustic emission sensor and accelerometer. These results demonstrate the feasibility of integrating conformal piezoelectric sensing into a bearing component that carries load and provide a practical route toward condition perception close to the excitation source in intelligent bearings with integrated sensing capabilities.