低 频 强 磁 复 合 感 知 的 零 介 入 叶 端 定 时 方 法

Blade tip timing (BTT) technology, characterized by its non-contact nature and capability for full-annulus blade monitoring, has become an important approach for vibration measurement and condition monitoring of rotating blades. Its core lies in the high-precision acquisition of blade time-of-arrival (ToA). However, existing BTT sensors are typically installed via casing penetrations, which may compromise the structural integrity of the casing. Meanwhile, conventional high-frequency eddy current methods are limited by the skin effect, making it difficult to detect blade-passing signals within the casing without drilling holes. To address these issues, a non-intrusive BTT method based on low-frequency, strong-magnetic-field composite sensing is proposed. The proposed method employs a low-frequency alternating magnetic field to establish a through-casing sensing channel and introduces a bias magnetic field to enhance the modulation of motional eddy currents on the local magnetic field during blade sweeping, thereby improving the detectability of blade-passing signals. A three-dimensional finite element model is established in COMSOL to analyze the electromagnetic field distribution and magnetic flux transient characteristics within a 5 mm non-ferromagnetic aluminum alloy casing, and to identify the observable boundary of blade-passing signals outside the casing under shielding conditions. Furthermore, preliminary experiments under laboratory conditions are conducted using an aluminum alloy casing, in which pulse response waveforms corresponding to blade passage are successfully obtained, thereby validating the feasibility of electromagnetic coupling sensing through the casing. Using a multi-stage signal-processing framework, stable extraction of ToA sequences is achieved on an industrial fan platform. The results demonstrate that the proposed method can obtain clear blade-passing-induced pulses without casing penetration, providing a new non-intrusive sensing approach for online vibration monitoring of aero-engine blades.