Magnetoelastic-Based Noncontact Torque Sensing via Multicoil Differential Probes for Unmodified Shaft Systems

Torque measurement is critical in robotics, aerospace systems, and mechanical engineering. However, conventional torque sensors typically require direct installation on the shaft, limiting their applicability in scenarios where shaft modification is impractical. To address this limitation, this article presents a noncontact magnetoelastic torque sensor based on a lateral configuration featuring a multicoil differential probe. The system comprises an excitation coil and four differentially connected receiving coils that detect permeability variations induced by torsional stress, requiring neither physical contact nor shaft modification. Key innovations include the following: 1) a high-frequency mutual inductance model incorporating anisotropic media effects, validated for frequencies up to 100 kHz; and 2) an optimized probe geometry with uniform air gaps (0.3–0.5 mm) for enhanced sensitivity. Experimental results demonstrate a sensitivity of 10 mV/N·m and a repeatability error of 5.78%. The design is validated through finite-element simulations and servo-controlled bench tests, indicating its potential for real-time monitoring in applications such as robotic joints and aerospace transmissions.