A high-precision LC resonant sensor with dual-parameter extraction and noise-optimised resolution for non-contact stress estimation in metallic components

Accurate stress measurement in metallic structures is essential for structural health monitoring. However, conventional strain-gauge-based methods require direct contact and complex installation, limiting long-term and large-scale deployment. This study presents a non-contact stress sensing system based on an LC resonant circuit and a low-cost inductance-to-digital converter (LDC). Mechanical stress in ferromagnetic materials alters magnetic permeability and electrical conductivity, modifying the coil–material electromagnetic coupling and causing variations in resonant frequency fr and equivalent parallel resistance Rp. A planar PCB coil operating at approximately 2 MHz was integrated with an LDC1101-based acquisition system. The sensor was experimentally validated using industrial boiler water-wall tubes under tensile stresses from 83.3 to 333.3 MPa. Both fr and Rp exhibited monotonic responses to applied stress. Noise characteristics were quantitatively evaluated using power spectral density and Allan deviation analysis. With an optimized averaging time of 6.0 s, the minimum detectable stress reached 2.49 MPa under the 2σ criterion. The proposed approach combines dual-parameter extraction, quantitative noise evaluation, and resolution–latency optimization, providing a compact and cost-effective solution for non-contact static stress monitoring.