High-precision wireless displacement monitoring microsystem based on TMR effect for structural health monitoring

This study presents a high-precision wireless displacement monitoring microsystem that utilizes the tunnel magnetoresistance (TMR) effect for structural health monitoring (SHM). The system overcomes limitations of traditional SHM methods, providing high-precision, intelligent and lightweight measurements. We established an analytical model of magnetic field displacement and optimized its linear range. Considering the measurement error caused by magnetic field decay, we designed an adaptive sensitivity correction method, thus avoiding the tedious magnetic field numerical fitting process. The system's accuracy and stability are validated through comparison with laser ranging, showing high accuracy within the range of ±7.5 mm, a resolution of 0.4 μm, and a long-term working accuracy better than 2.25 μm. The core system is less than 3.84 cm³ in size and is inexpensive to manufacture, making it ideal for mass deployment across a broad range of infrastructure. This work outperforms other state-of-the-art methods in the field in terms of accuracy, cost, size, and power consumption. Practical applications in monitoring concrete deformation, crack width changes, and bridge beam end slip deformation highlight its versatility and effectiveness. Its stable performance in long-term autonomous operation has also been verified in a 39-day actual bridge test, making it a valuable tool for enhancing infrastructure maintenance and safety.