Field-validated high-sensitivity distributed mass sensing using a triple-taper-based Φ-OTDR sensor

We propose a phase-sensitive optical time-domain reflectometry (Φ-OTDR) sensor using a triple-tapered fiber structure to enhance loading mass detection sensitivity. The sensor features a 5 m sensing region with three sequential tapers reduced to a 20 µm diameter, strengthening light mechanical interaction compared to a non-tapered fiber. Experimental results show a maximum signal-to-noise ratio (SNR) of 27.16 dB, representing an approximately 30% improvement over a standard 5 m non-tapered sensor, along with a maximum detectable phase shift of 0.168±0.009rad and a mass sensitivity of 0.601±0.017µs/g. Refractive index variations extracted from the Φ-OTDR signal closely agree with theoretical predictions, yielding an average percentage error (APE) of 7.592×10^-3%. Field validation further confirmed reliability, achieving strong correlation with laboratory benchmarks (RMSE=0.826, MAPE=1.92%), demonstrating consistent and accurate loaded-mass estimation. Field experiments validated sensor performance under realistic conditions using calibrated load masses of simulated animals on sand surfaces above the embedded fiber. The sensor accurately detected and quantified unknown loads, showing excellent agreement between predicted and realistic measurements. These results highlight the enhanced sensitivity, accuracy, and stability of the proposed triple-taper Φ-OTDR sensor for advanced distributed sensing applications.