Design and characterization of LC strain sensors with novel inductor for sensitivity enhancement

This paper presents a LC strain sensor with a novel encapsulated serpentine helical inductor. The helical coil of the inductor is formed by serpentine wire to reduce the radial rigidity. Also the inductor is encapsulated by material with high Poisson's ratio. When an axial deformation is applied to this encapsulated inductor, the cross-sectional area of the helical coil will have more evident change due to lower radial rigidity and encapsulation. Therefore, the variation of inductance or LC resonant frequency can be enhanced to provide better sensitivity of the LC strain sensor. By using PDMS as encapsulated material, it is shown that the sensitivity of the conventional helical inductor with or without encapsulation are both about 73.0 kHz/0.01ε, which means that encapsulation on the conventional helical inductor does not help to improve the sensitivity due to high radial rigidity of the conventional helical coil. It is also found that the encapsulated serpentine helical inductor has better sensitivity (121.9 kHz/0.01ε) than the serpentine helical inductor without encapsulation (62.7 kHz/0.01ε), which verifies the sensitivity enhancing capability of the proposed encapsulated serpentine helical inductor design. The error between simulation and measurement results on sensitivity of LC strain sensor with the encapsulated serpentine inductor is about 5.57%, which verifies the accuracy of the simulation model. The wireless sensing capability is also successfully demonstrated.