An Embeddable Strain Sensor with 30 Nano-Strain Resolution Based on Optical Interferometry

Chen Zhu,Jie Huang,Yiyang Zhuang,Fujian Tang,Yizheng Chen

doi:10.3390/inventions3020020

Chen Zhu, Jie Huang + Show 3 more

Open Access

https://doi.org/10.3390/inventions3020020

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Abstract

A cost-effective, robust and embeddable optical interferometric strain sensor with nanoscale strain resolution is presented in this paper. The sensor consists of an optical fiber, a quartz rod with one end coated with a thin gold layer, and two metal shells employed to transfer the strain and orient and protect the optical fiber and the quartz rod. The optical fiber endface, combining with the gold-coated surface, forms an extrinsic Fabry–Perot interferometer. The sensor was firstly calibrated, and the result showed that our prototype sensor could provide a measurement resolution of 30 nano-strain (nε) and a sensitivity of 10.01 µε/µm over a range of 1000 µε. After calibration of the sensor, the shrinkage strain of a cubic brick of mortar in real time during the drying process was monitored. The strain sensor was compared with a commercial linear variable displacement transducer, and the comparison results in four weeks demonstrated that our sensor had much higher measurement resolution and gained more detailed and useful information. Due to the advantages of the extremely simple, robust and cost-effective configuration, it is believed that the sensor is significantly beneficial to practical applications, especially for structural health monitoring.

Highlights

The measurement of strain is of high importance in many applications, from experimental labs to structural health monitoring (SHM), aerospace, civil engineering, and nanotechnology [1]
The principal part of the sensor consists of an optical fiber, a quartz rod with one end coated with a thin layer of gold, and two metal shells made of stainless steel
The principal sensor structure consists of an optical fiber, a quartz rod with one end coated with gold, and two metal shells

Summary

Introduction

The measurement of strain is of high importance in many applications, from experimental labs to structural health monitoring (SHM), aerospace, civil engineering, and nanotechnology [1]. Gagliardi et al demonstrated a strain measurement at the 10−13 ε·Hz−1/2 scale using an FBG resonator with a diode-laser source which is stabilized against quartz-disciplined optical frequency comb [1]; Huang et al proposed a static-strain sensor with a resolution of 1.0 nε based on a π-phase-shifted. The majority of reported EFPI strain sensors have a relatively low measurement resolution due to the physical structures of the sensors, such as the well-known fiber-in-capillary structure [19]. From another perspective, EFPI sensors are good choices for ultra-small displacement measurements. Considering that strain is the fractional length change, with judicious mechanical design and packaging, EFPI sensors can achieve strain measurements at nano-strain levels. The result was compared with a commercial linear variable displacement transducer (LVDT), demonstrating that our sensor has an excellent performance regarding measurement resolution and reliability

Sensor Structure and Principle

Experimental Results and Discussions

Conclusions