Research On PDMS-based Optical Fiber Strain Sensor

Strain is an important parameter to evaluate the health of wearable devices,engineering equipment and civil structures.The methods of strain measurement can be mainly divided into two categories,namely electronic sensors and fiber optic sensors.Among them,optical fiber sensors have the advantages of anti-electromagnetic interference,anti-corrosion ability,good wear resistance,high sensitivity etc.Strain sensors based on optical fiber sensing technology emerge in an endless stream.However,due to the fragility of optical fiber,its strain limit cannot exceed 0.01 ε,which makes it no longer suitable in some large scale measurement scenes.In order to solve this problem,the combination of optical fiber and polymer came into being,among which polydimethylsiloxane(PDMS)is one of the most concerned polymer materials.In recent years,research on the combination of high elastic materials such as PDMS with optical fibers has increased,and has excellent performance in the field of strain measurement.This thesis mainly studies and discusses the PDMS-based optical fiber strain sensor.The main contents of this thesis are as follows:1.By referring to the literature about strain sensor,the research background and significance of strain measurement are expounded,and the previous research results are listed and introduced.This thesis introduces the existing electronic and optical methods in the field of strain measurement,and mainly introduces the research status,sensing structure and principle of optical fiber strain sensors.In particularly,the application and advantages of the optical fiber sensors combined with new materials are mainly introduced.2.A no-core PDMS optical sensor was proposed and demonstrated,which was suitable for large scale strain measurement.The proposed no-core PDMS fiber was composed of polydimethylsiloxane and curing agent in a certain proportion.The intensity loss of its output spectrum varies with strain or surroundings.Experimental results showed that the highest sensitivity of 350.7 %/ε to strain is achieved with the range from 0 to 0.25 ε.In addition,the influence of external environment on the output spectral intensity of no-core PDMS fiber is also studied.3.An optical fiber plane strain sensor with droplet-like structure encapsulated by PDMS was proposed and demonstrated.The droplet-like structure was formed by directly bending a single-mode fiber and fixed by glass microtubes.The plane strain tests in three directions of 0°,45°,and 90° were carried out in the experiment.Results showed that the strain sensitivity in different directions was different,which made the proposed sensor owning the ability of the strain direction distinguish.Meanwhile,the temperature sensitivity of the sensor was monitored to be-1.557 nm/℃.4.The temperature compensation of the droplet-like optical fiber pressure sensor was studied.The temperature sensitivity of the sensor was-1.232 nm/℃ after increasing the thickness of the PDMS package.The temperature sensitivity of the sensor with a reference arm was-0.396 nm/℃,which was reduced by 67.86 %compared with the single arm.Finally,the temperature sensitivity was reduced to-0.011 nm/℃ by improving the demodulation algorithm,which was 99.11% lower.The results showed that although the pressure sensitivity would be decreased to a certain extent through the above methods,the cross-effect of temperature could be effectively reduced.