基于多模干涉的光纤冰体应变传感器

Fiber Optic Ice Body Strain Sensor Based on Multimode Interference

基于“单模-无芯-单模”光纤传感器对冰体进行应变测量研究。传感器以“分层冰冻”的方法植入冰体,冰体应变变化导致传感器干涉光谱波长偏移,通过监测光谱波长实现冰体应变测量。对于实际环境中已经存在的冰体,对“分层冰冻”方法进行优化,通过在冰面上铺设光纤,之后注水冰冻的方式,实现光纤在已有冰体中的植入。利用光谱相邻波谷温度灵敏度相近的特点,将相邻波谷波长差应用于应变测量,可以不受冰体温度变化影响。实验结果显示,冰体承载力大于500 g时,其应变显著增加,当承载力大于600 g时,冰体出现脆性断裂,传感器有效提取了该区间内冰体“韧-脆”转变过程中的应变信号。融化实验显示,传感器可以监测到冰体自然融化过程中完整的应变变化过程,测量结果不受冰体内部温度变化的影响。

In severe cold climates,the bearing capacity of ice body depends on its thickness.As a carrying medium,the ice body with enough thickness expands the human activity area.However,when the bearing capacity of the ice body is insufficient,brittle failure will occur,leading to serious consequences such as casualties and property damage.Therefore,the research on the strain of the ice body measurement technology is of great significance to ensure the reasonable bearing capacity of the ice body.The traditional electromechanical strain measurement systems have some disadvantages,such as large volume and difficult sensor installation and disassembly.The current measurement methods of spectroscopy mainly focus on theoretical simulation and exploration of ideas,while there are few specific plans and experimental studies.In this paper,the Single-mode No-core Single-mode(SNS)fiber optic sensor for strain measurement of ice bodies is proposed.SNS fiber optic sensor is implanted into ice bodies in a layered freezing manner.When the strain of ice changes,it modulates the sensor,causing the wavelength of the interference spectrum to shift.By monitoring the spectral wavelength,ice strain measurement is achieved.By utilizing the similar temperature sensitivity of adjacent spectral troughs,the wavelength difference between adjacent troughs can be applied to strain measurement,which is not affected by changes in ice body temperature.The length,width,and height of the ice body are 250 mm×150 mm×16 mm.When the temperature of ice body increases from-20℃to 0℃,the wavelength shifts of Dip1 and Dip2 in the spectrum are very close.The temperature sensitivities of Dip1 and Dip2 are 9.8 pm/℃and 9.5 pm/℃,respectively,with a relative difference of only~2.5%.Therefore,by using the wavelength difference between Dip1 and Dip2 as the measurement factor for ice bearing capacity,temperature independent bearing capacity measurement can be achieved.Establish an experimental system to study the strain response of ice under different bearing capacities.Place weights at the center of the upper surface of the ice body,to apply bearing capacity to the ice body.The weights are loaded from 0 g to 600 g.Results show that when the bearing capacity of the manufactured ice body exceeds 500 g,its strain significantly increases.When the bearing capacity exceeds 600 g,the ice body undergoes brittle fracture,and the sensor effectively extracts the strain signal during the ductile-brittle transition process of the ice body within this range.The melting experiment shows that the sensor can monitor the complete strain change process during the natural melting of ice,and the measurement results are not affected by the temperature changes inside the ice.For existing ice body in actual testing environments,fiber optic cannot be pre-embedded inside.Improvement is needed for the layered freezing method.Firstly,determine the location to be monitored on the ice surface,known as the monitoring point.Place the fiber optic in a natural straight state on the ice surface,aligning the SNS sensor on the fiber optic with the monitoring point.Place ice block on the fiber optic on both sides of the SNS sensor to secure the fibers.During the fixation process,slowly inject water into the gap between the ice block and the ice surface,and naturally freeze for 5 min.The ice block and ice surface are completely frozen,thus achieving the fixation of the fiber optic.Afterwards,slowly inject water into the ice body until the ice blocks are submerged.After 1 h of natural freezing,the injected water is frozen together with the original ice body,thus completing the implantation of optical fibers into the existing ice body.It should be noted that the ice body itself is a 3D structure,and when a single sensor is implanted,only the strain information of the monitoring point where the sensor is located can be obtained.To accurately describe the overall strain of the ice body as much as possible,research can be conducted through fiber optic measurement schemes with good reusability such as fiber Bragg grating.