Optimization Design And Signal Processing For Medium-high Frequency FBG Accelerometer

Vibration is a common phenomenon.For large-scale engineering structures(mechanical equipments or architectural buildings),harmful vibration will cause the loss of life and property.In order to avoid the occurrence of catastrophe accident,to establish a practical monitoring system for vibration accelerometer is very important.Compared with traditional electromagnetic type sensors,Fiber Bragg grating(FBG)sensors have attracted much attention for their intrinsic advantages such as small size,resistance to corrosion,anti-electromagnetic interference,the capability of remote operation,etc.Now,FBG sensing technology is considered as one of research hotspots in on-line real time safety monitoring of large-scale engineering structures.In this paper,a new type FBG accelerometer based on flexible gemels is proposed,vibration detection by FBG is achieved,and dynamic monitoring system is designed.The main research contents are as follow:(1)A new type FBG accelerometer based on flexible gemels is proposed and the working principle of this sensor is discussed.As the most important part,flexible gemels,the equations of its rotational stiffness are studied in detail.The equations of nature frequency and sensitivity of the FBG accelerometer are deduced.The links between boundary dimensions of the sensors and eigenfrequency or sensitivity are cleared.Set certain nature frequency as main constraint and maximize sensitivity as objective function,the optimal sizes of three sensors are designed by optimization design of the softwares,LINGO and MATLAB.(2)The models of the finite element are established.The modal analysis and harmonic response analysis are completed.The results of finite element analysis are well in agreement with optimization design.According to the optimal sizes of the sensors,the three sensors are manufactured and packaged.Properties of those sensors are tested.It shows that the nature frequencies of the three sensors are about 600 Hz,1800 Hz and 3100 Hz.The sensitivities in exciting frequency are 313.8 pm/G,44.6 pm/G and 14.3 pm/G.Moreover,the linearity of sensitivity curve is more than 99%.The temperature tests are respectively 12.3 pm/?,10.4 pm/? and 14.8 pm/?.The transverse response amplitude is little than 8% at most of that in work direction.In the other word,this type sensor has a perfect anti-interference capacity.The results of experiments are consistent with optimization design and finite element analysis.It means the theoretical calculation is right.Test the common machine equipment and rotating equipment by using manufactured FBG accelerometer.On the other hand,piezoelectric accelerometer is also used as comparison.By analyzing the time domain and frequency range chart,we can get to know that the test results of FBG accelerometers and piezo-electric accelerometers are similar.It can be concluded that the manufactured FBG accelerometers have the capacity to test vibration.(3)Real dynamic monitoring software system based on medium-high frequency FBG accelerometers are designed.The scanning signal of single-four channel is extracted,analyzed and handled.Additionally,the real-time signal is displayed in the system.We can judge the state of the sensors,exchange and save the information about it.The information of four channels,which is 64 FBG sensors can be processed and displayed in this system.