To meet the requirements for medium-high frequency vibration monitoring, a new type fiber Bragg grating (FBG) accelerometer with an integrative matrix structure is proposed. Two symmetrical flexible gemels are used as elastic elements, which drive respective inertial mass moving reversely when exciting vibration exists, leading to doubling the wavelength shift of the FBG. The mechanics model and a numerical method are presented in this paper, by which the influence of the structural parameters on the sensitivity and eigenfrequency is discussed. Sensitivity higher than 200 pm/g and an eigenfrequency larger than 3000 Hz can be realized separately, but both cannot be achieved simultaneously. Aiming for a broader measuring frequency range, a prototype accelerometer with an eigenfrequency near 3000 Hz is designed, and results from a shake table test are also demonstrated.
A novel (to our knowledge) 3D microstructure manufactured by a femtosecond laser in fiber Bragg grating (FBG) fiber cladding is proposed. The special spiral parameters including single thread and double thread with certain pitches of 60 and 80 μm are controlled by the feed and rotation speed of a rotary fixture. Moreover, supermagnetostrictive TbDyFe film with a thickness of nearly 6 μm is deposited on microgrooves of a FBG by magnetron sputtering technology to form the magnetic field sensing probe. Experimental results demonstrate that a FBG with a double-thread microstructure has a sensitivity of 1.1 pm/mT responding to a magnetic field, and in a theoretical situation, it is approximately six times higher than the original optical fiber grating (approximately 0.2 pm/mT). This new microstructure and method show great prospect in the magnetic field sensing domain.
Different novel kinds of 3D microstructure manufactured in the cladding of FBG are proposed. Femtosecond laser and special rotary are used to fabricate microstructure such as single thread, double thread and annulus. The thread pitch is 60μm, 80μm controlled by feed and rotary speed. In addition, a thickness of 300nm copper film is coated in the microgrooves by magnetron sputtering technology. Temperature experiment has also been set up and done. Experiment result shows that the FBG sensor with double thread of 80μm is the most sensitive one responding to temperature change. It is approximately five times higher than the standard FBG sensor .This new type of FBG sensor shows great prospect in temperature sensing. 1.INTRODUCTIONSince professor K.O. Hill developed the first optical fiber Bragg grating by inserting standing wave in optical fiber in1978 1 . Optical fiber sensing technology has attracted many research interest and attention for its superior characteristics over the common optical fiber such as immunity to electromagnetic radiation, resistance to chemical corrosion, small size, high accuracy, and capability of remote operation 2-3 . On the other hand, laser ablation is a promising technique for improving fabrication efficiency and it is a promising tool for many hard and brittle materials due to its high peak power, short pulse and other excellent properties. This unique properties have attracted lots of people to study laser processing for transparent materials 4-5 . As for temperature FBG sensor. In 1989,W. W. Morey and his team obtained the result of FBG's sensitivity responding to temperature, it was about 1.1× 10 -3 nm/ . It was the first time that FBG's temperature sensing was studied. Ever since, researchers and scholars began to think of different ways to improve FBG's sensitivity to temperature. Jia Zhen'an and Guan Bo'ou used high thermal expansion coefficient polymeride to fix FBG, and thus the sensitivity of temperature improved by sixteen times. On the other hand ,more and more temperature sensor began to have more parameters responding to temperature. In 2001 ,X. Y.Dong fixed FBG at the junction between fixed point A and beam B, when the cantilever beam was affected, the strain and temperature coefficient was changed, and thus the value of temperature and strain could be detected 6-7 .In this paper, 3D microstructure is proposed and manufactured on FBG by femtosecond laser. In addition, copper thin film (300nm thickness) is also sputtered in the microgrooves of cladding. With the combination of these two technologies, the temperature sensing probe is successfully developed and experimental results show great high sensitivity in detecting temperature change. Because of its miniature size, easy fabrication, convenient operation and repeatable testing, this new method shows great potential for future temperature sensing. 2.THEORY BACKGROUND AND PROPOSED MICROSTRUCTUREWhen light source from outside pass through the fiber Bragg grating, it will generate different phenomenon, such as reflection...
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