In this paper, we propose techniques to design and fabricate polymer micro-cantilevers for attachment onto the end of standard single mode fibers using laser machining. The polymer cantilever is fabricated by laser micro-machining a sheet of polymer into the required shape and then bonded onto the top of a ceramic ferrule by photo resist as a flat supporting and bonding layer. The dimension of resulting cantilever is ~1.2 mm long, ~300 μm wide, and 25 μm thick. In this work we describe the fabrication of single sensors, however the process could be scaled to offer a route towards mass production. Cantilever vibration caused by vibration signal are monitored by a DFB laser based phase interrogation system. Proof-of-concept experiments show that the sensor is capable of detecting vibration signal with a frequency range of 0-800Hz. By using thinner polymer sheet and machining longer cantilever, the frequency response range can be extended up to a few kHz.
Optical fiber Bragg grating (FBG) displacement sensors play an important role in various areas due to the high
sensitivity to displacement. However, it becomes a serious problem of FBG cross-sensitivity of temperature and
displacement in applications with FBG displacement sensing. This paper presents a method of temperature insensitive
measurement of displacement via using an appropriate layout of the sensor. A displacement sensor is constructed with
two FBGs mounted on the opposite surface of a cantilever beam. The wavelengths of the FBGs shift with a horizontal
direction displacement acting on the cantilever beam. Displacement measurement can be achieved by demodulating the
wavelengths difference of the two FBGs. In this case, the difference of the two FBGs’ wavelengths can be taken in order
to compensate for the temperature effects. Four cantilever beams with different shapes are designed and the FBG strain
distribution is quite different from each other. The deformation and strain distribution of cantilever beams are simulated
by using finite element analysis, which is used to optimize the layout of the FBG displacement sensor. Experimental
results show that an obvious increase in the sensitivity of this change on the displacement is obtained while temperature
dependence greatly reduced. A change in the wavelength can be found with the increase of displacement from 0 to
10mm for a cantilever beam. The physical size of the FBG displacement sensor head can be adjusted to meet the need of
different applications, such as structure health monitoring, smart material sensing, aerospace, etc.
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