Vibration and Shape Control in Opto-mechanical Systems Using Distributed Fiber-optic Bragg Grating Sensors

Abstract

High-precision opto-mechanical systems are characterized by significant interactions between structural dynamics and optics. Novel sensing techniques for the vibration and shape control of such structures are investigated. Owing to the number of necessary sensors and the required precision, fiber-optic Bragg grating (FBG) sensors could be an attractive option for this task. They allow the simultaneous measurement of strain at many locations in a structure. Many FBG sensor systems provide high precision, but their delay time and maximum acquisition frequency makes them difficult to use for vibration control purposes. Therefore, a novel multi-channel FBG sensor system was developed using a position sensitive detector for the wavelength interrogation which has much less delay time than a charge coupled device-based system and a theoretical maximum bandwidth of over 300 kHz. This system was tested for high-precision static strain measurements for shape control applications at low frequencies in an experimental test rig ( < 0 .3 μm/m) as well as for high-frequency strain measurements of more than 10 kHz. Its application potential for shape and vibration control application was demonstrated experimentally as well as its applicability to modal analysis. This could be an interesting alternative to the use of piezo-strain sensors in structural control applications where high frequencies are needed, as well as an alternative for shape control where high-resolution strain measurements are desirable.

Strain Measurement in Aluminium Alloy during the Solidification Process Using Embedded Fibre Bragg Gratings

“…Based on the linear relation between the fibre length and the modification of the grating period, the term $\delta \mathsf{\Lambda }/\mathsf{\Lambda }$ passes over to $\delta ϵ$. Equation (2) simplifies to [23,24]: $\frac{\mathsf{\Delta }{\lambda }_b}{{\lambda }_b}=(1-P)\mathsf{\Delta }ϵ$ where P = $\frac{1}{2}{n}_{eff}^2(p_{12}-\nu (p_{11}+p_{12}))$ and is called the photoelastic coefficient. This coefficient depends on Pockel’s coefficients $p_{11}$ and $p_{12}$ and on the Poisson number ν .…”

Theoretical Assessment of an All-Optical Temporal Low-Pass Filter for Dynamic Fiber Bragg Grating Signals

“…As expected, the amplitude of the FBG COG trend rapidly decreases for high signal frequencies. Figure 5: Calculated transfer functions for the proposed system with different configurations according to (10). An increasing low-pass behaviour for increasing decay times of the luminescent material is observable.…”

“…Currently, there is an increasing interest in the application of FBG sensors for the acquisition of dynamic loads [6]. Among those dynamic quantities to be measured are accelerations [7,8], lamb wave propagation in composite structures [9], dynamic structural shape monitoring [10], and so forth. In general, the acquisition of dynamic loads requires a low-pass filtering of the signal before quantization and sampling.…”

Tapered Polymer Fiber Sensors for Reinforced Concrete Beam Vibration Detection

“…However, a multichannel FBG sensor system was proposed by Mueller et al using a position-sensitive detector for wavelength interrogation [17]. A theoretical maximum bandwidth of over 300 kHz was achieved by using this approach, which is much higher than other systems.…”