High pressure sensing and dynamics using high speed fiber Bragg grating interrogation systems

Abstract

Fiber Bragg gratings (FBGs) are developing into useful sensing tools for measuring high pressure dynamics in extreme environments under shock loading conditions. Approaches using traditional diode array coupled FBG interrogation systems are often limited to readout speeds in the sub-MHz range. For shock wave physics, required detection speeds approaching 100 MHz are desired. We explore the use of two types of FBG sensing systems that are aimed at applying this technology as embedded high pressure probes for transient shock events. Both approaches measure time resolved spectral shifts in the return light from short (few mm long) uniform FBGs at 1550 nm. In the first approach, we use a fiber coupled spectrometer to demultiplex spectral channels into an array (up to 12) of single element InGaAs photoreceivers. By monitoring the detectors during a shock impact event with high speed recording, we are able to track the pressure induced spectral shifting in FBG down to a time resolution of 20 ns. In the second approach, developed at the Special Technologies Lab, a coherent mode-locked fiber laser is used to illuminate the FBG sensor. After the sensor, wavelength-to-time mapping is accomplished with a chromatic dispersive element, and entire spectra are sampled using a single detector at the modelocked laser repetition rate of 50 MHz. By sampling with a 12 GHz InGaAs detector, direct wavelength mapping in time is recorded, and the pressure induced FBG spectral shift is sampled at 50 MHz. Here, the sensing systems are used to monitor the spectral shifts of FBGs that are immersed into liquid water and shock compressed using explosives. In this configuration, the gratings survive to pressures approaching 50 kbar. We describe both approaches and present the measured spectral shifts from the shock experiments.

Towards traceable transient pressure metrology

“…al. [31] for poly(methyl methacrylate)-FBG (PMMA-FBG) complex indicating the response of our composite is dominated by PDMS.…”

Ultrafast Fiber Bragg Grating Interrogation for Sensing in Detonation and Shock Wave Experiments

“…Undesirable non-monotonic signal voltage versus time is observed when low amplitude shocks or pressure waves perturb, but do not destroy, the sensor [4,18,19]. Instead, the FBG sensor spectrum shifts due to the applied stress (or temperature) and renders the data extraction analysis described in the previous section inapplicable.…”

“…In some of our early experiments, we became aware of possible complications associated with the spectrally-integrated approach when shock pressures were not sufficiently high enough to destructively “process” the FBG for position information. Undesirable non-monotonic signal voltage versus time is observed when low amplitude shocks or pressure waves perturb, but do not destroy, the sensor [ 4 , 18 , 19 ]. Instead, the FBG sensor spectrum shifts due to the applied stress (or temperature) and renders the data extraction analysis described in the previous section inapplicable.…”

A Preliminary Assessment of an FBG-Based Hard Landing Monitoring System

“…Fibre Optic Sensors have proven to be a potentially excellent technique for the real-time in situ monitoring of these structures due to their numerous advantages, such as immunity to electromagnetic interference, small size, light weight, durability and high bandwidth, which allows for a great number of sensors to operate in the same system and to be integrated within the material [21]. Apart from static and quasi-static loading, FBG-based systems show in fact good potentiality for use in dynamics (very high deformation rates); interrogation systems for high speed and high strain measurements are reported in [22]. Fibre optic sensing technology for aircraft wing shape measurement has been gradually proven to be a real-time and online dynamic measurement method with many excellent characteristics [23].…”