Increasing signal amplitude in fiber Bragg grating detection of Lamb waves using remote bonding

Abstract

Networks of fiber Bragg grating (FBG) sensors can serve as structural health monitoring systems for large-scale structures based on the collection of ultrasonic waves. The demodulation of structural Lamb waves using FBG sensors requires a high signal-to-noise ratio because the Lamb waves are of low amplitudes. This paper compares the signal transfer amplitudes between two adhesive mounting configurations for an FBG to detect Lamb waves propagating in an aluminum plate: a directly bonded FBG and a remotely bonded FBG. In the directly bonded FBG case, the Lamb waves create in-plane and out-of-plane displacements, which are transferred through the adhesive bond and detected by the FBG sensor. In the remotely bonded FBG case, the Lamb waves are converted into longitudinal and flexural traveling waves in the optical fiber at the adhesive bond, which propagate through the optical fiber and are detected by the FBG sensor. A theoretical prediction of overall signal attenuation also is performed, which is the combination of material attenuation in the plate and optical fiber and attenuation due to wave spreading in the plate. The experimental results demonstrate that remote bonding of the FBG significantly increases the signal amplitude measured by the FBG.

Pressure Sensitive Adhesive Tape: A Versatile Material Platform for Optical Sensors

“…This produces a shift in the Bragg wavelength, which is related to variations in the fiber strain. A relevant application of these optical strain sensors is structural health monitoring based on the collection of ultrasonic waves [ 101 , 102 , 103 , 104 ]. For this purpose, adhesives are typically used for bonding the strain measuring fiber and the host structure in order to assure permanent mechanical coupling between both elements, thus avoiding losses due to sliding.…”

“…For this purpose, adhesives are typically used for bonding the strain measuring fiber and the host structure in order to assure permanent mechanical coupling between both elements, thus avoiding losses due to sliding. The adhesive not only provides fixing but also plays a key role in the sensor performance since longitudinal and transverse displacements at the surface produced by Lamb waves in the structure are transferred to the optical fiber through the adhesive, leading to axial strain along the FBG optical fiber axis [ 102 , 103 ]. In particular, the symmetric S0 or antisymmetric A0 Lamb waves are coupled to guided L01 waves in an optical fiber at the adhesive bond location, resulting in L01 modes of equal amplitudes propagating in both directions along the optical fiber.…”

Ultrasonic Structural Health Monitoring Using Fiber Bragg Grating

“…Wee et al researched the sensitivity of the remote sensing structure by considering the wave attenuation [ 97 ] and then indicated that ultrasonic waves can propagate both forward and backward along an optical fiber [ 98 ]. Furthermore, Yu et al performed simulations to clarify how the adhesive length in the remote sensing configuration influenced ultrasonic detection [ 99 ].…”

Fiber Bragg Grating Sensors for the Oil Industry

“…In these sensors, the detection of vibration information is achieved through the wavelength interrogation of FBGs. Of course, the intensity of reflection spectrum can also be used to monitor vibration by employing side-band filtering techniques [97,98,99]. These sensors provide high dynamic strain sensitivity and realize the compensation of temperature over a full range.…”