2-D Statistical Damage Detection of Concrete Structures Combining Smart Piezoelectric Materials and Scanning Laser Doppler Vibrometry

In the present study a new structural health monitoring (SHM) technique isproposed as well as a new damage index based on 2-D error statistics. The proposedtechnique combines the electromechanical impedance technique (EMI) which is based onthe use of piezoelectric Lead Zirconate Titanate (PZT) patches and Scanning LaserDoppler Vibrometry (SLDV) for damage detection purposes of concrete structures andearly age monitoring. Typically the EMI technique utilizes the direct and inversepiezoelectric effect of a PZT patch attached to a host structure via an impedance analyzerthat is used for both the actuation and sensing the response of the PZT-Host structuresystem. In the proposed technique the attached PZTs are actuated via a function generatorand the PZT-Host structure response is obtained by a Scanning Laser DopplerVibrometer. Spectrums of oscillation velocity of the surface of the attached PZTs verticalto the laser beam versus frequency are obtained and are evaluated for SHM purposes.This damage detection approach also includes the use of a damage index denoted asECAR (Ellipse to Circle Area Ratio) based on 2-D error statistics and is compared to theRoot Mean Square Deviation (RMSD) damage index commonly used in SHMapplications. Experimental results include ascending uniaxial compressive load ofconcrete cubic specimens, ascending three point bending of reinforced concrete beamspecimens and early age monitoring of concrete. Results illustrate the efficiency of theproposed technique in damage detection as well as early age monitoring as, in the firstcase, both severity and location of damage can be determined by examining the values ofdamage indices for each damaged state and in the early age monitoring case damageindices follow the strength gain curve.

Integrated heterodyne laser Doppler vibrometer based on stress-optic frequency shift in silicon nitride

We demonstrate a compact heterodyne Laser Doppler Vibrometer (LDV) based on the realization of optical frequency shift in the silicon nitride photonic integration platform (TriPleX). We theoretically study, and experimentally evaluate two different photonic integrated optical frequency shifters (OFSs), utilizing serrodyne and single- sideband (SSB) modulation. Both OFSs employ stress-optic modulators (SOMs) based on the non-resonant piezoelectrical actuation of lead zirconate titanate (PZT) thin- films, deposited on top of the silicon nitride waveguides with a wafer-scale process. To improve the modulation bandwidth of the SOMs we investigate a novel configuration of the electrodes used for the actuation, where both electrodes are placed on top of the PZT layer. Using this top-top electrode configuration we report frequency shift of 100 kHz and 2.5 MHz, and suppression ratio of the unwanted sidebands of 22.1 dB and 39 dB, using the serrodyne and the SSB OFS, respectively. The best performing SOM structure induces 0.25π peak-to-peak sinusoidal phase-shift with 156 mW power dissipation at 2.5 MHz. We use the SSB-OFS in our compact LDV system to demonstrate vibration measurements in the kHz regime. The system comprises a dual-polarization coherent detector built in the PolyBoard platform, utilizing hybrid integration of InP photodiodes (PDs). High quality LDV performance with measurement of vibration frequencies up to several hundreds of kHz and displacement resolution of 10 pm are supported with our system.