Vibro-Thermal Wave Radar: Application of Barker coded amplitude modulation for enhanced low-power vibrothermographic inspection of composites

TL;DR

This paper introduces Vibro-Thermal Wave Radar (VTWR), a low-power, Barker coded amplitude modulation technique that enhances the depth resolution and defect detection in composite materials compared to traditional methods.

Contribution

It presents a novel VTWR method using Barker coding and matched filtering, demonstrating improved defect resolution and depth imaging in composites at low power levels.

Findings

VTWR outperforms classical lock-in vibrothermography in defect detection.

Barker coding enhances probing depth and defect resolution.

Successful experimental demonstration on carbon fiber composite with deep delamination detection.

Abstract

This paper investigates the performance of the thermal wave radar imaging technique in low-power vibrothermography, so-called vibro-thermal wave radar (VTWR), for non-destructive inspection of composites. VTWR is applied by binary phase modulation of the vibrational excitation using a 5 bit Barker coded waveform, followed by matched filtering of the thermal response. The depth resolvability of VTWR is analyzed by a 1D analytical formulation in which defects are modeled as subsurface heating sources. The obtained results reveal the outperformance of VTWR compared to the classical lock-in vibrothermography (LVT), i.e. a sinusoidal amplitude modulation. Furthermore, the VTWR technique is experimentally demonstrated on a 5.5 mm thick carbon fiber reinforced polymer coupon with barely visible impact damage. A local defect resonance frequency of a backside delamination is selected as the vibrational carrier frequency. This allows for implementing VTWR in the low-power regime (input power < 1 Watt). It is shown that the Barker coded amplitude modulation and the resultant pulse compression efficiency lead to an increased probing depth, and can fully resolve the deep backside delamination. It is also shown that VTWR approach allows depth-selective imaging of defects through the lag of the compressed pulse.