Logarithmic Frequency Modulated Thermal Wave Imaging for Subsurface Analysis

Abstract

Capturing the spatio temporal radiation in the infrared portion of the spectrum from any object renders the temperature evolution of it and culminates in presenting the information about the hidden subsurface anomalies within the object. However deeper depth scanning and higher depth resolution with enhanced subsurface visualization are the significant challenges generally encountered in these studies that demands various stimulation and processing mechanism to explore these details. This manuscript introduces a novel log frequency modulation-based stimulation along with various post-processing approaches that caters to these requirements. This modality facilitates a band of low frequencies with increased energy in the stimulus for deeper depth scanning and spectral processing approaches to provide enhanced depth resolution in a single experimentation cycle. The hypothesis is validated through the experimentation carried out over a carbon fiber-reinforced plastic specimen with embedded flat bottom holes. A qualitative comparison between various signal processing approaches using thermographic metrics like the sizing of the defects and signal-to-noise ratio recommends the superiority of proposed stimulation and processing techniques for enhanced defect detection.