Chirp Z transform based enhanced frequency resolution for depth resolvable non stationary thermal wave imaging

Area of Science:

• Non-destructive testing
• Materials science
• Signal processing

Background:

• Frequency modulated thermal wave imaging (FMTWI) is a non-destructive testing (NDT) technique.
• Enhancing depth resolution in FMTWI is crucial for accurate defect characterization.
• Current methods may have limitations in resolving defects at varying depths.

Purpose of the Study:

• To propose and validate a novel post-processing modality for FMTWI.
• To enhance the depth resolution capabilities of FMTWI.
• To compare the defect detection performance against existing techniques.

Main Methods:

• Utilized the chirp Z transform (CZT) for spectral zooming.
• Developed a novel post-processing technique based on CZT.
• Experimentally validated the method on carbon fiber reinforced plastic (CFRP) and mild steel specimens.
• Evaluated defect detection using signal-to-noise ratio (SNR).

Main Results:

• The proposed post-processing modality significantly enhances depth resolution in FMTWI.
• Spectral zooming feature of CZT effectively improves the ability to discern defects at different depths.
• Experimental validation confirmed the effectiveness on CFRP and mild steel.
• The new modality shows competitive or superior defect detection capabilities compared to other methods based on SNR.

Conclusions:

• The novel post-processing modality using chirp Z transform offers superior depth resolution for FMTWI.
• This technique provides an effective approach for enhanced defect detection in NDT applications.
• The findings contribute to advancing thermal wave imaging for material characterization.