The photothermal wave field and high-resolution photothermal pulse compression thermography for ceramic/metal composite solids

Thermal wave radar (TWR) thermography is a high-efficient nondestructive testing technique to increase the signal-to-noise ratio (SNR) and to enhance target detection capability. However, the detection of subsurface defects, especially small-size defects, usually requires a distinctively high SNR and depth resolvability. This paper proposed an orthogonal phase-coded linear frequency modulated (OPCLFM) excitation waveform, which has significantly improved the SNR and depth resolvability of TWR compared to the LFM waveform. The pulse compression quality of the OPCLFM waveform was initially evaluated through a 1D thermal wave analytical model of carbon fiber reinforced polymer (CFRP) laminate. Results show that the OPCLFM waveform combined with the Kaiser window function compresses the largest sidelobe at least by 18.39 dB compared to the LFM waveform. Furthermore, the superior depth resolvability performance of the OPCLFM waveform was also validated by 3D finite element simulation. Finally, the effect of thermal conductivity on the depth resolvability performance of the OPCLFM waveform was evaluated quantitatively by a delaminated CFRP laminate.

Advanced orthogonal frequency and phase modulated waveform for contrast-enhanced photothermal wave radar thermography

Beer's law is the foundation of the classic radiative transfer theory. Recently, many studies have pointed out the existence of non-Beerian transport behavior in spatially correlated and statistically non-homogeneous and anisotropic particulate systems. However, there still lacks a comprehensive quantitative evalution of the applicability of Beer's law in particulate medium from random to regular arrangement. In this work, a numerical approach is proposed to quantitatively analyze and determine the applicability of Beer's law in particulate systems from regular arrangement to random arrangement. A simple approach for characterizing structural randomness of particulate system is presented. The results show that the non-Beerian behaviors exist in statistically isotropic and homogeneous particulate media. The structural randomness has a significant influence on the transmission distribution and hence the applicability of Beer's law in particulate systems. Quantitative dependent relation of validity of Beer's law on structural randomness in particulate system is obtained. Both particle spacing and structural randomness have significant impact on the applicability of Beer's law. This work is helpful for the understanding of non-Beerian radiative transfer in particulate media and guiding related engineering applications of radiative transfer theory.

Applicability of Beer's law in particulate system from random to regular arrangement: A numerical evaluation

Laser-Induced Thermography: An Effective Detection Approach for Multiple-type Defects of Printed Circuit Boards (PCBs) Multilayer Complex Structure

Conjugate heat transfer analysis of laser-irradiated cylindrical-shaped biological tissue embedded with the optical inhomogeneity

The accurate description of the total diffuse-photon-density-wave field inside turbid media, especially in the near-field region, is extremely critical but challenging for many decades. Here, the total diffuse-photon-density-wave field of semi-infinite turbid media was calculated by the third-order simplified spherical harmonics approximation (SP3) and compared with Monte Carlo simulations. To improve the SP3 approximation, the extrapolated Beer–Lambert law model considering the contribution of the coherent-photon-density-wave in the near-field region was proposed and implemented by Levenberg–Marquardt and universal global optimization methods. Last, we demonstrated the superiority of the proposed model over the existing model in fitting the accuracy and applicable source–detector distance range. The high accuracy and simplicity of the proposed model would be extremely helpful for biomedical applications involving photothermal radiometry, and rapidly determining optical properties of media, along with photoacoustic imaging and photodynamic therapy.

Sheng Wang

Papers

Investigation of total diffuse-photon-density-wave field in semi-infinite turbid media based on the extrapolated Beer-Lambert law

The researches on convolutional beamforming for linear-array photoacoustic tomography