![]() In 20, a liquid crystal display projector served as an optical heat source for AT pixel-wise structured heating. A laser beam was split into two coherent beams, and their interference in a specimen was exploited to obtain the depth information of features. Structured heating is another method for accounting for lateral heat flow, which was first implemented in 19. In the third part, the numerical results are validated using experimental data.įor a temperature gradient, \(\nabla T\), heat flows from the warm location to the cold location according to Fourier’s law, \(\dot\) (1), at the surface for a heat-generated delta source at depth d based on the equation for the optical Abbe diffraction is described in 18 and depends not on the thermal properties of the specimen, but on the geometrical properties and the signal-to-noise ratio (SNR). In the second part, the numerical limitations of the method are described regarding the blind frequency (BF) shift, feature detection, depth range, feature separation, and lateral resolution. The first part explains the basics of the lock-in thermography compensation method (LTC). The paper is divided into three sections. Furthermore, the edge sharpness and separability of features are improved, ultimately improving the feature-detection efficiency. The proposed compensation method can bypass the blind frequency of LT and make the inspection largely independent of the excitation frequency. The vanishing lateral gradients convert the problem into a 1D problem, which can be adequately solved by the LT approach. Herein, we present a method for reducing the local temperature gradients at feature areas and minimizing the induced lateral heat flux in optical lock-in thermography (LT) measurements through spatial- and temporal-structured heating. Most AT evaluation methods are based on 1D approaches, and measured 3D heat fluxes are frequently not considered, which is why edges, small features, or gradients are often blurred. In contrast to sound or light waves, thermal waves are lossy consequently, it is difficult to interpret measured 2D temperature fields. Active thermography (AT) exploits such differences to gain information on the internal structure, morphology, or geometry of technical components or biological specimens. Heat flux hyperbolic heat conduction inverse problem multilayer tissue.The naturally diffusive heat flow in solids often results in differences in surface temperatures. Results show that an excellent estimation on the time-dependent surface heat flux can be obtained for the test cases considered in this study. The influence of measurement errors on the precision of the estimated results is also investigated. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The inverse solutions will be justified based on the numerical experiments in which two different heat flux distributions are to be determined. The concept of finite heat propagation velocity is applied to the modeling of the bioheat transfer problem. Subsequently, the temperature distributions in the tissue can be calculated as well. In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to solve the inverse hyperbolic heat conduction problem in estimating the unknown time-dependent surface heat flux in a skin tissue, which is stratified into epidermis, dermis, and subcutaneous layers, from the temperature measurements taken within the medium.
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