13411 Thermal Imaging

The thermal imaging method, recently advanced through new high-performance focal-plane array detectors, is based on the early work of Parker et al. [55]. This method assumes that the front surface of the sample is heated instantaneously. The rate of heat conduction through the sample is related to the thermal diffusiv-ity of the material and is determined by measuring the rate of temperature rise at the back surface. Figure 13.25 shows a theoretically predicted back-surface temperature T as a function of time t and specimen thickness L, where TM is the maximum back-surface temperature. One method to determine the thermal diffusivity is the "half-rise-time" (T1/2) method [51]. When the back-surface temperature rise has reached half of its maximum, that is, T/ TM = 0.5, thermal diffusivity, a, can be determined as a = 1.37L2/n2t1/2. The accuracy of the

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