Burgholzer Peter, Hendorfer Günther
Christian Doppler Laboratory for Photoacoustic Imaging and Laser Ultrasonics, Research Center for Non Destructive Testing GmbH (RECENDT), Altenberger Strasse 69, 4040 Linz, Austria.
FHOOE Forschungs & Entwicklungs GmbH, Stelzhamerstr. 23, 4600 Wels, Austria.
Int J Thermophys. 2013;34(8):1617-1632. doi: 10.1007/s10765-013-1513-0. Epub 2013 Oct 2.
In this work the measured variable, such as temperature, is a random variable showing fluctuations. The loss of information caused by diffusion waves in non-destructive testing can be described by stochastic processes. In non-destructive imaging, the information about the spatial pattern of a samples interior has to be transferred to the sample surface by certain waves, e.g., thermal waves. At the sample surface these waves can be detected and the interior structure is reconstructed from the measured signals. The amount of information about the interior of the sample, which can be gained from the detected waves on the sample surface, is essentially influenced by the propagation from its excitation to the surface. Diffusion causes entropy production and information loss for the propagating waves. Mandelis has developed a unifying framework for treating diverse diffusion-related periodic phenomena under the global mathematical label of diffusion-wave fields, such as thermal waves. Thermography uses the time-dependent diffusion of heat (either pulsed or modulated periodically) which goes along with entropy production and a loss of information. Several attempts have been made to compensate for this diffusive effect to get a higher resolution for the reconstructed images of the samples interior. In this work it is shown that fluctuations limit this compensation. Therefore, the spatial resolution for non-destructive imaging at a certain depth is also limited by theory.
在这项工作中，诸如温度等测量变量是呈现波动的随机变量。无损检测中扩散波导致的信息损失可以用随机过程来描述。在无损成像中，关于样品内部空间模式的信息必须通过某些波，例如热波，传递到样品表面。在样品表面可以检测到这些波，并根据测量信号重建内部结构。从样品表面检测到的波中能够获取的关于样品内部的信息量，本质上受到从其激发到表面传播过程的影响。扩散会导致传播波的熵产生和信息损失。曼德利斯已经建立了一个统一框架，用于处理在扩散波场这一全局数学标签下的各种与扩散相关的周期性现象，比如热波。热成像利用热（脉冲式或周期性调制）随时间的扩散，这伴随着熵产生和信息损失。已经进行了几次尝试来补偿这种扩散效应，以获得样品内部重建图像的更高分辨率。在这项工作中表明，波动限制了这种补偿。因此，在一定深度下无损成像的空间分辨率在理论上也是有限的。
