The reflected wave interferes with the surface wave, producing an oscillating interference pattern, which can be measured in terms of amplitude, or phase angle, that, respectively, produces amplitude, or phase, images. The depth range for the amplitude image is given by �� which is calculated from the thermal diffusivity �� and the wave frequency f = ��/2�� as follows:��=����f.(2)The maximum depth selleck catalog p, which can be reached for the phase image, corresponds to 1.8�� [16�C19]. The material thickness, which can be inspected, depends on the wave period (the longer the period, the deeper the penetration) and on the material properties (e.g., thermal diffusivity).2.3. Infrared CamerasDifferent infrared cameras by FLIR systems are used which include either high performance cooled detector cameras, which are suitable for the research field, or handheld cameras that are more appropriate for in situ inspections.
All the handheld cameras are equipped with microbolometer detectors working in the long wave infrared band generally from 8 up to 12 microns. They differentiate for thermal sensitivity and mainly for spatial resolution. In particular, the B4 and B360 have both 320 �� 240 pixels, but the B360 offers the advantage of a more ergonomic configuration with the possibility to rotate the lens and take images also in presence of problematical optical access. Of the same ergonomic configuration but of better resolution is the T640 which has 640 �� 480 pixels; the same number of pixels both P640 and P660 also have, the latter being an upgrade of the P640 with obviously a better performance.
As a general characteristic, for all the new generation handheld cameras, images are stored on flash memory cards. The cooled detector cameras used by the author for architectural applications include four cameras. Two cameras, equipped with a single MCT detector working in the 8�C12 microns and cooled with liquid nitrogen, are the Agema 880 of 140 �� 140 pixels and digitalization at 8 bits and the Agema 900 of 272 �� 136 pixels and digitalization at 12 bits. Two cameras, including FPA QWIP second generation sensors working in the 8-9 microns with Stirling cooler, are the SC3000 of 320 �� 240 pixels and the SC6000 of 640 �� 512 pixels (FLIR systems). Herein, only some peculiar results obtained by either uncooled or cooled detector cameras are shown as examples.3.
Tests and Data Analysis Tests were carried out partly in laboratory to assess testing procedures and data analysis and partly in situ including either civil habitations or archaeological sites as well as works of art. 3.1. Laboratory TestsLaboratory tests are carried out by considering two types of specimens which simulate one- and two-layer GSK-3 structures, with defects of different geometry and nature, located at different depths .