Skin depth shallow

To reduce conductor loss in high frequency ranges, it is necessary to take an proach that reduces conductor resistance to the minimum (refer to Chapter 1). Since the inductance of the conductor inside increases at high frequencies, current flows only near the surface of the conductor layer. The thickness of the area where the current flows is called skin depth. Figure 10-1 shows the relationship between the frequency of each type of conductor and the skin depth. The relationship with skin depth ( ) is in accordance with the formula below, and there is a tendency for the skin depth to become shallower as the frequency increases with materials that are not magnetized. 

Shallow-dose equivalent (Us), which applies to the external exposure of the skin or an extremity, is the dose equivalent at a tissue depth of 0.007 cm (7 mg/cm2) averaged over an area of 1 cm2. 

PA-FTIR depth profiling results are consistent with the known layer stmcture of a packaging laminate film and an adhesive label [477]. Doublelayered PET/PET, PP/PET and PET/PP laminates were studied by PA-FTIR [478]. PA-FTIR and DSC identified a skin layer and a core in injection moulded PET plates [479]. Plastic-coated paper was analysed by both PA-FTIR and DRIFTS allowing for shallow- and deep-sampling, respectively [453]. PA-FTIR is also a suitable tool for the analysis of polymer films used as a barrier coating on beverage and food containers at variance to specular reflectance measurements surface flatness is not critical. 

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