AM-FM image of a commercial coffee packaging bag. A piece of the bag was first coated with a thin layer (about 0.5 mm) of epoxy and the cross-section was cut with a Leica microtome at -160°C, 1 mm/sec with a diamond knife. The bright yellow band shows the aluminum layer attached to two vapor barrier layers (orange layers) by a ?tie? layer (dark purple). The resonance frequency shifts range ~2 kHz around the second mode resonance of ~1.8 MHz. 30 µm scan.