Originally Posted by
linsj
Not all underwire bras set off the metal detector. I've been wearing Balis and Playtex for decades with no alarm.
Never had a problem with Victoria's Secret (C/D cup depending on style). I can imagine there are sizes which would have significantly more metal...
My mother's
favored bra provides massive support with huge bands of elastic rather than underwires. (I'm not sure this link is her exact bra, but the concept is the same...) I know it is a PITA to pick a new bra to accommodate the TSA, but perhaps it's the lesser of two evils.
Originally Posted by
Flaflyer
Since it works on magnetic fields, ferrous
should set it off more than nickel/stainless which are slightly magnetic more than brass/copper/gold. However I have learned the hard way that the 1 by 1 inch foil seal on a single Benedryl blister pack tab will set it off. The foil appears to be aluminum but the WTMD is real sensitive to it.
Metal detectors use an AC current to induce another current (an eddy current) on the surface of the metal object. The magnetometer then detects the phase lag of the induced current. So alarming a WTMD has just as much to do with the
conductivity of the metal as its inherent magnetic properties.
In addition to aluminum being a great conductor, the foil you mentioned is very thin. It's almost all surface area and very little thickness. This can actually increase the intensity of the signal. This phenomenon can be used to monitor, for example, the
thickness of the aluminum skin on an airplane.