I used to work airport/industrial security for a Walk through metal detector company....travelled to nuclear power plants, prisons-max security wards inside with the inmates, airport checkpoints, industrial plants, coin counting centers, the like.....
I can say with fair authority there are only two ways to detect guns/weapons, with any walk through metal detector, which is why the full body X ray machines are now used a lot, and will become universal....
the metal detectors for typical airport/industrial use will not stay stable enough if using RF tuning/balanced circuits as outside EMI is too great, the units will false alarm something fierce, and if desensitized enough would not pick up the FAA standard of the times.....a 4" long 1/2 inch long steel rod....
simulating a gun barrel or frame or slide....if taken apart....
now there is yet another way these things work....that is the pulse field method....differant metals have wildly differant signatures when subjected to pulse field magnetics.....turn on a magnetic coil with DC .....hit the transmit, energise the coil, ramp the current up to your required/legal limit, then turn it off, if the coil is 'critically damped' the ring in the counter wound balanced receiver coils is nearly nil......you EE's can imagine this....one coil is 7' long as the transmitter on one side of the archway....the other is the receiver on the other side with two 7' long 8" wide coils, they are faraday shielded and counter wound so the two coils are bucking each other from the pattern of the transmitter, their position being nearly symmetrical in the unit...one side to another....so what happens is when a piece of moving metal passes through the machine, one side sends off a stronger signal, then the other side sends off the same signal in the opposite polarity....
this is used as a additive pulse by electronic signal processing....so your final output through a lo pass filter is about a ten hertz rolloff to catch a tossed weapon.....buddy system...
now there is one achilles heal to this system, of course, and at one point it was a 'national security' issue, so this was .gov and house knowledge .....
ONE of the stainless type series was not visible through pulse field machines.....3 series of stainless are common enough.....300-400-500, I know 400 is super easy to see and so is one of the other types.....but I fortget if it's 300 or 500 that is impossible to see with a pulse field detector....RF can see it fine....but it's too unstable for typical EMI laden installations and airports are certainly THAT......
SO the folks to find that out were, of course...PRISONERS......no one ever thought of it, but certain types of KITCHEN stainless metals were not seen and of course used as weapons in prisons.....nothing to keep a company from making guns from it....but by Federal law or just demands, under wraps to the manufacturers they never used that stainless....
NOW, with all that knowledgte I can assure you that various other metals give off signals that are longer lasting and stronger than steel, but the signature of decay from induced eddy currents are far different, but depending on orientation in the arch, size, composition, they can induce a signature pattern enough to false trigger even our discrimination filtering.....
I can say this, trying to watch a one hz signal on a scope can get blinding....do it enough and you go crazy.....
a normal person takes about 3 seconds to clear the archway, a crook with a buddy can flip a gun through in ONE second....that was the standard.....one second to see the gun/metal......:hunter::hunter::hunter:
SO to the extent they still use 'magnetometers' for airport security, I can make a gun and walk through it with a full loaded .44 and not set it off....
:hi:
