hypothetically, how can I defeat them ?
put your aluminium bag inside a steel box. Then they will only detect the steel.
In principle, you could make an active device with thousands of small antennas or magnetic coils that would nullify the detection field like noise cancelling headphones, but good luck with that. It's probably beyond current technology and you have a boatload of electronics and wires instead of a regular case.
In two words, "You can't!"
Of course, if you can keep it far enough away from the detector so it's out of range for the detector, but I'm sure you know that. You don't state the conditions and circumstances of your question. Are you talking about something you have to walk through like airport security, or walking down the street with a metal bag, and from what distance to the detector? If you are trying to use it to hide something from a store security gate, forget it!
A detector will sense a block of metal before it will sense a small piece of thin aluminum foil, but either way, if it's close enough, it will sense it no matter the size or thickness of the metal.
Make a portable oscillator generates the same frequency like the metal detector does. It will fool the detector.
Ask the FBI when they arrive. Sorry I couldn't resist.
If I am carrying an aluminium bag. and someone is using a detector
hypothetically, how can I defeat them ?
