metal detector knows how much cash is in your wallet
Jacob Aron has long had an urban legend that the security bars found in American banknotes have allowed shady government agencies to use metal detectors to track how much cash you carry.
Although these straps are made of plastic, the legend is so common that it used to be in the TV series X-Files.
Now it seems that conspiracy theory may be half-half;
Concealed banknotes printed in magnetic ink can be detected and counted.
Vending machines have used these inks to verify the authenticity of individual notes, but physicists Christopher Fuller and Chen Antao at the University of Washington in Seattle realize that a large number of notes will contain enough magnetic material, it can be detected in the distance and may allow police to catch people trying to smuggle cash at the border.
A large bundle of banknotes contains enough magnetic material to be detected in the distance. They found an ordinary hand-held metal detector capable of picking up a dollar note from 3 cm away and placing the note behind the plastic, cardboard and cloth with little blocking signal.
Add more dollar bills;
5 increments increase the intensity of the signal, making it possible to calculate the number of bills, although it will be difficult to convert it into actual dollar value due to the fact that banknotes of different denominations contain the same amount of magnetic ink.
The use of larger metal detectors, such as metal detectors found at airports, should also increase the sensing range, although it would be more tricky to detect banknotes in this case, as many other sources may interfere with the signal.
\"In practice, the signal will be noisy and may require some kind of digital signal processing,\" Chen said . \".
\"The published results come from feasibility studies and require a lot of development work to be achieved.
\"He will introduce the work at the defense, security and sensing conference in Baltimore, Maryland next month.
Markus Kuhn, a computer scientist at the University of Cambridge, said the test was a \"good idea \", but metal detectors may react similarly to other magnetic objects found in luggage, laptop power cords, etc.
He suggested adding equipment to the detector to receive other aspects of the signal, such as timing, would allow for more detailed analysis.