Money Controls, UK

Tom Shelley reports for Eureka on counterfeit detection for modern currency and coins.

...The infrared is crucial, because many notes employ areas that absorb infra red light, instead of reflecting it, in order to easily distinguish genuine notes from photocopies. A side benefit apparently of particular interest to casino owners is that images of notes can be retained, so that if a gambler believes he or she has not been credited with the correct denomination, the image of the last note can be instantly displayed...

Positions of coins in the machines are located optically, but surfaces and the constructions of the coins are examined by pairs of coils on each side of the coin – five each, in most of the company’s machines, running at a range of frequencies and phase relationships.... Forged one-pound coins, in one well established example in wide circulation, are made of white metal, sprayed gold, which reproduces the electrical behaviour of genuine coins. So accepting equipment strikes them against a piezo device, mounted on a special anvil...