The United States Federal Reserve began circulating a new $100 bill yesterday.The redesigned bill was supposed to be released in 2011 but was delayed due to a printing error that cost the US Bureau of Engraving and Printing $3.8 million.Woven into the new bill is a 3D security ribbon and images of bells that, when tilted, change to 100s.A copper inkwell with a copper bell inside it is another feature designed to make the $100 bill “easier to authenticate, but harder to replicate”, said US Federal Reserve Board Governor Jerome H Powell.The bell inside the inkwell changes colours when tilted, allowing “the public to more easily verify its authenticity”, he said.The $100 note presents a unique issue for the US Federal Reserve as it is the most counterfeited US note, according to Lones Smith, an economist at the University of Wisconsin-Madison who has studied counterfeiting.Although people are legally obliged to turn in a fake note, without a refund there is no incentive, and people are more likely to just pass it on, he said.Although the proportion of counterfeit notes in circulation is minuscule, the US Federal Reserve needs to do whatever it can to make the job hard for counterfeiters, said Ed Nosal, vice President and senior research advisor at the Federal Reserve Bank of Chicago.