Various images seen with different wavelength lights.
Banknotes have different security features which can be detected at a specific frequency light. Banknote counters emit 3 kinds of light and analyze the reflected or penetrated images to very quickly (within 0.001 sec) decide whether it is genuine or counterfeit notes.
Visible Light Sensor sees the banknote images just like our eyes look at something.
This image is usually used to determine its denomination, capture its serial number and detect fake note.
IR (Infra Red) Light Sensor sees the banknote images with low frequency light.
Different from visible light, which uses only reflected images, IR light is used to acquire both reflected and penetrated images.
UV (Ultra Violet) Light Sensor sees the banknote images with high frequency light.
Usually banknotes do not reflect any UV light whereas commonly used photocopied counterfeits reflect UV light.
Both reflected and penetrated images are used.
Banknote has magnetic material. Magnetic sensor captures magnetic field for the analysis.
Some machines use single channel magnetic sensor which is called "MR Header". Because of its low SNR (Signal to Noise Ratio: if low, signal gets very weak and can miss small signal) and low resolution (only 1 channel), MR Header is not a good solution for high-end banknote counter/fitness sorter. Its low sensitivity comes from its underlying technology (faraday effect, in which signal depends on the moving speed of magnetic material)
On contrary, MR Sensor can provide better SNR and high resolution. Higher resolution of MR Sensor comes from its underlying technology (hall effect, in which signal does NOT depend on the moving speed of magnetic material). MR Sensor has 6~7 times higher resolution than MR Header, which means that banknote counter with MR sensor can analyze magnetic signal of banknote 6~7 times more precisely than those with MR header.
Because of its poor performance, banknote counter with MR Header has difficulty in passing strict technical test.
MR Header has only one channel information of magnetic signal, whereas MR Sensor has 8~10 channels. With additional channels (a.k.a. resolution), MR sensor can analyze magnetic signal of banknotes more precisely.
MR Sensor is flat and has no rectangular area in the middle, whereas MR Header has it.
Thickness of the banknote is also measured to check whether there is transparent tape on the banknote. There are two kinds of the thickness sensor: Ultra Sonic and Mechanical method.
Ultra Sonic is quiet but tape detection rate is low and sensitive to ambient change.
Mechanical method is more noisy but tape detection rate is higher and insensitive to ambient change.
banknote with transparent scotch tape on
Test Result of various machines' tape detection capability.
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