Optically Variable Characteristics Research And Automatic Identification Exploration Of Security Thread In New RMB

Because of its outstanding advantages,optically variable anti-counterfeiting technology has gradually used in currency security for the world.Since 2005,the RMB has been adopting this anti-counterfeiting technology,which is mainly reflected in the optically variable denomination numbers and optically variable security threads.Optically variable anti-counterfeiting technology is mainly divided into photochromic,polarize optically variable,diffraction optically variable and interference optically variable.And the RMB adopts the way of interference optically variable.The interference optically variable utilizes angle-dependent optical effect which reflects that different angles show different colors of optical thin film.The interference optically variable also falls into broken film-type anti-counterfeiting and whole film-type anti-counterfeiting.Broken film-type anti-counterfeiting means that crushing the optical thin film and mix it with ink to be optically variable ink,and an example is the denomination of RMB released in 2005.Whole film-type anti-counterfeiting is a pattern that plate the optical thin film on a PET substrate first and then gravure it on the currency.The representative is the optically variable security threads of RMB in 2015.As a "first-line security" technology,optically variable anti-counterfeiting feature is easy to be recognized by the eyes.But,it is not simple for the machine.For the detection of optically variable anti-counterfeiting feature,ATM adopts the real-time image recognition technology which just identifies the shape and size of optically variable pattern.There are patents point out that employs both vertical color sensor and tilt color sensor to detect the color difference between different angles.There is also a way of using camera or image sensor to scan optical images.These methods above are costly and difficult to implement.In this paper,we deeply researched the optically variable characteristics of security threads in new version 100 RMB,and proposed a simple and fast automatic identification method to detect it.In the paper,according to the color-shifting principle of optical thin film,we researched the security thread and fabricated the optically variable security thread thin-film.We measured the reflectance spectrum of optically variable security thread using a spectrophotometer firstly,and then design the film structure of air/Cr/Si02/Al/PET according to actual spectrum.In the last,with the electron beam vacuum deposition technique to deposit the color film and compare it with the actual security thread.With the reflection spectrum of security thread,we proposed a detection method which makes the laser as the light source and makes the light intensity as the received signal.In this method,we irradiated the security thread at 55°and 15° angle with 532nm laser and 650nm laser.And through collecting the reflected intensity and comparing the difference between real currency and counterfeit currency to complete recognition.The experiment verifies the correctness of the theory and the feasibility of the method by constructing the optical path system.On the basis of experiment,we designed the detection device and set up detection system to detect the real currency and counterfeit currency.Detection system required the result that the voltage of real currency is about 4V and the voltage of counterfeit currency is about 0.5V.The obvious difference proves the reliability of the detection system.