Passive Optical Card of High Storage Capacity Readable by Smartphone Optically
optical card of storage capacity higher than barcode and QR cod, passive(no electronics nor magnetics )made of general purpose material, readable optically by smartphone camera or special reader
The card is covered with an array of dots made from a transparent material of known refraction index. A ray of visible light is reflected from the surface of each dot while a part of the ray is refracted and then reflected from the inside surface beneath the dot. The two reflected rays interfere constructively or destructively or in between because of the path difference between them and produce a point image of intensity depending on the thickness of the dot. A thickness of lambda/2 (lambda=wavelength of the light) produces constructive interference (logic level 1), while lambda/4 produces destructive interference (Level 0). An array of these 2 thicknesses produces 1bit per dot. If we have thicknesses from the sset of lambda/2N, this produces N levels - log2N bits.
The camera (or reader) image pixels are scanned and read and transformed into logic levels. The dots are spaced sufficiently apart to allow for visible light resolution (0.1mm is good). In this arrangement, an 8cmX8cm card can store 20 Kbytes for 1 bit, 40 Kbytes for 2bits (N=4) and so on.
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