French smartcard maker Gemplus thinks bank and credit cards would look more trendy if they were made transparent (WO 02/45008). This is easier said than done because cash machines and phone booths rely on the card being opaque to infrared light. So Gemplus has devised a card with filters that block infrared but let through visible light.
Its trick is to embed several layers of filtering dyes, each of which blocks a different part of the spectrum in the range 700 to 1000 nanometres. The result? To the eye, the card looks transparent, but to a card reader it…
