Importance

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Abstract

An identification card is disclosed as for supporting commercial or other significant transactions involving a designated subject. The card incorporates a machine-readable record and is produced with an individual birefringent characteristic to modulate a light beam for card identification. In one embodiment, the card incorporates apparent stress waves to modulate an orientation-frequency characteristic (e.g. polarization angle) of a light beam. The machine-readable record on the card indicates the characteristic birefringence for confirming the card to be authentic. Methods are disclosed for producing and testing the cards. A system is disclosed for sensing card characteristics by modulated light including polarized light techniques to record and verify the cards with allowance for changes, as by card aging.

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First Claim