| 摘要 |
According to the invention, ultrasound waves are introduced into the material of a security document comprising microsphere inclusions with predetermined acoustic characteristics disposed in the security document and subsequently retrieved for detecting the response of the microsphere inclusions to ultrasound exposure. The response of the microsphere inclusions to ultrasound exposure is monitored by measuring either the harmonic generation from the pulsating microsphere inclusions of the pulse-echo or/and the through-transmission of an incident acoustic wave, thereby enabling the monitoring of predetermined patterns for identification and/or authentication of security documents.
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