Patent ID: 9683972
Date: 2017-06-20
CPC Classifications: B42D,G01N,G07D

Claim:
1. A method for examining a sheet-shaped or card-shaped value document of a specified type with a security feature having one or more cavities configured in the value document, the width of the cavity or cavities in at least one respectively specified direction exceeding 10 μm, the method comprising the steps of: establishing, in a locally resolved manner, transmission values for the transmission of ultrasound in a specified frequency range, checking whether a specified number of the transmission values is smaller than a specified transmission threshold value which corresponds to a transmission that is smaller than the transmission of at least one reference region of the value document or of at least one reference value document not having the cavity or cavities, and in dependence on the result of the checking step, forming a signal which represents an indication of the authenticity of the value document and/or which represents an indication of the presence of a forgery of the value document.