Method and device for examining a sheet-shaped or card-shaped valuable document having a security feature having one or more cavities

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.

2. The method according to claim 1 , wherein the ultrasound has a frequency in the range of 50 kHz to 800 kHz.

3. The method according to claim 1 , wherein ultrasonic pulses are employed for establishing the transmission values.

4. The method according to claim 1 , wherein the transmission threshold value is determined using the established transmission values.

5. The method according to claim 1 , wherein the transmission threshold value was established by examinations of reference value documents of the same type.

6. The method according to claim 1 , wherein upon the check it is established whether the respective transmission value lies within a specified interval whose upper limit is the transmission threshold value.

7. The method according to claim 1 , wherein only transmission values for a specified region of the value document are used when performing the checking step.

8. The method according to claim 7 , wherein the checking step further includes checking whether the distribution of the transmission values in the specified region and/or of those transmission values in the specified region that are smaller than the transmission threshold value satisfies a specified distribution criterion.

9. The method according to claim 1 , wherein it is additionally checked whether the locations corresponding to the specified number of transmission values forms a contiguous structure.

10. The method according to claim 1 , wherein an extension of the cavity or cavities in the or another direction specified for the respective cavity, parallel to a surface of the value document, is greater than 100 μm.

11. The method according to claim 1 , wherein an extension of the cavity or cavities in a direction perpendicular to a surface of the value document is greater than 30% of the total thickness of the value document in the region of the cavity or cavities and/or greater than 20 μm.

12. The method according to claim 1 , wherein the cavity or at least two of the cavities are of line-shaped configuration.

13. The method according to claim 1 , wherein the value document comprises a substrate which has partial or complete piercings, and the piercings are covered on both sides by cover layers held on the substrate, and the covered piercings form the cavities.

14. The method according to claim 13 , wherein the piercings are disposed in a motif region of the value document.

15. The method according to claim 14 , wherein the motif region has a changed visual impression in incident light and/or transmitted light, and/or is configured in the form of a pattern, signs or an encoding.

16. The method according to claim 13 , wherein the piercings are of line-shaped configuration and have a width between 0.05 mm and 1 mm.

17. An apparatus for examining a value document 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 apparatus comprising:

an ultrasound transmission sensor for detecting locally resolved transmission values for the transmission of ultrasound in a specified frequency range through the value document;

a control and evaluation device connected to the ultrasound transmission sensor via a signal connection for evaluation thereof;

a transport device for transporting the value document through the ultrasound transmission sensor, wherein the transmission values are detected during the transport of the value document through the ultrasound transmission sensor;

wherein the control and evaluation device is configured for checking whether a specified number of transmission values is smaller than a specified transmission threshold value corresponding to a transmission 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

for 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 in dependence on the result of the checking step.

18. The apparatus of claim 17 , further comprising a data processing device which has a field-programmable gate array (FPGA).

19. The apparatus of claim 17 , further comprising a data processing device which has a microcontroller.

20. The apparatus of claim 17 , further comprising a data processing device which has a processor and a memory with a data processing program stored therein.