Methods and devices for verifying the authenticity of sheet-type products

1. A method for checking the authenticity of sheet material, in particular bank notes, by means of ultraviolet light, comprising:

illuminating the sheet material with ultraviolet light;

evaluating the ultraviolet light transmitted by the sheet material to check the authenticity of the sheet material; and

identifying the sheet as authentic or as a forgery based solely on the transmitted ultraviolet light.

2. A method according to claim 1 , wherein at least one threshold value or at least one pattern for the transmitted ultraviolet light is derived from at least one authentic piece of sheet material for checking the authenticity of the sheet material.

3. A method according to claim 1 , wherein it is checked whether the ultraviolet light is converted by the sheet material to light of another wavelength.

4. A method for checking the authenticity of sheet material, in particular bank notes, by means of ultraviolet light, comprising:

illuminating the sheet material with ultraviolet light and a second light with a wavelength different from the ultraviolet light;

setting the ultraviolet light transmitted by the sheet material and the second light transmitted by the sheet material in a mutual relation;

evaluating the relation to check the authenticity of the sheet material; and

identifying the sheet as authentic or as a forgery based solely on the transmitted ultraviolet light.

5. A method according to claim 4 , wherein at least one threshold value or at least one pattern for the relation is derived from at least one authentic piece of sheet material for checking the authenticity of the sheet material.

6. A method according to claim 4 , wherein the transmitted ultraviolet light and the transmitted second light come from the same place on the sheet material to be checked.

7. A method according to claim 4 , wherein the transmitted ultraviolet light and the transmitted second light are evaluated at the same time.

8. A method according to claim 4 , wherein it is checked whether the ultraviolet light is converted by the sheet material to light of another wavelength.

9. An apparatus for checking the authenticity of sheet material, in particular bank notes, by means of ultraviolet light, having a light source for producing the ultraviolet light, whereby the light source illuminates the sheet material with ultraviolet light, and a sensor which produces values for ultraviolet light transmitted by the sheet material, and an evaluation unit for checking the authenticity of the sheet material solely on the basis of the values of the sensor.

10. An apparatus according to claim 9 , wherein several sensors and/or light sources are present for detecting several tracks of the sheet material.

11. An apparatus according to claim 10 , wherein the sensors detect the surface of the sheet material completely.

12. An apparatus according to claim 9 , wherein a memory is connected to the evaluation unit and contains at least one threshold value or at least one pattern which are derived from at least one authentic piece of sheet material for checking the authenticity of the sheet material, and are compared by the evaluation unit with the values or the sensor.

13. An apparatus according to claim 9 , wherein a lock-in amplifier amplifies the signal of at least one of the first sensor or sensors and the further sensor.

14. An apparatus for checking the authenticity of sheet material, in particular bank notes, by means of ultraviolet light, having a first light source for producing the ultraviolet light, whereby the light source illuminates the sheet material with ultraviolet light, and a first sensor which produces values for light of the first light source transmitted by the sheet material, a second light source for producing ultraviolet light with a smaller wavelength than the ultraviolet light of the first light source, and a second sensor which produces values for light of the second light source transmitted by the sheet material, and an evaluation unit for checking the authenticity of the sheet material solely on the basis of a relation of the values of the first sensor to the values of the second sensor.

15. An apparatus according to claim 14 , wherein the sensors detect the same place on the sheet material.

16. An apparatus according to claim 14 , wherein the sensors detect the sheet material at the same time.

17. An apparatus according to claim 14 , wherein several sensors and/or light sources are present for detecting several tracks of the sheet material.

18. An apparatus according to claim 17 , wherein the sensors detect the surface of the sheet material completely.

19. An apparatus according to claim 14 , wherein a memory is connected to the evaluation unit and contains at least one threshold value or at least one pattern which are derived from at least one authentic piece of sheet material for checking the authenticity of the sheet material, and are compared by the evaluation unit with the relation of the values of the sensor or sensors to the values of the second sensor or sensors.