Security device

1. A security device comprising:

a region of piezochromic material;

a first discrete absorbing region;

a second discrete absorbing region; and

an integrated relief structure that includes structural modulations, wherein

when the region of piezochromic material and the integrated relief structure are together subjected to a stress, an optical effect is generated in the region of piezochromic material by the stress causing localized modulations in the deformation of the piezochromic material, which are representative of the structural modulations of the integrated relief structure, such that the optical effect generated is representative of the structural modulations of the relief of the integrated relief structure;

at least one of the first discrete absorbing region and the second discrete absorbing region comprises the integrated relief structure; and

the structural modulations are modulations of the at least one of the first discrete absorbing region and the second discrete absorbing region.

2. The security device according to claim 1 , wherein each of the first discrete absorbing region and the second discrete absorbing region comprises a relief structure.

3. The security device according to claim 2 , wherein a first part of a composite image is represented in the first discrete absorbing region, and a second part of a composite image is represented in the second discrete absorbing region, such that the first and second images form a resultant composite image when combined.

4. The security device according to claim 1 , wherein the first discrete absorbing region and the second discrete absorbing region are provided on opposing sides of the security device.

5. The security device according to claim 1 , wherein the first discrete absorbing region and the second discrete absorbing region are of different colors.

6. The security device according to claim 1 , wherein the integrated relief structure comprises perforated regions, an embossed surface, or a printed surface.

7. The security device according to claim 1 , wherein the integrated relief structure is coupled to the region of piezochromic material.

8. The security device according to claim 1 , wherein the security device further comprises an absorbing layer positioned between the region of piezochromic material and the integrated relief structure.

9. The security device according to claim 1 , wherein the region of piezochromic material contains an absorbing phase.

10. The security device according to claim 1 , wherein the integrated relief structure is mounted to or forms part of a substrate.

11. The security device according to claim 10 , wherein a plurality of relief structures are provided.

12. The security device according to claim 11 , wherein a first part of a composite image is represented in a first of the plurality of relief structures, and a second part of a composite image is represented in a second of the plurality of relief structures, such that the first part and the second part form a resultant composite image when combined.

13. The security device according to claim 11 , wherein the plurality of relief structures are provided on opposing faces of the substrate.

14. The security device according to claim 11 , wherein a first region of piezochromic material is provided to interact with a first of the plurality of relief structures and a second region of piezochromic material is provided to interact with a second of the plurality of relief structures.

15. The security device according to claim 1 , wherein the security device further comprises a printed ink layer having a color that is substantially the same as at least one of: the color of the integrated relief structure; the color of light reflected from the region of piezochromic material when in a stressed state; or the color of light reflected from the region of piezochromic material when in an unstressed state.

16. The security device according to claim 1 , wherein the region of piezochromic material is provided as a film.

17. The security device according to claim 1 , wherein the region of piezochromic material is formed as a pigmented coating or a printed layer.

18. The security device according to claim 1 , wherein the region of piezochromic material is partially transparent.

19. The security device according to claim 1 , wherein the piezochromic material comprises nanoparticles.

20. The security device according to claim 1 , wherein the integrated relief structure comprises a region that is raised or lowered with respect to surrounding material.

21. The security device according to claim 1 , wherein when the integrated relief structure is arranged as an image, the optical effect reproduces the image.

22. The security device according to claim 1 , wherein in the absence of the stress, the region of piezochromic material generates a first optical effect, and the optical effect generated as a result of the stress is a second optical effect.

23. The security device according to claim 22 , wherein at least one of the first optical effect and the second optical effect is an optically variable effect.

24. The security device according to claim 1 , wherein at least one of the first optical effect and the second optical effect is an effect in one of the ultra-violet, visible, or infra-red parts of the electromagnetic spectrum.

25. The security device according to claim 1 , further comprising a transparent cover layer.

26. The security device according to claim 1 , wherein the stress causes a temporary or permanent distortion within the structure of the region of piezochromic material.

27. The security device according to claim 1 , wherein the stress is an internal stress or an applied compressive stress.

28. The security device according to claim 1 , wherein the security device comprises a self-supporting layer.

29. The security device according to claim 1 , wherein the security device is machine-readable.

30. The security device according to claim 1 , wherein the region of piezochromic material is a photonic crystal.

31. A security document comprising the security device according to claim 1 .

32. The security document according to claim 31 , wherein the security device is located within the security document such that the region of piezochromic material has a first face on a first side of the security document, and a second face on an opposing side of the security document.

33. The security document according to claim 31 , wherein the region of piezochromic material is mounted to a window in the security document.