摘要:
A surface relief hologram that comprises two or more patterns, each pattern being sensitive to different radiation wavelengths. The hologram is made by defining relief features that are sensitive to different wavelengths, and in particular to one wavelength that is visible to the unaided human eye and to one wavelength that is invisible to the unaided human eye. These relief features of different sensitivities are interspersed over the surface of the substrate in which the hologram is defined. By providing two patterns of different sensitivities, when the hologram is used in a security device, security is improved. Despite this improved security, the hologram can be mass manufactured using known techniques.
摘要:
The present invention relates to a test cell 1 suitable for use in applying directionally variable three dimensional stress fields to cylindrical test specimens 6 normally obtained by conventional coring techniques used for sample recovery. The test cell 1 comprises a cell body 2 having a barrel 4 extending therethrough for receiving a test specimen 6. The barrel 4 has an array 8 of elongate tubes 10 mounted side-by-side so as to line the inside wall 12 of the barrel. The tubes 10 have flexible side walls 14 and are formed and arranged for connection to a pressurized fluid supply 16. The test cell 1 also includes a control system 15 so that at least one tube 10a can be supplied with pressurized fluid at a different pressure to that in another tube 10b so as to provide an angularly variable radial pressure loading on the test specimen 6 mounted in the barrel 2.