Abstract: A method of training an artificial intelligence circuit is provided. The method includes the steps of providing a training data set, the training data set encompassing training data of a frequency spectrum including a guard band and/or training data concerning a radio frequency power in the guard band, and feeding the training data set into the artificial intelligence circuit to be trained, which processes the training data set in order to learn a standard frequency spectrum and/or a standard radio frequency power in the guard band, thereby enabling the artificial intelligence circuit, when trained, to determine a deviation from the standard frequency spectrum and/or to determine a deviation from the standard radio frequency power in the guard band. In addition, a monitoring method for identifying an anomaly in a radio frequency spectrum as well as a system for monitoring a radio frequency environment are described.

Abstract: A magnetizable anisotropic material layer having a pattern of regions of differently aligned material has an initial pattern of remanent magnetization, when manufactured by applying directional magnetic fields. This pattern is not easily restored, and is generally impossible to restore, after demagnetization or remagnetization. By preserving the residual pattern and selectively removing it in use by the application of a magnetic field, a security feature is provided. A secure document system using such a feature is provided.

Abstract: A secure document is produced by securely attaching to a support a body of including a security feature and having a shape which conveys information to the eye. For example the body is a layer of magnetizable material having apertures of letters, numbers and the like. The document can be examined by both magnetic and optical examination apparatus to cross-check that no alteration has been made. A method of making a secure document and examination apparatus is also described. The security feature may be a pattern of magnetic anisotropy fixed into the material.