Modeling of inner magnetic shielding assemblies in cathode ray tubes by 3-dimensional finite element method

The effect the Earth magnetic field has on the electron beams present inside cathode ray tubes (CRTs) becomes more evident for larger tubes dominant in the high-definition television (HDTV) and computer displays. Consequently, the quality of an image formed on the screen deteriorates what can be visually perceived as the image distortion and degradation of the color purity. In this paper, we describe a computer suite developed for the design and numerical modeling of inner magnetic shielding assemblies employed to minimize this negative field-beam interaction for trinitron type tubes. Till now such assemblies were mostly designed by an expensive experimentation based on the 'cut and try' approach. By applying the 3-D finite element method the actual magnetic characteristics of assembly parts formed magnetically by degaussing, the grille anisotropy and the frame bulkiness can be considered. Also, a set of design tools developed to evaluate the assembly shielding performance is described.