By generalizing the stability treatment of Thiele to include the presence of a permalloy pattern, a magnetostatic energy model for describing field access devices is derived. The general implications of the model with regard to minimum drive fields and propagation margins are discussed and calculated magnetostatic energy profiles for noninteracting chevrons are presented. The question of when the permalloy elements begin to interact is examined to provide justification for treating the permalloy elements independently. Finally, a magnetoresistance model for detector analysis is proposed which may be incorporated easily into the existing modeling framework. The paper concludes by suggesting further areas of application and by discussing areas which need further improvement.