Development of Extended Range Shielded Enclosures

This paper presents the results of a research and development program launched by the Sprague Electric Company five years ago having a primary objective of furthering the state of the art of low frequency, low impedance (magnetic) shielded enclosure performance. The paper describes in detail the evaluation of shielded materials, compares several methods of measuring shielded effectiveness with theoretical performance, and details the development of ancillary devices. Discontinuities in shields such as doors, ventilation aperatures, filters, and other miscellaneous penetrations have always presented the weakest parts of shielded enclosures. This paper also treats the development of methods to improve the performance of such discontinuities to acceptable levels. Presented in graphical form is shielding information on various shield membranes and ancillary equipment -- usable as design guides to achieve a wide variety of performance requirements.