[Brewer89] R. Brewer Design Tips for EMI Shielding., Machine Design, (March 23, 1989):85--88. [This paper explains the difficulty in deciding whether enough shielding has been used and mentions that ElectroMagnetic Interference (EMI) was suspected in Army Blackhawk helicopter crashes because the Navy version has more shielding and fewer crashes. A graph is used to show shielding effectiveness versus frequency for electrical and magnetic fields using two different materials.]