Fast Protector Against EMP Using Thin Epitaxial and Polycrystalline Manganite Films

A new fast high-power fault current limiter made from epitaxial and polycrystalline
$\hbox{La}_{0.83}\hbox{Sr}_{0.17}\hbox{MnO}_{3}$
thin films and operating at 80 K has been demonstrated. An epitaxial film that exhibits a current-induced increase in its resistance is connected in series with a 50-
$\Omega$
-impedance transmission line, while a polycrystalline film whose resistance decreases with an increase in current is connected in parallel. It has been demonstrated that, when the fault current pulse has an amplitude of 200 V, a rise time of 0.5 ns, and a pulselength of 18 ns, the limitation of its amplitude is 3.5 dB after the rise time and 8 dB at the end of the pulse.