Apparatus for preventing unwanted exposure of one or more devices to one
or more undesirable substances includes at least one barrier disposed
between the device and the undesirable substance. At least one shield
substance is provided between the barrier and the device. The shield
substance is capable of permeating the barrier sufficient to preclude at
least substantial permeation of the undesirable substance through the
barrier from the exterior of the barrier, preventing unwanted exposure of
the device to the undesirable substance.