A barrier or enclosure that prevents or reduces the penetration of an electric or magnetic field into a particular region.
Geology and Earth Sciences
1. A tunnel borer consisting of a conventional shield with thrust rams and erector system. The cutter head and support are inside the shield. This type of machine is usually employed in soils or variable materials, e.g. a sand–rock–gravel sequence.
2.Seecraton.
Geography
The very old, rigid core of relatively stable rocks within a continent. See Stein (2003) Precamb. Res. 123, 1–2 on the formation of the Arabian-Nubian Shield, and Lidmar–Bergström (1995) Geomorph. 12, 1 on the Baltic Shield.