The Fallacy of Shields

The Fallacy of Shields

Shields have their uses, although they are unpleasant in most factory production processes, expensive, and often a quality problem; however, the engineer should remember that there is no ground in most wireless sensor network nodes. In most cases, "shields" do not function as their designers believe they do — as Faraday shields to stop capacitive coupling. Usually, shields function as another circuit board layer to redistribute return currents in a more favorable way. It is nearly always true that, with proper circuit board design, shields are unnecessary to meet the performance requirements typical of a wireless sensor network node. An exception can be discrete frequency generation circuits (VCO, synthesizer, etc.) of a transmitter, which may receive energy coupled from the antenna sufficient to cause improper operation if shielding is not used. In most wireless sensor network nodes, however, these components are largely integrated, so this exception rarely occurs.