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.
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