Types of Electromagnetic Coupling: Conducted, Radiation, Magnetic Field, Electric Filed
Electric Field Coupling
The EF lines start on positive charge and end on negative charge from higher voltage conductors to lower voltage conductors. Any two conductors at different potentials (voltages) have electric field lines between them. EF shields are connected to “ground” to maximize their effectiveness.
The electric field lines are passing through ungrounded metallic planes.
Grounding a copper enclosure does not increase or decrease its shielding property but it reduces the crosstalk within the product itself. The ungrounded shield allows coupling signals from circuits within the shielded enclosure. If the device is connected via external cable to another module the ungrounded shield can serve to capacitively couple signals from outside the enclosure.