What is the phenomenon of electrostatic shielding?
In a conductor in electrostatic equilibrium, the internal electric field strength is zero everywhere. The inner space of the cavity conductor (whether grounded or not) is not affected by external charges and electric fields; for grounded cavity conductors, the space outside the cavity is not affected by the electric charges and electric fields in the cavity. This phenomenon is called electrostatic shielding. Electrostatic shielding is divided into outer shielding and full shielding. The cavity conductor is in electrostatic equilibrium in the external electric field, and the internal field strength is always equal to zero. Therefore, the external electric field cannot have any influence on its inner space. If the cavity conductor is grounded, the induced charge on the outer surface is neutralized by the ground charge, so there is no charge. Metal cavities are zero equipotential bodies. If the cavity conductor is grounded and there is a charged body outside the cavity, the induced charge on the outer surface is partially neutralized by the ground charge, and the amount of the electric charge must ensure that the electric charge in the cavity, the inner surface of the cavity, the outer surface of the cavity and the outer cavity of the cavity are in the conductor. The field strength generated in the body is zero, that is, the electrostatic equilibrium condition is satisfied. Metal cavities are zero potential. When the cavity conductor is grounded, the metal cavity is a zero equipotential body, which can be proved by the uniqueness theorem of the electrostatic field boundary value problem: any electric field in the shell at this time does not affect the outside world, nor is it affected by the outside world.
The application of electrostatic shielding
Shielding makes the instrument or working environment in the metal conductor shell not affected by the external electric field, nor does it have any influence on the external electric field. In the military or industry, some electronic military signal jammer or measuring equipment must implement electrostatic shielding in order to avoid interference, such as the metal cover outside the military jammer, which is used to prevent external electric field interference. The lead sheet on the outside of the military communication cable, or a layer of metal wire on the outside, is for the effect of electrostatic shielding, so that the signal is not disturbed, etc. The metal mesh cover, the metal tube casing for the electronic tube. Another example is a power transformer that is widely used in the military, and is used for full-wave rectification or bridge rectification. Between the primary winding and the secondary winding, a metal sheet is wrapped or a layer of enameled wire is wound and grounded to achieve a shielding effect. During high-voltage live work on military equipment, operators and maintenance personnel put on pressure-equalizing suits woven with metal wires or conductive fibers, which can shield and protect the human body.
Another example is the military signal jammer installed on military projects or facilities: if the area to be shielded is large, a metal shielding net can also be used, which also has a good shielding effect. In military electronic instruments, in order to avoid electrostatic interference, the grounded metal casing of the instrument is often used as a shielding device. The wire insulation of some connecting wires in electrical measuring instruments is covered with a layer of wire mesh as a shield.
Shielding products: In recent years, an anti-static jammer bag has emerged. This anti-static shielding bag is made of APET/CPP (semi-aluminized film/polypropylene cast film) with good transparency, weak tear resistance and relatively hard hand feel, or good heat sealability, good tear resistance, strong tensile force and relatively hand feeling. Soft APET/CPE (semi-aluminized film/polyethylene film) is made of material, which can effectively isolate items from external electrostatic fields, prevent static electricity from being generated in the bag, and protect items from electrostatic hazards. This kind of bag is generally used to protect electrostatic sensitive components such as PCB and LED, and can protect the electrostatic sensitive components from potential electrostatic hazards to the greatest extent.
In addition, some electronic products such as electrostatic shielding detection table, electrostatic shielding detector, etc., as well as some anti-static clothing, anti-static shoes, anti-static hats, etc. With the further development of science and technology, electrostatic shielding has become more and more widely used in various aspects, and its effect will also become greater and greater.