We all know that computer networks are now in every corner of the world. Of course, I believe you don't know much about shielded wiring. The following editor will talk about the types of shielded wiring and the common materials for shielded wiring.
What are the types of shielded wiring
1. Static shielding
Surround the positively charged conductor with a complete metal shield, the same amount of negative charge as the charged conductor will be induced on the inner side of the shield, and the same amount of positive charge as the charged conductor will appear on the outside, if the metal shield is grounded, then The positive charges on the outside will flow into the ground, and there will be no electric field on the outside, that is, the electric field of the positively charged conductor is shielded in the metal shield.
2. Alternating electric field shielding
In order to reduce the coupling interference voltage of the alternating electric field to the sensitive circuit, a metal shielding body with good conductivity can be arranged between the interference source and the sensitive circuit, and the metal shielding body can be grounded. The coupling interference voltage of the alternating electric field to the sensitive circuit depends on the product of the alternating electric field voltage, the coupling capacitance and the grounding resistance of the metal shield. As long as the metal shield is well grounded, the coupling interference voltage of the alternating electric field to the sensitive circuit can be reduced. The electric field shielding is mainly based on reflection, so the thickness of the shielding body does not need to be too large, but the structural strength is the main consideration.
3. Alternating magnetic field shielding
Alternating magnetic field shielding is divided into high frequency and low frequency. Low-frequency magnetic field shielding uses materials with high magnetic permeability to form a low magnetic resistance path, so that most of the magnetic field is concentrated in the shielding body. The higher the magnetic permeability of the shield, the greater the thickness, the smaller the magnetic resistance, and the better the magnetic field shielding effect. Of course, it must be coordinated with the weight of the equipment. The shielding of the high-frequency magnetic field is achieved by using the reverse magnetic field of the eddy current generated by the high-conductivity material to cancel the interference magnetic field.
4. Alternating electromagnetic field shielding
Generally, a material with high conductivity is used as the shielding body, and the shielding body is grounded. It uses the shielding body to generate the eddy current magnetic field in the opposite direction under the action of the high-frequency magnetic field to cancel the original magnetic field to weaken the interference of the high-frequency magnetic field, and realize the electric field shielding because the shielding body is grounded. The thickness of the shield does not need to be too large, but the skin depth and structural strength are the main considerations.
What are the common materials for shielded wiring
1. Rubber core braided mesh shielding gasket
Rubber and metal wire optional (Monel wire, tinned steel core copper wire), used in chassis, cabinet gap shielding, shielding room and shielding shelter. There are two ways of groove mount and surface mount.
2. Conductive rubber shielding gasket
Mainly include: conductive rubber sheet, conductive rubber shielding strip, double-layer conductive rubber shielding pad inner layer: silicone rubber, outer layer: conductive rubber.
3. Beryllium copper reed shield gasket
Reeds made of beryllium copper are suitable for the design of gaps in equipment such as communications, computers, shielded rooms, and shielded shelters. It not only solves the problem that other gaskets cannot withstand tangential motion, but also has high shielding efficiency, and also has the characteristics of high thermal conductivity and good pressure resistance.
4. Conductive glue
Mainly include: silicone grease conductive adhesive, used for bonding conductive rubber sheet and metal; conductive rubber strip and metal bonding; epoxy conductive adhesive, used for metal-to-metal bonding, printed circuit board circuit connection, microwave component lead connection, Wire mesh shielding strips are fixed.
5. Conductive filler (conductive putty)
Application: used for shielding at the gap where shielding gasket cannot be added.
6. Magnetic field shielding material
The magnetic field shielding at the working frequency or below 100kHz needs to provide a very low magnetoresistive surface to complete, and the magnetic field shielding material provides a high magnetic permeability shielding material.
7. Shield glass
Application: Electronic equipment needs light-transmitting windows, such as: CRT, instrumentation night crystal display window.
8. Light-transmitting conductive polyester film
Electronic equipment display window shielding, light transmittance: 70%, best shielding efficiency: 40 ~ 60dB.
9. Shielded ventilation panels
10. Shielding tape
Mainly include: electromagnetic shielding tape, conductive flange protection tape.
The above is all about the types of shielded wiring and the common materials of shielded wiring. In fact, there is a lot of knowledge about shielded wiring. In summary, the above is just the tip of the iceberg in shielded wiring
