Materials Used for Shielding

Materials Used for ShieldingWhen electric current passes through a conductor, it produces electromagnetic energy. The strength depends on the amplitude and the frequency of the current. Some energy will be induced in any conductor placed inside this field. Accordingly, spurious coupling may occur between various parts of the system.Sometimes this effect may be reduced by proper placement of electric circuit elements. The voltages induced in the conductor should be equal but opposite in sign.This is why sometimes two AC conductors are stranded together. This method is effective at frequencies of up to 5 kHz. Its effectiveness also depends on how evenly and tightly the conductors are twisted.Sometimes it is enough to place the elements of the circuit farther from the sources of radiation. The amount of energy reduces with the increase in distance. In case none of the above solutions works, you may have to stop the radiated field with the help of a conducting screen.A conductive screen is an effective solution and there are two reasons for this.First of all, it absorbs energy as the waves pass through conducting medium. Secondly, energy is reflected at the border of two mediums.Both the effects depend on the frequency as well as on the material of the screen.Shielding is used to reduce the radiated electromagnetic field as much as possible. The choice of the shielding material depends on whether the field is mostly electric or magnetic. In an average case magnetic materials can absorb more electromagnetic energy. Good conductors such as copper and aluminium also have excellent reflecting properties.The latter two are effective at shielding from electric fields. However, their effectiveness decreases as the frequency grows. In any case, aluminium is widely used for shielding of I.F. circuits in the range of 30 to 300 MHz.As the frequency falls aluminium AC magnetic field shielding becomes less effective. This is why alloys with greater magnetic inductive capacity such as mumetal and permalloy are used for effective screening from electric fields in the low-(sound) frequency ranges.