When two frequencies are added together, the beat frequency and the average frequency are an octave apart?

One of the frequency is double of the lower frequency.

Beat frequency is defined as the difference in frequency produced by two waves.

The beat frequency, F = F₂ - F₁

The average of the two frequencies is calculated as follows;

When the beat frequency and the average frequency are an octave apart;

Thus, we can conclude that one of the frequency is double of the lower frequency.

Learn more here:link

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia