Dear friend Hengyu Zhang

The dielectric constant, also known as the relative permittivity, of a material is a measure of the ability of the material to store electrical energy in an electric field. In a composite material made of two or more different materials, the dielectric constant of the composite depends on the dielectric properties of each individual material and the relative amounts of each material in the composite.

When a conductive material A is added to a non-conductive material to form a composite, the dielectric constant of the composite will increase as the concentration of conductive material A increases. This is because the conductive material A will have a higher dielectric constant than the non-conductive material, and as the concentration of A increases, the overall dielectric constant of the composite will increase.

However, when a composite conductive filler B is added to the mixture of A and a non-conductive material, the situation can become more complex. The presence of the conductive filler B can cause the electrical charges in the conductive material A to become more mobile, leading to an increase in electrical conductivity. As a result, the overall dielectric constant of the composite may decrease with increasing concentration of A, due to the increased conductivity of the composite.

Moreover, the presence of the conductive filler B can also cause the electric field lines to preferentially concentrate around the conductive filler B, reducing the effective permittivity of the composite. This effect can be especially pronounced if the conductive filler B is present in a high concentration, leading to a decrease in the dielectric constant of the composite as the concentration of A increases. This effect is commonly observed in composite materials made from conductive fillers and non-conductive matrices and is known as the "percolation threshold" phenomenon.