建筑土木系探地雷达外文中英对照翻译(5)

Figure: 3-5 Dipole moment density induced by applied electric field and relation to displacement

current.

The creation of a dipole moment distribution in the material is associated with charge movement. The electric current associated with this charge movement is referred to as displacement current. The displacement current is mathemati-cally defined as the time rate of change of the dipole moment density.

The electric permittivity is never zero. Even in a vacuum, the permittivity, takes on a finite value of 8.85 x 10-12F/m (Farads per meter). The explanation for this lies in the field of quantum electrodynamics and is far beyond the scope of this discussion.

It is often more convenient to deal with a dimensionless term called relative permittivity or dielectric constant, K. As depicted in Figure 3-6 , the relative permittivity is the ratio of material permittivity to the permittivity of a vacuum.

Figure: 3-6 Dielectric constant or relative permittivity is the ratio of permittivity of material to that

of free space.

3.4 TOTAL CURRENT FLOW

In any natural material, the current which flows in response to the application of

an electric field is a mixture of con-duction and displacement currents. Depending on