Most of the time-dependent and time-harmonic formulations use a quasistatic approximation. The approximation assumes that the currents and charges generating the electromagnetic fields vary so slowly in time that the electromagnetic fields are practically the same at every instant as if they had been generated by stationary sources.
One major difference between quasistatic and high-frequency modeling is that the formulations depend on the electrical size of the structure. This dimensionless measure is the ratio of the largest distance between two points in the structure to the wavelength of the electromagnetic fields. The quasistatic physics interfaces in this module are suitable for simulations of structures with an electrical size in the range up to 1/10.