SIMION deals only with static and low-frequency oscillating electrode voltages. By low frequency, we generally mean that the wavelength (lambda = c / nu) is much larger than the length of the electrodes under study. When this is true, we can typically ignore any magnetic fields generated from the oscillations in the electric field (e.g. radio antennas). Such low frequencies are sometimes called quasistatic, and this approximation is then refered to as the quasistatic approximation of Maxwell's equations, in which the time derivatives are omitted.
Examples of low-frequency devices simulated by SIMION include quadrupoles and ion traps.