The present invention relates to a method, a device and a computer program product for determining an electromagnetic near-field of a field excitation source of an electrical system. The method includes defining electrical and magnetic properties of the system, defining a field excitation source, determining electromagnetic near-field components by solving Maxwell's equations of the near-field, where each near-field component of each partition is represented by a linear position of M orthogonal ansatz functions weighted with field coefficients, whereby spatial and/or time derivatives of the near-field component are determined as a linear position of these ansatz functions weighted with derivative coefficients, which can be determined from the field coefficients and the derivative coefficients, so that the determination effort rises linearly with the complexity of the electrical system.