An electronic card and a method for processing data stored in the electronic card. The electronic card includes a memory containing data to be read by a card reader. The electronic card may include a programmable field source containing wire structures geometrically configured and energized in a manner that drives an electric current through only two wire structures at a time for generating a time varying magnetic field that induces a readback signal in the card reader as the electronic card is being swiped through the card reader. An electrical current in at least one wire in the electronic card generates a time varying magnetic field and may include a finite time derivative of electrical current whose magnitude does not exceed a specified maximum time derivative of electrical current corresponding to a peak voltage threshold (Vth) and an overshoot ratio (f) of the card reader.