In this work an ion source for IMS (Ion Mobility Spectrometry) and FAIMS (Field Asymmetric Ion Mobility Spectrometry) systems is described. The ion source exploits the field ionization principle (non-uniform strong electric field). Moreover, the designed ion source takes into account a heating system to control the overall temperature, which can affect the mobility of the ions and the selectivity of the entire system. After a literature search, we designed a simple geometry with the aim to understand the basic principles for developing an effective and efficient ion source for portable IMS and FAIMS systems. The main aspects that have been considered are: integrability, portability, operation at ambient pressure, low voltages, lifetime, efficiency and cost. 2D simulations have been performed using COMSOL Multiphysics® 4.0.