Plasma synthetic jet (PSJ), or Sparkjet, actuators seem to be a promising technology to improve the aircraft performances due to their short response time, high jet velocities and absence of moving parts. This paper aims at presenting a combined numerical and experimental investigation, to obtain information about the frequency response of the device. From the numerical point of view, an innovative lumped-element model (LEM), able to predict the temporal evolution of the main fluid-dynamic variables of the device, is presented. It is fully based on the gasdynamics equations, it includes viscous losses as well as radiative and convective heat transfer mechanisms at walls, and it considers the air as a real gas. OpenFOAM numerical computations have been carried out to perform a first calibration of the lumped model through the determination of key fitting parameters. Results for both single pulse mode and repetitive working regimes are reported, providing insights on the major actuation characteristics. To validate the model, a home-designed actuator has been manufactured, together with the control electric circuit. Experimental measurements of the jet velocity complete the actuator characterization and the model validation.