In this study we present a theoretical and experimental investigation of a microelectromechanical system (MEMS). The device is constituted of a clamped-clamped polysilicon microbeam electrostatically and electrodynamically actuated. The microbeam has imperfections in the geometry, which are related to the microfabrication process. Using a laser Doppler vibrometer, experimental testing based on forward and backward sweeps is conducted in a neighborhood of the first symmetric natural frequency. Our aim is that of introducing a simple mechanical model, which, despite the inevitable approximations, is able to catch and predict the most relevant aspects of the device response. Many parameters of the microbeam are unknown. Their values are identified by developing a parametric analysis, which is based on matching the experimental natural frequencies and the experimental frequency response diagrams. Extensive simulations are performed. Theoretical and experimental frequency responses are analyzed in detail at increasing values of electrodynamic excitation. A satisfactory concurrence of results is achieved, not only at low electrodynamic loads, but also at higher ones, when the escape (dynamic pull-in) becomes impending. This confirms that, despite the apparent simplicity, the proposed theoretical model is able to simulate the complex dynamics of the device accurately and properly. Keywords: microelectromechanical systems;parameter identification;frequency response;nonlinear dynamics.