The invention relates to the manufacture of composite electromechanical resonators with a very high vibratory amplitude. These transducers comprise an electric excitation unit (3) (piezoelectric or magnetostrictive). The metal masses (30 and 40) consist in whole or in part of ferromagnetic alloys selected for their low internal coefficient of friction. A double servo system makes it possible: to power the electric excitation at the resonant frequency of the resonator, whatever the latter's drift; to re-establish the maximum amplitudes of the mechanical vibrations, whatever the acoustic impedance and damping of the noiseless medium. Its operation is based on the magnetostrictive effect. In fact, the vibrations of the ferromagnetic mass (30) produce variations in the magnetisation in this material which are reflected by flux variations across the coil (60). The resultant induced current (20) correctly represents the state of vibration of the material. This current is subjected to a simple electronic treatment in the filter-dephaser (1) before being amplified in amplifier (2) powering the electric excitation unit (3). In addition, the electronic comparator (4) maintains the mechanical vibrations at their maximum amplitude through the action of the controlling device (5) which continuously rebalances the resonator at the level of the free end (31) of the damping mass (30) and may maintain the fixation plane in harmony with a nodal plane (6). These resonators constitute powerful ultrasonic generators and also facilitate the study of: high-amplitude vibrations and their propagation in various materials; the properties of these materials in the non-linear field and especially their fatigue and ageing.