A resonator is provided with a tuning element based on piezoelectricity. The piezoelectric basic element includes at least one piezoelectric layer and a metal layer. Such a basic element is first coated with a thin insulating layer and then with a good conductor. The thickness of the conductive coating is greater than the skin depth of a field corresponding to the operating frequency of the structure in the conductor. The tuning element formed in this manner is fastened on, e.g., some inner surface of the resonator cavity and acts to change the natural frequency of the resonator by electric control. When using the tuning element, no mechanical arrangement is required for moving the tuning element. Furthermore, the tuning element does not cause considerable dielectric losses nor intermodulation when being in a radiofrequency electromagnetic field, because the field cannot significantly penetrate through said conductive coating into the piezoelectric material.