The present invention concerns A sonotrode with a wheel-shaped portion having a wheel axis and of a diameter d, which has two substantially circular main surfaces and a substantially cylindrical sealing surface of the width b, that connects the main surfaces. To provide a corresponding sonotrode in which the triangular frequency differs markedly from the main frequency it is proposed according to the invention that at least one main surface has a non-central thickened portion which in a sectional view perpendicularly to the main surface has a convex region which is not arranged on the wheel axis.