Patent attributes
The system controls the frequency of an ultrasonic signal to be applied to a waveguide, such that the frequency corresponds to a preferred resonance mode of the waveguide and not to adjacent undesirable resonance modes. The system operates by carrying out a first scan of a predetermined portion of the generated signal, determining the number of resonance modes of the waveguide within this portion and selecting from these resonance modes either that one mode which is at a central frequency or that one mode which is at a frequency nearest thereto. The system may also set limits on each side of the selected resonance mode and carry out a second scan within these limits each time that the generator is activated to check whether the selected resonance mode is drifting.
