The present invention relates a power ultrasound device for fluids processing. An ultrasonic resonator comprises: an exciter section having a longitudinal axis and dimensioned to be resonant in a direction along the longitudinal axis when the exciter section is energized with high frequency vibrations; and a radiator section having a connection stub and coupled to the exciter section through the connection stub, wherein the radiator section is configured to receive the vibrations from the exciter section and transmit the vibrations as acoustic waves, wherein an axial length of the exciter section is less than a half-wavelength, wherein the connection stub completes the half-wavelength when coupled to the excited section to allow the ultrasonic resonator operate in resonance at design frequency. The radiator section includes a radiator body having at least three sides to provide a plurality of external radiating surfaces, and two opposite faces having a plurality of orifices formed therein, wherein walls of the orifices are configured to provide a plurality of internal radiating surfaces, and wherein the internal and the external surfaces are configured to transmit the vibrations as acoustic waves.