EXPERIMENTAL STUDY OF NONLINEARITY IN FREE PROGRESSIVE ACOUSTIC WAVES IN AIR AT 20 kHz

On a étudié expérimentalement la propagation d'ondes d'amplitude finie dans l'air à 20 kHz. La source utilisée est un générateur aérien de puissance d'un type nouveau, capable d'atteindre avec une grande directivité des niveaux quasi-monochromatiques de l'ordre de 160 dB. Les expériences en ondes entretenues ont été conduites dans une chambre de dimensions 7,4 x 5,5 x 5,5 m3. Les mesures essentielles ont porté sur les amplitudes du fondamental et des trois premiers harmoniques pour différents niveaux d'émission et à des distances variables dans le champ éloigné. Les formes d'ondes et les diagrammes de directivités correspondants ont été également enregistrés. Les résultats obtenus confirment la limitation d'amplitude transmissible par propagation non linéaire. On a pu mettre clairement en évidence le phénomène de saturation acoustique. L'évolution des formes d'ondes et des diagrammes de directivité illustrent également ce comportement non linéaire.This paper describes an experimental investigation of the propagation of periodic waves of finite amplitude in air at 20 kHz. The acoustic source used in our experimental work is a new high-power ultrasonic transducer for use in air. This transducer, which emits a directive radiation, is able to generate a nearly pure sinusoïdal wave up to sound pressure levels over 160 dB. The experiments were done in a 7.4 m long, 5.5 m wide and 5.5 m high anechoic chamber, using cw mode. They consisted essentially of measuring the amplitude of the fundamental component of the wave and its first three harmonics for different source pressure levels and at different distances in the farfield. In addition, oscillograms and directivity patterns were recorded. The obtained results confirm the strong limitations in the transmission of intense waves due to nonlinear distortion. The phenomenon of acoustic saturation at high source levels is clearly observed. Also the evolution of waveforms and the changes in the radiation patterns show the effect of nonlinear behaviour

Applications of an ultrasonic high pressure roller press : effects of ultrasounds assistance on grinding process and products properties

International audienc

Development of an ultrasonic high‐pressure roller press

International audienceIt is widely known that particle size reduction processes have a low energetic efficiency. In this paper, we present experimental results obtained by a new grinding machine using ultrasound to enhance the performance of a roller mill. The required energy consumption for a comminution operation appears to be significantly reduced by careful application of an ultrasonic field in the grinding zone. A lower stress on the shafts and a reduction of the required torque were also observed. The lower mechanical stress should also cause less abrasive wear on the rolls