Ultrasounds in Bubbly Liquids: Unidirectional Propagation and Switch

The presence of oscillating gas bubbles in a liquid generates attenuation, dispersion, and nonlinearity. We take advantage of these effects to set the theoretical basis for two new devices. An acoustic diode that blocks the propagation of ultrasonic waves in one direction and let them pass in the other direction is proposed. The system is based on two adjacent layers made up of two bubbly liquids of different bubble sizes. This acoustic diode is an alternative system to other devices previously proposed by other groups and that rely on periodical structures (sonic crystals, metal plates). An acoustic switch that allows the control (switch-on or switch-off) of the propagation of the main ultrasonic wave by means of a secondary ultrasonic field able to generate a cavitation field (at low or high ultrasonic frequency) is also presented. This system is an alternative to an acoustic switch set previously by our group. The theoretical design of both structures relies on experimental observations and numerical simulations.