Project Description

I built and analyzed an acoustic levitation system, investigating the properties of high amplitude sound waves that allow acoustic levitation to occur. I successfully levitated multiple polystyrene beads at distances of 1/2 the wavelength of the emitted sound wave, which I determined from the frequency of my transducer (36 kHz). Flaws in my system motivated me to explore the concept of nonlinear acoustics, which is the theory behind the sound’s ability to levitate objects. The nonlinear nature of sound waves comes from the idea that sound moves more quickly at the peak of the wave, which is where the pressure is greatest and has a slightly increased zone of higher temperature. Because of this, the pressure from our sound wave is best expressed as the Taylor expansion of the pressure as a function of density. We find that the second order term in the expansion creates a time averaged positive force on an object that can balance the downward force of gravity on the object, thus causing the object to levitate.