Electric-acoustic force balance for sorting microparticles on a chip

Electronic waste is the fastest growing solid waste stream in the world, accounting for 54 million tons of waste globally. Such waste contains valuable chemical elements, such as gold, palladium, copper, silver, tin, and nickel that could be recycled back into the economy. Here, we present a proof-of-concept device to test a new electric-acoustic force balance to separate particles based on their electrical and mechanical properties. The device applies an acoustic force and electric force simultaneously causing microparticles to move to a position where the forces are equal. We used interdigitated transducers to generate a standing acoustic wave in the channel, collimating the particles at the pressure nodes. We then applied an electric field by applying a voltage between two electrodes patterned on either side of the microfluidic channel. This electric force changed the position where the microparticles collimated. The vision is to test microparticles from new waste recovery processes and show how they separate in our force balance to inform large scale separation technology.