Glauber Silva (Universidade federal de Alagoas, Brazil)

Angular Momentum in Acoustic Waves: From Spin and Orbital Components to Acoustophoresis

The transfer of angular momentum from acoustic waves to matter is becoming a central theme in wave physics and its applications. Unlike linear momentum, angular momentum in acoustics separates into two fundamentally distinct contributions: spin angular momentum, associated with the circular polarization of particle velocity fields, and orbital angular momentum, linked to the topology and vorticity of the wavefront. In this lecture, I will present a framework for distinguishing spin and orbital angular momentum in acoustic fields, highlighting their measurable signatures and their roles in shaping the acoustic radiation torque. I will then show how these concepts extend to acoustophoresis, where angular momentum effects can be exploited for selective trapping, rotation, and clustering of particles and cells. Finally, I will discuss perspectives for the fabrication of biomedical acoustofluidic chips using low-cost and scalable materials and methods, offering new opportunities for particle and cell manipulation in lab-on-chip platforms.