Angular momentum conservation and symmetry

Abstract

The conservation of angular momentum during the interactions of sound fields with objects is associated with the symmetry in the fields and the objects. Simple arguments of symmetry and/or conservation can have efficient applications in analyses of angular momentum transfer during the interactions. Scenarios that will be illustrated include: (a) conserved phase distribution for analysis of torques exerted by vortex beams on axis-symmetric objects for its connection with absorption [L. Zhang and P. L. Marston, JASA 129, 1679–1680 (2011); Phys. Rev. E. 84, 065601 (2011)], (b) symmetric superposition of vortex beams for analysis of torques exerted by orthogonal waves on a small compressible object in a slightly viscous fluid [L. Zhang and P. L. Marston, JASA 136, 2917–2921 (2014)], and (c) broken symmetry in a planar meta-screen for introducing angular momentum into a plane sound field of null angular momentum [Y. Li et al., Phys. Rev. Appl. 4, 024003 (2015); X. Jiang et al., in preparation].