Fig. 4: Analogy to Discrete Phased Acoustic Sources.
From: Elastic orbital angular momentum transfer from an elastic pipe to a fluid
a FEM geometry showing ring of 12-point acoustic sources (coloured spheres), with relative phase and amplitude shown by their colour and size respectively, atop cylindrical region of water with cylindrical radiation conditions on all boundaries. b geometry of case (I) for conventional approximation of acoustic OAM beams; real pressure, phase, and acoustic intensity are shown in c, d, e respectively for this case at a depth of 20 mm below the source position. f geometry of case (II), where amplitude modulation is incorporated by an additional central source and by altering the amplitudes of three of the sources around the ring. g–i are analogous to c–e respectively for case (II), showing the amplitude modulation of the acoustic OAM beam.
