The numerical simulations in Fig. 3C were conducted using COMSOL Multiphysics finite element software. This model was validated by comparing the streaming pattern from the simulation with that from the experiment of a microswimmer fixed parallel to the bottom (fig. S9). The streaming phenomenon was simulated by considering a perturbation expansion approach wherein the flow variables were separated into their first- and second-order components (40). The first-order components, which are indicative of the acoustic response of the system, were considered to be harmonically oscillating (with a frequency equal to the actuation frequency). In contrast, the second-order components represent the time-averaged response of the system, evolving on a much slower time scale than the acoustic wave period. This separation of variables results in the reduction of Navier-Stokes equations into two separate systems of equations for the first- and second-order components of the flow variables. These systems of equations were solved in a sequential manner wherein the first-order system of equations was solved using a frequency-domain approach, while steady-state solutions were sought for the time-averaged, second-order system of equations. We performed a 2D simulation on a rectangular domain with a length of 100 μm and a width of 140 μm. We used impedance boundary conditions at all boundaries, except the water-air interface. The acoustic actuation was modeled using a Dirichlet boundary condition at the water-air interface, which was assumed to be oscillating at the actuation frequency in the radial direction. An unstructured triangular mesh with 7975 elements was used. We used P1-P2 composite elements for the pressure and velocity, where P1 and P2 denote the triangular elements with Lagrange polynomials of orders 1 and 2, respectively. For both the first- and second-order systems of equations, a direct solver was used to obtain the solution.

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