Arranging Ellipsoidal Particles in Three-Dimensional User-Specified Orientations with Ultrasound-Directed Self-Assembly

Ultrasound-directed self-assembly (DSA) enables particles to be arranged into user-specified patterns, which finds application in a myriad of engineering applications. However, using ultrasound DSA with nonspherical particles requires the ability to explicitly control their orientation. We theoretically derive a method to determine the operating parameters (amplitude and phase) of any arrangement of ultrasound transducers required to explicitly align ellipsoidal particles in any three-dimensional user-specified ori-entation. This method locally minimizes the acoustic radiation potential at user-specified locations and optimizes the curvature of the acoustic radiation potential to direct ellipsoidal particles into user-specified orientations. We show experimental validation using a single ellipsoidal expanded polystyrene particle in air and quantify the difference between the user-specified and experimentally obtained orientations. This work finds application in using ultrasound DSA in industrial processes and as a manufacturing method for engineered materials.