Aligning High-Aspect-Ratio Particles in User-Specified Orientations with Ultrasound-Directed Self-Assembly

We use ultrasound directed self-assembly (DSA) to create two-dimensional patterns of high-aspect-ratio particles with user-specified orientation. We theoretically derive a method to determine the operating parameters of any arrangement of ultrasound transducers required to align high-aspect-ratio particles in any user-specified orientation. The method finds the ultrasound wave field that maximizes the curvature of the acoustic radiation potential orthogonal to the user-specified particle orientation and in user-specified locations. We simulate the theoretical solution resulting from this method and experimentally validate it using carbon microfibers in water and quantify the position and orientation error. This method enables controlling the location and orientation of high-aspect-ratio particles, including simultaneously orienting multiple high-aspect-ratio particles in different directions. This work finds application in the biomedical field and in using ultrasound DSA as a processing or manufacturing method for engineered materials.