We use ultrasound directed self-assembly to organize particles dispersed in a fluid medium into a three-dimensional (3D) user-specified pattern. The technique employs ultrasound transducers that line the boundary of a fluid reservoir to create a standing ultrasound wave field. The acoustic radiation force associated with the wave field drives particles dispersed in the fluid medium into organized patterns, assuming that the particles are much smaller than the wavelength and do not interact with each other. We have theoretically derived a direct solution method to calculate the ultrasound transducer operating parameters that are required to assemble a user-specified 3D pattern of particles in a fluid reservoir of arbitrary geometry. We formulate the direct solution method as a constrained optimization problem that reduces to eigendecomposition. We experimentally validate the solution method by assembling 3D patterns of carbon nanoparticles in a water reservoir and observe good quantitative agreement between theory and experiment. Additionally, we demonstrate the versatility of the solution method by simulating ultrasound directed self-assembly of complex 3D patterns of particles. The method works for any 3D simple, closed fluid reservoir geometry in combination with any arrangement of ultrasound transducers and enables employing ultrasound directed self-assembly in a myriad of engineering applications, including biomedical and materials fabrication processes.

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Ultrasound noncontact particle manipulation (NPM) is based on the acoustic radiation force associated with an ultrasound wave field, and enables a myriad of engineering applications with the ability to noninvasively manipulate particles in a fluid medium. We use multiple phased arrays of ultrasound transducers to dynamically move a 3D pattern of particles along a userspecified trajectory following a sequence of affine transformations. We numerically simulate and experimentally validate the NPM method using spherical expanded polystyrene particles in air, and observe good quantitative agreement. The ultrasound NPM method enables dynamic control over the user-specified pattern of particles in three dimensions. Hence, this experimental demonstration shows that ultrasound NPM can be implemented in engineering applications, such as container-less transport and measurement techniques, and manufacturing of engineered materials.

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 we quantify the position and orientation error. The 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.

Ultrasound directed self-assembly (DSA) enables noninvasively aligning high aspect ratio particles in three-dimensional (3D) user-specified orientations, which finds application in a myriad of engineering applications, including manufacturing engineered materials. However, the number of ultrasound transducers and their spatial arrangement limit the accuracy of the particle alignment with any 3D user-specified orientation. We define a set of 3D user-specified orientations and use numerical simulations to quantitatively evaluate the effect of the number of ultrasound transducers, their spatial arrangement including a sphere, cube, and two parallel plates, and the size of the spatial arrangement on the orientation error of a high aspect ratio particle in a standing ultrasound wave field. We demonstrate that a spatial arrangement of ultrasound transducers with more than two unique wave propagating directions is required to orient a high aspect ratio particle in 3D, and we determine that the orientation error decreases with the increasing number of unique wave propagation directions. Furthermore, we show that in a spherical arrangement of ultrasound transducers, the orientation error is independent of the size of the arrangement of transducers. This knowledge facilitates using ultrasound DSA as a fabrication method for engineered composite materials that derive their function from the location and orientation of particle inclusions.