University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Holograms for acoustics.

Abstract: Holograms for sound waves, encoded in a 3D printed plate, are used to shape sound fields that can be used for the contactless manipulation of objects. Sound, especially ultrasound, can be used for contactless manipulation of objects in liquid and air, a phenomenon with applications in medical imaging, non-destructive testing and metrology. Usually, the desired sound field is shaped with arrays of transducers that must be carefully connected and controlled. Here Peer Fischer and colleagues describe a relatively simple technique for creating acoustic holograms and demonstrate their potential for use in matter manipulation. The acoustic holograms are encoded in a polymer plate by 3D printing and then used to shape a sound field that can be used for contactless manipulation of objects. The method can produce complex fields with reconstruction degrees of freedom two orders of magnitude greater than existing approaches. Because the holograms are inexpensive and fast to make, the method could be widely adopted to enable new applications with ultrasound manipulation. Holographic techniques are fundamental to applications such as volumetric displays1, high-density data storage and optical tweezers that require spatial control of intricate optical2 or acoustic fields3,4 within a three-dimensional volume. The basis of holography is spatial storage of the phase and/or amplitude profile of the desired wavefront5,6 in a manner that allows that wavefront to be reconstructed by interference when the hologram is illuminated with a suitable coherent source. Modern computer-generated holography7 skips the process of recording a hologram from a physical scene, and instead calculates the required phase profile before rendering it for reconstruction. In ultrasound applications, the phase profile is typically generated by discrete and independently driven ultrasound sources3,4,8,9,10,11,12; however, these can only be used in small numbers, which limits the complexity or degrees of freedom that can be attained in the wavefront. Here we introduce monolithic acoustic holograms, which can reconstruct diffraction-limited acoustic pressure fields and thus arbitrary ultrasound beams. We use rapid fabrication to craft the holograms and achieve reconstruction degrees of freedom two orders of magnitude higher than commercial phased array sources. The technique is inexpensive, appropriate for both transmission and reflection elements, and scales well to higher information content, larger aperture size and higher power. The complex three-dimensional pressure and phase distributions produced by these acoustic holograms allow us to demonstrate new approaches to controlled ultrasonic manipulation of solids in water, and of liquids and solids in air. We expect that acoustic holograms will enable new capabilities in beam-steering and the contactless transfer of power, improve medical imaging, and drive new applications of ultrasound.

Processing and applications of intermetallic γ-TiAl-based alloys

Abstract: Development and processing of high-temperature materials is the key to technological advancements in engineering areas where materials have to meet extreme requirements. Examples for such areas are the aerospace and spacecraft industry or the automotive industry. New structural materials have to be “stronger, stiffer, hotter, and lighter” to withstand the extremely demanding conditions in the next generation of aircraft engines, space vehicles, and automotive engines. Intermetallic γ-TiAl-based alloys show a great potential to fulfill these demands.

Topological defects and interactions in nematic emulsions

Abstract: Inverse nematic emulsions, in which surfactant-coated water droplets are dispersed in a nematic host fluid, have distinctive properties that set them apart from dispersions of two isotropic fluids or of nematic droplets in an isotropic fluid. We present a comprehensive theoretical study of the distortions produced in the nematic host by the dispersed droplets and of solvent-mediated dipolar interactions between droplets that lead to their experimentally observed chaining. A single droplet in a nematic host acts like a macroscopic hedgehog defect. Global boundary conditions force the nucleation of compensating topological defects in the nematic host. Using variational techniques, we show that in the lowest energy configuration, a single water droplet draws a single hedgehog out of the nematic host to form a tightly bound dipole. Configurations in which the water droplet is encircled by a disclination ring have higher energy. The droplet dipole induces distortions in the nematic host that lead to an effective dipole-dipole interaction between droplets, and hence to chaining.