Holograms for acoustics

Abstract

Holographic techniques are fundamental to applications such as volumetric displays, high-density data storage and optical tweezers that require spatial control of intricate optical or acoustic fields within a three-dimensional volume. The basis of holography is spatial storage of the phase and/or amplitude profile of the desired wavefront 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 holography 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 sources; 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.

Acoustic Tweezing and Patterning of Concentration Fields in Microfluidics

“…Sparked by the ambition to dynamically manipulate microparticles in solution, there have been major advances in the development of experimental methods to control ultrasound acoustic fields at the microscale [1,2]: for example, using bulk acoustic waves [3][4][5], surface acoustic waves [6][7][8][9], transducer arrays [10][11][12], and 3D-printed transmission holograms [13]. The acoustic radiation force acting on particles in acoustic fields is used in these systems to manipulate particles and cells, thereby concentrating [14], trapping [15,16], separating [17], and sorting [18] bioparticles and cells based on their acoustomechanical properties.…”

Design of multi-frequency acoustic kinoforms

“…This is because the kinoforms need to focus over a greater number of target points using the same spacebandwidth product or number of pixels. 1,7 Similarly, increasing the image complexity or area decreases the contrast. The complexity of features that can be realised is also limited by diffraction for each wavelength.…”

“…The precise manipulation of acoustic fields in 3-D is vital to a wide range of applications in physical acoustics. [1][2][3] Recently, a new approach for the generation of complex diffraction limited acoustic fields in 3-D was introduced. 1 This works by mapping the continuous wave output of a planar single element transducer onto a pre-determined phase distribution which then diffracts to form a target acoustic field.…”

Generating arbitrary ultrasound fields with tailored optoacoustic surface profiles

“…Promising uses include the precise correction for aberrations introduced by the skull 5 and the manipulation of particles. 6 This work was funded by the Engineering and Physical Sciences Research Council and the UCL EPSRC Centre for Doctoral Training in Medical Imaging. …”

“…This has led to a number of works exploring novel alternatives including sparse 2-D piezoelectric arrays, 3 acoustic kinoforms created using metamaterials, 5 or profiles fabricated using three-dimensional (3-D) printing techniques. 6 The optical generation of ultrasound (OGUS) using the photoacoustic effect is particularly well suited for the generation of these patterned fields. The lack of electrical connections allows a "transducer" to be deposited on any surface that can be illuminated.…”