Ultrasound waves can propagate through an intact human skull and alter nerve activity through targeted delivery. Low-intensity focused ultrasound (LIFU) has shown great promise for the modulation of brain function and reversal of neurological and psychiatric dysfunction. In this work, acoustic holographic lenses are designed using time-reversal and phase conjugation techniques to compensate for skull aberrations as well as pattern the ultrasonic field to target precise locations in the brain. We verify our work using numerical simulations and submerged experiments using a 3D printed skull phantom. Multiphysics simulations were also implemented to study the effects of elastic wave propagation, i.e. shear effects and attenuation of the skull.
Focused ultrasound (FU) is an emerging non-invasive and non-ionizing therapeutic technology that has the potential to treat a variety of medical conditions. FU can heat up, destroy, or change target tissue while minimizing damage to tissue outside the target area by precisely focusing on ultrasonic beams. Understanding and characterizing high-intensity FU is essential for planning and administering therapeutic procedures safely. Modeling nonlinear ultrasound is a computationally demanding problem. The complex diffraction structure requires the use of accurate diffraction models and a fine spatial numerical grid. In this work, we will propose an accelerated and more efficient strategy in which the nonlinearity in the simulation is monitored, and a corresponding increase in the resolution required to resolve higher harmonics is actively implemented.
Acoustic patterning and focusing is an interdisciplinary topic covering a wide range of applications. A particular challenge arises from the nonlinear distortion of the pressure waveforms that occurs at high acoustic intensities. Such a phenomenon, if not treated, limits the control of the sound field in the nonlinear range, reducing the localization and efficiency. In this work, we investigate acoustic holographic lenses for constructing precise nonlinear acoustic fields. Such passive structures provide higher fidelity at a fraction of the cost of the expensive and complex phased array transducers.
This work introduces and investigates a metallic acoustic holographic lens to create an arbitrary acoustic pressure pattern in a target plane, using sound reflection phenomenon. The lens performs as a spatial sound modulator by introducing a relative phase shift to the reflected wavefront. The phase-shifting lens is designed using an iterative angular spectrum algorithm, and 3D-printed from powdered aluminum through direct metal laser melting. Then its capabilities to construct diffraction-limited complex pressure patterns and create multifocal areas are tested under water, numerically and experimentally. The proposed holographic lens design can drive immense improvements in applications involving medical ultrasound, ultrasonic energy transfer, and particle manipulation.
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