MSc thesis project proposal
 Acoustic holograms for precise generation of focused ultrasound waves
The emerging field of ultrasound neuromodulation  is demanding the emergence of a new generation of focused ultrasound transducer technologies. The ideal transducer would be able to, firstly, generate focused ultrasound waves with spatial-resolution approaching the sizes of single neurons (~10 micrometers), and secondly, digital steer the focused wave to any pre-determined location in the three-dimensional space. This ultimate scientific tool would allow neuroscientists to better understand how ultrasound and neurons interact, and would pave the way to a powerful addition to the toolbox of physicians for the treatment of a vast range of neurological  and immunologic diseases .
Yet, the traditional method to produce steerable focused ultrasound waves relies on 2D phased-array transmit beamforming chips . These devices feature equally-spaced 2D arrays of ultrasound transducer elements, each paired with an electronic beamforming circuit. Altogether, these devices can produce any arbitrary type of lens in the electrical domain by tuning the phase of each driving signal, which is then translated into a focused ultrasound wave by the ultrasound transducers. However, to accurately produced focused waves, the spacing in between these elements needs to be half of a wavelength. This creates a fundamental bottleneck with this approach: ultrasound wavelengths of ~10 micrometers would be required to focus the waves in single neurons, however, this means that each transduce element and electronic beamforming circuit would need to be implemented in an area of 5 x 5 squared micrometers. However, current 2D phased-array transmit beamforming chips still require areas greater than 100 x 100 squared micrometers for proper operation, which drastically limit spatial resolution.
To overcome this fundamental limitation, this project aims at developing acoustic holograms [5,6]. Here, the focusing relies on the fabrication of phase-encoded materials, such as Fresnel lenses, to manipulate waves. For this reason, only single transducer and driving circuit is required to create a planar incident ultrasound wave into the hologram, which then produces the focused wave. The objective of this project is to explore the manufacturing of acoustic holograms using micro and nanofabrication techniques. Here, since the feature size can be smaller than 1 micrometer, we hypothesize that the spatial resolution of focused ultrasound waves can improve by at least one order of magnitude when compared with current 2D phased-array beamforming techniques.
1. Tufail, Y. et al. Transcranial pulsed ultrasound stimulates intact brain circuits. Neuron 66, 681–94 (2010).
2. J. Blackmore, S. Shrivastava, J. Sallet, C. R. Butler, and R. O. Cleveland, "Ultrasound Neuromodulation: A Review of Results, Mechanisms and Safety," Ultrasound Med Biol, vol. 45, no. 7, pp. 1509--1536, 2019, doi: 10.1016/J.ULTRASMEDBIO.2018.12.015.
3. T. Costa, C. Shi, K. Tien, J. Elloian, F. A. Cardoso, and K. Shepard, "An Integrated 2D Ultrasound Phased Array Transmitter in CMOS with Pixel Pitch-Matched Beamforming," IEEE Transactions on Biomedical Circuits and Systems, vol. 15, no. 4, pp. 731-742, 2021
4. L. V. Borovikova et al., "Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin," Nature, vol. 405, no. 6785, pp. 458--462, 2000, doi: 10.1038/35013070.
5. T. Costa, C. Shi, K. Tien, J. Elloian, F. A. Cardoso, and K. Shepard, "An Integrated 2D Ultrasound Phased Array Transmitter in CMOS with Pixel Pitch-Matched Beamforming," IEEE Transactions on Biomedical Circuits and Systems, vol. 15, no. 4, pp. 731-742, 2021, doi: 10.1109/tbcas.2021.3096722.
6. Y. Xie et al., "Acoustic Holographic Rendering with Two-dimensional Metamaterial-based Passive Phased Array," Scientific Reports, vol. 6, no. 1, p. 35437, 2016, doi: 10.1038/srep35437.
7. F. Ma, Z. Huang, C. Liu, and J. H. Wu, "Acoustic focusing and imaging via phononic crystal and acoustic metamaterials," Journal of Applied Physics, vol. 131, no. 1, p. 011103, 2022, doi: 10.1063/5.0074503.
1st part: Literature review of acoustic hologram technology.
2nd part: Design, fabrication and testing of acoustic hologram topology that maximizes spatial resolution
MSc students from Microelectronics, Biomedical Engineering or Mechanical Engineering. Interested students should include their CV, the list of courses attended, and a motivation letter.
dr. Tiago Costa
Department of Microelectronics
Last modified: 2022-02-25