Ultrasound Phased Array Systems for Neuromodulation
Open Access
- Author:
- Ilham, Sheikh Jawad
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 24, 2024
- Committee Members:
- Qiming Zhang, Major Field Member
Nanyin Zhang, Outside Unit & Field Member
Mehdi Kiani, Chair & Dissertation Advisor
Nilanjan Ray Chaudhuri, Major Field Member
Madhavan Swaminathan, Program Head/Chair - Keywords:
- Ultrasound
Phased Array
Beamforming
Crossed-Beam
Software-Hardware Co-Design Platform
Multi-Channel HV Driver - Abstract:
- Neuromodulation has the potential in treating various neural, neurological and neuropathic conditions as well as in augmenting cognitive, sensory, and motor functions. Neuromodulation technologies like Transcranial Magnetic Stimulation (TMS) and Transcranial Direct/ Alternating Current Stimulation (tDCS/ tACS), have limitations, including low specificity, shallow penetrability, and less control. In contrast, Transcranial Focused Ultrasound Stimulation (tFUS) offers a true non-invasive alternative overcoming some of these limitations. However, conventional tFUS systems often rely on bulky single-element transducers limiting large-scale neuromodulation applications with challenges such as, manual maneuvering of the ultrasound beam, poor power efficiency, and less flexibility in tuning relevant wave-parameters. This dissertation addresses these challenges through four key contributions. First, an optimal design methodology is presented for phased array transducers, which maximizes spatial resolution and power efficiency. This approach introduces a new figure of merit (FoM) that balances these metrics while minimizing off-target stimulation. This innovative approach offers the designers an efficient framework for designing high-performance ultrasound transducer arrays. Second, thin-film Piezoelectric Micromachined Ultrasound Transducer (PMUTs) arrays are introduced for tFUS applications, utilizing a 1.5 $\mu$m PZT thin film to achieve high acoustic pressure output at lower voltage. A comprehensive comparison is provided between thin-film (PMUT) and bulk PZT transducer arrays, highlighting the trade-offs in performance, power consumption, and fabrication complexity. This advancement opens the door for more compact and energy-efficient tFUS devices. Third, crossed-beam ultrasound technology is implemented to improve the axial resolution of tFUS, where two phased-array beams are crossed to create a composite beam with significantly enhanced resolution and spatial peak pressure, validated through detailed simulations and experimental results. Finally, a custom-built, FPGA-based software-hardware co-design platform is developed for dynamic beamforming. This platform, capable of handling high-voltage driver electronics, allows for flexible wave-pattern generation and dynamic control over relevant wave-parameters, enabling real-time reconfiguration and efficient operation in tFUS systems. Together, these contributions lay the groundwork for developing high-performance and more scalable ultrasound neuromodulation systems which hold the promise for both fundamental neuroscience research and clinical applications.