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Transcranial focused ultrasound stimulation (tFUS) has emerged as a potential noninvasive therapeutic technology. Due to skull attenuations at high ultrasound (US) frequencies, successful tFUS with sufficient penetration depth requires sub-MHz US waves, leading to relatively poor stimulation specificity particularly in the axial direction (perpendicular to the US transducer). This shortcoming can potentially be overcome by utilizing two individual US beams properly crossed in time and space. For large-scale tFUS, a phased array is also required to dynamically steer focused US beams at desired neural targets. This article presents the theoretical foundation and optimization (through a wave-propagation simulator) of crossed-beam formation using two US phased arrays.
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InFocus: A spatial coding technique to mitigate misfocus in near-field LoS beamforming
Phased arrays, commonly used in IEEE 802.11ad and 5G radios, are capable of focusing radio frequency signals in a specific direction or a spatial region. Beamforming achieves such directional or spatial concentration of signals and enables phased array-based radios to achieve high data rates. Designing beams for millimeter wave and terahertz communication using massive phased arrays, however, is challenging due to hardware constraints and the wide bandwidth in these systems. For example, beams which are optimal at the center frequency may perform poor in wideband communication systems where the radio frequencies differ substantially from the center frequency. The poor performance in such systems is due to differences in the optimal beamformers corresponding to distinct radio frequencies within the wide bandwidth. Such a mismatch leads to a misfocus effect in near-field systems and the beam squint effect in far-field systems. In this paper, we investigate the misfocus effect and propose InFocus, a low complexity technique to construct beams that are well suited for massive wideband phased arrays. The beams are constructed using a carefully designed frequency modulated waveform in the spatial dimension. InFocus mitigates beam misfocus and beam squint when applied to near-field and far-field systems.
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- PAR ID:
- 10296102
- Date Published:
- Journal Name:
- IEEE Transactions on Wireless Communications
- ISSN:
- 1536-1276
- Page Range / eLocation ID:
- 1 to 1
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1109/TWC.2021.3110011
