The ever-increasing demand for wireless communication has led to an incentive to increase the data rate and reduce the size of communication devices, be it antennas or other components of RF front-ends. The emphasis is primarily on increasing data rate, which leads to the use of higher frequency bands and wider bandwidths in modern communication technology research and innovations. However, increasing frequency in many technology areas cannot necessarily be beneficial because of physical constraints. For example, communication under seawater or other RF harsh environment requires very-low-frequency (VLF) or ultra-low-frequency (ULF) signals to penetrate lossy media that block high-frequency signals. Furthermore, recent advances in neuroscience have demonstrated the potential of VLF and ULF electromagnetic (EM) waves for studying brain function and treating neurological conditions. The main challenge is that most VLF and ULF generators are large and power-hungry, making them impractical to use in many applications. As a result, recent approaches using permanent magnets have started to provide groundbreaking solutions that can revolutionize VLF/ULF communication.
This work presents a new method for generating low-frequency EM waves for navigation and communication in challenging environments, such as underwater and underground, as well as magnetic stimulation of brain neurons. The key concept is to disturb the magnetic energy stored around a permanent magnet in a time-variant fashion. The magnetic reluctance of the medium around the permanent magnet is modulated to alter the magnetic flux intensity and direction (disturb the stored energy) in order to achieve this goal. The nonlinear properties of the surrounding magnetic material are a critical phenomenon for efficient and effective modulation. Since the proposed method of generating the EM field is not based on a second-order system (resonant structure), the bandwidth of any modulation schema is not limited to the overall system quality factor. A transmitter is prototyped as a proof of concept, and the generated field is measured. Compared to the rotating magnet, the prototyped transmitter can modulate up to 50% of the permanent magnet's stored energy with much lower power consumption.
The magnetic equivalent circuit (MEC) approach is also used to analyze the transmitter. Finally, the transmitter is optimized, and the measurement results show a 7 dB improvement in efficiency compared to the primary structure. As a result of promising performance, we propose that this method be used to improve the performance of transcranial magnetic stimulation (TMS) devices. Furthermore, the comparison simulated results back up the validity of the proposed technique, revealing that focality and penetration depth are improved while utilizing much less power than traditional TMS devices. / Doctor of Philosophy / The growing demand for wireless communication has created an incentive to increase the data rate while decreasing the size of communication devices, whether they are antennas or other radio frequency (RF) components between the antenna and at least one mixing stage of a receiver and/or the power amplifier of the transmitter. The emphasis is primarily on increasing data rate, which leads to the use of higher frequency bands and wider bandwidths in modern communication technology research and innovations. However, increasing frequency in many technology areas may not be beneficial because of physical constraints. For example, communication under seawater or underground requires very-low-frequency (VLF) or ultra-low-frequency (ULF) signals to penetrate lossy media that block high-frequency signals. Furthermore, recent advances in neuroscience have demonstrated the potential of VLF and ULF electromagnetic (EM) waves for studying brain function and treating neurological conditions. The main challenge is that most VLF and ULF generators are large and power-hungry, making them unsuitable for many applications. As a result, recent approaches using permanent magnets have started to provide groundbreaking solutions that can revolutionize VLF/ULF communication.
This work presents a new method for generating low-frequency EM waves for navigation and communication in challenging environments, such as underwater and underground, as well as magnetic stimulation of brain neurons. The key idea is to disturb the magnetic energy stored around a permanent magnet in a time-variant fashion. The magnetic reluctance of the medium around the permanent magnet is modulated to change the magnetic flux intensity and direction (disturb the stored energy) in order to achieve this goal. The nonlinear properties of the surrounding magnetic material are a critical factor in achieving efficient and effective modulation. Since the proposed method of generating the EM field does not rely on a second-order system (resonant structure), the bandwidth of any modulation schema is not constrained by the overall system quality factor. As a proof of concept, a transmitter is prototyped, and the generated field is measured. Compared to the rotating magnet, the prototyped transmitter can modulate up to 50% of the permanent magnet's stored energy with much lower power consumption.
The magnetic equivalent circuit (MEC) approach is also used to analyze the transmitter. Finally, the transmitter is optimized, and the measurement results show a 7 dB improvement in efficiency compared to the primary structure. As a result of promising performance, we propose that this method be used to improve the performance of transcranial magnetic stimulation (TMS) devices. Furthermore, the comparison simulated results support the validity of the proposed technique, revealing that focality and penetration depth are improved while using much less power than traditional TMS devices.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/108074 |
| Date | 01 February 2022 |
| Creators | Hosseini Fahraji, Ali |
| Contributors | Electrical Engineering, Manteghi, Majid, Scales, Wayne A., Adjerid, Slimane, Yang, Yaling, Safaai-Jazi, Ahmad |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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