Noninvasive electric stimulation-based treatments for neuropsychiatric disorders are of high interest in both research and clinical studies. Among them, transcranial magnetic stimulation (TMS) is widely accepted as a safe and effective method. Enhancing the performance of the apparatus requires stimulation of deeper brain regions which isn’t accessible with current coils due to the increased depth-spread tradeoff at deeper regions. In addition, focal rodent coils need to be developed to better understand brain stimulation mechanisms. Due to the smaller size of the rodent brain, a variety of challenges like the depth-spread tradeoff and high energy requirement arise when stimulating a functionally specific brain region. In this study, we have introduced tilted, wire-wrapped, multi-stacked coils for the purpose of enhancing brain stimulation for primates and non-primates. To improve the performance of the coils, we added different types of ferromagnetic cores to understand the efficacy of these cores on the distribution, decay rate, and the focality of the induced electric field. The analysis was performed using Finite Element Model (FEM) simulations, and the results were then verified using 3-d printed coils and experimental procedures. The performance of the coils was dependent on the relative permeability of the ferromagnetic core, demonstrating a general improvement in the focality and energy requirement of these TMS coils.
ZnSe has been a great choice for the rare-earth and transition metal doping to develop lasers. It is an excellent material for variety of optical applications due to wide transparency range, good fabricability and very low optical absorption similar to other selenides. NASA Marshall Space Flight Center has developed large crystals using physical vapor deposition (PVD) doped with transition metals for lasing. GaAs based quasi-phase matched structures have a lot of limitations including difficulty of frequency conversion from available high-power lasers. We are developing Si- and GaAs- based templates and using microfabrication process to deposit ZnSe using physical vapor transport (PVT) method. Experimental results of the fabrication of templates and growth of ZnSe on templates will be presented.
Transcranial magnetic stimulation (TMS) is one of the most effective non-invasive neuromodulation techniques used to treat neurological and psychiatric disorders. It is also highly popular to be used for studying and understanding brain functions and mechanisms. Multisite simultaneous or sequential stimulation of different brain regions provides a new methodology to study and comprehend the functional dependence and causal relationships among different regions and networks. However, due to the large coil size, which doesn't allow more than two coils being simultaneously utilized, and the non-ideal field focality and penetration depth of existing commercial coils, multisite simulation methods have not been well exploited. In this study, an angle-wrapped and multi-stacked circular coil is proposed to form an array of coils and used for this purpose. The induced electric field hot spot of the single coil and the coil array designs for fixed multisite stimulation were studied with the finite element method. The FEM simulations were then verified with experiments performed on fabricated coils. The performed simulations and experiments indicated the proposed coils' enhanced performance regarding the hot spot size and electric field decay rate compared to conventional circular coils. The successfully demonstrated close proximity and small spot size of stimulation show great potential for future fixed and adjustable multisite brain stimulation.
There are several mechanisms which have been proposed for the existence of colossal dielectric constant in the class of perovskite calcium copper titanate (CaCu3Ti4O12 or CCTO) materials. Researches indicate that existence of twinning parallel to (100) (001) and (010) planes causes planar defects and causes changes in local electronic structure. This change can cause insulating barriers locally which contribute to the large dielectric values irrespective of processing. The combination of insulating barriers, defects and displacements caused by twinning have been attributed to the generation of large dielectric constant in CCTO. To examine some of these arguments some researchers replaced Ca with other elements and evaluated this concept. In this study we present the synthesis and characterization of Ga2/3Cu3Ti4O12-xNx (GCTON) material. This provides both distortion due to atomic size difference and defects due to insertion of nitrogen. The morphology of the compound was determined to show that processing has tremendous effect on the dielectric values. The resistivity of GCTON was several order higher than CCTO and dielectric constant was higher than 10,000.
In recent years, there is an increasing interest in noninvasive treatments for neurological disorders like Alzheimer and Depression. Transcranial magnetic stimulation (TMS) is one of the most effective methods used for this purpose. The performance of TMS highly depends on the coils used for the generation of magnetic field and induced electric field particularly their designs affecting depth and focality tradeoff characteristics. Among a variety of proposed and used TMS coil designs, circular coils are commonly used both in research and medical and clinical applications. In current study, we focus on changing the outer and inner sizes (diameter) and winding turns of ring coils and try to reach deeper brain regions without significant field strength decay. The induced electric field and the decay rate of the generated field with depth were studied with finite element method calculations. The results of the performed simulations indicate that larger diameter coils have a larger equivalent field emission aperture and produce larger footprint of induced electric field initially. However, their emission solid angles are smaller and, as a result, the field divergence or the decay rates of the generated field with depth are smaller as well, which give them a good potential to perform better for deep brain stimulation compared with that of smaller coil.
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