Mario Fernandez Pantoja

Objective. Despite the growing interest in cerebellar transcranial magnetic stimulation (TMS), dedicated coil designs for cerebellar targeting remain limited. This work introduces a systematic framework for the design of TMS coils specifically tailored for cerebellar stimulation. The aim of this study is to achieve flexible and accurate targeting of cerebellar regions while minimising unintended effects of adjacent cortical structures. Approach. Coil geometries were adapted to anatomically realistic head models derived from magnetic resonance imaging data of eight subjects. An inverse boundary element method was combined with a multi-objective optimisation problem (MOP) framework to explicitly control the focality and penetration depth of the induced electric field, yielding up to 100 candidate optimal coil designs. Two curved geometries were optimised for single-site and multi-locus stimulation using a combination of three coils. The characteristics of the resulting coils were evaluated by computing the electric field on spherical and anatomically realistic head models implemented in SimNIBS 4.5. Main results. The optimised designs demonstrated improved trade-off between focality and depth compared with conventional figure-of-eight and double-cone coils. When assessed in realistic head models, both geometries achieved higher spatial specificity within the cerebellum, inducing approximately 24% more volume of the region of interest and 66% less in the non-target region. Furthermore, with the proposed MOP framework, we identified a three-coil configuration capable of electronically steering stimulation within a 20 mm cerebellar region. Significance. The proposed approach enables anatomically adapted coil design with explicit field control, enhancing the precision and efficiency of cerebellar TMS. This framework establishes a robust basis for creating custom TMS coils with improved performance on future experimental and therapeutic applications involving the cerebellum.

This work presents the design, fabrication, and characterization of a flexible planar inverted-F antennas (PIFA) based on coplanar waveguide (CPW) technology, operating at 2.4 GHz and intended for Internet of Things (IoT) applications. The proposed antenna features a slot-based surrounding ground conductor, enabling its use in antenna array configurations without interconnection wires. Two low-cost and low-profile fabrication alternatives are assessed: 1) robot-assisted additive manufacturing using inkjet technology with conductive silver-based ink and 2) metallization through conductive spray sputtering on laser-patterned masks. The impact of conductivity on the antenna performance metrics is examined, revealing that increasing the amount of conductive paint sputtered in prototypes fabricated by method (2) enhances the conductivity but decreases mechanical flexibility. The optimized design achieves a bandwidth of ~150 MHz and a gain of 2.9 and 2.6 dBi for antennas fabricated using methods (1) and (2), respectively. The influence of the bending angle along the $x$ - and $y$ -axes is also evaluated, demonstrating a negligible degradation in S-parameter measurements. Mechanical stress tests involving 50 and 100 bending cycles were conducted, revealing minimal deterioration. Radiation patterns are characterized using the three-antenna method in an anechoic chamber, confirming similar performance for both (1) and (2) manufacturing methods. This comprehensive study paves the way for future low-cost antennas aimed at flexible IoT applications.

Objective: Interleaving transcranial magnetic stimulation with magnetic resonance imaging (TMS–MRI) is a promising tool for neuroscience. However, its development is limited by the strong interactions between the TMS current pulse and the high magnetic field present within the MRI environment. The objective of this study is to develop methodologies for designing TMS coils that can operate safely inside MRI scanners. Methods: By using an inverse boundary element method design framework, we study the effects of controlling different norms of the Lorentz force in the design process to produce more durable TMS coils. We apply this method to design rodent–specific TMS coils capable of withstanding the high static magnetic fields present in small animal MRI scanners. The performance of the proposed TMS coils is validated under realistic simulations using practical coil plate materials and pulses in the COMSOL Multiphysics software. Results: The numerical simulations indicate that minimising the maximum magnitude ($l^{\infty}$ norm) of the Lorentz force distribution produces TMS coils with improved mechanical behaviour when operating within an MRI environment. Significance: The proposed design strategy offers an effective solution for producing TMS coils with enhanced mechanical durability. This improvement may be particularly valuable to address the current challenges faced in interleaved TMS–MRI applications.

Full-wave simulations of lighting systems in the automotive industry remain as a computational challenge for electromagnetic compatibility (EMC) purposes. This is mainly due to the need to simulate complex nonlinear electronic systems in computationally large environments. In this letter, we present a numerical procedure that accurately predicts conducted interferences in such systems. This procedure is based on the concurrent use of electronic-electromagnetic solvers linked by multiple source ports characterized in terms of S-and Y-parameters. Numerical results are validated, using a feature-selective validation (FSV) algorithm, when confronted with measurements taken at the input terminals of the line impedance stabilization network (LISN). Further representation of currents on the main board demonstrates the unique ability of full-wave simulations to provide their physical distribution, a result of interest not only for EMC purposes but also for further structural and thermal validations.

This work introduces a new equivalent circuit generation method which can compute an accurate equivalent circuit representation for the known/measured impedance characteristics of antennas, which may assist in matching circuit design, non-Foster matching network design, and deep-learning antenna design. The method utilizes a modified Drude-Lorentz resonator representation inspired by optical material dispersion modeling to create multiple sub-circuits based on determined resonances in the impedance spectrum. Each computed sub-circuit is necessarily composed of physically realizable resistors, capacitors, and inductors, and they are connected in series to accurately reconstruct the device’s corresponding impedance characteristics over a specified region of interest. The process is automated and applicable to a wide range of antennas and electromagnetic devices with multiple resonance phenomena. Current equivalent circuit design methods are limited by a lack of generalization and can require complex, active, or non-realizable circuit topologies. The proposed Drude-Lorentz-based approach can provide valuable insight into an antenna’s resonant behavior while remaining general-purpose and only requiring passive components which are physically realizable. This improved generality is achieved by not requiring physical insights, but rather only requiring the impedance data alone. Additionally, the method creates simpler circuits than other general methods, requiring less components and component types. This method is employed to create equivalent circuits of four different exemplary types of antennas, a patch antenna, a loop antenna, a spherical helix antenna, and a metantenna unit cell. The impedances generated from these circuit examples are compared with results of their full-wave simulation counterparts and found to be in excellent agreement.

This work presents a framework to develop optimal coils of arbitrary geometry for deep transcranial magnetic stimulation (dTMS). It has been based on a continuous current density inverse boundary element method to generate dTMS coils with depth control and minimum power dissipation. Novel coil geometries that readily adapted to human head have been studied to provide focal stimulation in areas on both prefrontal cortex and right temporal lobe. The designed dTMS coils performance has been numerically validated in a realistic human head model, and prototypes have been built for experimental evaluation. The numerical simulations indicate that the proposed dTMS coils focally stimulate the prescribed brain regions with the desired target depth. The calculated metrics demonstrate that the presented designs outperform existing dTMS coils (the stimulation depth can be increased more than 15%compared to conventional dTMS coils with similar focality). Continuous current density IBEM can be used to develop novel dTMS coils with improved properties for a wide range of geometries. The proposed design method opens up a possibility for exploring new coil solutions based on complex shapes to focally deliver a desired stimulation dose to relatively deep brain targets, which might allow novel and more effective brain stimulation protocols.

Elliptical loop antennas represent a natural generalization of circular loop antennas, which have themselves received substantial attention in the last decade. The characteristics of the latter were extended to the high GHz and low THz region, where lossy materials play a major role. This paper seeks to extend these derivations to elliptical loops as well as demonstrate that elliptical loops, possessing more degrees of freedom than their circular counterparts, afford additional benefits. The asymmetric geometrical parameters of elliptical loops force some modifications to the standard calculational procedure, resulting in a closed-form solution to the fundamental equations and a computationally fast method of solution. Results show a high level of accuracy compared to full-wave solvers and reveal some remarkable features of the elliptical loops. At low frequencies, the admittance plots indicate higher Q values at the resonances for elliptical loops than those of circular loops. The higher Q values correspond to increasing ellipticity. At higher frequencies loss occurs in metals, with resonance reaching saturation in the infrared as expected with circular loops. Interestingly, it is also shown that elliptical loops can be properly engineered to radiate near-pure multipoles of a given order, further distinguishing their performance from that of circular loops.

Here a minimum power dissipation coil transducer has been designed to allow in-flight noise characterization of a low-frequency magnetic measurement system. The coil was produced using PCB technology to provide mechanical stability and easy integration close to the magnetic sensors. The transducer design strategy relies on an inverse boundary element method, which has been efficiently adapted to produce optimal multilayer PCB coils subjected to different geometrical and performance constraints. The resulting coil transducer was simulated and experimentally validated under realistic conditions where the payload is magnetically shielded from low-frequency fluctuations by using a three-layer cylindrical mu-metal enclosure. The results show that the specific transducer coil proposed efficiently produces stable magnetic conditions for adequate validation of the magnetic diagnostic system while providing reduced power dissipation and optimal mechanical stability.