United States

In-wheel motor is regarded as the most promising drive system of next generation electric vehicles in merit of high transmission efficiency, flexible control and compact
structure [1]. Since the in-wheel motor often operates under different conditions and possesses multiple external heat sources, electromagnetism-thermal analysis is essential during the
motor design stage [2]. Generally, the current electromagnetism-thermal analysis is based on finite element analysis (FEA), the large time-consumptions of this method brings challenges to
the design of this kind of motor [3]. Therefore, a rapid design method of in-wheel motor based on a common-node magneto-thermal bidirectional coupling network (CMTBCN) model is
proposed in this paper. In the CMTBCN model, some nodes of the motor are used as common nodes of the equivalent magnetic network (EMN) model and the equivalent thermal network
(ETN) model to avoid repeated modeling. Then the effect of temperature on the coercivity and permeability of permanent magnets is considered in EMN, the losses calculated by EMN at
initial temperature are used as the heat sources of ETN to calculate the new temperature. The temperature of each component of the motor and the electromagnetic performance under
different working conditions can be obtained more accurately by using the bidirectional coupling method. Finally, an in-wheel motor is designed and optimized based on CMTBCN model.
Fig. 1 (a) shows the 3D structure and parametric model of the in-wheel motor. Fig. 1 (b) shows the proposed common-node magneto-thermal bidirectional coupling network model. Fig. 2
(a) compared the airgap flux density and its harmonic analysis obtained by CMTBCN and FEA. Fig. 2 (b) compared the A-phase no-load flux linkage and back-EMF obtained by
CMTBCN and FEA at -20 and 100 degrees Celsius. Fig. 2 (c) shows the static temperature distribution of the in-wheel motor under the rated load obtained by FEA. Fig. 2 (d) shows the
prototype of stator and rotor of the proposed in-wheel motor.
More detailed analysis and experimental verification will be presented in the full paper.&lt;br&gt;

**References:**&lt;br&gt;

[1] P. Liang, F. Chai and Y. Yu, IEEE Transactions on Industrial Electronics, vol. 66, no. 2, pp. 1162-1171, Feb. 2019.&lt;br&gt;
[2] X. Chen and G. Li, 2020 13th International Conference on Intelligent Computation Technology and Automation (ICICTA), 2020, pp. 683-686.&lt;br&gt;
[3] X. Li, F. Shen and S. Yu, IEEE Transactions on Industrial Electronics, vol. 68, no. 8, pp. 6560-6573, Aug. 2021.&lt;br&gt;

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MMM 2022

Optimization Design and Analysis of an In Wheel PM Motor Based on Common

In-wheel motor is regarded as the most promising drive system of next generation electric vehicles in merit of high transmission efficiency, flexible control and compact
structure [1]. Since the in-wheel motor often operates under different conditions and possesses multiple external heat sources, electromagnetism-thermal analysis is essential during the
motor design stage [2]. Generally, the current electromagnetism-thermal analysis is based on finite element analysis (FEA), the large time-consumptions of this method brings challenges to
the design of this kind of motor [3]. Therefore, a rapid design method of in-wheel motor based on a common-node magneto-thermal bidirectional coupling network (CMTBCN) model is
proposed in this paper. In the CMTBCN model, some nodes of the motor are used as common nodes of the equivalent magnetic network (EMN) model and the equivalent thermal network
(ETN) model to avoid repeated modeling. Then the effect of temperature on the coercivity and permeability of permanent magnets is considered in EMN, the losses calculated by EMN at
initial temperature are used as the heat sources of ETN to calculate the new temperature. The temperature of each component of the motor and the electromagnetic performance under
different working conditions can be obtained more accurately by using the bidirectional coupling method. Finally, an in-wheel motor is designed and optimized based on CMTBCN model.
Fig. 1 (a) shows the 3D structure and parametric model of the in-wheel motor. Fig. 1 (b) shows the proposed common-node magneto-thermal bidirectional coupling network model. Fig. 2
(a) compared the airgap flux density and its harmonic analysis obtained by CMTBCN and FEA. Fig. 2 (b) compared the A-phase no-load flux linkage and back-EMF obtained by
CMTBCN and FEA at -20 and 100 degrees Celsius. Fig. 2 (c) shows the static temperature distribution of the in-wheel motor under the rated load obtained by FEA. Fig. 2 (d) shows the
prototype of stator and rotor of the proposed in-wheel motor.
More detailed analysis and experimental verification will be presented in the full paper. 

**References:** 

[1] P. Liang, F. Chai and Y. Yu, IEEE Transactions on Industrial Electronics, vol. 66, no. 2, pp. 1162-1171, Feb. 2019. 
[2] X. Chen and G. Li, 2020 13th International Conference on Intelligent Computation Technology and Automation (ICICTA), 2020, pp. 683-686. 
[3] X. Li, F. Shen and S. Yu, IEEE Transactions on Industrial Electronics, vol. 68, no. 8, pp. 6560-6573, Aug. 2021. 

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poster

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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For tickets to the event, please register at the following link: https://magnetism.org/registration

Please register for the MMM 2022 conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

In-wheel motors have been considered as one of the core technologies for the future developments of electric vehicles (EVs), where the outstanding feature is that the drive
motor is directly connected to the vehicle wheel [1]. It indicates that, to the EVs, the short transmission chain and high transmission efficiency can be achieved potentially by adopting the
in-wheel motor [2]. Yet, the direct-drive with in-wheel motor gaining advantages of power transmission, while it also makes the motor straightly faced with the complex drive environment,
such as the diverse operation conditions and road conditions. It means that, to the in-wheel motor, the problems of vibration and noise are more prominent and worthy of concern. This is
essential for realizing the high reliability and desirable comfort of EVs. Therefore, how to effectively suppress the vibrations and reduce noise is becoming a hot research field and full of
challenge. Then, a new perspective of radial electromagnetic force (REF) modulation is proposed for studying the vibration characteristic of a V-shaped PM in-wheel (VPM-IW) motor in
this paper. By purposely considering the modulation effect of REF into motor design, the electromagnetic vibration of VPM-IW motor is suppressed effectively.
Firstly, Fig.1(a) shows that the VPM-IW motor with the pole-slot combination of 40-pole/24-slot is selected as the design example. Fig.1(b) shows the deformation on the motor caused by
the different orders of REF. And Fig. 1(c) shows the principle of REF modulation. Then, Fig. 2(a)-Fig. 2(d) show the relationship between radial flux density (RFD) and REF. It can be
seen that, the dominant spatial order of REF, such as 4th, is generated by 4kth RFD harmonics. Hence, 4th REF can be suppressed by reducing 4kth RFD harmonics. Next, the multiobjective
genetic algorithm (MOGA) is adopted considering the force modulation effect. Fig. 2(g) to Fig. 2(n) show the comparison of performances. Fig. 2(m) and Fig. 2(n) show that the
optimal structure realizes the reduction of vibration and noise and the highest vibration peak appears around 4979 Hz, which is frequency of 4th mode.
The more detailed theoretical analysis and research results will be provided in the full paper. 

**References:** 

[1]W. N. Fu and S. L. Ho, IEEE Transactions on Magnetics, vol. 46, no. 1, pp. 127-134, Jan. 2010. 
[2] S. Zuo, F. Lin and X. Wu, IEEE Transactions on Industrial Electronics, vol. 62, no. 10, pp. 6204-6212, Oct. 2015. 

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Research on Vibration Characteristic of a V shaped PM In

I Introduction:
Typically, EVs adopt lithium-ion batteries as power supply. Therefore, constant current (CC) mode and constant voltage (CV) mode can be implemented for battery charging applications.
At present, various control strategies have been proposed. However, these methods require complex control strategies and additional components, often lead to increased switching
losses[1] and frequency bifurcation[2], and are difficult to achieve with zero phase angle input (ZPA). In this paper, a switchable hybrid compensation structure is designed to achieve loadindependent
output current and load-independent output voltage under ZPA conditions by switching the receiver-side compensation structure without additional devices and complex
control methods.
II Method and Discussion
A hybrid topology using different compensations in the receiver side, i.e., LC-LC compensation and LC-LCCL compensation is developed. Meanwhile, the compensation coil is integrated
into the receiving coil, the magnetic field is enhanced without any reactive power flow between the compensation and receiving coils, which can effectively improve the power
transmission distance, efficiency, and capacity. At a fixed frequency, no complicated control methods are required, and constant voltage and constant current can be achieved under ZPA
conditions. Besides, by optimizing the integrated coil and designing compensation parameters, the system can still maintain good CC-CV output characteristics when misalignment
happens.
III Conclusion
According to the experimental results, the wireless charging system can operate within 100mm misalignment in X-axis when the maximum fluctuations of the charging current IB in CC
mode and the charging voltage VB in CV mode are less than 7% which is consistent well with the theoretical analysis. Besides, the wireless charging system can achieve the maximum
efficiency at 93.43% with a 15-cm air gap when delivering 1442 W to the load. 

**References:** 

[1] Z. Li, C. Zhu, J. Jiang, K. Song, and G. Wei, “A 3 kW wireless power transfer system for sightseeing car supercapacitor charge,” IEEE Trans. Power Electron., vol. 32, no.
5, pp. 3301–3316, May. 2017. 
[2] C. W. Wang, G. A. Covic, and O. H. Stielau, “Power transfer capability and bifurcation phenomena of loosely coupled inductive power transfer systems,” IEEE Trans. Ind. Electron.,
vol. 51, no. 1, pp. 148–157, Feb. 2004 

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Analysis and Design of Constant Current and Constant Voltage Outputs of Integrated Coil Wireless EV Charging System

Numerical analyses should include the computation of magnetic hysteresis to estimate the performance of electric machines accurately. However, the finite element method
(FEM) requires significant time to simulate the hysteretic field because a hysteretic function modeled by, e.g., the Preisach model or the play model [1] must be called for each element and
time step.
The model order reduction (MOR) methods can effectively reduce the computation time of the FEM. This study aims to establish a new hysteretic MOR method for electric machines.
Specifically, we incorporate the hysteretic characteristics to the Cauer ladder network (CLN) method [2], a spatial mode decomposition technique showing superior convergence. It retains
physical interpretation, i.e., the inductances and resistances of the ladder network are directly computed from the decomposed modes. Therefore the nonlinear magnetic characteristics can
be directly incorporated [3].
The hysteresis effect is incorporated in the first inductor shown in Fig. 1. The magnetic fluxes flowing through the inductors are used as state variables. A semi-implicit time-marching
scheme is developed to reflect hysteretic properties without nonlinear iterations. Static I-φ loops are used to identify the scalar play model representing the first inductor. Those loops are
obtained by FE magnetostatic analysis, where the hysteretic behavior is calculated by the vector play model [1].
The reversible component is used to represent the second or later inductors, considering the characteristics of the minor loop [4]. The resistances of the CLN are prepared as functions of the
first stage magnetic flux with anhysteretic approximation.
3. Numerical analysis
An iron-cored inductor was analyzed, where a PWM voltage input was applied to the coil. Fig. 2 shows the locus of total current I1 and the first stage magnetic flux φ1 obtained by the
proposed CLN method (solid red line), which agreed with the transient FEM result (solid black line) better than the conventional equivalent circuit (dotted red line). 

**References:** 

[1] R. Mitsuoka et al., IEEE Trans. Magn., vol. 49, no. 5, pp. 1689–1692 (2013). 
[2] A. Kameari et al., IEEE Trans. Magn., vol. 54, no. 3, 7201804 (2017). 
[3] H. Eskandari and T. Matsuo, IEEE Trans. Magn., vol. 56, no. 2, 7505904 (2020). 
[4] Y. Shindo, T. Miyazaki and T. Matsuo, IEEE Trans. Magn., vol. 52, no. 3, 6300504, (2016). 

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A Model Order Reduction of Hysteretic Eddy current Fields in Electric Machines Using Cauer Ladder Network Method

In the marine environment, energy supply for distributed sensors is one of the main difficulties facing Internet of Things technology. Up to now, a variety of energy
harvesters have been created to convert wave kinetic energy into electrical energy through electromagnetic induction, piezoelectric effects and other principles. At present, although some
wave energy harvesters can collect wave energy and provide power for some low-power products, the overall output response frequency is greater than 1Hz[1], which is higher than the
most common wave frequency of 0.25Hz-1.0Hz. Some experts with extensive achievements in energy harvesters are committed to the research of low-frequency and broadband, however,
the output voltage of the designed wave energy harvester is too small[2], meantime the overall structure is extremely complex[3]. In addition, scholars have not explored the multidirectional
energy harvesting enough, and the existing studies are mostly based on the spherical friction structure[4], but spherical shapes can lead to lower energy density or material
utilization. In this paper, an electromagnetic wave energy harvester with a special double pendulum structure (as shown in Fig.1) has been proposed, the energy harvester can also capture
vibrational energy in multiple directions, responding to minimum frequencies of less than 0.25Hz and to currents with velocities of approximately 0.4m/s. This energy harvester can charge
a 220μF capacitor to about 32V in 50s with a peak power of 120mW under vibration conditions with a vertical height of 50 cm and a frequency of 1.0Hz, and can charge the capacitor to
about 16V in 50s at a horizontal speed of 0.72m/s (as shown in Fig.2). The results show that the wave energy harvester designed in this paper can respond to multi-directional vibrations,
and the response frequency is lower and wider, which is more favorable for wave energy harvesting. 

**References** 

[1] H. Liang, G. Hao and O. Z. Olszewski, International Journal of Mechanical Sciences., Vol. 219, 107130 (2022) 
[2] M. Li, X. Jing, Energy Conversion and Management., Vol. 244, 114466 (2021) 
[3] Z. Li, X. Jiang and P. Yin, Applied Energy., Vol. 302, 117569 (2021) 
[4] Q. Gao, Y. Xu and X. Yu, ACS Nano., Vol. 16, p.6781-6788 (2022) 

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Extremely Low Frequency Multi Directional Electromagnetic Wave Energy Harvester Based on Special Double Pendulum Structure

Variable flux memory machines (VFMM) using low coercive force (LCF) permanent magnets (PM) have been extensively investigated [1]-[5]. Normally, the series hybrid
magnet topology equipped with both PM with high coercive force (HCF) and LCF PMs to achieve high torque density and extended constant power speed range simultaneously, and two
kinds of PMs are magnetically connected in series to avoid unintentional demagnetization in LCF magnets. Nevertheless, the role LCF PM acts in the series magnetic circuit and its
potential effect on the air-gap flux density remain unclear. In this paper, the flux barrier effect of LCF PM on series VFMM is revealed and investigated, and an approach to preventing the
air-gap flux density drop is presented.
The conventional series hybrid magnet VFMM and interior permanent magnet (IPM) machine sharing identical usage of HCF PMs are shown in Fig.1. In Fig.1(e), the back-EMF amplitude
of the series VFMM is lower than that of the IPM machine. This is mainly due to the fact that the air-gap flux enhancement by the magnetomotive force of the LCF PM cannot compete
with the weakening effect by the magnetic reluctance of LCF PM. As a result, the flux barrier effect of the LCF PMs is identified, which further leads to a reduction of the torque density.
The topology of VFMM with dual-layer PMs is shown in Fig.1(c). The separation of the PMs weakens the barrier effect on the HCF PM and the bypass flux path reduces the equivalent
reluctance in the magnetic circuit. It can be observed in Fig.1 (d) that the air-gap flux density and flux variable range are improved. That is to say, the magnetic flux barrier effect of LCF
PM is reduced with the proposed dual-layer PM design.
The test results of the open-circuit back-EMF of the dual-layer series hybrid magnet VFMM prototype are shown in Fig.2. The experiments agree well with the FE-predicted results. The
detailed analysis, suppression methods of the flux barrier effect, and the detailed test results, will be given in the full paper. 

**References:** 

[1] V. Ostovic, "Memory motors," IEEE Ind. Appl. Mag., vol. 9, no. 1, pp. 52-61, Jan./Feb. 2003. 
[2] K. Sakai, K. Yuki, Y. Hashiba, N. Takahashi and K. Yasui, "Principle of the variable-magnetic-force memory motor," in Proc. Inter. Conf. Elec. Mach. System. (ICEMS), 2009, pp. 1-6. 
[3] N. Limsuwan, T. Kato, K. Akatsu and R. D. Lorenz, "Design and evaluation of a variable-flux flux-intensifying interior permanent-magnet machine," IEEE Trans. Ind. Appl., vol. 50,
no. 2, pp. 1015-1024, Mar./Apr. 2014. 
[4] H. Hua, Z. Q. Zhu, A. Pride, R. Deodhar and T. Sasaki, "A novel variable flux memory machine with series hybrid magnets," in Proc. 2016 IEEE Energy Conversion Congress and
Exposition (ECCE), 2016, pp. 1-8. 
[5] H. Yang, H. Zheng, H. Lin, Z. Q. Zhu and S. Lyu, "A novel variable flux dual-layer hybrid magnet memory machine with bypass airspace barriers," in Proc. 2019 IEEE International
Electric Machines & Drives Conference (IEMDC), 2019, pp. 2259-2264. 

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Analysis of flux barrier effect of LCF PM in series hybrid magnet variable flux memory machine

This paper presents the effects of magnetostriction of core loss and sound level on the design of power transformers and the results of analysis via the particle swarm
optimization (PSO) method. The core losses and the magnetostrictive forces in the ferromagnetic cores of transformers of various capacities, ranging from 15 MVA to 120 MVA, were
found to be significantly different from each other, as shown in Figure 1. Further, core loss was approximately proportional to capacity and core volume. However, the sound level
performance was not linear because of the squareness ratio (). This study utilized three types of soft core material: 30ZH105, 27ZH100 (Japan), and 27PH100 (Korea). The hysteresis loop
and magnetostriction were measured for various magnetic parameters. It was found that extremely high does not directly affect core loss. Whenwith respect to the sound level is high, the
experimental and design values are almost the same. The PSO method simulation results for transformers with several capacities, with respect to sound level and core loss performance,
were analyzed and compared with experimental values, as shown in Figure 2. 

**References:** 

[1] L. Bernard, , et. al., “Effect of stress on switched reluctance motors: A magnetoelastic finite-element approach based on multiscale constitutive laws,” IEEE Trans. on
Magnetics, vol. 47, no. 9, pp. 2171–2178, 2011. 
[2] Chang-Hung Hsu, et. al., “Reduction of vibration and sound-level for a single-phase power transformer with large capacity,” IEEE Trans. on Magnetics, vol. 51, no. 11, pp. 8403204-1-
4, 2015. 

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The Influence of Electromagnetic Noise of Volume Magnetostriction Anisotropy on Power Transformers

Introduction: Transcranial Magnetic Stimulation (TMS) is a neuromodulation technique currently FDA approved to treat depression, migraine and obsessive-compulsive
disorder (OCD). TMS outcomes are known to vary based on individual neuroanatomy, tractography derived structural connectivity, and functional connectivity which is not well
understood [1,2]. There is a disconnection between what is measured empirically in resting motor threshold (RMT)/treatment outcomes, and computer simulated induced electric fields (EField)
values based on Magnetic Resonance Imaging (MRI) derived head models. In this study, we aim to gain an understanding and explanation of this variability and offer an
improvement by taking region of interest (ROI) specific gray matter (GMV) and white matter volume (WMV) over a previously published relationship between the brain scalp distance
(BSD) and E-Field in the Transcranial Magnetic Stimulation (TMS).
Experimental Details: Twenty-six mild-to-moderate traumatic brain injury (mTBI) patients were recruited as described in our previous publication [3]. Participants underwent MRI scans
followed by guided repetitive TMS using a NextStim NBS4 figure-of-eight double coil. RMTs were taken as a percentage of the maximum stimulator output (%MSO). T1 weighted MRI
images went through SimNIBS pipeline (v3.2.6) to create anatomically accurate head models for each patient. Head models were imported into Meshmixer (v3.5) where BSD and
individual segment volume were taken from the precentral gyrus (knob) as described in [4].
Results: Preliminary analysis indicates a weak but negative correlation between both GMV (R2 = 0.0307, p = 0.392) and WMV (R2 = 0.0388, p = 0.335) versus RMT. And a stronger
positive correlation between BSD (R2 = 0.29, p = 0.0046) and RMT.
Conclusion: Segmented ROI brain volume didn’t improve the correlation between RMT and 3D brain-scalp volume compared to RMT and 1D brain-scalp distance. Further investigations
into E-Field and correlating empirically collected patient outcomes will enable better TMS dosages as a percentage of patient specific RMT for TMS procedures. 

**References:** 

[1] T. Herbsman, L. Forster, C. Molnar, et al., Human Brain Mapping., 30(7), 2044-2055 (2009). Motor threshold in transcranial magnetic stimulation: the impact of white
matter fiber orientation and skull-to-cortex distance. 
[2] N. Mittal, B. Thakkar, C. B. Hodges, C. Lewis, Y. Cho, R. L. Hadimani, & C. L. Peterson, Human Brain Mapping, 1-16 (2022). Effect of neuroanatomy on corticomotor excitability
during and after transcranial magnetic stimulation and intermittent theta burst stimulation. 
[3] L. M. Franke, G. T. Gitchel, R. A. Perera, R. L. Hadimani, K. L. Holloway & W. C. Walker, Brain Injurty, 36:5, p. 683-692, (2022) Randomized trial of rTMS in traumatic brain injury:
improved subjective neurobehavioral symptoms and increases in EEG delta activity. 
[4] T. A. Yousry, U. D. Schmid, H. Alkadhi, D. Schmidt, A. Peraud, A. Buettner, P. Winkler, Brain, Vol. 120, p.141-157 (1997) Localization of the motor hand area to a knob on the
precentral gyrus. A new landmark. 

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Relationship Between Resting Motor Threshold and Neuroanatomy in Mild to Moderate Traumatic Brain Injury Patients during Transcranial Magnetic Stimulation

Lowering the power requirements of transcranial magnetic stimulation (TMS) would allow reducing the size and form factor of the stimulating coils, increasing the focality and penetration depth during the stimulation. Commercial TMS equipment typically uses frequencies from 1 to 5 kHz, while the coil currents vary from 1 to 5 kA. According to the Maxwell-Faraday equation, a large â€“dB/dt is required in the coil to induce an E-field above a stimulation threshold around 100 V/m at the target (Fig 1). Therefore, the development of technologies able to obtain similar E-field strength with lower currents is required. This work shows the design, construction, and tests of a novel high-frequency TM stimulator. For the first time to our knowledge, we have used analog modulations (AM/DSB-SC) over a carrier of 25 kHz to obtain a â€“dB/dt 10 times larger than the commercial stimulators. This permitted the reduction of the TMS currents in the same ratio, with a stimulation tone of 1.5 kHz over the carrier. The modulation shifts the stimulating energy out of the TMS band and audible range, leading to soundless operation compared to the uncomfortable clicking sound in current TMS equipment. Our results demonstrated: a reduction of currents to reach the referential E-field threshold of 100 V/m; a decrease of power dissipation in coils with possibility of unrestricted repetitive TMS (rTMS); a reduction in the coil sizes with increased focality and penetration depth; and hardware requirement reduction. Experimental work with rodents is in progress to demonstrate that, although the modulated signal will not stimulate neurons directly at such high frequency (due to the low-frequency response of the cell membrane), the demodulated version of it, obtained within the brain tissue with the superposition of a non-modulated carrier, can effectively recover the low-frequency envelope, stimulate neurons and induce motor evoked potentials (MEPs) (Fig. 1 and 2).

Development of Novel Transcranial Magnetic Stimulation Technique Using High frequency Modulation for Treatment of Parkinson’s Disease

Transcranial Magnetic Stimulation (TMS) coils are usually specialized for use in either deep brain or focal stimulation. One of the challenges in the development of TMS
therapy is the ability to deliver a focused magnetic field to the desires target in the brain. In the process of delivering a sufficiently strong H field to the target, surrounding areas of the brain
can be stimulated unnecessarily. A new technique is used here whereby deep and focal stimulation can be achieved using temporal interference (TI). TI is a method that allows for control
of steerability, focality, and depth of penetration. TI uses the frequency difference of two independent electric fields [1]. The TI stimulation frequencies in at 10kHz and is filtered by the
brain’s inherent lowpass [2] behavior [3]. The frequency difference between the two induced electric fields results in an envelope which allows improved focality of stimulation. By using a
coil assembly as shown in Figure 1, and using TI, the focality of the peak induced electric can be increased with respect to the surrounding area as shown inf Figure 2.. This focal point can
also be steered along the centerline between the two coils. Our current work involves using Sim4Life software on 50 unique head models derived from magnetic resonance imaging (MRI)
scans. We are investigating the focality of the induced electric field using our coil design with TI signals. The results will be compared with the commonly used figure-of-eight TMS coil
and the novel design Quadruple Butterfly Coil (QBC) [4]. 

**References:** 

[1] M. Zaeimbashi, A. Khalifa, C. Dong, Y. Wei, S. Cash, and N. Sun, “Magnetic Temporal Interference For Noninvasive, High-resolution, and Localized Deep Brain
Stimulation: Concept Validation,” 2020. 
[2] B. Hutcheon and Y. Yarom, “Resonance, oscillation and the intrinsic frequency preferences of neurons,” Trends in Neurosciences, vol. 23, no. 5, pp. 216–222, 2000. 
[3] M. M. Sorkhabi, K. Wendt, and T. Denison, “Temporally Interfering TMS: Focal and Dynamic Stimulation Location,” 2020 42nd Annual International Conference of the IEEE
Engineering in Medicine & Biology Society (EMBC), 2020. 
[4] P. Rastogi, “Novel coil designs for different neurological disorders in transcranial magnetic stimulation,” PhD Thesis, Iowa State University, Ames, IA, USA, 2019. Available:
https://lib.dr.iastate.edu/etd/17547
Brain Mapping, vol. 29, no. 1, pp. 82–96, 2007. 

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Temporal Interference for Increased Focality of Transcranial Magnetic Stimulation

In this in vivo study, we have used Magnetic Pen or MagPen (see Fig. 1(a)) to stimulate the rat sciatic nerve which led to the report of the dosage response curve for
micromagnetic stimulation (μMS). As reported earlier [1], the MagPen prototype consists of sub-mm size microcoil (μcoil) at its tip (see Fig. 1(b)). When driven by alternating current, this
μcoil generates a time-varying magnetic field, which induces an electric field on any conductor (here, the sciatic nerve) according to Faraday’s Law of electromagnetic induction. This
induced electric field activates the nerve. This work reports how the directionality of the magnetic μcoil plays a direct role in activating nerves directly observed in hind limb muscle
twitches. These limb twitches have been quantitatively characterized using electromyography (EMG) recordings. Furthermore, we have studied how on varying the amplitude and
frequency of the micromagnetic stimuli, alters hind limb muscle movements. Thereby, a dosage response curve for μMS was generated. The highlight of this dosage response curve is that,
at higher frequencies, significantly smaller amplitudes of MagPen stimuli can trigger limb twitches. This frequency-dependent nerve activation can be explained directly from Faraday’s
Law as the magnitude of the induced electric field used in neuromodulation is proportional to frequency. In our previous work of in vitro μMS of rat hippocampal slices [1], we explained
the frequency-dependent, low-power activation of μMS through numerical simulations. This work further corroborates the same concept through experiments. Implantable μMS is a novel
neuromodulation technique which is still in its infancy and aims to address the potential drawbacks of electrical implants in terms of MRI compatibility and biofouling. Since the induced
electric fields from these magnetic μcoils are not in galvanic contact with the nerve, μMS offers flexibility in applying waveforms to drive these magnetic implants (see Fig. 1(c)).
Fig 1. (a) Different directionalities of the MagPen prototype. Only Type V can activate the sciatic nerve. (b) Size of the sub-mm size μcoil implant compared to a rice grain. (c) The
waveform that activated the nerve. 

**References:** 

[1] Saha R., Faramarji S et al. (2022) Strength-frequency curve for micromagnetic neurostimulation (μMS) through EPSPs and numerical modeling. J. Neural Eng. 19 016018. 

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