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Introduction:&lt;br/&gt;Transcranial magnetic stimulation (TMS) is extensively used in research and clinical applications pertaining to psychiatric and neurological disorders [1]. The current TMS treatments are all single-focus treatments. To satisfy the requirements of clinical treatment and improve the understanding of the synergies among different brain regions [2,3], researchers are investigating TMS that can stimulate multi brain regions. However, it is not clear whether the TMS can also develop multiple stimulation focal points in the deep brain region.&lt;br/&gt;&lt;br/&gt;Purpose: The purpose of this study is to investigate whether is it possible to use TMS for multi-focus deep brain stimulation&lt;br/&gt;&lt;br/&gt;Methods: We first established a mathematical relationship between the multi-focus electric field distribution and the winding of the TMS coil, thereby realizing the stream-function-based inverse design algorithm that can automatically generate the TMS coil winding pattern by setting the target E-field. Thereafter, we fixed the offset distance between the two-focal points of target electric fields and generated the corresponding coils by setting the focal points at different depths, thereby verifying whether the TMS coil can achieve multi-focus E-field to the deep target.&lt;br/&gt;&lt;br/&gt;Results: When the distance between the two focal points was set to 5 cm, through different depth settings and appropriate parameter selection, we theoretically found that the TMS coil can be developed for a depth that is several times the distance between the two focal points. Moreover, after further verification of the electric field generated by these coils, we found that they all meet the conditions for generating multiple focal points in the deep brain regions. Therefore, we theoretically confirmed that it is possible to use TMS for multi-focus deep brain stimulation.

![](https://assets.underline.io/uploads/markdown_image/1/image/e36c6a4ee603254bec558c7ce93578d4.jpg)

Fig.1 Generation of multi-focus TMS winding when the distance between the two focal points is fixed at 5 cm and are at different depths.

2022 Joint MMM-INTERMAG

Is it possible to use transcranial magnetic stimulation for multi-focus deep brain stimulation?

The 15th Joint MMM-INTERMAG Conference (2022 Joint) 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 plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag 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.

Introduction: Transcranial magnetic stimulation (TMS) is extensively used in research and clinical applications pertaining to psychiatric and neurological disorders [1]. The current TMS treatments are all single-focus treatments. To satisfy the requirements of clinical treatment and improve the understanding of the synergies among different brain regions [2,3], researchers are investigating TMS that can stimulate multi brain regions. However, it is not clear whether the TMS can also develop multiple stimulation focal points in the deep brain region. Purpose: The purpose of this study is to investigate whether is it possible to use TMS for multi-focus deep brain stimulation Methods: We first established a mathematical relationship between the multi-focus electric field distribution and the winding of the TMS coil, thereby realizing the stream-function-based inverse design algorithm that can automatically generate the TMS coil winding pattern by setting the target E-field. Thereafter, we fixed the offset distance between the two-focal points of target electric fields and generated the corresponding coils by setting the focal points at different depths, thereby verifying whether the TMS coil can achieve multi-focus E-field to the deep target. Results: When the distance between the two focal points was set to 5 cm, through different depth settings and appropriate parameter selection, we theoretically found that the TMS coil can be developed for a depth that is several times the distance between the two focal points. Moreover, after further verification of the electric field generated by these coils, we found that they all meet the conditions for generating multiple focal points in the deep brain regions. Therefore, we theoretically confirmed that it is possible to use TMS for multi-focus deep brain stimulation.

![](https://assets.underline.io/uploads/markdown_image/1/image/e36c6a4ee603254bec558c7ce93578d4.jpg)

Fig.1 Generation of multi-focus TMS winding when the distance between the two focal points is fixed at 5 cm and are at different depths.

poster

Introduction It is important to detect corrosion or defects on the opposite side of steel walls used for structures in petrochemical plants. In this research, the detection method of the opposite side defect in the steel plate by applying vibration due to electromagnetic force and measuring its vibration is proposed. The proposed sensor probe consists of a permanent magnet, an AC excitation coil and a vibration sensor. The defect is evaluated by the excitation frequency component of the measured the vibration intensity. The vibration distribution by the electromagnetic force in the steel plate with and without the defect is evaluated by the electromagnetic nonlinear 3D-FEM and the displacement 3D-FEM analysis. In addition, the verification experiment is also carried out. Inspection model and conditions Fig. 1 shows a proposed sensor using an AC magnetic field of 2A at 700Hz. The alternating current of 700Hz and 2A is passed to the exciting coil. In the proposed sensor, the electromagnetic vibration inside the steel plate is generated by the eddy current from an exciting coil and static flux density from the permanent magnet. Then, a ceramic bar is connected to the vibration sensor, and the vibration on the surface the steel plate is measured. Inspection result and discussions Fig.2 shows the distribution of the displacement at each position on the steel plate when the proposed sensor is moved in the x-direction. Fig.2 (a) shows the calculated results, and Fig.2 (b) shows the measured results, respectively. Fig.2 (a) shows the calculated displacement distribution of the vibration sensor inside the proposed sensor by 3D displacement analysis and 3D electromagnetic nonlinear analysis. This figure denotes that the displacement is increased near the defect in the steel plate. This is because, the density of the steel plate is decreased near the defect. Fig. 2(b) denotes that the detection signal is increased near the defect, similar to the analysis result of Fig.2 (a). From these results, the opposite side defect in the steel plate is detected by the vibration intensity of the steady frequency.

![](https://assets.underline.io/uploads/markdown_image/1/image/81f55cc0ea115021b4f77fa775f55330.jpg)

Proposed sensor and Inspection model

![](https://assets.underline.io/uploads/markdown_image/1/image/c0296a6704b129d5622293ae1f645b74.jpg)

Comparison of analysis results and experimental results

Proposal of inspection method for opposite side defect in steel plate using electromagnetic force vibration

Introduction It is important to detect an opposite side defect in steel wall in petrochemical plants. As the inspection for the defect, the electromagnetic inspection method using static and alternating magnetic field is examined [1]. However, this method is required two types of power supplies of static and alternating current. On the other hand, when the full-wave rectified magnetic field is expanded by fourier series, it is the combined magnetic field of static and alternating magnetic field. Therefore, in this paper, the inspection method by the full-wave rectified magnetic field using only one power supply is investigated. Since the magnetic property inside the steel plate in this method is minor loop, the flux density is analyzed by 3D nonlinear FEM using the “play model [2]” taking account of minor loop magnetization property. In this research, the usefulness of the inspection method is evaluated by the “play model” and verification experiment. Inspection model and results Fig.1 shows an inspection model using 2 kHz and 1A at a full-wave rectified exciting current. Although the full-wave rectified magnetic field is an AC magnetic field, the flux density is penetrated deep into the steel plate. If there is an opposite side defect, the flux density is distributed around the defect, and leakage flux is generated on the surface of the steel plate. The defect is evaluated by detecting this leakage flux. Fig.2 shows the comparison between calculated and measured results of the detection signal. The vertical axis is the rate of change ηd with respect to the presence or absence of defect in the output voltage, and the horizontal axis is the moving position of the sensor. This figure denotes that the detection signal is increased at the center position of the defect. And, the calculated result is also same tendency as measured result. The inspection of the opposite side defect in the steel plate is possible by impressed the full-wave rectified magnetic field.

![](https://assets.underline.io/uploads/markdown_image/1/image/41552b283ec6eeda7685f2cc051f4bc5.jpg)

Proposed inspection model using full-wave rectified magnetic field(1/2 model).

![](https://assets.underline.io/uploads/markdown_image/1/image/40796d4744f1a8945c2d416adf7650d1.jpg)

Detection signals of the opposite side defect in the steel plate using the full-wave rectified magnetic field (2kHz, 1A0-p).

Examination of electromagnetic inspection method for opposite side defect on steel plate using full-wave rectified alternating magnetic field

Hybrid magnonic systems host a variety of characteristic quantum phenomena such as the magnetically-induced transparency (MIT) and Purcell effect, which are considered useful for future coherent quantum information processing [1-2]. Here, we experimentally demonstrate a tunable MIT effect in the YIG/Py magnon-magnon coupled system via changing the magnetic field orientations. By probing the magneto-optical Kerr and Faraday effects of Py and YIG, we identify clear features of MIT spectra induced by the mode hybridization between the ferromagnetic resonance of Py and the perpendicular standing spin-wave of YIG. By changing the external magnetic field orientation, we observe a tunable coupling strength between the YIG's spin-wave modes and the Py's uniform mode, upon the application of an out-of-plane magnetic field. Our findings show high promise for investigating tunable coherent phenomena with hybrid magnonic platforms.

Facile Magneto-optic Detection of Tunable Magnetically-Induced Transparency Spectra in Magnon-Magnon Coupled Bilayers

The imaging of magnetic nanoparticle (MNP) distributions is a promising biomedical imaging technique for detecting cancers [1]. A method is magnetic nanoparticle tomography (MNT), in which multiple magnetic sensors are used to detect the harmonic signal of MNPs [2] [3]. In our previous study [2] [3], a linear amplifier power supply with low power efficiency was used to generate the excitation magnetic field. In this study, a square-wave inverter was alternatively used to provide high efficiency. However, the third harmonic excitation field was generated by the general square-wave inverter excitation, degrading the imaging performance. Therefore, we developed a method to suppress the third harmonic by shifting the switching phase of the inverter. The experimental setup is shown in Fig. 1. A full-bridge inverter was used to generate a square excitation voltage. Generally, a square-wave voltage was generated by shifting the switching phase of the left- and right-arms by 180°. The square voltage generated using this method contained the third harmonic. We developed a method to suppress the third harmonic by shifting the switching phase by 120°. In this case, the third harmonic does not appear theoretically. The Resovist MNP sample (500 mg-Fe / 150 mg) was arranged and magnetized by an alternating-current magnetic field in the Z-axis using an excitation coil. The sample moved on the x-y plane, and the third harmonic signal of the MNPs was obtained using 16 detection coils. The distance between the excitation coil and the sample was set to 35 mm. Figs. 2(a) and (b) show the third harmonic signal distribution from MNPs using 180° and 120° shifts, respectively, detected by a detection coil. The signal from the MNPs was masked by the excitation field noise (Fig. 2(a)). In contrast, the peak and trough were visible. The results show that the proposed method increases the feasibility of MNT using a square wave inverter excitation. This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Number JP21H01342).

![](https://assets.underline.io/uploads/markdown_image/1/image/777fa0726302b15db535960bf43377e8.jpg)

Fig.1. Experimental setup

![](https://assets.underline.io/uploads/markdown_image/1/image/885c75975b872192e473feafc18347b4.jpg)

Fig. 2. Third harmonic signal distributions of MNPs using (a) 180° and (b) 120° shifts (The cross mark indicates the position of a detection coil.)

Square-Wave Inverter Excitation for Magnetic Nanoparticle Tomography

Interfacial Dzyaloshinskii-Moriya interaction (iDMI) [1,2] along with perpendicular magnetic anisotropy (PMA) [3,4] in the ultrathin ferromagnetic material/heavy metal (FM/HM) interface has garnered significant attention in recent studies [5,6]. Field-induced domain wall motion has been observed in quasi-perpendicularly magnetized Pt/Co/Pt trilayers with interfacial Dzyaloshinskii-Moriya interaction (iDMI) using differential Kerr microscopy method in the creep regime (shown in Fig.1). Vineeth et al. [7] reported a quasi-PMA system whose magnetic easy axis is tilted with respect to the z-axis. An oblique angle sputter deposition technique had introduced a thickness gradient in one of the layers of a trilayer, results in a small tilt of magnetic anisotropy from the film normal. The tilt angle has been estimated in each trilayer by determining the shift in the out-of-plane magnetization hysteresis measurements under a bias magnetic field applied along with various in-plane directions. The effective in-plane field at the domain wall due to iDMI has been determined by decomposing the symmetric and asymmetric contributions of the domain wall motion. Furthermore, the asymmetric contribution has been decomposed into two contributions due to the tilted magnetic anisotropy and the exponentially decaying chiral damping. The nature of the asymmetric contribution owing to the tilted anisotropy was studied by the collective coordinate model (shown in Fig.2) and a functional form of the total asymmetric contribution has been determined and used to fit the asymmetric contribution [8].

![](https://assets.underline.io/uploads/markdown_image/1/image/5efdf9ff8cc28df94d0815f6a78b3176.jpg)

Fig.1: Field-induced domain wall motion for all the trilayers obtained using differential polar Kerr microscopy technique. Corresponding applied Hx and pulsed Hz with the pulse-width Δt are mentioned under the images. Azimuthal orientation of the tilted magnetic anisotropy has been shown using a white arrow for each trilayer.

![](https://assets.underline.io/uploads/markdown_image/1/image/41d857e809588a526d2249dfb541c16a.jpg)

Fig.2: Dependence of asymmetric contribution, Ha on Hz have been shown for azimuthal orientation along the x-axis for all the trilayers. All the solid lines through the data points validate the CCM.



Asymmetric magnetic domain wall motion in a quasi-perpendicularly magnetized with interfacial Dzyaloshinskii-Moriya interaction

The diagnosis and prevention of iron-steel infrastructure deterioration have become critical issues in recent years. To detect steel corrosion, a preliminary study of thickness measurement (extremely low-frequency eddy current testing : ELECT) using a magnetic sensor at extremely low-frequency ranges has been previously reported [1]. Iron-steel materials exhibit large variations in electromagnetic characteristics. In this study, the effect of electromagnetic characteristics on the magnetic thickness measurement was investigated to improve the thickness estimation. Four types of iron-steel plates (SS400, SM400A, SM490A, SMA400AW) with thickness ranging from 1 mm to 20 mm were measured via ELECT. The detected magnetic signal, consisting of a real and an imaginary component at each frequency, was plotted to obtain the magnetic spectrum. The differential magnetic vector between two appropriate frequencies is extracted from the magnetic spectrum, and the plate thickness is then estimated from the phase of the differential magnetic vector. For instance, the linearity of the calibration curves between the phase and thickness for each type of steel plate was obtained in the thickness range of 6–12 mm using a differential vector, which was obtained by subtracting the 3 Hz vector from the 5 Hz vector. However, the calibration curves for each type of steel plate did not coincide. To analyze the phase shift phenomenon, the electromagnetic characteristics (the permeability μ, the obtained magnetization curve, and the conductivity σ) of each type of steel plate were measured. The μσ magnitude relationship for each type of steel is as follows: SM400 &gt; SMA400AW &gt; SS400 &gt; SM490A. The parameter of σμ was correlated in each calibration curve shift, and the linearity region in the curve was shifted to the low-thickness region according to the increment of frequency. Therefore, the difference in calibration curve for each type of iron-steel could be explained by the difference in σμ parameter. In summary, this study clarified the relationship between the electromagnetic properties of various types of iron steel and the phase of detected magnetic signal in the thickness measurement.

Magnetic measurement for various types of iron steel thickness using magnetic sensor and the effect of their electromagnetic characteristics

Magnetic nanoparticles (MNPs) prepared as a stable colloidal suspension dispersed in water have attracted special interest for different applications in theranostics [1]. MNPs of maghemite obtained by a laser target evaporation (LTE) were shown to be excellent candidates for this purpose [2]. Magnetic suspension flowing through the blood vessel creates magnetic fields which can be detected by giant magnetoimpedance magnetic field sensor (GMI) [3]. In this work, we develop a computer model for calculation of the distribution of blood flow velocity V and magnetic fields H in the area of a blood vessel with stenosis. Finite element model (FEM) is used to analyze the properties of the model system reconstructed from the image obtained during routine examination of a patient using angiography. Figures show selected results of the studies. It was shown that the relative change of the magnetic field strength in the area inside the blood vessel doesn’t depend on the value of the external magnetic field He and the value of additional magnetic field connected to the blood flow is proportional to the concentration of MNPs. To describe the results obtained for a model of a real vessel, a model of a vessel in the form of a cylinder with different radius of curvature and thickness was studied. The results of calculations the flow of MNPs in the vessel showed that at 1.5 wt % of MNPs concentration (c=1.5 wt %) the relative change in the magnetic field in the area of stenosis is 0.43%, and in the area before stenosis is 0.33%. According to experimental data, the observed difference in the distribution of magnetic fields at a concentration of LTE MNPs from 0 to 2% can be measured using a thin-film detector of small magnetic fields GMI. This study was supported by the Ministry of Science and Higher Education of the Russian Federation (project No. FEUZ -2020-0051).

![](https://assets.underline.io/uploads/markdown_image/1/image/c3552b4a706a15d7f35085e81cea29cb.jpg)

Fig.1. Velocity distribution in a blood vessel with stenosis. The inset shows the value along the cross-section indicated by horizontal red line.

![](https://assets.underline.io/uploads/markdown_image/1/image/826311968a42b753a82900dafb6fb368.jpg)

Fig.2. Magnetic field (H) distribution in a blood vessel with stenosis. The inset shows the value along the cross-section indicated by horizontal red line. He = 5 Oe and is directed from left to right, c=1.5 wt %.

The Modeling of Magnetic Detection of Iron Oxide Nanoparticles in the Stream of Patient-Specific Coronary Artery with Stenotic Lesion: the Effects of Vessel Geometry and Particle Concentration

Introduction: Simulation based transcranial magnetic stimulation (TMS) studies have demonstrated the importance of anatomical variations in TMS treatments [1]. Most of the studies use magnetic resonance image (MRI) derived heterogeneous head models but lack anisotropy in their electrical and magnetic properties. Our objective was to use modeling and simulation techniques to determine the effect of neuroanatomy on resting motor thresholds (RMT) recorded from the first dorsal interosseous (FDI). Experimental Details: TMS was performed on 10 healthy patients using a Magstim BiStim2 and 70mm figure-of-eight coil and RMT values were collected using electromyography signals as a percentage of the maximum stimulator output (%MSO) [2]. MRI scans including diffusion tensor imaging (DTI) were used for fiber tract extraction (Fig 1), where individual fiber tract surface areas and tract fiber counts for the FDI were determined. T1 and T2 weighted images were taken from the MRI scans for segmentation and creation of anatomically accurate head models using SimNIBS pipeline [1]. Brain scalp distance (BSD) was measured at the point of stimulation in the models. TMS of the head models was simulated using finite element analysis to calculate cortical peak electric fields using Sim4Life (Fig 2) [3]. A linear mixed effects model was used to assess the effects of these parameters on RMT. Results: Peak induced electric fields were in the range of 90.5-147 V/m with a mean of 118.9 V/m at the cortical hotspot. Electric field and RMT are correlated, dependent on fiber tract surface area (p = 0.036) and tract fiber count (p = 0.004), but not on BSD (p = 0.423). Conclusion: The relationship between RMT and electric field intensity depended on both fiber tract surface area and tract count, emphasizing the effect of site-specific cortical architecture. The induced electric field at the hotspot region of the grey matter depended on the stimulator output (i.e. current in the coil). We found that MRI modeling techniques relate to the empirically collected data, suggesting an MRI based approach may be predictive of dosage determination and TMS outcomes.

![](https://assets.underline.io/uploads/markdown_image/1/image/69f60456d51bb65ffad9ae0005c0a087.jpg)

Fig. 1 Fiber tracts extracted from DTI [4].

![](https://assets.underline.io/uploads/markdown_image/1/image/ac2c26188bc7225953ab57da364583e9.jpg)

Fig. 2 M1 region peak electric field intensity.

Effect of Fiber Tracts on Resting Motor Thresholds During Transcranial Magnetic Stimulation

Various magnetic robots have been widely investigated as a possible means to replace conventional biomedical technologies [1, 2]. The use of multi-modular helical magnetic millirobots (MHMMs), such as the one shown in Fig. 1, has especially attracted attention since an MHMM can increase the number of modules by simply attaching additional modules along the longitudinal direction of the body without changing their radial dimensions [3]. Thus, an MHMM may employ multiple functional modules to perform complex tasks within a confined tubular environment such as the human blood vessel. In this research, we analytically and experimentally investigated the locomotive characteristics of the MHMM with respect to a different number of modules. It was seen that the MHMM becomes geometrically more suitable to navigate in a curved and narrow tube as the number of modules increases, even when the overall length of the MHMM does not change. We established a condition to calculate the least required number of modules to make the MHMM navigate in a given tubular condition. It was also seen that the nonlinear characteristics of the MHMM’s rotational movement transmission derived from the universal joint mechanism used to connect modules decreases as the number of modules increases. Therefore, an MHMM composed of a large number of modules can navigate in a tube with a relatively harsh condition in a steady manner. In this research, we constructed prototype MHMMs with a different number of modules, as shown in Fig. 2, and demonstrated various navigating motions to show the validity of the proposed structure. Results showed that the MHMM composed of the largest number of modules (5) can navigate in a more confined tubular environment (high curvature and small diameter) compared to other MHMMs. This research can contribute to the development of multifunctional intravascular robots with high locomotive characteristics for various biomedical applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/0f6802d8590f3f83e7e5e81ab0f1fb6c.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/95675a398c69cfb84924c7db950380d1.jpg)

A Study on the Locomotive Advantages of a Multi-Modular Helical Magnetic Millirobot in Curved and Narrow Blood Vessels

A Study on the Locomotive Advantages of a Multi-Modular Helical Magnetic Millirobot in Curved and Narrow Blood Vessels

Implantable drug delivery system is a prevailing approach for the drug administration [1]. The main challenge of implantable drug delivery systems is reliable implementation of a low power actuation device and a micropump with an accurate flow rate. Here we introduce a low flow rate implantable micropump fabricated using 3D printing, based on a low-power electromagnetic actuating system. We have designed the micropump structure shown in Fig. 1(a), made from polydimethylsiloxane (PDMS). The top membrane, which is 100 μm thick, was created using the spin coating. The cylindrical NdFeB magnet was placed on the membrane. The micropump structure and the membrane were bonded by 20 s of oxygen plasma. A solenoid with 2000 turns was applied as the actuator for the micropump, and it was located 2mm above the micropump as Fig. 1(b) depicts. Fig. 1(c) shows how we use the diffuser-nozzle element to achieve valveless one-direction flow. The electromagnetically actuated field could provide a periodic force on the membrane, so this top layer could deflect downward and upward. During the upward motion, negative relative pressure would be created inside the chamber and there will be more liquid drawn into the pump chamber through the inlet. On the contrary, during the membrane’s downward motion, the pressure inside the chamber rises thus more liquid exit through the nozzle than the diffuser. Therefore, a net volume of liquid would be transferred from the diffuser to the nozzle for every period [2]. Under the actuation of a varying magnetic field generated by the electromagnet, micropump can produce a flow rate of 6±0.21 μl/s, which is close to previously simulated work [3]. The fabricated micropump is shown in Fig. 1(d). In summary, we successfully designed and fabricated an implantable drug delivery system, with high precision drug release [4]. The valveless unidirectional flow is achieved by using the diffuser-nozzle structure. More studies will be performed to implement a miniaturized, fully automatic and comfortable system for daily injection applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/b7fc911ea854a9ba203ad4d87fa786ce.jpg)

3D Printed Electromagnetics Micropump for Implantable Drug Delivery

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