United States

Enormous research activities to develop advanced superparamagnetic iron oxide nanoparticles (SPIONPs) enabling to generate higher AC heat induction temperature (TAC) or specific loss power (SLP) at the biologically safe and physiologically tolerable range of AC magnetic field (HAC) (HAC,safe &lt; 1.8 × 109 A m-1 s-1, fappl &lt; 120 kHz, Happl &lt; 190 Oe (12.5 A m-1)) have been intensively made in the past two decades for magnetic hyperthermia application [1-3]. According to the reports made so far, a high magnetic softness (or high magnetic moment m) and a high initial susceptibility (χ0) at the DC magnetic field were revealed to be critical parameters in enhancing the TAC (SLP) due to the correspondingly enhanced Néel relaxation time constant (τN), which is the same as the effective relaxation time constant (τeff), τN ≈ τeff , in solid-state SPIONPs. However, MnFe2O4 SPIONPs with high magnetic moment usually show low TAC (SLP) compared to magnetically semi-hard CoFe2O4 SPIONPs with a relatively low m [4,5].&lt;br&gt;
In this work, our research efforts primarily focused on exploring the physical and chemical reasons why MnFe2O4 SPIONPs with high DC magnetic softness show an extremely low TAC (SLP) by systematically investigating the physical role of magnetically semi-hard Co2+ cation addition in enhancing TAC (SLP) of solid (CoxMn1-x)Fe2O4 SPIONPs. According to the experimentally and theoretically analyzed results, it was clearly demonstrated that the enhancement of magnetic anisotropy (Ku)-dependent AC magnetic softness including the Néel relaxation time constant τN (≈ τeff), and its dependent out-of-phase susceptibility (χ″) are the most dominant parameters to enhance the TAC (SLP). This clarified result strongly suggests that the development of new design and synthesis methods enabling to significantly enhance the Ku by improving the crystalline, shape, stress (magnetoelastic), thermally-induced, and exchange anisotropies is the most critical to enhance the TAC (SLP) of SPIONPs at the HAC,safe (particularly at the lower fappl &lt; 120 kHz) for clinically safe magnetic nanoparticle hyperthermia.&lt;br&gt;
**References:**&lt;br&gt;[1] Joshi et al, J. Phys. Chem. C, 113, 17761-17767 (2009)&lt;br&gt;
[2] Lee et al, Nat. Nanotechnol., 6, 418-422 (2011)&lt;br&gt;
[3] Sathya et al, Chem. Mater., 28 1769-1780 (2016)&lt;br&gt;
[4] Mameli et al, Nanoscale, 8 10124-10137 (2016)&lt;br&gt;
[5] Albino et al, J. Phys. Chem. C, 123, 6148-6157 (2019)&lt;br&gt;



MMM 2022

The Role of Co2+ Cation Addition in Enhancing the AC Heat Induction Power of (CoxMn1 x)Fe2O4 Superparamagnetic Nanoparticles

Enormous research activities to develop advanced superparamagnetic iron oxide nanoparticles (SPIONPs) enabling to generate higher AC heat induction temperature (TAC) or specific loss power (SLP) at the biologically safe and physiologically tolerable range of AC magnetic field (HAC) (HAC,safe < 1.8 × 109 A m-1 s-1, fappl < 120 kHz, Happl < 190 Oe (12.5 A m-1)) have been intensively made in the past two decades for magnetic hyperthermia application [1-3]. According to the reports made so far, a high magnetic softness (or high magnetic moment m) and a high initial susceptibility (χ0) at the DC magnetic field were revealed to be critical parameters in enhancing the TAC (SLP) due to the correspondingly enhanced Néel relaxation time constant (τN), which is the same as the effective relaxation time constant (τeff), τN ≈ τeff , in solid-state SPIONPs. However, MnFe2O4 SPIONPs with high magnetic moment usually show low TAC (SLP) compared to magnetically semi-hard CoFe2O4 SPIONPs with a relatively low m [4,5]. 
In this work, our research efforts primarily focused on exploring the physical and chemical reasons why MnFe2O4 SPIONPs with high DC magnetic softness show an extremely low TAC (SLP) by systematically investigating the physical role of magnetically semi-hard Co2+ cation addition in enhancing TAC (SLP) of solid (CoxMn1-x)Fe2O4 SPIONPs. According to the experimentally and theoretically analyzed results, it was clearly demonstrated that the enhancement of magnetic anisotropy (Ku)-dependent AC magnetic softness including the Néel relaxation time constant τN (≈ τeff), and its dependent out-of-phase susceptibility (χ″) are the most dominant parameters to enhance the TAC (SLP). This clarified result strongly suggests that the development of new design and synthesis methods enabling to significantly enhance the Ku by improving the crystalline, shape, stress (magnetoelastic), thermally-induced, and exchange anisotropies is the most critical to enhance the TAC (SLP) of SPIONPs at the HAC,safe (particularly at the lower fappl < 120 kHz) for clinically safe magnetic nanoparticle hyperthermia. 
**References:** [1] Joshi et al, J. Phys. Chem. C, 113, 17761-17767 (2009) 
[2] Lee et al, Nat. Nanotechnol., 6, 418-422 (2011) 
[3] Sathya et al, Chem. Mater., 28 1769-1780 (2016) 
[4] Mameli et al, Nanoscale, 8 10124-10137 (2016) 
[5] Albino et al, J. Phys. Chem. C, 123, 6148-6157 (2019)

technical paper

#### 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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Rare earth (RE)â€“transition metal (TM) ferrimagnet is receving of great interest [1], because the unique coupling of RE and TM moments enables the antiferromagnetic spin dynamics [2]. Since magnetic moments of RE material originates primarily from the 4f-electrons which locates far below the Fermi level while that of TM arises from the 3d-electrons near the Fermi level [3], magnetic moment configuration at different energy levels should be studied more carefully. However, such energy-level dependent approaches have largely been ignored in spintronic researches. Here we present the experimental evidences for the energy-level-dependent distinct magnetic moment configuration in ferrimagnetic TbCo alloys. Four different approaches such as Hall measurement, VSM measurement, TR-MOKE measurement, THz emission measurement, were used to study the magnetic moment at different energy levels. We found that the magnetic moments at deeper energy level are rather easily altered by the external magnetic field than those at Fermi level, suggesting that the magnetic moment responds differently depending on the energy level. Further investigation on the temperature dependence shows that the Tb moment exhibits the spin glass-like freezing possibly induced by the random anisotropy of Tb. Our results reveal the important energy-level dependent characteristics of RE-TM ferrimagnets and therefore pave the way towards a better understanding of antiferromagnetic spin dynamics in RE-TM ferrimagnets

Energy level

Spinel oxides (AB2O4) are well known materials which possess two important features making them prone to exhibit unusual magnetic properties: (i) competing exchange interactions (JAB, JBB, and JAA) and (ii) the topology of B-sublattice, particularly favorable to the development of geometrical frustration [1,2]. Among the various classes of spinels, ZnFe2O4 is a unique system where the B site cations form a network of tetrahedra sharing their corners (similar to Pyrochlore systems), giving rise to high degree of magnetic frustration. These pyrochlore like structures have great applications in magneto-electronic devices [3,4]. In the current work we focus on the magnetic relaxation dynamics and heat capacity (CP(T)) studies of polycrystalline bulk Zn(Fe1–xMnx)2O4 where the combined effects from dilute substitution of Jahn-Teller active Cu2+ and Mn3+ ions are expected to alter the exchange coupling significantly by lifting the ground state degeneracy. Our results revealed coexistence of ferrimagnetism (FiM) and spin-glass state in Zn0.8Cu0.2FeMnO4 without signatures of standard long-range ordering, as inferred from the ac-susceptibility (χ′ and χ′′) and CP(T,H) studies. From the χ′′(T) (loss spectrum) shown in fig. 1a, we obtain a main cusp ~ 47.2K along with two more anomalies at 8.9K and 63K. Moreover, the differential analysis (∂(χ′T)/∂T vs. T) yields a local minimum at 79K, referred to as the FiM Néel temperature, TFiM. Frequency dispersion noticed in both χ′(T) and χ′′(T) (fig. 1b) provide the signatures of spin-glass state below TFiM. The empirical-scaling-laws like Vogel-Fulcher law and Power-Law (τ=τ0[(T–TSG)/TSG]–zυ) are used to determine the spin freezing temperature TSG=41.8K, the critical exponent zυ=8.9 and the relaxation time τ0=1.5×10–10s resulting in the evidence of cluster-spin-glass like state present in Zn0.8Cu0.2FeMnO4. A detailed dc-field dependent static (χDC) and dynamic susceptibility studies further support the glassy characteristics of the system below TFiM. 
**References** [1] S. T. Bramwell, M. J. Harris, B. C. den Hertog, M. J. P. Gingras, J. S. Gardner, D. F. McMorrow, A. R. Wildes, A. L. Cornelius, J. D. M. Champion, R. G. Melko, and T. Fennell, Phys. Rev. Lett. 87, 047205 (2001) 
[2] G. Srinivasan and M. S. Seehra, Phys. Rev. B 28, 1 (1983) 
[3] E. Maniv, R. A. Murphy, S. C. Haley, S. Doyle, C. John, A. Maniv, S. K. Ramakrishna, Y. L. Tang, P. Ercius, R. Ramesh, A. P. Reyes, J. R. Long, and J. G. Analytis, Nat. Phys. 17, 525 (2021) 
[4] W. Schiessl, W. Potzel, H. Karzel, M. Steiner, G. M. Kalvius, A. Martin, M. K. Krause, I. Halevy, J. Gal, W. Schäfer, G. Will, M. Hillberg, and R. Wäppling, Phys. Rev. B 53, 9143 (1996) 
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Magnetic Relaxation Dynamics of Frustrated Glassy Tetragonal Spinel Cu0.2Zn0.8FeMnO4

The structurally coupled interaction between a piezoelectric and ferromagnetic magnetostrictive material can be exploited to develop magnetoelectric systems which have potential to rival current technologies with reduced power consumption and size. In a magnetoelectric multiferroic system the bilateral control of the magnetic and piezoelectric response is dictated by the material properties, where a soft magnetic material with large magnetostriction facilitates the large voltage-induced strain in the piezo/ferroelectric layer. Thin film deposition techniques utilized for device fabrication often complicate the optimization of the interaction between layers due to inherent stresses occurring during deposition which are often deleterious to the magnetoelectric functionality. While incorporation of metalloid substitutions, such as in (Fe0.5Co0.5)1-xCx, and (Fe0.5Co0.5)1-xBx are able to reduce the inherent coercive field and retain a high magnetostrictive and piezomagnetic properties the as-deposited stress states are rarely discussed [1,2]. To this end we have studied the incorporation of Hafnium in to an Fe50Co50 matrix with a focus on correlation between the film stress and magnetic properties. In these sputter-deposited thin films we find a relationship among the magnetic and stress properties as a function of doping percentage. With increasing Hf composition the system exhibits a minimum coercive field occurring at a crossover from a compressive to tensile stress state. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) of the (Fe0.5Co0.5)1-xHfx system reveal the magnetic softening is also correlated to emergence of an amorphous phase with reduced grain size for these sputter-deposited films. This ternary alloy presents an additional avenue for optimization of artificial magnetoelectric systems and has applications for multiple types of microelectromechanical devices. 
**References:** [1] J. Wang, Phys. Rev. Applied 12, 034011 (2019) 
[2] J. Lou, Appl. Phys. Lett. 91, 182504 (2007)

Development of a Hafnium Iron

High-performance magneto-dielectrics with high permeability and permittivity, low magnetic and dielectric losses, and high cutoff frequency are promising candidate materials for next-generation communication applications, owing to their significant advantages for antenna miniaturization and bandwidth enhancement. Due to limited resonant frequencies and large natural resonance linewidths, conventional microwave ferrites and their composites, which are usually used over the frequency range from several hundred MHz to several GHz, do not meet the requirements for 5G communications.1-3 A unique type of hexaferrites named Mg-Zn 18H hexaferrite, whose crystal structure can be interpreted as the structure of Y-type hexaferrites with intercalation of a three-layered hexagonal barium titanate block into the middle of the T-block as shown in Fig. 1a, has been synthesized, and its microwave properties have been comprehensively investigated for the first time.4 The Mg-Zn 18H hexaferrite shows an extremely low damping coefficient of 0.1-0.2, indicating concentrated magnetic loss within a narrow frequency band and a narrow ferrimagnetic resonance linewidth of 486-660 Oe. Owing to this remarkably low damping coefficient, the Mg-Zn 18H hexaferrite possesses an excellent magnetic loss tangent as low as 0.06 and a small dielectric loss tangent less than 0.006 over 2-4 GHz, representing superior magneto-dielectric performance among the reported microwave ferrites for the S band applications as shown in Fig. 1b. Moreover, excellent thermal stability for the damping coefficient is observed to be 0.0004 K-1 over the temperature variation of most practical applications. When employed as the substrate of a 3.6-GHz patch antenna, the Mg-Zn 18H hexaferrite shows a miniaturization factor of ~5 and significant bandwidth improvement of ~50-110% over conventional dielectrics. These results imply the great technological potential and commercial value of the 18H hexaferrites for 5G communications. 
**References:** 1V. G. Harris, IEEE Trans. Mag. 48, 1075 (2012). 
2V. G. Harris, A. Geiler, Y. Chen, S. Yoon, M. Wu, A. Yang, Z. Chen, P. He, P. V. Parimi, X. Zuo, C. E. Patton, M. Abe, O. Acher, and C. Vittoria, J. Magn. Magn. Mater. 321, 2035 (2009). 
3Q. Li, Y. Chen, C. Yu, K. Qian, V. G. Harris, J. Am. Ceram. Soc. 103, 5076 (2020). 
4Q. Li, Y. Chen, C. Yu, L, Young, J. Spector, and V. G. Harris, Acta Mater. 231, 117854 (2022). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/b2b57c67782800adf088a5c437a9d3be.png) 
(a) Schematic illustration of the Mg 18H hexaferrite unit cell with the stacking subunit blocks denoted. (b) Performance of magneto-dielectric materials for microwave applications. The figure of merit (FOM) are indicated by the dashed lines.

Emerging Magneto Dielectric Materials for 5G Antenna Miniaturization: 18H Hexaferrites

Tunable perpendicular magnetic anisotropy (PMA) in thin film magnetic devices provides an isotropic in-plane permeability, necessary for integrated microwave and mm-wave devices and an opportunity to break inversion symmetry that allows implementations of non-reciprocal devices like circulators and isolators. In ferrimagnetic alloys like GdxCo1-x, this is usually achieved by changing the composition such that the magnetic properties lie on either side of the composition-dependent magnetic compensation at room temperature, as shown in Fig. 1. Different compositions achieved in this work by changing the sputtering power of the Gd target show that magnetic compensation window lies between x = 28-32, and the effective anisotropy diverges about the compensation point. 

One less explored pathway is the incorporation of oxygen, which until now has been ruled out as a detriment to the ferrimagnetic properties [1]. Here, we show that preferential oxygenation of GdxCo1-x through a reactive sputtering process, such that the cation (Gd and Co) to oxygen anion ratio is 1:1, increases the effective anisotropy energy density by two orders of magnitude compared to the corresponding alloys without oxygen. X-ray photoelectron spectroscopy reveals that strong PMA with an optimal oxygen flow results in a Co-deficient stoichiometry of Gd21Co28O51, which suggests that strong ferrimagnetic order likely arises from a superexchange-like coupling between Gd and Co via the non-magnetic O [2]. This can produce a spontaneous magnetization in the out-of-plane direction due to weaker exchange interactions within the alloy in a heavy-metal/ferrimagnet heterostructure for PMA. Even greater anisotropy fields on the order of 11 kOe are achieved in a super-lattice with 10 repetitions of the GdxCo1-x heterostructure unit-cell, which corresponds to an operating frequency of 30 GHz. Therefore, not only does oxygenation increase PMA and provide tunable anisotropy to amorphous Gd-Co films, but the oxygen incorporation itself also increases the resistivity of the film, making it even more suitable for that frequency range. 
**References:** [1] K. Ueda, A. J. Tan, and G. S. D. Beach, AIP Advances, vol. 8, no. 12, p. 125204, Dec. 2018. 
[2] R. J. Gambino and J. J. Cuomo, Journal of Vacuum Science and Technology, vol. 15, no. 2, pp. 296–301, Mar. 1978. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/0641d84a745d89c9edb1bbc17e16653a.png) 
Fig. 1. Saturation Magnetization and Effective Anisotropy Energy Density for varying GdxCo1-x compositions for x = 18-39.

Role of Composition and Oxygen in Ferrimagnetic GdxCo1 x Alloys for Microwave/mm

Transcranial magnetic stimulation (TMS) is a non-invasive, effective, and safe neuromodulation technique used to diagnose and treat neurological disorders [1]-[2]. A key
challenge involved with TMS is to determine stimulation strength in critical regions of the brain accurately. The induced electric field is affected by complexity and heterogeneity of the
brain and numerical computation methods like finite element analysis (FEA) can be used to estimate electric field distribution. However, these methods need exceedingly high
computational resources and are time-consuming [3]-[6]. The purpose of this study was to develop and test a machine learning algorithm that can efficiently predict stimulation strength
based on neuroanatomy. Head models were developed from magnetic resonance images of eleven recruited subjects using SimNIBS pipeline [7]-[8]. We used Sim4Life, an FEA software
to compute induced electric fields due to simulated TMS; the induced electric fields served as training data. A deep convolutional neural network (DCNN) inspired encoder-decoder
network (Fig 1) was developed to predict induced electric fields from T1-weighted and T2-weighted magnetic resonance imaging (MRI) based anatomical slices. Three representative cases
of electric fields predicted by the DCNN algorithm, along with the corresponding reference electric fields are shown in Fig 2. For the trained network, the training data and the testing data
peak signal to noise ratios are 32.83dB and 28.01dB respectively. The key contribution of this study is the ability to predict the induced electric fields in real-time as well as accurately and
efficiently predicting TMS strength in the targeted brain regions saving both time and computational resources.
Acknowledgment: This work was supported by VCU CERSE. Further funding was provided by the CCI CVN (Proposal ID #: FP00010500). 

**References:** 

[1] D. J. Stultz, S. Osburn, T. Burns, S. Pawlowska-Wajswol, and R. Walton, Transcranial magnetic stimulation (TMS) safety with respect to seizures: A literature review,
Neuropsychiatric disease and treatment, vol. 16, p. 2989 (2020). 
[2] M. Kobayashi, and A. Pascual-Leone, 2003. Transcranial magnetic stimulation in neurology, The Lancet Neurology, vol. 2, no. 3, p. 145-156 (2003). 
[3] E. G. Lee, W. Duffy, R. L. Hadimani, M. Waris, W. Siddiqui, F. Islam, M. Rajamani, R. Nathan, and D. C. Jiles, Investigational effect of brain-scalp distance on the efficacy of
transcranial magnetic stimulation treatment in depression, IEEE Transactions on Magnetics, vol. 52, no. 7, p. 1–4 (2016). 
[4] L. J. Crowther, R. L. Hadimani, A. G. Kanthasamy, and D. C. Jiles, Transcranial magnetic stimulation of mouse brain using high-resolution anatomical models, Journal of Applied
Physics, vol. 115, no. 17, p. 17B303 (2014). 
[5] F. Syeda, H. Magsood, E. G. Lee, A. A. El-Gendy, D. C. Jiles, R. L. Hadimani, Effect of anatomical variability in brain on transcranial magnetic stimulation treatment, AIP Advances,
vol. 7, no. 5, p. 056711 (2017). 
[6] F. Syeda, K. Holloway, A. A. El-Gendy, and R. L. Hadimani, Computational analysis of transcranial magnetic stimulation in the presence of deep brain stimulation probes, AIP
Advances, vol. 7, no. 5, p. 056709 (2017). 
[7] N. Mittal, C. Lewis, Y. Cho, C. L. Peterson, and R. L. Hadimani, Effect of fiber tracts and depolarized brain volume on resting Motor thresholds during transcranial magnetic
stimulation, IEEE Transactions on Magnetics (2022). 
[8] N. Mittal, B. Thakkar, C. B. Hodges, C. Lewis, Y. Cho, R. L. Hadimani, and C. L. Peterson, Effect of neuroanatomy on corticomotor excitability during and after transcranial magnetic
stimulation and intermittent theta burst stimulation, Human Brain Mapping (2022). 

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Prediction of Stimulation Strength of Transcranial Magnetic Stimulation in the Brain with Deep Convolutional Neural Network based Encoder Decoder Network

Magnetic catheter (MC) controlled by a magnetic navigation system (MNS) and a feeding device have been developed to overcome the steerability and the pushability of
conventional catheters.1,2 External magnetic field (EMF) produced from the MNS generates magnetic torque at the magnets in the MC to remotely steer the MC’s distal end while the
feeding device pushes the proximal end of the MC to move the MC forward.3,4 Sometimes, it does not work effectively when buckling of a flexible catheter occurs in complex blood
vessels.
We propose a position control method (PCM) of the Robotically Assisted MAgnetic Navigation (RAMAN) system to improve the pushability of the MC by maximizing magnetic force
(MF). Fig 1(a). shows the developed RAMAN system in which the 7-axis stage robot can move the 8 electromagnets (EMs) and the workspace surrounded by them. Fig 1(b). shows the MF
in the region of interest (ROI) which is 80% of the workspace. The PCM takes advantage of the fact that the MF increases as the magnet moves close to the EM. When the MF generated at
the MC is not sufficient, the PCM compares the MF of each vertex in the ROI and controls the 7-axis stage robot to move the ROI in such a way that the MC is located close to one of the
EMs to generate maximum MF. Fig 2. shows calculated maximum MF at the center of the ROI and at the point selected by the PCM where an axially magnetized ring magnet (OD: 2 mm,
ID: 1 mm, Length: 10 mm) of NdFeB 52 is located along θ and Φ directions. It shows that the PCM generates larger MF in any directions and 5 times larger MF on average than the
maximum MF generated at the center. We performed a navigation experiment of the MC along the aorta to the right coronary artery in a cardiac vascular phantom model. We observed a
buckling of the MC, and the maximum MF of 2.61 mN at the center did not overcome the buckling. We applied the PCM which generated the MF of 20.1 mN to release the buckling of the
MC. The PCM may contribute to controlling of the MC for robotic endovascular intervention. 

**References:** 

1B. J. Nelson, I. K. Kaliakatsos, and J. J. Abbott, Annual Review of Biomedical Engineering., Vol. 12, 55 (2010).
2N. Kim, S. Lee, W. Lee, and G. Jang, AIP Advances, Vol. 8, 056708 (2018).
3J. Nam, W. Lee, E. Jung, and G. Jang, IEEE Transactions on Industrial Electronics, Vol. 65, 5673 (2018)..
4E. Jung, W. Lee, N. Kim, J. Kim, J. Park, and G. Jang, AIP Advances, Vol 9, 125230 (2019). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1c5902cf7e1a3cdb456194b529d812ca.png)

Position Control Method of a Robotically Assisted Magnetic Navigation System to Improve the Pushability of a Magnetic Catheter by Maximizing Magnetic Force

Micro helical robots actuated by an external magnetic field have been investigated for a possible application to treat occlusive vascular disease. It requires a high-speed
rotating magnetic field (RMF) which generates fast drilling motion of the micro helical robot to tunnel the clogged lesions in blood vessels.1-3 The RMF is generated by the magnetic
navigation systems (MNSs) composed of multiple coils or electromagnets. However, as the frequency increases, the impedance from the inductance of the coils decreases the current and
the magnetic field. To overcome this problem, prior researchers utilized a resonance by including additional capacitance to their MNS.2,3 The electromagnets with magnetic cores generate
a large magnetic field.4 Unlike the MNS with coils only, the MNS with electromagnets has significant mutual-inductance due to the magnetic flux linkages between electromagnets, but
any resonance method suppressing the self and mutual inductances of the electromagnets of the MNS has not been reported.
We propose a method to suppress both the self and mutual-inductance effect of the 3-phase MNS with multiple electromagnets. First, we set the imaginary part and the real parts except the
resistance in the voltage equation to be zero to express the resonance. After solving the real part of the voltage equation and the actuation matrix equation which relates applied current with
flux density together, we can determine 3-phase currents and corresponding phases at resonance. The capacitance at resonance can be determined by solving the imaginary part in the
voltage equation. Fig. 1 shows the 3-phase MNS developed for the experiments and Fig. 2 shows the calculated and measured 3-phase currents and RMF with the application of the
proposed method to generate a magnetic flux density of 10 mT. It shows that the calculated current matches well with the measured one within 5 % discrepancy. The proposed method in
this research can contribute to improving the tunneling performance of micro helical robots by generating a high-speed RMF even in the MNS with the electromagnets. 

**References:** 

1Q. Wang, X. Du, and L. Zhang, “Real-time ultrasound Doppler tracking and autonomous navigation of a miniature helical robot for accelerating thrombolysis in dynamic
blood flow,” ACS Nano, vol. 16, no. 1 (2022). 
2K. T. Nguyen, B. Kang and J. Park, “High-frequency and High-powered electromagnetic actuation system utilizing Two-stage resonant effects,” IEEE/ASME Transactions on
Mechatronics, vol. 25, no. 5 (2020). 
3J. Nam, W. Lee, and G. Jang, “Magnetic navigation system utilizing resonant effect to enhance magnetic field applied to magnetic robots,” IEEE Transactions on Industrial Electronics,
vol. 64, no. 6 (2017). 
4J. Nam, W. Lee, E. Jung, and G. Jang, “Magnetic navigation system utilizing a closed magnetic circuit to maximize magnetic field and a mapping method to precisely control magnetic
field in real time,” IEEE Transactions on Industrial Electronics, vol. 65, no. 7 (2018). 

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Resonant Control Method to Suppress the Self and Mutual Inductances of a 3 phase Magnetic Navigation System for Fast Drilling Motion of Micro Helical Robots

Most research on remotely driven magnetic micro-robots focuses on their manipulation within fluids [1]. Actuating their motion in soft media and living tissue raises
challenges along with new opportunities for minimally invasive medicine. In contrast to fluids, moving solids in soft media irreversibly rearranges the material, leading to highly non-linear
and history dependent reaction forces. The present work demonstrates that this behavior enables solutions of certain long-standing problems. One problem stems from using magnetic field
gradients to generate forces which limits their range particularly for sub-millimeter size magnetic robots. Locomotion by the transfer of energy via a time varying uniform magnetic field
provides an alternative. In fluids where locomotion effectively occurs through swimming at low Reynolds numbers, this strategy can be costly, requiring more complex shapes (e.g. a screw
[2]) and control over a non-reciprocal motion gait [3]. In tissues, such complex shapes have difficulties in changing their trajectory direction over short distances. The novel finding in this
work is that soft media enables locomotion of simple solids, such as a pair of spheres (see Fig. 1), without requiring them to execute a complex motion gait. Using an external uniform
magnetic field to change the relative orientations of the magnetic moments, the disconnected spherical solids of slightly different diameters can locomote as one in a soft medium via
ratchet-like movements that are completely reciprocal. Such a configuration also allows the pair to change the direction of locomotion quickly. A demonstration is carried out in this work
via development of a theoretical model and its numerical simulation, although some experimental observations support these findings. 

**References:** 

[1] J. J. Abbott et al., "How should microrobots swim?," The international journal of Robotics Research, vol. 28, no. 11-12, pp. 1434-1447, 2009. 
[2] T. W. Fountain, P. V. Kailat, and J. J. Abbott, "Wireless control of magnetic helical microrobots using a rotating-permanent-magnet manipulator," in 2010 IEEE International
Conference on Robotics and Automation, 2010: IEEE, pp. 576-581. 
[3] E. Lauga, "Life around the scallop theorem," Soft Matter, vol. 7, no. 7, pp. 3060-3065, 2011. 

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On Locomotion of Magnetized Spherical Solids in Soft Media

Magnetorheological fluids (MRFs) consist of micron-sized magnetic particles dispersed in a carrier fluid for which rheological properties can be tuned reversibly with
magnetic field.1 If an MRF is contained in a cellular elastomeric encapsulant (CEE), its mechanical properties, such as stiffness and damping, can be controlled via magnetic field. Such
tunability can be exploited for adaptive vibration control or energy absorption systems. A magnetorheological damper often uses an accumulator to modulate pressure injected by external
forces applied to the damper.2 An accumulator is implemented into the cellular encapsulant to enable essentially incompressible fluid to enter the accumulator and to allow compression of
the cellular material to take place, and also enables a mechanical bulge stiffness to the design.
Here, MRF was prepared with silicon oil (40% vol. fraction). Thermoplastic polyurethane (TPU) was 3-D printed as the CEE system. (Fig. 1 a). The MRF was injected into the TPU-CEE,
followed by the printing of a sealing layer. The wall adjacent to the sealing layer had a circular opening and a TPU membrane was bonded to its perimeter so that the pressurized MRF
could flow through the opening and be accumulated in the resulting pocket.
An external magnetic field (0 and 7 kG) was applied along the sample longitudinal axis at the time of uniaxial dynamic testing with 5% pre-strain. The TPU-CEE samples were
characterized via force-displacement tests at 1 Hz under strain amplitudes. The MR effect on the dynamic stiffness is defined as the ratio of the dynamic stiffness under the maximum
magnetic field to the dynamic stiffness in the absence of a magnetic field. Dynamic stiffness in the presence as opposed to the absence of magnetic field was 264%. (Fig.2a) The area of the
force-displacement curve of the system with an accumulator is about 41% greater than one without an accumulator. The accumulator enhanced the increase in damping (Fig. 2b). The
increase in damping capacity generally increased as strain amplitude increased. 

**References:** 

1. Ashtiani M, Hashemabadi SH, Ghaffari A. A review on the magnetorheological fluid preparation and stabilization. Journal of Magnetism and Magnetic Materials. 374, 716.
(2015) 
2. Yu, Jianqiang & Dong, Xiaomin & Wang, Xuhong & Pan, Chengwang & Zhou, Yaqin. Asymmetric Dynamic Model of Temperature-Dependent Magnetorheological Damper and
Application for Semi-active System. Frontiers in Materials. 6. 227. (2019) 

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