Heating ability of elongated magnetic nanoparticles

Low-frequency hysteresis loops and specific absorption rate (SAR) of various assemblies of elongated spheroidal magnetite nanoparticles have been calculated for a range of particle semiaxis ratios a/b = 1.0–3.0. The SAR of a dilute randomly oriented assembly of magnetite nanoparticles in an alternating magnetic field of moderate frequency, f = 300 kHz, and amplitude H0 = 100–200 Oe is shown to decrease significantly with an increase in the aspect ratio of nanoparticles. In addition, there is a narrowing and shift of the intervals of optimal particle diameters towards smaller particle sizes. However, the orientation of a dilute assembly of elongated nanoparticles in a magnetic field leads to an almost twofold increase in SAR at the same frequency and amplitude of the alternating magnetic field, the range of optimal particle diameters remaining unchanged. The effect of the magneto-dipole interaction on the SAR of a dilute assembly of oriented clusters of elongated magnetite nanoparticles has also been investigated depending on the volume fraction of nanoparticles in a cluster. It has been found that the SAR of the assembly of oriented clusters decreases by approximately an order of magnitude with an increase in the volume fraction of nanoparticles in a cluster in the range of 0.04–0.2.

A novel detection of weld defects by magneto-optical imaging under combined magnetic field

To overcome the shortcomings of existing magneto-optical imaging, such as the saturation of an image under a constant magnetic field and the ambiguity of an image under an alternating magnetic field, imaging using a combined magnetic field is presented in this research. Weld defect samples include a laser-cut groove, a wire-cut penetrating groove, a pit and a Z-shaped crack. Magneto-optical imaging experiments were carried out under different magnetic fields. Contour extraction and standard deviation calculations were carried out for all magneto-optical images and the maximum standard deviation of the laser-cut groove under an alternating magnetic field was 20.9, which was less than the maximum value of 37.4 under a combined magnetic field. The experimental results show that the contrast of a magneto-optical image obtained under the combined magnetic field is greater than that obtained under the alternating magnetic field for all defects. The proposed combined magnetic field could optimise the magneto-optical imaging effect for weld defects under the existing excitation method to a certain extent.

Four-point probe stand for magnetoresistance measurement of unpatterned sample

An experimental stand for express diagnostics of multilayer spin tunnel structures has been developed. The current-in-plane tunnelling method (CIPT) requires no processing, is fast, and provides reliable data which are reflective of the deposition only. The stand is based on the four-probe method for measuring resistance at external alternating magnetic field. This technique can be applied after only a short processing route, thereby saving time and resources, and reducing the potential for damaging the junction.

Enhancing Magnetic Hyperthermia Nanoparticle Heating Efficiency with Non-Sinusoidal Alternating Magnetic Field Waveforms

For decades now, conventional sinusoidal signals have been exclusively used in magnetic hyperthermia as the only alternating magnetic field waveform to excite magnetic nanoparticles. However, there are no theoretical nor experimental reasons that prevent the use of different waveforms. The only justifiable motive behind using the sinusoidal signal is its availability and the facility to produce it. Following the development of a configurable alternating magnetic field generator, we aim to study the effect of various waveforms on the heat production effectiveness of magnetic nanoparticles, seeking to prove that signals with more significant slope values, such as the trapezoidal and almost-square signals, allow the nanoparticles to reach higher efficiency in heat generation. Furthermore, we seek to point out that the nanoparticle power dissipation is dependent on the waveform’s slope and not only the frequency, magnetic field intensity and the nanoparticle size. The experimental results showed a remarkably higher heat production performance of the nanoparticles when exposed to trapezoidal and almost-square signals than conventional sinusoidal signals. We conclude that the nanoparticles respond better to the trapezoidal and almost-square signals. On the other hand, the experimental results were used to calculate the normalized power dissipation value and prove its dependency on the slope. However, adjustments are necessary to the coil before proceeding with in vitro and in vivo studies to handle the magnetic fields required.

Novel Nanoparticle-Based Cancer Treatment, Effectively Inhibits Lung Metastases and Improves Survival in a Murine Breast Cancer Model

Sarah Nanoparticles (SaNPs) are unique multicore iron oxide-based nanoparticles, developed for the treatment of advanced cancer, following standard care, through the selective delivery of thermal energy to malignant cells upon exposure to an alternating magnetic field. For their therapeutic effect, SaNPs need to accumulate in the tumor. Since the potential accumulation and associated toxicity in normal tissues are an important risk consideration, biodistribution and toxicity were assessed in naïve BALB/c mice. Therapeutic efficacy and the effect on survival were investigated in the 4T1 murine model of metastatic breast cancer. Toxicity evaluation at various timepoints did not reveal any abnormal clinical signs, evidence of alterations in organ function, nor histopathologic adverse target organ toxicity, even after a follow up period of 25 weeks, confirming the safety of SaNP use. The biodistribution evaluation, following SaNP administration, indicated that SaNPs accumulate mainly in the liver and spleen. A comprehensive pharmacokinetics evaluation, demonstrated that the total percentage of SaNPs that accumulated in the blood and vital organs was ~78%, 46%, and 36% after 4, 13, and 25 weeks, respectively, suggesting a time-dependent clearance from the body. Efficacy studies in mice bearing 4T1 metastatic tumors revealed a 49.6% and 70% reduction in the number of lung metastases and their relative size, respectively, in treated vs. control mice, accompanied by a decrease in tumor cell viability in response to treatment. Moreover, SaNP treatment followed by alternating magnetic field exposure significantly improved the survival rate of treated mice compared to the controls. The median survival time was 29 ± 3.8 days in the treated group vs. 21.6 ± 4.9 days in the control, p-value 0.029. These assessments open new avenues for generating SaNPs and alternating magnetic field application as a potential novel therapeutic modality for metastatic cancer patients.

Screening current induced field characteristics of HTS quasi-isotropic and simply stacked strands in alternating magnetic field

The screening current induced field (SCIF) in the flat REBCO coated conductors (REBCO CCs) so called 2G HTS tapes cause undesirable effects in multiple applications. Their existence reduces the spatial uniformity and temporal stability of magnetic fields for applications of superconducting magnets. In this paper, we numerically and experimentally investigate the characterization of the screening current and SCIF of quasi-isotropic strand (Q-IS) and simply stacked strand (SSS) under external alternating magnetic field with various amplitudes, orientations, and excitation rates. The two-dimensional finite element method (2D FEM) based on T-A formulation is adopted for simulation, the Q-IS and SSS samples are fabricated for experiments. The field angle is in the range of 0° to 90° at intervals of 15°, the excitation rate varies from 20 mT/s to 800 mT/s. We display the distribution of screening current in both strands under various field amplitudes and orientations. Then the dependence of SCIF on the amplitude and orientation of external field is studied, respectively. The spatial distribution of SCIF of both strands with different amplitudes and angles of the external field are also discussed. Besides, we analyze the properties of SCIF under various excitation rates. As a result, the SCIF of Q-IS is much smaller and has quasi-isotropic distribution comparing with SSS, which represents that Q-IS has relative smaller screening effect. The spatial point with the largest SCIF of Q-IS locates at the corner of the strand and is independent of the external field, but the corresponding point in SSS varies with the angle and amplitude. The Q-IS is also less susceptible to the change of rate. Therefore, Q-IS has more advantages when the screening effect is considered in superconducting applications.