Solid Magnetic Materials Research Articles

Steady-state magnon entanglement and backaction-evading of a weak magnetic signal via two-tone modulated cavity electromagnonics

Cavity electromagnonics explore the coupling between microwave cavity fields and magnons in micromagnets. This field has emerged as a promising platform for probing fundamental aspects of quantum mechanics and advancing quantum technologies. This paper investigates a scheme involving two-tone frequency modulation to engineer simultaneous magnon-photon two-mode squeezing and beam-splitter-like interactions. We demonstrate that this scheme enables the direct generation of macroscopic magnonic squeezed and entangled states. Moreover, it facilitates ultra-sensitive magnon-based magnetic field sensing through quantum non-demolition (QND) interactions between magnons and photons. The present scheme provides promising opportunities for generating macroscopic nonclassical quantum states in solid magnetic materials and developing spintronics-related quantum devices.

Exploiting ferrofluidic wetting for miniature soft machines

Miniature magnetic soft machines could significantly impact minimally invasive robotics and biomedical applications. However, most soft machines are limited to solid magnetic materials, whereas further progress also relies on fluidic constructs obtained by reconfiguring liquid magnetic materials, such as ferrofluid. Here we show how harnessing the wettability of ferrofluids allows for controlled reconfigurability and the ability to create versatile soft machines. The ferrofluid droplet exhibits multimodal motions, and a single droplet can be controlled to split into multiple sub-droplets and then re-fuse back on demand. The soft droplet machine can negotiate changing terrains in unstructured environments. In addition, the ferrofluid droplets can be configured as a liquid capsule, enabling cargo delivery; a wireless omnidirectional liquid cilia matrix capable of pumping biofluids; and a wireless liquid skin, allowing multiple types of miniature soft machine construction. This work improves small magnetic soft machines’ achievable complexity and boosts their future biomedical applications capabilities.

Integrated Locomotion and Deformation of a Magnetic Soft Robot: Modeling, Control, and Experiments

Magnetic robots have shown great potential in small-scale applications due to their wireless control mode. However, the existing efforts only deal with solid magnetic materials that could not deform. In this article, we focus on integrated locomotion and deformation of a class of magnetic soft robot made of ferrofluid. To this end, the magnetic model and dynamics model that takes the nonlinearity into account are first established. Then, the corresponding motion controllers are proposed, based on the results of feedback linearization and frequency-domain test results. Furthermore, an extended state observer is designed to reduce the perturbation due to model uncertainties. By integrating the control strategies of locomotion and active deformation, we demonstrate that the soft robot possesses the capability of conducting complex tasks such as passing through narrow environment and transporting multiple objects. Various experiments are also performed to demonstrate the effectiveness of the proposed control methods.

Miniaturization Techniques Using Magnetic Materials for Broadband Antenna Applications

This paper investigates the instrumentation necessary to analyze frequency-dependent complex parameters of solid magnetic materials based on T/R-based waveguide measurement technique proposed by W. B. Weir. Based on the magnitude and phase values of transmission and reflection coefficients measured using vector network analyzer, complex permittivity and permeability are calculated using the expressions defined. Equations necessary for calculating the complex parameters as a function of frequency with required step size are derived from the experimental results. To validate mathematical expressions developed for composite magnetic materials, the design of a compact 2-18 GHz cavity-backed spiral antenna using off-the-shelf magnetic materials is presented. The electrical performance of the cavity along with stack of high contrast magnetic materials of varying dimensions is modeled and simulated in ANSYS HFSS software.

Research on the low-frequency pressure generator based on magnetic fluid

To solve the problems that the existing pressure generators require high mechanical excitation frequency, need large manufacturing cost and are hard to control, a kind of pressure generator with low-frequency based on magnetic fluid is proposed in this paper. Magnetic fluid possesses the advantages of both magnetism of solid magnetic material and fluidity of liquid. The first-order buoyancy of magnetic fluid changes with low frequency alternating magnetic field. Based on this, the superimposed magnetic field is generated by electrifying the conical solenoid coil connected with the long solenoid coil with magnetic core in parallel. Magnetic field and magnetic force in the model are analyzed, then the relationship between input current and output pressure is calculated. In addition, the experimental platform is built and the performance of the device is tested. The result shows that the pressure generator can produce the corresponding pressure signal according to the input current.

A frequency tuner for resonant inverters suitable for magnetic hyperthermia applications

In this study, a frequency tuner system is developed for generating variable frequency magnetic fields for magnetic hyperthermia applications. The tuning device contains three specially designed phase lock loop devices that drive a resonant inverter working in the frequency band of 180–525 kHz. This tuner system can be adapted for other resonant inverters employed in the studies of ferrofluids with superparamagnetic nanoparticles. The performance of the whole system is also examined. Our findings were in agreement with the theoretical expectations of phase locking and frequency tuning. The system is tested for samples of a solid magnetic material of cylindrical shape and ferrofluids with differing concentrations of powdered magnetite. The observations indicate significant frequency changes of the magnetic field due to heating of the samples. These frequency variations can be a source of errors, which should not be neglected in experiments determining the specific absorption rate or power dissipated density.

Progress of room temperature magnetic refrigeration technology

refrigeration technology. It has been considered as one of promising alternatives to traditional vapor compression refrigeration technology. Magnetic refrigeration, in which solid magnetic materials instead of gaseous refrigerants are used, is based on the magnetocaloric effect. When magnetocaloric material moves in or out of magnetic field, it releases heat due to magnetization or absorbs heat due to demagnetization, respectively. In this paper, magnetocaloric effects (MCEs) and basic thermodynamic cycles are briefly described at first. Some typical magnetic refrigeration cycles are introduced from the viewpoint of thermodynamics, which include hybrid cycle, cycle based on the active magnetic regenerator and cycle based on the active magnetic regenerator coupled with gas regenerative refrigeration. Specifically, magnetic refrigeration cycle based on the active magnetic regenerator (AMR) coupled with gas regenerative refrigeration is a novel idea that combines the magnetocaloric effect with the regenerative gas expansion refrigeration. And it has been under the way to try to achieve greater refrigeration performance of the coupled refrigerator in the research institutions. Thereafter, the paper reviews the existing different numerical models of AMR refrigerator. Analyzing and optimizing an AMR magnetic refrigerator are typical complicated multi-physics problems, which include heat transfer, fluid dynamics and magnetics. The majority of models published are based on one-dimensional simplification, which requires shorter computation time and lower computation resources. Because a one-dimensional model idealizes many factors important for the system performance, two- or three- dimensional numerical models have been setup. Besides, some key items for the model are described in detail, such as magnetocaloric effect, thermal conduction, thermal losses, demagnetizing effect and magnetic hysteresis. Considering the accuracy, convergence and computation time, it is quite vital for numerical models to choose some influential factors reasonably. Then, the recent typical room magnetic refrigeration systems are listed and grouped into four types, i.e., reciprocating-magnet type, reciprocating-regenerator type, rotary-magnet type, and rotaryregenerators type. Different characteristics of these four types are compared. Reciprocating magnetic refrigerators have the advantages of simple construction and max magnetic field intensity difference. Rotary magnetic refrigerator due to compact construction, higher operational frequency and better performance is deemed as a more promising type, in the progress of magnetic refrigeration technology. Meanwhile there are still some key challenges in the practical implementation of magnetic refrigeration technology, such as the development and preparation technologies of high-performance MCE materials, powerful magnetic circuit system and flowing condition. Finally, possible applications are discussed and the tendency of future development is given.

Review on Optical Fiber Sensors Based on the Refractive Index Tunability of Ferrofluid

Ferrofluid is a novel kind of functional materials, which possesses both the magnetism of solid magnetic material and fluidity of liquid material. Due to its unique optical properties, especially the refractive index tunability under magnetic field, ferrofluid has been widely utilized for magnetic field and current sensing combined with various optical fiber structures. Hence, in this paper, the refractive index tunability of ferrofluid, which is mainly applied into the optical fiber sensors, is first reviewed and illustrated in detail. Then we mainly introduce our work on the applications of ferrofluid in optical fiber sensors based on the refractive index tunability of ferrofluid, including the whole physical configurations, the operating principles, and the performances of these optical fiber sensors. At last, the deficiencies of ferrofluid in the applications of optical fiber sensors as well as valuable potential prospects in further research are analyzed and presented. From all the above reviews and discussions, it can be foreseen that the characteristics of ferrofluid will be improved and the applications of ferrofluid-based optical fiber sensors will be developed rapidly and maturely.

A Novel Sinusoidal Pressure Generator Based on Magnetic Liquid

A novel sinusoidal pressure generator with low frequency(0.1 Hz ~ 100 Hz) based on magnetic liquid is proposed in this paper. Magnetic liquid possess both magnetism characteristic of solid magnetic material and fluidity of the liquid. The magnetic liquid acts as a reciprocating piston, when it is placed in the alternating magnetic field. Based on this, we devised a setup use of magnetic liquid to generate micro differential pressure, which varies sinusoidal and has the same frequency with the exciting current. The relation between input current and output pressure was also analyzed in this paper. Magnetic field and magnetic force is calculated. Meanwhile, the experimental platform was built for testing the performance of the setup and some experimental is performed. Both the theoretical analysis and the experiment results prove that this kind of new sinusoidal pressure generator satisfies the design demand.

Iron-Loss Modeling for Rotating Machines: Comparison Between Bertotti's Three-Term Expression and 3-D Eddy-Current Analysis

Two calculation methods for iron-loss estimation of rotating machines are investigated. One is based on the conventional three-term expression. In this case, the losses are calculated from the time variation in the flux density obtained by the finite element analysis, which approximates the stator and rotor cores as solid magnetic materials without conductivity. The other is based on the 3-D eddy current analysis in the electrical steel sheet. In this case, the excess loss is calculated with a simple approximation. It is clarified that both methods can estimate the no-load iron loss in the similar accuracy and that the method based on the eddy-current analysis is suitable for the estimation of high-order harmonic iron losses.

Model of a porous regenerator used for magnetic refrigeration at room temperature

A transient three-dimensional model of a porous regenerator operating at room temperature is presented. The solid magnetic material and the regeneration fluid are modeled separately. The fluid flows through interstitial channels formed by a regular matrix of solid particles. The velocity, pressure and temperature fields are obtained from the simultaneous solution of the Navier–Stokes and energy equations with variable properties in the solid and the Boussinesq approximation for the fluid. The magnetocaloric effect (MCE) is taken into account by the inclusion of a source term in the energy equation for the magnetic solid. Special numerical schemes are used to avoid unrealistic computation time and memory requirements. Typical velocity fields and transient temperature profiles are presented.

駆動方式磁気冷凍機

The requirement for a helium refrigerator with high efficiency and compactness has been growing for cooling superconducting devices.We have developed a reciprocating magnetic refrigerator for liquefying helium from the temperature of 20K region which uses gadolinium-gallium-garnet (GGG) for the magnetic material. The working material (GGG single crystal, 30mm in diameter and 40mm in length) is placed at the end of the each piston, and those two pistons are driven by a pneumatic jack. When the working material is placed in a high-intensity magnetic field (4.5T), the temperature of the GGG rises to 15K. The inner surface of the cylinder is cooled by the auxiliary refrigerator (a G-M refrigerator), and heat is removed through the narrow gap (less than 50μm) filled with gaseous helium between the GGG and the cylinder. When the magnetic field given to the GGG is eliminated by moving the piston, temperature of the GGG goes below 4.2K. Here the refrigeration of liquid helium occurs by condensing the gaseous helium on the surface of the GGG.Technical emphasis was placed on the realization of a high heat exchange rate between the solid magnetic material and gaseous helium. A sufficient heat transfer rate was achieved after several component-level experiments. Sources of inefficiency to the refrigeration capacity has been also discussed.Finally the refrigeration power of 0.95W at 4.2K was achieved at 0.38Hz operation.