Maximum Levitation Force Research Articles

Comparison of Levitation Properties between Bulk High-Temperature Superconductor Blocks and High-Temperature Superconductor Tape Stacks Prepared from Commercial Coated Conductors.

Bulk high-temperature superconductors (HTSs) such as REBa2Cu3O7-x (REBCO, RE = Y, Gd) are commonly used in rotationally symmetric superconducting magnetic bearings. However, such bulks have several disadvantages such as brittleness, limited availability and high costs due to the time-consuming and energy-intensive fabrication process. Alternatively, tape stacks of HTS-coated conductors might be used for these devices promising an improved bearing efficiency due to a simplification of manufacturing processes for the required shapes, higher mechanical strength, improved thermal performance, higher availability and therefore potentially reduced costs. Hence, tape stacks with a base area of (12 × 12) mm2 and a height of up to 12 mm were prepared and compared to commercial bulks of the same size. The trapped field measurements at 77 K showed slightly higher values for the tape stacks if compared to bulks with the same size. Afterwards, the maximum levitation forces in zero field (ZFC) and field cooling (FC) modes were measured while approaching a permanent magnet, which allows the stiffness in the vertical and lateral directions to be determined. Similar levitation forces were measured in the vertical direction for bulk samples and tape stacks in ZFC and FC modes, whereas the lateral forces were almost zero for stacks with the REBCO films parallel to the magnet. A 90° rotation of the tape stacks with respect to the magnet results in the opposite behavior, i.e., a high lateral but negligible vertical stiffness. This anisotropy originates from the arrangement of decoupled superconducting layers in the tape stacks. Therefore, a combination of stacks with vertical and lateral alignment is required for stable levitation in a bearing.

Orientation optimization of the Halbach PMG for the levitation and guidance performance of the HTS maglev system

High-temperature superconducting maglev technology has great application potential in rail transit applications due to its advantages such as passive stable levitation and green environmental protection. As one of the key components of the HTS maglev system, the Halbach-type permanent magnet guideway (PMG) enhances the magnetic field on one side of the guideway and weakens that on the other side. Optimizing the PMG, including the geometry and magnetic properties of the magnet, is an effective method to improve the levitation and guidance performance of the system. In addition, since NdFeB permanent magnets are expensive, optimizing the design of the PMG for the HTS maglev system is also an important work to reduce the application cost. In this paper, the Nelder–Mead Simplex method (NMS) in the optimization solver in COMSOL software is used to optimize the geometric parameters of the Halbach PMG according to the different objective requirements of the HTS maglev system. The optimization objectives include the maximum levitation force and guidance force under the constraint of the maximum cross-sectional area of the PMG, as well as the minimum cross-sectional area of the PMG with a minimum levitation force constraint. The results indicate that the NMS method is effective. By comparing four PMGs during the optimization process, it is found that this method can fully improve the utilization of the magnetic field by changing the geometric parameters of the Halbach PMG. This study can provide a valuable reference for the optimal design of the PMG for HTS maglev systems in the future.

Optimizing superconducting magnetic bearings of HTS flywheel systems based on 3D H-[formula omitted] formulation

The superconducting flywheel system exploiting the magnetic coupling between the bulk high temperature superconductors (HTSs) and permanent magnets (PMs) exhibits excellent performance of self-stable levitation, and is promising for power applications. In this paper, we use the H-ϕ formulation combined with moving mesh to establish a full 3D model for the thrust type and journal type bearings in the HTS flywheel system. We then proposed different Halbach schemes to enhance the magnetic flux density of the rotor and thus the coupling, and investigated the levitation force, relaxation characteristics, electromagnetic transient distribution, and temperature characteristics of the bearings. Results show that, under axial zero field-cooled (ZFC) condition, the optimized PM rotor scheme can significantly improve the maximum levitation force and stiffness by 4.0 and 2.3 times respectively for the thrust type bearing, and the maximum levitation force of journal type bearing can be improved by a factor of 5.5. Under the radial ZFC condition, the maximum levitation force and stiffness of the journal type bearing have been increased by 4.9 times and 2.9 times. For the relaxation of both bearings during operation, the optimized PM rotors lead to relatively greater attenuation of levitation force. The proximity of the optimized PM rotors intensifies the magnetic flux movement of the HTS bulks but only brings about a limited temperature rise, and the superconductors still maintain a good low-temperature working environment. This study provides an effective methodology for analyzing the HTS bearing systems and good references for the optimal design of compact HTS flywheel energy storage systems (FESSs).

Investigation of saturation levitation force and optimization of permanent magnet guideway based on multi-seeded superconducting bulks model

After more than 20 years of research, the superconducting maglev has advanced to the engineering research stage. In engineering applications, multi-seeded superconducting bulks have been widely used in high-temperature superconducting (HTS) maglev systems, but there remains a deficiency in terms of the theoretical model description of multi-seeded superconducting bulks. In this paper, the fully coupled, partially coupled, and uncoupled models of the multi-seeded superconductor are presented to simulate HTS multi-seeded bulk. Then, the levitation performance and trapped field of three kinds of HTS bulks were experimentally tested, revealing a saturation levitation performance on the permanent magnet guideway (PMG). Therefore, the levitation force and trapped field of HTS bulks with different critical current density are further studied by 3D simulation. Taking the 90% and 95% of the maximum levitation force as the benchmarks, the corresponding critical current density of HTS bulks are respectively 4.6 × 108 A m−2 and 6.1 × 108 A m−2. Further, a mapping coupled boundary method was adopted to automatic optimize the PMG to increase the levitation force above the PMG. After optimization, the levitation force under a unit of the permanent magnet is increased by 19%, while the maximum levitation force above multi-period Halbach PMG is increased by 9.23%. This study provides a general multi-seeded superconducting bulk simulation model and levitation force optimization method, which can serve as a reference for selecting suitable superconducting bulk.

Levitation Force Compensation Study for HTS Maglev System Based on the Input of Electromagnetic Force

The advantages of levitation and guidance integration make the high-temperature superconducting (HTS) maglev system have great potential in the field of high-speed transportation. However, due to the influence of some factors such as the Dewar (a low temperature thermostat for superconductors) vacuum increases and magnetic field irregularity, the levitation force will decline and working height will drop. To solve the problems, this paper proposes a compensation method based on electromagnetic auxiliary device. Firstly, the thought and purpose of this method are explained in detail. Secondly, the effectiveness of levitation force compensation is verified by experiment. Then, electromagnetic simulation model is established and its correctness is verified by comparing simulation results and experimental data. Finally, dynamic simulation is conducted based on the verified model to study the vibration characteristics of Dewar system. The results show that the auxiliary device can compensate the levitation force and suppress vibration well. Meanwhile, comparing with the field cooling height (FCH) at 20 mm and 30 mm, the compensation effect of former is better than latter, but the overall maximum levitation force of latter is higher than former. This research provides an economical and effective way to achieve the levitation force compensation of HTS maglev system. Furthermore, the electromagnetic auxiliary device is an active energy input port, providing the possibility for the active control of HTS system. It is expected to provide reference for future practice in relevant application fields.

Enhancing magnetic levitation and guidance force and weight efficiency of high‐temperature superconducting maglev systems by using sliced bulk YBCO

AbstractWe aimed to enhance the magnetic force efficiency of Maglev systems without increasing total weight. For this aim, we divided YBCO bulks into three slices horizontally to utilize the YBCO‐permanent magnetic guideway (PMG) interaction surface as much as possible. We used whole YBCO above PMGs with different magnetic pole directions (PMG‐A and PMG‐B) in two lying positions of transversal and longitudinal and investigated levitation and guidance force performances. It is determined that levitation and guidance forces by using YBCO in transversal lying mode are bigger compared to the longitudinal mode. For sliced YBCO, the maximum levitation force increased by 69% and 78%, while the guidance force enhancements are determined as 212% and 91%, compared to the whole YBCO above PMG‐A and PMG‐B, respectively. The levitation and guidance force density with respect to the total mass of unit a set of slices YBCO increased by 92% and 106%, respectively, compared to the whole YBCO above PMG‐B in transversal mode. Since the higher levitation force and the lower total weight of the onboard unit are important parameters in point of the energy efficiency in Maglev and other levitation applications, the result of this study supplies useful data for the engineers and industrial partners.

Dynamic Characteristics and Working Modes of Permanent Magnet Electrodynamic Suspension Vehicle System Based on Six Wheels of Annular Halbach Structure

A novel type of suspension system for maglev vehicles using six permanent magnet electrodynamic wheels (EDW) and conductor plate has been designed. It has the advantages of high speed, environmental protection, and a low turning radius. Differing from existing maglev vehicles, this paper proposes a new maglev vehicle utilizing six EDWs to respectively provide driving force and levitation force. This structure can keep the levitation force at a large constant value and obtain enough driving force at low rotational speeds by adjusting the motor speed. First, the structure of the electrodynamic wheel is given. The accuracy and validity of the FEM results are verified by the experiments. Moreover, based on the finite element method (FEM), the optimal structure of the EDWs is obtained with the objective of maximum levitation force. Then, the simplified electromagnetic force model is obtained by using MATLAB Toolbox. Third, using a co-simulation of Simulink and Adams to design and build a 1:50 maglev vehicle model, this article studies the dynamic response characteristics of the maglev vehicle model from the perspective of dynamics and proposes a feedback control strategy by adjusting the rotational speed to control the maglev vehicle. This paper also proposes a method to realize the car’s pivot steering to reduce the car’s turning radius and help the drivers pass narrow road sections. This article verifies the feasibility of the maglev vehicle with six EDWs and is expected to provide a certain reference for the development of permanent magnet electrodynamic suspension vehicles.

Levitation behaviours of an eccentric SC-PM system with multi-degree-of-freedom motion

The high temperature superconducting (HTS) magnetic levitation is actually a self-stable levitation with multi-degree-of-freedom (DoF). However, the research of HTS magnetic levitation focuses on the axial or radial levitation behaviour with single-DoF motion independently. This article mainly discusses the 3-D modelling and the levitation behaviours of an eccentric superconductor-permanent magnet (SC-PM) system with multi-DoF motion. Firstly, the Power-Law E − J relation is used to obtain the relationship of equivalent conductivity-electric field strength for the superconductor. Then, a 3-D finite element model (FEM) of SC-PM system is established and calculated in software MagNet. At the same time, the result of the simulation is verified by the experimental measurements. The axial levitation behaviour is analysed by establishing and solving the 3-D FEM in eccentric SC-PM system with different multi-DoF motions. The results show that the maximum axial levitation force decreases with the increase of the static eccentricity distance. When the PM rotor exhibits dynamic eccentricity, the axial levitation force presents periodic fluctuations of which the amplitude and period are related to the dynamic eccentric distance and speed.

Influence of cooling temperature on load-carrying performance of a radial HTS magnetic bearing

High temperature superconducting (HTS) magnetic bearing can operate in the harsh environment of low temperature and negative pressure with low loss and self-stability. Therefore, it has been gradually applied in flywheel energy storage, cryogenic liquid pump, cold compressor and some other cryogenic rotating machinery. The load-carrying performance of HTS magnetic bearing is affected by the cooling temperature of HTS directly. In this paper, the linear model is used to modify the temperature dependence to evaluate the influence of cooling temperature on load-carrying performance quantitatively, and the results are analyzed and displayed from the aspects of maximum levitation force, levitation stiffness and hysteresis effect. The research results of this paper have practical significance for the design and safe operation of HTS levitation system.

Study of Levitation Force Improvement Structure of Magnetic Levitation System for Logistics Transport considering Leakage Flux

In this paper, we propose a structural modification to improve levitation force of an EMS (Electro-Magnetic Suspension) C-type levitation system operated by an electromagnet. When the size of the transport system is limited, a study has to be conducted on design techniques to allow maximum levitation force within constraints. This study considered the shape of the stator teeth to improve the levitation force without affecting overall size of system. In addition, slot design parameters resulting from changed teeth shapes were summarized. The shape with maximum levitation force was derived by analyzing the magnetic flux contributing to the levitation force and the leakage flux according to the size of the design variable. Finally, the validity of the study was verified by comparing the levitation force results of the basic and improved models through FEA (Finite Element Analysis).

Strong Magnetic Field Dependence of Micro-YBCO Superconductor Levitated Above Halbach Guideway

For a regular-geometry superconductor, due to a nonuniform external magnetic field, the effect of the field dependence (i.e., <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> anisotropy and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) property) on the levitation force is complex and indistinct. For a relative microsample, its applied field is uniform, and the phenomenon caused by the field dependence should be more obvious. A novel instrument with a parallel-structure is therefore developed to accurately measure the micro force, and the device achieves a 4 mN precision. Based on this specialized apparatus, the experimental results present several rare phenomena caused by the field dependence. (a) Force attenuation (near the guideway during the superconductor descent) occurs in the small-width superconductor at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis⊥ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> condition, which is attributed to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ). (b) The maximum levitation force (MLF) position offset of bulks do not appear in the stack. (c) For the stack, the MLF curve varies in a sinusoidal way with the lateral position and fits well with the applied field | <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_z</i> |, which depicts that the anisotropic feature of the stack is much stronger than that of the bulk. An analytical critical-state model based on the assumptions of a uniform external field and saturated magnetization is proposed for describing these results that accurately reflect the experimental phenomenon. In addition, the finite element simulation of the micro superconductor in COMSOL is discussed, and a force formulation from this analytical model improves the calculated result.

Structure and Levitation Force Characteristics Analysis for Novel Radial Hybrid Magnetic Bearing

A new three-pole AC radial hybrid magnetic bearing (RHMB) is proposed. It has three characteristics of the levitation windings installed in the axial space, the permanent magnet mounted on the rotor and each stator core isolated by nonmagnetic materials. The structure and working principle are firstly introduced. Next, the force-current relationship is derived. According to the design requirement, the electromagnetic parameters are designed. Finally, the magnetic circuits, force-current curves and force coupling performance are calculated and analyzed. Furthermore, the maximum levitation forces are measured. The results show that the structure, magnetic circuit and working principle are correct, and the force-current relationship is further verified.

Design of the Six-Pole Hybrid Magnetic Bearing With Separated Magnetic Circuit to Generate Symmetrical Levitation Force

To solve the problem of generating the different two-degree-of-freedom (two-DOF) maximum levitation forces, a novel six-pole hybrid magnetic bearing (HMB), adopted combined stator and magnetic path structure, and its design method are proposed. Firstly, the configuration of the combined magnetic circuits and levitation principle are introduced. Then, the force-current relationships are derived. Furthermore, according to flux saturation, the permanent magnetic flux density is designed. Moreover, the combined magnetic circuit, force-current curves and design method are calculated and analyzed by Magnet 3D. Finally, the levitation forces are tested. The combined stator, levitation principle, force-current relationship and the design are proved to be correct.

Magnetic levitation force and trapped field properties of multiseeded YBCO with triangular arrangement of seeds

AbstractAlthough there are studies in literature using different number of seeds with different arrangements, especially line and rectangular, it is seen that there is no detailed study handling the levitation force together with trapped field properties of triangular arrangement of seed in YBCO. Therefore, to further investigate the magnetic properties of seeded YBCO superconductors, we have fabricated cylindrical YBCO (YBa2Cu3O7) superconductors with triangular arrangement of the seeds with different seed distances. Maximum levitation force values were obtained as 39.4 N and 57.1 N, while the maximum guidance force values were obtained as −4.6 N, and −8.7 N, respectively, with single‐seeded and triangular‐seeded samples with seed distance of 14 mm. It was determined that the trapped field, levitation force, and guidance force firstly decreased from the single‐seeded sample to the triangular‐seeded sample with small seed distance and then increased with increasing seed distance. Increased field trapping and levitation force performances in the triangular‐seeded samples with suitable seed distance indicate that the triangular arrangement of seeds is an eligible method to produce larger dimension YBCO samples with bigger shielding current radius and bigger averaged trapped field values.

Design and Experimental Studies on Superconducting Maglev Systems With Multisurface HTS–PMG Arrangements

In this article, we have designed and constructed a new multisurface (MS) high temperature superconductor (HTS) Maglev measurement system to investigate the enhancement of magnetic force properties of Maglev systems via MS HTS configurations above conventional permanent magnetic guideway (PMG). We have investigated both the static force and stiffness behavior and dynamic response characteristics of these MS HTS-PMG arrangements in different field cooling heights (FCHs). Optimum cooling height is determined as FCH 20-30 for both six- and four-HTS configurations. The maximum levitation force values of HTS-PMG arrangement with six-HTS were obtained bigger than that of four-HTS in the unit cryostat volume of MS arrangement, indicating that the HTSs at the bottom side of the cryostat make contribution to the loading capacity of Maglev systems. In the present article, it is observed that the magnetic flux density of bottom surface in addition to upper surface of the PMG can make a contribution to loading performance, vertical and lateral stability of Maglev systems. It is thought that the designed measurement facility and results of this study will be beneficial to increase the magnetic flux density in the unit volume via MS HTS-PMG arrangements for future design and construction of the HTS Maglev systems.

Levitation force of Graphene added bulk MgB2 superconductor

The effect of Graphene addition on levitation/suspension force of bulk MgB2 superconductor has been studied in both zero field cooling (ZFC) and field cooling (FC) conditions at different temperatures. For this, the pristine, 0.5, 1 and 3 wt% of Graphene added bulk MgB2 samples are prepared by solid state reaction method under argon atmosphere. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) of prepared samples have been performed for structural characterization and surface morphology respectively. The structural characterization shows well developed phase of MgB2 while hexagonal shaped grains are evident in SEM photographs. Electrical resistivity measured between 20 K and 300 K confirms a decrease in superconducting transition temperature (TC) and increase in normal state resistivity of pristine MgB2 due to Graphene addition. The levitation force measurement under zero field cooling condition reveals that low level (0.5 wt%) of Graphene addition enhances the levitation force throughout the investigated temperature range. However the levitation force measurements performed at different initial field height under field cooling condition confirm the presence of both attractive and repulsive force. Further, the maximum levitation force (FMLF) and maximum attractive force (FMAF) estimated from the field cooling data of pure and Graphene added MgB2 is found to be a strong function of initial field cooling height (HFC). The maximum repulsive/levitation force (FMLF) increases exponentially with increase in initial field cooling height, while an exponential decrease in attractive force (FMAF) of MgB2 has been observed with increase in initial field cooling height.

Determination of magnetic levitation force properties of bulk MgB2 for different permanent magnetic guideways in different cooling heights

Abstract In our study as different from the literature, the magnetic levitation force between a bulk MgB2 and two different permanent magnetic guideway (PMG) arrangements, which are Halbach and Conventional PMGs, were investigated in different cooling heights (CHs) and Field-Cooled (FC) condition at the temperatures of 37 K and 33 K. The cylindrical bulk MgB2 superconductor was fabricated by in-situ solid state reaction process with the diameter of 18 mm and the height of 5 mm. The XRD data indicates well developed MgB2 phase and the Jc value was obtained as 68 kA/cm2 at 30 K in the self-field. Experimental results show that MgB2 bulk above the Halbach PMG can exhibit better load capability at all the cooling heights between the bulk MgB2 and the PMG due to a more suitable magnetic field distribution. The maximum levitation force for Halbach PMG corresponds to 16.86 N whereas the conventional PMG shows 9.02 N at 37 K in cooling height of 77 mm. Additionally, the maximum levitation force increases while the CH increases because flux exclusion is more effective for larger CHs. It is considered that the experimental results obtained in study are very useful for future Maglev applications, because there are limited number of studies on magnetic levitation force of MgB2 bulk for different MgB2-PMG arrangements.

Radial and axial stiffness of superconducting bearings based on YBCO single-domain bulks processed with artificial holes

Superconducting magnetic bearings are becoming more widespread, due to the unique properties they provide. Their efficiency is unparallel, there are no issues such as contact, friction, and wear. They require low or minimal maintenance, no lubrication and they work under extreme conditions (cryogenic temperatures, high vacuum). In this contribution, the influence of geometric properties of superconducting bulks on the performance of superconducting bearings was studied. The main focus was paid to load capacity, radial and axial stiffnesses. Two samples with a significantly higher aspect ratio compared to conventional bulks were prepared. One of these samples was synthesized with artificially created holes. The samples were prepared using top-seeded melt-growth process with an additional source of a liquid phase in the form of an underlaying pad. The original thickness of 16 mm of the samples with a diameter of 28 mm was repeatedly ground down. Levitation force and trapped field were measured after each grinding step. Using this approach, the dependence of properties of the bulks on their thickness, scaling of these properties with thickness and the influence that artificial holes can make on the properties of finished single domain bulks were studied. The maximum levitation force was greatly improved for bulks with thicknesses of 2–6 mm. Such data is of the utmost importance in the field of superconducting YBCO single domain bulk ceramics, as it allows for better understanding and further improvement of both the manufacturing process and real-world applications of these materials.

Effect of Gd211 Addition on the Vertical Levitation Force of Gd123 Superconductors

We investigated the microstructure and magnetic properties of Gd123:Gd211 = 1-y : y (y = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) bulk superconductors with the diameter of 13 mm and thickness of 5 mm fabricated by melt-textured method. The vertical levitation force between melt-textured bulk superconductors and a permanent magnet is measured at 30, 40, 50, 60, and 77 K under zero-field-cooling (ZFC) and field-cooling (FC) regimes by Magnetic Levitation Force Measurement System (MLFMS). The phase and microstructures properties of all samples are determined by SEM (Scanning Electron Microscope). The measurements of superconducting characteristics showed that the maximum vertical levitation forces of the Gd01 sample were noted as 3.04, 2.30, 1.53, 0.91 and 0.16 N at the temperatures of 30, 40, 50, 60 and 77 K, respectively. The present results perform that a high-performance good-quality GdBCO can improve from laboratory conditions to technological applications for large scale levitated system.

Influence of NiFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; nanoparticle doping on properties of single-domain YBCO bulk superconductors

NiFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; (NFO) nanoparticle doped YBCO bulk superconductors are fabricated by using a novel top-seed infiltration growth (TSIG) technique. The growth morphology, microstructure and superconducting properties are investigated. The results show that at low doping levels, the normal growth of YBCO single domain is not affected by the NFO doping, but at high doping levels, obvious random nucleation appears at the edge of the sample. The measurement of levitation force indicates that the maximum levitation force on the sample first increases and then decreases with the increase of the NFO doping amount, and the largest levitation force is obtained to be 33.93 N for the sample with a doping level of 0.2% (weight percent). Low-temperature magnetization measurement shows that the YBCO sample exhibits that &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; value decreases with NFO amount increasing, and the superconducting transition width (Δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;) also broadens gradually. The sample with the optimal doping (0.2% weight percent) presents an enhanced zero-field &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; value of 8.68 × 10&lt;sup&gt;4&lt;/sup&gt; A/cm&lt;sup&gt;2&lt;/sup&gt;, which is 31% higher than the sample without dopant. In addition, a more obvious secondary peak of 4.37 × 10&lt;sup&gt;4&lt;/sup&gt; A/cm&lt;sup&gt;2&lt;/sup&gt; at a field of 1 T is observed for the 0.2 wt.% NFO doped sample, which indicates the existence of enhanced &lt;italic/&gt;δ&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; pinning in the bulk. The SEM measurement shows that two types of particles are trapped in the Y-123 matrix for YBCO sample doped with 0.2% weight percent NFO: one is the large particle with a size mainly ranging from 0.5 μm to 2.0 μm, and the other is small nano-inclusion mainly ranging from dozens of nanometers to about several hundreds of nanometers. Such a microstructure is very similar to the microstructure of the undoped sample we reported earlier. So whether the NFO nanoparticles exist in the microstructure cannot be judged just from the morphology of the nano-inclusions. The electron probe microarea analysis (EPMA) result shows that different concentration distributions of Ni and Fe elements are observed in the sample doped with 0.2% weight percent NFO, which indicates the separation of NFO nanoparticles in the heat treatment process, and the dissolved Ni and Fe ions finally exist in the form of element substitutions in the YBCO bulk. Such element substitutions can introduce local lattice distortions and weak-superconducting regions into the superconducting matrix, which can act as effective flux pinning centers, and hence improving the properties of the samples.