Search Results (214)

Incipient stator interturn short-circuit faults in permanent magnet synchronous motors produce only weak changes in the terminal currents, which limits the sensitivity of conventional amplitude- and unbalance-based indicators. This paper proposes a phase-wise diagnostic framework that combines multiscale sample entropy (MSE), topological data analysis (TDA), and a Gaussian mixture model (GMM). For each three-period current window, ten scale-dependent sample-entropy components and two persistent-entropy components are concatenated into a 12-dimensional feature vector. A separate GMM is trained for each phase using healthy data only. The resulting likelihood-based health scores are used for fault detection and faulty-phase localization, while physically defined score boundaries calibrated from measured short-circuit-current groups are used for severity assessment. Experiments on a 1.5 kW, 8-pole, 12-slot PMSM demonstrate class-wise recalls of 96.50–100% and an overall accuracy of 97.50% under the investigated operating conditions. The results show that the combined temporal and topological representation can reveal weak current changes that are difficult to distinguish using conventional terminal-current indicators. Full article

Reliable motor-current-based bearing diagnosis requires evaluation on unseen physical bearings and operating conditions. This study uses the Paderborn University benchmark, acquired from a 425 W permanent-magnet synchronous motor (PMSM) test rig, to evaluate time–frequency deep transfer learning under strict bearing-level grouping. Four representations—continuous wavelet transform (CWT), short-time Fourier transform (STFT), wavelet synchrosqueezed transform (WSST), and Fourier synchrosqueezed transform (FSST)—are combined with pretrained CNN backbones across four binary targets: aged-only A/B and artificial-plus-aged C/D, with mixed-fault bearings excluded/included within each pair. The workflow includes pooled-condition candidate discovery, exploratory Main-split leave-one-operating-condition-out (LOCO) screening, and a retrospective multi-split LOCO audit. The audit contains 288 crossed condition–split–seed evaluations. Because pooled test summaries and Main-split LOCO results informed later stages, these evaluations provide descriptive robustness evidence rather than an independent post-selection test. Target A achieved the highest all-split mean balanced accuracy (0.736 for CWT–EfficientNetB0). The pairs for Targets B and C were near-ties, and the Target D ordering reversed when Main was excluded. Across the eight audited candidates, mean sensitivity ranged from 0.618 to 0.948, whereas specificity ranged from 0.092 to 0.564. Target D combined approximately 0.89 sensitivity with an approximately 0.90 false-alarm rate. Thus, operating condition, fault-class composition, bearing split, and error-cost priorities all affect model interpretation. A matched current-domain baseline audit added 336 evaluations using handcrafted-feature RBF–SVM and Random Forest models and a compact raw-current 1D-CNN. The results show that instability is broader than the TF–CNN pipeline but is not uniform across model families: TF candidates were clearly stronger for Targets A and C, feature-based models were stronger for Target B, and Target D remained mixed and protocol-sensitive. A complementary bearing-level source-group analysis quantified six healthy/fault-source categories across the 37 current features; among the eight features with the largest mean between-group variance fraction, only spectral entropy and dominant power fraction preserved the same mixed-versus-non-mixed contrast direction across all four operating conditions. An additional matched Target D reference held the binary target, physical-bearing split, held-out condition, seed, fourth-order FSST representation, ResNet-50 backbone, and training settings fixed while changing the sensing channel. Across 24 matched runs, vibration showed descriptively higher mean balanced accuracy (0.642 vs. 0.503) and specificity (0.476 vs. 0.146), while sensitivity was slightly lower (0.807 vs. 0.859); the comparison does not establish universal modality superiority. Pooled-condition performance is useful for candidate discovery, but credible condition-generalization claims require explicit separation of exploratory selection and confirmatory testing. The numerical findings are specific to the evaluated PMSM benchmark and do not establish universal performance across electric-machine types. Full article

Vector magnetic anomaly detection on ocean buoys is challenged by attitude changes, non-stationary backgrounds, and weak targets that adaptive filters may absorb. We propose an online target-protected framework combining attitude compensation, constant-false-alarm-rate normalized innovation squared (CFAR-NIS) threshold adaptation, target-dwell gating, whitening based on a target-free calibration covariance, and weighted multiscale generalized likelihood ratio test-cumulative sum (GLRT-CUSUM) fusion. The target-protection mechanism constrains covariance adaptation and the effective Kalman gain during suspected target intervals, while dual-threshold confirmation suppresses isolated background spikes. We evaluated the method using publicly available buoy attitude and triaxial magnetometer background data with injected ship magnetic signatures under semi-physical conditions. At SNR ≈ 2.7, 200 paired Monte Carlo trials yielded a detection probability of 0.965, a background false-alarm rate of 0.045, and an average delay of 208.3 samples. Compared with standard and adaptive Kalman filtering, orthogonal-basis-function (OBF), minimum-entropy, and spectral-residual CUSUM baselines, the proposed method significantly improved detection probability and shortened delay. Its false-alarm rate was comparable to OBF and SR-CUSUM but higher than those of standard KF, adaptive KF, and minimum-entropy detection. Validation with real operational sea-trial data remains necessary. Full article

Non-equiatomic high-entropy alloys (HEAs) are promising candidates for low-dimensional magnetocaloric applications. In this work, Fe₂₅Ni₂₁Mn₂₄Si₁₃Ge₁₇ HEA-based nanoribbon arrays with spacings of 1 and 2 µm, together with companion thin films, were fabricated under the same technological conditions by magnetron co-sputtering from five sources. The effects of heat treatment and longitudinal strain (0–2%) on the structural, magnetic, and magnetocaloric properties were studied using TEM, SAED, AFM, and SQUID magnetometry. TEM, SAED, and AFM confirmed an amorphous structure with a single cubic-type short-range order and thermal stability up to 700 K. The nanoribbons exhibited shape-induced magnetic anisotropy that vanished at a 2 µm spacing, where the ribbons became magnetically decoupled. Within the elastic regime, longitudinal strain acted via magnetoelastic coupling, preserving the in-plane isotropy while enhancing the magnetic response above 100 K. Annealing at 700 K drove short-range atomic reordering and relieved fabrication-induced strain, increasing the saturation magnetization severalfold and raising the maximum isothermal magnetic entropy change −ΔS_M of the 1 µm nanoribbons from 1.25 to 1.35 JK⁻¹kg⁻¹ (at 140 K, ΔH = 50 kOe). The results demonstrate that strain engineering and thermal processing provide distinct, complementary routes for tuning the magnetic and magnetocaloric behavior of FeNiMnSiGe HEA nanoribbons. Full article

The work presents a thermodynamic analysis of phase equilibria in the subsolidus region of the three-component oxide system CoO–BaO–Fe₂O₃. The relevance of the study is due to the growing interest in ceramic ferrites with specified magnetic and electromagnetic properties, which are used in the creation of functional composite materials. The aim of the work was to establish thermodynamically stable binary and ternary phase combinations in the CoO–BaO–Fe₂O₃ system based on the analysis of solid-phase exchange reactions without taking into account ternary oxide compounds. This analysis represents a simplified thermodynamic model that considers only binary oxide compounds and excludes ternary ferrite phases. Thermodynamic calculations of Gibbs energy changes for model reactions of the type “2 = 2” were performed in the temperature range 1000–1800 K using the temperature dependencies of the enthalpies and entropies of compounds. To resolve contradictions arising from the analysis of the stability of individual conjugates, the method of conjugating exchange reactions with a transition to “3 = 2” type interaction mechanisms was applied. As a result of triangulation, nine thermodynamically stable binary combinations of compounds and ten stable triple phase combinations corresponding to elementary triangles of the subsolidus structure of the system were identified. The predisposition of the CoFe₂O₄–BaFe₁₂O₁₉ compound to destabilization is demonstrated, and its structural and phase stabilization due to the formation of an equilibrium three-phase combination of CoFe₂O₄–CoO–BaFe₁₂O₁₉ is substantiated. A general rule has been formulated for analyzing the thermodynamic stability of phase combinations in exchange reactions of the type “3 = 2”. The results obtained provide a physicochemical basis for predicting the phase composition of ferrite materials and composites in any concentration range of the CoO–BaO–Fe₂O₃ system and can be used in the development of technologies for the reaction synthesis of new ceramic ferrites. Full article

We investigated the structural, magnetic, magnetocaloric, and magnetotransport properties of Ni₅₀Mn₃₅In₁₅ Heusler alloys via partial substitution of Ni with 3 at.% Bi (Ni₄₇Bi₃Mn₃₅In₁₅) and 3 at.% Si (Ni₄₇Si₃Mn₃₅In₁₅) synthesized by arc melting. X-ray diffraction confirms a predominantly L2₁ cubic structure (space group Fm-3m), while SEM/EDX analysis verifies compositional homogeneity. Temperature-dependent magnetization measurements reveal that the Bi-substituted alloy exhibits a first-order magnetostructural transition associated with the martensitic transformation, followed by a second-order magnetic phase transition from ferromagnetic to paramagnetic behavior near the Curie temperature. In contrast, the Si-substituted alloy shows a single second-order transition with negligible thermal hysteresis, indicating suppression of the martensitic phase. The Curie temperature decreases from 324 K for the parent alloy to 313 K and 286 K for the Bi- and Si-substituted alloys, respectively. A maximum magnetic entropy change of 6.0 Jkg⁻¹K⁻¹ and 4.5 Jkg⁻¹K⁻¹ is observed for the Bi- and Si-substituted alloys, respectively, under an applied magnetic field change of 50 kOe, with corresponding relative cooling power values of 303 Jkg⁻¹ and 345 Jkg⁻¹. These results demonstrate that lattice expansion (Bi) and contraction (Si) distinctly modify Mn–Mn exchange interactions, enabling tunable magnetocaloric performance in Ni–Mn–In Heusler alloys. Full article

In this paper, a ternary Tb₆₅Co₂₅Ni₁₀ amorphous tape was successfully prepared, and the glass forming ability (GFA), magnetic properties, and magnetocaloric characteristics of the amorphous tape were studied in detail. The values of the reduced glass transition temperature T_rg, parameter γ and critical section thickness Z_c indicate the good GFA of the Tb₆₅Co₂₅Ni₁₀ amorphous tape. The Tb₆₅Co₂₅Ni₁₀ amorphous tape exhibits spin-glass-like behavior, with a Curie temperature of 83 K and a spin-freezing temperature (T_f) of 73 K, and a large coercivity below T_f. The spin-glass-like behavior significantly deteriorates the magnetic entropy change (−∆S_m) of the Tb₆₅Co₂₅Ni₁₀ amorphous tape at low temperatures, resulting in the deviation of magnetic entropy change behavior from the predicted results. However, the Tb₆₅Co₂₅Ni₁₀ amorphous tape still shows an excellent magnetocaloric effect (the peak value of −∆S_m of 9.46 J kg⁻¹ K⁻¹ and the refrigeration capacity of 569.5 J kg⁻¹ under 5 T, both of which are higher than those of most other heavy rare earth-based amorphous alloys), indicating the great application potential in the field of magnetic refrigeration for the amorphous tape. Full article

Four perovskite manganite samples, La_0.80Ag_0.20MnO₃ (LA), La_0.78Eu_0.02Ag_0.20MnO₃ (LEA), La_0.80Pb_0.05Ag_0.15MnO₃ (LPA), and La_0.77Eu_0.03Pb_0.05Ag_0.15MnO₃ (LEPA), were prepared by the Pechini sol–gel method. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and a magnetic property measurement system. A systematic investigation was conducted into the individual effects of Eu and Pb doping, as well as their co-doping, on the microstructural, magnetic and magnetocaloric properties of the materials. The results show that all samples are mainly composed of a rhombohedral perovskite phase with the $\mathrm{R}\overline{3}\mathrm{c}$ space group, accompanied by a trace amount of Ag. Addition of Eu³⁺ and Pb²⁺ induces lattice contraction and expansion, respectively. Under the same processing conditions, the average crystallite and particle sizes of the LEA sample (45.3 nm and 0.18 μm) are smaller than those of the other three samples (69.6~80.6 nm and 0.38~0.44 μm), indicating that the introduction of Eu alone suppresses crystallization ability, which can be avoided through Eu/Pb co-doping. All samples undergo a second-order ferromagnetic–paramagnetic transition, and the Curie temperature T_C shifts to either lower or higher temperatures upon the introduction of Eu or Pb alone (from 310.8 K to 298.0 K or 318.0 K, respectively), which is attributed to the variation of the Mn³⁺/Mn⁴⁺ double-exchange (DE) interaction resulting from the ionic size mismatch and lattice distortion. In the LPA sample, an additional contribution arises from the altered Mn³⁺/Mn⁴⁺ ratio and enhanced DE interaction caused by the substitution of Pb²⁺ for Ag⁺. By modifying the Eu/Pb ratio, the T_C of the LEPA sample was tuned to 299.3 K, and its maximum magnetic entropy change was enhanced to 3.90 J·kg⁻¹·K⁻¹ ($∆$H = 2 T). These results indicate that multicomponent synergistic regulation can improve the magnetocaloric performance of La-based perovskite manganites, providing a useful strategy for the development of room-temperature magnetic refrigeration materials. Full article

Magnetic and structural transitions can interact significantly, leading to an enhanced magnetocaloric effect (MCE), also known as the giant or colossal effect. In this study, we investigate how subtle microstructural changes impact the magnetocaloric behavior of a MnCoGeB_0.02 alloy fabricated via suction casting. We obtained conical samples and analyzed them to understand their structure and magnetic properties. X-ray diffraction patterns revealed a coexistence of a metastable high-temperature hexagonal phase and a stable low-temperature orthorhombic phase in different regions of each cone. The presence and proportion of these phases determine the degree of magneto-structural coupling, which in turn influences the MCE. The magnetic entropy change (|ΔS_Peak|) varied notably among the samples, ranging from 12.3 to 6 Jkg⁻¹K⁻¹ under a magnetic field change of Δµ₀H = 5.0 T. These findings demonstrate that even minor microstructural changes caused by differences in solidification during suction casting can lead to noticeable variations in magnetocaloric performance. Understanding and controlling these microstructural details is vital for optimizing the functional behavior of MnCoGe-based materials. Full article

In the present work, we selected an amorphous Nd₆₀Ni₄₀ alloy as a basic alloy and added Er with a higher effective magnetic moment and de Gennes factor to replace Nd for the purpose of improving the magnetocaloric performance of the Nd₆₀Ni₄₀ amorphous alloy. The formability, magnetization, and magnetocaloric behaviors of the Nd_60-xEr_xNi₄₀ (x = 5, 10, 15, 20) amorphous alloys were studied. It was found that Er substitution generally improved the glass formability, but simultaneously decreased the Curie temperature, coercivity, and magnetic entropy change peak of the basic alloy. The mechanism for these unexpected results was investigated, and it was supposed that the decreased Curie temperature and the deteriorated magnetocaloric properties may have resulted from the antiferromagnetic coupling between the Nd and Er atoms. Full article

The magnetocaloric response of an amorphous Er₆₉Ni₃₁ alloy was studied in the present work. The eutectic Er₆₉Ni₃₁ alloy was successfully melt-spun into an amorphous ribbon. The formability and magnetocaloric performance of the Er₆₉Ni₃₁ amorphous alloy were studied. The amorphous sample exhibits good glass formability and a remarkable magnetocaloric effect with a magnetic entropy change peak of ~16.65 J/(kg × K) near 10 K under 5 Tesla. The magnetization and magnetocaloric behaviors were investigated to reveal the effect of spin-glass-like behaviors on the magnetocaloric response of the binary amorphous sample. Full article

Co(NH₄)₂(SO₄)₂·6H₂O single crystal was grown via slow solvent evaporation at room temperature. The magnetic and magnetocaloric properties were investigated. The results show that Co(NH₄)₂(SO₄)₂·6H₂O exhibits paramagnetic behavior across 2–300 K. The maximum magnetic entropy change (−ΔS_M) of 13.90 J kg⁻¹ K⁻¹ under conditions of 2 K and μ₀ΔH = 5 T approaches the theoretical value of 14.58 J kg⁻¹ K⁻¹. In addition, the variation of −ΔS_M with temperature is relatively flat, suggesting a wide working temperature range for magnetic refrigeration, which provides the possibility for the application of Co²⁺-based compounds in the field of low-temperature magnetic refrigeration. Full article

Gd₄Co₃ is a promising magnetocaloric material with a high magnetic entropy value. However, it undergoes a first-order magnetic transition, which hinders practical applications. Hence, (Gd₄Co₃)_100−xGe_x (x = 5, 10, 15) were studied to obtain high magnetic entropy values and a second-order magnetic transition. To investigate the effects of Ge addition on the thermal stability, magnetocaloric properties, and critical behavior of Gd₄Co₃-based alloys, (Gd₄Co₃)_100−xGe_x (x = 5, 10, 15) melt spun ribbons were prepared. Phase analysis showed these alloys are mainly amorphous, with a minority nanocrystalline phase. All alloys undergo a second-order ferromagnetic-to-paramagnetic transition. The Curie temperature (T_C) increases linearly from 211 K (x = 5) to 217 K (x = 15) with increasing Ge content. Under a magnetic field variation of 5 T, the alloys with x = 5, 10, and 15 exhibit peak magnetic entropy change (−ΔS_M) values of 7.15, 6.83, and 6.71 J/(kg·K), respectively, along with considerable refrigerant capacity (RC) in the range of 435–458 J/kg. These excellent magnetocaloric properties collectively demonstrate their great potential for magnetic refrigeration applications. Critical behavior analysis revealed critical exponents broadly consistent with mean-field theory (MFT, β = 0.5, γ = 1.0, δ = 3.0), indicating nanocrystals in the amorphous matrix induce long-range magnetic interactions. Full article

Rare earth-rich NaZn₁₃-type La-Fe-Si-based alloys are promising candidates for near-room-temperature magnetocaloric applications. However, their poor corrosion resistance limits practical applications. The microstructure, corrosion behavior and magnetic entropy change of La_0.8Ce_0.2Fe_9.2Co_0.6Si_1.2 alloys after annealing were systematically investigated. Annealing treatments were conducted at 1423 K for durations of 4–24 h. As annealing time increased, the α-Fe phase content decreased monotonically from ~7.81wt% to ~2.92wt%, accompanied by significant microstructural evolution. For the 4 h-annealed sample, extensive and large corroded spots were observed, attributed to micro-galvanic corrosion where the α-Fe phase (cathode) and 1:13 matrix phase (anode) formed active electrochemical pairs. Prolonged annealing reduced the corrosion current density by ~50%, directly correlating with the α-Fe phase reduction and improved microstructural homogeneity. Notably, corrosion exhibited a negligible effect on the magnetic entropy change of the alloys. This study confirms that optimizing annealing time to decrease α-Fe content and enhance microstructural uniformity represents an effective strategy to improve corrosion resistance without compromising magnetocaloric performance. Full article

Intermetallic NiMn-based Heusler alloys (HAs) have garnered considerable attention due to their multifunctionality and applications in various fields, including sensors, actuation, refrigeration, and waste heat harvesters. Among the NiMn-based alloys, Ni-Mn-Sn alloys have gained considerable attention since their structural and magnetic transformations were discovered. Many studies have been conducted with various compositions and shapes to investigate the physical properties of Ni-Mn-Sn alloys, which offer several advantages, including non-toxicity, low cost, and abundant constituents. The Co-doping effect on the physical properties of Ni-Mn-Sn alloys has been widely reported. This doping can rectify the ternary Ni-Mn-Sn Heusler compound’s brittleness by crystallizing a disordered face-centered cubic (fcc) γ-phase. In this study, a polycrystalline Ni₄₂Mn₄₆CoSn₁₁ Heusler alloy was prepared by high-frequency fusion (HF), using a Lin Therm 600 device, from pure Ni, Mn, Sn, and Co elements with appropriate proportions. X-ray diffraction, scanning electron microscopy, and magnetic magnetometry devices were used to study the structural, microstructural, and magnetic properties. The XRD results revealed the coexistence of a disordered 7 M martensite phase (~88%) and a disordered cubic solid solution γ-phase (~12%). The alloy underwent a second-order ferromagnetic-to-paramagnetic phase transition at a Curie temperature of 350 K. Landau and Hamad’s theoretical models were used to plot the magnetic entropy change. The magnetocaloric properties (the maximum entropy change value, ΔS_M, the full width at half maximum of the entropy change curve, δT_FWHM, the relative cooling power, RCP, and the heat capacity, ΔC_P,H) were calculated using isothermal magnetization curves with the phenomenological model of Hamad. Full article