Induction Characteristics Research Articles

Thermal Effects of Electromagnetic Energy on Skin in Contact with Metal: A Numerical Analysis

It has been well recognized that interactions between electromagnetic fields and metals are very strong. The consequence of human tissue in contact with metal, when subjected to an alternating electromagnetic field, is an increase in tissue temperature, which results from metals absorbing the energy obtained through induction. However, the electromagnetic induction characteristics and tissue energy absorbed caused by various electromagnetic field exposure conditions have not been well understood. A computational model was developed and employed in this study to assess the temporal and spatial temperature increases in skin due to contact with a highly conductive metallic plate while subjected to a high-intensity electromagnetic field. The effects of plate material, plate thickness, coil distance, and exposure time on temperature increase in the skin were computationally investigated. The electromagnetic and temperature distributions in skin layers during exposure to electromagnetic fields were achieved using models of electromagnetic wave propagation and an unsteady bioheat transfer. The modeling approach used indicates that the plate thickness, plate material, coil distance, and exposure time have a significant impact on the temperature change in the skin. The most important parameter was found to be the metal type. Iron has the greatest effect on skin temperature increase when subjected to external electromagnetic induction. These results allow the researchers to estimate more precisely the exposure limits for induction coils.

An Implantable Wireless System for Remote Hemodynamic Monitoring of Heart Failure Patients.

This article presents an implantable wireless system for remote hemodynamic monitoring, which enables direct, continuous (24/7), and simultaneous measurement of pulmonary arterial pressure (PAP) and cross-sectional area (CSA) of the artery. The implantable device, which measures 3.2 mm × 2 mm × 10 mm, comprises a piezoresistive pressure sensor, an ASIC implemented in 180-nm CMOS, a piezoelectric ultrasound (US) transducer, and a nitinol anchoring loop. An energy-efficient pressure monitoring system, which employs duty-cycling and spinning excitation technique, achieves 0.44 mmHg resolution in a pressure range from -135 mmHg to +135 mmHg and consumes 1.1 nJ conversion energy. The artery diameter monitoring system utilizes the inductive characteristic of the implant's anchoring loop and achieves 0.24 mm resolution within a diameter range of 20 mm to 30 mm, four times higher than echocardiography lateral resolution. The wireless US power and data platform enables simultaneous power and data transfer employing a single piezoelectric transducer in the implant. The system is characterized with an 8.5 cm tissue phantom and achieves a US link efficiency of 1.8%. The uplink data is transmitted by using an ASK modulation scheme parallel to the power transfer and achieves a modulation index of 26%. The implantable system is tested in an in-vitro experimental setup, which emulates the arterial blood flow, and accurately detects fast pressure peaks for systolic and diastolic pressure changes at both 1.28 MHz and 1.6 MHz US powering frequencies, with corresponding uplink data rates of 40 kbps and 50 kbps.

Functional characterization of CYP1 enzymes: Complex formation, membrane localization and function

CYP1A1, CYP1A2, and CYP1B1 have a high degree of sequence similarity, similar substrate selectivities and induction characteristics. However, experiments suggest that there are significant differences in their quaternary structures and function. The goal of this study was to characterize the CYP1 proteins regarding their ability to form protein-protein complexes, lipid microdomain localization, and ultimately function. This was accomplished by examining (1) substrate metabolism of the CYP1s as a function of NADPH-cytochrome P450 reductase (POR) concentration, and (2) quaternary structure, using bioluminescence resonance energy transfer (BRET). Both CYP1As were able to form BRET-detectable homomeric complexes, which was not observed with CYP1B1. When activities were measured as a function of [POR], CYP1A1 and CYP1B1 showed a hyperbolic response, consistent with mass-action binding; however, CYP1A2 produced a sigmoidal response, suggesting that the homomeric complex affected its function. Differences were observed in their ability to form heteromeric complexes. Whereas CYP1B1 and CYP1A1 formed a complex, neither the CYP1A1/CYP1A2 nor the CYP1B1/CYP1A2 pair formed BRET-detectable complexes. These proteins also differed in their lipid microdomain localization, with CYP1A2 and CYP1B1 residing in ordered membranes, and CYP1A1 in the disordered lipid regions. Taken together, despite their sequence similarities, there are substantial differences in quaternary structures and microdomain localization that can influence enzymatic activities. As these proteins exist in the endoplasmic reticulum with other ER-resident proteins, the P450s need to be considered as part of multi-enzyme systems rather than simply monomeric proteins interacting with their redox partners.

Association between intrapartum antibiotic prophylaxis for Group B Streptococcus colonization and clinical chorioamnionitis among patients undergoing induction of labor at term

Rectovaginal colonization with Group B Streptococcus during pregnancy has historically been shown to be associated with an increased risk of clinical chorioamnionitis and peripartum infectious morbidity. Newer observational data in the era of intrapartum antibiotic prophylaxis suggest a possible reversal of this association; however, it is unclear if this is related to differences in labor management for those with and without Group B Streptococcus colonization. We therefore sought to assess the association between intrapartum antibiotic prophylaxis for Group B Streptococcus colonization and clinical chorioamnionitis within the context of a randomized induction of labor trial with a standardized labor protocol. We performed an exploratory secondary analysis of a randomized trial of patients undergoing term induction at a tertiary care center. Patients received third trimester Group B Streptococcus screening and intrapartum antibiotic prophylaxis as routine care. Group B Streptococcus detection was performed using a carrot broth-enhanced subculture to Group B Streptococcus Detect approach (Hardy Diagnostics, Santa Maria, CA). Labor management was protocolized per the trial. Patients with unknown Group B Streptococcus status or who did not receive intrapartum antibiotic prophylaxis, if indicated, were excluded. The primary outcome was diagnosis of clinical chorioamnionitis, compared between patients who received intrapartum antibiotic prophylaxis for known Group B Streptococcus positive status (by culture, history, or Group B Streptococcus bacteriuria) and those who were Group B Streptococcus negative and did not receive intrapartum antibiotic prophylaxis. Secondary outcomes included postpartum endometritis, wound infection, a composite maternal peripartum infectious morbidity, and neonatal outcomes. A total of 491 patients were enrolled in the trial. Of these, 466 had a known Group B Streptococcus status and received or did not receive intrapartum antibiotic prophylaxis accordingly and were included in this analysis: 292 (62.7%) were Group B Streptococcus negative and did not receive intrapartum antibiotic prophylaxis, and 174 (37.3%) were Group B Streptococcus positive and received intrapartum antibiotic prophylaxis. The majority of patients were Non-Hispanic Black (78.1%) and nulliparous (59.7%). There were no differences in demographic, clinical, induction or labor characteristics between groups. Patients who were Group B Streptococcus positive had a 49% lower rate of clinical chorioamnionitis (8.1% vs 14.7%, odds ratio, 0.51; P=.03) and a lower rate of peripartum infectious morbidity (8.1% vs 15.8%, odds ratio, 0.47; P=.02) compared to those who were Group B Streptococcus negative. Infants born to patients who were Group B Streptococcus positive were significantly less likely to be admitted to the neonatal intensive care unit (3.4% vs 15.1%, P<.001). Although Group B Streptococcus colonization has historically been considered a risk factor for clinical chorioamnionitis, in the era of universal antibiotic prophylaxis for Group B Streptococcus positive patients, our findings support the point that intrapartum antibiotic prophylaxis for Group B Streptococcus positivity is associated with lower rates of clinical chorioamnionitis and peripartum infectious morbidity among patients undergoing induction with protocolized labor management. These findings demonstrate that intrapartum antibiotic prophylaxis for Group B Streptococcus may protect against perinatal infectious morbidity, a phenomenon that warrants further investigation.

Innovative Approaches and Advances for Hair Follicle Regeneration.

Pathological hair loss (also known as alopecia) and shortage of hair follicle (HF) donors have posed an urgent requirement for HF regeneration. With the revelation of mechanisms in tissue engineering, the proliferation of HFs in vitro has achieved more promising trust for the treatments of alopecia and other skin impairments. Theoretically, HF organoids have great potential to develop into native HFs and attachments such as sweat glands after transplantation. However, since the rich extracellular matrix (ECM) deficiency, the induction characteristics of skin-derived cells gradually fade away along with their trichogenic capacity after continuous cell passaging in vitro. Therefore, ECM-mimicking support is an essential prelude before HF transplantation is implemented. This review summarizes the status of providing various epidermal and dermal cells with a three-dimensional (3D) scaffold to support the cell homeostasis and better mimic in vivo environments for the sake of HF regeneration. HF-relevant cells including dermal papilla cells (DPCs), hair follicle stem cells (HFSCs), and mesenchymal stem cells (MSCs) are able to be induced to form HF organoids in the vitro culture system. The niche microenvironment simulated by different forms of biomaterial scaffold can offer the cells a network of ordered growth environment to alleviate inductivity loss and promote the expression of functional proteins. The scaffolds often play the role of ECM substrates and bring about epithelial-mesenchymal interaction (EMI) through coculture to ensure the functional preservation of HF cells during in vitro passage. Functional HF organoids can be formed either before or after transplantation into the dermis layer. Here, we review and emphasize the importance of 3D culture in HF regeneration in vitro. Finally, the latest progress in treatment trials and critical analysis of the properties and benefits of different emerging biomaterials for HF regeneration along with the main challenges and prospects of HF regenerative approaches are discussed.

Nonlinear behavior mechanism and modeling method of wound SMD inductor

AbstractIn the actual use process, the characteristics of the wire‐wound power inductor will change. On the one hand, the DC bias will fluctuate because the working current of the wire‐wound power inductor is not constant; on the other hand, there is a variable magnetic field, which, according to the principle of electromagnetic, affects structural size, core permeability, and flux density, both of which affect the amount of inductance. As a result, this research examines the wire‐wound SMD inductor's nonlinear behavior and modeling approach. Under the condition of zero bias at normal temperature, the static model is determined by simulating Y parameters and comparing its main performance parameters. The influence factors of temperature and DC bias are studied. The nonlinear model circuit is written in Verilog‐A format, and the inductor‐current curve is fitted by polynomial. The dynamic model is verified by ADS and compared with the test data. SWPA series power inductor measurement data from Sunlord is used to verify the validation of the model proposed in this paper. The Y parameter and performance index under zero DC bias at room temperature, inductance characteristics under different currents and inductance characteristics under different temperatures were compared respectively. From the comparison results, it can be concluded that, The fitting accuracy of the model is good in the frequency range of 100 KHz ~ 100 MHz, DC bias range of 0 ~ 0.28 A, and different temperatures (−40, 25, 125°C).

Fractional equivalent circuit model and parameter identification of reactance components in high-frequency operation

PurposeThe purpose of this paper is to find a simpler model for the reactance components in the high-frequency range on the premise of ensuring the accuracy.Design/methodology/approachIn this paper, based on the fractional calculus theory and the traditional integer-order model, a reactance model suitable for high frequency is constructed, and the mutation cross differential evolution algorithm is used to identify the parameters in the model.FindingsBy comparing the integer-order model, high-frequency fractional-order model and the actual impedance characteristic curve of inductance and capacitance, it is verified that the proposed model can more accurately reflect the high-frequency characteristics of inductance and capacitance. The simulation and experimental results show that the oscillator constructed based on the proposed model can analyze the frequency and output waveform of the oscillator more accurately.Originality/valueThe model proposed in this paper has a simple structure and contains only two parameters to be identified. At the same time, the model has high precision. The fitting errors of impedance curve and phase-frequency characteristic curve are less than 5%. Therefore, the proposed model is helpful to improve the simplicity and accuracy of circuit system analysis and design.

Investigation of Unclamped Inductive Switch Characteristics in 4H-SiC MOSFETs With Different Cell Topologies

To investigate the unclamped inductive switch (UIS) characteristics, 1200 V silicon carbide (SiC) planar MOSFETs with four cell topologies of linear, current sharing linear, square, and hexagon are designed and manufactured. The experimental platform was built and tested. The results show that the single pulse avalanche energy density of the linear cell topology is 1.69 times higher than that of the square and 1.49 times that of the hexagon. Further, the UIS process is simulated by using physical simulation, which shows that the avalanche energy was concentrated near the corner of the P-base region in the UIS mode. From this, the avalanche energy distribution differences of the four cell topologies were analyzed and compared. A theoretical model of avalanche heating per unit area is proposed, which shows that the avalanche energy density is inversely proportional to the proportion of avalanche energy concentration region. This study may contribute to the cell topology design of SiC MOSFETs under the application scenario with high avalanche reliability requirements.

Improved MTPA Control for Variable-Flux Memory Machine With Operating Envelope Prediction-Based MS Manipulation

This article proposes an improved maximum torque per ampere (MTPA) control method for variable-flux memory machine (VFMM) with operating envelop prediction-based magnetization state (MS) manipulation. The proposed method can achieve the MTPA control under the voltage limitation and simplify the MS adjustment process for expanding the operating region. The mathematical model of the studied VFMM is established to calculate the reference current for MTPA control online as well as to predict the operating envelop at each MS. According to the calculated operating envelop, the proposed MS manipulation method can separate the magnetization and demagnetization processes by setting two MS manipulation boundaries correspondingly, which is easily implementable and can avoid frequent MS manipulation processes. Besides, the inductance characteristics of the machine are measured to improve the model accuracy and control performance. Experiments are carried out on a VFMM prototype to validate the feasibility and effectiveness of the proposed method.

Sensorless position detection of reluctance spherical motors based on inductive characteristics

The rotor attitude detection of spherical motors usually requires the installation of position sensors on the rotor shaft or stator to achieve, which occupy a large space and cause negative effects for the practical installation and application of spherical motors. In this paper, a sensorless position detection method for reluctance spherical motors based on the structure and operating characteristics of reluctance spherical motors is proposed. By detecting the stator coil inductance data at different rotor attitude angles, the position prediction model is constructed using the extreme learning machine algorithm. Through comparison and validation, it is demonstrated that the rotor attitude angle obtained by the method is highly accurate, providing a feasible idea for the control and application of reluctance spherical motors.

Transient stability enhancement using optimized PI tuning of static synchronous series compensator in wind power conversion system

Power systems are expanding comprehensively with the increase in load demand from both residential and industrial usage. Renewable energy is penetrating the power system to satisfy the power needs of the load demand. With its potential to generate power and compensate for a large portion of the load demand, wind generators make a major renewable power contribution. Power oscillations inherent in wind generator integration with the grid are a power quality issue to be addressed. Oscillation damping using flexible AC transmission system (FACTS) devices is a relevant solution for the power quality issue. There are multiple reasons for power oscillation. Mainly, power systems encounter fault conditions. The faults can be cleared, and the power system tries to retain stability. Sometimes, the system fails due to a longer settling time. A series-connected FACTS device utilized as a series compensator is referred to as a static synchronous series compensator (SSSC). Controlling the flow of electricity over a transmission line using this method is incredibly efficient. The capacity to switch between a capacitive and an inductive reactance characteristic is necessary. The SSSC regulates the flow of power in transmission lines to which it is linked by adjusting both the magnitude of the injected voltage and the phase angle of the injected voltage in series with the transmission line. This allows the SSSC to manage the power flow in the transmission lines. It does it by inserting a voltage that can be controlled into a transmission line in series with the fundamental frequency. This paper develops the optimally tuned SSSC in the wind-integrated grid system to dampen the oscillation. Teacher–learner-based optimization (TLBO) and gray wolf optimization (GWO) algorithms are used to tune the PI controller to improve the damping response. The obtained results show that the damping performance of the proposed controller is better than that of the other traditional controllers.

Calculation of a Current Vector Trajectory for Enhanced Operation of Synchronous Reluctance Generators Including Saturation

This article proposes a simple method to calculate a current vector trajectory for the enhanced operation of the electric power generation system based on a synchronous reluctance machine (SynRM). Owing to magnetic saturation and cross magnetization, the performance and the torque capability of a SynRM vary according to the position and the value of the stator current. State-of-the-art control methods usually assume parameters with constant values, especially the inductance, neglecting saturation, leading to possible uncertainty in the machine operation. Therefore, a current vector trajectory to operate this type of machine, as a generator, in an extended speed range, with enhanced performance and considering magnetic saturation is proposed. A straightforward algorithm based on the inductance characteristic of the machine is used to calculate the trajectory of the stator current vector. This trajectory is evaluated via the numerical simulation of an experimentally validated finite-element model of a SynRM. The results show that the proposed current vector trajectory can improve the torque capability to 5% concerning the estimated trajectory without considering saturation. Experimental results are also provided to demonstrate the enhanced operation of the generator.

A New Rotor Position Estimation Method for Spherical Reluctance Motor Based on Inductance Characteristics Obtained From Measurement

Since the spherical reluctance motor (SPRM) works in saturation, it is difficult to estimate the rotor position. In this paper, a new rotor position estimation method for SPRM is proposed. In order to accurately estimate the rotor position, according to the inherent characteristics between phase inductance, rotor angle and phase current, the phase inductance-rotor angle curve is divided into three segments. The idea of scaling is adopted to deal with the analytical expression of each segment, and the three analytical expressions corresponding to the three segments are generated through linear function and quadratic function. The coefficients of each analytical expression are determined through a small amount of the measured inductance data. Experiment and comparison results show that the proposed method can effectively and accurately estimate the rotor position.

Analysis of the Topology and Electromagnetic Characteristics of Novel Stator Partitioned Axial Flux Disk Generator for Vehicles

Internal combustion engines emit high-temperature, high-pressure, and high-speed exhaust gases, resulting in wasted energy and low thermal efficiency. In order to recover the available residual energy in the exhaust gas, this paper proposes a new topology of the disk-type axial flux stator-excited doubly salient generator (AFSDSG) with partitioned stator suitable for high-temperature and high-speed operation. Based on the analysis of the above generator inductance characteristics, the influence mechanism of three pole-slot structures on the induced electromotive force (IEMF) of the armature winding is clarified, the equivalent magnetic circuit method is used to analyze the influence of different winding arrangements on the no-load performance of the generator, and the principles of pole-slot structure optimization and winding arrangement are summarized. The finite element software is used to model and simulate different configuration. After focusing on the analysis of transient characteristics such as inductance, armature winding IEMF, and air-gap flux, it is concluded that different from the conventional pole-slot structure and winding connection method make that only the overlapping area of the stator and the rotor changes linearly can produce a constant voltage, the winding arrangement of Winding Partition Excitation Span 2 has a high IEMF amplitude value and low harmonic content. Finally, the prototype of a three-phase 12/8-pole was trial manufactured and tested. The consistency of the simulation results and experimental results is verified the innovation and feasibility of the new topology proposed in this paper.

Comparison of Two Drug Combinations in Total Intravenous Anaesthesia: Propofol-Ketamine and Propofol-Fentanyl

Introduction: TIVA has many advantages over inhalational anaesthesia such as minimal cardiac depression, decreased oxygen consumption, avoids postoperative diffusion hypoxemia, decreases the incidence of postoperative nausea and vomiting etc. This study was conducted to evaluate and compare two TIVA drug combinations using propofol- ketamine and propofol-fentanyl, and to examine the characteristics of induction of anaesthesia, maintenance, and recovery.&#x0D; Method: 34 patients of ASA grading 1,2 and 3 aged between 20 to 65 years of either sex undergoing short surgical procedures were included in the study. According to Comparison of systolic blood pressure of both the groups at intubation time of anaesthesia in group I and group II. Patients in group I received propofol and ketamine intravenously (IV) to induce anaesthesia. For group II, fentanyl and propofol were administered as IV bolus doses. All the results were tabulated and analyzed statistically.&#x0D; Result: Propofol-fentanyl combination produced a significantly greater fall in pulse rate and in both systolic and diastolic blood pressures as compared to propofol-ketamine during induction of anaesthesia. Propofol-ketamine combination produced stable hemodynamic during maintenance phase while on the other hand propofol-fentanyl was associated with a slight increase in both PR and BP. During recovery, ventilation score was better in group I while movement and wakefulness score was better in group II.&#x0D; Conclusions: Both propofol-ketamine and propofol-fentanyl combinations produce rapid, pleasant and safe anaesthesia with only a few untoward side effects and only minor hemodynamic effects.

Performance Assessment of Using Multilayer Inductors in Induction Installations for Heating Aluminum Billets

A mathematical model for numerically analyzing the electrical characteristics of a multilayer inductor – billet system is developed. The model is based on the finite element method and implemented in the ELCUT software package. The system electrical characteristics depending on different billet sizes, inductor geometry, gap sizes, and system design area sizes are obtained. The influence of end effects and magnetic core on the multilayer inductor – billet system is studied. Based on the simulation results, recommendations on improving the energy efficiency of induction installations for heating aluminum billets owing to smaller losses achieved by modifying the multilayer inductor designs have been developed.

Virtual composite impedance circulating current suppression strategy with adaptive adjustment capability

AbstractIn the process of accessing distributed power sources in microgrid, there will be serious coupling between active power and reactive power, which will lead to significant changes in the inverter outlet voltage and impedance and increase the circulating current phenomenon. The generation of circulating current will accelerate the aging of devices, reduce the inverter efficiency, and threaten the stable operation of the system. In this paper, the mechanism of circulating current generation is analysed, the basic characteristics of circulating current are studied, and an inverter parallel circulating current suppression strategy with adaptive virtual composite impedance and droop control dynamic adjustment algorithm is proposed. The virtual impedance setting can weaken the influence of line difference on system stability, make the system equivalent output impedance resistive, weaken the inductive device characteristics and reduce the circulating current amplitude; the adaptive droop algorithm implantation dynamically correlates the control power with the droop coefficient, enhance the power decoupling accuracy and weaken the circulating current influenced by power changes. The simulation platform and experimental setup established by the large‐scale simulation software PSCAD/EMTDC are used to study the basic scenarios of the inverter under two conditions of equal and unequal capacity, and the rationality of the proposed control strategy is tested.

A Current-Control Strategy for Grid-Connected Converter Based on Inductance Non-Linear Characteristic Compensation

Inductance is a necessary device for a grid-connected converter (GcC) to attenuate the switching-frequency harmonics in injected grid currents. However, in practice, the inductance decreases with an increase in output current. Especially when the amplitude of sinusoidal currents is higher, the inductance will vary over a wide range as the current value changes in a period. This variation may lead to system instability and cause output current fluctuation. To solve this issue, the model of the GcC with a proportional resonant regulator is firstly built, and the system stability with different current values is analyzed using the Nyquist criterion. The results show that the system stability decreases with an increase in current absolute value. Further, a loop gain compensation unit is embedded into the current regulator to maintain the loop gain constant and ensure the stability of the system under a wide variation range of current values. With this scheme, the compensation unit is only determined by the rated value and the non-linear characteristic of the filter inductance. Therefore, the loop gain compensation unit is independent of the original control system, and the traditional controller parameter design method can also be inherited. Finally, the simulated and experimental results from a 50 A static var generator (SVG) with wide filter inductance variation (using Mega-Flux core) have verified the correctness of the analyses and the effectiveness of the proposed method in this paper.

Two is Better than One? Testing a Deductive MARPOR-based Left-Right Index on Western Europe (1999-2019)

Most of the existing indexes measuring parties’ left-right positions through Manifesto Project (MARPOR) data, including the ‘RILE’, share a partially or fully inductive nature and an underlying assumption of left-right unidimensionality. However, as the structure of party competition in contemporary Western Europe has been recently moving away from traditional ‘left-libertarian/right-authoritarian’ patterns, the inductive and unidimensional characteristics of such instruments may hinder the quality of their measurements. In this article, I introduce and develop a new left-right instrument, which is wholly deductive and relies on an explicit linkage with theoretical sources in the conceptualisation of economic and cultural left and right as the basis for the subsequent index operationalisation through the justified selection of MARPOR items. After deriving the individual deductive economic and cultural left-right scores and employing them in the mathematical formalisation of a synthetic left-right measure to be compared with existing unidimensional instruments, I perform a comparison between the new left-right index and the RILE. Both instruments are empirically tested on a dataset made covering the 20-year period between 1999 and 2019 in 16 Western European countries, for a total of 72 elections and 474 party-election combinations. More specifically, the statistical probes take the form of rank correlation analyses between the election-specific left-right rankings of each index and those provided by the external benchmark of the “Chapel Hill Expert Survey” (CHES). Results are mixed and indicate that, whilst more traditional patterns of competition seem to still apply across the board in pre-Great-Recession years, the new left-right index is a more valid measure of parties’ left-right positions both in the ‘turbulent times’ of the 2010s and in the vast majority of the areas across the region. This is especially true in Southern Europe, for which the RILE is known to be particularly problematic. Hence, this work calls for further discussion on the different patterns of Western European party competition across space and time, as well as differentiated and context-specific deductive left-right measurement.

Inductance Characteristics of Flux-Switching Permanent Magnet Machine Based on General Air-Gap Filed Modulation Theory

Winding inductance is a crucial parameter of machines, which plays an essential role in flux-weakening capability, reluctance torque, power factor, etc. In this article, winding inductance characteristics of flux-switching permanent magnet (FSPM) machines are investigated from the perspective of air-gap modulation magnetic field. With the aid of the general air-gap field modulation theory, the air-gap magnetic field contributed by an arbitrary energized winding of FSPM machines is modeled and analyzed. Then, an analytical expression of winding inductance is derived based on winding function and single-phase magnetic field, through which the relationship between winding inductance and single-phase magnetic field harmonics is unveiled. It is found that the direct current (dc) and 2nd harmonic components of winding inductances in FSPM machines are caused by the dc and 2nd time-harmonic components of primitive harmonics, respectively, which are essentially different from that of traditional interior permanent magnet or reluctance machines. Finally, experiments on a prototype three-phase 12/10 FSPM machine are conducted to verify the theoretical analysis.