Variation Of Coupling Coefficient Research Articles

Analysis and Design of an S/SP Compensated IPT System to Minimize Output Voltage Fluctuation Versus Coupling Coefficient and Load Variation

The capability of misalignment tolerance is vital for inductive power transfer (IPT) systems. S/SP compensation topology can provide a strong capability of misalignment tolerance if it is properly designed. This paper presents a detailed deduction process to acquire the optimal coupling coefficient, tuned at which the system can achieve minimum output voltage fluctuation. The impact of primary and secondary coupling inductance on output voltage fluctuation versus load variation was also analyzed. The output voltage fluctuation is not affected by the primary coupling inductance, but it decreases when the secondary coupling inductance is increased. Theoretical analysis was validated by both simulation and experiment. Three 200-W IPT prototypes were built. An overall efficiency of 94.1% was achieved when the coupling coefficient was 0.1733. The output voltage fluctuation was as low as 1.5% when the coupling coefficient increased by 34.5%, from 0.1288 to 0.1733. With a 900% rise in load resistance (from 80 to 800 Ω), the output voltage fluctuation decreased from 5.8% to 4.0% when the secondary coupling inductance increased from 136.3 to 250.0 μ H.

Controls on Mid‐ocean Ridge Normal Fault Seismicity Across Spreading Rates From Rate‐and‐State Friction Models

AbstractRecent seismic and geodetic observations have led to a growing realization that a significant amount of fault slip at plate boundaries occurs aseismically and that the amount of aseismic slip varies across tectonic settings. Seismic moment release rates measured along the fast‐spreading East Pacific Rise suggest that the majority of fault slip occurs aseismically. By contrast, at the slow‐spreading Mid‐Atlantic Ridge seismic slip may represent up to 60% of total fault displacement. In this study, we use rate‐and‐state friction models to quantify the seismic coupling coefficient, defined as the fraction of total fault slip that occurs seismically, on mid‐ocean ridge normal faults and investigate controls on fault behavior that might produce variations in coupling observed at oceanic spreading centers. We find that the seismic coupling coefficient scales with the ratio of the downdip width of the seismogenic area (W) to the critical earthquake nucleation size (h*). At mid‐ocean ridges, W is expected to increase with decreasing spreading rate. Thus, the relationship between seismic coupling and W/h* predicted from our models explains the first‐order variations in seismic coupling coefficient as a function of spreading rate.

Impact of Longitudinal Variation of the Coupling Coefficient Due to Bending and Twisting on Inter-Core Crosstalk in Weakly-Coupled MCFs

A novel analytical discrete changes model (DCM) of inter-core crosstalk (ICXT) in weakly-coupled multi-core fibers (MCFs) that considers the inter-core coupling coefficient (ICCC) variation, induced by bending and twisting effects along the longitudinal direction of propagation, is proposed. An approximated closed-form expression of the ICCC is proposed for step-index MCFs and validated by comparison with the rigorous ICCC expression, solved numerically. The linearization of the ICCC, in a logarithmic scale, around the intrinsic ICCC, is proposed to simplify the derivation of the novel analytical DCM. The novel DCM is validated by comparison of the mean ICXT power estimates obtained analytically, which are very quick to estimate, with the ones obtained by solving the coupled-mode equations numerically, which are much more computationally demanding. It is shown that, in the range of tested MCF parameters, the proposed model allows for an improvement of the mean ICXT power estimates reaching 4.5 dB, compared to the estimates obtained without considering the longitudinal variation of the ICCC, depending on the fiber parameters. The improvement of the mean ICXT power estimates was assessed for MCFs between 100 m and 10 km long, core pitches between 30 $\mu$ m and 50 $\mu$ m, and normalized difference between the refractive index of the cores between $-0.028\%$ and $0.028\%$ , typical of weakly-coupled real homogeneous MCFs. The largest improvements of mean ICXT power estimates tend to occur for larger core pitches and for larger differences between the refractive index of the cores. Accurate mean ICXT power estimates obtained with the novel DCM for MCFs with typical fiber birefringence parameters are also reported.

Maximum Efficiency Tracking for Wireless Power Transfer Systems With Dynamic Coupling Coefficient Estimation

Maximum efficiency tracking is an important issue for wireless power transfer (WPT) system. Traditional maximum efficiency tracking method normally focuses on load impedance matching with fixed coupling condition. However, WPT system is a loosely coupling system, the coupling coefficient varies due to relative movement between the primary and secondary sides. Unknown to this variation may result in failure of the tracking. In this paper, a novel maximum efficiency tracking method is proposed with integrated dynamic coupling coefficient estimation. This method can take almost all requirements for maximum efficiency tracking into account including adaption for coupling coefficient and load variation, and output controllability. The tracking method is easy to implement because no additional circuitry or measurement is required. Experimental results have verified the correctness of the proposed coupling coefficient estimation method. And the maximum efficiency tracking results show the system can achieve a good performance against coupling coefficient and load variation with the proposed tracking method.

Butterfly-like phase shift: a novel gauge for critical coupling of add\u2013drop resonator

Optical transfer function for add–drop resonator is derived in the presence of coupling loss using the scattering matrix method. A critical coupling condition for ADR is calculated. The response of the ADR under variation of coupling losses and coupling coefficients is studied. The number of allowed states under the critical condition is determined. The full width at half maximum as sharp as 0.17 nm is achieved. It is found that the relative phase shifts of through and drop ports show the same responses under the critical coupling condition. This response emerges in a butterfly-like phase shift, which can be considered as a new evaluating factor for checking the system in critical coupling condition.

Impedance-Matching Range Extension Method for Maximum Power Transfer Tracking in IPT System

Maximum power transfer is an important index for an inductive power transfer (IPT) system to make full use of its power transfer capability, and such a capability is usually realized by impedance matching. Traditionally, impedance matching is implemented by placing a power electronics converter such as a dc–dc converter at the secondary side of an IPT system. However, the power electronics converter and its operation mode directly affect its impedance-matching range, which is very limited if a traditional power converter only operates at continuous conduction mode (CCM). To extend the impedance-matching range, this paper proposes a novel impedance matching method based on combined CCM and discontinuous conduction mode (DCM) operation of an impedance matching converter. The impedance-matching range is fully analyzed for CCM and DCM operation, respectively, by taking variation of coupling coefficient into consideration. The analysis results show that the impedance-matching range can be extended by more than double that of the traditional impedance matching method. In addition, a maximum power transfer tracking method is developed using the proposed impedance-matching range extension method, and the experimental results have verified the feasibility of the tracking method.

Cascade Magnetic Cumulation Generator on the Basis of Inductively Coupled Circuits with A Variable Coupling Coefficient

A scheme of a multicascade magnetic cumulation generator based on a dynamic variation of the coupling coefficient of inductively coupled circuits is proposed. Each cascade contains two circuits including two pairs of inductively coupled coils. One pair of coils is subjected to simultaneous deformation, and one of the coils in the other pair is arranged with the opposite connection. It is shown that the energy in the load can be gradually increased (from one cascade to another) by using additional cascades. By an example of a two-cascade system, the proposed circuit is compared to the known circuits of the cascade system design based on the magnetic cumulation principle (generator with a step-up transformer and dynamic transformer). Within the framework of the model that ignores the ohmic resistance of conductors, it is demonstrated that the proposed scheme allows one to obtain a greater energy in the high-inductance load than the schemes with a step-up or dynamic transformer owing to a change in the sign of the magnetic flux in the secondary circuit. It is found that the increase in energy in the new scheme is independent of the coupling coefficient (at high values of this coefficient) and becomes greater as the number of cascades is increased.

Design and analysis of a novel coupled inductor structure with variable coupling coefficient

This study presents a new coupled inductor magnetic structure with variable coupling coefficient. The new symmetrical magnetic structure is composed of stacked ferrite cores, where control legs are placed in the centre of the core structure, on equal distances from the outer legs. In that way, the coupling coefficient is controlled by the means of a DC current. The DC control flux is confined only to the control legs and it is equally balanced in both of the outer legs. Distribution of the control DC flux in the proposed structure is verified applying finite element analysis simulation of the three-dimensional model. Electrical properties of the new variable coupled inductor are derived applying analytical modelling and verified by experiments. Maximal variations of the controlled coupling coefficient value in respect to the different value of the leakage flux are obtained and presented. Design and experimental results are presented for application in an interleaved boost converter with a variable coupled inductor, achieving boundary conduction mode over a wide load variation.

Cascade Magnetocumulative Generator on the Basis of Inductively Coupled Circuits with a Variable Coupling Coefficient

Cascade Magnetocumulative Generator on the Basis of Inductively Coupled Circuits with a Variable Coupling Coefficient

Tunable Fano and coupled-resonator-induced transparency resonances in the waveguide-coupled inverted nested ring resonator

A waveguide-coupled inverted nested ring resonator structure is proposed and theoretically investigated. The effects of the parameters of such a structure on its transmission properties are demonstrated. Results show that both Fano resonance and coupled-resonator-induced transparency (CRIT) spectra can be produced within this structure, depending on the length ratio of the feedback waveguide and ring. In addition, the slope of the Fano resonance can be tuned and reversed by varying coupling coefficients and effective refractive index. Besides, CRIT-based tunable group delay can be obtained with high transmittance. Therefore, this structure has potential applications in optical sensors and optical communication.

Simulation of a Love wave device with ZnO nanorods for high mass sensitivity

The paper presents 3D finite element simulation and analysis of Love wave resonator with different guiding layer materials and investigation of the coupled resonance effect with ZnO nanorods on the device surface. Analytical estimation of phase velocity and mass sensitivity of Love wave device with SiO2, ZnO, gold, SU-8, and parylene-C as guiding layer materials is performed for comparative analysis. Simulations are carried out to study the variation in electromechanical coupling coefficient, displacement profile and frequency response of the Love wave resonator. SU-8 offers high mass sensitivity of 1044 m2/kg while gold layer provides maximum K2 of 8.6%. In comparison to SiO2 and ZnO, polymers exhibit sharp rise and fall in K2 within a narrow range of normalized layer thickness (0.03–0.1). ZnO nanorods of varying height and surface nanorod density are designed over the Love wave resonator with SiO2 as the waveguiding layer. In the presence of coupled resonance, the nanorods and substrate vibrate in unison causing an increase in average stress and mass sensitivity but leads to decrease in the electromechanical coupling coefficient of the device. Surface nanorod packing density of 25 μm−2 offers high mass sensitivity of 1304 m2/kg that is 20 times greater in comparison to the mass sensitivity of a plain Love wave device.

A Maximum Power Transfer Tracking Method for WPT Systems with Coupling Coefficient Identification Considering Two-Value Problem

Maximum power transfer tracking (MPTT) is meant to track the maximum power point during the system operation of wireless power transfer (WPT) systems. Traditionally, MPTT is achieved by impedance matching at the secondary side when the load resistance is varied. However, due to a loosely coupling characteristic, the variation of coupling coefficient will certainly affect the performance of impedance matching, therefore MPTT will fail accordingly. This paper presents an identification method of coupling coefficient for MPTT in WPT systems. Especially, the two-value issue during the identification is considered. The identification approach is easy to implement because it does not require additional circuit. Furthermore, MPTT is easy to realize because only two easily measured DC parameters are needed. The detailed identification procedure corresponding to the two-value issue and the maximum power transfer tracking process are presented, and both the simulation analysis and experimental results verified the identification method and MPTT.

Analysis of serial and parallel cascaded microring resonators: An FDTD approach

In this paper, we describe coupled microring resonators in serial and parallel fashion based on the mathematical analysis in terms of electric field equations at different ports of a microring resonator. The mathematical equations are supported by simulation results of the modelling of coupled resonators using finite difference time domain method. The variation of coupling coefficients between the ring and the bus waveguide is studied. Variation of attenuation coefficients with transmission is also analyzed. These integrated coupled ring resonators can be useful for routing applications as the route of the electric field propagation can be varied to different ports at different wavelengths. Also, the values of Q factor and on – off ratio achieved signify better performance of the modelled devices.

Dual Polarization Discrete Changes Model of Inter-Core Crosstalk in Multi-Core Fibers

The discrete changes model (DCM) of inter-core crosstalk (ICXT) in weakly-coupled homogeneous multi-core fibers (MCFs) is generalized to a dual polarization (DP) scheme. This model provides theoretical expressions for the two polarization fields of the ICXT at the MCF output. Therefore, it may be of particular interest in the design of direct-detection MCF systems, where the photodetected ICXT results mainly from the beating between the ICXT field at the MCF output and the carrier of the interfered core. The DP-DCM is validated by comparison of the mean ICXT power and ICXT field amplitude estimates with the ones obtained with a rigorous, yet much more computationally demanding, model based on the coupled local mode theory (CLMT). Good agreement between the mean ICXT power estimates obtained with the DP-DCM and CLMT is observed when the inter-core coupling coefficient variation along the MCF is small. Good agreement is also observed when comparing the probability density functions of the ICXT field amplitude.

Pulse train controlled buck converter with coupled inductors

Pulse train (PT) controlled switching DC/DC converters possess advantages of simple structure, fast dynamic response, good robustness etc. but also accompanied by undesirable low-frequency oscillation phenomenon when the converters are operated in continuous conduction mode (CCM). To mitigate the low-frequency oscillations of PT controlled buck converters, a novel buck converter with coupled inductor is proposed in this paper. Firstly, the mechanism of the low-frequency oscillation is analysed, the corresponding oscillation suppression method is discussed and the discrete-time model of the proposed converter is constructed. Furthermore, the bifurcation and time-domain diagrams of the output voltage and the switching peak current in terms of coupling coefficient and load variation are reported, and the influence from the coupling coefficient and load on low-frequency oscillation behaviours is revealed. The experimental results verify that the output voltage of the PT controlled proposed buck converter can be timely adjusted based on proper configuration of the coupling coefficient, and hence the low-frequency oscillation can be eliminated and the maximum switching peak current can be decreased.

Generation of electromagnetic energy in a magnetic cumulation generator with the use of inductively coupled circuits with a variable coupling coefficient

A method of generation of electromagnetic energy and magnetic flux in a magnetic cumulation generator is proposed. The method is based on dynamic variation of the circuit coupling coefficient. This circuit is compared with other available circuits of magnetic energy generation with the help of magnetic cumulation (classical magnetic cumulation generator, generator with transformer coupling, and generator with a dynamic transformer). It is demonstrated that the proposed method allows obtaining high values of magnetic energy. The proposed circuit is found to be more effective than the known transformer circuit. Experiments on electromagnetic energy generation are performed, which demonstrate the efficiency of the proposed method.

Optimisation design for series–series dynamic WPT system maintaining stable transfer power

In amount of practical applications of wireless power transfer (WPT), charging electric vehicles (EVs) has attracted much attention. Dynamic WPT is considered as a solution to the problem of battery bottleneck and the difficulty of convenient charging encountered in the development of EV. However, the transfer power can hardly be maintained stable under large coil misalignment in movement. What is more, the transfer efficiency will decline correspondingly. A method of optimisation design is presented from the perspective of against misalignment for dynamic series-series (SS) WPT system. The primary compensation capacitance is well designed to regulate transfer power fluctuation in WPT system. Then the optimal load is matched by DC-DC converter to guarantee the highest average transfer efficiency. A secondary-only resonant SS WPT system with fixed frequency is finally built. The power transfer profile is smooth against coupling coefficient to realise high tolerance to position as the power drop (raise) percentage is no more than 10% (20%) within 200% variation of coupling coefficient for different loads. Meanwhile, the efficiency can always be maintained at a high level.

Optimal interfacing with coupled-cavities slow-light waveguides: mimicking periodic structures with a compact device.

We present a design for optimal interfacing (I/O coupling) with slow-light structures consisting of coupled cavities. The I/O couplers are based on adding a small set of cavities with varying coupling coefficients at edges of the coupled cavities waveguide in order to match its impedance with that of the I/O waveguides. I/O efficiencies exceeding 99.9% are shown to be possible over a bandwidth which is larger than 50% of that of the coupled cavities waveguide. Consequently, the reflections at the edges of the slow-light structure are practically eliminated. We discuss the properties of the perfectly impedance matched slow-light structure as an effective (super-structure) cavity and study the impact of the number of cavities comprising the I/O coupler. We also consider in details the impact of errors and disorder in the I/O coupling sections.

Novel Transmitting Power Control Method without Signal Communication for Wireless Power Transfer via Magnetic Resonance Coupling

SUMMARYWireless power transfer (WPT) via magnetic resonance coupling has been widely studied for vehicle applications, particularly the stationary and dynamic charging of electric vehicles. Our research group previously proposed a wireless in‐wheel motor to improve the reliability and safety of in‐wheel motors. Transmit power control is necessary to achieve stable WPT. We proposed a control method that uses a feedforward controller on the primary side and a feedback controller on the secondary side. However, the control method may cause shortfalls in the transmission power owing to modeling error, coupling coefficient variation, and signal communication delay. In this paper, we propose a novel feedback control method for the primary side based on conversion ratio estimation. The effectiveness of the proposed method was verified by simulations and experiments on the load current control of a constant voltage load and load voltage control of a constant power load.

Generation of Electromagnetic Energy in a Magnetic Cumulation Generator with the use of Inductively Coupled Circuits with a Variable Coupling Coefficient

Generation of Electromagnetic Energy in a Magnetic Cumulation Generator with the use of Inductively Coupled Circuits with a Variable Coupling Coefficient