Coupling Coefficient Decrease Research Articles

양극성 자기장 커플러 구조를 가지는 무선전력전송 시스템의 누설 자기장 저감을 위한 페라이트 격벽 구조 설계

In this study, ferrite wall structures are proposed for reducing leakage magnetic field in a wireless power transfer system with a bipolar magnetic coupler structure in the form of a ferrite core inductor. In the proposed framework, the magnetic field of the transmitting coil remains on the ferrite wall, and the leakage magnetic field is minimized. However, when the magnetic field of the transmitting coil is induced in the ferrite wall, the mutual inductance and coupling coefficient decrease. Therefore, in this paper, the height of the ferrite wall structure is adjusted to minimize the decrease through simulations based on the reluctance circuit model. The performance of the proposed structure was verified through simulations and experiments. The simulation results indicated that the magnetic field leakage effectively decreased with an increase in the height of the ferrite wall structure. The results of experiments demonstrated that although the power transfer efficiency of the framework with the proposed ferrite wall was 3.6 % lower than that of the framework without the ferrite wall, the corresponding leakage magnetic field was reduced by more than 60 %.

A Thorough Analysis for the Impact of the Coupling Coefficient on the Behavior of the Coupled Inductor High Step-Up Converters

In this article, the impact of the coupling coefficient K on the static continuous conduction mode (CCM) dc voltage gain of the basic passive clamp coupled inductor boost converter is investigated. First, an analytical method for the extraction of the accurate static CCM dc voltage gain and all the necessary formulas for the comprehensively description of the operating behavior of the converter is presented. Next, a comparison between the previous methods from which the proposed approximate static CCM dc voltage gain formulas are derived and the proposed one takes place. Subsequently, from the analysis and the plots, it appears that the coupling coefficient creates a dependence on the operation by the output current of the converter, which is more intense as the coupling coefficient decreases. Furthermore, it is concluded that the decrease in the dc voltage gain depends not only on the coupling coefficient K , but also on the turns ratio of the coupled magnetic component. Finally, experimental results based on a 250-W laboratory prototype with four different magnetic components are presented for the evaluation of the theoretical analysis.

Research on the transmission efficiency of different shielding structures of wireless power transfer system for electric vehicles

Wireless Power Transfer (WPT) charging system can cause eddy loss on the steel part and the chassis of Electric Vehicle (EV). To study different shielding structures' influence on the transmission efficiency of the WPT system, boundary conditions and assumptions of WPT model in the quasi-stationary electromagnetic field were established and finite element method (FEM) was adopted. The shielding effectiveness of ferrite plate and annular aluminum plate was investigated as well as their effects on coupling coefficient of WPT. It was found that, the setting of ferrite core enhanced the transmission field strength, improved the coupling between two coils, and increased transmit power as well as the actual eddy loss. The actual necessary shielding-area was not confined into the same-size area but distributed around the edge of the ferrite. By arranging specialized size annular aluminum plate between chassis and ferrite core, the eddy loss can be effectively shielded and an optimal transmission efficiency was reached with acceptable coupling coefficient decrease. The optimized ferrite bar structure and its EMC characteristics were also studied. It was also found that with equal volume, the optimized ferrite bar structure had better performance in EMC and coupling enhancement than the full ferrite plate.

Dynamics of a System of Two Simplest Oscillators with Compactly Supported Nonlinear Feedbacks

In this paper, we consider a singularly perturbed system of two differential equations with delay, simulating two coupled oscillators with a nonlinear feedback. The feedback function is assumed to be compactly supported and piecewise-continuous and it is assumed that its sign is constant. In this paper, we prove the existence of relaxation periodic solutions and make conclusions about their stability. Using a special large-parameter method, we construct asymptotics of all solutions of the considered system under the assumption that the initial-value conditions belong to a certain class. Using this asymptotics, we construct a special mapping principally describing the dynamics of the original model. It is shown that the dynamics changes fundamentally as the coupling coefficient decreases: we have a stable homogeneous periodic solution if the coupling coefficient is on the order of unity and the dynamics become more complex as the coupling coefficient decreases (it is described by a special map). For small values of the coupling, we show that there are values of the parameters such that several different stable relaxation periodic regimes coexist in the original problem.

Influence of Saturant on Seismoelectric Coupling Response of Porous Media

The seismoelectric coupling phenomenon in porous medium saturated with gas and water was studied numerically. The numerical model was formulated based on Pride's theoretically developed seismoelectric coupling coefficient that describes conversion of seismic energy into electromagnetic radiation. The conversion is complex function of physical, electrical and poroelastic properties of the porous medium and the saturant. In this study, a porous medium that is partially saturated with water is considered. Pore spaces that are not saturated with water are considered to be filled with gas. The gas phase is methane. The water saturation was varied from 0.2 to 0.9. The physical and electrical properties of both phases are determined at a temperature of 325 °K. The porosity and permeability of the porous medium is 0.2 and 500 mD, respectively. The porous medium in this study is isotropic. Zeta potential was estimated using an empirically derived correlation. At 0.001 mol/lit salinity, zeta potential is 66.7 mv. The numerical study result shows that at a fixed seismic wave frequency, lower water saturation results in higher seismoelectric coupling coefficient. When water saturation increases, the seismoelectric coupling coefficient decreases. However, the rate of decline is lower at higher seismic frequency. The rate of decline at 10 kHz is 1.38 nV/Pa compared to 4.35 nV/Pa at 100 kHz. Higher frequencies result in stronger nonlinearities, which causes higher mechanical energy dissipation. As such, the result obtained in this study is consistent with what is normally expected when mechanical wave propagates through a porous media.

Design of an all-optical fractional-order differentiator with terahertz bandwidth based on a fiber Bragg grating in transmission.

All-optical fractional-order temporal differentiators with bandwidths reaching terahertz (THz) values are demonstrated with transmissive fiber Bragg gratings. Since the designed fractional-order differentiator is a minimum phase function, the reflective phase of the designed function can be chosen arbitrarily. As examples, we first design several 0.5th-order differentiators with bandwidths reaching the THz range for comparison. The reflective phases of the 0.5th-order differentiators are chosen to be linear phase, quadratic phase, cubic phase, and biquadratic phase, respectively. We find that both the maximum coupling coefficient and the spatial resolution of the designed grating increase when the reflective phase varies from quadratic function to cubic function to biquadratic function. Furthermore, when the reflective phase is chosen to be a quadratic function, the obtained grating coupling coefficient and period are more likely to be achieved in practice. Then we design fractional-order differentiators with different orders when the reflective phase is chosen to be a quadratic function. We see that when the designed order of the differentiator increases, the obtained maximum coupling coefficient also increases while the oscillation of the coupling coefficient decreases. Finally, we give the numerical performance of the designed 0.5th-order differentiator by showing its temporal response and calculating its cross-correlation coefficient.

Transfer functions of a transformer at different values of coupling coefficient

The low- and mid-frequency model of the transformer with resistive load is analysed for different values of coupling coefficients. The model comprising of coupling-dependent inductances is used to derive the following characteristics: voltage gain, current gain, bandwidth, input impedance, and transformer efficiency. It is shown that in the low- and mid-frequency range, the turns ratio between the windings is a strong function of the coupling coefficient, i.e., if the coupling coefficient decreases, then the effective turns ratio reduces. A practical transformer was designed, simulated, and tested. It was observed that the magnitudes of the voltage transfer function and current transfer function exhibit a maximum value each at a different value of coupling coefficient. In addition, as the coupling coefficient decreases, the transformer bandwidth also decreases. Furthermore, analytical expressions for the transformer efficiency for resistive loads are derived and its variation with respect to frequency at different coupling coefficients is investigated. It is shown that the transformer efficiency is maximum at any coupling coefficient if the input resistance is equal to the load resistance. Experimental validation of the theoretical results was performed using a practical transformer set-up. The theoretical predictions were found to be in good agreement with the experimental results.

Measurement of Thermoelectric Potential Coupling Coefficient for Sandstone Rock Sample

Excessive water production is one of the main problems that occur during hydrocarbon production. During water injection, the less viscous water which has higher mobility than the reservoir fluid, tends to by-pass the oil. This phenomenon is normally called water fingering. Density difference between denser water and oil makes the water segregate to the bottom of layer, creating water tongue. Uncontrolled excessive water production will reduce oil production potential and increase the cost for water management and treatment. This phenomenon is economical unfavorable. Intelligent well integrated with monitoring systems and inflow control valve (ICV) has been applied in producing hydrocarbon. The excessive flow of water into well can be controlled using ICV. There are various methods and approaches been proposed to control water production. One of them is by measuring the spontaneous potential (SP) using permanent sensor outside the insulated casing. However, thermoelectric (TE) potential could also contribute to the measurement of the SP. The main objective of this experiment is to measure TE potential across sandstone rock sample at four different salinities which are 0.001M, 0.01M, 0.1M, and 1.0M of brine (NaCl). The core samples dimension is 7.62 cm in length and 3.81 cm in diameter. Temperature difference up to 80°C was applied to rock sample inducing different TE potentials at different salinities. Gradual heating technique was applied in creating temperature difference by using a temperature controller. Three different experiments were conducted for each salinity and real-time voltage (V) and temperature (T) were recorded using data acquisition system. Then the TE coupling coefficient can be determined by calculating the slope after plotting Voltage versus Temperature Difference. The result is as the salinity increases, TE coupling coefficient decrease and drop to zero around 0.1M. The result shows small but still measurable thermoelectric coupling coefficients.

Study on the Wireless Power Transmission Technology for the Implantable Cardiac Pacemaker

The working principle of a Wireless Power Transmission technology (WPT) system of the implantable cardiac pacemaker was introduced. Then, based on Ansoft Maxwell software, the three-dimensional finite element model of the WPT system was established. Finally the influence of some parameters, such as the gap and radial migration of the primary and secondary winding, ferrite core, working frequency on the self - inductance, mutual inductance, and the coupling performance were studied. The results show that with the gap or radial migration increasing, the self- inductance is almost same, but the mutual inductance and coupling coefficient decrease; the ferrite core may significantly enhance the inductance and coupling performance; the inductance and coupling coefficient has nothing to do with the working frequency.

Structural, dielectric and piezoelectric properties of xBiFeO3–(1−x)BaTi0.9Zr0.1O3 ceramics

Effect of BiFeO3 (BFO) content on the microstructure and electrical properties of BaTi0.9Zr0.1O3 (BTZ) ceramics prepared by the solid-state reaction technique was investigated. X-ray diffraction analyses show that BFO diffused into the lattice of BTZ to form a solid solution with perovskite structure. The relative density of the BTZ ceramics is increased by the introduction of BFO. The dielectric study reveals that the dielectric constant and the average dielectric loss of the solid solution decreased simultaneously with an increase in BFO content. The materials undergo a diffuse type ferroelectric phase transition. The diffusivity increases with increase in BFO contents in the studied composition range. On the other hand, the piezoelectric coefficient and electromechanical coupling coefficient decrease simultaneously with increasing the BFO content, whereas the mechanical quality factor increases gradually. The structure–property relationship and the mechanism associated with the change of the electrical properties are discussed intensively.

Fabrication-tolerant active-passive integration scheme for vertically coupled microring resonator

The large-scale photonic integration of microring resonators in three dimensions made possible by recent developments in vertical coupling and wafer bonding technology is shown to be sensitive to lateral mask misalignment for the ring and bus waveguides introduced during the fabrication process. For a typical 20-/spl mu/m radius, vertically coupled microring calculations reveal a linear relationship between deviation in the coupling coefficient and lateral misalignment. A coupling coefficient reduction of 50% is predicted for a lateral misalignment of 0.3 /spl mu/m, which is typical for an alignment accuracy limited by the current state-of-the-art mask alignment process. The use of a wide multimode bus waveguide is proposed to ameliorate this alignment sensitivity. The mode-expanded bus waveguide, together with its physically wider structure, reduces the dependence of modal overlap and coupling length on precise alignment, resulting in significantly relaxed fabrication tolerance. Deviation of coupling coefficient decreases by an order of magnitude for the new ring coupler geometry, where a sole reduction of 5% is obtained for the same amount of misalignment. The implications of the proposed structure are subsequently investigated for microring laser performance. The differential slope efficiency is shown to be at least five times less sensitive to lateral misalignment for the proposed structure within a small misalignment regime. This readily adaptable coupler geometry based on existing vertical coupling architectures is transferable to any fabrication scheme with multiple waveguide layers coupled vertically, and is of particular importance to microring resonators with small radii.

Proton-exchanged Z-cut LiNbO/sub 3/ waveguides for surface acoustic waves

Proton-exchanged (PE) waveguides in Z-cut LiNbO/sub 3/ have been fabricated using benzoic acid. Secondary-ion mass spectrometry (SIMS) measurements show that the distribution of hydrogen in the PE Z-cut LiNbO/sub 3/ samples exhibits a step-like profile with the diffusion constant D/sub 0/ and the activation energy Q of about 2.82/spl times/10/sup 8/ /spl mu/m/sup 2//h and 87.76 kJ/mol, respectively. On the other hand, the important parameters for the design of surface acoustic wave (SAW) devices are measured and discussed. The results show that the phase velocity and electromechanical coupling coefficient decrease with the increase of kd, where k is the wavenumber and d is the waveguide depth. The variation of insertion loss becomes saturated at about kd=0.068 with a maximum increase of about 4/spl sim/5 dB. The temperature coefficient of delay calculated from the frequency change of the output of SAW delay line shows an evident increase in the PE layer. Moreover, the effects of postannealing can result in a restoration of the decreased velocity and an improvement of the insertion loss.

Effect of third-order dispersion on pulse dynamics in nonlinear directional coupler

The authors show that third-order dispersion can lead to a serious decrease in the effectiveness of pulse switching in a nonlinear directional coupler. In contrast to the case of vanishing third-order dispersion, the pulse shape is a cricial limitation. The influence of the third-order dispersion diminishes when the coupling coefficient decreases.

Measurement of surface coupling coefficients between nematic liquid crystals and various substrates

AbstractThere are still problems not fully solved concerning the characteristics and magnitude of interaction between liquid crystals and the surfaces of substrates. It is thought that the number of electrodes in a matrix display device can be increased and its display panel can contain a memory function by the weak boundary‐coupling effect (i.e., by reducing the coupling of the liquid crystal and the substrate surface). Thus, it is necessary to investigate the strength of the coupling between liquid crystals and the surfaces of various substrates. The coupling strength is measured by curve fitting of the electrostatic capacitance–applied voltage characteristic (the C ‐ V characteristic) of a nematic liquid crystal cell. In this method the measured result of the C ‐ V characteristic is compared with the result of calculation in which the surface coupling coefficient is used as parameter. Two kinds of surface treatment (i.e., oblique vacuum‐evaporation of silicon monoxide and rubbing after coating with polyvinyl alcohol film) are investigated. The nematic liquid crystals used in this study are phenyl cyclohexane‐based. The coupling coefficient is of the order of 10−3 J/m2. When the temperature is raised, the coupling coefficient decreases.