Coupling Coefficient Research Articles

Constant Current Charging and Transfer Efficiency Improvements for a Dynamic Wireless Charging System

Dynamic Wireless Charging (DWC) systems for electric vehicles (EVs) are being studied and developed for wide applications. To ensure a long life for lithium-ion batteries, Constant Current (CC) charging is required. However, the equivalent load of the battery changes during CC charging, which reduces the system's efficiency. To solve that problem, this paper proposes a new control method that combines CC charging and improves transfer efficiency using only an active rectifier on the secondary side of the DWC system. Moreover, this study also proposes a method to estimate the coupling coefficient through the parameters measured on the secondary side without the need for wireless communication between the two sides. A model of a 1.5 kW DWC system with a transfer distance of 150 mm was built in a laboratory to verify the accuracy of the proposed method. The results showed that the charging current reached the required value, and the maximum system efficiency was 85%.

Nonlocal effective medium theory for phononic temporal metamaterials

We have developed a nonlocal effective medium theory (EMT) for phononic temporal metamaterials using the multiscale technique. Our EMT yields closed-form expressions for effective constitutive parameters and reveals these materials as reciprocal media with symmetric band dispersion. Even without spatial symmetry breaking, nonzero Willis coupling coefficients emerge with time modulation and broken time-reversal symmetry, when the nonlocal effect is taken into account. Compared to the local EMT, our nonlocal version is more accurate for calculating the bulk band at high wavenumbers and essential for understanding nonlocal effects at temporal boundaries. This nonlocal EMT can be a valuable tool for studying and designing phononic temporal metamaterials beyond the long-wavelength limit.

The Extraction of Coupling-of-Modes Parameters in a Layered Piezoelectric Substrate and Its Application to a Double-Mode SAW Filter.

This paper presents an advanced method that combines coupling-of-modes (COM) theory and the finite element method (FEM), which enables the quick extraction of COM parameters and the accurate prediction of the electroacoustic and temperature behavior of surface acoustic wave (SAW) devices. For validation, firstly, the proposed method is performed for a normal SAW resonator. Then, the validated method is applied to analysis of an I.H.P. SAW resonator based on a 29°YX-LT/SiO2/SiC structure. Via optimization, the electromechanical coupling coefficient (K2) is increased up to 13.92% and a high quality (Q) value of 1265 is obtained; meanwhile, the corresponding temperature coefficient of frequency (TCF) is -10.67 ppm/°C. Furthermore, a double-mode SAW (DMS) filter with low insertion loss and excellent temperature stability is also produced. It is demonstrated that the proposed method is effective even for SAW devices with complex structures, providing a useful tool for the design of SAW devices with improved performance.

Formation Control With Unknown Directions and General Coupling Coefficients

Formation Control With Unknown Directions and General Coupling Coefficients

Research on high sensitivity integrated transmit and receive hydroacoustic transducer

In response to the application demand in the field of hydroacoustic for high efficiency transmitting and high sensitivity receiving, overlapping frequency bands of transmitting and receiving, and structurally integrated high frequency hydroacoustic transducer. In this paper, a high-sensitivity transducer with integrated transmit and receive is developed. The transducer consists of two parts: the transmitting unit is 1–3 type piezoelectric composite material; the receiving unit is single metal plate air column array structure, and the effective electromechanical coupling coefficient is improved by changing the piezoelectric ceramic structure, thus improving the receiving sensitivity. Through theoretical analysis and finite element analysis determined the conditions of integration of transmitting and receiving. Finally, the transducer prototype was fabricated and tested. The results showed that the resonant frequency of the transmitter unit was 249 kHz, the anti-resonant frequency of the receiver unit was 253 kHz, and the maximum transmit voltage response and receive sensitivity were 180.1 dB and −175.8 dB, respectively, which satisfied the transceiver condition and high sensitivity performance.

Piezoelectric energy harvesting and synchronization of excited and modified Huygens's pendulums.

We consider a model of modified Huygens pendulums in order to be able to study the dynamics of such a system and carry out piezoelectric energy harvesting and the effects of phenomena encountered on this energy harvesting. The modifications made to the system here are the use of compound pendulums, a parametric force, and the addition of a piezoelectric transducer for energy harvesting. Thanks to the Lagrangian formalism, the governing equations were established and the numerical resolution was made using the fourth-order Runge-Kutta algorithm. We observed the presence of several types of synchronization (in-phase, anti-phase, quadrature-phase) and the existence of periodic, multi-periodic, or chaotic dynamics. Also, synchronization plays an important role in energy harvesting, in particular, in-phase synchronization, which promises much better performance than anti-phase synchronization. The effects of system parameters (amplitude and frequency of parametric force, stiffness coefficient, electromechanical coupling coefficient, etc.) are also studied on synchronization and energy harvesting. These results have applications in the manufacture of sensors and actuators, the power supply of electronic devices, and the manufacture of autonomous devices.

Cavity online measurements with a coaxial electrical probe in an X band integrally sealed relativistic klystron amplifier.

The electromagnetic characteristics of the input cavity with electron beams loaded are measured successfully in an X-band triaxial relativistic klystron amplifier (TKA) with a high frequency electrical probe. To solve the frequency response issue in the X band, a coaxial electrical probe is optimized and inserted obliquely into the input cavity at the designed angle so that the microwaves in the cavity can be sampled and extracted with the required coupling coefficient while the probe does not interfere with the solenoid coil, which is tightly integrated outside the TKA. Besides, the TKA is redesigned as a structure integrally sealed by the solenoid coil, and the secondary sealing induced by probe insertion is implemented on the flange of the solenoid coils rather than on the wall of the TKA, which is conducive to simplifying the coupling structure while maintaining the high vacuum level. The design is examined in a GW level TKA experiment, indicating that microwaves with a power of about 670MW are generated in the input cavity at a frequency of 8.40GHz, which is completely consistent with the injected and output microwave frequencies.

Electromechanical sensitivity of ZnO thin films at high-pressure regime for SAW strain sensor applications

This paper employs Density Functional Theory (DFT) to investigate the influence of high hydrostatic pressure on the piezo-elastic properties of ZnO with a specific focus on its repercussions for Surface Acoustic Wave (SAW) devices. Our findings reveal a significant enhancement in the piezoelectric coefficient d33 under high-pressure conditions, particularly reaching 13.09 pC/N at 8 GPa compared to the unpressurized state. This noteworthy improvement directly contributes to an overall enhancement in the electromechanical coupling coefficients (K2), emphasizing for the first time the potential of high-pressure conditions to positively influence the performance of ZnO/Al2O3 SAW devices. To confirm that, we utilized the Finite Element Method (FEM) to analyze the performance of a Surface Acoustic Wave (SAW) device based on ZnO for both propagating modes, namely Rayleigh and Sezawa, under elevated pressure conditions. We observed an improvement in the electromechanical coupling factor (K2) for the Rayleigh and the Sezawa modes, with enhancements of approximately 23% and 52%, respectively, under an applied pressure of 8 GPa compared to 0 GPa. Furthermore, we found that the Sezawa mode exhibits eight times greater sensitivity to pressure variations compared to the Rayleigh mode. These findings provide designers with a better understanding of the electromechanical responsivity and sensitivity of the ZnO-SAW devices to high level of applied pressure.

Transverse mode distribution in multimode diode-pumped Raman fiber laser

Raman lasers based on multimode graded-index fibers may generate high-quality (M2∼2) Stokes beams when pumped by highly multimode (M2>30) laser diodes. Here we, examine, both experimentally and theoretically, the energy distribution of the output Stokes beam across the principal quantum mode number n in a bent multimode fiber operating well above the Raman threshold. In contrast to Kerr spatial beam cleaning, leading to a Rayleigh–Jeans mode power distribution, in a multimode Raman fiber laser, we find that the output mode powers approach an exponential distribution. We introduce a coupled-mode equations model, including random linear coupling between neighboring mode groups, and obtain a good agreement between numerical simulations and experimental results. The model shows that, for typical mode coupling coefficients, the randomization of the mode power distribution is compensated by both nonlinear (Raman and Kerr) effects and linear filtering from the fs-inscribed fiber Bragg grating, both acting on the Stokes beam over successive round trips. When random coupling becomes the dominating factor, the mode power distribution of the Stokes beam tends to equipartition, similar to what is observed with large-size highly multimode beams of low intensity (and nonlinearity) in the absence of any filtering.

Optimization of magnetic coupling structure of electric vehicle wireless charging DD coil

The charging coil plays an important role in the wireless charging system system. However, there are still some problems in the design of the wireless charging coil, such as the low coupling coefficient. In order to improve the coupling effect, this paper proposes an optimized design scheme for the metal shielding layer structure of DD coil. Firstly, the influence of the structure size of DD coil metal plate on the coupling coefficient is studied by the mathematical modeling analysis. Futhermore, the maxwell simulation is used to study the metal plate coupling coefficients with varying structure sizes, addressing receiving uniformity issues. The optimal size of the shielding layer is designed for optimal magnetic coupling in wireless charging. Finally, this paper validates the feasibility of the improved metal shielding layer through experiments. The research in this paper may have a reference role in the wireless charging system of electric vehicles.

Investigation of noise correlations in the phase-locked class-A VECSEL array

We theoretically and experimentally study the noise correlations in an array of lasers based on a VECSEL (Vertical External Cavity Surface Emitting Laser) architecture. The array of two or three lasers is created inside a planar degenerate cavity with a mask placed in a self-imaging position. Injection from each laser to its neighbors is created by diffraction, which creates a controllable complex coupling coefficient. The noise correlations between the different modes are observed to be dramatically different when the lasers are phase-locked or unlocked. These results are well explained by a rate equation model that takes into account the class-A dynamics of the lasers. This model permits the isolatation of the influence of the complex coupling coefficients and of the Henry α-factor on the noise behavior of the laser array.

Elementary coupling coefficients for the Wigner supermultiplet symmetry

An algorithm for evaluating Wigner coefficients of U(4) ⊃ SUS(2) ⊗ SUT(2) for the coupling [n14,n24,n34,n44]⊗[1,0,0,0]↓[m14,m24,m34,m44] with arbitrary irreducible representation [n14,n24,n34,n44] is provided based on the algebraic expressions with the expansion coefficients of the U(4)⊃SUS(2)⊗SUT(2) states in terms of those in the U(4) canonical basis and the Clebsch-Gordan coefficients of U(4) in the canonical basis. The state expansion coefficients are evaluated as the components of the null space vectors of the spin-isospin projection matrices. Program summaryProgram Title: Wigner-U4-SU2xSU2CPC Library link to program files:https://doi.org/10.17632/4b7gf2phh2.1Licensing provisions: GPLv3Programming language: Wolfram Mathematica version 9.0.1.0 and beyondNature of problem: Numerical evaluation of the elementary Wigner coefficients (EWCs) of U(4)⊃SUS(2)⊗SUT(2).Solution method: Mathematica implementation of the EWCs of U(4)⊃SUS(2)⊗SUT(2) [1] using the expansion coefficients of U(4)⊃SUS(2)⊗SUT(2) states in terms of those of the U(4) canonical basis determined as components of the null space vectors of the spin-isospin projection matrices [2].

Current imbalance analysis of multichip influenced by parasitic inductance within PP-IEGT

The Press-Pack Injection Enhanced Gate Transistor (PP-IEGT) technology is frequently employed in converters for high power systems. In the device packaging, the imbalanced current sharing among chips has become a significant issue for device reliability. Considering the semiconductor structure of IEGT is different from the conventional power devices, the main prerequisite for fully quantifying the current distribution is to establish a suitable electrical model for IEGT. Thus, this paper proposes an IEGT single chip lumped-charge model taking into account the effect of carrier injection enhancement in the emitter. Furthermore, as for the parallel branches in PP-IEGT, the parasitic inductance of the drive board and pillars within the package are extracted by Ansys simulation, and the validity of Ansys simulation is verified by the port S-parameter method. Finally, combining the electrical model and the effect of mutual inductance, the switching inconsistency is evaluated. It is demonstrated that the farther the branch from the gate inlet, the greater the gate inductance withstands. Besides, the mutual inductance is an important factor to influence the electrical parameter distribution. Both mutual coupling coefficient and current density display degressive trends with the increases of the gap between parallel chips.

Theoretical and experimental investigation on the advantages of auxetic nonlinear vortex-induced vibration energy harvesting

Due to its wide applicability, vortex-induced vibration (VIV) from wind and water flow has been explored for piezoelectric energy harvesting. However, the broadband VIV energy harvesting at low wind speeds is still a great challenge. In this paper, an auxetic nonlinear VIV energy harvester (ANVEH) is proposed. For the first time, the advantages of monostable softening behavior using magnetic attraction are investigated. It is found theoretically and experimentally that the monostable softening can broaden the working wind speed range whereas decreasing the peak energy output. Thus, the auxetic structure is proposed to compensate the decrease of peak energy output with the monostable softening due to its negative Poisson’s ratio and high stress distribution. Utilizing the experimentally validated theoretical model, parametric investigations are undertaken to examine the effects of various factors, including the magnetic separation distance, the stiffness and mass of the harvester, the dimension of the bluff body, the connected resistance, and the electromechanical coupling coefficient. Results show that no matter how the system parameters vary, the ANVEH has the superior performance than the plain nonlinear VIV energy harvester (PNVEH).

Effects of coupling coefficient dispersion on the Fermi-Pasta-Ulam-Tsingou recurrence in two-core optical fibers

In a two-core optical fiber (TCF), the linear coupling coefficient between the two cores in general varies with the optical wavelength, a phenomenon known as coupling coefficient dispersion (CCD). Here we study the effects of CCD on the Fermi-Pasta-Ulam-Tsingou recurrence (FPUT) phenomena in a TCF. Modulation instability tends to be a precursor in the formation of breathers. The subsequent decay of breathers and re-emergence of modulation instability lead to FPUT type periodic patterns. For the symmetric or antisymmetric continuous-wave (CW) state of a TCF, CCD does not affect the modulation instability gain spectra. However, if asymmetric perturbations are applied to a symmetric CW state, CCD can drastically modify FPUT. In the anomalous dispersion regime, without CCD, only FPUT dynamics without energy transfer between the two cores occurs. With CCD effects, FPUT dynamics with strong energy transfer between the two cores can arise. As CCD increases, FPUT dynamics without energy transfer never vanishes, but the corresponding number of FPUT cycles can be drastically reduced to only one. In the normal dispersion regime, no FPUT dynamics with energy transfer between the two cores occurs. The major CCD effect is to significantly decrease the FPUT cycles, and only one FPUT cycle can be observed at relatively large magnitude of CCD values. As the magnitude of CCD increases further, more FPUT cycles arise again. Moreover, larger CCD will lead to higher (lower) propagation speed of the wave patterns in the anomalous (normal) dispersion regime respectively. To enhance theoretical insight, we perform a Floquet analysis for the linearized stability equations with periodic coefficients based on the FPUT dynamics in the normal dispersion regime. The monodromy matrix and eigenvalues can be computed explicitly. Larger eigenvalues correlate with stronger instability and more rapid disintegration of the periodic patterns, agreeing well with the trends of the numerical simulations.

An improved van der Pol wake oscillator model for a 1DOF circular cylinder undergoing vortex induced vibrations

An optimization procedure is presented for prescribing the empirical coupling parameters of a modified coupled van der Pol (VDP) wake oscillator and mass–spring–damper system for a one degree of freedom (1DOF) circular cylinder system undergoing vortex induced vibrations (VIV). This approach allows for the generalization of the traditional VDP model to cover a large VIV parameter range. The procedure is developed using experimental data covering the parameter space: 3<U∗<11, 8<m∗<20, 0.003<ζ<0.063, ReD=4000. The VDP model contains empirical coupling coefficients that describe the regime specific dynamic damping, ϵ, and wake coupling, β. Two calibration procedures are considered and the improvements over the traditional VDP model in predicting the VIV response are discussed. Subsequently, a regression fit is used to prescribe the two empirical coupling coefficients as functions of m∗, ζ and U∗. The generalized model results in a better prediction of the VIV response in terms of identification of lock-in regimes, lock-in frequency and amplitude response over several regimes when compared to the classical models. The use of a functional representation replaces the need for using tables and reduces user input for determining regime-specific coupling coefficients.

Design of a volumetric cylindrical coil-tuned at 298 MHz for 7 T imaging

The concept of a 2D cylindrical High Pass Ladder (2D c-HPL) is used in the development of this ultra-high radio frequency (UHRF) volumetric head coil for 7 T tuned at the Larmor frequency of 298 MHz. The architecture of the 2D c-HPL helps to overcome the challenges associated with non-uniform magnetic field distribution. The prototype consists of an individual resonating array of inductance-capacitance (LC) elements and each component is tuned to the precise fo frequency. The tuning of the (i) inductance, (ii) capacitance, (iii) mesh size, and (iv) coupling coefficient play critical roles to attain the desired Larmor frequency. For this proof-of-concept, the prototype of a volumetric head coil consists of a cylindrical array size of 4 × 6, with individual LC components of inductance magnitude, 98 nH and four fixed value capacitors and one tunable capacitor that allowed to achieve the desired precession frequency, fr  = 298 MHz. The model was tested for three different fo values of 269, 275, and 286 MHz. The mutual coupling and the eigenfrequencies were compared through bench testing and dispersion equation. The experimental data were in good agreement (<5%) with the theoretical eigenfrequencies from the dispersion relation. The theoretical eigenfrequencies and the experimental eigenfrequencies are in good agreement for eigenmodes (1,2), (1,3), (2,2), (2,3), and (4,3).

Rock drilling performance of rotary ultrasonic tools incorporating PZT piezoceramic and Mn:PIN-PMN-PT piezocrystal

High performance Mn:PIN-PMN-PT piezocrystal material is investigated to understand if its extraordinary properties can replace the traditional hard piezoceramic material for space exploration applications. A bolted Langevin-style ultrasonic drill tool incorporating a pair of Mn:PIN-PMN-PT piezocrystal rings is built to compare with a same configuration ultrasonic drill tool actuated with a pair of hard piezoceramic rings, which are tuned to the first longitudinal mode (L1) at around 20 kHz. From the characterisation results, it is observed that the piezocrystal material presents significantly greater values of relative permittivity, electromechanical coupling coefficient, and piezoelectric charge coefficient than the hard piezoceramic material. Despite these outstanding properties, the piezocrystal driven ultrasonic drill tool shows similar displacement amplitudes to its counterpart. Nonetheless, the impedance magnitude of the piezocrystal driven ultrasonic drill tool at resonance is a magnitude lower than the piezoceramic actuated drill tool, due to the large piezoelectric charge coefficient d33. Ultrasonic rock drilling experiments suggest that the cutting force for sandstone and marble are greatly reduced, but limestone and tuff are less affected.In general, the piezocrystal driven ultrasonic drill tool demonstrates a marginally improved cutting performance than the piezoceramic actuated drill tool, in terms of lower cutting force and motor power consumption, however, the tool wear appears slightly poorer. The research outcome of this paper indicates that the thickness mode of the piezocrystal rings might not be the optimal form of excitation, which could be due to the piezoelectric losses at high excitation levels, so other excitation conditions and vibration modes will need to be explored to fully adopt the extraordinary material properties of the piezocrystal material.

Simulation on continuous-wave silicon carbide Raman laser pumped by 1550 nm lasers

We present a detailed simulation-based analysis of continuous-wave (CW) Raman laser in silicon carbide (SiC) waveguide based on SiC-on-insulator (SiCOI). Both Fabry–Perot (FP) cavity and ring-resonator configurations were designed for Raman lasing, which are pumped by 1550 lasers. According to the Raman coupled wave equation, for FP cavity Raman laser, the relations between laser output performances and key parameters such as output reflectivity, waveguide length, and pump power had been systematically analyzed. Similarly, the effects of ring length, coupling coefficient, and coupler position on the output performance were also investigated based on the ring resonator. The results demonstrate the significant potential of near-infrared Raman lasing from SiC. It provides theoretical guidance for the experimental design of the on-chip SiC Raman laser.

Multi-wavelength sub-100 Hz linewidth Brillouin fiber laser with cascaded SBS polarization parity-time symmetry

A multi-wavelength sub-100 Hz linewidth Brillouin fiber laser (BFL) with cascaded stimulated Brillouin scattering (SBS) polarization parity-time (PT) symmetry is proposed and experimentally investigated. Multi-order Stokes wave generation using a structure consisting of a main fiber ring (MFR) and a sub fiber loop (SFL). The MFR is used to excite the Stokes laser and to guarantee single longitudinal mode (SLM) operation of the generated stokes laser of each order and the SFL cascades each Stokes lasing emission to act as a Brillouin pump for the next order of Stokes generation. A Sagnac loop in the MFR consisting of optical coupler (OC), polarization beam splitter (PBS) and two polarization controllers (PCs), is used to achieve cascaded SBS polarization PT symmetry. By tuning the PC to control the polarization state of each order linearly polarized light injected into PBS at each order, thus controlling the gain and loss of the loop corresponding to the two backpropagating light waves. When the gain and loss of the coupling loops are the same in magnitude and greater than the coupling coefficient, the cascaded SBS polarization PT symmetry is broken, resulting in SLM operation for each order of Stokes waves. Experimental results reveal that thirteen Stokes waves were obtained from two different output ports at an erbium-doped fiber amplifier (EDFA) output power of 28 dBm. The measured linewidths at — 20 dB power were 0.34, 0.39, 0.33, 0.4, 0.39 and 0.43 kHz for the 1st-6th order Stokes emission, corresponding to linewidths of 17.1, 19.6, 16.6, 20.1 19.6 and 21.6 Hz, respectively, while the maximum side mode suppression ratios (SMSRs) were measured to be 47, 45, 49, 44, 41 and 41 dB for the 1st-6th order Stokes emission. Within 60 min of the stability experiment, the wavelength and power stability were ±2 pm and ±0.6 dB, respectively. Compared with previous studies, the present design guarantees the operation of SLM for each order of Stokes waves with sub-100 Hz laser linewidth.