Optimal Resonance Conditions Research Articles

Optimal Resonant Condition for Maximum Output Power in Tightly-Coupled WPT Systems Considering Harmonics

Optimal Resonant Condition for Maximum Output Power in Tightly-Coupled WPT Systems Considering Harmonics

Energy transfer mechanism in luminescence Eu(III) and Tb(III) complexes of coumarin-3-carboxylic acid: A theoretical study.

Excited state energy level diagrams of coumarin-3-carboxylic acid (HCCA) chromophore, Eu(CCA)Cl2(H2O)2 (1), Eu(CCA)2Cl(H2O)2 (2), Eu(CCA)3(H2O)3 (3), Tb(CCA)2Cl(H2O) (4) and Tb(CCA)2(NO3)(H2O) (5) in gas phase and polar solution have been calculated by means of DFT/TDDFT/ωB97XD methods. Based on these results, the ability of CCA to sensitize Eu(III) and Tb(III) luminescence has been examined. The competitive excited state processes in the complexes - fluorescence, intersystem crossing (ISC) and phosphorescence, were analyzed depending on the environment, number of the ligands, Ln(III) ion type (Eu and Tb) and counteranion (Cl- and NO3-). It has been found that the environment altered the S1 state energy, oscillator strength, fluorescence lifetime as well as the S1 character - polar solution stabilized the S1(ππ*) state, whereas non-polar solution (gas phase, solid state) stabilized the S1(nπ*) state. The S1(nπ*) state was decisive for the efficient energy transfer as it suppressed the S1 emission of CCA and favored ISC or direct transfer to the emitting levels of Eu(III). The HCCA triplet (T1) state minimum energy (~2.7, ~2.6ZPE eV) and (ππ*) character were retained in Eu/Tb-CCA complexes regardless of the environment. The energy gap between the higher energy T1 donor state and the acceptor levels 5D1 of Eu(III) (~0.5eV) and 5D4 of Tb(III) (~0.1eV) provided optimal resonance conditions for effective energy transfer for Eu(III), but less probability for Tb(III). The nonradiative energy (CCA→Eu(III)) transfer rates and quantum luminescence yield for 2 and 3 were calculated by a strategy combining DFT geometries, INDO/S excitation energies and calculated Judd-Ofelt parameters. The excitation channel T1→5D0 through an exchange mechanism was predicted as the most probable one to populate the main emissive Eu-centered state in complexes 2 and 3. The more efficient luminescence of 3 than that of 2 was discussed and explained.

Investigation on Stray-Capacitance Influences of Coaxial Cables in Capacitive Transducers for a Space Inertial Sensor.

Ultra-sensitive inertial sensors are one of the key components in satellite Earth’s gravity field recovery missions and space gravitational wave detection missions. Low-noise capacitive position transducers are crucial to these missions to achieve the scientific goal. However, in actual engineering applications, the sensor head and electronics unit usually place separately in the satellite platform where a connecting cable is needed. In this paper, we focus on the stray-capacitance influences of coaxial cables which are used to connect the mechanical core and the electronics. Specially, for the capacitive transducer with a differential transformer bridge structure usually used in high-precision space inertial sensors, a connecting method of a coaxial cable between the transformer’s secondary winding and front-end circuit’s preamplifier is proposed to transmit the AC modulated analog voltage signal. The measurement and noise models including the stray-capacitance of the coaxial cable under this configuration is analyzed. A prototype system is set up to investigate the influences of the cables experimentally. Three different types and lengths of coaxial cables are chosen in our experiments to compare their performances. The analysis shows that the stray-capacitance will alter the circuit’s resonant frequency which could be adjusted by additional tuning capacitance, then under the optimal resonant condition, the output voltage noises of the preamplifier are measured and the sensitivity coefficients are also calibrated. Meanwhile, the stray-capacitance of the cables is estimated. Finally, the experimental results show that the noise level of this circuit with the selected cables could all achieve 1–2 × 10−7 pF/Hz1/2 at 0.1 Hz.

Determination of the Optimal Resonant Condition for Multireceiver Wireless Power Transfer Systems Considering the Transfer Efficiency and Different Rated Powers With Altered Coupling Effects

Recently, there has been an ever-growing demand for multireceiver wireless power transfer (WPT) systems with a high power transfer efficiency. In this article, a novel optimization-based method is proposed to precisely determine the optimal resonant condition for multireceiver WPT systems in order to maximize the power transfer efficiency while satisfying all the rated power that can be differently required in each receiver module. The proposed method links the optimization module and the analysis module to iteratively update the design variables during optimization based on electric performance evaluated in the analysis module. After being verified with a “single-transmitter-to-a-single-receiver” WPT system which has a well-known resonance condition, the proposed method is applied to determine the optimal resonant condition for various “single-transmitter-to-multiple-receiver” WPT systems in both initial and disturbed configurations. The experimental validation demonstrates the performance and potential of the proposed method to compensate the coupling changes of multireceiver WPT systems.

Acoustic streaming in turbulent compressible channel flow for heat transfer enhancement

Acoustic streaming in high-speed compressible channel flow and its impact on heat and momentum transfer is analysed numerically at two different Mach numbers, and 1.5, and moderate Reynolds numbers, and 6000. An external time-periodic forcing function is implemented to model the effect of acoustic drivers placed on the sidewalls. The excitation frequency is chosen according to the linear stability analysis of the background (unexcited) flow. High-fidelity numerical simulations performed at the optimal resonant condition reveal an initially exponential growth of perturbations followed by a nonlinear regime leading to the limit-cycle oscillations. In the last stage, we observe an acoustic (steady) streaming appearing as a result of nonlinear interactions between the periodic external wave and the background flow. This causes a steady enhancement in heat transfer at a rate higher than the skin-friction augmentation. We also show that perturbations of similar amplitude, but at suboptimal frequencies, may not lead to such limit-cycle oscillations and cannot make any noticeable modifications to the time-averaged flow quantities. The present research is the first study to demonstrate the acoustic streaming in compressible turbulent flows, and it introduces a novel technique towards enhancing the heat transfer with minimal skin-friction production.

Comparative analysis of fiber ring resonator based on different fibers

Abstract A fiber ring resonator (FRR) is the core element in a resonant fiber optic gyro (RFOG) and its resonant depth, finesse and sensitivity determine the performance of RFOG. A configuration of FRR based on air-core photonic bandgap fiber (PBF), photonic crystal fiber (PCF) and panda polarization-maintaining fiber (PMF) is proposed, and the resonant depth, finesse and sensitivity of the FRR are comparative analyzed fully and in depth. It's found that: the FRR using PCF and PBF have better resonant depth than that of using PMF; the FRR using PCF has nearly the same performance as that using PMF, and may be a trade-off used in FRR before the existence of better PBF; the key factor that whether the FRR resonates in optimal resonant state is whether αc and kc of directional coupler satisfy the optimal resonant condition. These theoretical results are helpful to further study and optimize the RFOG based on different fibers.

X-ray emission from relativistic electrons in a transverse high intensity optical lattice

A new scheme of all-optical free electron laser (FEL), operating in the X-ray range and triggered by interaction of a moderately relativistic electron bunch with a transverse high intensity optical lattice is presented. The ponderomotive potential of the optical lattice forms guiding channels, where the electrons are trapped and oscillate transversely. The collective oscillations of the guided electron bunch scatter the laser beams and amplify the signal at the Stokes frequency, thereby yielding a coherent beam at the Doppler-shifted frequency in the XUV or X-ray domain. Analytic descriptions of a small signal amplification in such a system are presented, and the optimal resonance conditions are defined. The gain scaling laws are confirmed by numerical simulations using a simplified kinetic model in the co-propagating reference frame.

Probing High-Pressure Phase Transitions in Ti-Based Perovskite-Type Ferroelectrics Using Visible Resonance Raman Spectroscopy

We report unprecedented dramatic changes in the 647.1 nm Raman signal of PbZr(0.6)Ti(0.4)O(3) occurring in the same pressure ranges as the critical pressures of the antiferrodistortive and ferroelectric-paraelectric phase transitions. This huge decrease in intensity of both the Raman modes and the background, observed for both pressure transmitting media used (glycerol or 4:1 methanol ethanol mixture), is shown to originate from the two-step loss of a resonance Raman effect and the concomitant fluorescence. Changes in the local titanium environment (first with the onset of octahedral tilting and then with the removal of polar cation displacements) alter the electronic band structure and modify the resonance conditions. Furthermore, the optimal resonance conditions are found to be particularly narrow, as shown by the fluorescence spectrum of PbZr(0.6)Ti(0.4)O(3) at atmospheric pressure characterized by the presence of a very well-defined sharp peak (fwhm = 8 nm) centered around 647.1 nm. These results thus demonstrate that visible resonance Raman spectroscopy can be used as a quick and efficient technique for probing phase transitions in PbZr(1-x)Ti(x)O(3) (PZT) and other technologically important perovskite-type materials such as PMN-xPT, PZN-xPT relaxors, lead free piezoelectrics, and ferroelectric nanopowders. This technique appears also a good alternative to UV Raman spectroscopy for probing the polar order at the nanoscale in ultrathinfilms and superlattices.