- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Low-Loss, High-Frequency and Large-Coupling SH SAW Resonators Based on SiN/LiNbO<inf>3</inf>/Si
摘要： Low-loss, high-frequency and large-coupling-coefficient SAW resonators based on SiN/LN/Si are demonstrated in this study. By bonding the high-velocity Si substrate to the sub-wavelength-thick LN layer, the shear-horizontal mode SAW resonator no longer couples with the bulk modes in substrate and the leaky component is effectively eliminated. As the propagation loss is no longer the main concern for the cut angle selection, the ultra-large cut angle can be used to achieve high coupling coefficient (κ2). By carefully designing the SiN/LN/Si structure, the high-frequency and large-κ2 SAW resonators with low loss are achieved. The fabricated SAW resonators show great potential for current and next generation front ends.
关键词： SiN/LN/Si,large coupling coefficient,high frequency,low loss,SAW resonators
更新于2025-09-23 15:22:29
-
Propulsion effects after laser ablation in water, confined by different geometries
摘要： A Nd:YAG laser with 7-ns pulses and pulse energies up to 10 mJ is used to induce an optical breakdown in the front surface of an aluminum rod, covered by a water layer. The rod is part of a ballistic pendulum. In this way, we study the propulsion effects by means of coupling coefficient and energy-conversion efficiency with respect to different confining geometries, volumes of water applied to the front surface of the rod, and the distance of this surface from the laser-beam focus. Holes with different dimensions are drilled on the target surface and filled with different volumes of water to examine the influence of the confinement by the liquid (a free boundary) and a solid-surface geometry on laser ablation effects. The rod movement and the water ejection after laser ablation are acquired by a high-speed camera with 10k frames per second. The results show that the confinement by cavity substantially increases the propulsion effects by shaping the ejected flow of the liquid; while the cavitation bubble, induced inside the water layer, plays a significant role in propulsion efficiency. From the presented results, it follows that the laser-propelled rod carries below 0.5% of the total mechanical energy after propulsion, while the rest of this energy represents the kinetic energy of the ablated water. As expected, moving the target surface away from the focal position decreases the ablative-propulsion efficiency. When the focus is moved inside the solid target, the decrease occurs due to lower conversion of the pulse energy into the energy of the cavitation bubble. If the focus is moved from the surface outward, the bubble moves towards the liquid–gas interface and it is not able to efficiently eject all the liquid from the target.
关键词： Cavitation bubble,Coupling coefficient,Laser propulsion,Nanosecond laser,Energy-conversion efficiency,Laser ablation
更新于2025-09-23 15:21:01
-
Impact of fourth order dispersion on modulational instabilities in asymmetrical three-core optical fiber
摘要： In this paper we investigate the impact of linear coupling coefficient and coupling coefficient dispersion on modulational instability (MI) in the presence of fourth order dispersion (FOD) in an asymmetric three core optical fiber under normal and anomalous dispersion regime. In addition, we also considered the impact of symmetric and asymmetric power ratio on MI characteristics. It is found that there is significant influence by linear coupling coefficient and frequencies is highly controlled by FOD, but the amplitude of MI gain found to be reduced with increasing FOD under each dispersion regimes. In case of CCD, the impact of FOD found to be quite insensitive and found no MI gain in the absence of CCD under symmetric power ratio under coupling coefficient dispersion (CCD) on MI under different dispersion regimes. In anomalous dispersion regime, at β4 < 0 the generation of smaller MI secondary side bands were observed at higher frequencies while at normal dispersion the effect of FOD leads to breaking of MI gain at different values of coupling coefficient. Though the appearance of the MI gain at different frequencies is highly controlled by FOD, but the amplitude of MI gain found to be reduced with increasing FOD under each dispersion regimes.
关键词： modulational instability,asymmetrical three-core optical fiber,fourth order dispersion,linear coupling coefficient,coupling coefficient dispersion
更新于2025-09-23 15:19:57
-
Crosstalk Limitations due to Intercore Coupling on the BER Performance of an Optical Communication System with Homogeneous Multi-core Fiber
摘要： The effect of crosstalk due to inter-core coupling on the bit error rate (BER) performance of a fiber optic communication link with a homogeneous multi-core optical fiber (MCF) and a direct detection receiver with optical preamplifier is analytically evaluated and presented in this paper. Coupling coefficients due to inter-core coupling in a 7-core MCF is evaluated numerically with as a function of core-to-core distance (pitch) and relative refractive index contrast. Coupling length is determined against various index contrasts and at different core pitches. Crosstalk power, Signal to Crosstalk plus Noise Ratio (SCNR), BER and power penalty at any output core with light launched into other core of a 7-core MCF are determined analytically. The results show that there is mentionable deterioration in BER performance due to coupling induced crosstalk, and system suffers distinct power penalty at a given BER. For example, power penalty at BER of 10e-9 is found to be 4.0 dB and 4.3 dB for a MCF link of 10 km corresponding to relative refractive index difference of 0.0036 and 0.0030, respectively, for a pitch value of 30 μm and core radius of 4.5 μm.
关键词： Bit Error Rate,coupling length,mode coupling,coupling coefficient,multi-core fiber,crosstalk
更新于2025-09-16 10:30:52
-
Improvement of electromechanical coupling coefficient in shear-mode of piezoelectric ceramics
摘要： Shear vibration mode of piezoelectric ceramic has been widely used in energy harvesting for its high electromechanical coupling coefficient (k15) and high piezoelectric constant (d15). In this study, the effects of dimensions on the piezoelectric shear performance of PZT-5A type ceramic were initially studied with ATILA/GiD finite element simulation to improve k15, and verified by experiments. We found out k15 dominantly correlates with the ratio of width to thickness, and dimension optimization was conducted for the first and high order shear vibrations. As a result, a maximum electromechanical coupling coefficient for k15 shear-mode reaching 0.612 was obtained in the first order harmonics. It is worth to note that the dimension ratio for optimized electromechanical coupling factor were in a similar scale regardless of the order of harmonics. In addition to the dimension optimization, the effect of mode coupling between shear vibration mode and unwanted mode was also investigated. The coupling between two vibrations did not only affect electromechanical coupling coefficient but also distorted resonance peak spectrum. Thus, the dimension ratios to avoid mode coupling was provided as the length should far away from the thickness. Finally, the effects of dimensions on mechanical quality factor were examined and the results were discussed. The mechanical quality factor will decrease when the mode coupling happens.
关键词： Electromechanical coupling coefficient,k15 shear-mode,Finite element analysis,Piezoelectric ceramics
更新于2025-09-10 09:29:36
-
Piezoelectric Materials || Piezoelectric Properties and Microstructure of (K,Na)NbO3– KTiNbO5 Composite Lead-Free Piezoelectric Ceramic
摘要： We developed a (K,Na)NbO3-based lead-free piezoelectric ceramic with a KTiNbO5 system, (K1?xNax)0.86Ca0.04Li0.02Nb0.85O3?δ–KTiNbO5–BaZrO3–Co3O4–Fe2O3–ZnO (KNN–NTK composite). This KNN–NTK composite exhibits a very dense microstructure, ε33T/ε0 = 1600, and d33 = 252 pC/N. We found that a portion of the KTiNbO5 converted into K2(Ti,Nb,Co,Zn)6O13 and/or CoZnTiO4. We were able to reproducibly prepare granulated powder of KNN–NTK in batches of 100 kg using a spray-dryer. In addition, we performed a detailed investigation of the microstructure of KNN–NTK composite. The results show that a tetragonal and an orthorhombic phase coexist in a main KNN phase over a wide range of 0.56 ≤ x ≤ 0.75. The granular nanodomains of the orthorhombic phase dispersed within the tetragonal matrix in the KNN phase. A maximum value of kp = 0.56 occurred for x = 0.56. The Na fraction x corresponding to maximum kp was also the minimum x required to generate the orthorhombic phase. We conclude that the KNN–NTK composite exhibits excellent piezoelectric properties because of the two-phase coexisting state. This gentle phase transition of KNN–NTK composite seems to be a relaxor, but the diffuseness degree γ = 1.07 suggests otherwise.
关键词： coupling coefficient,(K,Na)NbO3,microstructure,two-phase coexisting,lead-free
更新于2025-09-09 09:28:46
-
Theoretical improvement of coupling parameters directional fiber coupler using Bessel function
摘要： We have investigated the optimum parameter to fabricate multi fiber of silica material for directional coupler based on fusion and elongation techniques. Coupling coefficient between the fibers was derived by using Bessel function. However, the fusion temperature was experimentally determined as function of elongation speed. Good performance of multi fiber coupler has been obtained for fabrication parameters of fusion temperature and elongation speed of 1350 oC and 125 μm/s respectively. The proposed coupling coefficient shows a better accuracy with empirical one for various coupling length. It is exponentially increased by reducing the distance between fibers. Finally, the microscopic analysis of coupling region deformation has shown that the silica material was well dispersed and distributed.
关键词： Bessel Function,Coupling Coefficient,Fusion temperature and Elongation speed
更新于2025-09-09 09:28:46
-
An advanced technique of fabricating multi silica directional fiber coupler
摘要： We have investigated the optimum parameter to fabricate multi fiber of silica material for directional coupler based on fusion and elongation techniques. Coupling coefficient between the fibers was derived by using Hankel and Bessel function. However, the fusion temperature was experimentally determined as function of elongation speed. Good performance of multi fiber coupler has been obtained for fabrication parameters of fusion temperature and elongation speed of 1350 oC and 125 μm/s respectively. The proposed coupling coefficient shows a better accuracy with empirical one for various coupling length. It is exponentially increased by reducing the distance between fibers. Finally, the microscopic analysis of coupling region deformation has shown that the silica material was well dispersed and distributed.
关键词： Multi silica fiber coupler,coupling coefficient,fusion and elongation techniques
更新于2025-09-04 15:30:14