Papers by Keyword: Quality Factor

Abstract: In this study, we investigate the sensitive photonic crystal sensor formed by the coupling between two photonic crystals containing a superconducting layer. We consider TE polarization and normal incidence for the analysis presented in this work. Our study shows that the cavity mode resulting from this coupling is strongly dependent on the temperature of the superconductor layer. The effect of the temperature of the superconducting layer and thicknesses on the quality factor is examined. The results show that the sensor superconducting structure gives a high quality factor. This structure can be used to realize a highly sensitive photonic crystal sensor.

Abstract: This study investigates the fabrication of a cylindrical dielectric resonator antenna (CDRA) using ceramic microwave dielectric composites as a resonator. The composites (1-x) Li₃MgNbO₅-(x) Sr₃V₂O₈ (x=0.25-0.40) have been synthesized via the conventional solid-state reaction method, incorporating 1% B₂O₃ to lower the sintering temperature. The 0.70-0.30 composite exhibited optimal microwave dielectric properties with a dielectric constant (ε_r) of 19.20, a quality factor (Q x f) of 3738 GHz, and a temperature coefficient (τ_f)of -43 ppm/°C. These characteristics render the 0.70-0.30 composite suitable for CDRA applications. The experimentally obtained microwave dielectric parameters were used to simulate the CDRA design using the High-Frequency Structure Simulator design software. A single-feed cylindrical antenna has been fabricated using this composite material as a resonator with a radius × height of 5×6 mm², mounted on an FR4 substrate measuring close to 25×25×1.6 mm³ and Cu strip as a feed line. The simulated and experimentally measured parameters, including S11, voltage standing wave ratio, and radiation pattern, demonstrated excellent agreement, validating the composite's efficacy for antenna design.

Abstract: The influence of sintering temperature on the microwave dielectric properties and microstructure of the (1-y)Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃-yCa_0.8Sr_0.2TiO₃ ceramic system were investigated with a view to their application in microwave devices. The (1-y)Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃-yCa_0.8Sr_0.2TiO₃ ceramic systems were prepared using the conventional solid-state method. The X-ray diffraction patterns of the (1-y)Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃-yCa_0.8Sr_0.2TiO₃ ceramic system shifted to higher angle as y increased. A dielectric constant of 38.2, a quality factor (Q×f) of 53,500 GHz, and a temperature coefficient of resonant frequency of-3 ppm/°Cwere obtained when the 0.4 Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system was sintered at 1600 °C for 4h.

Abstract: We fabricated electrostatically-excited single-crystalline 4H-SiC microcantilever resonators with various thicknesses and lengths. Their resonant characteristics were investigated from room temperature (RT) up to 600°C. The resonant frequency of the cantilevers decreased with increasing temperature. From the results, the temperature dependence of Young’s modulus of single-crystalline 4H-SiC was obtained, i.e., 3% decrement with increasing temperature from RT to 600°C. The cantilevers with different thicknesses showed different temperature dependences of the quality factor. A 2-μm-thick cantilever exhibited a high quality factor (Q) (250,000) at RT and the Q decreased to 6,000 at 600°C, which can be explained by thermoelastic damping. On the other hand, a Q of a 0.45-μm-thick cantilever was still high (50,000) even at 600°C.

Abstract: Printed antennas fabricated using conductive ink printed on flexible substrate is low-cost and environmental friendly. The inductance and the quality factor are two important parameters for designing RFID antenna and were studied for the printed RFID antennas. The results show that the inductance is not only determined by the size of the designed RFID antenna but also related to the resistance of the printed antenna coils. The inductance increases with the increasing testing frequency, while the Q value decreases with the increasing testing frequency. The soft magnetic ink prepared with γ-Fe₂O₃ was used to enhance the inductance of the printed antennas with printing technology. The inductance of the printed antenna with the magnetic core layer is increased by 5.7% at 13.56 MHz.

Abstract: MEMS resonator represents currently one of the important research areas of Microelectromechanical Systems (MEMS). The usual applications of MEMS resonators are the radio-frequency electromechanical devices, MEMS gyroscopes and resonant sensors. The main part of a MEMS resonator is the mechanical vibrating structure that can be fabricated as microcantilevers, microbridges or in a more complex configuration as micromembranes. The scope of this paper is to investigate the dynamic behavior of an electrostatically actuated MEMS cantilever under different oscillating modes in order to determine the resonant frequency, amplitude and velocity of oscillations. Moreover, based on the resonant frequency experimental curves, the quality factor for different oscillating modes is determined. The effect of operating conditions on the frequency response of investigated microcantilever is monitored. As a consequence, the experimental tests are performed both in ambient conditions and in vacuum. The dynamic response of microcantilever in vacuum is influenced by the intrinsic dissipation energy and the sample behavior in air depends on the intrinsic losses as well as the extrinsic dissipation energy.

Abstract: By analyzing three-point oscillator of inductance feedback with the loss resistance of the inductor,we found the loss resistance of the inductor is a major factor in affecting circuit performance. Negative resistance in series with loss resistance can offset the impact of the loss resistance in the circuit. Oscillation circuit Start-up easilier. The quality factor Q increases and the selectivity is better.The oscillation shape closer to the ideal oscillator.

Abstract: The variation of soft magnetic properties of Sendust powder cores as a function of annealing temperature has been investigated. Toroid-shaped Sendust powder cores were prepared from Fe-Si-Al powder by machine pulverizing and subsequent cold pressing using inorganic insulating layer and organic binders, respectively. The influence of different compaction pressures and various annealing temperature on effective permeability and quality factor was investigated. Sendust powder cores using inorganic salt as insulating layer exhibit high effective permeability ( μ_e>110) up to 1 MHz, showing excellent frequency stable characteristics and high quality factor (Q>80) at 50 kHz. The optimized annealing temperature is 953K.

Abstract: Doping as one of the popular methods to manipulate the properties of nanomaterials has received extensive application in deriving different types of graphene derivates, while the understanding of the resonance properties of dopant graphene is still lacking in literature. Based on the large-scale molecular dynamics simulation, reactive empirical bond order potential, as well as the tersoff potential, the resonance properties of N-doped graphene were studied. The studied samples were established according to previous experiments with the N atom’s percentage ranging from 0.38%-2.93%, including three types of N dopant locations, i.e., graphitic N, pyrrolic N and pyridinic N. It is found that different percentages of N-dopant exert different influence to the resonance properties of the graphene, while the amount of N-dopant is not the only factor that determines its impact. For all the considered cases, a relative large percentage of N-dopant (2.65% graphitic N-dopant) is observed to introduce significant influence to the profile of the external energy, and thus lead to an extremely low Q-factor comparing with that of the pristine graphene. The most striking finding is that the natural frequency of the defective graphene with N-dopant’s percentage higher than 0.89% appears larger than its pristine counterpart. For the perfect graphene, the N-dopant shows larger influence to its natural frequency. This study will enrich the current understanding of the influence of dopants on graphene, which will eventually shed lights on the design of different molecules-doped graphene sheet.

Abstract: In this work, SiO₂ has been selected to be introduced into the system to improve the high-frequency magnetic properties of Ba_1.5Sr_1.5Co₂Fe₂₄O₄₁ hexaferrites. The influence of SiO₂ additive on the phase composition, microstructures and high-frequency magnetic properties of the samples prepared by solid-state reaction were investigated. The results indicate that the major phase of doped samples is Z-type ferrite. The addition of SiO₂ causes a decrease of the average grain size. Permeability measurements indicate that SiO₂ doping significantly improves the magnetic characteristics of those samples. With the doping content of SiO₂ increasing from 0 to 8wt%, the initial permeability decreases from 5.8 to 2.6, and the cut-off frequency rises up from 1.5GHz to over 1.8GHz. Meanwhile, the quality factor of the samples sintered at 1200°C varies with the SiO₂ content, and a maximum quality factor at 1GHz of Q=14 was found for x=4wt%. The improvements of magnetic properties and the high quality factors are crucial for applications of Z-type hexaferrites in high-frequency communication systems.