Admittance Ratio Research Articles

Band edge modulation for high-performance LL-SAW resonators on LiNbO3/SiC by introducing an ultra-thin intermediate oxide layer

With the exploding demand of rapid information transmission, high-frequency acoustic filtering devices are becoming an immediate need. Longitudinal leaky surface acoustic wave (LL-SAW) devices with unique advantages can be a promising platform. In this paper, we introduce a 100 nm intermediate oxide layer into the X-cut lithium niobate on silicon carbide (LiNbO3/SiC) to improve the in-band performance of LL-SAW resonators. First, the dispersion curves of the structures are analyzed by finite element method. In this part, we successfully interpret the intrinsic low quality factor (Q) of LL-SAW on LiNbO3/SiC in general design, and predict the enhancement of Q by introducing an intermediate oxide layer without degradation on spurious response. Then, one port resonators considered in the simulation are fabricated and measured. As a result, enhancements in Bode Q among the whole passband are confirmed. Compared with devices state of art, resonators with leading performances are demonstrated. The fabricated resonators have peak-valley admittance ratio of 63.87 dB, Bode Q of ∼300 at fr and ∼530 at far, keff2of 15.66 % and phase velocity of 6187.3 m/s. Additionally, the resonant frequency of SH1 mode shifts to higher frequency. This work enables the design of next generation high frequency mobile communication filters.

A generalized admittance criterion for dominant harmonic source determination without synchronous phasor measurements

The widespread integration of various nonlinear power electronic devices in modern power systems has made harmonic distortion more serious than ever before. Given the urgent need to improve power quality, the harmonic contribution evaluation (HCE) is of great importance since it can provide a strong basis for harmonic mitigation measures. However, the conventional HCE methods are not effective due to the lack of synchronous voltage and current phasor information in real-field practice. To overcome the phasor limitation, an HCE method based on a generalized admittance criterion (GAC) is proposed in this paper. The proposed GAC aims to determine the dominant harmonic source at the point of common coupling (PCC) from the utility side and customer side. Compared to the conventional method, the developed method only needs the RMS values of the PCC voltage, current, and phase angle difference. Therefore, the synchronous phasor information of voltage and current is no longer required. Meanwhile, a threshold to determine the dominant harmonic source is established by using the equivalent admittance ratio on both sides of PCC. The evaluation process of the proposed method is significantly simplified by comparing the generalized admittance limit with the proposed threshold, which also greatly improves the method evaluation accuracy. Moreover, the interference of background harmonic fluctuation is excluded by using the linear calibration-based harmonic admittance estimation method. Finally, multiple scenarios with various admittance characteristics were simulated to verify the performance of the proposed criterion, and the real-field measurement is also used to demonstrate the accuracy and validity of the proposed method.

Analysis of CNT-based SAW sensor for the detection of volatile organic compounds

This paper presents a multi-layer one-port surface acoustic wave (SAW) sensing device and its response based on the adsorption of different volatile organic compounds (VOCs). The finite element method was used to model and simulate a multi-layered SAW device. A piezoelectric substrate 128ᵒ YX-cut Lithium Niobate (LiNbO3), polyisobutylene (PIB) polymer, and carbon nanotube (CNT) multilayer SAW resonating sensor was modeled and used for generating Rayleigh waves. Electromechanical coupling coefficient (K2), admittance (Y11), S-parameter (S11), and metallization ratio (MR) were computed for the proposed heterostructured device. The sensing properties of proposed SAW sensor was investigated for several organic compounds such as trichloroethylene (C2HCl3), trichloromethane (CHCl₃), acetone (C3H6O), acetonitrile (C2H3N), cyclohexane (C6H12), dichloromethane (CH2Cl2) and diethyl ether (C4H10O). Eigenfrequency analysis of the SAW sensor was evaluated from 100 ppm to 500 ppm gas concentration at room temperature. The observed results were compared with the existing research and found to be more effective in terms of sensitivity.

Analysis of longitudinal leaky surface acoustic waves on bonded structures consisting of similar and dissimilar materials

The propagation and resonance properties of longitudinal leaky surface acoustic waves on structures consisting of a LiTaO3 (LT) thin plate bonded to a quartz (Qz) similar-material bonded structure were investigated theoretically. It was found by surface acoustic wave (SAW) propagation analysis that a small attenuation can be obtained by combining an LT thin plate and a Qz similar-material bonded structure with appropriate Euler angles. Furthermore, regarding SAW resonance analysis, resonances with admittance ratios exceeding 50 dB and Q factors exceeding 1000 were obtained in the LT/Qz/Qz bonded structure. Such a small propagation loss and high Q can be obtained with a larger LT plate thickness than in the case of the LT/Qz bonded structure.

New method for determining time constant of resistors.

We report a new method for determining the time constant of ac resistors with values around 10 kΩ using a digital impedance bridge for the comparison of two nominally equal resistors. This method involves adding a probing capacitor in parallel to one of the resistors to induce a quadratic frequency dependence in the real component of the admittance ratio between the two resistors. The magnitude of this quadratic effect is proportional to the self-capacitance of the unperturbed resistor, enabling us to determine its value and the associated time constant with an estimated standard uncertainty (k = 1) of 0.02 pF and 0.2ns, respectively.

Chronic Noise Affects Middle Ear Resonance and Absorbance in Industrial Workers.

The effect of chronic noise on the middle ear is not fully known. This study aimed to evaluate the middle ear functions of metal workers exposed to chronic noise using wideband tympanometry. In this study, 62 male workers exposed to chronic noise and 30 healthy men were included. Workers exposed to chronic noise were divided into 2 groups according to their pure tone averages. Totally 30 workers (60 ears) with pure tone average less than 20 dB were included in group I, and 32 workers (64 ears) with pure tone average more than 20 dB were included in group II. All individuals were subjected to wideband tympanometry. Tympanometric peak pressure, equivalent ear canal volume, static acoustic admittance, resonance frequency, and absorbance ratios at peak pressure and ambient pressure values were analyzed. There was no difference between the groups in terms of traditional tympanometric parameters such as tympanometric peak pressure, equivalent ear canal volume, and static acoustic admittance (P >.05). Resonance frequency of workers exposed to chronic noise (group I and group II) was lower than the control group (P <.05). The absorbance ratios of workers exposed to chronic noise at approximately 4 kHz were lower in both peak pressures and ambient pressures (P <.05). Chronic noise does not only damage the inner ear but also causes changes in the middle ear structures. Wideband tympanometry can be used to detect minor auditory damage due to noise that cannot be detected by audiogram early. In this way, necessary measures can be taken in the early period before noise-induced hearing loss occurs.

Analysis of longitudinal leaky surface acoustic waves on quartz thin plate bonded to similar-material substrate

The propagation and resonance properties of longitudinal leaky surface acoustic waves (LLSAWs) on bonded structures consisting of a quartz (Qz) thin plate and a Qz support substrate with different Euler angles were investigated theoretically. By using both an X-cut Qz thin plate and a Qz support substrate with optimal Euler angles, we obtained LLSAWs with a larger coupling factor, a smaller attenuation, and a lower temperature coefficient of frequency than those on a single Qz substrate. Furthermore, from the resonance properties simulated by the finite element method, the bonded structures were found to exhibit a large admittance ratio and a high quality factor, which could not be obtained when using a single Qz substrate; the bandwidth, however, was as small as 0.016%–0.086%.

A convex problem optimization solution for information management in edge computing platforms

AbstractIntelligent computing and social optimization techniques have been used to manage mobile edge (ME) environments for pervasive services. However, the service demand is the prime cause for requiring flawless information management. This article proposes a coherent information management (CIM) process for resolving the convex optimization problems by considering the flaws in raw information management. The information management problem for pervasiveness is defined as a nonlinear problem for user‐to‐information availability. According to the CIM, pervasive convergence is identified for the available information. Furthermore, convolutional neural learning identifies unavailable or utilized information between the service provider and the end‐user layers. This identification improves the training rate for convergence improvement and information coherency. Therefore, the nonlinear pervasiveness is distributed between different service providers, improving efficiency. Therefore, the proposed optimization method achieves a 7.4% high admittance ratio, 8.28% high utilization, 25.25% less allocation time, and 24.4% less waiting time for different availability ratios for different information availability ratios.

Efficiency of room acoustic simulations with time-domain FEM including frequency-dependent absorbing boundary conditions: Comparison with frequency-domain FEM

Recent wave-based room acoustic simulations in the time domain can incorporate frequency-dependent absorbing boundary conditions (BCs), by which time responses including a broad frequency component are calculable with a single computational run. However, their performance over the frequency-domain method remains poorly understood. This paper presents a discussion of the capabilities of a recently developed implicit time-domain finite element method (TD-FEM) for room acoustics simulation by comparison with a fourth-order accurate frequency-domain FEM (FD-FEM). First, the implicit TD-FEM accuracy is examined via an impedance tube problem, having frequency-dependent absorbing BCs at the tube end, where a specific acoustic admittance ratio of rigidly backed porous sound absorbers is imposed. Results indicate that the implicit TD-FEM has the same solution convergence rate as that of FD-FEM. The solution converges to the FD-FEM solution when using a sufficiently small time interval. A performance comparison of both methods is then made using two real-scale 2D room acoustic problems in an office room and a complexly shaped concert hall. Numerical results show that the implicit TD-FEM can be useful for acoustic simulation in practical-sized rooms at broad frequency ranges with markedly smaller computational costs than those of FD-FEM while maintaining similar accuracy.

Analysis of leaky surface acoustic waves on quartz thin plates bonded to similar-material substrate

The propagation and resonance properties of a leaky surface acoustic wave (LSAW) on quartz thin plates bonded to a similar-material substrate are investigated theoretically. The electromechanical coupling factor K 2 on Z-cut quartz (Z–Q) thin plates bonded to an AT-cut 0°X-propagating quartz (AT0°X-Q) support substrate is calculated to be 0.43%, which is approximately three times larger than the maximum value of a single quartz substrate. A positive temperature coefficient of frequency for LSAW can be produced on a quartz thin plate bonded to a quartz substrate with a different cut angle. By the finite element method, the aluminum thin-film thickness dependence of the resonance properties of LSAW on LST-cut quartz (LST-Q) and LST-Q/AT0°X-Q is analyzed. In the simulation with the optimal Al thin-film thickness, the admittance ratio on the LST-Q/AT0°X-Q is found to be larger than that for the single LST-Q.

Hierarchical virtual inertia control of DC distribution system for plug-and-play electric vehicle integration

DC distribution system will play a significant role in future urban distribution system, while the integration of electric vehicle has a tremendous influence on the stability of DC distribution system. This paper presents an assessment and mitigation strategy of such negative impact on DC distribution system. Mathematical modelling and analysis of the load/source admittances are provided to evaluate the overall system stability based on the Nyquist admittance ratio criterion. The theoretical analysis shows that the integration of electric vehicle introduces incremental negative admittances which significantly degrades the system stability. Therefore, a hierarchical virtual inertia control strategy, consisted of a local-level control and a system-level control, is proposed to improve the system damping and suppress the negative influence. The local-level virtual inertia control can suppress the instability caused by electric vehicle integration, while the disturbance caused by the fluctuations of other DC loads or sources can be suppressed by the system-level virtual inertia control. Numerical examples verify the effectiveness of the method, which can improve the stability of DC distribution system and satisfy the requirement of electric vehicle plug-and-play.

Planar Reconfigurable Balanced Rat-Race Coupler With Improved Amplitude Imbalance Performance and Common-Mode Noise Absorption

In this article, the design method for absorptive balanced rat-race couplers with reconfigurable power-dividing ratio is proposed for the first time. First, the differential-mode (DM) and common-mode (CM) port equivalent impedances of the eight-port balanced network is derived by the even–odd mode method under the mixed-mode isolation and matching conditions. The power-dividing ratio is tuned by changing the admittance ratio of the network components, which greatly extends the amplitude imbalance bandwidth. Then, a nonabsorptive reconfigurable balanced rat-race coupler that consists of transmission lines with adjustable characteristic impedance is proposed. Furthermore, based on the derived DM and CM port equivalent impedances, an absorptive network is designed. Finally, the absorptive reconfigurable balanced rat-race coupler is achieved by attaching the absorptive network at the balanced ports of the designed nonabsorptive reconfigurable balanced rat-race coupler. For verification, the 2-GHz nonabsorptive and absorptive reconfigurable balanced rat-race couplers are designed and measured. The measured results agree well with the simulations. For the nonabsorptive coupler, the measured power-dividing ratio is tuned from −8.5 to 8.9 dB, while the 15-dB DM matching and isolation bandwidth is greater than 370 MHz. For the absorptive coupler, the measured power-dividing ratio is tuned from −8.3 to 9.0 dB, while the 15-dB DM matching and isolation bandwidth and 15-dB CM matching bandwidth are greater than 450 and 1150 MHz, respectively. The measured 0.5-dB amplitude imbalance bandwidths of the nonabsorptive and absorptive couplers are 6%–14.5% and 7%–15.6%, respectively.

Analysis of longitudinal leaky surface acoustic waves on LiNbO3/amorphous layer/quartz structure

Recently, bonded structures comprising a quartz substrate and a LiNbO3 (LN) or LiTaO3 thin-plate have been attracting attention as a means of obtaining enhanced properties for surface acoustic wave (SAW) devices. It was reported that the bonding strength was extremely improved by utilizing an amorphous thin film as a middle layer. In this research, the propagation and resonance characteristics of longitudinal leaky SAWs on an amorphous layer inserted to the boundary between an X-cut 36°Y-propagating LN (X36°Y-LN) and X35°Y-quartz were investigated. For the metallized surface of an X36°Y-LN/Al2O3/X35°Y-quartz structure, an attenuation of 0.0001 dB /λ was obtained at an LT thin-plate thickness of 0.072λ (λ: wavelength), which was better than that of an X36°Y-LN/X35°Y-quartz structure. Utilizing a finite element method, we found that the admittance ratio and Q factor for the X36°Y-LN/Al2O3/X35°Y-quartz model were improved owing to the reduction of the leakage due to the shear-vertical particle displacement.

Analysis of leaky surface acoustic waves on LiNbO3 or LiTaO3 thin plate bonded to similar-material substrates

To obtain a bonded structure with low attenuation for leaky surface acoustic waves (LSAWs), the propagation and resonance properties of LSAWs on a similar-material thin plate bonded to a LiTaO3 (LT) or LiNbO3 (LN) support substrate were theoretically analyzed. It was found that zero attenuation can be simultaneously obtained for free and metallized surfaces by utilizing the similar-material bonded structure but not when using a single structure. For a 10°YX-LN/66°YX-LN structure, the antiresonance Qa and the admittance ratio of the bonded structure were 1570 and 99 dB, respectively, even taking into consideration a mechanical loss of 1/Qm = 10−3, and were higher than those of a single LN structure. For a YX-LT/36°YX-LT structure, we observed the same or less attenuation and an approximately 1.3 times higher coupling factor than those for a single 36°YX-LT structure. The LT similar-material bonded structure had slightly superior resonance properties to the single structure.

Novel Approach for Center Frequency and Bandwidth Tuning in Multimode Resonator Based Microstrip Dual-Mode Bandpass Filter

In this paper, a novel approach for both center frequency and bandwidth tuning in a dual mode bandpass filter is demonstrated. The proposed filter is configured from a half wavelength multimode resonator structure. The Ultra-wide bandpass response of the multimode resonator is extracted using an inter-digital feed structure which provides good input/output coupling. By deploying stepped admittance structure perturbation element into the symmetrical plane of the multimode resonator, the dual-mode response is achieved with three upper stopband transmission zeros (TZs). The coupling between two degenerative mode frequencies is controlled by the admittance ratio (Y) of the stepped admittance structure. Changing admittance ratio (Y) of stepped admittance structure, resulted in the change in even mode resonance frequency and location of three upper stopband transmission zeros while keeping odd mode frequency fixed. The proposed filter has a size of 14.0 x 30.0 mm2.

Novel Approach For Center Frequency And Bandwidth Tuning In Multimode Resonator Based Microstrip Dual-Mode Bandpass Filter

Abstract This paper demonstrates a novel approach for both center frequency and bandwidth tuning in dual mode Bandpass filter. The proposed filter is configured from a half wavelength multimode resonator structure. The Ultra-wide bandpass response of multimode resonator is extracted using an inter-digital feed structure which provides good input/output coupling. By deploying stepped admittance structure perturbation element in to the symmetrical plane of multimode resonator, dual-mode response is achieved with three upper stop band transmission zeros(TZs). The coupling between two degenerative mode frequencies is controlled by admittance ratio Y of stepped admittance structure. Changing admittance ratio(Y) of stepped admittance structure, results in change in even mode resonance frequency and location of three upper stop band transmission zeros while keeping odd mode frequency fixed. Proposed filter has size of 14mm*30mm.

Longitudinal leaky surface acoustic wave with low attenuation on LiTaO3 or LiNbO3 thin plate bonded to quartz substrate

To obtain a bonded structure with low attenuation for longitudinal leaky surface acoustic waves (LLSAWs), the propagation and resonance properties on a LiTaO3 (LT) or LiNbO3 thin plate bonded to an X-cut quartz substrate were theoretically analyzed. The attenuation of an X-cut 31°Y-propagating LT (X31°Y-LT)/X32°Y-quartz (X32°Y-Q) was calculated to be 0.0005 dB/λ at the normalized LT thin plate thickness h/λ = 0.062 (λ: wavelength) and was lower than that on an X31°Y-LT/AT45°X-Q. Using a finite element method, for the X31°Y-LT/X32°Y-Q, the admittance ratio and Q factor were improved to 120 dB and 53 400 from 62 dB and 1000 for the X31°Y-LT/AT45°X-Q, respectively. Then, the propagation and resonance properties were measured. For the X31°Y-LT/X32°Y-Q, the measured electromechanical coupling factor (K2) and Q factor increased to 5.6% and 280 from 1.8% and 32 for the single LT, respectively. The temperature coefficient of frequency of the LLSAW was measured to be −26.2 ppm °C−1.

Static Voltage Stability Analysis of Distribution Systems Based on Network-Load Admittance Ratio

It is well known that a single (constant power) load infinite-bus system reaches a static voltage stability limit point, or equivalently, a singularity point of the power flow Jacobian, at the unity line-load admittance ratio, i.e., the equivalent admittance of the load has the same modulus as the transmission line admittance. In this paper, we rigorously extend this result to generic distribution systems with distributed generators (DGs). We introduce a new concept called the network-load admittance ratio that is in terms of the parameters of power network, loads, and DGs. This concept is a generalization of the line-load admittance ratio that characterizes the loading status of a distribution system with the effects of DGs included. We prove that the power flow Jacobian is singular if and only if the network-load admittance ratio is unity, which provides new insights into the mechanism of voltage stability. In addition, we establish a new voltage stability index by using the network-load admittance ratio. Numerical simulations on several IEEE test systems show that the index has good linearity with load increase and estimates voltage stability margin with high precision. The index also reflects the impact of DG penetration level and control mode on voltage stability. The obtained results can be extended to ZIP load models, unbalanced three-phase networks, and mesh networks with slight modifications.

Research on influencing factors and improving methods for DC distribution system stability

In this paper, the Nyquist admittance ratio criterion was used to analyse the influencing factors on the stability of the system, such as the parameters of DC line, the intensity of interconnected AC power grid, the droop coefficient and etc. The theoretical analysis showed that the increase of the DC line resistance would decrease the system stability margin, while the increase of the DC line inductance had small effect on the system stability margin; the weaker the gird intensity was, the smaller the system stability margin was, while the larger the droop coefficient was, the larger the system stability margin was. In the case that AC and DC line parameters were the same, the system stability margin under U dc-I dc droop control mode was larger than that under U dc-P droop control mode. According to these influencing factors, suggestions were given to improve system damping and system stability through reducing the impedance of DC line, enhancing the interconnection of AC power grid and optimising the droop coefficient. Finally, a detailed simulation model was built with DIgSILENT simulation tool to verify the correctness of the above theoretical analysis by time-domain simulation results.

Phase‐reshaping strategy for enhancing grid‐connected inverter robustness to grid impedance

As the grid inductor increases the phase difference between the inverter admittance and the grid admittance increases at their intersection frequency showing that the harmonic amplification coefficient is enhanced. When the phase difference exceeds 180° the admittance ratio cannot satisfy Nyquist criterion and the system becomes unstable. To address this problem a phase-reshaping strategy aiming to revise the phase of the inverter admittance in a wide frequency region without using any real-time information referring to the grid impedance or the resonant frequency is proposed. The strategy is realised by the combination of the feedforward of the voltage at the point of common coupling (PCC) and the harmonic compensators. In the feedforward, a phase lag network is employed to modify the admittance phase in a wide frequency region. The harmonic compensator in parallel to the current controller is used to offset the magnitude rise brought in by the PCC voltage feedforward. After adopting the proposed strategy, the upper limit of the phase difference is constrained at 150° and the magnitude of the inverter admittance is lower than that of the original one at low-order odd-harmonic frequency. The validity of the proposed strategy is verified by the experimental results.