Resonance Frequency Difference Research Articles

Frequency drift insensitive broadband wireless power transfer system

The resonant frequency of coils in a four-coil magnetic coupling resonance wireless power transfer (MCR-WPT) system has a direct impact on transfer coefficient. For efficient power transfer, most of the systems operate at high-Q resonant state, causing a narrow bandwidth and reducing the system tolerance to resonant frequency deviation. To deal with the problem, a four-coil MCR-WPT system characterized with broadband performance is investigated. Based on the equivalent circuit, the transfer coefficient and the input impedance are firstly calculated. The transfer characteristic at different resonant frequency under different transfer distances is discussed. By comparing the number and variance of the extreme values of transfer coefficient under different resonant frequencies, the resonant frequency for excellent broadband transmission is determined. To validate the broadband performance, frequency drift caused by capacitance variations is investigated at the resonant frequency of 19 MHz under the transfer distance of 45 mm. The results indicate that the MRC-WPT system generally maintains broadband transmission and the transfer coefficient at the excitation frequency of 19 MHz remains above 0.9 when the resonant frequency is deviated. Experiments have been performed to validate the excellent broadband performance. The results are generally consistent with the simulation analysis.

Effects of bracings and motion coupling on resonance features of semi-submersible platform under irregular wave conditions

Resonance is a critical consideration in the design of offshore floating structures. This paper aims at analysing the nonlinear effects of bracings and motion coupling on the resonance features of a semi-submersible platform. An improved mathematical model based on potential theory is proposed to simulate the motion response of a semi-submersible platform under irregular wave conditions, considering both the variations of hydrostatic and hydrodynamic forces induced by the bracings entering and exiting the water and the nonlinear coupling induced by the platform motions. For comparison purposes, numerical simulations are also performed using a mathematical model without considering the aforementioned effects. Validated by results of wave basin tests and numerical simulations, the proposed model performs much better in capturing the characteristic resonance features of pitch motion in low-frequency region. The nonlinear hydrostatic effect of bracings leads to the increase of resonance frequency as the motion amplitude increases, while the hydrodynamic force on the bracings and the nonlinear motion coupling only influence the amplitude of resonance spectral peak. In addition, factors influencing the nonlinear effects such as the vertical position and diameter of bracings and the pitch restoring coefficient are further investigated. It is revealed that the deviation of pitch resonance frequency has evident dependence on the ratio between nonlinear and linear volumetric variations, and an empirical formula estimating the resonance frequency is proposed using the observed dependence. Theoretically, both smaller bracing radius and larger pitch restoring coefficient are beneficial for suppressing the resonance induced by the nonlinear effects. The proposed model can be an effective tool for predicting the motion response, and the understanding of the resonance features is helpful for the design of semi-submersibles.

Research on Linear Vibration Feeder Driven by Langzhiwan Oscillator

In order to overcome the shortcomings of electromagnetic interference and noise of electromagnetic vibration feeder, a linear feeder driven by Langzhiwan oscillator is designed, its working principle is analyzed, and the prototype of feeder is tested. The experimental results show that the resonant frequency of feeder is 17.5 kHz, the amplitude is 28μm when the driving source voltage is 200 V. The transmission speed of M2 nuts is 102 mm/s, and the feeder has the ability to transport materials in the frequency range of 17.1 kHz to 17.9 kHz. In addition, with the increase of voltage, the conveying speed increases linearly, and the conveying performance is greatly weakened due to the deviation of resonance frequency.

Foreign Object Detection in Inductive Charging Systems Based on Primary Side Measurements

A foreign object detection (FOD) method for inductive charging systems is introduced in this article. The proposed FOD only requires primary side measurements, i.e., primary resonant current and resonance frequency deviation. The proposed FOD incorporates a mechanism for effective discrimination of foreign object intrusion, horizontal and vertical alignment variations of the transmitter and receiver magnetic pads. Alignment variations of primary and secondary magnetic pads as well as intrusion of conductive/magnetic foreign object both impact electromagnetic characteristics, consequently the resonant frequency. FOD for large size objects works properly based on resonance frequency deviation, however, there is the need for discrimination between the FOD for small objects and misalignment. Thereby, both disturbances can be detected by online monitoring of the resonance frequency deviation, and be discriminated from each other by real-time measurement of the primary current. The proposed FOD technique can be added as a protection scheme to the self-tuning controllers of inductive power transfer (IPT) systems operating off its resonance frequency. Finite element analysis along with theoretical formulation of the studied IPT circuit is presented using the proposed method. Conductive FOD method based on frequency deviation and discrimination method using primary resonance current are implemented on an IPT setup, and the experimental results verify its effectiveness in both standby and full-power modes. The test results show that the frequency deviation based FOD method has a high speed in detection of even small scale objects such as a coin.

Single-Cycle-Lag Compensator-Based Active Damping for Digitally Controlled LCL/LLCL-Type Grid-Connected Inverters

The control delay weakens the active damping (AD) performance of digitally controlled LCL/LLCL -type grid-connected inverters (GCIs). The equivalent virtual impedance paralleled with the filter branch explains the effect of the capacitor-current-feedback AD. However, the virtual impedance appears capacitive or even negative due to the delay, which significantly weakens the effectiveness of AD. This paper proposes a single-cycle-lag compensator (SCLC) to eliminate the adverse effects caused by the control delay. The method retains effectiveness in applications with high resonant frequency or large control delay. It keeps system a positive equivalent resistance with a high equivalent inductance. The positive equivalent resistance leads to positive damping effect, while the high equivalent inductance causing little resonant frequency deviation can be neglected. Moreover, the effect of the impedance variation that causes the resonant frequency deviation is analyzed and the restrictions of the proposed method are discussed. By optimizing the LCL/LLCL filter parameters, the adaptability of the SCLC to the grid impedance variation can be further improved. With the SCLC, the LCL/LLCL -type GCIs achieve better steady-state and dynamic performances. Finally, experimental results are presented to verify the proposed method.

A method of determining microwave dissipation of Josephson junctions with non-linear frequency response

Based on Josephson junction (JJ), superconducting quantum bit (qubit) is operated at frequencies of several GHz. Dissipation of JJs in this frequency range can cause energy relaxation in qubits, and limit coherence time, therefore it is highly concerned and needs to be determined quantitatively. The dissipation of JJs can be quantified by microwave quality factor. It is usually done at very low temperature (~mK) to determine whether a JJ is suitable for qubit devices by measuring the quality factor. In this paper, a method based on nonlinear frequency response of JJs is proposed to determine the quality factor. This method can be used in thermal activation regime, which may bring great conveniences to experiments. To analyze high frequency properties of JJs, the dynamic equation of a current-biased JJ, which describes high frequency oscillation of the JJ, is introduced. A fourth-order potential approximation is used to obtain the analytical equation of non-linear response. The dependence on quality factor, as well as on amplitude, of difference between JJ’s plasma frequency and resonant frequency, is derived from the equation. The approximate treatment is quantitatively validated by our numerical simulations with practical JJ parameters including different environment influences. Thus, based on nonlinear frequency response of JJs, a reliable and simple method to determine quality factor of JJ is proposed, which is desirable for exploring JJ based microwave devices such as parametric amplifier, superconducting qubit. Being driven well into the nonlinear microwave response regime, due to frequency-amplitude interaction, the resonant frequency of a current bias JJ deviates from the JJ’s plasma frequency. The deviation is directly related to the microwave quality factor. Hence, the quality factor can be deducted from the experimental measurement of the resonant frequency deviation, with different microwave power values applied. In comparison with linear resonance experiment, the nonlinear resonance used by the proposed method produces stronger signal. Therefore it is more robust against external noise. When being conducted at high temperature, the proposed method is more reliable. The accuracy of the measured quality factor primarily depends on those of the JJ’s parameters such as critical current and capacitance, while those parameters can be experimentally determined with high precision.

Dynamic liquid level detection method based on resonant frequency difference for oil wells

The dynamic liquid level of an oil well can be used to determine the oil production strategies and analyze the reservoir performance. Therefore, it is important to measure the dynamic liquid level in an oil field. This paper proposes a novel dynamic liquid level measurement method for oil wells, where the resonant frequency difference (RFD) of the resonant acoustic signal in annular is used to calculate the dynamic liquid level. To solve the noise interference problem in the resonant acoustic signal, a spectral fast Fourier transform (FFT) method based on Welch power spectrum is proposed to obtain the RFD. First, the Welch power spectrum approach is employed to process the resonant acoustic signal, and a high-pass filter is designed to filter the inherent envelope of low frequency in the power spectrum. In particular, a clear and smooth power spectrum can be obtained by choosing a suitable window and a sectional length. Furthermore, the short-time Fourier transform method is used to extract the strongest energy spectrum of the power spectrum. Finally, the RFD of two adjacent resonant harmonics can be accurately obtained by using FFT for the strongest energy spectrum. Experimental results show the effectiveness of the proposed approach.

Effect of Substrate Scaling on Microstrip Patch Antenna Performance

The Maxwell field equations (MFEs), as ecumenical model of electromagnetic phenomena, are scale-invariant under Lorentz Transformation (LT). To apply LT, some considerations are required which are not all practically available or technologically attainable; hence, the scale-invariant feature may not be reached effectively. Paving the way to focus on this issue, the effect of substrate thickness scaling as an uncontrollable parameter, is explored on eight identical patch antennas with different substrate thicknesses. In this way, the resonant frequency and complex value of return loss are measured. The effect of manufacturing tolerances of dielectric thickness on resonant frequency deviation and return loss magnitude are carefully studied, too. Also the unwanted distortive effect of selected electrical connection, say as a female SMA connector, is investigated at higher frequencies. The obtained results are comparatively analyzed which confirm the practical bottlenecks in meeting the antenna parameters scaling.

Increased multiplexing of superconducting microresonator arrays by post-characterization adaptation of the on-chip capacitors

We present an interdigitated capacitor trimming technique for fine-tuning the resonance frequency of superconducting microresonators and increasing the multiplexing factor. We first measure the optical response of the array with a beam mapping system to link all resonances to their physical resonators. Then, a new set of resonance frequencies with uniform spacing and higher multiplexing factor is designed. We use simulations to deduce the lengths that we should trim from the capacitor fingers in order to shift the resonances to the desired frequencies. The sample is then modified using contact lithography and re-measured using the same setup. We demonstrate this technique on a 112-pixel aluminum lumped-element kinetic-inductance detector array. Before trimming, the resonance frequency deviation of this array is investigated. The variation of the inductor width plays the main role for the deviation. After trimming, the mean fractional frequency error for identified resonators is −6.4 × 10−4, with a standard deviation of 1.8 × 10−4. The final optical yield is increased from 70.5% to 96.7% with no observable crosstalk beyond −15 dB during mapping. This technique could be applied to other photon-sensitive superconducting microresonator arrays for increasing the yield and multiplexing factor.

Single-Layer Frequency Selective Surface With Angular Stability Property

In this letter, a single-layer frequency selective surface (FSS) with high angular stability is proposed. By combining two modified cross loops, the proposed combined FSS (CFSS) element is obtained. Due to the rotationally symmetrical structure, the CFSS is insensitive to the TE or TM polarizations incidence. By the combination, the angular stability property is achieved that the maximum resonant frequency deviation is 0.08 GHz when the incident angle ranges from 0° to 85°. The mechanism of the CFSS is studied by both the equivalent circuit model and numerical analysis. A prototype is manufactured and measured in an anechoic chamber to verify the theoretical analysis. The simulated and measured results have good agreements, and all the performances are proved.

A Low-Profile Angle-Insensitive Bandpass Frequency-Selective Surface Based on Vias

In this letter, a low-profile bandpass frequency-selective surface (FSS) that is independent of incident angle and polarization is proposed. This FSS is composed of two identical metallic convoluted cross slot layers with vertical metal vias. The whole structure is ultrathin with a thickness of $0.042\lambda$ , where $\lambda$ represents the resonant wavelength in free space. This FSS works as a spatial bandpass filter and exhibits great resonant stability with incident angle ranging from 0° (normal incident) to 75° for both transverse electric (TE) and transverse magnetic (TM) polarizations. At 75° oblique incidence, the resonant frequency deviation is about 0% and 2.02% for TE and TM polarizations, respectively. To verify the design, a prototype of the FSS was fabricated. The measured transmission responses agree reasonably with that of the simulated ones.

Energy Leakage and Characteristic Analysis of HMSIW and Implement in Multi-layered Structure Equalizer Design

The phase constant and attenuation constant of half mode substrate integrated waveguide (HMSIW) are calculated using an improved quicker multi-line method in this paper. A mathematical method is proposed to analyze the energy leakage of HMSIW theoretically. The radiation and leakage character of electromagnetic field at open face of HMSIW is different with different relative permittivity. An equalizer loaded multi-layered HMSIW resonant cavities is proposed based on the energy leakage excitation without external coupling structure. Compared with the other planar circuits, these structures have superiorities of small size, simple structure, low loss and high Q, suitable for the miniaturization development, and are easily integrated with other circuits. Furthermore, this proposed equalizer has a simpler design procedure than other HMSIW equalizers without resonant frequency deviation.

High‐accuracy multi‐rate implementation of resonant integrator using FPGA

Second-order generalised integrator or resonant integrator (RI) has wide range of applications. Forward and backward Euler's approximation based two integrator realisation of RI is an easily implementable frequency adaptive method. However, it suffers from resonant frequency deviation due to discretisation. The discretisation methods that lead to accurate realisation of RI require online calculation or lookup table of trigonometric functions to accommodate frequency variation. In this study, multi-rate computation-based implementation of two integrator-based RI has been proposed to minimise resonant frequency deviation. In this method, no additional logic elements are consumed to achieve accurate resonant frequency location. This along with down-sampling leads to lesser phase lag of RI. The effect of quantisation on resonant frequency deviation has been analysed for proper choice of calculation time. It is also shown that appropriate choice of down-sampling instants give a range of phase response characteristics around the nominal continuous time RI phase response. The accuracy of resonant frequency emulation has been experimentally verified by implementing a proportional–resonant controller as current controller.

Evaluation of magnetic field homogeneity using in-out signal cycle mapping in gradient recalled echo images of a mixed water/oil phantom as a rough indication for daily quality control

Objective: Magnetic field (B 0 ) homogeneity is important for the performance of a magnetic resonance imaging (MRI) system. Traditionally, B 0 homogeneity was measured using the spectral peak or phase-mapping methods. However, these procedures are not generally accessible to the MRI operator and are rarely performed routinely. This study proposes a novel method for measuring B 0 homogeneity that can be implemented in daily quality control (QC). Methods: When a uniformly mixed water/oil phantom was imaged using a gradient recalled echo (GRE) pulse sequence, the signal intensity dynamically changed with echo time (TE). From this, the resonant frequency was calculated with a simplex curve-fitting algorithm on a pixel-by-pixel basis. The standard deviation of resonant frequency (SD) was used as the index of B 0 homogeneity. The appropriate TE pattern and feasibility of B 0 homogeneity evaluation were examined. Results: Over seven TEs (choosing nominal in-phase, out-phase, and the midpoints of both) were required to measure stable SD in a 1.5-T scanner. As B 0 homogeneity worsened, the SD became larger at the off-center position. Although a positive correlation was observed with the width of the spectral peak obtained by the phase-difference method, the SD value was about 5 × 10 4 times greater. Therefore, SD can be used only as an index of B 0 homogeneity. Similar results were obtained using a 0.3-T scanner. A map and SD can be obtained by acquiring several GRE images of a water/oil mixed phantom within a few minutes. Conclusions: In-out signal cycle mapping can be easily implemented for daily QC in all MRI scanners.

Transfer function of optical waveguide ring resonator in frequency domain for micro-optic gyro

Resonator micro optic gyro (R-MOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. Optical waveguide ring resonator is the core-sensing element in R-MOG. According to the feature of the input signal, we established the transfer function of a Si-based ring resonator model in frequency domain for R-MOG with the coupled-mode theory. According to using the derived transfer function in the frequency domain, we analyzed the demodulation characteristics of R-MOG using Bessel function expansion based on laser frequency modulation spectrum technique. And we analyzed the relationship between the frequency modulation demodulation output signal and the resonant frequency deviation and obtained the best modulation coefficient applied in laser PZT drive. When the modulation coefficient M=2, the maximum linear interval slope, the demodulation curve is the best.

A COMPACT STABLE FREQUENCY SELECTIVE SURFACE USING NOVEL Y-TYPE ELEMENT

In this letter, A compact stable bandpass frequency selective surface (FSS) operating at 3.14 GHz is proposed by using a novel Y-type element. The measured and numerical results are in good agreement, except a little deviation of resonant frequency and a little change of bandwidth, which show that the proposed FSS has good angle and polarization stability. Numerical results show that the dimension of the element is only 0.042λ0 × 0.042λ0 ,w hereλ0 represents the wavelength at the resonant frequency 3.14 GHz. Thus, the FSS is suitable for practical application in limited space.

Nonlinear oscillations of a sessile drop on a hydrophobic surface induced by ac electrowetting.

We examine the nature of ac electrowetting (EW)-driven axisymmetric oscillations of a sessile water drop on a dielectric substrate. In ac EW, small-amplitude oscillations of a drop differ from the Rayleigh linear modes of freely oscillating drops. In this paper, we demonstrate that changes in the time-averaged contact angle of the sessile drop attributed to the presence of an electric field and a solid substrate mainly caused this discrepancy. We combine the domain perturbation method with the Lindsted-Poincaré method to derive an asymptotic formula for resonant frequency. Theoretical analysis shows that the resonant frequency is a function of the time-averaged contact angle. Each mode of the resonance frequency is a linear function of ɛ(1), which is the magnitude of the cosine of the time-averaged contact angle. The most dominant mode in this study, that is, the fundamental mode n=2, decreases linearly with ɛ(1). The results of the theoretical model are compared with those of both the experiments and numerical simulations. The average resonant frequency deviation between the perturbation solutions and numerical simulations is 4.3%, whereas that between the perturbation solutions and the experiments is 1.8%.

An efficient tuning method for narrowband superconducting filters with interdigital capacitor resonators in the time domain

This article proposes an effective tuning method based on the time domain for improving the performance of high-temperature superconducting (HTS) bandpass filters with interdigital capacitor resonators (ICRs). Analysis of the causes of HTS filter performance deterioration reveal that such deterioration is primarily caused by the resonant frequency deviation of the resonator of the HTS filter; this deviation results from fabrication errors and from the non-uniformity of the thickness and dielectric constant of the substrate. The sensitivity of the filter, which arises from the non-uniformity of the substrate thickness and dielectric constant, is related to the type of the resonator and the group delay characteristic of the filter. A 0.4% fractional bandwidth HTS filter with ICRs at the UHF band is fabricated and tuned using mechanical rods in the time domain. By applying this method, the resonant frequency deviation of each resonator and the coupling coefficient between resonators can be measured and tuned individually. The insertion loss of the HTS filter is improved from 1.06dB to 0.43dB, whereas the return loss is improved from 9.57dB to 15.1dB.

Dual-Polarized Angularly Stable High-Impedance Surface

The angular and polarization stability of the effective magnetic wall behavior is critical for successful applications of high-impedance surfaces, especially in low-profile antennas. We suggest an approach to realization of a high-impedance surface with unique magnetic-wall resonance for all incidence angles and for both TE-and TM-polarizations of incident plane waves. In order to achieve this goal we apply the concept of a grounded uniaxial material slab as a realization of a HIS surface and find the effective material parameters required for the unique parallel resonance of the surface impedance. We show that these parameters can be realized with a racemic arrangement of quasi-planar resonant chiral particles. The analytical model of the structure agrees well with full-wave numerical simulations of particular realizations. The maximal deviation of the magnetic-wall resonance frequency in the simulated example is smaller than 0.2% for both polarizations and for the incidence angles varying from 0 to 85 degrees. To our knowledge, this is a qualitatively significant improvement of previously obtained results.

Experimental Study on Monitoring Steel Beam Local Corrosion Based on EMI Technique

The corrosion of the steel structure not only causes the economic losses, but also poses a threat to the safety of the structure. The steel structure corrosion form is divided into uniform corrosion and local corrosion. Lead zirconate titanate (PZT) as a smart material was widely used in structural health monitoring (SHM) in recent years. For local corrosion damage in the form, a steel beam local corrosion monitoring experiments based on Electro-Mechanical Impedance (EMI) technique was designed. Marine environment was simulated and the steel beam local corrosion condition was designed firstly. Then the surface-mounted PZT transducer was used on the structure for long-term monitoring. The development process of corrosion and the admittance change was researched. The result shows that EMI technique is available to the beam local corrosion monitoring by analyzing the change rule of admittance signal and resonant frequency deviation ratio index with the steel beam corrosion.