Respective Resonant Frequencies Research Articles

Effects of Aerodynamic Damping and Gyroscopic Moments on Dynamic Responses of a Semi-Submersible Floating Vertical Axis Wind Turbine: An Experimental Study

Abstract Floating vertical-axis wind turbines (VAWTs) offer certain advantages over floating horizontal-axis wind turbines (HAWTs), particularly in terms of the potential to lower the cost of energy. In this study, a 5 MW floating VAWT concept with three straight blades and a semi-submersible hull deployed in a water depth of 42 m was presented. In addition, the experimental setup is introduced, and calibration tests are also performed to validate the physical model system. Subsequently, the aerodynamic damping and gyroscopic moment effects were investigated by wind/wave basin model tests with a scale ratio of 1/50. Results indicate that aerodynamic damping can suppress the fluctuations of the platform's surge and pitch motion at their respective resonance frequencies and tends to increase with wind speed at below-rated wind speed. Additionally, surge-induced and pitch-induced aerodynamic damping hardly affect the wave frequency response. Meanwhile, the surge natural frequency is substantially altered due to the wind loads. The rotating rotor and pitch motion of the platform together excite significant gyroscopic moments, leading to noticeable oscillations in roll motion. Additionally, there is an increasing trend in the gyroscopic moment effect with rotational speed. During normal operation of the floating VAWT, aerodynamic damping and gyroscopic moment together influence hull roll/pitch motions. Overall, this study contributes to providing valuable insights into the motion characteristics of floating VAWTs.

Explainable AI to Facilitate Understanding of Neural Network-Based Metabolite Profiling Using NMR Spectroscopy.

Neural networks (NNs) are emerging as a rapid and scalable method for quantifying metabolites directly from nuclear magnetic resonance (NMR) spectra, but the nonlinear nature of NNs precludes understanding of how a model makes predictions. This study implements an explainable artificial intelligence algorithm called integrated gradients (IG) to elucidate which regions of input spectra are the most important for the quantification of specific analytes. The approach is first validated in simulated mixture spectra of eight aqueous metabolites and then investigated in experimentally acquired lipid spectra of a reference standard mixture and a murine hepatic extract. The IG method revealed that, like a human spectroscopist, NNs recognize and quantify analytes based on an analyte's respective resonance line-shapes, amplitudes, and frequencies. NNs can compensate for peak overlap and prioritize specific resonances most important for concentration determination. Further, we show how modifying a NN training dataset can affect how a model makes decisions, and we provide examples of how this approach can be used to de-bug issues with model performance. Overall, results show that the IG technique facilitates a visual and quantitative understanding of how model inputs relate to model outputs, potentially making NNs a more attractive option for targeted and automated NMR-based metabolomics.

Improving the output performance of magnetic energy harvesters through coupling beam

We propose a novel magnetic energy harvester (MEH) with multiple resonance modes. The MEH consists of low-frequency and high-frequency piezoelectric cantilevers connected by a coupling beam. Theoretical modeling, simulation, and experiments were conducted to validate the multiple resonance phenomenon. The results from these investigations are consistent with each other. It is evident that the internal coupling (IC) effect resulting from the coupling beam facilitates significant voltage outputs from both cantilevers at their respective resonant frequencies, i.e. the low-frequency beam (LFB) resonates at the resonant frequency of the high-frequency beam (HFB), resulting in a remarkable 122% increase in the output voltage. Conversely, the HFB resonates at the resonant frequency of the LFB, leading to an astounding 1200% increase in the output voltage. As a result of the IC phenomenon, the operating frequency bandwidth for harvesting an output voltage of more than 1 V in the LFB has been extended by 35.3%, while that of the HFB for capturing an output voltage of more than 0.5 V has been extended by 62.5%. Additionally, the coupling effect significantly enhances the power output of the MEH.

Spectral-angular distribution of radiation generated by a train of electron bunches passing through the centre of a ball

We present the results of theoretical investigations of the spectral and angular distributions of the radiation generated by a train of electron bunches crossing a dielectric ball. The numerical examples are given for a dielectric ball made of fused quartz. It is shown that strong peaks appear in the spectral-angular distribution of the radiation intensity for certain values of the problem parameters. The heights of the peaks in the spectral density of the radiated energy are essentially increased when the frequency of the succession of the bunches in the train becomes equal to the respective resonant frequency of the ball.

In situ calibrated angle between the quantization axis and the propagating direction of the light field for trapping neutral atoms

The recently developed magic-intensity trapping technique of neutral atoms efficiently mitigates the detrimental effect of light shifts on atomic qubits and substantially enhances the coherence time. This technique relies on applying a bias magnetic field precisely parallel to the wave vector of a circularly polarized trapping laser field. However, due to the presence of the vector light shift experienced by the trapped atoms, it is challenging to precisely define a parallel magnetic field, especially at a low bias magnetic field strength, for the magic-intensity trapping of 85Rb qubits. In this work, we present a method to calibrate the angle between the bias magnetic field and the trapping laser field with the compensating magnetic fields in the other two directions orthogonal to the bias magnetic field direction. Experimentally, with a constant-depth trap and a fixed bias magnetic field, we measure the respective resonant frequencies of the atomic qubits in a linearly polarized trap and a circularly polarized one via the conventional microwave Rabi spectra with different compensating magnetic fields and obtain the corresponding total magnetic fields via the respective resonant frequencies using the Breit–Rabi formula. With known total magnetic fields, the angle is a function of the other two compensating magnetic fields. Finally, the projection value of the angle on either of the directions orthogonal to the bias magnetic field direction can be reduced to 0(4)° by applying specific compensating magnetic fields. The measurement error is mainly attributed to the fluctuation of atomic temperature. Moreover, it also demonstrates that, even for a small angle, the effect is strong enough to cause large decoherence of Rabi oscillation in a magic-intensity trap. Although the compensation method demonstrated here is explored for the magic-intensity trapping technique, it can be applied to a variety of similar precision measurements with trapped neutral atoms.

Design of the negative stiffness NegSV mechanism for structural vibration attenuation exploiting resonance

The principle of influencing oscillation amplitudes of a primary system via secondary attachments can be enhanced with inclusion of nonlinear mechanisms towards energy absorption. This work exploits such a scheme, termed the NegSV device, which harnesses a geometrically nonlinear mechanism to create a negative stiffness system for vibration attenuation. The suggested device succeeds in shifting the stiffness characteristics of the primary system and, therefore, alters the overall dynamics without additional mass requirements. The top part of a structure can act as a resonator with respect to the lower by matching the respective resonant frequencies and thus directing energy at specified locations. Analytical solutions demonstrate the improvement of the dynamic performance of a system, which is modified with attachment of the proposed device. Physical testing on a 3 dimensional frame structure is further performed, via shaking table tests, with the proposed nonlinear mechanism mounted at the top storey of the experimental structure. The experiment reveals reduction of acceleration and inter-storey drift response at all levels below the retrofit, while the requirement of increased top-storey drifts is identified. Nonlinear finite element analyses are finally performed on a detailed numerical model, which demonstrate agreement with the experimental measurements and are exploited for additional improvement of the mechanism’s design. The proposed nonlinear device shows significant potential in attenuating structural vibration, while further offering the benefit of ease of installation.

Application of electroplated Ni–Fe thick film to magnetostrictive material in vibration power generator

Ni100−xFex (at. %) films of about 37 μm thickness are electroplated on Cu base plates of 50 mm length, 10 mm width, and 300 μm thickness by varying the composition from x = 0 to 99. They are applied to cantilevers in magnetostrictive vibration power generators. The influences of magnetic and magnetostrictive properties of electroplated film on the vibration power generation property are systematically investigated. The films with x = 41–65 show low coercivities of about 4 Oe reflecting the low magnetocrystalline anisotropy constants. Large negative magnetostriction is recognized for the films with x = 0–14, whereas large positive magnetostriction is observed for the films with x = 57–80. The cantilevers are vibrated at the respective resonance frequencies of about 105–115 Hz and with the acceleration of 1.5 G while applying the bias magnetic field in a range of 0–300 Oe along the length direction. The output voltages are detected by using a coil with 8000 turns. Peak voltages higher than 1 V are obtained for the films with x = 61–65 whose coercivities are low and magnetostrictions are large. The present study has shown that an Ni–Fe film not only with large magnetostriction but also with low magnetic anisotropy constant is useful as the magnetostrictive material in vibration power generator.

Dual Sensing Acousto-electric Sensor.

Simultaneous monitoring of multiple physiological parameters are highly desirable for disease diagnosis and management. However, simultaneous interrogations of parameters from miniaturized sensors can be difficult; to overcome this difficulties, we present the dual sensing acousto-electric sensor capable of simultaneously measuring pressure and pH. The dual sensing is achieved by two electrically decoupled LC tanks emitting RF signal at their respective resonant frequencies under ultrasonic excitation. We designed, fabricated, and tested the dual sensing acousto-electric sensor.

A Compact SIW Cavity-Backed Self-Multiplexing Antenna for Hexa-Band Operation

In this communication a compact planar-fed substrate integrated waveguide (SIW)-based self-multiplexing (SM) antenna for hexa-band operation is proposed for the first time. Six different patches with planar <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\Omega $ </tex-math></inline-formula> feed lines are designed and attached to the top side of the rectangular SIW cavity. The antenna operates at six different frequencies (5.33, 5.76, 6.31, 6.86, 7.34, and 7.8 GHz) simultaneously. The antenna attains 4.5, 4.94, 4.9, 5.12, 6.12, and 6.6 dBi peak gain at respective resonant frequencies. Port relocation, stepped patches, and additional vias are exploited to maintain isolation (>23 dB) between any two ports. The front-to-back ratios (FTBRs) are between 10 and 20 dB and Co-pol to Cross-pol ratios are between 10 and 29 dB. The design supports single-variable independent frequency tuning for all six patches and eligible for wide range of applications. The proposed design is fabricated and results are validated through measurement. The antenna is suitable for planar microwave devices.

Analysis and Experimental Comparison of Acoustic Noise of Three Switched Reluctance Motors Made of Conventional Steel, High Silicon Steel, and Amorphous Iron

In this article, three test motors are fabricated with different iron materials, conventional steel, high silicon steel, and amorphous iron. Among the three materials, the high silicon steel has the lowest magnetostriction and the amorphous iron has the highest magnetostriction and the lowest saturated flux density. Hammer test is carried out to identify the respective resonant frequency and the optimum Young's modulus and Poisson ratio are identified from the measured resonant frequency for each core. Furthermore, the acoustic noise is measured in load test and it is found that the high silicon steel has the lowest acoustic noise. Then, the electromagnetic finite element analysis (FEA) and acoustic noise analysis are carried out. According to the FEA results, the acoustic noise of the amorphous iron motor is the lowest, while it is the highest in an experiment. This discrepancy is considered to be resulted from the magnetostriction property of the magnetic materials that are ignored in FEA so far. Therefore, the magnetostriction of three iron sheets is measured and the FEAs that take magnetostriction into consideration are carried out. From the results of the improved FEAs, it is found that the magnetostriction plays an important role in acoustic noise analysis.

Single‐stage pulse frequency controlled AC–AC resonant converter for different material vessel induction cooking applications

SummaryThis paper presents a single‐stage AC–AC resonant converter configuration for different material vessel induction cooking. The proposed configuration features input power factor correction, boost operation, and integrated bridge inverter configuration for multiple loads. In this topology the inverter legs are operated at two different frequencies to power induction cooking loads of steel and aluminum vessels. The induction cooking loads are operated at frequencies closer to their respective resonant frequencies. The load powers are independently controlled by pulse frequency modulation (PFM) technique. The proposed topology eliminates the use of electromechanical switches. The proposed single‐stage AC–AC resonant converter configuration has been tested with two different vessels of steel and aluminum. The simulation and experimental results of the proposed configuration are in good agreement. This topology offers the advantages of low component count, high efficiency, and suitability for different material induction cooking.

Vibration Response Aspects of a Main Landing Gear Composite Door Designed for High-Speed Rotorcraft

One of the crucial issues affecting the structural safety of propeller vehicles is the propeller tonal excitation and related vibrations. Propeller rotation during flight generates vibrating sources depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust, and blade geometry. Generally, the higher energy levels generated are confined to 1st blade passing frequency (BPF) and its harmonics, while additional broadband components, mainly linked with the blade shape, the developed engine power, and the turbulent boundary layer (TBL), also contribute to the excitation levels. The vibrations problem takes on particular relevance in the case of composite structures. The laminates in fact could exert damping levels generally lower than metallic structures, where the greater amount of bolted joints allow for dissipating more vibration energy. The prediction and reduction of aircraft vibration levels are therefore significant considerations for conventional propeller aircrafts now entering the commercial market as well as for models currently being developed. In the Clean Sky 2 framework, the present study focuses on a practical case inherent to the AIRBUS-Racer program aiming to design and develop a multi-tasking fast rotorcraft. This paper defines a finite elements (FE)-based procedure for the characterization of the vibration levels of a main landing gear (MLG) composite door with respect to the expected operating tonal loads. A parametric assessment was carried out to evaluate the principal modal parameters (transfer functions and respective resonance frequencies, mode shapes, and damping coefficients) of the landing gear-door assembly in order to achieve reduced vibration levels. Based on the FE analysis results, the influence of the extra-damping, location, and number of ballast elements, the boundary conditions were investigated with respect to failure scenarios of the kinematic line opening the study towards aeroelastic evaluations. Further experimental ground test results serve as a validation database for the prediction numerical methods representative of the composite door dynamic response.

Cascaded full‐bridge resonant inverter configuration for different material vessel induction cooking

This paper presents a cascaded full-bridge resonant inverter configuration for different material vessel induction cooking. The proposed inverter configuration features simultaneous heating of three different material vessels, and independent power control. In this proposed work, three different induction heating loads are simultaneously operated at their respective resonant frequencies. Vessels of iron, steel, and aluminium materials are used. The output powers are independently controlled by an asymmetric duty cycle control. The proposed inverter is designed and hardware prototype has been implemented. Experimental results are validated with simulation results.

Surrogate-based computational analysis and design for H-shaped microstrip antenna

ABSTRACT A conceptual Kriging surrogate model (KSM) for the computational analysis and design of H-shaped microstrip antennas (HMAs) is proposed in this study. A dataset contains 216 simulated HMAs with different physical/electrical parameters of the HMAs and the respective resonant frequency (RF) values are employed in construction and test processes of the KSM. The performance of the KSM is tested and verified through 20 and 13 HMAs by an extensive comparison with the state-of-the-art models. The results illustrate that KSM computes the most accurate RF values of 20 and 13 HMAs with absolute percent error (APE) of 0.48% and 0.76%, respectively. Moreover, a miniaturized HMA is optimally designed through the KSM as 27% smaller than the smallest design in the dataset for operating at about 2.40 GHz. Therefore, the performance of the proposed method is validated by means of the fabrication of the miniaturized HMA.

Experimental and Theoretical Dynamic Investigation of MEMS Polymer Mass-Spring Systems

This paper presents the experimental, analytical and numerical dynamic analysis of SU-8 polymer MEMS mass-spring systems using two different attachment beams, dual and quad. Beam thicknesses of $4.48~\mu \text{m}$ and $8.21~\mu \text{m}$ produce two different sets of prototypes using dual-beam attachments. Those using quad-beam are only $8.21~\mu \text{m}$ thick. Using Lazer Doppler Vibrometer (LDV), dynamic characterization is performed to measure respective resonance frequencies of 1325 Hz and 1813 Hz for dual and quad-beam attachments having a thickness of $8.21~\mu \text{m}$ . Numerical and analytical dynamic analysis are performed to investigate the frequency response of systems using both attachment structures. Using measured key geometric dimensions, numerical and analytical resonance frequencies are evaluated. Theoretical and experimental values are in good agreement with maximum errors of 16% and 12% for dual and quad-beam structures, respectively. The low-cost microfabrication process can be used to incorporate a piezoresistive material/nanomaterial in locations of maximum stress on the beams producing dual and quad-beam MEMS piezoresistive sensors. Numerical analysis is performed to show that the resonance frequency is not affected which proves that the developed dynamic analysis stays valid.

Quartz-Enhanced Photoacoustic Detection of Ethane in the Near-IR Exploiting a Highly Performant Spectrophone

In this paper the performances of two spectrophones for quartz-enhanced photoacoustic spectroscopy (QEPAS)-based ethane gas sensing were tested and compared. Each spectrophone contains a quartz tuning fork (QTF) acoustically coupled with a pair of micro-resonator tubes and having a fundamental mode resonance frequency of 32.7 kHz (standard QTF) and 12.4 kHz (custom QTF), respectively. The spectrophones were implemented into a QEPAS acoustic detection module (ADM) together with a preamplifier having a gain bandwidth optimized for the respective QTF resonance frequency. Each ADM was tested for ethane QEPAS sensing, employing a custom pigtailed laser diode emitting at ~1684 nm as the exciting light source. By flowing 1% ethane at atmospheric pressure, a signal-to-noise ratio of 453.2 was measured by implementing the 12.4 kHz QTF-based ADM, ~3.3 times greater than the value obtained using a standard QTF. The minimum ethane concentration detectable using a 100 ms lock-in integration time achieving the 12.4 kHz custom QTF was 22 ppm.

Second harmonic generation from complementary triangular Au metamaterials

Sub-wavelength square array of a triangular Au platelet and its complementary structure (i.e. that of a triangular hole in a square film of Au) are compared in terms of second harmonic generation efficiency for fundamental light in the near infrared and visible region of spectrum for normal incidence. Electric field strength around the convex corners of a triangular particle is at least 10 times larger than the one around the concave corners of triangular hole in the complementary structure. Nevertheless the SHG intensity at the respective resonant frequency is found to be comparable, which are numerically estimated by an overlap integral of nonlinear polarization and electric field at the SHG frequency in the nonlinear optical scattering theory originally proposed by Roke et al. (Phys. Rev. B 70, 115106 (2004)). The reason is due to the large electric field strength at the sides of the triangular hole at the resonance frequency, which compensates the suppressed electric field at the concave corners in the overlap integral.

Low-Profile Independently- and Concurrently-Tunable Quad-Band Antenna for Single Chain Sub-6GHz 5G New Radio Applications

This paper presents a quad-band frequency agile antenna, with independent and concurrent frequency tunability in each band, for a tunable, concurrent, quad-band single chain radio receiver for 5G New Radio (NR). More specifically, the antenna comprises of four planar slots etched in a ground plane and fed through a single microstrip feedline, without any impedance matching network. The structure is optimized to maximize isolation between the individual slots and their respective resonant frequencies. Furthermore, a novel high order harmonic suppression method is demonstrated, which controls the current distribution via creating a fictitious short circuit in the slot antenna–enabling the antenna to achieve a much wider tuning range. Numerical simulations are verified using experimental implementation and measurements, with good agreement observed. The four slots resonate around the 830 MHz, 1.8 GHz, 2.4 GHz and 3.4 GHz frequency bands, which are independently tuned (using a varactor diode in each slot) to achieve tuning ranges of approximately 64%, 66%, 27% and 33%, respectively. More importantly, the contiguous four bands covers a total frequency tuning from 0.6 to 3.6 GHz i.e. a tuning range of approximately 143%. Finally, far-field measurements are performed and the antenna is evaluated in over-the-air testbed (quad-band radio receiver), which measures the Error Vector Magnitude performance for the individual channels. Good performance is observed, confirming acceptable isolation performance between the four bands. The data reported in this paper is available, from ORDA-The University of Sheffield Research Data Catalogue and Repository, at https://doi.org/10.15131/shef.data.11219000.v1 .

Semi-analytical modeling and optimization of a traveling wave sandwich piezoelectric transducer with a beam-ring combined structure

Abstract Boasting the advantages of low maximum ground pressure and low locomotion resistance of tracked mechanisms, a traveling wave sandwich piezoelectric transducer with a beam-ring combined structure was proposed and developed to directly drive a metal track, and preliminary experimental investigations have confirmed the feasibility of the transducer design and its operating principle. However, the dynamic behavior of the sandwich piezoelectric transducer has not yet been studied theoretically. To enable practical applications, the sandwich piezoelectric transducer needs to be optimized for better output performances. Therefore, a semi-analytical model is of significance to describe the dynamic behavior of the sandwich piezoelectric transducer, to predict its driving effect, and to improve its output performance. In this study, an electromechanical coupling model is developed for the sandwich piezoelectric transducer by employing the transfer matrix method, in which a novel longitudinal-bending coupling vibration transfer matrix is created for the combined PZT elements and an in-plane bending vibration transfer matrix is developed for the closed curved beam element. To validate the proposed model, experimental investigations are carried out to measure the dynamic behavior of the transducer prototype and compare to calculation results. The differences between the measured and calculated resonant frequencies for two operating vibration modes are, respectively, 74 Hz and 63 Hz. Also the vibration shapes at the respective resonant frequencies match well. Comparisons demonstrate the feasibility of the developed transfer matrix model. To improve the output performance of the transducer, model-based optimization is conducted. The optimized geometrical sizes are obtained to meet optimization goals of the transducer.

High gain dual band slot antenna loaded with frequency selective surface for WLAN/fixed wireless communication

AbstractThis study shows the gain enhancement achieved through dual band slot antenna incorporated with dual band frequency selective surface. In order to do this, at first, a dual band novel 7 × 7 spanner shape FSS is designed, and its operations is analyzed by using the ray tracing method. The second step involves designing the dual band slot antenna resonating at 3.53 and 6.2 GHz, respectively. The designed FSS is then used as superstrate on the slot antenna in which cavity resonance occurs due to multiple reflections and leaked out waves, thereby enhancing antenna's gain significantly on both the bands. Further, the overall gain of slot antenna with the superstrate is achieved as 13.00 and 13.92 dBi on the 2 respective resonant frequencies; this in turn results in a gain enhancement of 8.0 and 6.82 dB at 3.53 and 6.2 GHz, respectively. The measured results coincide verifying the results of the simulated structure. This is followed by a parametric analysis for air gap between FSS and the radiating antennas, which in turn have been designed for wireless and satellite communications.