Amplitude Characteristics Research Articles

Plucking and linear-to-rotary hybrid harvester for low-amplitude vibrations of high-speed railway with an innovative three-step amplification mechanism

By harvesting the pervasive vibration energy, self-powered wireless sensor network (WSN) installed along the track can play an important role in structure health monitoring of high-speed railway. However, a considerable part of vibration energy of the rail is difficult to be harvested due to the characteristics of ultra-low frequency, small amplitude and large load. A hybrid frequency up-conversion energy harvester is designed and optimized in this paper aiming to address this critical problem. By utilization of a unique three-step amplification design for reducing inefficient transmission due to the possible gap of gear or ball-screw systems, high-efficient energy harvesting is realized for the small-amplitude excitation with both electromagnetic and piezoelectric conversion structures. The experiment results verify that the gapless amplification achieved by the flexible hinge structure as the first-step mechanism is effective for solving the gap issue. Compared with harvesters without the flexible hinges, the power is 250% higher under an excitation of low frequency (5 Hz) and ultra-small amplitude (0.3 mm). Moreover, based on the hybrid energy harvesting mechanism, more appreciable energy is obtained by introducing the plucking piezoelectric structure in addition to the electromagnetic unit.

Near-to-Far Field RCS Calculation Using Correction Optimization Technique

Radar cross section (RCS) is a scattering measure of an object that scatters to the radar. However, existing methods for near-field (NF) measurement and data processing rarely extract amplitude characteristics, and there is a lack of effective verification of far-field (FF) data in the process of NF to FF transformation, which leads to inaccuracies in FF prediction accuracy. In this paper, we propose a method to establish the relationship between the NF and FF RCS using the state space method (SSM), which is based on accurate estimation of the NF amplitude in NF measurement, and then deriving the FF RCS from the NF scattering signal convolved with a near-to-far kernel. The proposed solution to address the uncertainty issue in reference FF data involves using the geometric theory of diffraction (GTD) scattering center model as the reference FF data and establishing a linear equation with the derived FF model. The negative gradient search (NGS) system identification concept is used to optimize the FF model in order to reduce the discrepancy between the reference and derived values. Finally, the corrected RCS error is provided as additional proof of the effectiveness of these techniques in enhancing near-to-far transformation accuracy by examining the outcomes of three experiments.

Strong-motion simulation for the 1944 Tonankai earthquake based on the statistical green’s function method and stochastic representation of complex source process

Precisely evaluating the source, path, and site terms in a broadband frequency range is indispensable for quantitatively predicting strong motions. We conducted a generalized spectral inversion of strong motion in Japan to delineate both the spectral amplitude and phase characteristics for statistical Green’s functions. To predict ground motion from future megathrust earthquakes, we also need to model a kinematic source with a stochastic representation of the slip and rupture velocities on the fault surface. In this fundamental study, we first reported the basic features of statistical Green’s functions used for summation. We then demonstrated the construction of a kinematic source with distinctive strong-motion-generation areas with spatially random slip and rupture velocity variations. After the summation of statistical Green’s functions following the constructed kinematic source, we found that the peak ground accelerations and peak ground velocities of synthetics for the Mw8.2 1944 Tonankai earthquake are in good agreement with those of the well-established empirical formula in Japan because the medians of the synthetic values are well within the average plus/minus one standard deviation of the formula. Based on the simulation results of conducted parametric studies, we observed relatively small but meaningful effects of random slip distribution, as well as relatively small effects of random rupture velocity perturbation. In conclusion, our implementation of the complex source model and the empirically obtained statistical Green’s function used as an element source can be a viable combination for broadband (0.1 to 20 Hz) strong-motion simulations, realistic in terms of the amplitude and duration, without any hybrid scheme.Graphical

Boundary recognition of tunnel lining void from ground-penetrating radar data

Abstract Relatively low ground-penetrating radar antenna frequencies are usually selected for tunnel inspection due to the thickness of the lining, which causes the geometric features of voids in the image to be blurred and difficult to identify. Therefore, the boundary points of the voids are determined by combining reflection and attenuation coefficients, and the geometric features are constructed to identify the voids. Depending on the electromagnetic differences between the void and other mediums in the lining, when the electromagnetic wave propagates from the lining concrete to the void, the reflection coefficient is positive, and the phase of the reflected wave is the same as the incident wave. Conversely, the phase of the reflected wave is opposite to the incident wave. Therefore, the boundary point can be determined in the one dimension time-waveform diagram (A-Scan) based on the phase change. Moreover, the amplitude of the electromagnetic wave attenuates exponentially in the concrete, but it attenuates slowly in the void. Also, electromagnetic waves exhibit high-frequency characteristics in the lining but low-frequency characteristics in the voids. Boundary points that conform to the variation of amplitude and frequency characteristics in the void are screened. These boundary points are then constructed in two-dimensional scan data (B-Scan) to identify the voids by using the geometry of the voids. This method is applied to the Hu Sa Tunnel. The voids are successfully identified in the mileage section YK81+310–YK81+422 of the Hu Sa Tunnel, and the depth of cover and the area of voids are correctly estimated.

Design of a 3-bit encoded THz ultra-wideband vortex beam generator based on a metasurface

With the rapid development of high-speed THz communications, there has been a growing interest in exploring the potential of the orbital angular momentum (OAM) of electromagnetic waves. In this study, we propose a cross-polarized reflective broadband metasurface operating in the THz band to harness the benefits of OAM in the optical field. We quantitatively analyze the reflection amplitude and phase characteristics of the metasurface elements, which supports the design of a reflective broadband element surface array with an ordered arrangement of 3-bit elements. By combining the 3-bit metasurface elements in an array, linearly polarized waves can effectively be converted into vortex beams in the operating frequency range of 0.6THz-1.3THz. The simulation results demonstrate that the designed metasurface element structure can achieve not only efficient cross-polarization reflection amplitude but also effective phase control by adjusting the size parameters. Our proposed metasurface is able to convert linearly polarized waves into vortex beams with an efficiency exceeding 85% and can achieve high-purity OAM beam acquisition. Furthermore, the metasurface structure is simple to implement and can be easily integrated with photoelectric circuits, making it ideal for use in ultrahigh-speed THz communications.

Investigation of rolling contact fatigue cracks using the transmitter-receiver eddy current testing under moving conditions

ABSTRACT Rolling contact fatigue (RCF) cracks online detection using eddy current testing (ECT) is in urgent demand. However, RCF cracks detection and evaluation in this way under moving conditions remains challenging due to the velocity effect in ECT. This paper aims to study the response of a transmitter-receiver eddy current probe to cracks under moving conditions and evaluate the depth and inclination angle of RCF cracks. In this paper, a high-speed eddy current testing system is developed to experimentally investigate the influence of coil gap, detection speed, and the lift-off on the eddy current probe’s response under moving conditions. In addition, the temporal and amplitude features of the eddy current signal are extracted to characterise the depth and inclination angle of the RCF cracks. The experimental results indicate the eddy current probe’s response can be improved by increasing the coil gap (coil centre distance) suitably, which can be done to compensate for the attenuation of the eddy current signal caused by detection speed and lift-off. The probe’s response hardly changes with an increase in detection speed when the driver and pick-up coils of the eddy current probe completely overlap. The crack depth and inclination angle can be evaluated under moving conditions.

Performance of a transverse ridge located through the contact zone of an ultra-thin film including surface force effect

PurposeThe purpose of this paper is to investigate the performance of an ultra-thin film lubricated conjunction through the elastohydrodynamic lubrication of point contacts for various ridge shapes and sizes located within the contact zone including flat-top, triangle and cosine wave profiles, considering the influence of surface forces of solvation and Van der Waals’ in addition to the hydrodynamic effect to predict an optimum geometric characteristics for surface texture for lubricated conjunctions.Design/methodology/approachSurface features are simulated in a variety of sizes and shapes including flat-top, triangle and cosine wave profiles. While estimating the elastic deformation of the contacting surfaces, surface forces of solvation and Van der Waals’ are taken into account. The Reynolds equation is solved using the Newton–Raphson method to get the pressure profile and film thickness including the elastic deformation, and surface feature.FindingsThe geometrical characteristics of the ridge, its placement in relation to the contact zone and its height all have a significant impact on the performance of ultra-thin film lubricated conjunction. When the triangular-shaped ridge is present in contact, it forecasts even sharper peaks in film thickness and pressure. More friction, wear and eventually contact fatigue are brought on by this more acute pressure and film thickness peaks. The flat-top ridge shape shows a better performance for lubricated conjunction where, the minimum film thickness value is comparable to that obtained for the case of a smooth contact surface. This behavior is attributed to the effect of intermolecular force of solvation. An increase in the size of the ridge results in a step increase in the film thickness for different ridge shapes, particularly for the flat-topped ridge pattern.Originality/valueEvaluation of the performance of elastohydrodynamic lubricated ultra-thin film conjunction related to film thickness and pressure profile for various ridge surface features of different amplitudes, shapes and sizes located through the contact zone considering the influence of surface forces of solvation and Van der Waals’ in addition to the hydrodynamic effect.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0062/

A Nonintrusive Load Identification Method Based on Improved Gramian Angular Field and ResNet18

Image classification methods based on deep learning have been widely used in the study of nonintrusive load identification. However, in the process of encoding the load electrical signals into images, how to fully retain features of the raw data and thus increase the recognizability of loads carried with very similar current signals are still challenging, and the loss of load features will cause the overall accuracy of load identification to decrease. To deal with this problem, this paper proposes a nonintrusive load identification method based on the improved Gramian angular field (iGAF) and ResNet18. In the proposed method, fast Fourier transform is used to calculate the amplitude spectrum and the phase spectrum to reconstruct the pixel matrices of the B channel, G channel, and R channel of generated GAF images so that the color image fused by the three channels contains more information. This improvement to the GAF method enables generated images to retain the amplitude feature and phase feature of the raw data that are usually missed in the general GAF image. ResNet18 is trained with iGAF images for nonintrusive load identification. Experiments are conducted on two private datasets, ESEAD and EMCAD, and two public datasets, PLAID and WHITED. Experimental results suggest that the proposed method performs well on both private and public datasets, achieving overall identification accuracies of 99.545%, 99.375%, 98.964%, and 100% on the four datasets, respectively. In particular, the method demonstrates significant identification effects for loads with similar current waveforms in private datasets.

Polarimetric Range Extended Target Detection via Adaptive Range Weighted Feature Extraction

In ground static target detection, polarimetric high-resolution radar can distinguish the target from the strong ground clutter by reducing the clutter power in the range cell and providing additional polarimetric features. Since the energy of a target is split over several range cells, the resulting detection problem is called polarimetric range extended target (RET) detection, where all target scattering centers should be considered. In this paper, we propose a novel polarimetric RET detection method via adaptive range weighted feature extraction. Specifically, polarimetric features of range cells are extracted, and a pretrained attention-mechanism-based module is used to adaptively calculate range cells weights, which are used to accumulate the range cells features as detection statistics. While calculating weights, both amplitude and polarimetric features are considered. This method can make the most of polarization information and improve the accumulation effect, thus increasing the discrimination between targets and clutter. The effectiveness of the proposed method is verified compared to both popular energy-domain detection methods and existing feature-domain detection methods, and the results show that our method exhibits superior detection performance. Moreover, we further analyze our method on different target models and different clutter distributions to prove that our method is suitable for different types of targets and clutter.

Evolution of mechanical-acoustic-electrical properties on SiC filament underlaying an oxidation treatment

Accurately obtaining the acoustic emission (AE) and electrical resistance (ER) responses of SiC filaments in the damage process is one of the keys to realizing the damage monitoring of SiC/SiC composite structures. A novel mechanical-electrical coupling specimen for fiber filament was designed based on the strength test strategy. During tensile failure, the difference in AE and ER responses between original and oxidation-treated SiC filaments was studied. The ER monitoring results show that the initial resistivity of SiC filaments is negatively correlated with their tensile strength. With increasing oxidation treatment temperature, the tensile strength of SiC filaments gradually decreases while the initial resistivity gradually increases. The AE monitoring results show that the AE signal of SiC fiber fracture has the characteristics of high amplitude, high energy, long duration, short rise time, and low peak frequency. A strong positive correlation is observed between the amplitude and energy of the AE signals of fiber fracture and the tensile strength of SiC filaments; the greater the tensile strength, the greater the amplitude, duration, and energy of the AE signals generated when the fiber fracture. In addition, the tensile modulus and resistance sensitivity coefficient of SiC filaments were measured.

A Diagnostic Method for Open-Circuit Faults of Loads and Semiconductors in 3L-NPC Inverters

Open-circuit (OC) faults of inverter switch, clamping diode and load are easily misdiagnosed by most of the existing methods due to the extremely similar fault features. In this regard, a diagnostic method based on line voltage over-modulation and amplitude features is proposed in this paper to accurately locate coupling faults of three-level neutral-point-clamped (3L-NPC) inverter and load. Only two line voltages are used as diagnosis variables, and additional sensor is not required. The proposed diagnosis method consists of two parts: fault detection and fault classification. The fault detective algorithm only requires a small amount of computation and is suitable for uninterrupted execution. The classification algorithm starts immediately when the fault is detected, and the over-modulated voltage features are used to locate the fault. The proposed method can usually complete the diagnosis in 1/4 of fundamental period. The proposed method is also robust to different modulations, carrier frequencies and load variations. Experiments demonstrate that the proposed method can distinguish the OC faults of semiconductors (including switches and clamping diodes) and load effectively.

Tensile Properties Analysis of 3D Flat-Knitted Inlay Fabric Reinforced Composites Using Acoustic Emission

Abstract In this work, based on the quasi-static tensile test and acoustic emission technology, the tensile properties of two types of three-dimensional flat-knitted inlay fabrics reinforced composites are investigated, and the acoustic emission characteristic parameters of various damage mechanisms are obtained. The transverse tensile process of specimens could be divided into the elastic stage, yield stage, and fracture stage. We found that, compared with the fluctuation of the stress-strain curve in the yield stage, weft insertion yarns in composite with interlock structure broke almost simultaneously, while the composite with plain stitch broke successively. The transverse and longitudinal tensile strength of the composite with interlock structure was 44.70% and 28.63% higher than the composite with plain structure, respectively. The SEM micrographs showed that the damage mechanism of the composites was matrix fracture, fiber-matrix debonding, and fiber breakage. The amplitude ranges of the three damage mechanisms were 50–65 dB, 65–80 dB, and 90–100 dB, respectively, and the frequency ranges were 35–114 kHz, 116–187 kHz, and 252–281 kHz, respectively. Fiber-matrix debonding and matrix fracture had large cumulative AE energy, numerous events, and long duration time, while fiber breakage had the characteristics of large amplitude, high frequency, low cumulative AE energy, few events, and short duration time.

Acoustic characteristics of sibilant fricatives and affricates in Mandarin-speaking children with cochlear implants

The purpose of the study was to examine the acoustic features of sibilant fricatives and affricates produced by prelingually deafened Mandarin-speaking children with cochlear implants (CIs) in comparison to their age-matched normal-hearing (NH) peers. The speakers included 21 children with NH aged between 3.25 and 10 years old and 35 children with CIs aged between 3.77 and 15 years old who were assigned into chronological-age-matched and hearing-age-matched subgroups. All speakers were recorded producing Mandarin words containing nine sibilant fricatives and affricates (/s, ɕ, ʂ, ts, tsʰ, tɕ, tɕʰ, tʂ, tʂʰ/) located at the word-initial position. Acoustic analysis was conducted to examine consonant duration, normalized amplitude, rise time, and spectral peak. The results revealed that the CI children, regardless of whether chronological-age-matched or hearing-age-matched, approximated the NH peers in the features of duration, amplitude, and rise time. However, the spectral peaks of the alveolar and alveolopalatal sounds in the CI children were significantly lower than in the NH children. The lower spectral peaks of the alveolar and alveolopalatal sounds resulted in less distinctive place contrast with the retroflex sounds in the CI children than in the NH peers, which might partially account for the lower intelligibility of high-frequency consonants in children with CIs.

Mathematical Modeling of the Amplitude, Angular, and Time Characteristics of Short Radio Waves in Slightly Oblique Sounding of the Ionosphere

The method of bicharacteristics is used to study the propagation of decameter radio waves in the ionosphere containing the E, F1, and F2 layers and a traveling ionospheric disturbance (TID) upon slightly oblique sounding with frequency-modulated signals. The propagation of both ordinary and extraordinary waves is considered, the ionograms are compared, and their relative shift is studied. The structure of ionograms in the vicinity of caustics, which appear at the reception point at frequencies reflected in the vicinity of the E layer and TID, is studied. The divergence of the ray flux at the point of radiation reception, which determines a decrease in the amplitude, is calculated.

Mathematical Modeling of the Amplitude, Angular, and Time Characteristics of Short Radio Waves in Slightly Oblique Sounding of the Ionosphere

Mathematical Modeling of the Amplitude, Angular, and Time Characteristics of Short Radio Waves in Slightly Oblique Sounding of the Ionosphere

Simultaneous Amplitude- and Phase-Tunable Coupler With Wide Phase Tuning Range

In this article, a coupler with simultaneously tunable power division ratio (PDR) and phase difference is proposed based on a multivector summation method. Two groups of varactor diodes are installed on the cross-shaped quarter-wavelength coupled lines to realize the proposed tunable coupler. The horizontal coupled lines serve as the subcouplers to generate multiple vectors, while the vertical coupled lines serve as the phase-tunable units (PTUs) to control the phase of the vectors. The phases of the PTUs can be therefore tuned by the varactor diodes. With a proper combination of the capacitance of the varactor diodes, the amplitude and phase characteristics of the proposed coupler can be controlled independently. For demonstration, a highly tunable coupler operating at 1.8 GHz is designed, fabricated, and measured. The PDR of the coupler can be tuned from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 7 to 1 dB with a 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> phase difference, while the phase difference of the coupler can be tuned within a wide range from 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> to 165 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> with equal power division. Better than 10-dB return loss and 15-dB isolation can be observed under different states.

Polarized gravitational waves in the parity violating scalar-nonmetricity theory

There has been increasing interest in investigating the possible parity violating features in the gravity theory and on the cosmological scales. In this work, we consider a class of scalar-nonmetricity theory, of which the Lagrangian is polynomial built of the nonmetricity tensor and a scalar field. The nonmetricity tensor is coupled with the scalar field through its first order derivative. Besides the monomials that are quadratic order in the nonmetricity tensor, we also construct monomials that are cubic order in the nonmetricity tensor in both the parity preserving and violating cases. These monomials act as the non-canonical (i.e., non-quadratic) kinetic terms for the spacetime metric, and will change the behavior in the propagation of the gravitational waves. We find that the gravitational waves are generally polarized, which present both the amplitude and velocity birefringence features due to the parity violation of the theory. Due to the term proportional to 1/k in the phase velocities, one of the two polarization modes suffers from the gradient instability on large scales.

Numerical and computational investigation of soliton propagation in physical systems via computational schemes: (1+1)-dimensional [formula omitted] integrable equation

This study utilizes computational and numerical techniques to investigate the (1+1)-dimensional Mikhailov–Novikov–Wang (MNW) integrable equation, a nonlinear partial differential equation that governs the propagation of solitons in various physical systems, including plasma physics and fluid dynamics. The numerical methods proposed in this research provide an accurate and efficient means of obtaining wave solutions for the MNW equation. Through the application of these techniques, new soliton solutions are derived, expressed in terms of hyperbolic and trigonometric functions, and analyzed to determine their amplitude and shape characteristics. The results obtained demonstrate the potential of the proposed numerical methods to solve other nonlinear partial differential equations in fields such as engineering and physics. The findings of this study have significant implications for understanding the dynamics of solitons in physical systems and may facilitate the development of more effective numerical methods for solving nonlinear partial differential equations.

Seismic signatures and site characterization of an intermittent stream in dry and flood conditions: an implication for soil losses and landslide triggering

Identifying ambient noise-based (ANb) signatures together with the erosion-prone site conditions retrieved from georadar attribute analysis of streams can help in the estimation of their erosive potential (EP) that promotes reverie landslides and soil losses in the fluvial valleys. This is particularly imperative on flooding or rainy days, leading to stronger erosion-prone conditions (colluvium and boulders) of the valley beds. Developing such research direction can benefit the local communities, as is the case with the Cerrado region of Brazil, where these phenomena have high destructive potential with social, economic, and climatic implications. For the present study, a seasonal stream in the Federal District of Brazil was investigated by ANb monitoring supported by ground penetration radar (GPR) for site characterization. The ANb monitoring was conducted (at a safe distance) with a seismometer over several durations of dry and rainy conditions. The power spectral density (PSDs) as a function of several weather conditions (rainfall, wind speed, and pressure), time–frequency spectrograms, and ambient noise displacement root mean square (dRMS) were computed. This analysis also considered the single station horizontal-to-vertical spectral ratio (HVSR), where rain, wind, pressure, river flow and anthropogenic signatures were evident (at selective frequency ranges). Multi-peaks that emerged on the HVSR curve were further analyzed to identify amplitude and frequency changes, with the three peaks shifting on average to a lower position during the rainy period. The GPR amplitude and waveform variation features were attributed to the stratigraphy of the floodplain and regions susceptible to erosion, such as erosion-prone lithological spots, which provide the basis for non-destructive monitoring tools that enable the detection of “seismic signatures” and weak spots of the fluvial channels for improving environmental management.

Exploring nonlinearity to enhance the sensitivity and bandwidth performance of a novel tapered beam micro-gyroscope

In this paper, nonlinearity is used to enhance the sensitivity and bandwidth performance of tapered beam micro-gyroscopes. Considering the electrostatic force nonlinearity and fringing field effects, the governing equations of system are derived by Euler angular transformation and Hamilton principle. The influences of parameters such as the shape factors and DC voltage on static deflection, pull-in voltage and natural frequency of tapered beam micro-gyroscope are analyzed by the Adomian decomposition method (ADM). Galerkin discretization is performed on the governing equations of the tapered beam micro-gyroscope. Frequency-response equation of the system is deduced and solved by applying the method of multi-scale (MMS). The convergence analysis of the frequency response curve is performed, and then verified by the Runge-Kutta method. Finally, the performance of the tapered beam micro-gyroscope is analyzed in terms of bandwidth, sensitivity, and calibration curve nonlinearity under the different shape factors. The maximum amplitude of response in the driving and sensing directions increases significantly with the change of shape factors of the tapered beam in the dynamics analysis. Compared with the straight beam micro-gyroscope, the tapered beam micro-gyroscope has the higher amplitude and pronounced nonlinear characteristics. Due to the electrostatic force nonlinearity, the amplitude of motion in the driving direction has a high response over a wide frequency band, while also effectively increasing the detection bandwidth. In addition, the nonlinear micro-gyroscope has less loss of sensitivity performance during damping fluctuations. Therefore, in view of the contradiction between bandwidth and sensitivity of the traditional micro-gyroscope, this paper proposes a solution from the perspective of structural design and nonlinear characteristics of the tapered beam micro-gyroscope.