Strong Harmonics Research Articles

Experimental and Numerical Study of the Flow Around Rigid and Flexible Hydrofoils for Wetted and Cavitating Flow Conditions

Abstract The hydro-elastic response of a flexible NACA 0015 hydrofoil is investigated for both wetted and cavitating flow conditions. Computational fluid dynamics (CFD) analysis are performed using a fully implicit coupling between the ISIS-CFD solver (developed by the METHRIC team at Ecole Centrale de-Nantes) and a modal approach for the structure. The Reynolds-averaged Navier–Stokes (RANS) solver is first validated for wetted and cavitating flow conditions around a similar rigid hydrofoil, with experimental results carried out at the hydrodynamic tunnel of the French Naval Academy, including lift and drag measurements and high speed camera images. Then the numerical predictions for the flexible hydrofoil response are compared with experimental bending shapes and vibrations amplitudes, with a focus on cavitating flow conditions. For wetted flow conditions, numerical results show a good agreement with the experiments, for both rigid and flexible hydrofoils. For cavitating flow conditions, the hydro-elastic response is dominated by vibrations at the hydrofoil modal frequencies and the reentrant jet instability frequency. For the lowest values of the cavitation number, a large amplitude peak is experimentally observed in the frequency response spectra, due to lock-in between the first modal frequency and the reentrant jet frequency. Strong harmonics of this dominant peak also appear in the spectra, revealing a nonlinear response of the hydrofoil. While the amplitudes of vibrations are well predicted by the computations, the frequency lock-in observed in the experiments is not captured by the numerical model.

Electric field and higher harmonics of RF plasma slit jet measured by antennas and VI probes

The cold atmospheric plasma jets change their character when interacting with the different surfaces. Since such interaction is the primary area of plasma jet applications, it is essential to monitor the process. The non-linearity of the RF plasma slit jet (PSJ) was analyzed using the VI probes and a novel method, the non-intrusive antenna measurements. Regardless of the experimental setup and gas mixture (Ar, Ar/O2, Ar/N2), the PSJ frequency spectrum consisted of the following main features: dominant fundamental frequency peak, relatively strong odd harmonics, and significantly weaker even harmonics. The lowest degree of non-linearity was recorded for the Ar PSJ ignited against a grounded target. Admixing a molecular gas increased the discharge non-linearity. It was attributed to the enhancement of secondary electron emission from the dielectric surfaces. In addition to the non-linearity analysis, the antenna spectra were for the first time used to determine the semi-quantitative values of the PSJ-radiated electric field. The electric fields decreased by a factor of 2 after the admixing of nitrogen and oxygen molecular gases. Out of the studied targets, the highest electric fields were observed when plasma impinged on the grounded targets, followed by the floating target (2× lower) and the PSJ ignited in the open space configuration (4× lower than in the grounded target configuration).

Atomic versus molecular plasmas for frequency conversion of laser radiation: stronger harmonics, larger cutoffs, better stability, resonance, and quasi-phase-matching enhancement

Atomic versus molecular plasmas for frequency conversion of laser radiation: stronger harmonics, larger cutoffs, better stability, resonance, and quasi-phase-matching enhancement

High-order harmonics enhancement in laser-induced plasma

The methods of enhancement of the strong high-order harmonics of femtosecond pulses in laser-induced plasma are demonstrated. It comprises the application of the four techniques allowing the enhancement of harmonics in different spectral ranges. Among them are the selection of targets for ablation to create the conditions for resonance enhancement of single harmonic, formation of the quasi-phase-matching of a spectrally tunable group of harmonics, application of the two-color pump of plasma, and the formation of nanoparticles-contained plasmas. The number of generated coherent XUV photons increased in the region of single resonantly enhanced harmonic (62 nm) and the shorter-wavelength region (30–50 nm). The above techniques of harmonics enhancement allowed a significant (up to 50 times) growth in a whole harmonic yield in the case of indium plasma. We discuss the reasons preventing the joint implementation of the four methods of harmonics enhancement in the same spectral region.

Fault Diagnosis of Train Wheelset Bearing Roadside Acoustics Considering Sparse Operation with GA-RBF

Trackside acoustic signals are useful for non-contact measurements as well as early warnings in the diagnosis of train wheelset bearing faults. However, there are two important problems when using roadside acoustic signals to diagnose wheel-to-wheel bearing faults; one is the presence of strong interference from strong noise and high harmonics in the signal, and the other is the low efficiency of bearing fault identification caused by it. Therefore, from the viewpoint of solving the two problems, a sparse operation method is proposed for denoising and detuning the modulation of the roadside acoustic signal, and a machine learning classifier with a Genetic Algorithm (GA)-optimized Radial Basis Neural Network (RBFNN) is proposed to improve the rate at which the features of roadside acoustic signal faults are recognized. Firstly, the background noise is filtered out from the Doppler-corrected acoustic signal using the Sparse Representation method, and the inverse wavelet transform is reconstructed into a noiseless signal. Secondly, the interference high-harmonic signal in the signal is filtered out using the Resonant Sparse Signal Decomposition (RSSD) method. Then, the GA is selected to optimize the parameters of the RBF neural network and build a fault diagnosis model. Finally, the extracted acoustic signal feature set is trained on the network model, and the trained model is used for testing. In summary, the sparse operation on the roadside acoustic signal processing and the GA-RBFNN diagnosis model were verified as being very effective in the diagnosis of roadside acoustic train wheel pair faults through the simulation experiment.

Three-color pump of laser-induced plasmas: sum and difference frequency generation.

The generation of strong harmonics and sum and difference frequencies using the propagation of three pulses of different wavelengths and polarizations through Ag, Au, Pb, B, and C plasmas is examined. It is demonstrated that the difference frequency mixing is more efficient compared with the sum frequency mixing. At optimal conditions for the laser-plasma interaction, the intensities of the sum and especially the difference components are almost equal to the intensities of neighboring harmonics attributed to the strong 806 nm pump.

An adaptive group sparse feature decomposition method in frequency domain for rolling bearing fault diagnosis

Group-sparse mode decomposition (GSMD) is a decomposition method designed based on the group sparse property of signals in frequency domain. It is proved to be highly efficient and robust against noise, showing bright prospects for bearing fault diagnosis. However, the following adverse factors may impede its application for incipient bearing fault feature extraction: Initially, the GSMD method did not consider the impulsiveness and periodicity of the bearing fault feature. As a result, the ideal filter bank generated by GSMD may not accurately cover the fault frequency band because it may produce over-coarse or over-narrow filter bank under the condition of strong interference harmonics, large random shocks and heavy noise. Moreover, the location of informative frequency band was obstructed since the bearing fault signal shows complicated distribution in frequency domain. To overcome the abovementioned limitations, an adaptive group sparse feature decomposition (AGSFD) method is proposed. Firstly, the harmonics, large-amplitude random shocks and periodic transient feature are modeled as limited bandwidth signals in the frequency domain. On this basis, an autocorrection of envelope derivation operator harmonic to noise ratio (AEDOHNR) indicator is proposed to guild the construction and optimization of the filter bank of AGSFD. Also, the regularization parameters of AGSFD are adaptively determined. With the optimized filter bank, the original bearing fault is decomposed into a serial of components with AGSFD method, where the sensitive fault-induced periodic transient component is maintained using the AEDOHNR indicator. Finally, the studies of the simulation and two experimental items are carried out to evaluate the feasibility and the superiority of AGSFD method. The results indicate the AGSFD method can identify the early failure in the presence of heavy noise, strong harmonics or random shocks and has better decomposition efficiency.

Fully Printed Dual-Layer Depolarizing Chipless RFID Tag for Wearable Applications

This work presents a cross-polar dual-layer chipless radio-frequency identification (RFID) tag based on a ladder-shaped resonator design. An integrated ground plane enables direct attachment to human skin without performance deterioration. Simulations show that the ladder-shaped resonator provides several advantages over traditional L-shaped and straight resonators, including a strong cross-polar radar cross section (-23.4 dBsm), third-order harmonics, orientation insensitivity, and compact size (0.062 λ2). The effects of the ground plane shape on the surface current distribution are investigated, and a circular tag of 20 mm radius is designed using ladder resonator groups and frequency shift encoding to provide an active area of 96.45 bits/λ2 and a unit frequency of 6.03 bits/GHz. The tag substrate is three-dimensionally (3D) printed with metallic resonator patterns that are subsequently screen-printed on the substrate. The maximum read range is measured at 40 mm using a cross-shaped, dual-polarized Vivaldi antenna connected to a network analyzer. The measured characteristics in free space are in good agreement with the simulation results, and practical on-body performance tests for the manufactured prototype using simulation and direct measurements indicate that the tag performance remains stable for both free space and on-body cases. The fully printed fabrication process makes the proposed tag design suitable for mass production at a low cost.

Practical Aspects of Instantaneous Magnetization Power Functions of Silicon Iron Laminations

Magnetic energy loss P of SiFe steel represents a key factor for the efficiency of soft magnetic machine cores. Traditionally, they are operated with 50 Hz (or 60 Hz), a frequency value that yields rather balanced portions of hysteresis loss and eddy current loss. In equivalent circuits of transformers, P tends to be represented by a magnetic power resistance RM, as a constant. For the most important case of sinusoidal induction B of 50 Hz, this would correspond to an instantaneous magnetization power function p(t) that is sinusoidal as well, however, with 100 Hz (or 120 Hz). On the other hand, from complex, non-linear mechanisms of hysteresis, it is obvious that p(t) should be strongly non-sinusoidal, even for exactly sinusoidal B(t). So far, almost all corresponding instantaneous investigations were restricted to calculated modelling of loss portions and transient modelling. On the other hand, for the first time, the present study was focussed on functions p(t) as measured at IEC-standardized samples of industrially relevant steel. Practical evaluations are discussed with respect to the revealed “history” of magnetization processes, as well as for product characterization. For these tasks, a novel digitized “Low-mass Single Sheet Tester” was developed that was applied for both non-oriented steel (NO) and grain-oriented steel (GO), for 50 Hz. Interpretations proved to be favoured by relating p(t) to total P, according to an instantaneous power ratio. As a result, both steel types revealed strongly non-sinusoidal power functions, with short durations of negative p. Negative p proved to be most pronounced for NO steel, as a measure for the onset of reversible turns of atomic moments. As a consequence, p(t) comprises strong upper harmonics of 200 Hz and even 300 Hz. Based on theoretical considerations, we split p(t) in a dissipative loss power function pL(t) and in a potential energy power function pP(t). Finally, we used p(t) to determine the corresponding power resistance RM(t) that proves to be a distinctly nonlinear function as well. It resembles a rectified co-sinus, also exhibiting short negative spikes that reflect the crystallographic dis-orientation of the polycrystalline material.

A new method to select frequency band for vibration signal demodulation and condition estimation of rolling bearings

The narrowband amplitude demodulation of vibration signals is widely used to extract components carrying information about rolling bearing faults for condition estimation. However, precisely selecting the frequency band determines the quality of demodulation. Although transient detection based methods have achieved satisfactory performance in some scenarios, they may be severely disturbed by strong random impulses or harmonics. Additionally, frequency division strategy is always considered as rough. Aiming at these problems, a new method is proposed to select the optimal frequency band by combining the frequency division strategy, genetic algorithm (GA) optimization, and an automatic fault characteristic order (FCO) search algorithm. Aimed at a signal, its sub-signals are extracted according to the frequency division strategy and the order tracing technology is implemented to obtain the order spectrum of each sub-signal at first. Then, the FCO and its multiples (FCOs) are automatically searched from each order spectrum, and their amplitude summation is calculated. Afterwards, the ratio of FCOs summation to noise amplitude (RFN) is measured as the basis to construct an RFNgram for selecting the primary optimal frequency band Finally, GA is implemented to select the optimized optimal frequency band where the signal is demodulated for estimating the bearing condition. RFN measures both the impulsiveness and periodicity of signals, and GA optimizes the result from a RFNgram, essentially making up for the shortcomings of previous methods under the condition of multiple interferences. RFN is measured through the order spectrum, which also allows it to be applicable to varying speeds, thus achieving a more comprehensive range of industrial applications. Three case studies are implemented to present the superiority of the proposed method in condition estimation for rolling bearings by comparison with four classical or advanced methods.

Relativistic high-order harmonic generation by a femto-second radially polarized laser pulse irradiating a ring plasma grating

A novel scheme for generating relativistic high-order harmonics by a relativistic radially polarized laser interacting with a plasma annular grating is proposed. The particle-in-cell results show that the radial laser field can drive the relativistic electron bunches to oscillate radially in all azimuth directions, resulting in the emission of strong harmonics. Firstly, the interference of the laser field on the plasma grating structure significantly enhances the radiated harmonics which match the phase conditions. Secondly, due to the common ring symmetry of the grating structure and laser polarization, the transverse distribution of harmonics presents a Bessel form, and there is a sharp bright spot in the center with relativistic intensity. Such high-intensity short-wave structured harmonics have broad applications in areas such as plasma diagnostics, high resolution imaging and detection.

Giant Third-Order Nonlinear Response of Mixed Perovskite Nanocrystals

Mixed (FAPbI3)0.92(MAPbBr3)0.08 perovskite thin films exhibit strong nonlinear optical responses, rendering them promising candidates for applications in photonics and optical communications. In this work, we present a systematic study on the ultrafast third-order nonlinear optical processes in mixed perovskite nanocrystals (NCs) by exploring the generation of third harmonic radiation and giant two-photon absorption-based photoluminescence (PL) when excited by femtosecond laser pulses of a 1030 nm central wavelength. A comparative analysis of the coherent third harmonic generation in the thin-film-containing perovskite nanocrystals has shown a 40× enhancement of the third harmonic signal compared to the signal generated in the pure quartz substrate. The cubic dependence of the third-nonlinear optical response of the (FAPbI3)0.92(MAPbBr3)0.08 perovskites on the intensity of the driving radiation was identified using broadband 38 femtosecond driving pulses. The positive nonlinear refractive index (γ = +1.4 × 10−12 cm2·W−1) is found to play an important role in improving the phase-matching conditions of the interacting pulses by generating a strong third order harmonic. The giant two-photon absorption (TPA)-assisted PL peak was monitored and a blue shift of the PL was obtained in the higher intensity range of the laser pulses, with the absorption coefficient β estimated to be~+7.0 cm·MW−1 at a 1030 nm laser wavelength.

On the Improvement of Baseband Section of Frequency-Domain Vector Chipless RFID Readers

This paper presents the design and fabrication of a high-performance frequency-domain vector reader focused on improving the baseband section of the reader. First, a wideband directive filter for canceling out the strong IF harmonics and local oscillator (LO) leakages is implemented in the baseband of the reader to improve the sensitivity of the reader. Then, a modified gain-phase detector (GPD) module is implemented to find the accurate phase of the tag’s received response, enabling the digital background calibration process in the reader. Later, a high featured and compact control unit is proposed for the digital section of the vector reader. To demonstrate the reading performance of the vector reader, we fabricated a modular single-antenna (SNGA) reader to detect the resonances of frequency-coded-based chipless RFID tags over the C-band (4-8 GHz). The reader uses digital and analogue calibrations to yield a high reading range of up to 60 cm while being compatible with the UWB regulations and at desirably compact geometries.

Waves model of three-dimensional cavity flow and its oscillation mode evolution

The high-speed flow passing through an open cavity will generate complex wave structures. The propagation and evolution of these waves can lead to the self-sustained oscillation of the cavity flow and cause strong noise. The cavity noise may contain multiple acoustic modes with discrete frequencies in the spectrum. A clear understanding of the evolution of the oscillation mode will provide a theoretical basis for the study of the noise control method. By analyzing the waves scattering process at both ends of the cavity at subsonic speed and supersonic speed and considering the three-dimensional spanwise flow, the three-dimensional wave model for subsonic cavity flow and supersonic cavity flow are established respectively. The model involves the nonlinear interaction between different waves in the cavity, which may produce other components different from the Rossiter mode. Based on the pressure signal data measured from the experiments on cavity flow for Mach numbers 0.9 and 1.5, the parameters in the model are linearly estimated. The pressure signals are analyzed by using FFT, bispectral analysis, and continuous wavelet transform. The results show that there are nonlinear interactions between the main oscillation modes, thus producing strong harmonics. The mode-switch phenomenon is observed in both the subsonic case and the supersonic case. The mode-switching exhibits low-frequency behavior and shows randomness as a whole.

Identification of Turbomachinery Noise Sources via Processing Beamforming Data Using Principal Component Analysis

Complex turbomachinery systems produce a wide range of noise components. The goal is to identify noise source categories, determine their characteristic noise patterns and locations. Researchers can then use this information to quantify the impact of these noise sources, based on which new design guidelines can be proposed. Phased array microphone measurements processed with acoustic beamforming technology provide noise source maps for pre-determined frequency bands (i.e., bins) of the investigated spectrum. However, multiple noise generation mechanisms can be active in any given frequency bin. Therefore, the identification of individual noise sources is difficult and time consuming when using conventional methods, such as manual sorting. This study presents a method for combining beamforming with Principal Component Analysis (PCA) methods in order to identify and separate apart turbomachinery noise sources with strong harmonics. The method is presented through the investigation of Counter-Rotating Open Rotor (CROR) noise sources. It has been found that the proposed semi-automatic method was able to extract even weak noise source patterns that repeat throughout the data set of the beamforming maps. The analysis yields results that are easy to comprehend without special prior knowledge and is an effective tool for identifying and localizing noise sources for the acoustic investigation of various turbomachinery applications.

Neural tracking of the fundamental frequency of the voice: The effect of voice characteristics.

Traditional electrophysiological methods to study temporal auditory processing of the fundamental frequency of the voice (f0) often use unnaturally repetitive stimuli. In this study, we investigated f0 processing of meaningful continuous speech. EEG responses evoked by stories in quiet were analysed with a novel method based on linear modelling that characterizes the neural tracking of the f0. We studied both the strength and the spatio-temporal properties of the f0-tracking response. Moreover, different samples of continuous speech (six stories by four speakers: two male and two female) were used to investigate the effect of voice characteristics on the f0 response. The results indicated that response strength is inversely related to f0 frequency and rate of f0 change throughout the story. As a result, the male-narrated stories in this study (low and steady f0) evoked stronger f0-tracking compared to female-narrated stories (high and variable f0), for which many responses were not significant. The spatio-temporal analysis revealed that f0-tracking response generators were not fixed in the brainstem but were voice-dependent as well. Voices with high and variable f0 evoked subcortically dominated responses with a latency between 7 and 12ms. Voices with low and steady f0 evoked responses that are both subcortically (latency of 13-15ms) and cortically (latency of 23-26ms) generated, with the right primary auditory cortex as a likely cortical source. Finally, additional experiments revealed that response strength greatly improves for voices with strong higher harmonics, which is particularly useful to boost the small responses evoked by voices with high f0.

Implementation of data access and use procedures in clinical data warehouses. A systematic review of literature and publicly available policies

BackgroundThe promises of improved health care and health research through data-intensive applications rely on a growing amount of health data. At the core of large-scale data integration efforts, clinical data warehouses (CDW) are also responsible for data governance, managing data access and (re)use. As the complexity of the data flow increases, greater transparency and standardization of criteria and procedures are required in order to maintain objective oversight and control. Therefore, the development of practice oriented and evidence-based policies is crucial. This study assessed the spectrum of data access and use criteria and procedures in clinical data warehouses governance internationally.MethodsWe performed a systematic review of (a) the published scientific literature on CDW and (b) publicly available information on CDW data access, e.g., data access policies. A qualitative thematic analysis was applied to all included literature and policies.ResultsTwenty-three scientific publications and one policy document were included in the final analysis. The qualitative analysis led to a final set of three main thematic categories: (1) requirements, including recipient requirements, reuse requirements, and formal requirements; (2) structures and processes, including review bodies and review values; and (3) access, including access limitations.ConclusionsThe description of data access and use governance in the scientific literature is characterized by a high level of heterogeneity and ambiguity. In practice, this might limit the effective data sharing needed to fulfil the high expectations of data-intensive approaches in medical research and health care. The lack of publicly available information on access policies conflicts with ethical requirements linked to principles of transparency and accountability.CDW should publicly disclose by whom and under which conditions data can be accessed, and provide designated governance structures and policies to increase transparency on data access. The results of this review may contribute to the development of practice-oriented minimal standards for the governance of data access, which could also result in a stronger harmonization, efficiency, and effectiveness of CDW.

Undulator and free-electron laser radiation with field harmonics and off-axis effects taken into account analytically

We present an analytic description of the generation of undulator radiation (UR) harmonics in a generalized elliptic undulator with field harmonics. The obtained analytic expressions for generalized Bessel and Airy functions describe the UR spectral lines and radiation intensity in the general and particular cases of two-frequency planar and helical undulators and also for other elliptic and planar undulators. We analytically describe the effect of finite electron beam size, beam emittance, off-axis deflection of electrons, electron energy spread, and beam-bending permanent magnetic components. The obtained analytic expressions distinguish the contributions made by each field component and by the beam and undulator parameters to the generation of radiation harmonics. Using an analytic model of single-pass free-electron lasers (FELs), we analyze the power evolution of harmonics in the LCLS, LEUTL, and SACLA FEL experiments. We discuss the effect that the beam and undulator parameters have on the generation of harmonics. It is shown that the strong second harmonics of radiation observed in experiments are caused by the detected beam deviation from the axis by 15μm over one gain length of 1.5 m in the X-ray LCLS FEL and by the large beam cross section of ∼ 200;μm in the LEUTL FEL. The results of modeling are fully consistent with experiments, which confirms the validity of the presented theoretical description of FEL power and radiation spectral density.

From modulated noise to natural speech: The effect of stimulus parameters on the envelope following response

Envelope following responses (EFRs) can be evoked by a wide range of auditory stimuli, but for many stimulus parameters the effect on EFR strength is not fully understood. This complicates the comparison of earlier studies and the design of new studies. Furthermore, the most optimal stimulus parameters are unknown. To help resolve this issue, we investigated the effects of four important stimulus parameters and their interactions on the EFR. Responses were measured in 16 normal hearing subjects evoked by stimuli with four levels of stimulus complexity (amplitude modulated noise, artificial vowels, natural vowels and vowel-consonant-vowel combinations), three fundamental frequencies (105 Hz, 185 Hz and 245 Hz), three fundamental frequency contours (upward sweeping, downward sweeping and flat) and three vowel identities (Flemish /a:/, /u:/, and /i:/). We found that EFRs evoked by artificial vowels were on average 4–6 dB SNR larger than responses evoked by the other stimulus complexities, probably because of (unnaturally) strong higher harmonics. Moreover, response amplitude decreased with fundamental frequency but response SNR remained largely unaffected. Thirdly, fundamental frequency variation within the stimulus did not impact EFR strength, but only when rate of change remained low (e.g. not the case for sweeping natural vowels). Finally, the vowel /i:/ appeared to evoke larger response amplitudes compared to /a:/ and /u:/, but analysis power was too small to confirm this statistically. Vowel-dependent differences in response strength have been suggested to stem from destructive interference between response components. We show how a model of the auditory periphery can simulate these interference patterns and predict response strength. Altogether, the results of this study can guide stimulus choice for future EFR research and practical applications.

Analysis and Design of Harmonic Rejection Low Noise Amplifier with an Embedded Notch Filter

This paper presents the analysis and design of the harmonic rejection (HR) low-noise amplifier (LNA) with the fully passive source degeneration notch filter. The proposed HR LNA provides the rejection for the strong harmonics ( 3 r d ) of the local oscillator (LO) frequencies, where the HR mixer does not provide sufficient HR performance. The proposed 3 r d harmonic notch filter modulates the source degeneration factor and the impedance matching performance thereafter. This effect further helps the blocking of the harmonic signal. The proposed LNA provides 11 dB gain at the fundamental frequency (2.1 GHz) while rejecting the 3rd harmonic component by 37 dBc. Compared to the conventional LNA, the 3rd harmonic notch performance is improved by 23 dB. Additionally, the LNA achieves a minimum noise figure of 3.1 dB, third order input intercept point ( I I P 3 ) of 0.5 dBm, input reflection (S 11 ) below −10 dB from 1.8 GHz–2.3 GHz operational frequency range, and consumed 19 mW of power from a 1.2 V supply.