Excitation Waveform Research Articles

Shear layer response to overmodulated acoustic perturbations

Shear layers act as demodulators when subjected to amplitude modulated, acoustic perturbations. Recent work explained that the demodulation is a result of the hypothesized relationship between the excitation waveform and the vorticity signal of the large-scale structures, which was represented by a half-wave rectification model. In this paper, this model is explored by overmodulating the excitation signal amplitude. The rectifier model predicts several effects of overmodulation on the flow response, including a doubling of the demodulated response frequency. To validate these predictions, a free, round jet that is excited acoustically upstream of the nozzle is studied using particle image velocimetry. Analytical results from the model are confirmed using a second experimental setup where a jet that emerges from a nozzle and attaches to an adjacent, inclined wall is excited acoustically. Beyond the insight it provides into shear layer vortex dynamics, overmodulation serves as a useful excitation technique for practical applications, where the shear layer response frequency can be increased at the expense of the response amplitude.

On acoustically modulated jet shear layers and the Nyquist–Shannon sampling theorem

The goal of this paper is to present the behavior of a jet shear layer in response to acoustic excitation from a signal processing perspective. The main idea is that the vortices that roll-up in the jet shear layer are similar to the discrete samples of a digital control system, and, hence, that the Nyquist–Shannon sampling theorem should apply. We further hypothesize that the strength of a vortex is determined by the mean amplitude of the excitation waveform during its creation. We also argue that, at least in some cases, demodulation occurs as a result of the vorticity signal generated by the convection of discrete vortices past a point in the shear layer. This vorticity signal is related to the amplitude modulation (AM) excitation waveform by a half-wave rectification operation, a common implementation of an AM demodulator. To investigate these ideas, a free, round jet that is excited upstream of the nozzle is studied using particle image velocimetry. Experiments are conducted that confirm that the sampling theorem applies, and an aliased response is observed when the Nyquist limit is exceeded. Previous authors have attributed demodulation to a vortex merging mechanism, but we demonstrate that merging is not always required for demodulation and suggest that it is one of two mechanisms at play.

Evaluation of Eddy Currents Dependent on Excitation Pattern in Design of Pulse Electromagnets

The evaluation of a new shift bump magnet for replacement of the J-PARC (Japan Proton Accelerator Research Complex) RCS (Rapid Cycling Synchrotron) confirmed that the measured magnetic field waveform was different from the excitation-current waveform. The reason for this is the eddy-current effect due to the fast trapezoidal excitation pattern of approximately 1.5 ms. The same result was confirmed by OPERA-3D. A high-precision injection-beam orbit that suppresses device radiation due to beam loss was necessary. Therefore, in the excitation waveform of the injection bump magnet, the variation range at the flat-top must be less than ±1.0%. We evaluated the effectiveness of the dynamic-magnetic field analysis of OPERA-3D comparison with the measurement results. An agreement with a 0.06% deviation in the magnetic field distribution, the effect of eddy currents on the magnetic field waveform, and the potential of the analysis software for system design were confirmed. We also calculated the amount of heat generated by the bump-magnet coil and the necessary measures for operation. Furthermore, we verified that probes can accurately evaluate the pulsed excitation waveforms.

Germanium silicon oxide achieves multi-coloured ultra-long phosphorescence and delayed fluorescence at high temperature

Colour-tuned phosphors are promising for advanced security applications such as multi-modal anti-counterfeiting and data encryption. The practical adoption of colour-tuned phosphors requires these materials to be responsive to multiple stimuli (e.g., excitation wavelength, excitation waveform, and temperature) and exhibit excellent materials stability simultaneously. Here we report germanium silicon oxide (GSO) – a heavy-metal-free inorganic phosphor – that exhibits colour-tuned ultra-long phosphorescence and delayed fluorescence across a broad temperature range (300 – 500 K) in air. We developed a sol-gel processing strategy to prepare amorphous oxides containing homogeneously dispersed Si and Ge atoms. The co-existence of Ge and Si luminescent centres (LC) leads to an excitation-dependent luminescence change across the UV-to-visible region. GSO exhibits Si LC-related ultra-long phosphorescence at room-temperature and thermally activated delayed fluorescence at temperatures as high as 573 K. This long-lived PL is sensitized via the energy transfer from Ge defects to Si LCs, which provides PL lifetime tunability for GSO phosphors. The oxide scaffold of GSO offers 500-day materials stability in air; and 1-week stability in strong acidic and basic solutions. Using GSO/polymer hybrids, we demonstrated colour-tuned security tags whose emission wavelength and lifetime can be controlled via the excitation wavelength, and temperature, indicating promise in security applications.

Effect of Single and Multi-Direction Coil for Differential Probe on Depth Crack Defect Measurement with Different Excitation Frequency Selection in Eddy Current Inspection

In recent years, a number of studies in Non-Destructive Evaluation (NDE) have been conducted on the sensitivity of probes in assessing the depth of cracks based on input stimulation. Range frequency and crack depth have been suggested as relevant features for input excitation waveform forms. The construction of an encircling coil for a differential probe (ECDP) and an encircling coil for an absolute probe (ECAP) was discussed in this paper. For the defect, the Multi-Frequency (MF) measuring method was used to compare ECDP with single direction and multi-direction turn coil growth. The measurement method was based on the coupling of ECDP and ECAP. By comparing the resulting signal between the probes, it is clear that the ECDP (with longitudinal and transverse coils) is very effective in measuring the various types of defects in the frequency ranges. The ideal excitation frequencies for inspection testing are 30kHz and 60kHz.

Nonlinear characteristic and chip breaking mechanism for an axial low-frequency self-excited vibration drilling robot

Drilling is one of the essential material removal methods in the aerospace field. This study proposes a flexible variable-stiffness axial low-frequency self-excited vibration drilling scheme for automatic manufacturing platforms. Firstly, an elastic zone active conversion mechanism of the drilling actuator is established, which could realize robot stiffness control in different directions and the directional tool vibration excitation. Then, the nonlinear characteristic of self-excited vibration excitation and vibration waveform is analyzed under various inherent characteristics and drilling parameters. An interface separation chip breaking condition of dual-frequency self-excited vibration drilling is proposed based on the dynamic equivalent undamped state. Finally, the self-excited vibration drilling state, tool trajectory, chip breaking performance, chip morphology, and action mechanism of parameters coupling characteristics are investigated based on experiment and simulation results. This drilling system could produce stable self-excited vibration and smooth chip breaking without a vibration excitation device.

Dual functions of alternating current electroluminescent device for light emission and humidity detection

Alternating current electroluminescent (AC-EL) device can be considered as a potential candidate for next generation of multifunctional light-emitting sources. In this work, we present a new design of AC-EL device with inclusion of a silver oxide humidity-sensing layer instead of an insulating buffer layer for humidity detection. The ZnS:Cu, Cl and ZnS:Ag+(Zn,Cd)S:Ag phosphors were used as an emissive layer prepared by screen printing method. The silver oxide (AgO/Ag2O) nanoparticles synthesized via a green method were employed as a humidity sensing layer. The developed AC-EL devices exhibited high response, good productivity, high stability, high repeatability and linear relationship with humidity in range of 10%–90% RH as well as no significant effects with several VOCs/gases such as NH3, CO2, acetone, methanol, toluene and propan at room temperature. The effects of parameters such as excitation frequency, applied voltage, and waveforms on the luminance intensity are discussed. The development of the present AC-EL device offers a simplified architecture to enable sensing functions of the AC-EL device via monitoring of light emission changing.

Enhancement of Portable Mass Spectrometer Sensitivity and Selectivity by a Qualitative Pre-Scan Waveform (QPSW)

While portability is a key aspect of small mass spectrometers, they also need to be able to effectively screen the analytes from complex matrices. The accuracy and performance of mass spectrometers depend not only on the identification of parent ion signals in targets but also fragment ion signals. This paper reports on the construction of a device that uses a new time-domain excitation waveform called qualitative pre-scan waveform (QPSW) for its quadrupole ion trap mass spectrometry analyzer. This approach uses scanning to eliminate interfering ions, thus improving the sensitivity for the analyte and removing the cumbersome steps required to convert conventional stored waveform inverse Fourier transform (SWIFT) waveforms from the frequency domain to the time domain. Tests show that the target ions can be fragmented just by introducing air at the moment when the pinch valve is opened without any need for a carrier gas. This simplifies the equipment required, making the mass spectrometer more portable. Tests were undertaken to compare the performance with the use of conventional SWIFT waveforms and to optimize its experimental parameters so that the target ions were effectively accumulated in the ion trap. An approximate 5-fold improvement in sensitivity was achieved by QPSW compared to the SWIFT for 2 μg/mL ketamine. A 5-fold reduction in the limit of detection (LOD) to 20 ng/mL was also obtained for enrofloxacin. In addition, the stability was improved by QPSW with a relative standard deviation less than 13% compared to 16% for SWIFT.

Advanced orthogonal frequency and phase modulated waveform for contrast-enhanced photothermal wave radar thermography

Thermal wave radar (TWR) thermography is a high-efficient nondestructive testing technique to increase the signal-to-noise ratio (SNR) and to enhance target detection capability. However, the detection of subsurface defects, especially small-size defects, usually requires a distinctively high SNR and depth resolvability. This paper proposed an orthogonal phase-coded linear frequency modulated (OPCLFM) excitation waveform, which has significantly improved the SNR and depth resolvability of TWR compared to the LFM waveform. The pulse compression quality of the OPCLFM waveform was initially evaluated through a 1D thermal wave analytical model of carbon fiber reinforced polymer (CFRP) laminate. Results show that the OPCLFM waveform combined with the Kaiser window function compresses the largest sidelobe at least by 18.39 dB compared to the LFM waveform. Furthermore, the superior depth resolvability performance of the OPCLFM waveform was also validated by 3D finite element simulation. Finally, the effect of thermal conductivity on the depth resolvability performance of the OPCLFM waveform was evaluated quantitatively by a delaminated CFRP laminate.

ZnO piezoelectric coatings used for the ultrasonic excitation of longitudinal-transverse waves and their application for smart bolts

The accurate measurement of the prestress for bolt has been intensively investigated in recent years. Many research studies have been conducted to improve the accuracy of prestress measurement using ultrasound techniques; in particular, the real-time prestress of bolt can be obtained without the requirements to calibrate the original load when ultrasonic longitudinal and transverse waves are applied simultaneously. However, there are few studies that have focused on ultrasonic transducers that can generate longitudinal and transverse waves simultaneously. Furthermore, research on coatings deposited directly on the top of the bolts for the excitation of longitudinal and transverse waves has not been reported. ZnO coating is widely used for the ultrasonic transducer due to its excellent piezoelectric property and stable structure in high temperatures. Therefore, it is an outstanding candidate for the excitation of both longitudinal and transverse waves and has a good application prospect in the field of bolt prestress measurement by ultrasonic sound wave with high accuracy. In this paper, ZnO piezoelectric coatings were deposited on (100)-oriented Si substrates by radio frequency sputtering techniques. The morphology, structure, and echo signal characteristics of the coatings were characterized by SEM, AFM, XRD, and ultrasonic measurement instruments. The experimental results showed that Ar/O2 ratio and deposition position exhibited significant effects on the excitation waveform of the ZnO piezoelectric coating. When the Ar/O2 ratio reduced to 1:3, the coating could excite both transverse and longitudinal waves. However, when the deposition position gradually moved away from the sputtering center, the transverse wave gradually enhanced. The coating could excite a pure transverse wave when the sample was at the edge of the effective sputtering area, which showed that the type of the excitation wave and the relative intensity of each wave could be well controlled by the Ar/O2 ratio and deposition position. These research results have a good application prospect in bolt stress measurement.

Striations in dual-low-frequency (2/10 MHz) driven capacitively coupled CF4 plasmas

In electronegative radiofrequency plasmas, striations (STRs) can appear if the bulk plasma is dominated by positive and negative ions that can react to the driving frequency. Here, we investigate such self-organized structures in dual-frequency (2/10 MHz) capacitively coupled CF4 plasmas by phase-resolved optical emission spectroscopy and particle-in-cell/Monte Carlo collision simulations. This choice of the frequencies is made to ensure that the ions can react to both the lower (2 MHz, ‘low frequency’, LF) and the higher (10 MHz, ‘high frequency’, HF) components of the excitation waveform. A strong interplay of the two excitation components is revealed. As the STRs appear in the plasma bulk, their number depends on the length of this region. By increasing the LF voltage, ϕ LF, the sheath widths at both electrodes increase, the bulk is compressed and the number of STRs decreases. The maximum ion density decreases slightly as a function of ϕ LF, too, due to the compressed plasma bulk, while the minimum of the ion density remains almost constant. The spatio-temporal distributions of the excitation and ionization rates are modulated both by the LF and HF with maxima that occur at the first HF period that follows the complete sheath collapse at a given electrode. These maxima are caused by a high local ambipolar electric field. At a given phase within a HF period the current density is different at different phases within the LF period because of frequency coupling. The LF components of the F− ion velocity and of the electric field are much lower than the respective HF components due to the lower LF component of the displacement current in the sheaths. The LF component of the total current is dominated by the ion current at low values of ϕ LF but by the electron current at high values. The HF component of the total current is dominated by the electron current and decreases slightly as a function of ϕ LF.

Image quality improvement of magneto-acousto-electrical tomography with Barker coded excitation

Magneto-acousto-electrical tomography (MAET) combines the advantages of the high resolution of ultrasound imaging and the high contrast of electrical impedance tomography for imaging the conductivity of tissues. The traditional MAET uses a short pulse as the excitation waveform, and the amplitude of the MAE signal for a single acquisition is very weak. Thus, the multiple-acquisition mode for averaging was adopted to reduce the system noise while significantly increasing the data acquisition time. In this study, a coded-based MAET method was proposed to improve the image quality of MAET. We theoretically derived the principle of the coded-based MAET and analyzed the performance of different pulse compression techniques. The 13-bit Barker code was selected, and phantoms of different shapes and conductivity were used to verify the proposed method experimentally. Finally, in vitro experiment was conducted to investigate the performance of the proposed method in tissue level application. The experimental results show that the proposed method can significantly improve image quality and speed up the imaging time.

Case study: Effect of asymmetry of vibration on the perceived illusion force

The illusion force perceived by exciting asymmetric vibration has been studied, and the kinesthetic effect is recently clarified to be largely influenced by the asymmetry of the excited vibration waveforms. However, it has not yet been investigated how the extent of asymmetry influenced the perception of the illusion force. In this study, the effect of the asymmetry of the input vibration waveform on the extent of induced traction force was experimentally investigated by changing the extent of asymmetry that is controlled by the summation order of Fourier series expansion of the original waveform. As a result, it was confirmed that the extent of induced traction form increases as the extent of asymmetry of the actuated sawtooth waveform increases up to the summation order of 3; however, the induced traction form does not increase in case of n of over 4.

Study on enhanced heat transfer process under the effect of waveform excitation in micro-channel

Waveform excitation is an effective means to improve the heat transfer effect of micro-channel heat exchanger. In order to study the influence of excitation conditions and heat exchanger parameters on the flow heat transfer of the working fluid in the channel, a numerical model of dynamic wall heat exchanger is constructed, and the influence of excitation parameters such as wavelength, frequency and amplitude on the pumping performance and heat transfer coefficient of the heat exchanger is analyzed. The results show that increasing both wavelength and frequency increase the pumping performance of the heat exchanger under the same inlet pressure conditions, but the effect on the heat transfer coefficient of the heat exchanger shows a non-linear pattern; the inlet height has a significant effect on the pumping performance, and its pumping performance is increased by a maximum of 680% and its heat transfer coefficient is increased by a maximum of 794% compared to the static heat exchanger.

Influence of De-Trapped Charge Polarity in Sensing Health of Power Transformer Insulation

Assessment of insulation condition by sensing and subsequent analysis of oil-impregnated paper response at periodic intervals is necessary for reliable operation of transformers. Sensing frequency domain insulation response requires the application of either a sinusoidal excitation voltage (over a wide range) or a custom excitation waveform. This not only requires a specially designed variable-frequency variable-amplitude excitation voltage source but also makes measurement practically problematic. Measurement of low-frequency data is time-consuming and the data tends to get affected by field noise. In comparison, a simpler and cheaper alternative is the analysis of time-domain insulation response. This involves the measurement of low amplitude polarization and depolarization current. A pico-ammeter or Electrometer is generally used for this purpose. The available interpretation scheme of time domain response sensed using Electrometer does not consider the de-trapping charge’s polarity. The result presented in the paper shows that such an assumption inadvertently leads to inaccurate diagnosis. This, in turn, generates doubt regarding the current sensing capability of the Electrometer involved. In the present work, a better interpretation scheme of the data sensed by the Electrometer is discussed. The significance and influence of de-trapped charge polarity on polarization and depolarization currents are investigated. The analysis is tested on data collected from real-life in-service power transformers.

A mitigation technique for torque ripple in a brushless DC motor by controlled switching of small DC link capacitor

High performance applications are now days utilizing the brushless DC motor (BLDC) drives due to its ruggedness, compactness, high torque to weight ratio, high dynamic response etc. the feature of square-wave current excitation waveforms in BLDC motor drives allows some major system simplifications for trapezoidal BLDC motors. The developed torque is constant in ideal conditions in this motor when its back emf waveform is of trapezoidal type. Despite this, due to the physical construction of the motor and its settings, torque ripple exists in the output torque and is an undesired phenomenon in the BLDC motor drives and are also linked to the motor's control and driver sides. This paper provides a new way for reducing torque ripple and is simple, compact and cost effective. To prove the correctness of the compensation technique, circuit is modelled and simulations are carried to examine the theoretical performance of the BLDC motor drive. Experiments on a prototype drive were conducted to further validate the theoretical analysis as well as the utility of the proposed technique.

Analysis on harmonic characteristic of transformer DC bias caused by metro stray current

With the continuous improvement of the economic level, urban rail transit has been vigorously developed. However, the metro stray current will be generated during the actual operation of urban rail, which will cause transformer DC bias along the metro line. In order to effectively evaluate the influence of the transformer on the DC bias under urban rail operation, the stray current distribution model with single and double-ended power supply mode was established, and the numerical calculation of the stray current was realized. Based on the real-time dynamic change characteristics of the stray current, a synchronous simulation model of the transformer DC bias was established, and the harmonic characteristics of the transformer excitation current were further analyzed. The simulation test shows that when the direct current is injected into the neutral point of the transformer, the excitation current waveform is asymmetrical along the positive and negative semi-axes, and the odd and even harmonics coexist. And the influence of transformer DC bias is weakened when transformer air core reactance is increased. The characteristic quantities such as excitation current amplitude, waveform characteristics, and harmonic content have been quantitatively analyzed in this paper, which has certain guiding significance for evaluating the influence of transformer DC bias.

Evaluation of the Applicability of IFRA for Short Circuit Fault Detection of Stator Windings in Synchronous Machines

A machine is a device to realize the mutual conversion of electric energy and mechanical energy. This work mainly discusses the applicability of impulse frequency response analysis to detect the stator winding short circuit faults. The parameters of excitation waveform and signal sampling were carefully selected. A solid-state nanosecond pulsed power source prototype was developed for resonant excitation of windings. The proposed method was then verified on a 5 kVA, 380V, 2-pole, the salient synchronous machine through artificial fault experiments. Finally, the proposed method was compared with other traditional methods. The method has the advantages of fast measurement, rich high frequencies, high stability, and low cost. Since the principle of impulse frequency response analysis is also applicable to large synchronous machines, this method and device may also be applied to detect large synchronous machines winding short circuit faults. It can be used as an auxiliary and alternative method in the non-destructive fault detection of synchronous machines.

Characteristic Mode Analysis Prediction and Guidance of Electromagnetic Coupling Measurements to a UAV Model

In this work, we study the current coupled to a simplified Unmanned Aerial Vehicle (UAV) model using a dual computational and experimental approach. The simplified surrogate structure reduced the computational burden and facilitated the experimental measurement of the coupled currents. For a practical system, a wide range of simulations and measurements must be performed to analyze the induced current variations with respect to properties of the incident excitation waveform, such as the frequency, angle of incidence, and polarization. To simplify this analysis, Characteristic Mode Analysis (CMA) was used to compute the eigen-currents of the UAV model and predict where and under which RF excitation conditions the coupled current is maximized. We verified these predictions using direct experimental measurement of the coupled currents. The presented simulations and measurements show the usefulness of CMA for studying electromagnetic coupling to practical systems.

Characterizing power transformer frequency responses using bipolar pseudo-random current impulses

The behaviour of a power transformer is complex and difficult to predict during transient conditions or during operation at frequencies below or above its nominal frequency, a phenomenon common in renewable energy plants due to harmonic distortion. Furthermore, the accuracy of a power system simulation depends on the models of critical subsystems such as the power transformers. This paper presents the use of a unique excitation waveform comprising of pseudo-random current impulses to accurately identify the wideband characteristics of a power transformer. By injecting the excitation waveform to the relevant transformer terminals, frequency responses are determined by cross-correlation of the perturbation signal, and the measured response. Compared to the traditional transformer identification methods, the pseudo-random current impulses offer a wideband excitation with a higher degree of controllability such that its spectral energy can be focused in the frequency band of interest. The proposed method was investigated on a 16 kVA, 22 kV/240 V single-phase transformer. The obtained wideband frequency responses provide useful information in harmonic penetration and over-voltage studies and are also used to estimate, with a high degree of accuracy, the lumped parameters of the equivalent transformer broadband circuit model.