Pulse Excitation Method Research Articles

Evaluation of bone integrity around the acetabular cup using noninvasive laser resonance frequency analysis.

Resonance frequency analysis (RFA) is valuable for assessing implant status. In a previous investigation, acetabular cup fixation was assessed using laser RFA and the pull-down force was predicted in an in vitro setting. While the pull-down force alone is sufficient for initial fixation evaluation, it is desirable to evaluate the bone strength of the foundation for subsequent fixation. Diminished bone quality causes micromotion, migration, and protracted osseointegration, consequently elevating susceptibility to periprosthetic fractures and failure of ingrained trabecular bone. Limited research exists on the evaluation of bone mineral density (BMD) around the cup using RFA. For in vivo application of laser RFA, we implemented the sweep pulse excitation method and engineered an innovative laser RFA device having low laser energy and small dimensions. We focused on a specific frequency range (2500-4500 Hz), where the peak frequency was presumed to be influenced by foundational density. Quantitative computed tomography with a phantom was employed to assess periprosthetic BMD. Correlation between the resonance frequency within the designated range and the density around the cup was evaluated both in the laboratory and in vivo using the novel laser RFA device. The Kruskal-Wallis test showed robust correlations in both experiments (laboratory study: R = 0.728, p < 0.001; in vivo study: R = 0.619, p < 0.001). Our laser RFA system can assess the quality of bone surrounding the cup. Laser RFA holds promise in predicting the risk of loosening and might aid in the decision-making process for additional fixation through screw insertion.

Prediction of flame transfer function and combustion instability on a partially premixed swirling combustor by the system identification and CFD methods

Combustion instability can lead to high amplitude oscillations of pressure in the combustion chamber, which would seriously affect the normal operation of the combustion system. In order to reduce the cost and time of combustion chamber design and testing, combustion instability of the partially premixed swirl combustor was predicted, by solving the Helmholtz equation coupled the flame transfer unction (FTF). In the experimental study, by changing the equivalence ratio, the pressure in the combustion chamber appeared to oscillate in different forms including combustion noise, intermittent oscillation and limit cycle oscillation, while the frequency of the self-excited oscillations was obtained to be 165 Hz at the equivalence ratio of 0.7. In Computational Fluid Dynamics (CFD) Simulations, by applying Discrete Random Binary Signal (DRBS) excitation at the inlet, the FTF has been calculated by system identification method, where the excitation results of perturbation signals with different magnitudes were studied. And the result was basically consistent with the FTF calculated by the single-frequency excitation method, which means that the system identification method is suitable for calculating the FTF of the partially premixed swirl combustor. The pulse excitation method has been proposed to determine the selection of the filtering order, and the accuracy of the method has been validated through comparing the FTF results obtained by using different filter orders for discrimination. Moreover, coupling the FTF into the Helmholtz equation, the oscillation frequency of the system was predicted as 159.7 Hz, compared with the experimentally measured oscillation frequency of 165 Hz, which verified that the model could be effectively used for the prediction of oscillation frequency in the partially premixed combustion systems.

P-N Bonds-Mediated Atomic-Level Charge-Transfer Channel Fabricated between Violet Phosphorus and Carbon Nitride Favors Charge Separation and Water Splitting.

Heterostructures are widely employed in photocatalysis to promote charge separation and photocatalytic activity. However, their benefits are limited by the linkages and contact environment at the interface. Herein, violet phosphorus quantum dots (VPQDs) and graphitic carbon nitride (g-C3N4) are employed as model materials to form VPQDs/g-C3N4 heterostructures by a simple ultrasonic pulse excitation method. The heterostructure contains strong interfacial P-N bonds that mitigate interfacial charge-separation issues. P-P bond breakage occurs in the distinctive cage-like [P9] VPQD units during longitudinal disruption, thereby exposing numerous active P sites that bond with N atoms in g-C3N4 under ultrasonic pulse excitation. The atomic-level interfacial P-N bonds of the Z-scheme VPQDs/g-C3N4 heterostructure serve as photogenerated charge-transfer channels for improved electron-hole separation efficiency. This results in excellent photocatalytic performance with a hydrogen evolution rate of 7.70mmolg-1h-1 (over 9.2 and 8.5 times greater than those of pure g-C3N4 and VPQDs, respectively) and apparent quantum yield of 11.68% at 400nm. Using atomic-level chemical bonds to promote interfacial charge separation in phosphorene heterostructures is a feasible and effective design strategy for photocatalytic water-splitting materials.

Research on the vibration mechanism of compressor complex exhaust pipeline based on transient flow

The periodic exhaust of the compressor often induces gas flow fluctuations within the pipeline, leading to vibrations. Excessive vibration can lead to fatigue, cracks, loosening of components, and resulting in local leakage, which may easily lead to fire, explosion, and secondary hazards. Therefore, in this paper, a computational model for the transient flow field of the compressor exhaust pipeline was established, using the pulse excitation method and Fluent software, the natural frequencies of the gas column in the pipeline were calculated, and the patterns of oscillation decay of the gas column wave propagating back and forth within three exhaust pipes were researched. The mechanism behind the pipeline pressure pulsation and the influence of pipeline structural parameters on the natural frequencies of the gas column were explored. The calculation results show that the first-order natural frequency of the gas column is very close to the double frequency of the compressor excitation frequency at 3.33Hz, and the second-order natural frequency of the gas column is very close to the quadruple frequency of the compressor excitation frequency at 3.33Hz, which may cause significant pipeline vibrations. Altering the pipeline structure, especially when influenced by airflow branching after a tee junction, results in complex changes in the natural frequencies of the gas column. Furthermore, the structural natural frequencies of the pipeline were obtained through the finite element. It has been observed that resonance phenomena exist among the structural natural frequencies and their harmonics of the pipeline and the natural frequencies of the gas column and their harmonics, as well as multiples of the excitation frequency. These results lay the foundation for understanding the vibration mechanism of the pipeline and finding ways to reduce vibration.

Uncertainty analysis and performance evaluation of thermophysical property measurement of liquid Au in microgravity

A new method for quantifying facility performance has been discussed in this study that encompasses uncertainties associated with thermophysical property measurement. Four key thermophysical properties: density, volumetric thermal expansion coefficient, surface tension, and viscosity of liquid Au have been measured in microgravity environment using two different levitation facilities. Levitation experiments were conducted using the Electrostatic Levitation Furnace (ELF) onboard the ISS in Argon and air, and the TEMPUS Electromagnetic Levitation (EML) facility on a Novespace Zero-G aircraft parabolic flight in Argon. The traditional Maximum Amplitude method was augmented through the use of Frequency Crossover method to identify the natural frequency for oscillations induced on a molten sample during Faraday forcing in ESL. The EML tests were conducted using a pulse excitation method where two techniques, one imaging and one non-imaging, were used to study surface oscillations. The results from both facilities are in excellent agreement with the published literature values. A detailed study of the accuracy and precision of the measured values has also been presented in this work to evaluate facility performance.

Ultrafast quantum path interferometry to determine the electronic decoherence time of the electron-phonon coupled system in n -type gallium arsenide

Quantum coherence is the key to new quantum technologies, although the details of decoherence processes and times are still not well understood in solids. We demonstrate how to measure the decoherence time of electronic excited states in $n$-type gallium arsenide ($n$-GaAs) crystals using a relative-phase locked double pulse excitation method and quantitatively evaluate with a simple model including temperature dependence. The interference patterns of both electronic and phonon coherence are observed in $n$-GaAs using ultrafast quantum path interferometry with $\ensuremath{\pi}/4$ polarized femtosecond pulses, via the amplitude of longitudinal optical phonons as a function of pump-pump delay. The electronic coherence shows uplifting and splitting in the collapse and revival of the electronic interference, which is sensitive to temperature, and these features are well reproduced using a simple quantum mechanical model. The decoherence time is determined using quantum calculations, from the splitting and uplifting in the interference shape, to be $27.8\ifmmode\pm\else\textpm\fi{}0.5, 23.0\ifmmode\pm\else\textpm\fi{}0.3$, and $12.9\ifmmode\pm\else\textpm\fi{}0.3$ fs at 10, 90, and 290 K, respectively. The temperature dependence of the decoherence time is well reproduced by the density of electrons in the conduction band with the group velocity of the photoinduced electrons.

Nonlinear vibration characteristics of composite pyramidal truss sandwich cylindrical shell panels with amplitude dependence

Recently studies on the bending, compression, buckling, and other static issues of composite pyramidal truss sandwich cylindrical shell (CPTSCS) panels have been reported. However, rare literature has explored the nonlinear vibration characteristics of the CPTSCS panels. In this paper, their amplitude-dependent vibration properties are studied both experimentally and theoretically. First, a fabrication flowchart is proposed to obtain such panel specimens, and a pulse excitation method via a hammer and sweeping frequency and fixed excitation techniques provided by a base vibration shaker are employed to measure the nonlinear variation of vibration parameters. As a result, the amplitude-dependent vibration phenomenon is confirmed to exist in both the pyramidal truss core and composite skins. After the nonlinear assumptions of Young's moduli, shear moduli, and loss factors of the pyramidal truss core and composite skins are defined based on Jones-Nelson nonlinear material theory, complex modulus method, Gibson equivalent principle, etc., a novel theoretical model is developed to predict the nonlinear natural frequencies, damping ratios, and resonant responses under different base excitation energies, in which the first order shear deformation theory, Rayleigh Ritz variation method, modal strain energy approach, and modal superposition technique are adopted to solve key vibration parameters. The pre-defined amplitude-dependent fitting coefficients that are vital to the completeness of the current model are further identified using the measured frequency and damping data. Also, detailed tests are done to make sure that both the proposed model and the predictions are correct. Finally, the effects of critical geometric and material parameters of the CPTSCS panels on the amplitude-dependent vibration characteristics are evaluated based on the calculated dynamic results, with some practical suggestions being refined for improving the vibration suppression capability of such advanced composite structures.

Deep Tissue Characterization with Optical Coherence Elastography: A Comparison of Different Methods

The measurement of the biomechanical properties of the skin is of great interest since these properties play an important role in the development of several diseases such as skin cancer and systemic sclerosis. In this direction, several diagnostic tools have been developed to analyze the mechanical properties of the skin. Optical coherence elastography (OCE) is one of the emerging imaging techniques used for the characterization of the mechanical properties of the tissue quantitatively. In systemic sclerosis patients, the measurement of the mechanical properties of the deeper skin layers is desirable compared to the superficial layers. There are several variants of OCE that exist, but it is still not clear which method is more suitable for the measurement of the mechanical properties of the deeper tissue. In this work, we tested three common methods, the pulsed excitation method, the continuous wave excitation method, and the resonant frequency method, for the measurement of the mechanical properties of the deeper layers in the tissue. We found out that the pulsed wave excitation method provides the most reliable measurements in the shortest possible time compared to the other two methods.

Magnetoelectric effects in a composite ferromagnet–piezoelectric heterostructure under pulsed excitation

Magnetoelectric (ME) effects in multiferroic ferromagnet–piezoelectric (PE) composite heterostructures result in a change in the electric polarization under the action of magnetic field or a change in the magnetization under the action of electric field and, therefore, are interesting from scientific point of view and for applications. In this work, the direct and converse ME effects are experimentally studied when a planar amorphous ferromagnet–PE lead zirconate–titanate structure is excited by magnetic and electrical field pulses with duration from microseconds to tens of milliseconds. Under the action of magnetic field pulses, the structure generates damped voltage oscillations with a frequency equal to the acoustic resonance frequency of the structure, as well as an exponentially decreasing dc voltage. By choosing the duration of magnetic pulses, it is possible selectively excite the linear ME effect in the structure or generate the second voltage harmonic at the resonance frequency. Electrical field pulses result in the excitation of damped magnetization oscillations at the resonance frequency of the heterostructure. The pulsed excitation method allows to estimate the ME conversion coefficients for both the direct and converse ME effects.

Dynamic Calibration of a Thin-Film Heat-Flux Sensor in Time and Frequency Domains.

This paper mainly studies the model design of a thin-film heat-flux sensor (TFHFS), and focuses on the comparison of three dynamic calibration methods. The primary motivation for studying this came from the urgent need for heat-flux dynamic measurements in extreme environments, and the one-sidedness of the dynamic performance evaluation of the corresponding TFHFS. The dynamic theoretical model of the TFHFS was originally established on the principle of a temperature gradient on the basis of a thermal radiation boundary. Then, a novel TFHFS sensor was developed, which can be used at temperatures above 880 °C and has a high sensitivity of 2.0 × 10−5 mV/(W/m2). It can function stably for long durations under a heat-flux density of 3 MW/m2. The steady-state, transient, and frequency calibration of a TFHFS were compared to comprehensively analyze the dynamic characteristics of the TFHFS. The steady-state response time measured by the step excitation method was found to be 0.978 s. The QR decomposition method was applied to the steady-state response experimental model construction, and the fitting degree of a second-order transfer function model obtained was 98.61%. Secondly, the transient response time of the TFHFS was 0.31 ms based on the pulse-excitation method. The transient relationship between the surface temperature and the heat flux, and the pulse-width dependence of the TFHFS transient response time were established. Surprisingly, the response frequency of the TFHFS, about 3000 Hz, was efficiently tested using the frequency response function (FRF), which benefitted from the harmonic characteristics of a periodic square-wave excitation signal. Finally, a comprehensive evaluation of the dynamic performance of the TFHFS was realized.

Sweep Pulse Excitation Method for Enhancing Photoacoustic Elastic Waves at Different Laser Irradiation Parameters.

Laser remote sensing using a sweep pulse excitation method, in which a laser beam is irradiated at the same repetition frequency as the natural frequency, for enhancing photoacoustic elastic waves through resonance effect has been studied. The sweep pulse excitation method, which is based on the principle of detecting natural frequency fluctuations, such as hammering tests, can detect natural frequencies in the audible sound region with low average laser power and contribute to the convenience and low cost of an installation strength diagnosis of fastening bolts. In this study, we investigated the dynamics of the swept excitation method for optimization by evaluating the dependence of the laser irradiation conditions (pulse width, spot size, and average power) on different metal disc samples. We discovered that the magnitude of the photoacoustic elastic wave is proportional to the absorption of laser power, and the spatiotemporal dynamics can be explained through thermal diffusion phenomena. These findings contribute to the development of laser-sensing technology based on photoacoustic elastic waves.

Pulsed excitation method provides path forward for tracing triplet excitons in OLEDs

Measurements of angle-resolved delayed electroluminescence in the setting of triplet-triplet fusion use singlet excitons to study the kinetics of nonemissive triplets.

Highly Sensitive Low-Energy Laser Sensing Based on Sweep Pulse Excitation for Bolt Loosening Diagnosis

The hammering method used by inspectors is generally applied to inspection of looseness of bolted parts. This method entails active sensing through the input of an excitation signal produced by the inspectors, and has the advantage of practical experience acquired over many years. The sound (vibration) and sensation produced upon excitation by a hammer can be used as indices, but also leads to the disadvantage of unavoidable qualitative testing and human error. Laser remote sensing (LRS) uses the same diagnostic principle as the hammering test for remote, high-speed, and quantitative inspection. However, the accuracy of LRS must be improved and the required pulse energy must be reduced. Hence, we propose the sweep pulse excitation method, which realizes LRS with low pulse energy through the resonance oscillation caused by sweeping the laser irradiation frequency. A performance test on bolted joints was conducted with regard to bolt loosening diagnosis using two methods, namely, the conventional single-pulse excitation method and the sweep pulse excitation method. With the sweep pulse excitation method, the laser-induced vibration is produced only by absorbing the laser pulse energy which is caused by thermo-elastic waves and without using the elastic wave induced by the laser ablation. The experimental and calculation results reveal that, with the proposed method, the measurement accuracy improved by 104 times, while the required pulse energy decreased by 102 times. The adaptability of the low-pulse energy laser contributes toward the development of inspection systems because it achieves size and cost reduction, and inspection convenience.

Estimation of carrier mobilities and recombination lifetime in halide perovskites films using the moving grating technique

Pulsed excitation methods followed by time-resolved measurements have been questioned as a valid procedure to deduce transport properties of halide perovskites (HaPs). Measurements of both the majority and minority carrier’s phototransport properties, under illumination conditions as close as possible to one sun, are needed to obtain reliable information on recombination mechanisms. In this work, we show that the moving photocarrier grating technique (MGT) fulfills the above-mentioned conditions. In this method, both carriers mobilities and the common recombination lifetime are deduced from the DC short circuit current induced by the movement of an interference pattern along the sample surface. We show that the method, originally developed to measure the transport parameters of amorphous semiconductors, can be fully applied to HaPs films. We briefly describe the technique, we perform measurements as a function of the grating period and the light intensity, and we discuss the best approach to extract the transport parameters from MGT measurements. Finally, we find the exponents that describe the intensity dependence of the transport parameters of majority and minority carriers in a HaP sample.

High-efficiency modal analysis and deformation prediction of rice transplanter based on effective independent method

The vibration problem associated with rice transplanters not only affects the quality and effect of the transplanting operation but also reduces the service life of the machine. With a focus on the vibration problem in the working process of a high-speed rice transplanter, a mechanical deformation prediction system based on the effective independence method for modal analysis was developed. This system simulates the vibration of the support arm of the transplanter during the working process of agricultural machinery. The deformation is predicted. With the use of the effective independence method, the measuring points that contribute the most to the target modal vector independence can be screened and retained as much as possible. In this way, there is greater assurance of more modal information being obtained under the limited sensor. Accuracy and mode requirements for experimental data were identified. In this paper, the experimental mode adopts the effective homology method to select the best measuring point and uses the pulse excitation method to collect data and analyze and calculate the DH5902 dynamic signal acquisition and analysis system to obtain the natural frequency and vibration mode of the support arm. Based on this, the SolidWorks software is used to model the key components of the transplanter power transmission system. The model is imported into ANSYS Workbench and combined with the Lanczos Method solution to solve the natural frequency and vibration mode. The accuracy of this modal test analysis method was verified. The results show that the first-order natural frequency of the transplanter is 102.68 Hz, which is within the excitation frequency range of the engine (86.67–120 Hz). Therefore, when the rice transplanter is working at high speed, the engine and the support arm will resonate, thus impacting the seedlings and machinery. The service life is also impacted. The research results provide a theoretical basis for the deformation prediction during the use of the support arm of the transplanter and provide a reference for the vibration-damping optimization design of the support arm structure and size of the subsequent transplanter.

High Precision Vibration-Type Densitometers Based on Pulsed Excitation Measurements.

Glass flexural resonators have established themselves as one of the de-facto standard methods for measuring the density of liquids in a laboratory environment. The core of this sensor is a U-Tube measuring cell whose oscillator’s resonance frequency changes with the mass of the liquid within the tube. This relationship can be used to derive the density of liquids in a fast and reliable way. In order to achieve the highest accuracy for the density measurement multiple physical effects (e.g., damping due to viscosity effects) need to be taken into account. For a reliable correction, additional measurements are required. The pulsed excitation method is able to produce these additional parameters along with a superior measurement performance compared to previous techniques.

Frequency Dependence of Receiving Sensitivity of Ultrasonic Transducers and Acoustic Emission Sensors.

Receiving displacement sensitivities (Rx) of ultrasonic transducers and acoustic emission (AE) sensors are evaluated using sinewave packet excitation method and compared to the corresponding data from pulse excitation method with a particular emphasis on low frequency behavior below 20 kHz, down to 10 Hz. Both methods rely on the determination of transmitter displacement characteristics using a laser interferometric method. Results obtained by two calibration methods are in good agreement, with average spectral differences below 1 dB, indicating that the two calibration methods yield identical receiving sensitivities. At low test frequencies, effects of attenuation increase substantially due to increasing sensor impedance and Rx requires correction in order to evaluate the inherent sensitivity of a sensor, or open-circuit sensitivity. This can differ by more than 20 dB from results that used common preamplifiers with ~10 kΩ input impedance, leading to apparent velocity response below 100 kHz for typical AE sensors. Damped broadband sensors and ultrasonic transducers exhibit inherent velocity response (Type 1) below their main resonance frequency. In sensors with under-damped resonance, a steep sensitivity decrease occurs showing frequency dependence of f2~f5 (Type 2), while mass-loaded sensors exhibit flat displacement response (Type 0). Such behaviors originate from sensor characteristics that can best be described by the damped harmonic oscillator model. This model accounts for the three typical behaviors. At low frequencies, typically below 1 kHz, receiving sensitivity exhibits another Type 0 behavior of frequency independent Rx. Seven of 12 sensors showed this flat region, while three more appear to approach the Type 0 region. This appears to originate from the quasi-static piezoelectric response of a sensing element. In using impulse method, a minimum pulse duration is necessary to obtain spectral fidelity at low frequencies and an approximate rule is given. Various factors for sensitivity improvement are also discussed.

Can we use time-resolved measurements to get steady-state transport data for halide perovskites?

Time-resolved, pulsed excitation methods are widely used to deduce optoelectronic properties of semiconductors, including now also Halide Perovskites (HaPs), especially transport properties. However, as yet, no evaluation of their amenability and justification for the use of the results for the above-noted purposes has been reported. To check if we can learn from pulsed measurement results about steady-state phototransport properties, we show here that, although pulsed measurements can be useful to extract information on the recombination kinetics of HaPs, great care should be taken. One issue is that no changes in the material are induced during or as a result of the excitation, and another one concerns in how far pulsed excitation-derived data can be used to find relevant steady-state parameters. To answer the latter question, we revisited pulsed excitation and propose a novel way to compare between pulsed and steady state measurements at different excitation intensities. We performed steady-state photoconductivity and ambipolar diffusion length measurements, as well as pulsed time-resolved microwave conductivity and time-resolved photoluminescence measurements as a function of excitation intensity on the same samples of different MAPbI3 thin films, and found good quasi-quantitative agreement between the results, explaining them with a generalized single level recombination model that describes the basic physics of phototransport of HaP absorbers. Moreover, we find the first experimental manifestation of the boundaries between several effective recombination regimes that exist in HaPs, by analyzing their phototransport behavior as a function of excitation intensity.

Roller-Integrated Acoustic Wave Detection Technique for Rockfill Materials

This paper proposes a roller-integrated acoustic wave detection technique for rockfill materials. This technique can be divided into two parts: theoretical analysis and technical implementation. Based on Lamb’s problem and an infinite baffle piston radiation acoustic field model, a relationship model between the sound compaction value (SCV) and the dry density of the natural gravel materials (NGM) was established, namely, A-model. During the modeling process, an innovative differential pulse excitation method (DPEM) was used to find the numerical solution of the vertical displacement of the soil surface under harmonic loads. In this research, a continuous compaction control acoustic wave detection system (CAWDS) was developed and utilized along with real-time kinematic global positioning systems (RTK-GPS). The SCV was adopted as a characterization index for the compaction quality of rockfill materials. A case study on a reservoir project in Luoyang, China indicated that the SCV is highly linearly correlated with the number of compaction times, dry density, and compactness of the NGM. This new technique demonstrated several advantages, such as higher accuracy, discreetness, convenience, and suitability for detecting the compactness of the NGM. This technique is an effective tool for compaction quality control of rockfill materials and has a great potential for further applications.

Research on barker coded excitation method for magneto-acoustic imaging

Abstract Functional imaging method of biological electrical characteristics based on magneto-acoustic effect gives valuable information of tissue in early tumor diagnosis. Common exciting and measuring method is to use single pulse. The imaging quality and the imaging speed are limited by the signal to noise ratio (SNR). In this study, we propose a processing method based on coded excitation and pulse compression to improve SNR of magneto-acoustic imaging. Barker code is widely used in ultrasonic signal processing, which can effectively improve the signal to noise ratio. It is introduced to increase SNR of the magneto-acoustic signal. Simulations on magneto-acoustic signal and pulse compressed signal under Barker coded excitation with a group of bit lengths are computed. Experiments on sample made of pork and graphite slices are done to validate the proposed coded excitation method. The pork sample is imaged to validate this method. SNR is investigated using Barker codes with different bits. The results showed, the SNR of magneto-acoustic signal is improved by the coded excitation. When 13 bit Barker code mode is adopted as the exciting signal, SNR improved by 21.5 dB. For a similar SNR improvement, the processing time of coded excitation method can be shortened by 95.8% compare with single pulse excitation method. In a conclusion, the coded excitation method is effective to improve the magneto-acoustic signal SNR and imaging quality. It also improves the magneto-acoustic imaging speed.