Excitation Technique Research Articles

Modal Identification for Integrally Bladed Rotors Under Traveling Wave Excitation

Abstract The safety of a fielded integrally bladed rotor (IBR) is often assessed through vibration testing. Responses due to various types of excitation are measured and processed and can be inputs to follow-on analyses, such as mistuning identification. One such excitation technique is the traveling wave excitation (TWE) where all blades are simultaneously excited at phase differences that attempt to replicate naturally occurring mode shapes and certain operating conditions. This test relies on noncontact exciters, e.g., magnets and speakers, that are often not directly measured. As a result, formulating the frequency response function (FRF) is difficult and the extraction of system modal data using FRF fitting techniques in the absence of FRFs is not possible. This paper presents an approach to use measured responses from TWE tests. It is shown that the fast Fourier transform (FFT) of the TWE inputs is mostly independent over the prescribed frequency range. Consequently, the output spectral density matrix can be formulated in an operational modal analysis (OMA) sense, where direct measurement of the inputs is not needed. A full spectral density matrix is then formulated from a single measurement on each blade obtained during a single test, thus reducing the number of measurement locations and testing excitation conditions. This matrix is fit by a polyreference-least squares complex frequency-domain (P-LSCF) system identification technique tailored for OMA-type measurements. The methodology is tested using simulated TWE data for an IBR model using different damping levels. Comparisons between identified modal data and those used to create the model are made and show the methodology accurately predicts underlying system information even for closely spaced modes that are common to IBRs. Finally, the method is used on experimental TWE data of an industrial IBR.

Люминесцентные свойства индивидуальных центров "кремний-вакансия" в CVD-наноалмазах, выращенных на различных подложках

The application of the technique of resonant excitation of photoluminescence at low temperatures using a narrow-band tunable laser significantly expands the possibilities of spectral investigation of individual luminescent centers in nanodiamonds, even in conditions of high concentrations of such centers. In this paper, a comparative analysis of the spectral characteristics of individual Silicon-Vacancy (SiV) centers in nanodiamonds grown with a spontaneous nucleation technique on germanium and silicon substrates is carried out. Studied diamond nanoparticles have a characteristic size of 300 nm and contain large ensembles of SiV centers. It was found that during the transition from silicon substrates, which are traditionally used in the CVD synthesis of diamonds, to germanium substrates, the spectral characteristics of the photoluminescence of SiV centers almost do not change.

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.

Development of a laser spectroscopy method and a hard-software framework for ecological monitoring of underwater areas by remote operated vehicles

The results of the experimental development of the method and the hard-software framework for a remote-operated underwater vehicle are presented in this work. The method of laser induced fluorescence (LIF) and a small-sized laser spectrometer are designed to monitor of the dissolved oil products pollution of underwater areas and to assess the impact of pollution on the phytoplankton community state. The excitation technique of the sea water LIF was experimentally tested to simultaneously measure the concentration of chlorophyll A, the specific reproduction of dissolved organic matter by phytoplankton cells, and the concentration of oil products dissolved in sea water. It has been experimentally shown that to implement this technique, it is necessary to carry out the excitation of the LIF by two wavelength radiation. To measure the concentration of chlorophyll A and the specific reproduction of dissolved organic matter (DOM), it is necessary to use excitation by radiation in the green region of the spectrum (532 nm in this work). To measure the concentration of dissolved petroleum products in sea water, it is necessary to use UV radiation (278 nm in this work). The results of tests of the spectrometer under laboratory conditions on sea water samples containing phytoplankton cells and solutions of petroleum products are described. The results of the work create a methodological and software-hardware basis for carrying out the mission of ecological monitoring of underwater areas with the simultaneous solution of the problem of detecting oil pollution and assessing its impact on the phytoplankton community.

Effect of Elevated Temperature and Annealing Time on Mechanical Properties of Ti/Cu Bimetal

The paper presents the results of the elastoplastic properties of Ti/Cu bimetallic rods. They were obtained by extrusion and composed of a copper core with a covered titanium layer. Experiments were carried out at room temperature on virgin samples, and samples were subjected to prior annealing in the temperature range of 600-900 °C for 30, 60, and 90 min. The modern technique of impulse excitation of vibration was used to analyze the elastic properties of bimetal, obtaining the temperature and time characteristics of Young's modulus, internal friction, and resonance frequency variability. Subsequently, the samples were stretched to breakage, obtaining information on the values of limit stresses, their deformability, and the energy demand for uniform elastic-plastic deformation in terms of the effect of temperature and annealing time. The influence of thermal processes on the strengthening of the Ti/Cu bimetal was also examined, and microscopic observations and qualitative analysis of the diffusion zone at the interface of the phases were carried out. The research was to answer the question of how a short-term temperature increase in 600-900 °C affects the physical properties of Ti/Cu bimetallic rods. These rods were used as a high-density electric current carrier in metallurgical processes in environments of aggressive chemical compounds. Studies have shown that short-term annealing at elevated temperatures causes a drastic reduction in the strength of the Ti/Cu bimetal, leading to structural changes within the components, and the diffusion zone with the release of intermetallic compounds, leading to structural degradation. Heating at 900 °C for 60 and 90 min caused accelerated interface degradation and destruction of the Ti/Cu bimetal by delamination.

First La2O2S infrared transparent ceramics

Lanthanum oxysulfide (La2O2S) was investigated as infrared transparent ceramic to benefit from stronger chemical bonds and superior mechanical performances to that of non-oxide benchmark infrared materials. La2O2S ceramics were processed by hot-pressing powders prepared by combustion synthesis followed by a sulfurization treatment. Powders and ceramics were characterised through various techniques (XRD, UV-Vis-IR spectroscopy, particle size analysis, SEM, Impulse Excitation Technique, microhardness and fracture toughness tests) to assess their purity, study their microstructure and determine their optical and mechanical properties. The study reports the first IR transmission spectra, Poisson’s ratio, Young’s and shear moduli and fracture toughness values of La2O2S polycrystalline ceramics. The ceramics showed transparency in the 2–11 µm range and their mechanical performances were all superior to that of commercial infrared ceramics. The best transmission (89% of the theoretical transmission) was measured at 7.3 µm for 1 mm-thick ceramics hot-pressed at 1200–1250 °C.

Mid-IR pulse amplification to ∼millijoule energies in a single transverse mode using large core Er:ZBLAN fibers operating at 2.8µm.

We demonstrate single transverse mode and high energy nanosecond pulse amplification at ∼2.8-µm using large core Er:ZBLAN fibers. The highest energies achieved are 0.75mJ from a 50 µm core, and 420µJ from a 30 µm core fibers respectively, seeded with 95 ns long pulses generated by a ring-cavity Q-switched Er:ZBLAN fiber laser. Nearly diffraction-limited beams with M2 = 1.2-1.3 were obtained using a single-mode excitation technique of multi-mode core fibers. Achieved pulse energies exceed by approximately an order of magnitude the previously reported highest pulse energies in a single transverse mode from a fiber laser or amplifier at these mid-IR wavelengths.

Processing and Characterization of a New Quaternary Alloy Ti10Mo8Nb6Zr for Potential Biomedical Applications

The study of new metallic biomaterials for application in bone tissue repair has improved due to the increase in life expectancy and the aging of the world population. Titanium alloys are one of the main groups of biomaterials for these applications, and beta-type titanium alloys are more suitable for long-term bone implants. The objective of this work was to process and characterize a new Ti10Mo8Nb6Zr beta alloy. Alloy processing involves arc melting, heat treatment, and cold forging. The characterization techniques used in this study were X-ray fluorescence spectroscopy, X-ray diffraction, differential scanning calorimetry, optical microscopy, microhardness measurements, and pulse excitation technique. In vitro studies using adipose-derived stem cells (ADSC) were performed to evaluate the cytotoxicity and cell viability after 1, 4, and 7 days. The results showed that the main phase during the processing route was the beta phase. At the end of processing, the alloy showed beta phase, equiaxed grains with an average size of 228.7 µm, and low Young's modulus (83 GPa). In vitro studies revealed non-cytotoxicity and superior cell viability compared to CP Ti. The addition of zirconium led to a decrease in the beta-transus temperature and Young's modulus and improved the biocompatibility of the alloy. Therefore, the Ti10Mo8Nb6Zr alloy is a promising candidate for application in the biomedical field.

Research on vibration behavior and chatter stability of big-sized gear hobbing machine

Self-excited chatter vibrations are the most detrimental for the quality and safety of the machining operations. To reduce the undesired vibrations, the dynamic behaviors of the machine tool-workpiece system and the chatter stability models need to be studied. In this paper, gear hobbing is studied using analytical and experimental approaches. Firstly, based on the chatter stability theory in relation to milling, analytical model of chatter stability in gear hobbing process is derived. Secondly, a new approach is presented to identify dynamic modal parameters using operational modal analysis (OMA). Using natural excitation technique (NExT) and auto regressive moving average (ARMA) model time series analysis method. At last, the prediction capability is verified using machining experiments, and the results show that the stability diagrams is of great potential to supply guidance for the processing parameters development.

Simultaneous Nanoscale Excitation and Emission Mapping by Cathodoluminescence.

Free-electron-based spectroscopies can reveal the nanoscale optical properties of semiconductor materials and nanophotonic devices with a spatial resolution far beyond the diffraction limit of light. However, the retrieved spatial information is constrained to the excitation space defined by the electron beam position, while information on the delocalization associated with the spatial extension of the probed optical modes in the specimen has so far been missing, despite its relevance in ruling the optical properties of nanostructures. In this study, we demonstrate a cathodoluminescence method that can access both excitation and emission spaces at the nanoscale, illustrating the power of such a simultaneous excitation and emission mapping technique by revealing a subwavelength emission position modulation as well as by visualizing electromagnetic energy transport in nanoplasmonic systems. Besides the fundamental interest of these results, our technique grants us access into previously inaccessible nanoscale optical properties.

Quantifying F-actin patches in single melanoma cells using total-internal reflection fluorescence microscopy

Total-internal reflection fluorescence (TIRF) microscope is a unique technique for selective excitation of only those fluorophore molecules in a cellular environment, which are located at the sub-diffraction axial distance of a cell’s contact-area. Despite this prominent feature of the TIRF microscope, making quantitative use of this technique has been a challenge, since the excitation intensity strongly depends on the axial position of a fluorophore molecule. Here, we present an easy-implemented data analysis method to quantitatively characterize the fluorescent signal, without considering the intensity-value. We use F-actin patches in single-melanoma cells as an example and define two quantities of elongation and surface density for F-actin patches at the contact-area of a melanoma cell. The elongation parameter can evaluate the dispersion of F-actin patches at the contact-area of a cell and is useful to classify the attaching, spreading, and expanding stages of a cell. Following that, we present the profile of the surface density of F-actin patches as a quantity to probe the spatio-temporal distribution of the F-actin patches at the contact-area of a cell. The data analysis methods that are proposed here will also be applicable in the image analysis of the other advanced optical microscopic methods.

Analysis of Texture and Anisotropic Elastic Properties of Additively Manufactured Ni-Base Alloys

Additive manufacturing of metallic materials generates strong crystallographic textures, leading to anisotropic elastic properties on the macroscopic scale. The impact of the processing parameters on the resulting texture requires suitable techniques for the prediction and the experimental determination of elastic properties to exploit the anisotropy in the design process. Within this study mechanical as well as microstructure based approaches are applied on a batch of specimens manufactured from IN718 by selective laser melting to assess the elastic behavior on macroscropic scale. Tensile loading experiments and the impulse excitation technique are applied for the determination of elastic properties without additional constitutive data. Furthermore, the elastic behavior is estimated from single-crystal elastic properties and texture data measured by electron backscatter diffraction and high energy X-ray diffraction. The results of the applied approaches are discussed and compared, allowing also to assess the homogeneity of the elastic properties within the batch of specimens.

CLUSTERIZACIÓN EUCLIDIANA DE LA ESPECTROSCOPÍA MECÁNICA COMPARATIVA EXCITADA POR IMPULSO

ABSTRACT: An alternative methodology is presented to recognize the internal state of a material, which, unlike other methods, it is not necessary to take destructive tests, in addition to the high time and costs involved. The methodology in question is summarized in a technique based on the acoustic-vibrational behaviour of metal alloys, to correlate their acoustic properties and their internal structure. As a case study, a comparison between AISI-SAE 1018 steel and two alloys, one made of aluminum and the other of brass. The specimens are used according to ASTM E1876 for the Impulse Excitation Technique (IET) test. Steel cases were tested in their existing condition and heat treatment according to ASTM E1876 and subjected to a standardized process to compare the acoustic characteristics of the same material with different microstructures. By processing the acoustic response, frequency spectra describe the acoustic behaviour obtained. By processing the acoustic response, frequency spectra describe the vibrational behaviour. The methodology shows results that demonstrate the sensitivity of the test to microstructural changes in metallic materials, demonstrating that the IET test is functional as an alternative method for the identification of materials. Key Words: Mechanical spectroscopy, Impulse excitation, Euclidean clusterization, Non destructive test

An improved NExT method for modal identification with tests validation

The Natural Excitation Technique (NExT) is widely used in structural modal parameter identification. However, the cross-correlation function is susceptible to the mode shape of each order, which is obtained by the traditional NExT method combined with other modal identification methods between the two measuring points, resulting in large errors of the identified frequency and damping ratio of various modes. Therefore, in this study, to obtain the modal responses of the target order correctly and eliminate interaction of various modes, a new combined NExT method with improved Empirical Mode Decomposition (EMD) method is developed. The improved NExT method is introduced firstly, then, the structural modal parameters are identified by five different methods, which are Ibrahim Time Domain Technique, Sparse Time Domain Algorithm, Autoregressive Moving Average timing method, Least Square Complex Exponential and Eigensystem Realization Algorithm respectively. The correction and improvement of the new method are verified through a simple-supported beam experiment and a shaking table test of a 12-story benchmark tall building at Tongji University. The structural modal parameters are identified and compared through adopting traditional NExT method and the proposed new NExT algorithm. Results illustrate that the improved NExT algorithm in this paper has a higher accuracy and effectiveness than the traditional one in structural modal parameter identification.

Luminescence and microstructural characteristics of Eu2O3-doped SrAl2O4 single crystals

Single crystals of SrAl2O4 prepared with 0.2–2.0 mol% Eu2O3 were synthesized using the optical floating zone method using ceramic rods that had been prepared under reducing conditions to favor conversion of Eu3+ to Eu2+. Samples were then characterized by a combination of X-ray diffraction (XRD), X-ray photoelectron (XPS), positron annihilation, electron paramagnetic resonance (EPR), photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopic techniques, and their excited state lifetimes were measured. XRD showed that the crystal samples were all in the monoclinic phase. EPR and PL techniques indicated that they contained Eu2+, although XPS indicated that the Eu3+ reduction was only ∼50%. Positron annihilation spectroscopy demonstrated that all of the samples contained a considerable number of defects that act as positron traps, and were influenced by the amount of Eu2O3 used in the crystal synthesis. These defects did not show an EPR signal, which suggests that they may correspond structural vacancies, possibly due to the presence of cation vacancies as a result of incorporation of some Eu3+ in the divalent cation sites. However, EPR did reveal a small amount of anionic paramagnetic defects, and showed a progressive broadening of the Eu2+ resonance for crystals synthesized with Eu2O3 concentrations >0.5 mol%. The intensity of the PLE spectra increased with Eu2O3 concentration, and the relative proportions of the peaks at 3.62 eV (360 nm) and 3.13 eV (417 nm) changed with Eu2O3 concentration. The PL spectra showed a broad green emission peak at 2.52 eV (518 nm), which is attributed to 4f65d-4f7 charge transfer transitions in Eu2+. Both its intensity and fluorescence decay time increased with Eu2O3 concentration, reached a maximum with the sample prepared with 1.5 mol% Eu2O3, then decreased with higher Eu2O3 concentrations.

Excitation of "forbidden" guided-wave plasmon polariton modes via direct reflectance using a low refractive index polymer coupling layer.

A surface plasmon polariton (SPP) is an excitation resulting from the coupling of light to a surface charge oscillation at a metal-dielectric interface. The excitation and detection of SPPs is foundational to the operating mechanism of a number of important technologies, most of which require SPP excitation via direct reflectance, commonly achieved via Attenuated Total Reflection (ATR) using the Kretschmann configuration. As a result, the accessible modes are fundamentally high-loss “leaky modes,” presenting a critical performance barrier. Recently, our group provided the first demonstration of “forbidden,” or guided-wave plasmon polariton modes (GW-PPMs), collective modes of a MIM structure with oscillatory electric field amplitude in the central insulator layer with up to an order of magnitude larger propagation lengths than those of traditional SPPs. However, in that work, GW-PPMs were accessed by indirect reflectance using Otto configuration ATR, making them of limited applied relevance. In this paper, we demonstrate a technique for direct reflectance excitation and detection of GW-PPMs. Specifically, we replace the air gap used in traditional Otto ATR with a low refractive index polymer coupling layer, mirroring a technique previously demonstrated to access Long-Range Surface Plasmon Polariton modes. We fit experimental ATR data using a robust theoretical model to confirm the character of the modes, as well as to explore the potential of this approach to enable advantageous propagation lengths. The ability to excite GW-PPMs using a device configuration that does not require an air gap could potentially enable transformative performance enhancements in a number of critical technologies.

Reveal luminescence differences via comparative studies of dynamic spectra in Eu3+-activated BaLa2WO7 and SrLa2WO7 phosphors

Eu3+-doped BaLa2WO7 and SrLa2WO7 phosphors were prepared using the conventional solid-state reaction synthesis. The experiments have confirmed that the luminescence properties are completely different although they the isostructural monoclinic structure with a monoclinic space group of P21/b: compared with SrLa2WO7:Eu3+, BaLa2WO7:Eu3+ has stronger luminescence and higher thermal stability. The dynamic characteristics were studied via the laser site-selective excitation and luminescence technique. The two distinct Eu3+ centers Eu3+(A) and Eu3+(B) were confirmed corresponding to the substitution for La1 and La2, respectively. Eu3+(A) could transfer energy to Eu3+(B) in BaLa2WO7:Eu3+, but Eu3+(B) cannot realize back transfer to Eu3+(A). However, a mutual energy transfer could be achieved between Eu3+(A) and Eu3+(B) in SrLa2WO7:Eu3+ resulting in excitation energy diffusion. The energy dispersion may cause the excited electrons to be trapped in some defects and impurities, thereby reducing the luminescence effect. The results could help develop new reddish-orange emitting materials by introducing Eu3+ as a structural probe for doping sites and microstructure.

Modal identification of high-rise buildings by combined scheme of improved empirical wavelet transform and Hilbert transform techniques

Recently, the empirical wavelet transform technique has attracted much attention due to its advantage of dealing with non-stationary and nonlinear signals. For empirical wavelet transform-based methods, their performance is heavily dependent on the accuracy of Fourier spectral segmentation. Structural response signals of high-rise buildings under ambient excitations often include high-level noises, which may lead to inaccurate spectral estimation, thereby introducing errors in modal decomposition. To this end, an improved empirical wavelet transform method is presented in this paper to analyze the structural response signals with high-level noises, which employs the projection information of Fourier spectra to improve spectral representation. Then, the improved empirical wavelet transform method is combined with the natural excitation technique and Hilbert transform for identifying modal properties of super-tall buildings under ambient excitations. Through a numerical simulation study, the validity and accuracy of the combined scheme are verified even when structural response signals were embedded with high levels of noise. Furthermore, the proposed method is adopted for modal identification of a 600 m supertall building for evaluating its applicability in field measurements. It is demonstrated that the combined scheme can effectively and accurately evaluate the modal properties of the skyscraper under ambient vibrations with low amplitudes.

The Impacts of Membrane Pinholes on Performance and Hydrogen Crossover in PEM Water Electrolysis

Polymer electrolyte membrane (PEM) water electrolysis is a promising energy storage technology to produce highly pure hydrogen with high efficiency 1. However, to implement it on a larger scale, it is essential to understand the effects of defects and the required tolerances and quality controls during manufacturing or subsequent handling. Inhomogeneities in membrane electrode assembly (MEA) component materials caused by the manufacturing process or subsequent handling can lead to performance loss and failure 2. Defects such as membrane pinholes, cuts, tears, abrasions, or perforations can all potentially impact MEA performance. In terms of impact, a loss of integrity of the membrane can allow bulk gas transport (crossover) and/or electrical shorting 3.In particular, hydrogen crossover is a crucial issue for PEM water electrolysis in terms of safe operation and efficiency losses, especially at increased hydrogen pressures. Crossover reduces the overall efficiency of the system and poses flammability hazards under certain conditions 4. Pinholes that form during the manufacturing process or during operation through degradation of the membrane lead to dramatically increased hydrogen crossover.In this study, the impacts of membrane pinholes on the performance and hydrogen crossover of PEM water electrolyzer cells are studied. Pinholes with different sizes are artificially introduced to the MEA to investigate the effects on the initial cell performance and hydrogen crossover rate under various backpressure and current density conditions. Reference Liu, C.; Shviro, M.; Gago, A. S.; Zaccarine, S. F.; Bender, G.; Gazdzicki, P.; Morawietz, T.; Biswas, I.; Rasinski, M.; Everwand, A., Exploring the Interface of Skin‐Layered Titanium Fibers for Electrochemical Water Splitting. Adv Energy Mater 2021, 11 (8), 2002926.Ulsh, M.; DeBari, A.; Berliner, J. M.; Zenyuk, I. V.; Rupnowski, P.; Matvichuk, L.; Weber, A. Z.; Bender, G., The development of a through-plane reactive excitation technique for detection of pinholes in membrane-containing MEA sub-assemblies. Int J Hydrogen Energ 2019, 44 (16), 8533-8547.Phillips, A.; Ulsh, M.; Mackay, J.; Harris, T.; Shrivastava, N.; Chatterjee, A.; Porter, J.; Bender, G. J. F. C., The effect of membrane casting irregularities on initial fuel cell performance. 2020, 20 (1), 60-69.Martin, A.; Trinke, P.; Stähler, M.; Stähler, A.; Scheepers, F.; Bensmann, B.; Carmo, M.; Lehnert, W.; Hanke-Rauschenbach, R. J. J. o. T. E. S., The Effect of Cell Compression and Cathode Pressure on Hydrogen Crossover in PEM Water Electrolysis. 2022, 169 (1), 014502.

High Performance Micro Resonators-Based Sensors Using Multimode Excitation

We present a multi-mode excitation technique to significantly amplify the amplitude signal of micro-resonators-based sensors operating at their higher-order modes. We show that the multi-mode excitation can significantly reduce the noise effects, elevate the dynamic response level, and amplify the total amplitude response. We demonstrate the efficiency of the multi-mode excitation to enhance the performance of a gas sensor using electrothermally heated doubly-clamped buckled beams. The results indicate clear amplification for the response at the 2nd mode while detecting Helium compared to a single-source excitation. A 24-times amplitude magnification is achieved. The demonstrated approach provides a promising path to efficiently exploit the higher-order modes of resonant gas sensors leading to improved accuracy and resolution.