Narrow-band Excitation Research Articles

Low-cost instrumentation for high frequency ultrasonic guided wave laboratory research in free rock bolts

Guided wave ultrasound offers the ability to inspect slender structures from a single transducer location. However, the propagation of guided waves is more complex than the propagation of bulk waves used in conventional ultrasonic testing, and the experimental equipment required is more sophisticated. Typical equipment is expensive and may limit research and industrial application. This paper investigates what can be achieved by using low-cost instrumentation for laboratory measurements. The application is the measurement of guided waves in rock bolts (cylindrical rods) at relatively high frequencies (5 MHz). The dispersive wave propagation requires the use of narrowband excitation signals. The use of a bench-top waveform generator and oscilloscope is compared to the use of a compact and low-cost USB oscilloscope, which includes an arbitrary waveform generator. The introduction of a pre-amplifier mitigated the poorer noise performance of the USB oscilloscope, and comparable results were obtained from the two setups. It is demonstrated that waves propagated 9 m in a free rock bolt, with 10 dB/m attenuation, could be detected and analyzed with a measurement setup costing approximately USD 1110.

Collective polaritonic effects on chemical dynamics suppressed by disorder

We present a powerful formalism, disordered collective dynamics using truncated equations (d-CUT-E), to simulate the ultrafast quantum dynamics of molecular polaritons in the collective strong coupling regime, where a disordered ensemble of N≫106 molecules couples to a cavity mode. Notably, we can capture this dynamics with a cavity hosting a single molecule with ∼Nbins electronic states, where Nbins≪N is the number of bins discretizing the disorder distribution. Using d-CUT-E we conclude that strong coupling, as evaluated from linear optical spectra, can be a poor proxy for polariton chemistry. For highly disordered ensembles, total reaction yield upon broadband excitation is identical to that outside of the cavity, while narrowband excitation produces distinct reaction yields solely due to differences in the initial states prepared prior to the reaction. Published by the American Physical Society 2024

Resonant Versus Nonresonant Spin Readout of a Nitrogen-Vacancy Center in Diamond under Cryogenic Conditions.

The last decade has seen an explosive growth in the use of color centers for metrology applications, the paradigm example arguably being the nitrogen-vacancy (NV) center in diamond. Here, we focus on the regime of cryogenic temperatures and examine the impact of spin-selective, narrow-band laser excitation on NV readout. Specifically, we demonstrate a more than fourfold improvement in sensitivity compared to that possible with nonresonant (green) illumination, largely due to a boost in readout contrast and integrated photon count. We also leverage nuclear spin relaxation under resonant excitation to polarize the ^{14}N host, which we then prove beneficial for spin magnetometry. These results open opportunities in the application of NV sensing to the investigation of condensed matter systems, particularly those exhibiting superconducting, magnetic, or topological phases selectively present at low temperatures.

Detection of Barely Visible Impact Damage in Composite Structures Using Backward Sweep Vibro-thermography Technique Utilizing Asymmetry in Local Defect Resonance

ABSTRACT In this article, local defect resonance-based vibrothermography has been studied for different sweep direction and ranges. Two different carbon fiber-reinforced polymer (CFRP) composite plate has been fabricated from vacuum assisted resin transfer molding. In the first plate, a flat bottom hole has been made and two barely visible impact damages are created in other plate. The area of delamination has been determined from phased array ultrasound testing. Laser doppler vibrometry (LDV) has been performed first for different sweep ranges and directions. The CFRP plate is excited with a piezoelectric element at 150 Vpp and the vibration over defect area is captured using a single point laser doppler vibrometer, operating in scanning mode. It has been found that vibration amplitude at local defect resonance (LDR) frequency increases in narrow sweep range compared to a wideband excitation. Again, in both cases, it has been found that backward sweep produces more amplitude compared to forward one due to softening nonlinearity. An asymmetry in LDR frequency is also been observed when the sweep range is further narrowed. An uncooled microbolometer camera is used for reception in case of vibrothermography. Backward sweep is found to be more effective as compared to the forward one and the temperature increment increases in case of narrowband excitation range.

Spectral peak recovery in parametrically amplified THz-repetition-rate bursts.

Multi-photon resonant spectroscopies require tunable narrowband excitation to deliver spectral selectivity and, simultaneously, high temporal intensity to drive a nonlinear-optical process. These contradictory requirements are achievable with bursts of ultrashort pulses, which provides both high intensity and tunable narrowband peaks in the frequency domain arising from spectral interference. However, femtosecond pulse bursts need special attention during their amplification [Optica7, 1758 (2020)10.1364/OPTICA.403184], which requires spectral peak suppression to increase the energy safely extractable from a chirped-pulse amplifier (CPA). Here, we present a method combining safe laser CPA, relying on spectral scrambling, with a parametric frequency converter that automatically restores the desired spectral peak structure and delivers narrow linewidths for bursts of ultrashort pulses at microjoule energies. The shown results pave the way to new high-energy ultrafast laser sources with controllable spectral selectivity.

Bolt tightness monitoring using multiple reconstructed narrowband Lamb waves combined with piezoelectric ultrasonic transducer

Narrowband tone burst excitation with a carefully selected frequency is generally utilized to generate Lamb waves for mode purity, dispersion diminution and signal interpretability. Narrowband excitation exhibits saturation phenomenon and even non-monotonic trends with the development of bolt looseness. In this research, a piezoelectric ultrasonic transducer with high signal-to-noise ratio is designed and fabricated for bolt tightness monitoring. The chirp signal is utilized to drive the actuator to generate broadband Lamb waves in the connected plate, and a transfer function-based signal reconstruction algorithm is innovatively proposed to extract narrowband tone burst responses with different center frequencies from the broadband chirp response for bolt tightness monitoring. The leaked wave energy-based bolt tightness indexes (TIs) are calculated based on the extracted multiple tone burst responses and a feature-level data fusion strategy is proposed to combine the TIs for exploiting the merits of different-frequency inspecting waves for different bolt tightness conditions. The fused TI not only presents a monotonic tendency with the increasing of bolt tightness, but also tackles the low sensitivity of narrowband Lamb waves for embryo bolt looseness. The proposed method contributes a novel and stable scheme for bolt tightness monitoring and opens a new perspective for damage evaluation of structures.

Damage localization using contact and non-contact narrow frequency band elastic wave generation

In this paper analyses of non-contact elastic wave generation based on an air-coupled transducer (ACT) are presented. Authors compared contact piezoelectric based (PZT) wave generation, with non-contact one using ACT for a narrow frequency band excitation. Elastic wave sensing was based in both cases on a scanning laser Doppler vibrometer. The problem of ACT slope angle for the effectiveness of elastic wave modes generation is analysed. It was shown that for an excitation frequency of 40 kHz it is possible to generate A0 wave mode both in the case of PZT and ACT. Both methods of wave generation are compared based on an analysis of damage localisation results. For this purpose wave irregularity mapping (WIM) algorithm was utilised together with two attenuation compensation methods (based on energy normalisation and weighting function). Specimens in the form of simple square GFRP panel and bonded GFRP aerospace structure with omega stiffeners were investigated. The authors investigated simulated damage (Teflon inserts) and real delamination. In this research very cheap and popular, low-frequency ACT was utilised giving the possibility of realisation of low-cost excitation method. ACTs connected with a laser vibrometry sensing allows of realisation of full non-contact damage localisation method. Authors presented also non typical but very useful application of SLDV allowing to visualise the effect of acoustic wave generation in the air and determination of the pattern of generated acoustic waves. This was based on the photo-acoustic effect.

Equilibrium structures of selenium compounds: The torsionally flexible molecule of selenophenol.

The equilibrium structure of selenophenol has been investigated using rotational spectroscopy and high-level quantum mechanical calculations, offering electronic and structural insight into the scarcely studied selenium compounds. The jet-cooled broadband microwave spectrum was measured in the 2-8GHz cm-wave region using broadband (chirped-pulse) fast-passage techniques. Additional measurements up to 18GHz used narrow-band impulse excitation. Spectral signatures were obtained for six isotopic species of selenium (80Se, 78Se, 76Se, 82Se, 77Se, and 74Se), together with different monosubstituted 13C species. The (unsplit) rotational transitions associated with the non-inverting μa-dipole selection rules could be partially reproduced with a semirigid rotor model. However, the internal rotation barrier of the selenol group splits the vibrational ground state into two subtorsional levels, doubling the dipole-inverting μb transitions. The simulation of the double-minimum internal rotation gives a very low barrier height (B3PW91: 42cm-1), much smaller than for thiophenol (277cm-1). A monodimensional Hamiltonian then predicts a huge vibrational separation of 72.2GHz, justifying the non-observation of μb transitions in our frequency range. The experimental rotational parameters were compared with different MP2 and density functional theory calculations. The equilibrium structure was determined using several high-level abinitio calculations. A final Born-Oppenheimer (reBO) structure was obtained at the coupled-cluster CCSD(T)_ae/cc-wCVTZ level of theory, including small corrections for the wCVTZ → wCVQZ basis set enlargement calculated at the MP2 level. The mass-dependent method with predicates was used to produce an alternative rm(2) structure. The comparison between the two methods confirms the high accuracy of the reBO structure and offers information on other chalcogen-containing molecules.

Separating Vibrational Coherences in Ground/Excited Electronic States of Solvent/Solute Following Non-Resonant/Resonant Impulsive Excitation.

In a quest to track down the origin of coherent vibrational motions observed in femtosecond pump-probe transients, whether they arise from ground/excited electronic state of solute or are contributed by the solvent, we demonstrate a method for extricating vibrations under resonant and non-resonant impulsive excitations using a diatomic solute in condensed phase (iodine in carbon tetrachloride) with aid of spectral dispersion of the chirped broadband probe. Most importantly, we show how a sum over intensities for a select region of detection wavelengths and Fourier transform of data over select temporal window untwine contributions from vibrational modes of different origins. Thus, in a single pump-probe experiment, vibrational features specific to solute as well as solvent are disentangled that are otherwise spectrally overlapping and are non-separable in conventional (spontaneous/stimulated) Raman spectroscopy employing narrowband excitation. We envision wide-ranging applications of this method to unveil vibrational features in complex molecular systems.

The improvement of stochastic averaging method to solve the ship rolling response excited by narrow-band waves

The stochastic averaging method of energy envelope can accurately solve the random motion response under the excitation of white noise. The noise had to fulfill the condition of strong mixing which roughly means that the process has to be broad-band. However, the sea conditions in practical engineering conditions are narrow-band spectra. Research on applicability of the stochastic averaging method of energy envelope shows that for narrow-band excitation, the damping of the system and excitation intensity should be small, and the excitation bandwidth should be large. Based on the above background, the improvement of stochastic averaging method of energy envelope under narrow-band waves is studied. The phase angle θ is introduced to characterize the relationship between kinetic energy and potential energy of the system. The drift coefficients and diffusion coefficients are averaged with respect to the period of θ. When the excitation frequency is in the lock-in field, large parametric rolling appears. The stationary probability density function (PDF) of the roll angle obtained by solving the Fokker-Planck-Kolmogorov (FPK) equation compares well with Monte Carlo simulation in the lock-in field. The improved method can relax the limitation of broad-band excitation required by stochastic averaging method. It can also consider both the nonlinear damping and nonlinear restoring force of roll motion. Therefore, the improved method is an efficient way to calculate the nonlinear roll response of ships in real sea conditions.

A dictionary-reconstruction approach for separating helical-guided waves in cylindrical pipes

Pipes, which have a hollow cylindrical structure, are very susceptible to corrosion in industrial environments. Pipe wall loss can be evaluated by measuring helical-guided waves; however, various paths of these waves are easily superposed in the received signals due to the cyclic nature of the pipe’s geometry. The overlap phenomenon can be more serious when the guided wave contains multimodes. A signal-processing approach based on dictionary reconstruction for separating helical-guided waves in cylindrical pipes is established to get rid of this dilemma. The full-wave packet with a single mode and single path can be extracted successfully utilizing this method. In this work, the pipe wall is expanded into an infinite plane and a linear wave number model is adopted with the assumption of a narrowband excitation at the initial stage. After that, an over-completed dictionary containing all modes and propagation paths is designed based on this model to decompose the received signal. The specific process of decomposition is implemented through a single-layer neural network to solve the mode and path weight factors. Simulated and experimental cases are carried out to verify the effectiveness of the proposed approach. The results show that this method can completely separate the wave signals of all modes and paths even when the process is full of noise. This signal-processing approach can provide an important technical reference for high-precision imaging of helical-guided waves.

Fatigue Behavior Analysis and Life Prediction of Overhead Conductors Subject to Narrowband Vibration

This paper aims to present a contribution to the study of the effect of random vibration on the useful life of overhead conductors. This study compares two approaches based on an acquired vibration signal. The first one is the time-domain approach (based on rainflow cycle counting), while the second one is the frequency-domain approach (based on power spectral density moments). Laboratory simulation of aeolian vibration was used in finding the fatigue characteristics of a ACSR 397,5MCM – IBIS conductor. The S-N diagram was generated by performing 9 fatigue tests under constant amplitude conditions and 13 fatigue tests in narrowband excitation conditions. The reported tests were performed to assess the effect of random loading on fatigue life considering the two approaches for estimating fatigue life. A good correlation was found between the estimated fatigue lives using the time-domain and frequency-domain approaches and the experimental data.

Seismic Risk of Weak First-Story RC Structures with Inerter Dampers Subjected to Narrow-Band Seismic Excitations

This study evaluates the seismic risk of weak first-story reinforced concrete (RC) structures retrofitted with inerter dampers at their ground level when subjected to narrow-band seismic excitations. The main advantages brought about by the ground-level inerters are the reductions in seismic demands (e.g., drifts, floor accelerations). This study shows that structures with inerters are reliable systems in terms of peak story drifts for large ground motions. For moderate ground-motion intensities, the opposite could occur, mainly for soft soil sites. The reliabilities of structures with inerter dampers at their ground level are in general higher for buildings under seismic intensities associated to limit state of incipient collapse, especially for low-height buildings. This could be reversed for intensities associated to the limit state of damage limitation. The findings of this study could guide practicing engineers to use inerter-based dampers in retrofitting ductile structures consisting of moment-resisting reinforced concrete (RC) frames subjected to narrow-band earthquake excitations in regions such as Mexico City.

Enigmatic color centers in microdiamonds with bright, stable, and narrow-band fluorescence

Microdiamonds with color centers have unique photophysical properties. We discover extremely narrow spectral lines with full width at half maximum down to 0.5 nm (\ensuremath{\approx}390 GHz at wavelength 630.15 nm) at room temperature in photoluminescence of numerous high-pressure--high-temperature microdiamonds. Correlation spectroscopy proves that these lines originate from single photon emitters. Comprehensive experimental characterization of the emitters is performed by means of complementary scanning electron and fluorescence microscopy that allows morphological characterization and in time monitoring of the same labeled emitters. Study of photoluminescence and photoluminescence excitation spectra of single emitters showed negligible phonon sideband and narrowband excitation. Temperature sensitivity, stable photoluminescence, brightness, linear polarization, and fluorescence lifetime \ensuremath{\approx}1.5--2.5 ns are demonstrated. The results show great potential of the discovered ``enigmatic'' emitters for applications in quantum optics, fluorescence labeling, and high-resolution thermometry.

High-Fidelity Quantum Control by Polychromatic Pulse Trains

We introduce a quantum control technique using polychromatic pulse trains, consisting of pulses with different carrier frequencies, i.e., different detunings with respect to the qubit transition frequency. We derive numerous polychromatic pulse trains, which generate broadband, narrowband, and passband excitation profiles for different target transition probabilities. This makes it possible to create high-fidelity excitation profiles which are either (i)robust to deviations in the experimental parameters, which is attractive for quantum computing, or (ii)more sensitive to such variations, which is attractive for crosstalk elimination and quantum sensing. The method is demonstrated experimentally using one of IBM's superconducting quantum processors, in a very good agreement between theory and experiment. These results demonstrate both the excellent coherence properties of the IBM qubits and the accuracy, robustness, and flexibility of the proposed quantum control technique. They also show that the detuning is a control parameter which is as efficient as the pulse phase that is commonly used in composite pulses. Hence the method opens a variety of perspectives for quantum control in areas where phase manipulation is difficult or inaccurate.

Advancing measurement of zero-group-velocity Lamb waves using PVDF-TrFE transducers: first data and application to in situ health monitoring of multilayer bonded structures

Driven by the rapid advancement in manufacturing technologies, engineering structures with complex geometries are increasingly applied in various industries, posing challenges to the applicability and adaptability of existing structural health monitoring methods based on guided ultrasonic waves. To fulfill the characterization of defects in complex structures, a novel approach featuring a conjunction of zero-group-velocity (ZGV) Lamb waves and polarized poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) transducers is proposed. In this approach, the PVDF-TrFE solvent is deposited and in situ polarized on the structure surface to form thin and flexible coatings, with which the ZGV waves can be excited efficiently and measured reliably. On this basis, the defect can be characterized by investigating the defect-induced alteration in ZGV wave features. In experimental validations, disbond defects in multilayer bonded structures are evaluated using the ZGV waves measured with fabricated PVDF-TrFE transducers. For the first time, the ZGV waves are measured in a contact and in situ manner. Compared with conventional noncontact measurement of ZGV waves, the proposed approach features a remarkably improved reliability, convenience for narrowband excitation, immunity to measurement uncertainty and capability of in situ monitoring. The proposed approach can advance the ZGV wave-based methods toward the in situ health monitoring and enable the defect evaluation in emerging complex structures.

Dynamics of a tri-stable hybrid energy harvester under narrow-band random excitation

This paper aims to reveal the stochastic dynamics of a tri-stable piezoelectric–electromagnetic hybrid vibration energy harvester (HVEH) driven by narrow-band random excitation for purpose of enhancing the energy harvesting performance. The steady-state solutions of the electromechanical coupling tri-stable HVEH in the symmetric case are derived by the method of multiple scales, which are verified by Monte Carlo simulations. Results show that the stochastic jump phenomenon exists and the operational bandwidth of HVEH can be extended. The effects of narrow-band random excitation, critical system parameters and asymmetric potential function on stochastic dynamics are discussed. It is found that the miniaturization design of the HVEH can be optimized and the mean output power can be improved by selecting appropriate system parameters. Moreover, compared with the symmetric structure, in the case of the same highest potential-well depth, the asymmetric structure with a smaller potential-well distance is beneficial for HVEH to achieve high-energy inter-well oscillation under low-level excitation. Meanwhile, the power conversion efficiency reaches the maximum in the high-energy inter-well oscillations triggered at the critical excitation amplitude.

Fast Sub-Hz potentiostatic/galvanostatic bio-impedance measurements using chaotic oscillators.

The measurement of bio-impedance spectra at ultra low frequencies (sub-Hz) is known to require a considerably long time with the classical frequency-sweep method or other narrow-band periodic excitation signals. In this work, an impedance measurement technique based on using wide-band chaotic signals is proposed and experimentally validated over the frequency range [Formula: see text]. The technique was tested in both potentiostatic and galvanostatic modes, first using commercial components and then using an enhanced Howland current pump designed and fabricated in a 65nm CMOS technology. The accuracy of the proposed technique was assessed on fruit samples compared to measurements conducted using a research-grade Biologic VSP-300 electro-chemical station.

Experimental Demonstration of Composite Pulses on IBM’s Quantum Computer

We perform comprehensive experimental tests of various composite pulse sequences using one of the open-access IBM quantum processors, based on superconducting transmon qubits. We implement explicit pulse control of the qubit by making use of the opportunity of low-level access to the backend, provided by IBM Quantum. We obtain the excitation profiles for a huge variety of broadband, narrowband, and passband composite pulses, producing any prechosen target probabilities, ranging from zero to one. We also test universal composite pulses that compensate errors in any experimental parameter. In all experiments, we find excellent agreement between theoretical and experimental excitation profiles. This proves both the composite pulses as a very efficient and flexible quantum control tool and the high quality of the IBM quantum processor. As an extreme example, we test and observe a pronounced narrowband excitation profile for a composite sequence of as many as 1001 pulses.

Stochastic analysis of a time-delayed viscoelastic energy harvester subjected to narrow-band noise

Vibration energy harvester (VEH) has proven to be a favorable potential device to supply continuous energy for electric components. Researchers have done a lot of investigations on VEH in recent years. However, there are few studies on delayed VEH with viscoelastic property under random excitation. A new viscoelastic energy harvester with time delay subjected to narrow-band random excitation is investigated in this paper. Firstly, we utilize the multiple scales method to obtain the analytical approximations of the steady-state amplitude close to the primary resonance. Secondly, Monte Carlo simulations are applied to verify the correctness of the proposed method. Results demonstrate the satisfactory accuracy of the method presented in this paper. Then, the phenomena of stochastic jump, stochastic bifurcation, and the extension of the effective bandwidth of VEH can be found. Finally, the influence of system parameters on the mean square voltage and mean output power are discussed. It is shown that a negative feedback gain is profitable to the enhancement of the performance of VEH, and we find that the piezoelectric coupling term has a positive effect on the mean square voltage and mean output power. The mean square voltage and mean output power can reach the maximum at an appropriate time delay and feedback gain. These results indicate that the narrow-band random excitation has an important effect on the dynamics of the delayed vibration energy harvester with viscoelastic property, namely a large dose of noise intensity can decline the responses in the energy harvester.