Multimodal Excitation Research Articles

Unveiling multimodal hot carrier excitation in plasmonic bimetallic Au@Ag nanostars for photochemistry and SERS sensing

AbstractPlasmonic nanostructures stand at the forefront of nanophotonics research, particularly in sensing and energy conversion applications. Their unique ability to confine light energy at the nanoscale makes them indispensable for a wide array of technological advancements. The study of these structures often makes use of different materials and, even more extensively, explores new shapes and configurations to extend our common repertoire of useful nanophotonics tools. Exploring the creation of bimetallic plasmonic nanostructures combines these two dimensions determining the space of possible plasmonic resonators and opens the possibility of tailoring systems with behavior unavailable to single-metal plasmonic structures. In this paper, we delve into the exploration of bimetallic systems employing plasmonic nanostars. These structures have demonstrated remarkable capabilities for surface-enhanced Raman scattering (SERS) spectroscopy and photochemistry, due to the strong plasmonic response of their peaks, whose disposition following a spherical symmetry makes them largely polarization- and orientation-insensitive. Herein, we report the colloidal synthesis of two different water-stable Au@Ag nanostars, explore their performance as photocatalysts and SERS substrates, and provide an in-depth account of their non-trivial physical response.

Theoretical and experimental research on multi-modal vibration control of flexible beams via the multiple-input multiple-output decoupling control strategy

In this study, a multiple-input multiple-output decoupling control (MIMO-DC) strategy is proposed based on the linear active disturbance rejection control (LADRC) algorithm to suppress the multi-modal vibration of flexible beams. Firstly, the dynamic equation of flexible beams is established using the Euler-Bernoulli beam theory. Then, a virtual control vector is introduced to decouple the MIMO system. The effectiveness of the flexible beam model is verified by comparing it with the experimental frequency response. Finally, experimental studies are carried out to analyze the vibration suppression performance of three control forms in suppressing the vibration of flexible beams under first-order modal excitation, second-order modal excitation, multi-modal excitation, variable multi-modal excitation, and multi-modal excitation with random disturbance, respectively. The robustness of the MIMO-DC strategy against parameter perturbations is also studied. The results show that the proposed MIMO-DC strategy not only exhibits excellent control performance for various types of modal excitations but also has strong adaptability to variable multi-modal excitation and strong anti-disturbance ability. Furthermore, the strategy exhibits strong robustness against parameter perturbations.

Mechanical Shock Wave Suppression Structure in Hold-Down and Release Apparatus of Spacecraft

A lightweight and compact structural solution for mechanical shock suppression in spacecraft, such as the hold-down and release apparatus of satellites, is a critical and thorny issue. In this work, a ring-shaped structure is introduced to isolate mechanical waves within cylindrical shells. The underlying mechanism is that the ring-shaped structure undergoes different forms of deformation to counteract different modes of incident waves. A subwavelength Mn-Cu alloy ring is designed as a shock wave barrier in a typical spacecraft hold-down and release apparatus structure with multimodal wave excitation. We experimentally reveal that the Mn-Cu alloy ring reduces the peak value of the acceleration frequency response by 53.4% within a wide frequency range from 1 to 10 kHz. Meanwhile, in the time domain, the instantaneous acceleration peak can be weakened by 37.9%. This work provides a new strategy for shock control of shell structures in aerospace engineering and related fields.

Differential response under X-ray/UV dual-mode excitation in single-component defect state phosphor X-ray imaging and Wavelength-Multiplexing information storage

Multimodal Excitation Response (MMER) phosphors are gaining rapid attention due to their outstanding performance and emerging applications. Herein, a Eu2+, Mn2+ co-doping CaAl2Si2O8 phosphor is reported. Unlike common MMER phosphors, this system exhibits blue photo-/persistent luminescence under 365 nm UV excitation, orange photo-/persistent luminescence under X-ray excitation, and X-ray-induced photochromism. These diverse optical properties enable it to exhibit advanced bright/dark dual-field X-ray imaging and wavelength-multiplexing information storage. Furthermore, the testing results indicate that the varying color response to UV and X-ray excitation benefits from different excitation properties between Eu2+ and Mn2+ as well as precise emitter/trap local units. Thus, this work not only provides an excellent candidate for versatile applications but also offers a design approach for such materials.

An efficient determination of field distributions in E-plane dielectric loaded waveguides

ABSTRACT This paper proposes a new, fast, and efficient method for determining the electromagnetic field distribution in two-port E-plane dielectric-loaded uniform rectangular waveguides. The analysis region is divided into individual blocks in the absence and presence of dielectric obstacles. The non-zero electric and magnetic field components are constructed throughout the system via the proposed method by utilizing the generalized scattering matrix method between blocks for unimodal or multimodal excitation. The resulting field distributions are compared to those obtained from commercial software, with very close agreement achieved, but with a significantly reduced computational time for the proposed method. The method is applicable in a straightforward manner and has been tested on both a filter device with relatively complex geometry and a disjoint system with a modal coupling challenge between its elements. The field components' accuracy is also tested by calculating the Poynting vector along the system. Additionally, this approach provides the global scattering parameters at the physical ports as a co-product. The proposed method has the potential to be applied to various two-port networks by using the proposed method according to the considered problem.

Bidirectional motion characteristics of resonant inertial impact rotating piezoelectric motor based on self-clamping structure

A new working principle for multimodal excitation of a resonant bidirectional rotary inertial impact piezoelectric motor with a self-clamping structure was developed based on previous research on piezoelectric motors. Unlike previous piezoelectric motors that relied on single harmonic waves for unidirectional rotation, in this motor, we can simply change the driving signal characteristics of the motor without changing the structure of the piezoelectric motor to excite multiple vibration modes, thereby achieving rotation in both directions. Compared with other bidirectional resonant motors, the structure and control signal are simpler. The finite element simulation software COMSOL5.5 was used to simulate the working mode of the motor, and the results were in good agreement with the final experiment. During the experiments, the optimal operating frequency of the motor prototype was 900 Hz. The maximum output speed of the motor prototype was 3.9 rad/s, the maximum output torque was 15 N mm, and the maximum resolution was 0.248° under the conditions of 240 Vp-p voltage, 900 Hz frequency, and 7.8 N mm preload torque.

DMSENet: Deep multi-modal squeeze and excitation network for the diagnosis of Alzheimer's disease

ABSTRACT Alzheimer's Disease (AD) is an incurable neurodegenerative disorder that affects millions of older people worldwide. Compared to conventional methods, neuroimaging modalities along with the machine learning techniques detect the onset of AD more successfully. It has been established that multimodal classification provides better accuracy than single modal classification. Exploring the synergy between several multimodal neuroimages remains challenging due to the lack of available fusion techniques. The proposed Deep Multimodal Squeeze and Excitation network (DMSENet) uses the ResNet Squeeze and Excitation (SE) block to extract relevant features from MRI and PET images. Using the hierarchical fusion method, the extracted features are fused; subsequently, using the fused Feature Map (FM), the ResNet SE block retrieves additional higher-level and lower-level features. Hierarchical fusion methodology ensures the efficiency of Multimodal Fusion (MMF); the Attention Model(AM) then assigns the fusion ratio automatically by prioritizing the multimodal data. Moreover, the depth and efficiency of the attention network are ensured by the combination of identity mapping and Residual Block. In the DMSENet, both higher-level and lower-level features could be utilized simultaneously by employing both early and late fusion methodologies. The suggested framework is investigated using the ADNI dataset, providing greater precision than state-of-the-art methods.

Multi-mode excited Cs2NaBiCl6 Based Double Perovskite Phosphor for Anti-counterfeiting

Emission wavelength or color and excitation mode of luminescent materials play the decisive role in their applications of information hiding and anti-counterfeiting. Conventional luminescent anti-counterfeiting materials generally exhibit monochromatic emissions under the excitation of ultraviolet or near-infrared light, which are easily to be imitated or substituted. The development of multicolor and multimodal excitation in one single-phased host was regarded as effective strategy and significant challenges for luminescent anti-counterfeiting materials. As typical lead-free halide double perovskite material Cs2NaBiCl6 not only offers excellent stability and facile synthesis but also provides greater tolerance to rare earth and transitional ions, thus Er3+, Yb3+ and Mn2+ tri-doped Cs2NaBiCl6 was synthesized by co-precipitation method at room temperature in this paper. The efficient green up- and strong orange red down-conversion (UC and DC) emissions were realized through irradiation of 980/1550 nm infrared light and 365 nm near ultraviolet light. The possible UC mechanisms and energy transfer from Er3+ to Mn2+ were also investigated, and some fluorescent security patterns were also designed to demonstrate the potential applications of the present samples in anti-counterfeiting and concealing important information.

An experimental investigation of vortex-induced vibration of a curved flexible cylinder

Vortex-induced vibration of a curved flexible cylinder placed in the test section of a recirculating water tunnel and fixed at both ends is studied experimentally. Both the concave and the convex orientations (with respect to the incoming flow direction) are considered. The cylinder was hung by its own weight with a dimensionless radius of curvature of $R/D=66$ , and a low mass ratio of $m^{*} = 3.6$ . A high-speed imaging technique was employed to record the oscillations of the cylinder in the cross-flow direction for a reduced velocity range of $U^{*} = 3.7 - 48.4$ , corresponding to a Reynolds number range of $Re= 165 - 2146$ . Mono- and multi-frequency responses as well as transition from low-mode-number to high-mode-number oscillations were observed. Regardless of the type of curvature, both odd and even mode shapes were excited in the cross-flow directions. However, the response of the system, in terms of the excited modes, amplitudes and frequencies of the oscillations, was observed to be sensitive to the direction of the curvature (i.e. concave vs convex), in particular at higher reduced velocities, where mode transition occurred. Hydrogen bubble flow visualization exhibited highly three-dimensional vortex shedding patterns in the wake of the cylinder, where there existed spatial and temporal evolution of the vortex shedding modes along the length of the cylinder. The time-varying intermittent vortex shedding in the wake of the cylinder was linked to the spanwise travelling wave behaviour of the vortex-induced vibration response. The observed spatially altering wake corresponded to the multi-modal excitation and mode transition along the length of the cylinder.

Multimodal optical excitation pulsed thermography: Enhanced recognize debonding defects of the solid propellant rocket motor cladding layer

We demonstrated the multimodal optical excitation pulsed thermography, and this technique can enhance the defect detectability and the depth-resolution dynamic range for the propellant /cladding layer interface debonding defects of the solid propellant rocket motor. Firstly, three-dimensional (3D) thermal-wave model which stimulated by a pulse excitation thermal source was built. The temperature field distribution and the thermal-wave diffusion behavior were analyzed. Subsequently, multiple feature extraction algorithms were proposed and applied to extract characteristic images. The experimental set-up was developed and utilized to detect cladding layers with artificial defects. The results demonstrate that pulse thermography optimized by PLSR and ICA can achieve better detection of interface debonding defects. The characteristic profiles were analyzed to evaluate the ability of feature images to characterize the defect diameter and depth. The results depict that the 1st independent component has a better detection effect for defect depth and diameter.

MSENet: Multi-Modal Squeeze-and-Excitation Network for Brain Tumor Severity Prediction

Classification of brain tumors is one of the daunting tasks in medical imaging and incorrect decisions during the diagnosis process may lead to increased human fatality. Latest advances in artificial intelligence and deep learning have opened the path for the success of numerous medical image analysis tasks, including the recognition of brain tumors. In this paper, we propose a simple architecture based on deep learning that results in strong generalization without needing much preprocessing. The proposed Multi-modal Squeeze and Excitation model (MSENet) receives multiple representations of a given tumor image, learns end-to-end and effectively predicts the severity level of tumor. Convolution feature descriptors from multiple deep pre-trained models are used to effectively describe the tumor images and are supplied as input to the proposed MSENet. The squeeze and excitation blocks of the MSENet allow the model to prioritize tumor regions while giving less emphasis to the rest of the image, serving as an attention mechanism in the model. The proposed model is evaluated on the benchmark brain tumor dataset that is publicly accessible from the Figshare repository. Experimental studies reveal that in terms of model parameters, the proposed approach is simple and leads to competitive performance compared to those of existing complex models. By increasing complexity, the proposed model leads to generalize better and achieves state-of-the-art accuracy of 96.05% on Figshare dataset. Compared to the existing models, the proposed model neither uses segmentation nor uses augmentation techniques and without much pre-processing achieves competitive performance.

Multimodal Excitation to Model the Quasibiennial Oscillation.

The quasibiennial oscillation (QBO) of stratospheric winds is the most striking example of mean-flow generation and reversal by the nonlinear interactions of internal waves. Previous studies have used an idealized monochromatic forcing to investigate the QBO. Here we instead force a more realistic continuous wave spectrum. Unexpectedly, spreading the wave energy across a wide frequency range leads to more regular oscillations. We also find that different forcing spectra can yield the same QBO. Multimodal wave forcing is thus essential for understanding wave-mean-flow interactions in nature.

Broadband Seismic Isolation of Periodic Ladder Frame Structure

Abstract Ladder frame structures are used as models for multistorey buildings. These periodic structures exhibit alternating propagating and attenuating frequency bands. Of the six different wave modes of propagation, two modes strongly attenuate at all frequencies. The other four modes have nonoverlapping stop band characteristics. Thus, it is challenging to isolate such structures when subjected to broadband, multimodal base excitation. In this study, we seek to synthesize a periodic ladder frame structure that has attenuation characteristics over the maximal range of frequencies for all the modes of wave propagation. We synthesize a unit cell of the periodic structure, which comprises two distinct regions having different inertial, stiffness, and geometric properties. The eigenvalues of the transfer matrix of the unit cell determines the attenuating or the nonattenuating characteristics of the structure. A novel pictorial presentation in the form of eigenvalue map is developed. This is used to synthesize the optimal unit cell. Also, design guidelines for suitable selection of the design parameters are presented. It is shown that a large finite periodic structure comprising a unit cell synthesized using the present approach has significantly better isolation characteristics in comparison to the homogeneous or any other arbitrarily chosen periodic structure.

Forcing Pulsations by Means of a Siren for Gas Turbine Applications

A siren is a robust fast-valve that generates effective flow pulsations and powerful noise levels under well-controlled conditions. It operates under the inlet flow conditions of a gas turbine combustor. Its principle is based on a sonic air jet periodically sheared by a cogged wheel rotating at a given speed. It is used as an alternative to loudspeakers in combustion laboratories when the use of these is made difficult by aggressive flow conditions, such as hot air under pressure, possibly containing impurities. It is also a serious candidate as an effective flow actuator to be deployed on power gas turbine fleets. The authors have gathered more than twenty years of knowledge on siren technology. This pulsator was originally developed for research on thermoacoustics. By scanning through a given frequency range, one detects the acoustic resonance of specific parts of the combustor assembly, or possibly triggers a combustion instability during a sensitivity analysis of a flame to small perturbations. In 2010, Giuliani et al. developed a novel siren model with the capacity to vary the amplitude of pulsation independently from the frequency. In this contribution, the physics, the metrics, and the resulting parameters of the pulsator are discussed. Technical solutions are unveiled about visiting large frequency ranges (currently 6 kHz) and achieving elevated pressure fluctuations (150 dB SPL proven, possibly up to 155 dB SPL) with a compact device. A multimodal excitation is available with this technology, one idea being to dissipate the acoustic energy on nearby peaks. The contribution ends with a summary of the applications performed so far and the perspective of an industrial application.

Aluminum Nitride Combined Overtone Resonators for the 5G High Frequency Bands

This work presents a new acoustic MEMS resonator technology, dubbed Aluminum Nitride (AlN) Combined Overtone Resonator (COR), capable of addressing the filter requirements for the 5G high frequency bands in the 6-40GHz range. The COR exploits the multimodal excitation of two higher-order Lamb waves ( $2^{\mathbf {nd}}$ and $3^{\mathbf {rd}}$ order Asymmetrical Lamb Waves) in a suspended thin-film AlN plate to transduce a 2-dimensional vibration mode with high electromechanical coupling coefficient $k_{t}^{2}$ (up to 1.9%) and quality factor $Q>1100 $ at twice the frequency of a fundamental thickness-extensional mode in the same structure. Analytical and finite-element method (FEM) models are developed to describe the working principle of the COR technology and predict the achievable $k_{t}^{2}$ , Q and lithographic frequency tunability. An 8.8 GHz COR prototype was fabricated showing a high $k_{t}^{2}~\sim ~0.3$ % (using a simple top-electrode-only configuration with a 2-mask process) and a groundbreaking $Q\sim {1100}$ which is the highest ever achieved among piezoelectric resonators above 6 GHz. The $f - Q$ product $\sim 1\times 10 ^{\mathbf {13}}$ is the highest among all demonstrated piezoelectric resonators with metallic coverage >50%. Additionally, the capability of the COR technology to deliver contiguous filters with bandwidths between 355 and 592 MHz (aggregated BW >2GHz) in the mmWave spectrum, with relaxed lithographic requirements, is demonstrated by FEM. [2019-0229]

Simulation-Based Characterization of Mechanical Parameters and Thickness of Homogeneous Plates Using Guided Waves.

Properties of isotropic plates in terms of material constants and thickness are characterized by making use of dispersion characteristics of propagating Lamb waves. A numerical model is inversely optimized in order to match dispersion curves measured by laser vibrometry. This kind of material characterization has gained interest in recent research. Improvements in accuracy and efficiency of the optimization process are therefore important steps toward an industrial application of this technique to nondestructive testing and online monitoring. For this purpose, the use of a fast converging numerical model based on spectral collocation has been found to be well suited. Furthermore, we improved the signal-to-noise ratio by utilizing long-time broadband excitation signals for multimodal excitation of Lamb waves. The wavenumber spectrum up to 2.5 MHz is acquired by measurements with a laser-scanning vibrometer. In order to exploit the information contained in high-order modes, we present an algorithm to match the measured data to the calculated modes during the optimization process, leading to higher accuracy of the estimated model parameters. The characterization results are verified by comparison to measurements with a conventional ultrasonic method.

High kt2 Exceeding 6.4% Through Metal Frames in Aluminum Nitride 2-D Mode Resonators.

This work describes a new method to enhance the electromechanical coupling coefficient ( kt2 ) of 2-D mode resonators (2DMRs). This approach exploits the multimodal excitation of different Lamb waves to achieve a quasi-uniform vertical displacement distribution in the electrode regions of 2DMRs. To do so, the 2DMRs reported in this work rely on the use of metal frame structures placed at the edges of each metal strip forming the electrode gratings. To demonstrate the effectiveness of this new technique in enhancing kt2 , we report the design and simulated performance through the finite-element methods of a 2.5-GHz 2DMR using metal frames. Our analysis proves that this device can simultaneously exhibit high kt2 in excess of 6.4% and wide lithographic frequency tunability in excess of 10%, thus approaching the reported performance of aluminum nitride (AlN) film bulk acoustic resonators (FBARs) operating within the same frequency range.

Multimodal Shear Wave Deicing Using Fibre Piezoelectric Actuator on Composite for Aircraft Wings

The formation and accretion of ice on aircraft wings during flight can be potentially disastrous and existing in-flight deicing methods are either bulky or power consuming. This paper investigates the use of shear wave deicing driven by a macro fibre piezoelectric composite actuator on a composite plate typically used for aircraft wings. While the few existing research on this novel deicing approach focused on either theoretical studies or single frequency mode optimization that required high-excitation amplitudes, this study revealed that the use of multimodal excitation through broadband frequency sweeps has the potential to promote the chance of shear stress induced deicing at a relatively small excitation amplitude. The results reported here form the foundation for a pathway towards low power and lightweight deicing mechanism for in-flight aircraft wings.

Duct modes damping through an adjustable electroacoustic liner under grazing incidence

This paper deals with active sound attenuation in lined ducts with flow and its application to duct modes damping in aircraft engine nacelles. It presents an active lining concept based on an arrangement of electroacoustic absorbers flush mounted in the duct wall. Such feedback-controlled loudspeaker membranes are used to achieve locally reacting impedances with adjustable resistance and reactance. A broadband impedance model is formulated from the loudspeaker parameters and a design procedure is proposed to achieve specified acoustic resistances and reactances. The performance is studied for multimodal excitation by simulation using the finite element method and the results are compared to measurements made in a flow duct facility. This electroacoustic liner has an attenuation potential comparable to that of a conventional passive liner, but also offers greater flexibility to achieve the target acoustic impedance in the low frequencies. In addition, it is adaptive in real time to track variable engine speeds. It is shown with the liner prototype that the duct modes can be attenuated over a bandwidth of two octaves around the resonance frequency of the loudspeakers.

Multifrequency excitation and detection scheme in apertureless scattering near-field scanning optical microscopy.

Near-field scanning optical microscopy has revolutionized the study of fundamental physics, as it is one of very few label-free optical noninvasive nanoscale-resolved imaging techniques. However, its resolution remains strongly limited by the poor discrimination of weak near-field optical signals from a far-field background. Here, we theoretically and experimentally demonstrate a multifrequency excitation and detection scheme in apertureless near-field optical microscopy that exceeds current state-of-the-art sensitivity and background suppression. We achieved a twofold enhancement in sensitivity and deep subwavelength resolution in optical measurements. This method offers rich control over experimental degrees of freedom, breaking the ground for noninterferometric complete retrieval of the near-field signal.