Multimodal Propagation Research Articles

Bayesian identification of acoustic impedance in treated ducts.

The noise reduction of a liner placed in the nacelle of a turbofan engine is still difficult to predict due to the lack of knowledge of its acoustic impedance that depends on grazing flow profile, mode order, and sound pressure level. An eduction method, based on a Bayesian approach, is presented here to adjust an impedance model of the liner from sound pressures measured in a rectangular treated duct under multimodal propagation and flow. The cost function is regularized with prior information provided by Guess's [J. Sound Vib. 40, 119-137 (1975)] impedance of a perforated plate. The multi-parameter optimization is achieved with an Evolutionary-Markov-Chain-Monte-Carlo algorithm.

Matrix theory of wave propagation in hybrid electric/magnetic multiwire transmission line systems

Matrix methods to deal with multimodal propagation in electric multiwire transmission lines are quite well known. However, the matrix theory of magnetic multiwire transmission lines (MMTL) has been established only very recently. In this study, we advance the new subject of hybrid electric and MMTL, which has never been addressed in the literature. A complex system composed of N + 1 electric wires and n + 1 magnetic wires is theoretically analyzed from the viewpoint of their interaction/coupling, transmission line matrix equations, ABCD matrix formalism, and superposition of propagation modes.

Localization for broadband source by a single vector sensor in shallow water

The physical meaning of array invariant is the absolute traveling time of different modal from a source to a receiver under the average sound speed. It can be gotten by the derivative of the arriving time against the corresponding cosecant function of elevation angle for each modal, which can be used for the passive source localization. A vector sensor can be seen as a small volumetric array. It has its capability of elevation angle determination to describe the multi-modal propagation and the single-modal dispersion in shallow water, which may imply a chance to get the array invariant for the source localization. Here, we take advantage of the dispersion based short time Fourier transform and warping transform techniques for the time-frequency analysis of vector sensor signals. This technique can improve acoustic normal mode identification and thereby extract the modal data more accurately for array invariant determination. The idea had been effectively validated during the experiment that took place in ...

Multi-Modal Acoustic Flow Decomposition Examined in a Hard Walled Cylindrical Duct

Abstract Flow fields could be of great interest in the study of sound propagation in aeroengines. For ducts with rigid boundaries, the fluid-resonant category may contribute significantly to unwanted noise. An understanding of the multi-modal propagation of acoustic waves in ducts is of practical interest for use in the control of noise in, for example, aero-engines, automotive exhaust and heating or ventilation systems. The purpose of our experiments was to test the acoustic energy transmission of duct modes based on studies carried out by the sound intensity technique. Sound intensity patterns in circular duct are discussed of modal energy analysis with particular reference to proper orthogonal decomposition and dynamic mode decomposition. The authors try to justify some advantages of the sound intensity experimental research in this area. In the paper, the wide-band sound signal propagated from source approximated with loudspeaker in hard-walled duct is imaged using a sound intensity - based approach. For a simple duct geometry, the sound intensity field is examined visually and by performing a modal decomposition greater insight into the acoustic structures is obtained. The image of sound intensity fields below and above “cut-off” frequency region are found to compare acoustic modes which might resonate in duct.

Low Frequency Guided Wave Transmission in Water Pipe Systems

This paper addresses the multimodal acoustic wave propagation in elastic pipes which can carry multiphase fluids. The waveguide characteristics of circular fluid filled pipes and the influence of elasticity of the outer boundaries in relation to the compressibility of the filling liquid and the inner boundaries due to an additional fluid phase are discussed – in comparison to the assumption of rigid walls. As the main aspect for liquid monitoring systems the decrease of the sound velocity within the liquid below the bulk wave velocity is discussed in detail by numerical studies and empirical proofs. Further, it will be shown that an additional fluid phase causes a deterministic jumping of the wave modes and of the dispersion characteristics.

Levantamento das distribuições de temperatura em leito de arroz com casca durante o tratamento térmico por micro-ondas

Durante o aquecimento dielétrico, a distribuição do campo elétrico dentro de uma cavidade ocorre a partir de uma propagação multimodal, ocasionada por inúmeras reflexões das micro-ondas provenientes das paredes metálicas da cavidade. Essas reflexões múltiplas geram regiões de maior e menor intensidade de campo elétrico no espaço e, por consequência, um aquecimento não uniforme no produto. O objetivo deste estudo foi o levantamento dos valores de temperaturas obtidos durante o tratamento térmico por micro-ondas em um leito de arroz em casca úmido posicionado em um porta-amostra, dentro de uma cavidade que apresenta uma geometria prismática de seção sextavada. A cavidade foi desenhada para, operando em frequência de 5,8 GHz e potência máxima de 700 W, minimizar a heterogeneidade de distribuição das intensidades do campo elétrico, gerando um aquecimento mais uniforme do produto. Verificou-se que as diferenças de temperatura registradas pelos sensores no leito de arroz foram de 3,2 °C a 12,5 °C durante os tratamentos térmicos estudados. Não foi observado um comportamento padrão que indicasse uma região de maior aquecimento em relação à altura e direção radial do leito de arroz durante os tratamentos térmicos por micro-ondas

Content-oriented multimedia document understanding through cross-media correlation

This paper presents a novel method for multimedia document content analysis through modeling multimodal data correlations. We hypothesize that the correlation of different modalities from the same data source can help achieve better multimedia content understanding results than one which explores a single modality. We turn this task into two parts: multimedia data fusion and multimodal correlation propagation. During the first stage, we re-organize the training multimedia data into Modality semAntic Documents (MADs) after extracting quantized multimodal features, and then use multivariate Gaussian distributions to characterize the continuous quantity by latent topic modeling. Model parameters are asymmetrically learned to initialize multimodal correlations in the latent topic space. Accordingly, during the second stage, we construct a Multimodal Correlation Network (MCN) based on the initialized multimodal correlations, and a new mechanism of propagating inter-modality correlations and intra-modality similarities in MCN is further proposed to take the complementary from cross-modalities to facilitate multimedia content analysis. The experimental results of image-audio data retrieval on a 10-categories dataset and content-oriented web page recommendation on the USTODAY dataset show the effectiveness of our method.

Multimodal propagation of the electromagnetic wave on a structured perfect electric conductor (PEC) surface

Spoof surface plasmon (SSP) on structured perfect electric conductor (PEC)–air interface is usually modeled by an effective plasma frequency in the long wavelength limit. In this limit, the effective permittivity model suggests a purely exponential decay of the field profile on both sides of the interface, drawing an analogy with a surface plasmon polariton (SPP)-like single mode (TM) propagation. However, most of the practical applications and experiments involving SSP fall in the regime where the feature-size of the structure is comparable to the wavelength. In this wavelength regime of practical interest, we show that in contrast to surface plasmon polariton (SPP), the propagation of the surface wave is hybrid involving both TM and TE modes. By combining angular spectrum representation and vector nature of the electromagnetic fields, we show that the field profile of SSP on patterned PEC can be described accurately by superposition of multiple evanescent orders caused by the diffraction from sub-wavelength features at the interface. This multimodal nature of the surface wave readily explains the anisotropic propagation observed earlier. Also, inclusion of at least one mode from higher order Brillouin zone is necessary for describing the near-field above the interface with reasonable accuracy.

Data-driven matched field processing for Lamb wave structural health monitoring

Matched field processing is a model-based framework for localizing targets in complex propagation environments. In underwater acoustics, it has been extensively studied for improving localization performance in multimodal and multipath media. For guided wave structural health monitoring problems, matched field processing has not been widely applied but is an attractive option for damage localization due to equally complex propagation environments. Although effective, matched field processing is often challenging to implement because it requires accurate models of the propagation environment, and the optimization methods used to generate these models are often unreliable and computationally expensive. To address these obstacles, this paper introduces data-driven matched field processing, a framework to build models of multimodal propagation environments directly from measured data, and then use these models for localization. This paper presents the data-driven framework, analyzes its behavior under unmodeled multipath interference, and demonstrates its localization performance by distinguishing two nearby scatterers from experimental measurements of an aluminum plate. Compared with delay-based models that are commonly used in structural health monitoring, the data-driven matched field processing framework is shown to successfully localize two nearby scatterers with significantly smaller localization errors and finer resolutions.

Lamb wave frequency–wavenumber analysis and decomposition

Lamb waves have shown great potentials in damage detection of thin-walled structures due to their long propagation capability and sensitivity to a variety of damage types. However, their practical adoption has been hindered due to the complexity caused by their multimodal nature. Various wave modes that propagate at various velocities in the structure make the interpretation of Lamb wave signals very difficult. It is desired that the modes can be separated for independent analysis or further employment. In this article, we present our studies on the multimodal Lamb wave propagation and wave mode decomposition using frequency–wavenumber analysis. Wave representation in the frequency–wavenumber domain is obtained using multidimensional Fourier transform, where various Lamb wave modes can be easily discerned. This allows for separating them or extracting a desired wave mode through a filtering process, thus making it possible to use a single-mode Lamb wave for the detection of a certain type of damage in structural health monitoring applications. To retain the temporal and spatial information that is lost during Fourier transformation, a novel wavenumber analysis is also presented. These concepts are illustrated through experimental testing where high spatial resolution wavefields are measured by a scanning laser Doppler vibrometer.

Spatiotemporal dynamics of magnetostatic and spin waves in a transversely confined ferrite waveguide

Spatiotemporal dynamics of the multimodal propagation of magnetostatic waves in a transversally confined ferrite waveguide and the parametric excitation of spin wave under conditions of three-magnon decay processes are experimentally investigated by the Brillouin spectroscopy.

Sparse recovery of the multimodal and dispersive characteristics of Lamb waves

Guided waves in plates, known as Lamb waves, are characterized by complex, multimodal, and frequency dispersive wave propagation, which distort signals and make their analysis difficult. Estimating these multimodal and dispersive characteristics from experimental data becomes a difficult, underdetermined inverse problem. To accurately and robustly recover these multimodal and dispersive properties, this paper presents a methodology referred to as sparse wavenumber analysis based on sparse recovery methods. By utilizing a general model for Lamb waves, waves propagating in a plate structure, and robust l1 optimization strategies, sparse wavenumber analysis accurately recovers the Lamb wave's frequency-wavenumber representation with a limited number of surface mounted transducers. This is demonstrated with both simulated and experimental data in the presence of multipath reflections. With accurate frequency-wavenumber representations, sparse wavenumber synthesis is then used to accurately remove multipath interference in each measurement and predict the responses between arbitrary points on a plate.

Bright extreme-ultraviolet high-order-harmonic radiation from optimized pulse compression in short hollow waveguides

Multimodal nonlinear propagation dominates the evolution of intense laser pulses propagating in high-pressure gas-filled capillaries used for high harmonic generation. A fully multimodal nonlinear propagation model is used to predict pulse evolution along such a capillary, and the length and pressure distribution are optimized to produce the shortest pulses at the capillary output. This optimization is shown theoretically to result in self-compression of the pulse from $\ensuremath{\sim}$53 to $\ensuremath{\sim}$7 fs, and is shown experimentally to increase the flux of high harmonic radiation from the capillary by an order of magnitude over comparable capillary and gas jet designs.

Multimodal wave propagation in smart composite structures with shunted piezoelectric patches

Wave propagation in composite structures with shunted piezoelectric patches is investigated in this study. The wave finite element approach is first developed as a prediction tool for wave propagation characteristics such as dispersion curves in composite structures, and subsequently extended to consider shunted piezoelectric elements through the diffusion matrix model. A three-layered composite beam equipped with a pair of resistor–inductor shunted piezoelectric patches is modeled and analyzed carefully with these numerical techniques. Reflection and transmission coefficients of propagating waves in this smart composite structure are calculated, and the performance of shunted piezoelectric patches on the control of wave propagation is investigated numerically with the diffusion matrix model. Another finite element formulation, named modified wave finite element method, which is dedicated to the analysis of wave propagation in multilayered composite structures, is proposed and developed for considering piezoelectric elements in the structures. It is a dynamic substructuring technique that allows the dynamics of a typical layer cross section to be projected on a reduced local wave mode basis with appropriate dimensions. Results issued from this method are compared to those issued from the classical wave finite element and diffusion matrix model formulations to demonstrate the pertinence of the modelings.

Multi-modal wave propagation in smart structures with shunted piezoelectric patches

The propagation of wave modes in elastic structures with shunted piezoelectric patches is dealt with in this work. The wave finite element approach, which is based on the finite element method and periodical structure theory, is firstly developed as a prediction tool for wave propagation characteristics in beam like structures, and subsequently extended to consider shunted piezoelectric elements through the diffusion matrix model (DMM). With these numerical techniques, reflection and transmission coefficients of propagating waves in structures with shunted piezoelectric patches can be calculated. The performance of shunted piezoelectric patches on the control of wave propagation is investigated numerically with the DMM. Forced response of the smart structure can also be calculated, and based on which the time response of the structure can be obtained via an inverse discrete fourier transform approach. These general formulations can be applied to all types of slender structures. All these numerical tools can facilitate design modifications and systematic investigations of geometric and electric parameters of smart structures with shunted piezoelectric elements.

Guided wave expansion in warped curvelet frames

Lamb wave testing for structural health monitoring (SHM) often relies on analysis of wavefields recorded through scanning laser Doppler vibrometers (SLDVs) or ultrasonic scanners. Damage detection and characterization with these techniques requires isolation of defect-induced reflections in the wavefield from the injected wave packet and from scattering events associated with structural features such as boundaries, rivets, joints, etc. This is a challenging task when dealing with complex structures and multimodal, dispersive propagation regimes, whereby various wave contributions in both the time/space and the frequency/wavenumber domain overlap. A new mathematical tool named warped curvelet frames (WCFs) is proposed to effectively decompose the recorded wavefields. The presented technique results from the combination of two operators, i.e., the curvelet transform (CT) and the warped frequency transform (WFT). The CT provides an optimally sparse representation of nondispersive wave propagators. Combining the CT with the WFT allows for a flexible analysis of multimodal wave propagation in dispersive media. Exploiting the spatial and temporal localization of curvelets, as well as the spectro-temporal adaptation of the analysis frame to the characteristics of each propagating mode, provided by frequency warping, a convenient decomposition of guided waves is achieved and relevant contributions can be effectively isolated. The proposed approach is validated through dedicated simulations and further tested experimentally to demonstrate the effectiveness of the method in separating guided wave modes corresponding to acoustic events in close spatial proximity.

Broadband generation of ultrasonic guided waves using piezoceramics and sub-band decomposition

Classically, damage detection or dispersion curve determination using piezoceramic-generated guided waves has been based on analysis of propagation properties of multiple narrowband excitation signals. However, dispersion and multimodal propagation impair the determination of propagation properties. More recently, it has been proposed to consider broadband excitations for both damage imaging and group velocity estimation. Among existing transducer technologies, although laser excitation is prone to practical limitations in terms of dimensions and generated amplitudes, it allows generation of noncontact, point-like broadband displacement. Thus, broadband generation of guided waves using piezoceramics can be envisioned. However, direct impulse response measurements are limited by the generated amplitude, leading to low SNR measurements. For this purpose, chirp excitations have been proposed using variable-frequency bursts, leading to phase and amplitude variations with respect to the frequency, such that this approach is not suitable for precise estimation of time of flight (ToF) or modal amplitude. In this paper, a sub-band decomposition technique that allows high-SNR measurements of impulse response in a given frequency range is proposed. Broadband excitation is decomposed over a given number of frequency sub-bands, generated by a piezoceramic element and measurement is performed using a laser Doppler vibrometer (LDV) or a piezoceramic sensor. Application to experimental estimation of group velocity and damage detection in pitchcatch configuration is proposed. It is shown that the proposed method allows damage estimation without a priori knowledge of the damage size, whereas narrowband techniques can fail at specific wavelengths.

Generalized array invariant and its application on broadband source ranging

A passive source ranging method based on the array invariant in shallow water is discussed in this paper. The arriving time and elevation angle of sound are used to describe the multi-modal propagation and single-mode dispersion. Based on the two parameters, we rederive the array invariant in a different way, which allows simple physical interpretation. The array invariant in its original form is not exact invariant, but depends (weakly) on mode number and frequency. The accuracy of the method based on this notion is limited when the sound speed of seabed is different significantly from that in the water column. A modified technique ( generalized array invariant) is proposed in this talk to improve the problem provided when the sound speed of seabed is known. The proposed method is testified by simulation and experimental data.

Setting up an experimental apparatus for the study of multimodal acoustic propagation with turbulent mean flow

An experiment has been set up to study multimodal acoustic propagation inside a cylindrical duct in presence of a turbulent mean flow. This paper describes the preliminary work which has been found necessary for assembling the experiment together with first measurement results. In order to set up this experimental facility, a high level acoustic source was developed to generate higher propagating modes in the presence of mean flow. A microphonic antenna was designed for detecting the propagating modes. LDV measurements were performed and synchronous detection was used to extract both the mean flow and the acoustic components of the particle velocity. Results of aeraulic measurements are presented. Then, results of acoustic velocity measurements are compared to results obtained from the microphonic antenna.

Improving protein secondary structure prediction using a multi-modal BP method

Methods for predicting protein secondary structures provide information that is useful both in ab initio structure prediction and as additional restraints for fold recognition algorithms. Secondary structure predictions may also be used to guide the design of site directed mutagenesis studies, and to locate potential functionally important residues. In this article, we propose a multi-modal back propagation neural network (MMBP) method for predicting protein secondary structures. Using a Knowledge Discovery Theory based on Inner Cognitive Mechanism (KDTICM) method, we have constructed a compound pyramid model (CPM), which is composed of three layers of intelligent interface that integrate multi-modal back propagation neural network (MMBP), mixed-modal SVM (MMS), modified Knowledge Discovery in Databases (KDD ⁎) process and so on. The CPM method is both an integrated web server and a standalone application that exploits recent advancements in knowledge discovery and machine learning to perform very accurate protein secondary structure predictions. Using a non-redundant test dataset of 256 proteins from RCASP256, the CPM method achieves an average Q 3 score of 86.13% (SOV99=84.66%). Extensive testing indicates that this is significantly better than any other method currently available. Assessments using RS126 and CB513 datasets indicate that the CPM method can achieve average Q 3 score approaching 83.99% (SOV99=80.25%) and 85.58% (SOV99=81.15%). By using both sequence and structure databases and by exploiting the latest techniques in machine learning it is possible to routinely predict protein secondary structure with an accuracy well above 80%. A program and web server, called CPM, which performs these secondary structure predictions, is accessible at http://kdd.ustb.edu.cn/protein_Web/.