Broadband Signals Research Articles

Formulations and numerical techniques for computation of acoustic pressure and its gradient by integral method

Starting from the Ffowcs Williams-Hawkings surface integral formulation for a moving medium, the article proposes rather simple expressions for the radiated pressure and its gradient in the time domain, that are valid for solid or porous, fixed or moving integration surfaces. Moreover, these original expressions allow calculations with integration surfaces in supersonic motion (such as rotating surfaces around propellers or rotors). Versions dedicated to fixed integration surfaces are also proposed. The usual locally compact and the fully non-compact integration techniques are recalled, with, for both, a detailed description of efficient calculation algorithms. Particular attention is devoted to the order of precision of the calculations. The time derivation techniques and integration schemes used in this study lead to a theoretical second order that can easily be increased for the locally compact integration method. The results of these expressions and integration methods are compared to the analytical solution for the case of a fixed monopole and for that of a rotating monopole. They clearly show the benefit of the direct gradient calculation over a calculation by finite differences of the pressure around the observation point, particularly for broadband signals.

CMUT for ultrafast passive cavitation detection during ultrasound-induced blood–brain barrier disruption: proof of concept study

Objective.Cavitation dose monitoring plays a key role in ultrasound drug delivery to the brain. The use of capacitive micromachined ultrasonic transducer (CMUT) technology has a great potential for passive cavitation detection (PCD).Approach.Here, a circular (diameter 7 mm) CMUT centered at 5 MHz was designed to be inserted into a therapeutic transducer (1.5 MHz) used for ultrasound-induced blood-brain barrier (BBB) disruption on mice. CMUT-based real-time cavitation detection was performed during the ultrasound procedure (50μl intravenous injection of SonoVue microbubbles, frequency 1.5 MHz, PNP 480 kPa, duty Cycle 10%, PRF 10 Hz, duration 60 s). BBB disruption were confirmed by contrast-enhanced 7T-MRI.Main results.The CMUT device has a fractional bandwidth of 140%, almost twice a conventional piezocomposite PCD transducer. As expected, the CMUT device was able to detect the occurrence of harmonic, subharmonic and ultraharmonic frequencies as well as the increase of broadband signal indicating inertial cavitation in a wide frequency range (from 0.75 to 6 MHz). Signal-to-noise ratio was high enough (>40 dB) to perform ultrafast monitoring and follow the subtle intrapulse variations of frequency components at a rate of 10 kHz.Significance. This firstin vivoproof of concept demonstrates the interest of CMUT for PCD and encourages us to develop devices for PCD in larger animals by integrating an amplifier directly to the CMUT front-end to considerably increase the signal-to-noise ratio.

Hydroacoustic Evidence for Offshore Lava Emplacement During the 2018 Kīlauea Eruption

AbstractDuring the 2018 Kīlauea eruption, over half the erupted lava was deposited on the seafloor. Lava flows crossing the shoreline generated sounds that were recorded by a network of hydrophones. We show that short‐duration, broadband signals associated with lava‐water interactions occurred throughout the eruption but increased in number when the Ahalanui ocean entry initiated on July 11. These terminated in early August coincident with the eruption's end. We compare hydroacoustic data with transmission loss models and eruption photographs to show that coastal explosive activity was poorly recorded by the hydrophone network. Similarly, strong hydroacoustic signals did not correlate with observed activity. These results suggest that acoustic signals were generated by lava flowing up to 100 s of meters offshore. Offshore lava flows can be hazardous to boaters, but hydrophones provide a means by which these hazards can be detected.

Laplacian-enhanced non-synchronous measurements method

To address the challenges of physical geometric constraints of microphone arrays and the lack of a prior information about the operating frequencies of target signals, we propose a novel method for broadband multiple-sound-source localization: a non-synchronous measurements method for broadband multiple-sound-source localization based on Laplacian-enhanced low-rank tensor completion. Our method thoroughly analyzes the tensor data structure of broadband signals and introduces a multiplier-optimized alternating direction method. Through extensive simulation studies, our approach has achieved remarkable results. We validate the outstanding performance of the Laplacian-enhanced algorithm, demonstrating its ability to generate highly accurate sound maps, capturing five distinct speech signal sources. Compared to other methods, our approach provides a more comprehensive global view. This technological advancement brings substantial hope for the precise localization of multiple broadband sound sources in critical applications, offering significant potential for future applications.

Acoustic flow resonances in installed rectangular jets

Zonal Large Eddy Simulations (LES) of complex installed rectangular jet flows are performed for subsonic jet conditions of the Central Institute for Aviation Motors (CIAM) experiment, where a strong tone was reported. For far-field noise modelling, the zonal LES solutions are coupled with the permeable formulation of the Ffowcs Williams and Hawkings (FW-H) method. The obtained noise spectra predictions are compared with the acoustic measurements in the CIAM facility. To reduce statistical noise of the relatively short LES time series, contributions due to several dominant low frequency tones and the remaining broadband signal are computed separately, using a tailored Fourier transform technique for each signal type. For cross-validation, noise spectra measurements of an equivalent isolated round jet in the CIAM facility are compared with the empirical sJet model calibrated on the NASA Small Hot Jet Acoustic Rig (SHJAR) jet noise database. While the two datasets agree reasonably well for mid to high frequencies, larger discrepancies are observed for low frequencies, which are attributed to acoustic reflections in the non-anechoic CIAM facility. The differences in noise levels between the CIAM dataset and the sJet model representing the NASA jet noise data are used to determine the experimental uncertainty of the CIAM noise measurements for each frequency and observer angle. For the installed rectangular jet, it is shown that far-field noise spectra predictions of the zonal LES-FW-H method for both the fundamental tone, its sixth harmonic corresponding to the jet Strouhal number of around 1, and the broadband component are broadly within the experimental error bar for most observer angles. Some discrepancies between predictions of the zonal LES method and the CIAM measurements for the main low frequency tone for the 30o and 90o, where the experimental uncertainty at low frequencies is largest are also noted. After validating the acoustic solutions, spectral and conditional averaging analysis methods are applied to elucidate mechanisms of the acoustic-flow resonance in the installed rectangular jet flow. The numerical dispersion relation is obtained to analyse phase velocities of the upstream and downstream travelling pressure waves in the stream-wise direction. The conditional analysis of pressure fluctuations inside the jet reveals the emergence of internal reflection points corresponding to a rapid change of the acoustic wave phase as well as the saddle points interpreted as localised zones of vorticity shed from the side-wall edges. To independently investigate the effect of trailing edges and corner points of the jet embodiment geometry on closing the acoustic-flow resonance cycle, several modifications of the baseline rectangular nozzle are considered, such as introducing chevron-like lobes and cuts on the trailing edges of the side walls as well as smoothing the sharp corner points of the wall edges. Following the series of additional zonal LES runs with the modified installed nozzle geometries, an optimized tone-less modification of the original installed nozzle was obtained, in broad agreement with the conditional analysis results. The obtained tone-less modification of the installed rectangular jet is further analyzed to provide insights into its similarity and differences from the aeroacoustics of the reference isolated round jet in the same CIAM facility.

Система ввода цифровых предыскажений на основе обобщенной полиномиальной модели с памятью для GaN усилителей мощности

Modern power amplifiers based on GaN transistors face a number of problems related to their physical properties and operating conditions. The high output power of such power amplifiers is accompanied by significant nonlinear distortions, especially when operating in saturation mode. Amplifiers based on GaN transistors have pronounced «short» memory effects, which leads to the dependence of current distortions on previous signal states. At the same time, support for broadband signals requires high processing speeds and large computing resources. Classical digital pre-distortion methods do not always cope with the task of effectively compensating for real-time distortion for power amplifiers based on GaN transistors. These problems complicate the process of linearization of power amplifiers based on GaN transistors and require the development of new methods that can effectively compensate for non-linearities and memory effects without significantly increasing the cost and complexity of the system. The purpose of the work is to create and analyze the effectiveness of a digital pre-imaging system based on a generalized polynomial model with memory to improve the linearity and efficiency of power amplifiers based on GaN transistors in wireless communication systems. The paper presents the architecture of the digital preimage input system based on a generalized polynomial model with memory. The use of this model makes it possible to improve the efficiency of suppressing nonlinear distortions at the output of a power amplifier based on GaN transistors. Practical significance – the proposed architecture can be implemented on FPGAs, VLSI or SOC with a minimum amount of computing resources.

Research on Broadband Measurement Method of Power System based on Wavelet Transform

This study delves into the exploration of broadband measurement techniques for power systems, utilizing wavelet transform as a foundational tool for signal analysis. The research rigorously evaluates the efficacy of several machine learning algorithms, namely Support Vector Machines (SVM), Artificial Neural Networks (ANN), K-Nearest Neighbors (KNN), and Random Forest, in interpreting and analyzing broadband signals within power systems. Through a detailed analytical process, the performance of each algorithm is meticulously assessed based on several critical metrics: accuracy, precision, recall, and F1-score. The research investigates broadband measurement methods for power systems using wavelet transform and evaluates the performance of Support Vector Machines (SVM), Artificial Neural Networks (ANN), K-Nearest Neighbors (KNN), and Random Forest. Results show SVM achieving an accuracy of 85%, precision of 86%, recall of 82%, and F1-score of 84%. ANN yields 82% accuracy, 84% precision, 78% recall, and 81% F1 score. KNN demonstrates 87% accuracy, 88% precision, 84% recall, and 86% F1 score. DT achieves 79% accuracy, 80% precision, 75% recall, and 77% F1 score. Overall, the study provides insights into machine learning algorithms’ effectiveness in broadband power system measurement.

Determination of the resolution intervals in time and frequency under the influence of multiplicative noise based on the Woodworth criterion

Issues related to estimating the influence of quasi-deterministic and fluctuating multiplicative noise on the delay resolution and frequency resolution of systems processing radio signals based on the Woodward criterion for narrow-band and broadband signals are considered. The problem of resolution when detecting or measuring signal parameters can be considered both for useful signals alone and for cases when interfering signals are present as well. It is pointed out that the effect of multiplicative noise on the signal almost always leads to a resolution problem. It is shown, that under the influence of significant broadband multiplicative noise, the time resolution interval is determined only by the signal envelope and does not depend on its phase structure. For instance, for signals with a rectangular or bell-shaped envelope, it is equal to the equivalent signal duration. Examples of calculating resolution intervals under the influence of multiplicative noise are given. Taking into account the effect of multiplicative noise on signal resolution leads to an increase in the efficiency of radio systems, detection of objects being an example.

Modeling of Spectral Regrowth Effects of Passive Intermodulation With Broadband Signal Excitation

Modeling of Spectral Regrowth Effects of Passive Intermodulation With Broadband Signal Excitation

Data-driven aeroelastic analyses of structures in turbulent wind conditions using enhanced Gaussian Processes with aerodynamic priors

Recent advancements in data-driven aeroelasticity have been driven by the wealth of data available in the wind engineering practice, especially in modeling aerodynamic forces. Despite progress, challenges persist in addressing free-stream turbulence and incorporating physics knowledge into data-driven aerodynamic force models. This paper presents a hybrid Gaussian Process (GPs) methodology for non-linear modeling of aerodynamic forces induced by gusts and motion on bluff bodies. Building on a recently developed GP model of the motion-induced forces, we formulate a hybrid GP aerodynamic force model that incorporates both gust- and motion-induced angles of attack as exogenous inputs, alongside a semi-analytical quasi-steady (QS) model as a physics-based prior knowledge. In this manner, the GP model incorporates the absent physics of the QS model, and the non-dimensional hybrid formulation enhances its appeal from an aerodynamic perspective. We devise a training procedure that leverages simultaneous input signals of gust angles, based on random free-stream turbulence, and motion angles, based on random broadband signals. We verify the methodology through analytical linear aerodynamics of a flat plate and non-linear aerodynamics of a bridge deck using Computational Fluid Dynamics (CFD). The standout feature of the presented methodology is its applicability for aeroelastic buffeting analyses, showcasing robustness when handling broadband excitation. Importantly, the non-linear hybrid model preserves its capability to capture higher-order harmonics in the motion-induced forces and remains applicable for flutter analysis, while incorporating both motion and gust angles as input. Applications of the methodology are anticipated in the aeroelastic analysis and monitoring of slender line-like structures.

Survey on Advances in Broadband Signal Generation and Processing of ASIC Semiconductors for Defense Satellites

To replace the field-programmable gate array semiconductors used in the defense satellite industry, we conducted a technical investigation of application-specific integrated circuit (ASIC) semiconductors. The analysis results show that ASIC semiconductors have the heat dissipation, reliability, and radiation resistance capabilities required in a space environment and excellent performance indicators related to the resolution of synthetic aperture radar payloads, such as operating frequency. Research and development of mission-customized ASIC semiconductors that fit the requirements for NSP(new-space paradigm) should be preceded to expanse bases of the space industry, national security capabilities for next-generation space deveolpment also to secure competitiveness of technology and domestic supply chain as space parts itselfs.

Linear and nonlinear flame response prediction of turbulent flames using neural network models

Modelling the flame response of turbulent flames via data-driven approaches is challenging due, among others, to the presence of combustion noise. Neural network methods have shown good potential to infer laminar flames’ linear and nonlinear flame response when externally forced with broadband signals. The present work extends those studies and analyses the ability of neural network models to evaluate the linear and nonlinear flame response of turbulent flames. In the first part of this work, the neural network is trained to evaluate and interpolate the linear flame response model when presented with data obtained at various thermal conditions. In the second part, the neural network is trained to infer the nonlinear flame response model when presented with time series exhibiting sufficient large amplitudes. In both cases, the data is obtained from a large eddy simulation of an academic combustor when acoustically forced by broadband signals.

Super-Resolution Method for Microwave Front-Looking Imaging Using Broadband Signals and Spatial Spectrum Shifting

Super-Resolution Method for Microwave Front-Looking Imaging Using Broadband Signals and Spatial Spectrum Shifting

Exploiting environmental asymmetry for vessel localization from the vertical coherence of radiated noise.

A method to determine the range and bearing of a moving broadband acoustic source, such as a surface vessel, using the coherence measured on two omni-directional, vertically separated hydrophones is demonstrated using acoustic data recorded near Alvin Canyon on the New England shelf break. To estimate the vessel's range, two theoretical approaches, a half-space model and a Pekeris waveguide model based on normal modes, establish simple relationships between the broadband signal coherence and frequency, source range, and the vertical separation of the receiver hydrophones. A brute force inversion produces a passive acoustic estimate of vessel range. Rapidly changing bathymetry with large features, such as that near Alvin Canyon, produces azimuthal asymmetry in the plan-view coherence pattern about the receivers due to horizontal refraction, focussing, and the up- (down-) slope compression (extension) of modal interference patterns. For vessels with a constant speed and heading, this generates an asymmetry in the received power and vertical coherence fringing pattern. This effect is first demonstrated using reciprocal three-dimensional parabolic equation and raytracing models in an idealized Gaussian canyon, then observed in Alvin Canyon measurements. By comparing the experimental observations to the modeled coherence, the vessel's bearing and range relative to the receivers are obtained.

TRENDS OF THE MICROWAVE PHOTONIC RADARS

Today, the world's leading countries are intensively working on the development of new generation radars - microwave photonic radars. Microwave photonic radars make it possible to significantly reduce the mass and size characteristics of radar stations, to increase the information capability and range of target detection due to the reduction of losses in long communication lines when using optical fiber, to ensure high immunity due to the significantly lower sensitivity of optical-electronic equipment and fiber-optic lines of communication connection to external electromagnetic influences. Microwave photonics provides wide bandwidth, flat response, low loss transmission, multi-dimensional multiplexing, ultra-fast analog signal processing and immunity to electromagnetic interference. Radar implementation in the optical domain can provide better resolution, coverage, and speed performance, which would be difficult to implement with traditional electronics. The review article examines the state of development and system architectures of such photonic radars as optoelectronic hybrid radars, all-optical radars, multifunctional microwave photonic radar systems, distributed microwave photonic radars, software-defined radars, and cognitive radars. New technologies in this field and possible future directions of research are discussed. As an example, a broadband microwave photon radar reproduced on the basis of a microcircuit is considered. The broadband signal generator and receiver are built into the silicon crystal on the insulator. A high-precision distance measurement with a resolution of 2.7 cm and an error of less than 2.75 mm was obtained. Visualization of multiple targets with complex profiles has been implemented. But the performance of most integrated microwave photonic chips is not yet satisfactory for practical radar applications. Monolithic integration of key microwave photonic subsystems is also not mature enough for practical applications, so hybrid integration of devices fabricated on their optimal integration platforms is of practical interest. At present, indium phosphide, silicon nitride and silicon on insulator are the three leading platforms for photonic integration

Comprehensive hull structures diagnostics using a distributed fiber-optic sensors system

The possibility of constructing real-time systems that provide vibration diagnostics and acoustic diagnostics of complex man-made objects hull structures based on distributed fiber-optic sensors is substantiated. The problem of detecting and localizing sources of acoustic emission using a fiber-optic measuring system placed on a surface housing structure is considered. When solving the detection problem, the flow of acoustic emission signals is characterized by a statistically average pulse repetition rate, their amplitude and time distribution. All parameters of emission signals are random variables with a priori unknown characteristics. To solve the detection problem, the sequential Wald analysis algorithm is used according to the “M out of N” detection criterion. A fiber-optic measuring system has been developed and manufactured, combining the capabilities of vibration diagnostics and acoustic diagnostics of the hull structure. To increase the noise immunity of a fiber-optic measuring system, it is proposed to interrogate it with a broadband signal, for example, a signal with linear frequency modulation.

Blind channel evaluation using OFDM-FHSS technology

Pseudo-random tuning of the operating frequency (PRFC) is one of the effective methods of spectrum expansion, in which the signal occupies a frequency band significantly wider than the minimum required for transmitting information. Тhe operating frequency of the signal is hopped over a wide range of the frequency range allocated for communication in accordance with a pseudo-random code, known only on the receiving side and unknown to anyone trying to intercept a radio transmission or organize jamming. The main disadvantage of HFPR is the low data transfer rate. Therefore, recently there have been ideas of using the hopping method with broadband signals, for example OFDM-hopping where the frequency changes within a set of orthogonal carriers. This approach makes it possible to preserve the advantages of the frequency converter method, supplementing them with the ability to implement high-speed digital communications. The paper considers the situation when one OFDM symbol is transmitted in the time interval of one hop, formed without a prefix and postfix. In this case, the transmission signal in the time interval of one step was a set of sequentially transmitted complex samples of the OFDM symbol envelope. Samples of the OFDM symbol envelope, after they are generated during transmission in the OBPF block, must be sequentially transmitted over a communication channel whose properties are unknown. In the case when there is temporary dissipation of the energy of the transmitted signal in the channel (channel memory), during the sequential transmission of complex samples of the OFDM symbol envelope, due to temporary dissipation, each of the previous samples will have an interference effect on any transmitted sample at reception. Assuming that the channel parameters are constant over the analysis interval at the receiving location, it is necessary, with an unknown impulse response of the channel, to generate estimates of the OFDM symbol envelope samples, which, in order to solve the demodulation problem, must be subjected to the FFT calculation operation. The constancy of the channel parameters over the analysis interval allows us to solve the problem of estimating samples of the channel impulse response using blind identification based on the maximum likelihood method. In this case, it is necessary to use diversity reception and impose some non-burdensome restrictions on the statistical properties of the transmitted message. After solving the problem of identifying the impulse response of a channel with memory, the problem of estimating the components of the sample vector of the envelope of the received OFDM symbol is solved by the regularization method. Using the “reception “as a whole” with element-by-element assessment generation” (PCPFO) algorithm and using “assessment feedback” (EFE), minimization of the regularizing functional leads to the solution of a system of linear algebraic equations, the order of which is determined by the number of samples of the impulse response of the communication channel with memory. By modeling, the upper limit of noise immunity for receiving OFDM-QAM-4 signals was obtained with a Gaussian distribution of errors in estimating OFDM-symbol envelope samples. The proposed procedure for normalizing envelope samples after solving systems of linear equations eliminates the appearance of outliers characteristic of the generated noise sequence.

Research on direction of arrival estimation for mixed broadband signals

In practical applications, the signals received by a hydrophone array include coherent and incoherent signals, while estimating the direction of arrival (DOA) of coherent or incoherent signals has been studied for simplicity with poor performance for a mixed signal. The present study proposes a novel approach for estimating the DOA of mixed broadband signals to solve this problem, namely the oblique method. The unitary oblique method is simultaneously proposed to improve operational efficiency with the complex matrix shifted into a real valued matrix through a unitary transform. For independent signals, the incoherent signal subspace method (ISSM) is used to estimate the DOA. Matrix difference and oblique projection methods are adopted for multi-group coherent signals in order to eliminate the influence of incoherent signals and other groups of coherent signals. For broadband signals, the Tasseled Cap Transformation focusing transform is utilized to convert the broadband signal to the focusing frequency, and then the high-resolution Multiple Signal Classification algorithm method is employed to solve the problem. Simulation results indicate that the oblique method reconciles DOA estimation performance and computational efficiency and can be extended to other types of arrays.

Study on the volute optimization and mechanism of vortex loss reduction for a centrifugal fan

Abstract In order to reduce the flow loss in the volute and improve the efficiency of the centrifugal fan further, a new type volute with a diffusion profile was designed and optimized. The effects of diffusion angles were clarified by using numerical simulations and the method of design of experiment. The mechanism of vortex loss reduction of the diffusion-type volute was revealed. The results show that diffusion-type volute can reduce the flow loss in the volute by 30.8% compared with the original volute, and increase the efficiency of the fan by 2.24%. Parametric studies show that the diffusion angle of front disc has a great influence on the efficiency of the fan, and the effect of diffusion angle of rear disc is relatively less. Mechanism analysis shows that the diffusion-type volute can greatly reduce the vortex strength in the volute, especially eliminate the high-intensity vortex near the volute tongue. As a result, the volute loss is remarkably reduced. In addition, the diffusion-type volute can effectively reduce the amplitude of pressure fluctuation in terms of shaft frequency, characteristic frequency and broadband signals in the volute.

Duality of a coiled phononic crystal enables reflectionless interfaces

Recently, it has been demonstrated that one-dimensional bar-based phononic crystals can exhibit subwavelength Bragg bandgaps by coiling the bars and locking the nodal rotational degrees of freedom to create what is termed a coiled phononic crystal (CPnC) [C. L. Willey et al., Phys. Rev. Appl. 18, 014035 (2022)]. Here, it is shown that the CPnC exhibits duality of its dispersion curves relative to its coiling/twist angle, meaning that the dispersion curves are symmetric about a particular coiling/twist angle defined configuration. An exciting implication of this finding is that under a certain set of constraints, segments of dual unit cells with perpendicular wave propagation directions can be connected such that their wave transmission is equivalent to a finite CPnC entirely composed of identical unit cells with parallel wave propagation directions. The ability to link unit cells with different wave propagation orientations, but the same dispersion/dynamic stiffness, is used to create an elastic hierarchically coiled phononic crystal based on a fractal space-filling curve design. The novelty of this work is that it numerically demonstrates reflectionless wave propagation in large fractal architectures (created from specific combinations of dual unit cells) such that regular phononic properties (i.e., passbands and bandgaps) are preserved, allowing for propagation of broadband signals and filtering.