Line Array Research Articles

Analysis of split-beam spatial coherence statistics for discerning compact from non-compact littoral sonar clutter

Active sonar systems operating in the littoral environment are often reverberation-limited, which impacts detection performance by reducing the effective signal-to-noise ratio. Additionally, irregularities in the environment lead to excessive false alarms commonly referred to as sonar clutter. Clutter is found in all environments, but shallow-water littoral regions have been observed to be especially challenging. The irregularities that cause sonar clutter can have spatial scales ranging from much smaller to much greater than the dimensions of the sonar resolution cell. This talk will discuss physical interpretation and experimental assessment of signal statistics related to the transverse horizontal spatial coherence of reverberation estimated via split-beam processed data obtained from a line array. Multiple boundary interaction in shallow water depths and spatial variability randomize reverberation and may allow the use of Gaussian noise models. While match-filtered signal intensity is an optimal detection statistic in a Gaussian noise environment, spatial reverberation coherence statistics may provide complimentary information of the spatial scale of clutter features relative to the width of the beampattern. It is found these statistics may be used to help discern clutter types that are spatially compact from those that are non-compact when compared to the width of the sonar resolution cell.

Environmental characterization from passive acoustic data collected on a partially-spanning array

We show that with knowledge of the sound speed along a receiving, partially water-column-spanning vertical line array, mode wavenumber and geoacoustic estimates can be obtained without requiring knowledge of source location or range-rate. This estimation is accomplished simply by applying spatial smoothing and MUSIC to the sample covariance matrix. The method is demonstrated with simulation and subsequently on SWellEx-96 experimental data.

Coupled modeling of the seasonal transmission loss in the Beaufort Sea

An eight-element drifting vertical line array was deployed overwinter 2019–20 in the Beaufort Sea to record transmissions from two moored 35 Hz sources deployed as part of the Coordinated Arctic Acoustic Thermometry Experiment (CAATEX), and seven 925 Hz sources deployed by the Arctic Mobile Observing Systems (AMOS) experiment. Transmissions were received every day on the array at ranges of 10 to 850 km. A probabilistic rough-ice canopy was integrated to a Parabolic Equation code to predict the propagation loss. Sound speed profiles and percent ice cover along the propagation paths were obtained at daily resolution from data-assimilative Global Ice Ocean Prediction System (GIOPS, 20 km spatial resolution). Sea ice roughness and keel properties are empirically determined from the GIOPS ice thickness. The ice roughness is generated using a random pulse-train model with a characteristic wavenumber spectrum slope determined by ice age. Empirical probability distributions of ice keel depth, slope, and spatial densities are used to randomly add keels. Spatial averaging is used to account for signal bandwidth and uncertainty in receiver positions. The environment files and modeling are performed in piece-wise steps to manage memory footprints over long ranges. Modeled propagation losses compare well with the data and reproduce the seasonal variability observed in the measured results.

Depth estimation as a sequential process following array invariant range estimation

Range estimation based on the array invariant concept exploits the inherent properties of shallow-water waveguide propagation. Multipath arrivals observed on a vertical line array, indexed on vertical arrival angle and time difference of arrival, form what is known as a beam migration pattern in the shape of an ellipse that is a function of source range and the acoustic invariant beta. Fitting the beam migration pattern to an ellipse yields the source range. A property of this beam migration pattern is that it is independent of source depth. Source depth determines how the multipath arrivals are distributed along that ellipse. We will extend previous work on estimating range and present how to estimate depth. This decouples the two estimates and reduces a 2D search process to two 1D processes. We will explore the CRLB structure of the range and depth estimates and demonstrate the results of processing experiment data from the RADAR 2007 experiment in shallow water off the coast of Portugal.

Coral reef & temperate coastal soundscape features evident in directional and omnidirectional passive acoustic time series

Biologically complex coastal environments, such as coral reefs, demonstrate an equally rich ambient soundscape. Bioacoustic features of coastal soundscapes are closely tied with relative ecosystem health, functional groups present, and can be linked with specific behaviors. Biological contributions to ambient soundscapes have distinctive qualities as compared to sound associated with physical processes (i.e. wind and wave noise). While some biological components are readily identifiable, such as marine mammal or fish calls, the background noise associated with hundreds of thousands of biological clicks, snaps, and pops is not as well studied but contains a wealth of information about the ecosystem. A 64-element line array with 4.5 kHz design frequency was deployed for several field experiments off the coast of Kona, Hawaii in 2019 and 2020. Soundscape data from Hawaii were compared with comparable omnidirectional time series from Bermuda (2020) and coastal New England rocky reefs (2020–2021). Similarities in certain spectral features associated with biological sound sources were found between these unique ecosystems. The characteristic coral reef evening chorus, or significant increase in sound levels immediately prior to sunset, was consistent in Hawaii and Bermuda with comparable crepuscular changes in coastal New England.

Improvement of ray-based blind deconvolution through kurtosis-based phase correction

Ray-based blind deconvolution (RBD) has demonstrated remarkable performance on several in situ underwater acoustic data. RBD estimates the channel impulse response by compensating the source phase estimated by beamforming. However, when beamforming fails to achieve the desired signal-to-noise ratio, RBD fails to achieve the expected performance. To address this issue, we propose an improved RBD framework that uses the kurtosis of the channel impulse response to provide additional phase correction after beamforming. The proposed method is validated with the measurement data from the shallow-water acoustic variability experiment 2015 using a high-frequency (11–31 kHz) broadband source and a vertical line array of 16 sensors located approximately 3 km away. The results are compared with conventional RBD and discussed from an optimization point of view.

Theory of parametric receiving arrays processing utilizing sum and difference frequencies

The majority of highly directive receive arrays obtains their directivity from an often fully populated (lambda/2 spacing) array in one or more dimensions. Digital beamforming allows for steering of these densely populated arrays in multiple directions; however, if there is only one primary direction of interest, a similar highly directive receiver can be generated with just a few elements. Parametric receivers, such as parametric sources, can obtain enhanced directivity via a “virtual aperture” or a region in the medium where nonlinear mixing of a high intensity pump wave and a signal wave interact. For a parametric receiver, the pump element(s) with a frequency, F, and receiver element(s) are separated by a distance, L, and the signals of interest are the sum and difference frequency (F + /− f) between the pump frequency and an incoming signal frequency, f. The directivity of these parametric receivers are comparable to the end fire response of a line array of similar length, L. This paper will review the highlights of parametric receivers as well as detail the analysis to extend this phenomenon to include the sum and difference frequencies for single element pairing and arrays of pumps and receivers.

Sound field variability and mode coupling in the presence of internal Kelvin waves in Lake Kinneret, Israel

Spatiotemporal variability of the low- and mid-frequency sound field in the presence of internal Kelvin waves (IKWs) was studied theoretically and in experiment in Lake Kinneret, Israel. The experiments were done in 2021, where sound field was being recorded during two days (two periods of IKW) using two synchronized vertical line arrays (VLAs) of ten hydrophones each and 10 m between them, deployed in the center of the lake (depth ∼41 m). Wideband linearly frequency modulated sound signals (300Hz–7 kHz) were transmitted from the source deployed near the shore (depth ∼11 m, distance 5.5 km from VLA). IKWs were registered with thermistor strings together with CTD. Sound speed profile is characterized by the thermocline located between 15 and 20 m of the depth with sound speeds 1510 and 1480 m/s above and below the thermocline, respectively. The sound propagation modeling was done using a Parabolic Equation and Normal Modes approaches, considering the real parameters of the gas-saturated bottom and the bathymetry. Results show strong mode coupling along the acoustic track, initiating ∼12 dB variability of the sound intensity. Results of modeling are verified in the experiment. [This work was supported by RFBR, grant 20-55-S52005.]

Pacific Echo: A deep ocean collaborative experiment

This paper summarizes experiments carried out using towed line arrays in the Pacific Echo sea trials. Although John Preston was not a participant, the experiments are examples consistent with his efforts in promoting collaborative research at sea with horizontal arrays. The overall goal of Pacific Echo was to study the impact of thin sediment ocean bottom environments on sound propagation in deep water. The objective of the experiments described here was to study the evolution of young oceanic crust. The hypothesis was that the sound speed of young basalt increased with age of the crust. Sound speed was inferred from low frequency measurements of the reflection coefficient versus grazing angle at sites of increasing distance from the deep ocean spreading center. The experiments introduced a novel design for measuring the reflection coefficients using two ships and small explosive charges. The signals at the array were spatially filtered to resolve the specular reflections as the ships opened range on set courses. The data provided estimates of both the compressional and shear wave speeds of the basalt. Results from the broadside reflection technique showed that sound speed increased with crustal age and were consistent with measurements obtained from conventional seismic reflection surveys.

Modal dispersion curve extraction from shipping noise at two synchronized vertical arrays

The results of modal dispersion analysis, using low-frequency (20 to 250 Hz) shipping noise in shallow water with a soft bottom is presented. Experiments were carried out in the Sea of Galilee (Lake Kinneret, Israel) having a maximum depth of ∼40 m and a gassy upper sedimentary layer. A receiving system combined two synchronized, 10-hydrophone vertical line arrays (VLAs) located at the center of the lake with distance Dr = 40 m between them. The noise source, R/V “Hermona,” was moving along the straight line joining VLAs, up to 1 km from VLAs. A method of obtaining modal dispersion curves from shipping noise is proposed. For each frequency ω and variable horizontal wavenumber q = ω/cph the noise is spatially filtered at each VLA using calculated solution of the wave equation with the measured sound speed profile in water and the pressure-release condition imposed at the water surface. Then, the ratio of complex modal amplitudes at VLAs is calculated and multiplied by a factor of . The real part of the resulting 2-D structure exhibits the modal dispersion curves, which are used for acoustic characterization of the seabed. [Work supported by ISF, grant 946/20, and RFBR, grant 20-05-00119.]

Research on Underwater Acoustic Target Depth Classification Based on Modal Filtering Characteristics of Long Horizontal Line Array

Considering the problem of depth classification of underwater acoustic targets in shallow water, a classification method based on modal filtering characteristics of long horizontal line array(HLA) beamforming in a negative thermocline environment was proposed. Based on normal mode theory, the spatial filtering characteristics of long HLA are studied by beamforming, and it was found that this characteristic can filter a normal mode. In the negative thermocline environment, the acoustic fields excited by deep and shallow sources and received by deep receivers are controlled by different modes. Surface reflection bottom reflection (SRBR) mode and non-surface reflection bottom reflection (NSRBR) mode show different interference structures in range-spectrum. Based on the characteristics of modal filtering and sound field classification, a depth classification method for shallow water acoustic targets in a negative thermocline environment is established. Numerical results show that the proposed method is robust and can effectively distinguish the acoustic source targets above or below the thermocline (surface and underwater targets) without knowing the specific acoustic environment parameters in advance.

Integrated optics spiral photoconductive antennas coupled with 1D and 2D micron-size terahertz-wavelength plasmonic metal arrays

Terahertz (THz) photoconductive antenna (PCA) emitters having one-dimensional (1D) and two-dimensional (2D) micron-size metal line arrays (MLA's) at the transmission side of the semi-insulating GaAs substrate were fabricated via UV photolithography and electron beam deposition. At a fluence of ∼1.2 mJ/cm2 and 20 VPP bias, the enhancement in the THz signal peak-to-peak amplitudes are ∼6 times for 1D MLA and ∼11 times for 2D MLA, compared to the reference PCA, respectively. An all-optical effect via THz extraordinary transmission is conjectured for the enhancement mechanism. This metamaterial PCA design presents a feasible, yet more cost-effective alternative to photo-conducting gap nanostructure fabrication using e-beam lithography.

In This Issue

In This Issue

Deep-learning geoacoustic inversion using multi-range vertical array data in shallow water.

A multi-range vertical array data processing (MRP) method based on a convolutional neural network (CNN) is proposed to estimate geoacoustic parameters in shallow water. The network input is the normalized sample covariance matrices of the broadband multi-range data received by a vertical line array. Since the geoacoustic parameters (e.g., bottom sound speed, density, and attenuation) have different scales, the multi-task learning is used to estimate these parameters simultaneously. To reduce the influence of the uncertainty of the source position, the training and validation data are composed of the simulation data of different source depths. Simulation results demonstrate that compared with the conventional matched-field inversion (MFI), the CNN with MRP alleviates the coupling between the geoacoustic parameters and is more robust to different source depths in the shallow water environment. Based on the inversion results, better localization performance is achieved when the range-dependent environment is assumed to be a range-independent model. Real data from the East China Sea experiment are used to validate the MRP method. The results show that, compared with the MFI and the CNN with single-range vertical array data processing, the use of geoacoustic parameters from MRP achieves better localization performance.

Euphorbia hirta as a gold mine of high-value phytochemicals: A comprehensive review of its pharmacological activities and possible role against SARS-CoV-2

Euphorbia hirta is a common medicinal plant in folk and traditional medicine systems. This plant has shown promising effects against several human ailments and infectious diseases. Therefore, it is important to summarize the medicinal activities and value of Euphorbia hirta. The main intent of this literature review was to summarize the phytochemical content and pharmacological applications of Euphorbia hirta. The literature review about the pharmacology and phytochemistry of Euphorbia hirta was collected from different global platforms, such as Scopus, ERIC, PubMed, and Web of Science. E. hirta has a rich phytochemistry and exhibits remarkable activity against respiratory diseases, gastrointestinal disorders and venereal diseases. Different extracts of this plant have shown significant preclinical anticancer propensity against an array of different cancer cell lines. It acts as a highly active antiviral agent and has shown pronounced activity against coxsackievirus, human immunodeficiency virus, dengue virus, poliovirus and simian immunodeficiency virus. A clinical study showed its inhibitory responses against flu and fever in dengue patients. Most importantly, the plant possesses remarkable inhibitory action on ACE, which aids SARS-CoV-2 entry into host cells. The multidimensional role of Euphorbia hirta as a potential antiviral agent suggests its possible application to control COVID-19 along with modern and Western medicinal strategies. In conclusion, the literature review regarding Euphorbia hirta showed its strong pharmacological applications, such as antimicrobial, antimalarial, anti-asthmatic, antioxidant, antiviral and anticancer activities. Further in-depth research is necessary to monitor its role in the management of viral diseases, especially COVID-19.

A novel series arc fault detection method for photovoltaic system based on multi-input neural network

There is a risk of fire caused by series arc failure in the operation of photovoltaic (PV) system. Therefore, it is required to discuss a solution for rapid arc fault detection. To address the series arc fault (SAF) detection under different working conditions, a method based on squeeze-and-excitation (SE)-inception multi-input convolutional neural network (MICNN) is proposed. Firstly, normalization and Hankel-singular value decomposition algorithm are used to denoise the current, which effectively avoid the influence of switching frequency on the subsequent diagnostic accuracy. Subsequently, the filtered time-domain signal and the frequency-domain signal after Fourier transform are input into a variant one-dimensional convolutional neural network (1D-CNN) model for training and testing. The proposed model is characterized by transforming the traditional CNN into MICNN, and introducing the inception network with spatial scaling function and the SE network structure with channel attention mechanism. Extensive simulations are performed to evaluate the efficacy with a desirable result of 97.48%, which is superior to traditional methods such as CNN, wavelet decomposition, and mathematical statistics. The proposed method can not only detect arc faults occurring in different locations, but also resist the disturbance of dynamic shading, maximum power point tracking (MPPT), strong wind, etc. In addition, this model achieved satisfactory results in three cases of long line fault, single series and array ageing.

Hybrid Converter with Multiple Sources for Lithium Battery Charger Applications

This paper proposes a hybrid converter with multiple sources for lithium battery charger applications. Since the output voltage of a lithium battery charger is very low, its charger needs a higher step-down voltage for a utility line source or a step-down voltage for PV arrays. In order to implement the battery charger with utility line and PV arrays sources to simultaneously supply power to battery, a flyback converter is selected for utility line sources, and a buck converter is adopted for PV arrays source. Due to leakage inductor of transformer in flyback converter, an active clamp circuit is introduced into flyback converter to recover the energy stored in leakage inductor. In addition, flyback and buck converters can adopt switch integration techniques to simplify circuit structure. With this approach, the proposed hybrid converter has less components, is lighter weight and has smaller size and higher conversion efficiency. Finally, a prototype of the proposed hybrid converter with output voltage of 5 V~8.4 V and output maximum current of 12 A has been implement to verify its feasibility. It is suitable for the lithium battery charger applications.

Isolation and label-free detection of circulating tumour cells by fluidic diffraction chips with a reflective laser beam system

A photonic crystal (PC) based line array of poly(methacrylic acid) (PMAA) brushes was grafted from a photoresist template using a trench array. The array was functionalised with anti-epithelial cell adhesion molecule antibodies (EpY). A laser beam was employed to analyse the two-dimensional (2D) and three-dimensional (3D) reflective signals of PCs at an incidence angle of 45°. The EpY-tailed PMAA PC possessed an optical feature with a characteristic diffraction effect along two laser input configurations including the SII configuration, in which the projection of the laser beam on the plane of the SPM chip was parallel to the strips, and the ST configuration, in which they were perpendicular. A fluidic diffraction chip based on the EpY-tailed PMAA PC with 1-μm resolution was fabricated to examine the ability to detect circulating tumour cells (CTCs) along the ST configuration. The CTCs attached on the EpY-tailed PMAA PC, resulting in the change in the diffraction intensity. Dependence of change degree of the diffraction intensity exhibited a linear range of concentration of CTC from 0 to 64 cells and a limit of detection of 5 cells in 3 mL. CTC detection using both fluidic diffraction chips and a commercial IsoFlux system was carried out in clinical trials, including three healthy donors and 12 patients at various stages of colorectal cancer for comparison. Our platform provides a simple label-free method with high accuracy for rapid CTC counting, which has great potential in clinical treatment applications.

Effect of Copper Line Geometry and Process Parameters on Interconnect Microstructure and Degradation Processes

Abstract The atomic transport processes which could cause degradation mechanisms in Cu interconnects are described. The influence of interconnect line width, barrier type and anneal process on the microstructure and reliability of the inlaid Cu lines are discussed. Grain size and texture measurements have been performed at blanket films and at arrays of Cu lines using advanced analytical techniques. The median grain size decreases with decreasing line width, and it can be influenced by heat treatments. The crystallographic texture is predominantly {111} out-of-plane with sidewall-oriented grains in narrow Cu lines. The grains have an in-plane preferred orientation with the 〈110〉 direction parallel to the sidewall normal. The Cu texture is influenced by barrier structure and thickness.

Disclination lines in nematic liquid crystal between a structured photoalignment layer and a homeotropic alignment layer

Topological defects in nematic liquid crystals (NLCs) are an interesting material system to study both from a theoretical point of view and for applications in photonics, soft-robotics and colloidal assembly. By using a photo-aligned template at one or both confining substrates, different disclination interconnections in the bulk can be readily stabilized. We imposed a periodic defect grid of 1/2 and −1/2 defects at the surface with the help of photoalignment and combined this with a uniform homeotropic counter substrate. This alignment configuration was used to study the optical properties and the relative stability of different types of disclinations in detail. The arrays of disclination lines are investigated by polarizing optical microscopy for different orientations of the polarizers and for different applied voltages. A theoretical analysis is performed to understand the relative frequency of occurrence for distinct types of disclinations and numerical simulations are used to verify the difference in optical appearance. The unequal elastic constants for splay, twist and bend strongly influence both properties and make it possible to identify different types of disclination lines form their optical appearance.