Small Array Research Articles

Particle correlation and intermittency in simulated cosmic ray showers

AbstractWe study the correlations between charged particles in small cosmic ray air showers and determine the size and nature of their density fluctuations. We have used the CORSIKA simulation program to investigate this question. The result obtained shows the “intermittent” behaviour of the individual realisations of the density distributions. This is interesting in itself, and the specific values of the scaled factorial moments allow us to estimate the possible effects of these large non-Poissonian fluctuations. These may be relevant in the analysis of data from small shower arrays and other atypical measurement situations where cosmic ray particles provide an unwanted background.

Monitoring induced microseismicity in an urban context using very small seismic arrays: The case study of the Vendenheim EGS project

Monitoring the seismicity induced by fluid injections in deep geothermal reservoirs is often limited by the significant anthropogenic ambient noise level inherent to most enhanced geothermal system (EGS) projects in urban contexts. We report on the performance of a monitoring network made of three small aperture (72 m) seismic arrays composed of 21 3D nodes. We test the setup for four months (from 12 December 2020 to 8 April 2021) of the Strasbourg sequence of induced earthquakes (2019–2022) related to the EGS Georhin project (Vendenheim, France). The deployment starts a few days after the MLv = 3.6 induced earthquake of 4 December 2020 and covers the early shut-in period of the wells. We use a beamforming technique to characterize the main noise sources, which consist of slow apparent velocities of surface waves emitted from mobile anthropogenic sources (motorway and railway traffic). We detect events with a phase-weighted stacking method, which is efficient when wavefronts illuminate the arrays with a high apparent velocity. Earthquakes associated with these detections are located using a matched field processing technique. The obtained catalog includes 216 seismic events, which represent four times more events than the reference catalog from Le Bureau Central Sismologique Français–Renass (the national academic agency in charge of seismicity monitoring in France), and a reduction of the completeness magnitude from 0.3 to −0.5. The clustering of the seismicity is analyzed using waveform correlation. The enriched catalog reveals intermittent seismic activity during the slow and continuous decrease in fluid pressure after shut-in.

The association between body mass index and distribution intensity of tumor treating fields (TTFields) in the lungs.

e20559 Background: Tumor Treating Fields (TTFields) therapy is a first-in-class locoregional and noninvasive cancer treatment modality. TTFields are electric fields that disrupt processes necessary for cancer cell viability and tumor progression. A portable medical device generates TTFields, which are delivered noninvasively to the tumor area via 2 pairs of transducer arrays placed on the skin. TTFields therapy is currently approved for recurrent and newly diagnosed glioblastoma and pleural mesothelioma, with studies underway in other solid tumor types, including non-small cell lung cancer (NSCLC). Preclinical studies have shown that the effectiveness of TTFields depends on several factors, including field intensity. Given that 1 in 3 adults is overweight or obese, it is relevant to determine the effect of body mass index (BMI) on TTFields intensity to the lungs. Simulation-based methods were utilized, with the hypothesis that TTFields could be delivered to regions of interest (ROI) at therapeutic field intensities of > 1 V/cm, irrespective of BMI. Methods: Female computer phantom models with BMIs of 22 (healthy), 26 (overweight), and 30 (obese) were used to simulate TTFields intensity using small (13 disk) and large (20 disk) arrays placed on the thoracic region. The distribution of TTFields in each model was then determined using a computer-generated electric field intensity map. Field intensity values across the entire lungs were analyzed and compared. Results: When TTFields were delivered with large arrays, field intensities were clinically meaningful ( > 1 V/cm) in all lobes of the lungs for all BMI models. When TTFields were delivered with small arrays, meaningful levels of field intensity were achieved in all lung lobes, except for the BMI 30 model, where field intensities were slightly lower than 1 V/cm in the right middle lobe. Conclusions: These results show that TTFields can be delivered at therapeutic field intensities in patients with a BMI up to 30, providing the appropriate TTFields array size is used. Results from this simulation-based study support current clinical studies of TTFields therapy in lung cancer, (LUNAR, NCT02973789) and underscore the importance of appropriate array size selection. Additionally, these results may provide guidance for using TTFields therapy to treat a broad population of patients with lung tumors.

Joint estimation of DOA and coupling matrix based on linear prediction for small spacing antenna array

A method for joint estimation of DOA and coupling matrix based on linear prediction is proposed for low resolution of mutual coupling calibration method in the case of small spacing antenna array. This method augments array aperture virtually according to linear prediction principle and calculates the coupling matrix by this virtual array. Then, this coupling matrix is used as the initialization matrix of joint estimation algorithm for coupling calibration. Simulation results confirm the effectiveness of the proposed method and provide the theoretical foundation for engineering realization. This method could also be applied in the field of tactical anti-jamming communication.

A numerical modeling of thermal management of high CPV arrays using spray cooling

Liquid cooling is an efficient way of thermal management for high CPV cells, increasing the system performance by reducing cell's temperature. Thermal management complexity rises upon using an array of cells while the system becomes sizeable. The present numerical simulations follow a single cell study to investigate spray cooling for high CPV arrays with minimum number of injecting nozzles. The idea is to cool the cells by the liquid film formed on the thermal paste surface. Cooling the whole surface by the help of the liquid film decreases the number of nozzles to less than the number of cells. Both mass flow rate and pumping power are reduced, improving the system efficiency and lowering the liquid demands. To find cooling patterns, one-dimensional arrays with two and three cells and two-dimensional square arrays of order two and three are investigated at three solar concentrations; 500, 750, and 1000 Suns. The non-spraying cells' performance is assessed by consideration of two criteria; the damaging temperature and the increment rate of the difference between the cell power operating with and without injection. It is indicated that the patterns from smaller arrays can be applied to design the injection arrangement for the larger ones. Results from the cooling injection on a square array of order three demonstrate that decreasing the number of nozzles can reduce the mass flow rate by 55–89 % and increase the net power by 0.5–2.2 %, depending on the concentration ratio.

Synthesis and Preliminary Characterization of Putative Anle138b-Centered PROTACs against α-Synuclein Aggregation.

The search for disease-modifying agents targeted against Parkinson's disease led us to rationally design a small array of six Anle138b-centered PROTACs, 7a,b, 8a,b and 9a,b, targeting αSynuclein (αSyn) aggregates for binding, polyubiquitination by the E3 ligase Cereblon (CRBN), and proteasomal degradation. Lenalidomide and thalidomide were used as CRBN ligands and coupled with amino- and azido Anle138b derivatives through flexible linkers and coupling reactions (amidation, 'click' chemistry). Four Anle138b-PROTACs, 8a,b and 9a,b, were characterized against in vitro αSyn aggregation, monitoring them in a Thioflavin T (ThT) fluorescence assay and in dopaminergic neurons derived from a set of isogenic pluripotent stem cell (iPSC) lines with SNCA multiplications. Native and seeded αSyn aggregation was determined with a new biosensor, and a partial correlation between αSyn aggregation, cellular dysfunctions, and neuronal survival was obtained. Anle138b-PROTAC 8a was characterized as the most promising αSyn aggregation inhibitor/degradation inducer, with potential usefulness against synucleinopathies and cancer.

Room Temperature Defluorination of Poly(tetrafluoroethylene) by a Magnesium Reagent

Perfluoroalkyl substances (PFAS) are pervasive in the environment. The largest single use material within the PFAS compound class is poly(tetrafluoroethylene) (PTFE), a robust and chemically resistant polymer. Despite their widespread use and serious concerns about their role as pollutants, methods for repurposing PFAS are rare. Here we show that a nucleophilic magnesium reagent reacts with PTFE at room temperature, generating a molecular magnesium fluoride which is easily separated from the surface-modified polymer. The fluoride in turn can be used to transfer the fluorine atoms to a small array of compounds. This proof-of-concept study demonstrates that the atomic fluorine content of PTFE can be harvested and reused in chemical synthesis.

Development and Core Technologies for Intelligent SWaP3 Infrared Cameras: A Comprehensive Review and Analysis.

With the development of infrared detection and imaging technology, infrared cameras (IRCs) play an important role in many fields, such as military, industry, and civilian. Additionally, the requirements for the size, performance, and intelligence of IRCs are becoming more and more strict. Consequently, the associated research and development (R&D) of IRCs is gradually focused on the aspects of miniaturization, high performance, intelligence, low power consumption, and low cost, involving many frontier fields, including artificial intelligence, new materials, new optical systems, and electronics systems. In fact, there are continual studies on intelligent SWaP3 IRCs, but unfortunately, a systematic arrangement and analysis are lacking. Therefore, a systematical and comprehensive review for the developments and core technologies of the intelligent SWaP3 IRCs is really needed. In this paper, in terms of the aforementioned requirements, we conduct a review and analysis of current intelligent SWaP3 IRCs based on 90 literature and statistics in recent decades to provide the relevant developers with a helpful reference for facilitating the indicator optimization of intelligent SWaP3 IRCs with new developed technologies. We analyze the development of SWaP3 IRCs in the aspects of lightweight, miniaturization, low price, and high performance, including hyperspectral resolution, high spatial resolution, large field of view (FOV), and wide dynamic elaborately. Moreover, the development in low power consumption and intelligence is also discussed in detail. Additionally, we briefly summarize the primary applications of intelligent SWaP3 IRCs in military, scientific, and civil. Then, the core technologies comprising high-integration, lightweight, hyperspectral imaging (HSI), low-power consumption, as well as the realization of high performance such as high-resolution, high-frame, and wide-dynamic range of SWaP3 IRCs are discussed and analyzed in detail. Finally, we prospect for the intelligent SWaP3 IRCs that it is necessary to continuously expand the concept of SWaP3 by reliability, stability, extensibility, and safety. In addition, it is useful to embed cutting-edge technologies such as small pixel pitch array, multi-sensors fusion, and deploy intelligent algorithms to IRCs. Additionally, the improvement of the whole machine from multi-dimension such as chip, camera, and system is expected and needs to be taken more seriously. It is hoped that this paper can provide a reference for the R&D of intelligent SWaP3 IRCs in the future.

ISM-FLUX: MINFLUX with an array detector

Single-molecule localization based on the concept of MINFLUX allows for molecular resolution imaging and tracking with a laser-scanning microscopy architecture. In MINFLUX, a doughnut-shaped structured illumination beam sequentially excites the sample, thereby minimizing the localization uncertainty for a given number of photons. However, MINFLUX has a limited field of view (FOV) and therefore requires a precise prelocalization step. We mitigate this problem by introducing the single-molecule image scanning microscopy (smISM) concept. In smISM, the point detector of the laser-scanning microscope is replaced with a small single-photon detector array, thereby leveraging the benefits of both structured illumination and structured detection. We show via simulations that by combining smISM and MINFLUX (i.e., ISM-FLUX), we obtained a localization uncertainty between 1 and 15 nm over a FOV of more than 800 nm with 100 photons. In addition, smISM allows the localization of multiple molecules simultaneously. We calculate the effect of different parameters, such as the relative position of the doughnut beams, the number of detector pixels, the number of photons, and the signal-to-background ratio, on the localization uncertainty. We predict that the combination of a good localization precision and the enhanced robustness of ISM-FLUX will help the wide adoption of MINFLUX.

Acoustic full waveform inversion for 2-D ambient noise source imaging

SUMMARYWe present a method for estimating seismic ambient noise sources by acoustic full waveform inversion (FWI) of interstation cross-correlations. The method is valid at local scales for laterally heterogeneous media, and ambient noise sources confined to the Earth’s surface. Synthetic tests performed using an actual field array geometry, are used to illustrate three unique aspects of our work. First: the method is able to recover noise sources of arbitrary spatial distribution, both within and outside the receiver array, with high fidelity. This holds true for complex velocity models and does not require a good initial guess for inversion, thereby addressing an outstanding issue in the existing research literature. Second: we analyse the extent of biases in source inversion that arise due to inaccurate velocity models. Our findings indicate that source inversion using simplified (e.g. homogeneous) velocity models may work reliably when lateral variations in velocity structure are limited to 5 or 10 per cent in magnitude, but is vitiated by strong variations of 20 per cent or higher, wherein the effect of strong scattering and/or phase distortions become significant. Finally, our technique is implemented without the adjoint method, which is usually inextricably linked to FWI. Inversions are performed using source kernels computed for each receiver pair, and this approach is computationally tractable for real-world problems with small aperture seismic arrays.

Implementation of constrained swept synthetic aperture using a mechanical fixture.

Resolution and target detectability in ultrasound imaging are directly tied to the size of the imaging array. This is especially important for imaging at depth, such as in the detection and diagnosis of hepatocellular carcinoma and other lesions in the liver. Swept synthetic aperture (SSA) imaging has shown promise for building large effective apertures from small physical arrays using motion, but has required bulky fixtures and external motion tracking for precise positioning. In this study we present an approach that constrains the transducer motion with a simple linear sliding fixture and estimates motion from the ultrasound data itself using either speckle tracking or channel correlation. We demonstrate in simulation and phantom experiments the ability of both techniques to accurately estimate lateral transducer motion and form SSA images with improved resolution and target detectability. We observed errors under 83 μm across a 50 mm sweep in simulation and found improvements of up to 61% in resolution and up to 33% in lesion detectability experimentally even imaging through ex vivo tissue layers. This approach will increase the accessibility of SSA imaging and allow us to test its use in clinical settings.

Short-range transmission using OAM-carrying waves generated by uniform circular arrays

The orbital angular momentum (OAM or vortex) waves are expected to provide ten-fold and larger increases in wireless data rates, required for short-range communications within the beyond 5G and 6G concept of all-connected life and industry. We address the specifics of short-range communications employing OAM-carrying waves generated by small uniform circular arrays (UCAs) at lower, i.e., 10 GHz, transmission frequencies. Comparing the link budgets obtained using (i) asymptotic analytical formulas, (ii) numerical electromagnetic simulations, and (iii) measurements on two pairs of manufactured prototypes comprising 8 microstrip-patch-element UCAs, we point out the limitations of simplified models which do not account for various effects, such as coupling, parasitic radiation, and insertion loss. The observed effects are expected to be relevant at millimeter-wave frequencies as well.

Application of macros for automated performance of the same type operations when simulating SIW-based slotted waveguide antennas in Ansys HFSS CAD

SIW slotted waveguide antennas contain numerous equidistantly spaced vias and many slots distributed following a particular field distribution. Ansys HFSS CAD user must manually repeat the same type of operations when creating slots or vias. Automating these routine operations is advisable to eliminate design errors and speed up model construction. This paper aims at complete automation of SIW resonant slotted waveguide antenna arrays modelling in CAD Ansys HFSS, including model construction, running simulations and displaying simulation results. There are multiple procedures for slotted waveguide antenna synthesis. For small waveguide antenna arrays with a number of elements less than 15, the internal and external slots coupling consideration is beneficial, while for large waveguide antennas, no mutual coupling assumption can be made (so-called “energy method”). The energy method has been used to determine the coordinates of the longitudinal slots on the broad wall of the SIW based on a given side lobe level. The slot resonant length has been determined using substrate permittivity and operating frequency. The number of slots has been obtained based on the required half-power beamwidth. SIW dimensions have been calculated using the given operating frequency and the dimensions of the filled rectangular waveguide. An IronPython script has been developed to automate the antenna's model construction, automatic simulation and determination of its characteristics. All script commands have been taken from the “HFSS Scripting Guide” document integrated into Ansys HFSS. The tangible outcome of this work is the development of the IronPython script for fully automated modelling of SIW resonant slotted waveguide antennas. The script builds an antenna model from scratch based on a given antenna characteristics, assigns excitation port and radiation boundary conditions, and displays the simulation results – a radiation pattern at a fixed frequency. The script significantly reduces the antenna design time by eliminating the need to repeat the object creation operations.

Design of Planar Differential Microphone Array Beampatterns with Controllable Mainlobe Beamwidth and Sidelobe Level.

The differential microphone array, or differential beamformer, has attracted much attention for its frequency-invariant beampattern, high directivity factor and compact size. In this work, the design of differential beamformers with small inter-element spacing planar microphone arrays is concerned. In order to exactly control the main lobe beamwidth and sidelobe level and obtain minimum main lobe beamwidth with a given sidelobe level, we design the desired beampattern by applying the Chebyshev polynomials at first, via exploiting the structure of the frequency-independent beampattern of a theoretical Nth-order differential beamformer. Next, the so-called null constrained and least square beamformers, which can obtain approximately frequency-invariant beampattern at relatively low frequencies and can be steered to any direction without beampattern distortion, are proposed based on planar microphone arrays to approximate the designed desired beampatterns. Then, for dealing with the white noise amplification at low-frequency bands and beampattern divergence problems at high-frequency bands of the null constrained and least square beamformers, the so-called minimum norm and combined solutions are deduced, which can compromise among the white noise gain, directivity factor and beampattern distortion flexibly. Preliminary simulation results illustrate the properties and advantages of the proposed differential beamformers.

Towards optimal phased-array tile configurations for large new-generation radio telescopes and their application to NenuFAR

Context. Recent instrumental developments have aimed to build large digital radio telescopes made of ~100k antennas. The massive data rate required to digitise all elements drives the instrumental design towards the hierarchical distribution of elements by groups of 𝒪(10) that form small analogue phased arrays that lower the computational burden by one to two orders of magnitude. Aims. We study possible optimal layouts for a tile composed of five to 22 identical elements. We examine the impact of the tile layout on the overall response of an instrument. Methods. We used two optimisation algorithms to find optimal arrangements of elements in the tile using: (i) a deterministic method (Kogan) based on beam pattern derivative properties; and (ii) a stochastic method (modified simulated annealing) to find global optima minimising the side-lobe level while increasing the field of view (FOV) of the tile, a required condition for all-sky surveys. Results. We find that optimal tile arrangements are compact circular arrays that present some degree of circular symmetry while not being superimposable to any rotated version of themselves. The ‘optimal’ element number is found to be 16 or 17 antennas per tile. These could provide a maximum side-lobe level (SLL) of −33 dB (−24 dB) used with dipole (isotropic) elements. Due to constraints related to the analogue phasing implementation, we propose an approaching solution but with a regular arrangement on an equilateral lattice with 19 elements. By introducing random relative rotations between tiles, we compared and found that the 19-element equilateral tile results in better grating lobe mitigation and a larger FOV than that of rectangular tiles of 16 antennas. Conclusions. Optimal tile arrangements and their regular versions are useful to maximise the sensitivity of new-generation hierarchical radio telescopes. The proposed solution was implemented in NenuFAR, a pathfinder of SKA-LOW at the Nançay Radio Observatory.

Deconvolved Fractional Fourier Domain Beamforming for Linear Frequency Modulation Signals

To estimate the direction of arrival (DOA) of a linear frequency modulation (LFM) signal in a low signal-to-noise ratio (SNR) hydroacoustic environment by a small aperture array, a novel deconvolved beamforming method based on fractional Fourier domain delay-and-sum beamforming (FrFB) was proposed. Fractional Fourier transform (FrFT) was used to convert the received signal into the fractional Fourier domain, and delay-and-sum beamforming was subsequently performed. Noise resistance was acquired by focusing the energy of the LFM signal distributed in the time-frequency domain. Then, according to the convolution structure of the FrFB complex output, the influence of the fractional Fourier domain complex beam pattern was removed by deconvolution, and the target spatial distribution was restored. Therefore, an improved spatial resolution of DOA estimation was obtained without increasing the array aperture. The simulation and experimental results show that, with a small aperture array at low SNR, the proposed method possesses higher spatial resolution than FrFB and frequency-domain deconvolved conventional beamforming.

Improved response model of a superconducting nanowire array for high photon count rate communication

In high-speed photon-counting communication where the slot duration is close to the scale of detector reset time, the detection efficiency recovery characteristics of superconducting nanowire single photon detector (SNSPD) become the key factors affecting counting and communication performance. We introduced the nonlinear detection efficiency recovery model derived from the kinetic inductance model combined with the nonlinear efficiency-current relationship into the pulse position modulation (PPM) optical communication system based on the SNSPD array, and studied the impact of the recovery characteristics on the counting and communication performance of the system. On this basis, we introduce the efficiency recovery model into the correction of the channel logarithmic likelihood ratio (LLR) to estimate the SNR of each slot more accurately. Relevant results show that compared with the existing Poisson channel model, fixed deadtime model and detection efficiency exponential recovery model, this modification combined with FEC can provide the best decoding performance, especially in scenarios with high PPM order, small array pixel number and strong noise level. Besides, the nonlinear detection efficiency recovery model also reflects the best consistency with the experimental measurements of the SNSPD array in terms of response count rates near saturation.

Smart Gateway for Healthcare Networks Based on Beam Steering Technology

To ensure high-reliability communication in healthcare networks, this paper presents a smart gateway system that includes an angle-of-arrival (AOA) estimation and a beam steering function for a small circular antenna array. To form a beam toward healthcare sensors, the proposed antenna estimates the direction of the sensors utilizing the radio-frequency-based interferometric monopulse technique. The fabricated antenna was assessed based on the measurements of complex directivity and the over-the-air (OTA) testing in Rice propagation environments using a two-dimensional fading emulator. The measurement results reveal that the accuracy of the AOA estimation agrees well with that of the analytical data obtained through the Monte Carlo simulation. This antenna is embedded with a beam steering function employing phased array technology, which can form a beam spaced at 45° intervals. The ability of full-azimuth beam steering with regard to the proposed antenna was evaluated by beam propagation experiments using a human phantom in an indoor environment. The received signal of the proposed antenna with beam steering increases more than that of a conventional dipole antenna, confirming that the developed antenna has great potential of achieving high-reliability communication in a healthcare network.

Seismic Monitoring of Novaya Zemlya: Progress, Challenges, and Prospects

AbstractThe permanent seismic stations of the European Arctic maintain a detection threshold of around magnitude 2 for events on and around Novaya Zemlya. Events above magnitude 3 are clearly observed by multiple stations at regional and far-regional distances and, with improved travel-time models, can be located with high accuracy. The monitoring capability for smaller magnitude events is dominated by the small aperture seismic arrays ARCES and SPITS. We review the properties of Novaya Zemlya seismic signals on key stations and discuss how empirical signal processing may enhance detection and interpretation of future events in the region. We present a joint probabilistic location for 21 low-magnitude events between 1986 and 2020 in which the joint probability distribution for all events simultaneously exploits both constraints on earlier events from stations no longer in operation and constraints on newer events from more recently deployed stations. Advances in signal processing, enhanced exploitation of archive data, new permanent stations, and comparative multiple event analysis will all contribute both to a more robust and sensitive detection capability and higher confidence in signal interpretation.

Maintenance process for the joint seismic-and-electromagnetic monitoring in low-ambient noise areas: the seismic gradient system

The project of the joint seismic-and-electromagnetic monitoring in low-ambient noise areas is aimed at studying the phenomena associated with the deformation of the Earth’s crust. The arrangements set of the geophysical monitoring in low-ambient noise areas is proposed. The paper describes in detail the technological scheme being of monitoring of the modern geodynamic activity with a magnetotelluric soundings method and a small seismic array presented as the seismic gradient system (SGS). Technical explanations, safety rules, equipment calibration and maintenance, and the technological schemes of the method of obtaining and archiving data are given. Maintenance procedures using SGS with geophones in Tien Shan to determine the endogenous component of the seismic field are described. We investigate a common workflow chart for SGS and main programs for the data caption and data processing. The proposed scheme has been tested and requires the application and adoption to the passive geophysical monitoring routine.