Distributed Array Research Articles

Heat transfer characteristics investigations on liquid-cooled integrated micro pin-fin chip with gradient distribution arrays and double heating input for intra-chip micro-fluidic cooling

Targeting at improving temperature uniformity for intra-chip cooling, present work experimentally and numerically investigates the influence of flow rate, heat flux density, fluid inlet temperature and double side heating power on thermal performance in embedded micro-pin fin chip using HFE7100 as the coolant. It is found appropriately increasing flow rate to form enhanced flow fluctuations could effectively improve temperature uniformity by flow impingement, mixing and local acceleration effect. However, the influence of changing fluid inlet temperature is weak. With increasing flow rate, the proportion of convection thermal resistance gradually reaches a plateau and dominants the total thermal resistance. Importantly, double side heating power significantly exacerbates the challenge of thermal management, resulting in a 50% reduction of the addressed heat flux limit and almost one factor of increment in maximum temperature gradient. Notably, present gradient distribution design could address a heat flux limit of 140 W/cm2, increasing by 30 W/cm2 than that in uniform arrangement. According to local Nu curve, the significant heat transfer enhanced zones are obtained in gradient distribution chip where local Nu obviously increases. These zones effectively inhibit the rise of temperature and provide a more uniform temperature distribution downstream.

Undesired Radiation Suppression Technique with Adaptive Control for Distributed Array Antenna Systems in Mobile Environment

We have proposed a distributed array antenna (DAA) system for high-speed satellite communications. The DAA system uses multiple small tracking antennas and combines the transmission signals in-phase to increase the antenna gain. DAA system has a problem that the undesired radiation at the sidelobe direction increases as the antenna gain at the main lobe direction increases. In the mobile environment, the conventional technique can suppress the undesired radiation in the limited condition because of changing the direction of the undesired radiation according to the movement of the mobile station. This paper proposes a DAA technique that suppresses the undesired radiation by setting a transmission plate at each antenna aperture and moving them via adaptive control. The transmission plate consisting of a metal patch or slot retransmits electromagnetic waves and changes the amplitude and phase of the waves. To change the radiation patters of each antenna, the transmission plate rotates according to movement of the mobile station. After combining these changed signals, the adaptive control selects the rotate angle of the transmission plate to decrease the undesired radiation at the sidelobe direction. The antenna gain on the main lobe direction after combining is achieved with lower loss because the insertion loss through the transmission plate is smaller. The proposed technique offers more than $2.4$ dB improvement with three antennas and more than $3.5$ dB improvement with four antennas assuming each consists of $8 ¥times 8$ patches.

Synthesis and Measurement of a Circular-Polarized Deflection OAM Vortex Beam With Sidelobe Suppression Array

In this paper, a chamfer distribution antenna array is designed to generate a deflecting circular-polarized vortex beam carrying orbital angular momentum (OAM) mode. When the vortex beam is designed with a deflection angle, the sidelobe of the vortex beam will deteriorate. In order to solve this problem, an optimized array design is presented in this paper. Inspired by the Chebyshev distribution array synthesis method, the antenna elements in the four corners of the antenna array are cut out to realize the chamfer distribution array. Therefore, the sidelobe level of the deflected vortex beam can be effectively suppressed. Moreover, a simplified feeding network is designed to reduce the feeding network complexity by using circularly polarized structural center antenna element. The designed antenna array is simulated, fabricated, and measured at center frequency of 4.25 GHz in C-band. The far-field radiation pattern of the deflected vortex beam and the near E-field OAM vortex beam distribution are simulated and measured to verify the effectiveness of the proposed design method for sidelobe suppression array.

Guided wave sensitivity prediction for part and through-thickness crack-like defects

Guided waves allow for the efficient structural health monitoring of large structures using phased or distributed arrays of sensors. The sensitivity for specific defects can be improved by accounting for the angular scattering pattern. The scattering of the fundamental anti-symmetric guided wave mode (A0 Lamb mode) at through-thickness and part-through crack-like defects was studied experimentally and from three-dimensional finite element simulations. Experimentally, the scattered field around manufactured notches of different depths and lengths in an aluminium plate was measured using a laser interferometer. The scattered field was extracted by taking the complex difference in the frequency domain between baseline measurement and measurements around the defect. Good agreement was found between measurements and three-dimensional finite element simulations, and the amplitude and directionality pattern of the scattered field can be predicted accurately. The angular directionality pattern of the scattered field depending on the direction of the incident wave relative to the crack-like defect orientation, depth and length relative to the wavelength was investigated. For short and part-thickness defects, the main scattering effect is a reduction of the (forward) wave propagating past the defect with very limited backscattered amplitude. Significant energy scattered back towards the incident wave direction was only found for perpendicular incidence on long and deep defects. Even for large defects, almost no energy is scattered in certain directions from the defect, possibly complicating defect detection. Based on the predicted amplitude and angular dependency of the scattered guided waves, the sensitivity for defect detection using localized and distributed structural health monitoring sensor array systems can be quantified.

The Utility of a Fully-distributed Direct Current Resistivity and Induced Polarisation System with Common Voltage Referencing

SummaryThe direct current electrical resistivity and induced polarization (DCIP) method has received another significant upgrade through the introduction of common voltage referencing (CVR) in a fully-distributed array system. An array of single-channel receivers with a CVR wire allows for the extraction of an unprecedented volume of dipole data for the number of receivers deployed. In 3D implementation, this new method reduces noise levels and allows for the derivation of multi-scale and multi-azimuth receiver dipoles.Operational efficiencies in the CVR method include lower overall wire lengths, less equipment weight and less crew fatigue when compared with conventional and other distributed array methods. Cable-free mesh network capability in each receiver allows for real-time assessment of data quality metrics, safety information, location data, and system health data. These operational efficiencies translate directly to improvements in safety.With several hundred active receivers, data volume can reach 10s of millions of data records. Careful processing and selection of an optimised data subset with multi-scale and multi-azimuth information will inform highly accurate inversion imaging.

Combined Wireless Ranging and Frequency Transfer for Internode Coordination in Open-Loop Coherent Distributed Antenna Arrays

Beamforming in distributed antenna arrays requires accurate coordination of the relative phasing between the separate wireless nodes. Principally, this coordination constitutes measuring the node separations and transferring a stable frequency reference, enabling beamsteering and ensuring that the local oscillators on the separate platforms are locked. A 4.5-GHz wireless system for simultaneous high-accuracy estimation of node separation and estimation of a wirelessly transferred 10-MHz frequency reference is presented in this article. Ranging is achieved using a spectrally sparse two-tone waveform with a tone separation of 200 MHz and pulsewidth of $2~\mu \text{s}$ ; a 10-MHz frequency reference is modulated onto one of the ranging tones. The use of spectrally sparse waveforms allows simple transceiver designs compared to wideband ranging systems since the tones can be individually generated and received. The theoretical bounds for range and frequency estimation are derived for a set of common modulation formats, and experimental measurements of ranging accuracy and frequency estimation accuracy are presented, demonstrating that the proposed waveform can achieve high accuracy in both domains, with range accuracy of 3.35 mm and phase errors less than 18°, supporting coherent distributed array operations up to 5.96 GHz. The results show that the ranging estimation is effectively independent of the modulation format of the reference frequency and the frequency estimation performance is independent of the sparse waveform design for ranging. Thus, the performance of range estimation and frequency transfer may be approached independently but in the same waveform.

Does the Kuznets curve exist in Thailand? A two decades’ perspective (1993–2015)

To explore the relationship between income inequality and economic development, and particularly to prove the existence of the Kuznets curve in Thailand’s economy along these two decades, we propose the simultaneous smooth transition kink equations (SKE) model in which each regression parameter can be present in two different regimes, lower and upper. The regression coefficients split into two parts based on the unknown kink and smooth parameters in the logistic function. Thus, the model provides a flexible structure to capture and explain the relationship between income inequality and economic development following the inverted-U curve called the Kuznets curve. Also, we extend the analysis of the SKE model by modelling its nonlinear dependence structure through various Copula functions. Thus, the model becomes more flexible in coupling together the different marginal distributions. Before investigating the Kuznets curve, we conduct a simulation study to confirm the performance and accuracy of our proposed model. The satisfactory results are obtained from this simulation study as the estimated coefficient results are close to the true values under a wide array of simulated data models and distributions together with three smooth transition functions. Finally, according to the present empirical results, the Kuznets hypothesis does not hold at the country level, but it does for the North and Northeast regions. Also, our findings show alternative ways to reduce income inequality by increasing private sector contribution, GDP per capita, government expenditure and government subsidy. Additionally, this study applies the same method for investigating the Kuznets curve in the regions to answer the question ‘Are there regional Kuznets curves in Thailand?’ Our model shows some exciting results in income distribution in the different areas that may support the theory of Kuznets.

Wireless Time Transfer With Subpicosecond Accuracy Based on a Fully Integrated Injection-Locked Picosecond Pulse Detector

An injection-locked picosecond pulse detector is implemented in 65-nm CMOS technology. An on-chip slot planar inverted cone antenna receives picosecond pulses with a center frequency of 77 GHz and feeds the signal to a low-noise amplifier. A three-stage injection-locked frequency divider is used to lock the output signal to the 9.6-GHz repetition rate with an effective locking range of 142 MHz and a timing jitter of $0.29~\textrm {ps}_{\textrm {rms}}$ . The injection-locked detector is utilized in a wireless time transfer setup to demonstrate its application in widely spaced synchronized distributed arrays. This fully integrated system consumes 42 mW from a 1.3-V supply and occupies a total area of 0.9 mm2, including the on-chip antenna and the pads.

Source separation and localisation via tensor decomposition for distributed arrays

This study focuses on the problem of power spectra separation and localisation of multiple sources using distributed arrays. First, the array structure and signal model are discussed. By cross-correlating the multi-channel received signals in time-domain, a third tensor is constructed. Then, utilising the multi-dimensional characteristic, the tensor is decomposed to separate the array manifold matrix and the power spectra matrix through alternating least square (ALS) method. Finally, the sources are located using the relative x-y plane relationship between the distributed arrays and the direction of arrival (DOA), which can be estimated by spectrum analysis of each column of the array manifold matrix. The effectiveness and superiority of the proposed method is demonstrated by simulation results.

ScintPi: A Low‐Cost, Easy‐to‐Build GPS Ionospheric Scintillation Monitor for DASI Studies of Space Weather, Education, and Citizen Science Initiatives

AbstractWe report the proposal and results of a low‐cost, easy‐to‐build GPS‐based sensor for detection and monitoring ionospheric irregularities through the detection of amplitude scintillation. The system is based on the Raspberry Pi single‐board computer combined with an Adafruit Ultimate GPS peripheral, which is capable of measuring (at 10‐Hz rate) the intensity of the L1 signals transmitted by GPS satellites. We introduce and discuss results of short‐ and long‐term observations obtained with a prototype of this system deployed in Presidente Prudente, a low magnetic latitude site in Brazil. The deployment and observations were carried out to test the ability of the system to detect ionospheric scintillations and, therefore, monitor the occurrence of ionospheric irregularities associated with equatorial spread F. Our results show that this low‐cost sensor is indeed capable of detecting scintillation events associated with equatorial spread F. Comparison with simultaneous, collocated measurements made by a commercial scintillation monitor are also presented. The joint observations allowed us to quantify the performance of the low‐cost monitor and to identify sources of potential limitations. While the sensor cannot (and it was not intended to) substitute commercial scintillation monitors, the low cost allows its use in studies of ionospheric irregularities (space weather) that require observations made by distributed arrays of small instruments (DASI). Furthermore, the simplicity of the sensor design stimulates its use in educational and citizen science initiatives.

Gas Leakage Source Detection for Li-Ion Batteries by Distributed Sensor Array.

Lithium-based batteries operation is related to some safety risks of dangerous flaming, integrity destruction, or even explosion. Gas leakage is an early and reliable indicator for such irreversible malfunctioning of electrical accumulators. Often, accurate gas emission source location sensing is difficult especially in heavy operational conditions, related to temperature changes, vibrations, movements, accelerations, etc. In this paper we propose a gas detection system, with catalytic type sensor array, and a numerical reconstruction method for precise gas emission source location inside the battery pack. The detection system employs a distributed array of CO sensors. Proposed sensor array configurations significantly reduce the number of sensing nodes inside the battery pack and fewer sensors than the protected battery elements are used. This way, data acquisition process by sensor nodes is also simplified. Several array configurations are considered according to their measurement efficiency and accuracy. Reconstruction algorithm is based on fast interpolation technique very suitable for real-time data processing. Estimation of reconstruction method accuracy is made by computational model of the gas diffusion inside the pack.

Chiral plasmonic lens with Archimedes-spiral distributed nanoslits

A chiral plasmonic lens (CPL) suitable for circularly polarized light is proposed; it consists of multiple concentric grooves surrounded by two Archimedes-spiral distributed arrays of rectangular nanoslits milled into a gold film. We demonstrate both theoretically and numerically that the proposed CPL can convert an incident circular polarization beam with prescribed chirality into a long centrosymmetric focus with a size beyond the diffraction limit, but the circularly polarized one with the opposite chirality cannot be transmitted and focused by the same CPL due to the chirality of the proposed structure. Depending on the design parameters, an optical needle or optical tube in the focal field can be achieved; the attainable focus has a full-width at half-maximum of 0.43λ0 and an elongated depth of focus of 2.95λ0 with λ0 denoting the wavelength of illumination light.

Computational fluid dynamic study on the tribological performance of dimple-textured surface fabricated using the turning process

Purpose This study aims to simulate the influence of surface texturing produced via turning process toward pressure distribution and load capacity generation using computational fluid dynamics (CFD). Design/methodology/approach The dimple geometry was obtained via turning process, to be used for future application on piston skirt surfaces. Two cases were studied: a preliminary study using single periodic dimple assuming linear dimple distribution and an application study using multiple periodic dimples to address actual dimple orientation following the turning process. Findings For the first case, the dimple was proven to generate load capacity with regard to untextured surface, owing to the asymmetric pressure distribution. Increasing the Reynolds number, dimple width and dimple depth was found to increase load capacity. For the second case, although load capacity increases via surface texturing, the value was 97.4 per cent lower relative to the first case. This confirmed the importance of doing multiple dimple simulations for real applications to achieve more realistic and accurate results. Originality/value A new concept of dimple fabrication using a low-cost turning process has been developed, with a potential to increase the tribological performance under hydrodynamic lubrication. Previous CFD simulations to simulate these benefits have been done using a single periodic dimple, assuming equal distribution array between dimples. However, due to the different orientations present for dimples produced using turning process, a single periodic dimple simulation may not be accurate, and instead, multiple dimple simulation is required. Therefore, present research was conducted to compare the results between these two cases and to ensure the accuracy of CFD simulation for this type of dimple.

Multioctave Bandwidth of Parallel-Feeding Network Based on Impedance Transformer Concept

A generalized scheme to design a parallel-feeding network with a bandwidth of several octaves for uniform distribution arrays is proposed. Considering the entire network as a continuous impedance-transition device between the feed and all element ports, and therefore applying the design methods of the impedance transformer on the device, a broad matching bandwidth can be achieved without the traditional quarter-wavelength T-junctions concept. Three feeding networks based on the binomial and Chebyshev polynomial and exponential taper transformers for a $4 \times 4$ patch array are designed for demonstration, verification, and comparison of the proposed concept. An experimental sample of the taper network is fabricated and tested, and a fractional bandwidth better than 3:1 can be achieved. This method is not limited to the specific form of transmission lines and can perform even better for grander scale arrays.

Passive Joint Localization and Synchronization of Distributed Microphone Arrays

Collaborative processing of signals recorded by distributed sensors brings about new opportunities as well as challenges to classical array signal processing. In this letter, we present a method for passive self-calibration of a distributed system in which each distributed node consists of an array of sensors. The proposed method estimates the positions and orientations of distributed sensor arrays, the synchronization timeline offsets as well as the positions of spatially distributed events emitted by an uncontrolled source or sources. The proposed two-step optimization consists in finding the maximum likelihood estimate of the relative geometry of a distributed system based on Directions of Arrival (DoAs) observed independently at each array. Next, the final positions of distributed arrays, the positions of acoustic events, and the synchronization offsets between the nodes are computed by solving a linear least square problem based on the observed Time Differences of Arrival (TDoAs) between the arrays and the relative positions estimated in the first optimization step. The evaluation results indicate that passive self-calibration of distributed sensor arrays can be conveniently achieved by observing acoustic events generated by an uncontrolled source based on the measured DoAs and TDoAs.

Detection of sparse mixtures: higher criticism and scan statistic

We consider the problem of detecting a sparse mixture as studied by Ingster (1997) and Donoho and Jin (2004). We consider a wide array of base distributions. In particular, we study the situation when the base distribution has polynomial tails, a situation that has not received much attention in the literature. Perhaps surprisingly, we find that in the context of such a power-law distribution, the higher criticism does not achieve the detection boundary. However, the scan statistic does.

Relating a small-scale shock sensitivity experiment to large-scale failure diameter in an aluminized ammonium nitrate non-ideal explosive

The detonation failure process, specifically where a transient reaction occurs in an overdriven explosive due to a sub-critical charge diameter, has remained relatively unexplored, particularly regarding its relationship to shock initiation mechanisms. Detonation failure, here defined as a weakly supported shock wave traveling with a decaying velocity, of aluminized ammonium nitrate (AN/Al) was considered to investigate the relationship between the detonation failure process and shock sensitivity. Previous work has shown that the Al additive particle size alters the failure diameter, a measure of shock sensitivity, of AN/Al. Microwave interferometry was used to measure the transient shock wave velocity in the explosive system, which was lightly confined at a diameter below its critical diameter, in response to an overdriven shock insult in a small-scale experiment. An array of mixture ratios and particle size distributions of the explosive system was used to vary the sensitivity of the explosive and to facilitate exploration of the relationship between the shock velocity decay rate, initiation mechanisms, and large-scale shock sensitivity. Resulting shock velocity profiles in AN/Al indicate that micron-sized and larger Al particles can contribute to the detonation process. It is concluded that the rate at which the transient shock velocity approaches that of a compressive wave with no supporting reaction corresponds to the relative shock sensitivity of the system; it is therefore proposed that the measured shock velocity decay rate of an overdriven sub-critical diameter charge of AN/Al reveals quantifiable information about the relative shock sensitivity of a large-scale charge.

Using peer-to-peer energy-trading platforms to incentivize prosumers to form federated power plants

Power networks are undergoing a fundamental transition, with traditionally passive consumers becoming ‘prosumers’ — proactive consumers with distributed energy resources, actively managing their consumption, production and storage of energy. A key question that remains unresolved is: how can we incentivize coordination between vast numbers of distributed energy resources, each with different owners and characteristics? Virtual power plants and peer-to-peer (P2P) energy trading offer different sources of value to prosumers and the power network, and have been proposed as different potential structures for future prosumer electricity markets. In this Perspective, we argue they can be combined to capture the benefits of both. We thus propose the concept of the federated power plant, a virtual power plant formed through P2P transactions between self-organizing prosumers. This addresses social, institutional and economic issues faced by top-down strategies for coordinating virtual power plants, while unlocking additional value for P2P energy trading. The rise of prosumers has led to creation of virtual power plants and peer-to-peer trading to help manage a diverse and distributed array of energy sources. This Perspective proposes the federated power plant, which combines these concepts to meet some of their individual challenges and offer new value.

A deployable mechanism concept for the collection of small-to-medium-size space debris

Current efforts in active debris removal strategies and mission planning focus on removing the largest, most massive debris. It can be argued, however, that small untrackable debris, specifically those smaller than 5 cm in size, also pose a serious threat. In this work, we propose and analyze a mission to sweep the most crowded Low Earth Orbit with a large cupola device to remove small-to-medium-size debris. The cupola consists of a deployable mechanism expanding more than 25 times its storage size to extend a membrane covering its surface. The membrane is sufficiently stiff to capture most small debris and to slow down the medium-size objects, thus accelerating their fall. An overview of the design of a belt-driven rigid-link mechanism proposed to support the collecting cupola surface is presented, based on our previous work. Because of its large size, the cupola will be subject to significant aerodynamic drag; thus, orbit maintenance analysis is carried out using the DTM-2013 atmospheric density model and it predicts feasible requirements. While in operation, the device will also be subject to numerous hyper-velocity impacts which may significantly perturb its orientation from the desired attitude for debris collection. Thus, another important feature of the proposed debris removal device is a distributed array of flywheels mounted on the cupola for reorienting and stabilizing its attitude during the mission. Analysis using a stochastic modeling framework for hyper-velocity impacts demonstrates that three-axes attitude stabilization is achievable with the flywheels array. MASTER-2009 software is employed to provide relevant data for all debris related estimates, including the debris fluxes for the baseline mission design and for assessment of its expected performance. Space debris removal is a high priority for ensuring sustainability of space and continual launch and operation of man-made space assets. This manuscript presents the first analysis of a small-to-medium size debris removal mission, albeit finding it to not be economically viable at the present time.

Femtosecond FBG Written through the Coating for Sensing Applications.

Type I fiber Bragg gratings (FBG) written through the coating of various off-the-shelf silica fibers with a femtosecond laser and the phase-mask technique are reported. Inscription through most of the common coating compositions (acrylate, silicone and polyimide) is reported as well as writing through the polyimide coating of various fiber cladding diameters, down to 50 µm. The long term annealing behavior of type I gratings written in a pure silica core fiber is also reported as well as a comparison of the mechanical resistance of type I and II FBG. The high mechanical resistance of the resulting type I FBG is shown to be useful for the fabrication of various distributed FBG arrays written using a single period phase-mask. The strain sensing response of such distributed arrays is also presented.