Energy Leakage Research Articles

Circulant Shift-Based Beamforming for Secure Communication With Low-Resolution Phased Arrays

Millimeter wave (mmWave) technology can achieve high-speed communication due to the large available spectrum. Furthermore, the use of directional beams in mmWave system provides a natural defense against physical layer security attacks. In practice, however, the beams are imperfect due to mmWave hardware limitations such as the low-resolution of the phase shifters. These imperfections in the beam pattern introduce an energy leakage that can be exploited by an eavesdropper. To defend against such eavesdropping attacks, we propose a directional modulation-based defense technique where the transmitter applies random circulant shifts of a beamformer. We show that the use of random circulant shifts together with appropriate phase adjustment induces artificial phase noise (APN) in the directions different from that of the target receiver. Our method corrupts the phase at the eavesdropper without affecting the communication link of the target receiver. We also experimentally verify the APN induced due to circulant shifts, using channel measurements from a 2-bit mmWave phased array testbed. Using simulations, we study the performance of the proposed defense technique against a greedy eavesdropping strategy in a vehicle-to-infrastructure scenario. The proposed technique achieves better defense than the antenna subset modulation, without compromising on the communication link with the target receiver.

Review and comparison of methods for limiting leakage currents in single-phase transformerless PV inverter topologies

Transformerless inverters are widely used in different photovoltaic nonisolated ac module applications, mainly in grid-tied photovoltaic (PV) generation systems, due to the benefits of achieving high efficiency over a wide load range, and low cost. Various transformerless inverter topologies have been proposed to meet the safety requirement of low ground leakage currents, such as specified in the VDE-4105 standard and low-output ac-current distortion. Topology modifications of transformerless full bridge inverters are designed to balance and maintain a constant common mode output voltage, thereby eliminating or reducing leakage currents. This article reviews and compares the different methods for limiting leakage currents in known topologies of the full-bridge transformerless inverters, such as: H4, H5, H6, HERIC, and their improvements. The main topologies and strategies used to reduce the leakage current in transformerless schemes are summarized, highlighting advantages and disadvantages and establishing points of comparison with similar topologies. To compare the properties of different medium to high power inverters, PV inverter topologies were implemented using IGBTs and tested with the same components, same simulation parameters in PSPICE to evaluate their performance in terms of energy efficiency and leakage current characteristics. The detailed power stage operating principles, extended PWM modulator, and integrated universal gate driver with galvanic isolation in the transmission path of control signal for all IGBTs of the inverter, as well isolated and floating bias power supply for gate drivers are described.

Automatic optimization of miniaturized bound states in the continuum cavity.

Bound states in the continuum (BICs) provide, what we believe to be, a novel and efficient way for light trapping. However, using BICs to confine the light into a three-dimensional compact volume remains a challenging task, since the energy leakage at the lateral boundaries dominates the cavity loss when its footprint shrinks to considerably small, and hence, sophisticated boundary designs turn out to be inevitable. Conventional design methods fail in solving the lateral boundary problem because a large number of degree-of-freedoms (DOFs) are involved. Here, we propose a fully automatic optimization method to promote the performance of lateral confinement for a miniaturized BIC cavity. Briefly, we combine a random parameter adjustment process with a convolutional neural network (CNN), to automatically predict the optimal boundary design in the parameter space that contains a number of DOFs. As a result, the quality factor that is accounted for lateral leakage increases from 4.32 × 104 in the baseline design to 6.32 × 105 in the optimized design. This work confirms the effectiveness of using CNNs for photonic optimization and will motivate the development of compact optical cavities for on-chip lasers, OLEDs, and sensor arrays.

The Shapes of Stellar Spectra

Stellar atmospheres separate the hot and dense stellar interiors from the emptiness of space. Radiation escapes from the outermost layers of a star, carrying direct physical information. Underneath the atmosphere, the very high opacity keeps radiation thermalized and resembling a black body with the local temperature. In the atmosphere the opacity drops, and radiative energy leaks out, which is redistributed in wavelength according to the physical processes by which matter and radiation interact, in particular photoionization. In this article, I will evaluate the role of photoionization in shaping the stellar energy distribution of stars. To that end, I employ simple, state-of-the-art plane-parallel model atmospheres and a spectral synthesis code, dissecting the effects of photoionization from different chemical elements and species, for stars of different masses in the range of 0.3 to 2 M⊙. I examine and interpret the changes in the observed spectral energy distributions of the stars as a function of the atmospheric parameters. The photoionization of atomic hydrogen and H− are the most relevant contributors to the continuum opacity in the optical and near-infrared regions, while heavier elements become important in the ultraviolet region. In the spectra of the coolest stars (spectral types M and later), the continuum shape from photoionization is no longer recognizable due to the accumulation of lines, mainly from molecules. These facts have been known for a long time, but the calculations presented provide an updated quantitative evaluation and insight into the role of photoionization on the structure of stellar atmospheres.

Optimum location for energy recovery and leakage reduction in water distribution networks

Abstract The excess pressure in water distribution networks (WDNs) can be utilized to reduce leakage and produce energy by installing energy recovery devices (ERDs) like microturbines or pumps-as-turbines. The major challenge in adopting ERDs in pipe networks is to locate the optimum location for their placement. An optimization procedure is proposed in this work to find the optimum locations of energy recovery (ER) and leakage reduction (LR). The optimization method is based on the Rao algorithm, written in Python, coupled to an EPANET-implemented hydraulic model. With optimal ER of 543.46, 648.24 and 154.58 kWh/day and LR of 61.1, 13.6 and 6.8%, three benchmark networks – the 5-node, the 25-node and the 46-node network – serve as the basis for validating the proposed approach which converges to the best solution in only 2,000, 4,000 and 10,000 function evaluations. For large networks, solutions with two ideally located devices gave higher ER than three imperfectly located devices. This methodology is verified to give optimal ER locations and can be applied to any pipe network regardless of size and location. This work made it easier to analyse the potential for ER in WDNs and promotes the use of sustainable leakage management methods.

Torsional mode magnetostrictive patch transducer with TPSMs for liquid-filled pipes inspection

T (0,1) mode guided waves have no axial or radial vibration displacement. Therefore, the energy leakage is small in liquid-filled pipes, which is suitable for detecting the axial defects of the liquid-filled pipes. Fe–Co materials with high magnetostriction coefficient is fabricated. Its magnetic properties are tested. The size and distribution of static magnetic fields generated by different permanent magnets are verified by simulation. A new torsional mode guided wave magnetostrictive patch transducer with tile-shaped permanent magnets for defect detection of the liquid-filled pipes is proposed. The detection effect of the transducer on the liquid-filled pipes under different pressures is tested through experiments. The proposed transducer consists of four tile-shaped permanent magnets, eight triangular yokes, a coil, and two magnetostrictive patches. Four groups of tile permanent magnets are symmetrically distributed around the patch according to the polarity. Magnetic yokes are installed at both ends of each group of tile permanent magnets. The experiment verified that the magnetostrictive patch transducer realize the excitation and reception of guided wave signals in the magnetostrictive patches. The amplitude and signal-to-noise ratio of echo signals is improved. The position of pipe defects is determined according to the propagation time of guided wave. The influence of different pressures in the liquid-filled pipes on the amplitude of guided wave is verified.

Packet scheduling in rechargeable wireless sensor networks under SINR model

Two packet scheduling algorithms for rechargeable sensor networks are proposed based on the signal to interference plus noise ratio model. They allocate different transmission slots to conflicting packets and overcome the challenges caused by the fact that the channel state changes quickly and is uncontrollable. The first algorithm proposes a priority-based framework for packet scheduling in rechargeable sensor networks. Every packet is assigned a priority related to the transmission delay and the remaining energy of rechargeable batteries, and the packets with higher priority are scheduled first. The second algorithm mainly focuses on the energy efficiency of batteries. The priorities are related to the transmission distance of packets, and the packets with short transmission distance are scheduled first. The sensors are equipped with low-capacity rechargeable batteries, and the harvest-store-use model is used. We consider imperfect batteries. That is, the battery capacity is limited, and battery energy leaks over time. The energy harvesting rate, energy retention rate and transmission power are known. Extensive simulation results indicate that the battery capacity has little effect on the packet scheduling delay. Therefore, the algorithms proposed in this paper are very suitable for wireless sensor networks with low-capacity batteries.

Pipeline leak jet fire thermal characteristic induced by hydrogen-blended natural gas: Physical modeling of temperature profile based on virtual origin theory

Hydrogen-blended natural gas has widely used in energy fuel systems in industrial and domestic applications. During storage, transportation and usage of the fuel, temperature characteristics make a key contribution to energy leak gas fire accidents. In this manuscript experimentally, the buoyant turbulent diffusion axial temperature profile of a hydrogenated methane jet fire is experimentally investigated under free fire and wall fire. Different hydrogen addition ratios, nozzle diameters, and fire heat release rates were considered in the experimental conditions. Temperature profiles and virtual origins were recorded and analyzed. It is found that the wall fire temperature is somewhat higher than that in the free fire at a fixed height. And the vertical temperature of the jet fire increases with the increase of the hydrogen addition ratio, while the flame height decreases. With the addition of hydrogen, the virtual origin is increased, and virtual origin of wall fire is clearly larger than that of the free fire. Due to the restriction of air entrainment from the sidewall and the hydrogen addition, the physical mechanism of restricted air entrainment was analyzed. In addition, a non-dimensional model of the virtual origin was proposed and analyzed for different conditions. Finally, the normalized vertical temperature profile in the continuous flame region, intermittent flame region and buoyant plume region based on the virtual origin and mirror-approach are still well characterized for air entrainment under all conditions. The results of this paper may demonstrate the potential for the risk assessment of hydrogen-blended natural gas fire.

Wood‐framed binary eutectic polyethylene glycol (BEPEG) as phase change materials for thermal storage

AbstractPolyethylene glycol (PEG) is widely used in thermal energy storage, but leakage and lack of stability limit its further development. Wood is widely used as matrix to develop functional composites due to its porous structure and unique composition. In this study, a novel shape‐stabilized eutectic phase change material for thermal storage (EPCMTS) with enhanced thermal stability and superior chemical stability was fabricated by incorporating binary eutectic PEG (BEPEG) into porous wood flour (WF). It was found that BEPEG systems composed of PEG600 and PEG1000 at different proportions showed different thermal performances. This EPCMTS at its eutectic point exhibited a melting enthalpy of 45.26 J/g, which is higher than that of incomplete eutectic materials. Its thermal stability was enhanced at eutectic point because the melting temperature of 21.83°C was lower than that of each component. Moreover, the leakage rate can be lowered to only 1.1% at a PEG600:PEG1000 mass ratio of 9:1, which indicated that WF can effectively prevent PEG from leaking. No chemical reaction was detected in both PEG eutectic and WF modification processes. This kind of wood‐framed phase change material has broad application prospects in insulation building envelope.

Prototype Filter Design for Effectively Suppressing Out-of-Band Radiation in GFDM Systems

In this letter, a design method of a prototype filter for effectively suppressing out-of-band radiation (OOBR) in generalized frequency division multiplexing (GFDM) systems is proposed. A generic model that can suppress out-of-band energy leakage in the frequency-domain is introduced. The function that is solved in this model gives the target prototype filter. By adding several constraints such as the boundary, energy and spectral density energy concentration degree (SDECD) to the objective function, a finite-length optimized Nyquist prototype filter is designed. The optimized Nyquist pulse can suppress the OOBR of the GFDM system more effectively compared with the traditional Nyquist pulses.

Flood Detection in Steel Tubes Using Guided Wave Energy Leakage.

A study that evaluated the use of ultrasonic-guided waves to detect water in hollow pipes is presented. In this work, a guided wave system employed a 40 kHz piezoelectric (PZT) transmitter and a PZT ultrasound transducer. The transmitter was based on a battery-operated microcontroller, and the receiver was composed of a digital signal processor (DSP) module connected to a PC via a USB for monitoring purposes. The transmitter and receiver were attached, non-intrusively without perfect alignment, to the external wall of a steel tube 1 m × 270 mm × 2 mm in size. Flood detection was performed based on guided wave attenuation due to energy leakage from the internal steel wall of the tube to water. Two approaches were carried out. The former was an off-line signal response based on the wavelet energy entropy analysis of a received pulse; the latter was a real-time hit-and-miss analysis centered on measuring the time-space in-between two transmitted pulses. Experiments performed in the laboratory successfully identified flooded tubes.

Compact agile Tchebycheff transform variant for temporal compression of neural signals on brain-implantable microsystems

This paper proposes a new approximate variant of the Tchebycheff transform for the compression of intra-cortically-recorded neural signals on brain-implantable microsystems. The proposed approximate transform is achieved using an innovative algorithm that guarantees ‘partial orthogonality’ of the basis functions corresponding to the coefficients conveying the majority of the signal energy. This significantly reduces inter-coefficient energy leakage in the proposed transform variant, which helps meaningfully enhance the data compression rate. While keeping the signal reconstruction accuracy within the acceptable range, the proposed Tchebycheff transform variant is maximally truncated in order to reduce the hardware cost of the associated implementation. Based on the resulting truncated approximate transform, a hardware-efficient 256-channel neural signal compressor is designed, prototyped, and tested using pre-recorded neural signals. Operated at a clock rate of 960 kHz, the prototyped neural signal compressor exhibits a true compression rate of 1880 with an RMS reconstruction error of 2.8%.

Effects of Tip Clearance and Impeller Eccentricity on the Aerodynamic Performance of Mixed Flow Fan

The tip clearance and eccentricity of the impeller will affect the aerodynamic performance of the fan, and the impeller installation and vibration characteristics are relatively highly required if the tip clearance is too small. A reasonable tip clearance and excellent coaxially are necessary to ensure that the impeller does not rub with the shell and has superior aerodynamic performance when the fan is working. In the current study, a mixed flow fan was taken as the object and experimental explorations were performed on the C-type test rig designed according to GB/T1236 2000 Industrial fans-performance testing using standardized airways. By moving the airways to change the tip clearance, it was found that an overlarge tip clearance made the fan efficiency decrease significantly, and the efficiency change gradient was large. However, the gradient of efficiency change became smaller when reaching a certain clearance. Similarly, as the eccentricity became larger, the efficiency also decreased. To explore the influence of the optimal clearance and eccentricity of the fan on the fan’s performance, numerical simulations of the flow field inside the fan were carried out using FLUENT software corresponding to the experimental conditions. The influence of the tip clearance and eccentricity on the aerodynamic performance of the fan was revealed from the energy leakage perspective. Through theoretical and experimental analysis, we try to provide guidance on the design, installation and commissioning of fan tip clearance.

Evaluation of Acoustic Comfort and Sound Energy Transmission in a Yacht

After being neglected for a long time, in the last years, ships have been recognized and studied as sound emitters. The sound energy they generate impacts the outside, but it can also affect the indoor quality of life if the environments are not properly designed. In fact, acoustic comfort plays a pivotal role, particularly in recreational crafts. In the present work, room acoustics and acoustic camera measurements were performed, inside a 50 m length overall yacht, chosen as a case study in order to evaluate the acoustic comfort. The Italian classification procedure UNI 11367:2010 for buildings was applied, and results have been compared to other international comfort classes. However, all of these are based on prescription for standard buildings, and the present work highlights that they do not account for the effective ship’s acoustic issues: sound energy transfer from impacts over ceilings and sound energy leakage. While attention of shipbuilders in acoustic comfort is shown in the measured good reverberation times, the acoustic camera revealed sound energy leakages corresponding to hidden escape ways that have been poorly insulated. This compromises the standardized sound difference between contiguous compartments and also the thermal insulation, as leakage involves air passages. The present work attempts to evolve the classification procedure by also including, for the first time, the reverberation time, but future studies focused on finding correct standardized impact level noise for ship cases are needed. In fact, their values were very high and not comparable with those measured in actual buildings and for which reference values have been designed.

VLSI Architecture of DCT-Based Harmonic Wavelet Transform for Time–Frequency Analysis

The complex harmonic wavelet(CHW) is being used to directly compute frequency content with respect to time by employing discrete Fourier transform(DFT) and inverse discrete Fourier transform. However, DFT coefficients suffer severe leakage of energy from one band to another band of frequency. The leakage between bands is minimized by employing discrete cosine transform(DCT) in the harmonic wavelet transform, which leads to a better representation of the time-frequency spectrum. This paper introduces a new VLSI architecture for DCT-based harmonic wavelet for hardware implementation and prototyped on a commercially available virtex5 field-programmable gate array(xc5vlx110t). To validate the proposed implementation, its real-time captured results in the logic analyzer are verified with simulation results. The maximum operating frequency targeting the FPGA mentioned above device is reported as 114.34 MHz. The total On-Chip power of the above implementation is 1.102W, out of which 68mW is the dynamic power dissipation at a toggle rate of 12%. Finally, for the area utilization of the above implementation, its resource utilization targeting the above FPGA device is reported.

Field PMU Test and Calibration Method—PartII: Test Signal Identification Methods and FieldTest Applications

Synchrophasor measurement units (PMUs) provide synchronized measurement data for wide-area applications. To improve the effectiveness of synchrophasor-based applications, field PMUs must be tested to ensure their performance and data quality. In the companion paper (Part I), we proposed a field PMU test and calibration framework consisting of a PMU calibrator and analysis center. Part I presents the development and test of the PMU calibrator. This paper focuses on the analysis center and field test applications. First, the critical component of the analysis center is the signal identification module, for which the step and oscillation signal identification methods are proposed. Here, the performance evaluation criteria of PMU in these two cases are different from others. The methods include a step signal detection method based on singular value decomposition (SVD), which has the capability of weak step detection to account for energy leakage of the signal during the step process, and an oscillation signal identification method based on SVD and fast Fourier transform, which can accurately extract oscillation components that benefit from the adaptive threshold setting method. Second, the analysis center software is implemented based on identification results. By integrating the PMU calibrator in Part I with the analysis center in Part II, we can examine in depth the field PMU test applications in three test scenarios, including standard, playback, and field signal test. Results demonstrate the effectiveness and applicability of the proposed field PMU test methods from both Parts I and II.

Compressed Channel Estimation for Near-Field XL-MIMO Using Triple Parametric Decomposition

With the presence of the conventional angular-domain representation, the energy leakage effect is evident for the near-field extremely large-scale multiple-input-multiple-output (XL-MIMO) channel, which further leads to ambiguous channel power detection, significantly eroding channel estimation performance. To tackle this challenge, this paper proposes a novel Triple Parametric Decomposition (TPD) framework to facilitate compressed channel estimation in the XL-MIMO system. Specifically, we examine the case of a uniform planar array (UPA) with the geometry parameters involving a pair of azimuth-elevation angles and distances in an attempt to achieve independent decomposition by constructing their own covariance matrices. Then, by utilizing the on- and off-grid techniques, we obtain the sparse recovery of angles and distances information in the absence of energy leakage effect at reduced gridding complexity. Simulation results demonstrate that our proposed TPD achieves significant performance improvement over the state-of-the-art methods.

Real-Time Complex Dielectric Constant Measurement of Liquids Using Epsilon-Near-Zero Supercoupling Channels

This article proposes a device for real-time measurement of the complex dielectric constant of liquids at X-band. The device consists of a narrow waveguide channel operating at the cut-off frequency to achieve a large field enhancement based on Epsilon-Near-Zero (ENZ) supercoupling theory. A micro-3D-printed sample holder is placed inside the channel and connected to feeding tubes that are designed to prevent energy leakage from the channel. The field enhancement and confinement inside the channel creates a strong interaction with the liquids under test, thereby providing very sensitive measurements over a wide range of permittivities (approx. 1-65). Two variations of the device are fabricated. One that provides a higher accuracy and another that provides a higher sensitivity. A full-wave simulation based forward model is developed and optimized using a constrained Nelder-Mead simplex. An inversion is performed based on the optimized forward model to find the complex permittivity from the measured scattering parameters. Two sets of experiments are performed, one of static liquid mixtures and another of time-varying liquid mixtures. The static measurements are done with binary mixtures of ethanol-water and methanol-water. The time-varying measurements are done with ethanol-water-sugar mixtures and ethanol-water mixtures. The measured results are consistent between the two devices and are in very good agreement with the published literature over the entire range of dielectric constants tested.

Retracted] Analysis of VLF Wave Field Components and Characteristics Based on Finite Element Time‐Domain Method

Most traditional sound field calculation methods regard the seabed as the horizontal stratified liquid sea bottom and conduct simulation analysis based on the frequency domain. Hence, the generality of the above research methods is limited to varying degrees. To accurately clarify the propagation characteristics and mechanism of very low‐frequency (VLF, ≤100 Hz) sound waves in the shallow sea, a numerical calculation model is established using the finite element time‐domain method (FETD) based on the three‐dimensional cylindrical coordinate system. Using this model, the effects of sea‐bottom topographies and geoacoustic parameters on the composition and characteristics of VLF sound fields in the shallow sea and their corresponding mechanism are investigated through the comparative analysis of various numerical simulation examples. The simulation results demonstrate that the low‐frequency sound field in the full waveguide of the shallow sea is composed of normal mode waves in the seawater layer, Scholte waves at the liquid‐solid interface, and elastic waves at the sea bottom. Compared with the soft sea bottom, which has a more negligible elastic impedance, the hard sea bottom is more conducive to the long‐distance propagation of normal mode waves and the excitation of Scholte waves. The Scholte waves on the hard sea bottom are significantly stronger than those on the soft sea bottom. Compared with the horizontal sea bottom, the uphill topography enhances the sound energy leakage to the sea bottom. It is more favorable to receive Scholte waves at shallow depths, whereas the influence laws of downhill topography are the opposite.

Fourier Series Approximation of Vertical Walking Force-Time History through Frequentist and Bayesian Inference

The increased ambition of architects coupled with advancements in structural materials, as well as the rapidly increasing pressure on civil engineering sector to reduce embodied carbon, have resulted in longer spans and more slender pedestrian structures. These structures often have one or more low natural frequencies in the range of human walking accompanied with low modal masses and damping ratios. Thus, they are prone to excessive and often resonant vibrations that may compromise the serviceability limit state. Principally the uncertainty in prediction of the vibration serviceability limit state mainly originates from unreliable estimates of pedestrian loading. The key rationale behind this situation is the limited mathematical characterisation featuring in current design codes and guidelines pertinent to pedestrian-induced loading. The Fourier approximation is typically used to describe individual walking forces. Historically, such models are based on limited experimental data and deterministic mathematical descriptions. Current industry used load models featured in design codes and guidelines have been shown to incorporate inherent bias through limited intra-subject variation and poor correlation with real walking loads. This paper presents an improved Fourier model of vertical walking force across multiple harmonics, presented in a Bayesian and Frequentist statistical parameterisation. They are derived using the most comprehensive dataset to date, comprising of over ten hours of continuous vertical walking force signals. Dissimilar to previous Fourier models, the proposed models attempt to encapsulate the surround energy leakage around harmonic integers with a singular value. The proposed models provide consistently lower force amplitudes than any previous model and is shown to be more representative of real walking. The proposed model provides a closer approximation of a structural acceleration than any other similar Fourier-based model. The proposed model provides further evidence to combine the so called high and low frequency load models.