Time-domain Behavior Research Articles

Consensus of linear network systems diffusively coupled with exogenous disturbances: An ℋ∞ approach

AbstractThis paper addresses the consensus control problem in multi‐agent systems under the influence of diffusively coupled disturbances. Two different types of systems are considered regarding the homogeneity of the disturbance coupling parameters. The main goal is to derive conditions that guarantee the prescribed performance of the designed control system on disturbance attenuation. To estimate the disturbance attenuation performance of the controller, the norm of the transfer function from the redefined disturbance vector to the disagreement vector is measured. Then the sufficient conditions for the system to achieve consensus within the desired performance are derived in terms of linear matrix inequalities (LMI). Numerical examples of both one‐ and multi‐dimensional consensus control systems are provided to check the validity of the derived LMI feasibility test along with the illustration of consensus behavior in time domain.

A wearable low profile asymmetrical slotted ultra-wide band antenna for WBAN applications

In this article a low profile asymmetrical slotted Ultra-Wide Band (UWB) antenna is proposed for Wireless Body Area Networks (WBANs) applications. The antenna was fabricated using Printed Circuit Boards (PCBs). An improved radiation pattern was obtained with an optimized patch shape of the antenna that broadens the bandwidth and lowers the antenna’s profile. The proposed antenna is simulated in HFSS and CST Simulator, and the proposed antenna is fabricated on FR4 substrate with the reduced ground plane. In frequency ranges from 2.50 to 10.97 GHz simulation as well as measured results show that the reflection coefficient (S11) of the antenna is below − 10 dB and increased impedance bandwidth of 126%. The proposed antenna has desired radiation pattern and gain for wearable application. The wearable performance of proposed antenna on chest, leg, and the arms of the human body is analyzed with Specific Absorption Rate (SAR). The maximum value of the SAR is 0.785 W/Kg which is less than threshold value of 1.6 W/kg. The time-domain behavior of proposed antenna is investigated with the time domain parameters such as Group delay, Fidelity factor and Mean realized gain. The time domain results are evident for the proposed antenna is capable of pulse signal transmission and reception.

Extended RC Impedance and Relaxation Models for Dissipative Electrochemical Capacitors

Electrochemical capacitors are a class of energy devices in which complex mechanisms of accumulation and dissipation of electric energy take place when connected to a charging or discharging power system. Reliably modeling their frequency-domain and time-domain behaviors is crucial for their proper design and integration in engineering applications, knowing that electrochemical capacitors in general exhibit anomalous tendency that cannot be adequately captured with traditional integer-order-based models. In this study we first review some of the widely used fractional-oder models for the description of impedance and relaxation functions of dissipative resistive-capacitive system, namely the Cole-Cole, Davidson-Cole, and Havriliak-Negami models. We then propose and derive new q-deformed models based on modified evolution equations for the charge or voltage when the device is discharged into a parallel resistive load. We verify our results on anomalous spectral impedance response and time-domain relaxation data for voltage and charge obtained from a commercial supercapacitor.

A passive self-tuning vibration neutraliser using nonlinear coupling between the degrees of freedom

Vibration neutralisers are widely used to suppress vibration of a host structure subject to external excitation at a specific frequency. When attached to a structure, they create a notch filter in the frequency response, reducing the vibration levels considerably. An inherent limitation is related to the narrow frequency range in which they are effective. Over the years, there have been different attempts to make the vibration absorber more robust. These include using active and semi-active control strategies to change the tuning frequency, using piezoelectric elements with shunt circuits, electromagnetic actuators, servo motors, and even exploring nonlinear effects. In many cases, there is a need for an external power source to modify the characteristics of the system. This paper concerns a passive vibration neutraliser that can adapt automatically to one of two frequencies corresponding to the frequency of an external harmonic force. Importantly, it does this without the need for an external power source. The device consists of a beam-like neutraliser that is attached to the host structure at its centre through a roller bearing. The stiffness element is a rectangular beam that can rotate in the bearing, changing the stiffness it presents to the direction of excitation. The paper describes an experimental study into such a device, and an analytical model is proposed that qualitatively captures the time-domain behaviour of the experimental device. A possible mechanism by which the device self-tunes to either of the two frequencies of excitation is discussed. Supplementary material is also provided to show the device in operation.

Dual band‐notched ultra‐wideband antenna with T‐shape stub

An ultra-wideband (UWB) antenna with dual band-notched characteristics is proposed in this letter. The fabricated prototype of the proposed antenna has a compact size of 30 × 24 mm which operates at 3 to 14 GHz and attained dual notch-bands at 3.3 to 3.7 GHz and 5.15 to 5.825 GHz. The result shows that the proposed antenna is compact, easy to fabricate and provides good characteristics in radiation patterns and time-domain behaviours. The simulated and measured results displayed good agreement over the entire operating frequency band. The proposed antenna can be used for wideband frequency requirement systems like indoor positioning.

A dual-band CPW-fed miniature planar antenna for S-, C-, WiMAX, WLAN, UWB, and X-band applications

A miniature planar antenna is a vital component of any portable wireless communication device. The antenna in portable devices should provide wide/multiple operating bands to cover a good number of narrowband services as a multi-band antenna not only reduces the number of antennas but also lessens the system complexity, cost, and device size. To operate over S-, C-, WiMAX, WLAN, UWB, and X-communication bands, in this paper, a dual-band CPW-fed antenna is presented. The anticipated antenna is made up of a vertical bow-tie-shaped patch and two asymmetric ground planes and etched on the same side of the single-sided standard substrate material. To generate two distinct operating bands, an inverted L-shaped parasitic element is inserted within the modified U-shaped coplanar ground plane. The antenna achieved dual operating bands of 3.24–8.29 GHz and 9.12–11.25 GHz in measurement which helps the proposed antenna to cover S-, C-, WiMAX, WLAN, 4G LTE, 5G sub-6 GHz, UWB, and X-communication bands. In the two operating bands, the antenna realized a peak gain of 4.33 dBi, and 4.80 dBi, the maximum radiation efficiency of 86.6%, and 72.6%, and exhibits symmetric radiation patterns. In the operating bands, the antenna also exhibits good time-domain behavior which helps it to transmit the signal with minimum distortion.

Comprehensive experimental assessments of rheological models’ performance in elastography of soft tissues

Elastography researchers have utilized several rheological models to characterize soft tissue viscoelasticity over the past thirty years. Due to the frequency-dependent behavior of viscoelastic parameters as well as the different techniques and frequencies employed in various studies of soft tissues, rheological models have value in standardizing disparate techniques via explicit mathematical representations. However, the important question remains: which of the several available models should be considered for widespread adoption within a theoretical framework? We address this by evaluating the performance of three well established rheological models to characterize ex vivo bovine liver tissues: the Kelvin-Voigt (KV) model as a 2-parameter model, and the standard linear solid (SLS) and Kelvin-Voigt fractional derivative (KVFD) models as 3-parameter models. The assessments were based on the analysis of time domain behavior (using stress relaxation tests) and frequency domain behavior (by measuring shear wave speed (SWS) dispersion). SWS was measured over a wide range of frequency from 1 Hz to 1 kHz using three different tests: (i) harmonic shear tests using a rheometer, (ii) reverberant shear wave (RSW) ultrasound elastography scans, and (iii) RSW optical coherence elastography scans, with each test targeting a distinct frequency range. Our results demonstrated that the KVFD model produces the only mutually consistent rendering of time and frequency domain data for liver. Furthermore, it reduces to a 2-parameter model for liver (correspondingly to a 2-parameter “spring-pot” or power-law model for SWS dispersion) and provides the most accurate predictions of the material viscoelastic behavior in time (>98% accuracy) and frequency (>96% accuracy) domains. Statement of SignificanceRheological models are applied in quantifying tissues viscoelastic properties. This study is unique in presenting comprehensive assessments of rheological models:•We employed experimental data in both the frequency domain (shear wave speed (SWS) vs. frequency) and time domain (stress relaxation) to assess rheological models’ performances.•SWS were acquired over a wide frequency range, 1 Hz to 1 kHz, by three independent techniques.•Using the frequency domain analysis, we evaluated how well each model can predict measured time domain behaviors (and vice versa).•This presents wide-ranging experimental proofs as the most comprehensive study of its type in terms of the number of experiments, frequency range, and conjoined assessments of time and frequency domains behaviors, demonstrating the most appropriate rheological model for soft tissues.

Energy balance, efficiency and operational limits of the dynamo type flux pump

In rotating flux pumps, a rectified voltage, with non-zero DC component, is obtained at the terminals due to the combined effect of the distributed AC electromotive force, produced by one or more permanent magnets in circular motion and the non-linear resistivity of the superconductor. Overcritical currents are continuously induced in the tape during operation, giving rise to the DC voltage and producing, at the same time, dissipation. In this paper, the energy behavior of the flux pump is numerically investigated. It is shown that induced currents interact with the rotating magnet(s), producing a resistant torque that is little affected by the output current of the flux pump. Due to this interaction mechanism, a significant part of the mechanical power supplied to the rotor is converted into Joule heating within the tape. The paper also explores the operational limits of the flux pump, showing that the generator operation, involving an electric power delivered to the load combined with a mechanical power supplied to the rotor, can only be achieved in a restricted range of current and voltage at the terminals and that the maximum power transfer and efficiency are reached at the middle of the generator range. Under no conditions, the mechanical torque produced on the rotor can be reversed, reaching the motor mode involving an electric power absorbed at the terminals combined with a mechanical power produced on the rotor. A revised equivalent circuit comprising, besides the effective resistance reported in the literature, a further intrinsic resistance is proposed in the paper for taking all the dissipation mechanisms into account. It is shown that this equivalent circuit can predict the energization of an RL load both concerning the final steady values and the full time-domain behavior of the current (including ripples).

Time-domain model and optimization for single-axis kinetic energy harvesters driven by arbitrary non-harmonic excitation

Energy harvesting is employed to extend the life of battery-powered devices, however, demanding applications such as wildlife tracking collars, the operating conditions impose size and weight constraints. They also only provide non-harmonic mechanical motion, which renders much of the existing literature inapplicable, which focuses on harvesting energy from harmonic mechanical sources. As a solution, we propose an energy harvesting architecture that consists of variable number of evenly-spaced magnets, forming a fixed assembly that is free to move through a series of evenly-spaced coils, and is supported by a magnetic spring. We present an electromechanical model for this architecture, and evolutionary optimization process that finds the model parameters which describe the time-domain behaviour observed in ground truth measurements. The resulting model can predict the time-domain behaviour of the energy harvester for any configuration of the proposed architecture and for any mechanical excitation. We also propose an optimization process that, using the electromechanical model, optimizes the energy harvester configuration to maximize the power delivered to a resistive load. The resulting optimized harvester design is specific to the particular kind of non-harmonic mechanical excitation to which it will be exposed. To demonstrate the effectiveness of our proposed model and optimization procedure, we constructed four energy harvesters, each with different configurations, and compared their measured behaviour with that predicted by the model, given an excitation that approximates footstep-like motion. We show that the model predictions were consistently within 25% of the RMS load voltage. We then synthesize an optimal energy harvester using the proposed optimization process. The resulting optimal design was constructed and tested using the same footstep-like excitation, and delivered an average power of 1.526 mW to a 30Ωload. This is a 2.8-fold improvement over an unoptimized reference design. We conclude that our proposed behavioural model and optimization process allows the determination of energy harvester designs that are optimized for a non-harmonic and specific input excitation.

Switching Sequence Control 31-Level Asymmetric Cascaded of Reduced Switch Count Multilevel Inverter with Multi Carrier Pulse Width Modulation

Various pulse width modulation techniques, including as cascaded multilevel inverters (MLI), diode clamped multilevel inverters, and flying capacitor multilevel inverters, can be used to simply operate common inverters. Due to increased switching losses, current MLIs cannot reach high efficiency. Due to lower losses and THD than standard MLI topologies, the asymmetric cascaded multi-level H-bridge inverter architecture examined in this white paper employs fewer switches and more output voltage levels (Total Harmonic Distortion). The THD is less than the IEEE standard because of the suggested architecture. In this instance, phase difference (PD) multi-carrier PWM techniques are used to control the gate pulses using sinusoidal reference. Each switch receives a different pulse pattern thanks to a method of decimal-to-binary conversion. It is possible to utilise the suggested circuit for applications requiring moderate to high power, and it is quite simple to evaluate. Utilize the MATLAB/SIMULINK environment to simulate time-domain behaviour for the 31-level and 33-level multilevel inverter topologies.

An efficient method to model the time-domain behavior of viscoelastically damped systems based on an improved fractional derivative model

An efficient method to model the time-domain behavior of viscoelastically damped systems based on an improved fractional derivative model

Field-programmable gate arrays-based Morris-Lecar implementation using multiplierless digital approach and new divider-exponential modules

Simulation, modeling, and hardware implementation of different parts of central nervous system (CNS) are very attractive research areas in terms of neuromorphic engineering aspects. Considering the neuronal parts of the human brain, the hardware implementation of neural models of spiking neural networks should be evaluated from preparing a simple efficient model and optimal hardware implementation. In this paper, Morris-Lecar (ML) model as a biological neuronal model with nonlinear differential equations and hyperbolic functions is discussed. This original model with non-linear complex functions needs high-computational high-cost hardware implementation on Field-Programmable Gate Arrays (FPGA). This paper presents a new divider module and exponential term (2X) to provide low-cost and high-speed implementation of original ML called Division-Based ML (DBML). DBML model suggests simpler equations using division-based exponential terms, logical shifts and simple arithmetic operations. Thus, high-performance neuronal design is presented following original ML model in terms of time domain and different dynamic behaviors.

An Ultra-Wideband Vivaldi Antenna System for Long-Distance Electromagnetic Detection

Enlarging or reducing the antenna beam width of antennas can improve the positioning capability of detection systems. A miniaturized and easily fabricated ultra-wideband (UWB) antenna system for long-distance electromagnetic detection is proposed in this article. Two ultra-wideband Vivaldi antennae were designed. One was the transmitting antenna with a beam width of 90° or above, the other was a narrow beam antenna array with beam width less than 10°, as a receiving antenna. Both proposed antennae feature broadside gain diagrams with stable radiation patterns and wideband impedance matching in the frequency range between 2.5 GHz and 4 GHz. After detecting their frequency and time-domain behaviors, the detection system can achieve measurements covering a radius of 30 m.

Modeling and Simulation of Aquaculture Systems

In this work, models for aquaculture are developed with regard to their relevance in an automated recirculation system. The three subsystems fish, water, and feed are determined as modular components. A selection of relevant variables is determined. The relationships between feed, water quality, and fish growth are described on the basis of an initially qualitative description (causal network) and quantified using ODEs. The considered water treatment systems and control devices are used to describe the relationships between filtration, fresh water addition, and water quality. The numerical system model allows simulations of the overall system behavior in time domain including the full growth phase offish. As example, the conditions using rainbow trout are simulated in a recirculating system. Influences of different variables like water temperature, pH-value, or protein content in dependency of the fish feed variables are shown, as well as the influence of plant parameters. This allows a recording of water quality and also to monitor the optimal fish growth or well-being parameters. The developed model can be extended modularly and allows further considerations and analyses for the control of the plant volume flow or for carbon dioxide gassing.

Analysis of various soliton pulsation spectro-temporal dynamics in anomalous dispersion fiber laser

In this paper, we studied the effects of the output ratio and small-signal gain on soliton pulsation by modeling the anomalous dispersion carbon nanotube mode-locked fiber laser. Under different parameters, in addition to the conventional soliton pulsation, we also observed the soliton pulsation with obvious Kelly sideband and the soliton pulsation with soliton splitting. And we found the explosive-like soliton pulsation, which exhibits the time shift caused by soliton explosion. Specially, we observed the novel creeping vibrating soliton molecules that has creeping behavior in time-domain but vibrating behavior in spectral evolution. These findings can shed new insights into the soliton complex nonlinear behavior in dissipative systems.

Linking Time-Domain Vibration Behaviors to Spatial-Domain Propagating Waves in a Leaf-like Gradient-Index Phononic Crystal Lens

It is known that a propagating wave at a certain spatial point can be decomposed into plane waves propagating at different angles. In this work, by designing a gradient index phononic crystal lens (GRIN PCL) with transverse-continuous leaf-like unit cells, we theoretically and experimentally show that the spatial-domain propagating waves in finite periodic structures can be linked to their time-domain vibration behaviors. The full-field instantaneous focusing behaviors of Lamb waves in the proposed leaf-like GRIN PCL give an example of the wave-vibration linkage in finite periodic structures while allowing a certain complexity. The conclusion in this paper can help one skip iterative time-consuming finite element analysis (e.g., time-stepping solutions) to avoid possible numerical instabilities occurred in calculating transient wave field on practical finite metamaterials or phononic crystals having unit cells with complicated configurations.

Switching Sequence Control 31-Level Asymmetric Cascaded of Reduced Switch Count Multilevel Inverter with Multi Carrier Pulse Width Modulation

Various pulse width modulation techniques, including as cascaded multilevel inverters (MLI), diode clamped multilevel inverters, and flying capacitor multilevel inverters, can be used to simply operate common inverters. Due to increased switching losses, current MLIs cannot reach high efficiency. Due to lower losses and THD than standard MLI topologies, the asymmetric cascaded multi-level H-bridge inverter architecture examined in this white paper employs fewer switches and more output voltage levels (Total Harmonic Distortion). The THD is less than the IEEE standard because of the suggested architecture. In this instance, phase difference (PD) multi-carrier PWM techniques are used to control the gate pulses using sinusoidal reference. Each switch receives a different pulse pattern thanks to a method of decimal-to-binary conversion. It is possible to utilise the suggested circuit for applications requiring moderate to high power, and it is quite simple to evaluate. Utilize the MATLAB/SIMULINK environment to simulate time-domain behaviour for the 31-level and 33-level multilevel inverter topologies.

Time-Domain Circuit Modelling for Hybrid Supercapacitors

Classic circuit modeling for supercapacitors is limited in representing the strongly non-linear behavior of the hybrid supercapacitor technology. In this work, two novel modeling techniques suitable to represent the time-domain electrical behavior of a hybrid supercapacitor are presented. The first technique enhances a well-affirmed circuit model by introducing specific non-linearities. The second technique models the device through a black-box approach with a neural network. Both the modeling techniques are validated experimentally using a workbench to acquire data from a real hybrid supercapacitor. The proposed models, suitable for different supercapacitor technologies, achieve higher accuracy and generalization capabilities compared to those already presented in the literature. Both modeling techniques allow for an accurate representation of both short-time domain and steady-state simulations, providing a valuable asset in electrical designs featuring supercapacitors.

A bimodal burst energy distribution of a repeating fast radio burst source.

The event rate, energy distribution and time-domain behaviour of repeating fast radio bursts (FRBs) contain essential information regarding their physical nature and central engine, which are as yet unknown1,2. As the first precisely localized source, FRB 121102 (refs. 3-5) has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution6-8. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1,652 independent bursts with a peak burst rate of 122 h-1, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be approximately4.8 × 1037 erg at 1.25 GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allows sensitive periodicity searches between 1 ms and 1,000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavouring emission mechanisms with large energy requirements or contrived triggering conditions.

Power System Stabilizer Tuning Algorithm in a Multimachine System Based on S-Domain and Time Domain System Performance Measures

One of the main characteristics of power systems is keeping voltages within given limits, done by implementing fast automatic voltage regulators (AVR), which can raise generator voltage (i.e., excitation voltage) in a short time to ceiling voltage limits while simultaneously affecting the damping component of the synchronous generator electromagnetic torque. The efficient way to increase damping in the power system is to implement a power system stabilizer (PSS) in the excitation circuit of the synchronous generator. This paper proposes an enhanced algorithm for PSS tuning in the multimachine system. The algorithm is based on the analysis of system participation factors and the pole placement method while respecting the time domain behavior of the system after being subdued with a small disturbance. The observed time-domain outputs, namely active power, speed, and rotor angle of the synchronous generator, have been classified and validated with proposed weight functions based on the minimal square deviation between the initial values in a steady-state and all sampled values during the transitional process. The system weight function proposed in this algorithm comprises s-domain and time-domain indices and represents a novel approach for PSS tuning. The proposed algorithm performance is validated on IEEE 14-bus system with a detailed presentation of the results in a graphical and table form.