Independent Control Of Frequency Research Articles

Graphene‐Based Flexible Optically Transparent Dual‐Tunable Metasurface

AbstractDynamically tunable flexible metasurfaces with optical transparency are essentially useful in stealth, electromagnetic sensing, and camouflage while keeping continuous optical observation and communication. In this paper, a dual‐tunable graphene‐based metasurface is designed based on patterned graphene sandwich structures, showing independent dynamic control of reflection amplitude and resonance frequency, excellent optical transparency, and outstanding flexibility. Both the simulated and measured results demonstrate that the transition from dual band absorption at 12 and 24.8 GHz to broad band absorption from 10 to 25.7 GHz, and the absorption amplitude can be tuned between −5 and −15 dB on average in each case dynamically and independently by applying bias voltage to graphene layers. Lastly, the distributions of the induced electric field and surface currents, as well as an equivalent circuit model, are provided to illustrate the tunable electromagnetic absorption mechanism. The designed metasurface has potential applications that are speculated in the fields of electromagnetic tune and electromagnetic stealth.

Third-Order Quadrature Sinusoidal Oscillators Employing OTRAs with Independent Control of Oscillation Condition and Frequency of Oscillation

This communication presents two new voltage mode (VM) third-order quadrature sinusoidal oscillator (TOQSO) configurations employing three operational transresistance amplifiers (OTRAs), six resistors and three virtually grounded capacitors. The proposed circuits have independent control of condition of oscillation (CO) and frequency of oscillation (FO) utilizing the intrinsic current differencing property of the OTRA. The proposed TOQSOs have ideally zero output impedance, a feature suitable for easy cascadability. Nonideal and sensitivity analyses have been carried out and compared with those obtained from ideal analysis. The presented TOQSOs have been simulated using OTRAs implemented with macro model of off-the-shelf available AD844 ICs. Experimental results have also been included using OTRAs realized with commercially available AD844 CFOA ICs.

Feedback and Control of Linear Electromagnetic Actuators for Flapping Wing MAVs

We present a method for generating feedback and controlling multi-coil linear electromagnetic actuators for flapping wing systems. This has been achieved with a system capable of self-lifting, constructed using 3D-printed structures and miniaturised electromagnetic actuators with a combined weight of 3.07 g. Combining multiple magnets and coils into a single actuator with onboard feedback sensors has improved power densities upon existing linear electromagnetic systems present in the literature. The use of closed-loop control of the dynamics of the flapping profile allows for independent control of both flapping frequency and amplitude, which is differentiated from open-loop and resonance-based systems. This change will allow relatively precise control over the flapping dynamics of future systems while improving actuation efficiency.

Collaborative Control Framework of Multiple Electric Springs for Frequency Stabilization and Distribution Loss Reduction in Microgrids

Electric springs with capacitive energy storage (ES-1) have been proposed as a continuous demand-side management (DSM) technology to address the intermittency of renewables in power systems. The enabled smart load technology distinguishes itself from other DSM technologies with the unique function of achieving active power manipulation via reactive power control. However, the embedded coupled relationship between the active and reactive powers of the smart load usually results in the contradiction between grid frequency regulation and economic power flow with the conventional control scheme. To address this issue, a centralized control framework is proposed in this paper to achieve the collaborative operation of multiple ES-1s for frequency stabilization and economic power flow in microgrids. The proposed control framework exploits the power variations of the deferrable loads and enables the minimum reactive power flows in the microgrids, which leads to reduced storage requirement and minimum distribution loss. It is the first control framework to address the active and reactive power coupling issue of the ES-1 based smart loads, leading to the independent control of system frequency and optimal reactive power reallocation. The generalized and practical steady-state model of the ES-1 based smart load is investigated. The formulation for achieving the dual-objective optimization is established. Case studies based on experiments and simulations of a 110 V AC microgrid are performed to verify the effectiveness of the proposed control framework.

SLM-based interferometer for assessing the polychromatic neural transfer function of the eye.

A novel interferometric instrument for measuring neural transfer function (NTF) of the eye is presented. The device is based on a liquid-crystal-on-silicon spatial light modulator (SLM), which is used to create two laterally separated wavefronts in the pupil plane of the eye that interfere on the retina. The phase mask on the SLM, consisting of two diffraction gratings mixed in a checkerboard pattern and acting as a shearing interferometer, allows independent control of spatial frequency, orientation, and contrast of the fringes, as well as the field of view in a wide polychromatic spectrum. Coupled with a supercontinuum source, the system is able to produce achromatic fringes on the retina. The instrument was successfully tested in six normal subjects in four light conditions: polychromatic light and monochromatic blue, green and red light respectively (central wavelengths - 450, 550 and 650 nm). On average, the NTF in polychromatic light was approximately 20% higher than for green and red light, although not statistically significant due to high intersubject variability. Due to all-digital control of the interference fringes, the device is optically simple and virtually unsusceptible to vibrations, allowing its use in a non-laboratory environment. The study also contributes to color vision research, allowing to evaluate contrast sensitivity function without monochromatic or chromatic aberrations.

Synthesis of biquad filters using two VD-DIBAs with independent control of quality factor and natural frequency

This contribution presents the procedure to synthesis the voltage-mode active biquad filters using the active elements, voltage differencing differential input buffered amplifier (VD-DIBA). Two filtering categories, single input four output (SIFO) configuration and three input three output (TITO) configuration are proposed. Both proposed filters consist of two VD-DIBAs, two grounded capacitors and two resistors. All input voltage nodes for both biquad filters exhibit high impedance. The proposed SIFO biquad filter simultaneously provide four filtering responses, low pass (LP), band pass (BP), high pass (HP) and band reject (BR) functions, while the proposed TITO filter provides five filtering responses (including all pass (AP) function). The natural frequency (ω0) is linearly and electronically tuned without affecting the quality factor (Q). Also, the Q adjusting can be done without affecting the ω0. By modifying the proposed TITO biquad filter, the current controlled sinusoidal oscillator is achieved. The frequency of the generated sinewave is linearly tuned without affecting the condition of oscillation. The performances of the proposed circuits are simulated by Cadence software and the Spectre simulator of the Analog Design Environment using CMOS VD-DIBA in 0.18 μm TSMC CMOS technology and laboratory experiment using VD-DIBA constructed from commercially available ICs.

A Novel Buck Converter Based Three-Phase Inverter with Feedforward Supported Closed-Loop Control

This paper proposes a novel three-phase inverter based on buck converter and an efficient control method for the operation. The inverter circuit is comprised of moderate numbers of elements in terms of reducing design density and cost and improving operation capabilities. Unlike the similar studies in the literature, an efficient inverter control method that is feedforward supported closed-loop control is applied to the inverter to augment the response performance of the inverter output on different operation conditions. The inverter topology has a modular structure for each output phase that provides independent control of output voltage and frequency. Thus, the inverter can provide close to sine wave output voltage to supply balanced or unbalanced wye-connected three-phase loads or independent single-phase loads. Both simulation and experimental test studies are done for the proposed inverter. The inverter is designed for 1.5 kW, 0–100 Vp and 0–50 Hz operating rates. The test results prove both the theoretical and real-time accuracy of the proposed inverter for producing close to sine wave output voltages with less than 5% total harmonic distortion (THD) values on different working points.

On the design of OTA-C based field programmable analog arrays for continuous time low frequency applications

This work focuses on proposing FPAA architecture based on operational transconductance amplifier (OTA) as the basic block for low frequency continuous time signal processing. Two FPAA architectures are presented after a step by step development of the design structure. The architectures eliminate the use of switches for signal routing, instead they allow reconfigurability using a selecting network composed of OTAs. The proposed architectures demonstrate flexibility in architecture allowing the expansion of the basic structure. Both architectures allow the implementation of individual independent circuits with an option of cascading if required. Multiple filter circuits can be mapped on the FPAA with independent control and reconfigurability of gain, bandwidth, and notch frequency, thus allowing the use of the FPAA as a filter bank. As for the provided cascading feature, it allows the implementation of a system or a set of cascaded filters as desired by designer. Validation of proposed FPAA architecture and its characteristics is examined through simulation on LTspice using 90 nm CMOS technology with supply voltage of ±0.6 V. A single 4th-order lowpass filter is implemented first and then a combination of amplifier, notch filter and lowpass filter is implemented. Simulation results of the filters on proposed FPAA is compared to results acquired from simulation of the circuits alone (off-FPAA) showing excellent agreement between both results, hence confirming the proposed FPAA architecture.

Generation and application of sub-kilohertz oscillatory flows in microchannels

We present a user-friendly and versatile experimental technique that generates sub-kilohertz sinusoidal oscillatory flows within microchannels. The method involves the direct interfacing of microfluidic tubing with a loudspeaker diaphragm to generate oscillatory flow in microchannels with frequencies ranging from $10-1000$ Hz and amplitudes ranging from $10 - 600 \ \mu$m. The speaker-based apparatus allows independent control of frequency and amplitude that is unique to the speaker's manufacturing specifications. The performance of our technique is evaluated by Fourier spectral analysis of oscillatory motion of tracer particles, obtained by particle tracking velocimetry, as well as by comparing oscillatory flow profiles against theoretical benchmarks such as Stokes flow in a square channel and Stokes' second problem near a solid boundary. Applications that utilize both the oscillatory flow and the associated steady rectified flows are demonstrated in prototypical microfluidic configurations. These include inertial focusing and mixing at low Reynolds numbers, respectively.

Condition of phase angle for a new VDGA-based multiphase variable phase shift oscillator from 0<sup>o</sup> to 90<sup>o</sup>

A novel interesting type of variable phase angle voltage mode oscillator using modern building block has been presented in this paper. The new proposed oscillator configuration which uses four voltage differencing gain amplifier (VDGA) and two grounded capacitors can generate two sinusoidal signals that change out of phase by 0 to 90 degree. It has four floating and explicit voltage mode outputs where every two outputs have the same phase. The circuit is characterized by (i) the condition of phase angle of the oscillation (PO) (this concept is introduced for the first time in this paper) can be tuned electronically (ii) the gain of the floating outputs can be controlled independently (iii) it provides electronic control of condition of oscillation (CO) and independent control of frequency of oscillation (FO). The Total Harmonic Distortion (THD) of the output waveforms was obtained and the results were reasonability values (less than 4.5%). The non-ideal analysis and simulation results are investigated and confirmed the theoretical analysis based upon VDGAs implementable in 0.35μm CMOS technology. Simulation results include time response and frequency response outputs generated by using the PSPICE program.

Defining a vibrotactile toolkit for digital musical instruments: characterizing voice coil actuators, effects of loading, and equalization of the frequency response

The integration of vibrotactile feedback in digital music instruments (DMIs) is thought to improve the instrument’s response and make it more suitable for expert musical interactions. However, given the extreme requirements of musical performances, there is a need for solutions allowing for independent control of frequency and amplitude over a wide frequency bandwidth (40–1000 Hz) and low harmonic distortion, so that flexible and high-quality vibrotactile feedback can be displayed. In this paper, we evaluate cost-effective and portable solutions that meet these requirements. We first measure the magnitude–frequency and harmonic distortion characteristics of two vibrotactile actuators, where the harmonic distortion is quantified in the form of total harmonic distortion (THD). The magnitude–frequency and THD characteristics in two unloaded cases (actuator suspended freely or placed on a sandbag) are observed to be largely identical, with minor attenuation for actuators placed on the sandbag. Loading the actuator (when placed in a DMI) brings resonant features to its magnitude–frequency characteristics, increasing the output THD and imposing a dampening effect. To equalize the system’s frequency response, an autoregressive method that automatically estimates minimum-phase filter parameters is introduced, which by design, remains stable upon inversion A practical use of this method is demonstrated by implementing vibrotactile feedback in the poly vinyl chloride chassis of an unfinished DMI, the t-Stick. We finally compare the result of equalization by performing sinesweep measurements on the implementation and discuss the degree of equalization achieved using it.

A Novel Control Technique to Reduce the Effects of Torsional Interaction in Wind Turbine System

Though power electronic interface is prone to higher failure in wind turbine system (WTS), the failure downtime due to mechanical and generator malfunctioning is highest. Unforeseen electromechanical interactions caused due to dynamic load variation and transient torsional stress is a major cause for failures in the drive-train and generator in WTS. In the literature, several techniques, such as generator speed feedback, stress damping controller, and virtual inertia damping controller, have been proposed in regards to the problem stated. Though the techniques are promising, the factor of independent control of natural frequency and damping ratio has not been considered. This paper proposes speed difference damping controller (SDDC), which is a novel and improved control technique that decouples the two above-mentioned parameters and improves the electromechanical performance significantly, reducing the torsional vibration of the driveline. The controller gains are designed based on the derived two-inertia system model that is used to represent the first natural frequency torsional vibration. In this paper, theoretical analysis and control design of SDDC are articulately addressed. A detailed comparative study of SDDC is carried out with respect to the other proposed controllers. The modeled WTS is examined for the first torsional natural frequency under two extreme wind-input conditions, i.e., sinusoidal wind condition, wind impulse, and grid dynamic, and one real-wind test case scenario. For the experimental verification, a multimass test rig operating at the critical speed and dynamic impulse load variation is analyzed in parts.

Exploring the limits of semiconductor-laser-based optical frequency combs.

We report a study on the performance limits of stabilized optical frequency combs from semiconductor mode-locked diode lasers. Operating characteristics such as the number of comb lines, comb tooth linewidth, the physical parameters that affect the independent control of pulse repetition rate and offset frequency, and the potential for self-stabilization, are explored.

Voltage Differencing Transconductance Amplifier-Based Quadrature Oscillator and Biquadratic Filter Realization with All Grounded Passive Elements

The work realizes the sinusoidal quadrature oscillator and biquadratic filter with the same configuration using merely two voltage differencing transconductance amplifiers (VDTAs) as active devices and one grounded resistor and two grounded capacitor as passive elements. Performing the quadrature oscillator, the realized circuit is capable of producing two quadrature voltage outputs with almost equal amplitudes, and an independent electronic control of oscillation condition and oscillation frequency. Operating in voltage-mode biquadratic filter, the circuit can simultaneously generate the bandpass and lowpass filtering functions without any matching constraints. The natural angular frequency and the quality factor of the filter are independently and electronically adjustable. The effects of the VDTA non-idealities are also investigated in detail. Simulation results with TSMC 0.25 μm CMOS technology validate both working functions of the proposed circuit.

RF Wide-Band Bandpass Filter With Dynamic In-Band Multi-Interference Suppression Capability

A class of RF multi-functional bandpass filter with multiple frequency-reconfigurable rejected bands that are embedded into its broad transmission frequency range is reported. This filter concept exploits an original tunable multi-band quasi-bandstop section as constituent block. In this manner, unprecedented levels of spectral adaptivity are obtained for its in-band notches. Among them: 1) independent control of center frequency and rejection level; 2) notch-combination capability to conform wider rejected bands and make their number dynamically selectable; and 3) generation of dual-band bandpass responses with adjustable bandwidth and inter-band transmission zeros. This results in controllable in-band stopbands with reconfigurable bandwidth, attenuation level, and filtering-profile type. The devised filter architecture, which is appropriate for dynamic multi-interference mitigation in broad-band RF receivers, is scalable to any number of arbitrary-order in-band notches. For proof-of-concept purposes, a UHF-band microstrip prototype with up to two tunable in-band second-order stopbands is manufactured and measured.

Electronically Controllable Quadrature Sinusoidal Oscillator Using VD-DIBAs

A new voltage-mode quadrature sinusoidal oscillator (QSO) using two voltage differencing-differential input buffered amplifiers (VD-DIBAs) and only three passive components (two capacitors and a resistor) is presented. The proposed QSO circuit offers advantages of independent electronic control of both oscillation frequency and condition of oscillation, availability of two quadrature voltage outputs and low active and passive sensitivities. SPICE simulation results have been included using 0.35 μm MIETEC technology to confirm the validity of the proposed QSO oscillator.

Rebuttal to ‘Fully-uncoupled independent control of frequency and condition of oscillation: A caution’

Based upon the experimental results of the two CFOA-based fully-uncoupled sinusoidal oscillators proposed earlier by Bhaskar-Gupta-Senani-Singh, recently Abuelma’atti and Khalifa issued a caution that the classification of this class of oscillators providing independent control of condition of oscillation (CO) and frequency of oscillation (FO) through separate elements, as fully-uncoupled, does not appear to be correct. In this communication, we present the results of a recheck of the experimental data of Abuelma’atti and Khalifa and show that their experimental results are not repeatable and in most of the cases, the oscillations do not even exist and hence, the measurement data as given by them is misleading. Furthermore, it is shown that the measured oscillation frequencies, as shown by Abuelma’atti and Khalifa in four tables, do not tally with those calculated from their own formula as well as the experimental results taken by us. This communication thus, refutes the claims made in the quoted paper of Abuelma’atti and Khalifa published in this journal earlier.

Micro grid control strategy of DFIG unit based on improved DC grid connected topology

Aiming to the application of the DFIG connected to DC-Microgrids, an improved topology for the DFIG connected to DC-Microgrids is taken into account in this thesis. The stator side loses the support of voltage and frequency of AC point of common coupling bus. A novel control method suitable to the stator side converter (SSC) and the rotor side converter (RSC) of the topology is proposed. The independent control of stator voltage and frequency, the decoupled control of power and variable speed constant frequency of DFIG are achieved in the doubly-fed induction generator connected to DC-Microgrids. which can enhance the capacity of active power transmission of DFIG during the voltage variation.

Single Active Element-Based Tunable Square/Triangular Wave Generator with Grounded Passive Components

This paper presents a novel circuit of tunable square/triangular wave generator based on single active element and grounded passive components. The structure of the proposed generator is simple as it consists of one multiple-output differential voltage current conveyor transconductance amplifier (MO-DVCCTA) as active element and one grounded resistor and one grounded capacitor as passive components. The proposed generator provides triangular wave in voltage mode and square wave in both voltage mode and current mode simultaneously. The proposed generator enjoys the features of availability of square wave in both current mode and voltage mode, electronically tunable duty cycle via DC current over a 93–7% range, electronically and independently adjustable DC level of voltage-mode square wave and triangular wave via an additional DC current, independent and electronic control of amplitude of current-mode square wave by bias current and independent tunability of oscillation frequency by grounded capacitor. Moreover, the operation of the proposed generator at 50% duty cycle exhibits the electronic and independent control of oscillation frequency via bias current also. As an additional feature, the proposed generator exhibits <1% nonlinearity up to a frequency of 123.9 kHz. The maximum temperature coefficient of oscillation frequency over a temperature range of 0–50 \({^{\circ }}\)C is found 185 ppm/\({^{\circ }}\)C which is quite good in view of temperature stability of the oscillation frequency. The prototype of MO-DVCCTA based on commercial ICs has been used in the realization of circuit of the proposed generator. The PSPICE simulation results and experimental results are given to validate the proposed generator.

A New Voltage-Mode Universal Biquadratic Filter Using Single UVC

The paper presents a new universal biquadratic filter using single universal voltage conveyor (UVC), two resistors and two capacitors. The offered structure has three inputs and one output and can realise all the five basic biquadratic filters: high-pass (HP), low-pass (LP), band-reject (BR), band-pass (BP) and all-pass (AP) from the same circuit topology. The proposed universal filter also provides following advantageous features, not available simultaneously in any UVC based universal biquadratic filter so far: (i) low active and passive sensitivities, (ii) independent control of natural frequency (ω0) and bandwidth (BW) and (iii) no requirement of any component matching condition and inversion of input signal(s) (as needed in most of the earlier reported structures). The workability of proposed structure has been presented by SPICE (Version 16.5) simulation using 0.18 μm TSMC technology.