External Dc Bias Research Articles

A New Method to Synthesise the Sinusoidal Oscillator Based on Series Negative Resistance-Capacitance and its Implementation Using a Single Commercial IC, LT1228

An alternative method for synthesising the sinusoidal oscillator based on series negative resistance-capacitance is presented in this paper. The proposed topology is constructed with the series negative resistance-capacitance circuit connected in parallel with a grounded resistor and capacitor. To validate the proposed method, a new grounded series negative resistance-capacitance simulator is also proposed as a subcircuit for synthesising the sinusoidal oscillator. The series negative resistance-capacitance simulator is based on a commercially available integrated circuit (IC), LT1228. The equivalent negative resistance and equivalent negative capacitance can be adjusted electronically using an external DC bias current. The sinusoidal oscillator that is synthesised using the proposed method consists of a single LT1228, two capacitors, and three resistors. The frequency and the condition of the oscillation are orthogonally adjusted. Also, the condition of oscillation is electronically controlled. The amplitude of the sinusoidal waveform is adjustable. In addition, the output voltage node of the proposed oscillator has a low impedance, which allows it to connect to other circuits without using an additional buffer. Both PSPICE simulation and experiment are used to validate the proposed circuits.

Fabrication and DC-Bias Manipulation Frequency Characteristics of AlN-Based Piezoelectric Micromachined Ultrasonic Transducer.

Due to their excellent capabilities to generate and sense ultrasound signals in an efficient and well-controlled way at the microscale, piezoelectric micromechanical ultrasonic transducers (PMUTs) are being widely used in specific systems, such as medical imaging, biometric identification, and acoustic wireless communication systems. The ongoing demand for high-performance and adjustable PMUTs has inspired the idea of manipulating PMUTs by voltage. Here, PMUTs based on AlN thin films protected by a SiO2 layer of 200 nm were fabricated using a standard MEMS process with a resonant frequency of 505.94 kHz, a -6 dB bandwidth (BW) of 6.59 kHz, and an electromechanical coupling coefficient of 0.97%. A modification of 4.08 kHz for the resonant frequency and a bandwidth enlargement of 60.2% could be obtained when a DC bias voltage of -30 to 30 V was applied, corresponding to a maximum resonant frequency sensitivity of 83 Hz/V, which was attributed to the stress on the surface of the piezoelectric film induced by the external DC bias. These findings provide the possibility of receiving ultrasonic signals within a wider frequency range, which will play an important role in underwater three-dimensional imaging and nondestructive testing.

Dielectric response of high-κ hafnium oxide under finite electric field: nonlinearities from ab initio and experimental points of view.

Herein, we report on the dielectric-voltage nonlinearities under a constant electric field in metal insulator metal (MIM) capacitor-based hafnium oxide (HfO2) with respect to the frequency range. Via the Schottky emission mechanism obtained from the current-voltage characteristic (I-V), we calculated the optical dielectric constant εr,opt for different external DC bias values. The extracted εr,opt revealed a quadratic dependence on the applied external field. This confirmed that such dependence is a common feature of high-κ oxides in the low and high frequency ranges. The results were correlated with the ab initio calculations using the finite field (FF) method as implemented in the CRYSTAL 17 code. Good agreement between the results from the FF method, I-V plots, as well as the UV-visible spectrometry is observed. To assess any change in the dielectric constant upon the application of an external electric field, several parameters such as exchange-correlation functional, basis sets (BSs), as well as supercell expansion factor (N) were tested. The corresponding parameters have a great influence on the macroscopic electron density and voltage along the field direction and thus on the optical response. For N > 2 and rich basis sets, the hybrid functional B3LYP revealed good agreement with the experimental results as compared to other Hamiltonian's forms such as LDA, PW-GGA and HF.

Nonlinear Properties of an Inhomogeneous Diode Structure in a Strong Microwave Field

Results of experimental investigation of detection (rectification) of high power X-band microwave signal in diodes of various design (semiconductor p-n-junction, point-contact, Schottky, Metal-Isolator-Metal—MIM) are reported. The maximum of the detected direct voltage V vs. power P of microwave signal and subsequent polarity reversal, previously found in MIM diodes in the optical and microwave bands, have found to be characteristic of all investigated diodes as well. After the reversal of polarity, this dependence comes linear, and the sign of the voltage corresponds to thermoEMF. In some diodes, the hysteresis on V(P) was observed. All 5 types of V(P) of MIM diodes (have made from different pairs of metals), reported earlier, were reproduced on same p-n-junction diode by variable external DC bias. These results joined with abnormal frequency cutoff forced to suggest that there is an unknown mechanism for direct flow of charge carriers (and for generate direct current) in the high-frequency electrical field, which differs from the conventional rectification.

A linearly/electronically controllable high gain VDGA and its applications

Since the transconductance gains of an active building block namely voltage differencing gain amplifier (VDGA) is directly proportional to nonlinear (square root) function of external DC bias currents, affecting the narrow range tunability and low transconductance gains. This article aims to introduce a high gain VDGA by using CMOS current squaring circuits biasing in each transconductance cell. It offers high transconductance gains, wide range of tunability, linearity of controllability, larger input voltage range and nearly infinite input impedance. The proposed circuit was designed using a 0.18 µm CMOS transistors technology. The test was performed using PSpice program, it is consistent with the theoretical expectation. The total power consumption is 2.9 mW at ±1.5 V power supply. Even its power consumption is more than about 3 times of their previously proposed VDGAs, the figure of merit (FOM) of the proposed VDGA is much better than that of the previously proposed VDGAs (about 10 times). Additionally, the applications of the proposed VDGA as a capacitance multiplier, current multiplier/divider, summing amplifier, independently/electronically tunable multifunction filter, precision half-wave and full-wave rectifiers are included to insist the workability of the proposed VDGA.

Design and Implementation of Graphene-Based Tunable Microwave Filter for THz Applications.

A reconfigurable Substrate-Integrated Waveguide (SIW) filter operating in the THz region was designed in this work. Two SIW resonators were coupled through a magnetic iris to form a second-order filter with a double-layer substrate. The first substrate was silicon of permittivity 11.9; on top of it, silicon dioxide of permittivity 3.9 was placed. The ground and upper plane were composed of gold plates. Graphene material was then used for the tunability of the filter. A thin graphene sheet was sandwiched between the silicon dioxide substrate and the upper gold plate. An external DC bias voltage was then applied to change the chemical potential of graphene, which, in turn, managed to change the operational center frequency of the filter within the range of 1.289 THz to 1.297 THz, which translated to a bandwidth range of 8 GHz. The second part of this work centered on changing the aspect ratio of the graphene patch to change the center frequency. It was observed that the frequency changed within the range of 1.2908 THz to 1.2929 THz, which gave a bandwidth of 2.1 GHz change.

Low-profile metasurface-based dual-band graphene patch nanoantenna

This paper proposes a graphene patch antenna for dual-band operation while maintaining a low profile. The antenna consists of the metasurface-based 4 x 4 AMC configuration and the square graphene patch driven through the aperture coupling. The fundamental TM10 mode of graphene patch excites the first resonance frequency, while the TM10 and antiphase TM20 modes of metasurface simultaneously excite the second wide frequency band. The first resonance frequency excited by the graphene patch can be reconfigured by varying the external DC bias voltage on the graphene patch. An equivalent circuit of antenna using lumped elements has also been proposed using a vector fitting algorithm. The proposed antenna with a profile height of 0.12λ0 (where λ0 is free space wavelength) at a center frequency of 1.14 THz achieves the gain from 7.06 dB to 10.4 dB in the first band and an average gain of 10 dB in the second band.

Negative Capacitance Phenomenon and Origin in Alkali Niobate Film with Self‐Assembled Lattice Faults

AbstractNegative capacitance (NC) is an important phenomenon both in terms of the underlying fundamental science and its potential device application value. Achieving NC with adequate tunability in a scalable and reliable way is highly demanded for industrial applications. Herein, an electric‐field‐induced NC phenomenon and inductance‐like behavior in alkali‐deficient potassium sodium niobate thin film with self‐assembled planar faults are demonstrated. Our in‐depth investigation with the help of atomic‐scale microscopy and high‐temperature dielectric, conductivity, and X‐ray studies revealed that the compensated electronic charge at the planar faults is localized as bound polarons which convert to free polarons at high temperature as well as by an increased electric field. The collective response of such polaronic charge along the planar faults under an oscillating electric field results in the observed NC phenomenon and inductance effect. Large NC values are obtained which can be tuned in terms of magnitude and operating frequency by controlling the concentration of the free polarons via external DC bias. This work underpins the unique feature of the defect architecture obtained in the alkali deficient KNN film and provides a novel material design strategy and fundamental framework to realize NC and related exotic phenomena in defect‐engineered oxide materials.

Novel Active-C Voltage-Mode Quadrature Oscillator Realization Employing CCCIIs

Acurrent controlled sinusoidal voltage-mode quadrature oscillator circuit is presentedherewhich has employed three second-generation current-controlled-conveyors (CCCIIs) and two grounded capacitors(GCs). The condition of oscillation (CO) and frequency of oscillation (FO) of the proposed circuit are uncoupled and can be electronically controllable through an external dc bias current of CCCII. Sensitivities of active and passive elements are very low and the voltage outputs which are in 90ophase difference have high output impedances. Moreover, if apply the input at terminal Y of CCCII-03 it behaves as biquad filter which produce the band-pass (BP) and low-pass (LP) responses instantaneously and it have high input impedance which is very useful in cascading. The PSPICE simulation resultsverify the workability of the oscillator and filter circuit.

Enhanced Pyroelectric Coefficient in Ferroelectric Lead Zirconium Titanate Thick Films for Thermal Energy Harvesting Applications

Due to increase in growth population and energy demand, energy harvesting technology has become a sensational topic of research community. Amongst all the available energy harvesting technologies (mechanical, magnetic, wind, hydrothermal), harvesting waste heat has gained a lot of interest because of its cost effectiveness and availability of significant thermal fluctuations in industrial processes as well as in nearby surroundings. Therefore, efforts have been made on harvesting thermal energy through pyroelectric devices. Such devices have huge range of applications in fire alarms, heat sensors, infrared detectors, thermal imaging, gas analysis and so on. In the present study, the pyroelectric Lead Zirconium Titanate (PZT) thick films grown using modified sol-gel approach have been used for pyroelectric energy conversion. The effect of annealing temperature (450 °C, 450 °C and 650 °C) on the growth of PZT films has been monitored by investigating their dielectric, ferroelectric and pyroelectric properties. An appreciable enhancement in saturation and remnant polarizations from 17μC cm−2 to 24μC cm−2 and 13μC cm−2 to 22 μC cm−2 has been obtained when annealed temperature is increased from 550 °C to 650 °C respectively. A visible change in dielectric constant is also observed from 207 to 325 from dielectric constant–frequency curves with very small change in dielectric losses from 0.06 to 0.10 with increase in the annealing temperature from 550 °C to 650 °C at 1 MHz. The pyro electric coefficient and figure of merit are found to increase from 25 × 10−3 Cm−2K−1 to 230 × 10−3 Cm−2K−1 (p) and from 2.2 m2C−1 to 20 m2C−1 for the optimized PZT thick film based pyroelectric device with increase in the external DC bias field from 0.5 V to 2.5 V. The enhanced results of pyroelectric coefficient and figure of merit achieved in the present work are good indication of electrical energy harvesting through pyroelectricity.

Inter-grain Li+ conduction in Sc and Y doped LATP compounds

Low value of grain boundary conductivity in Li-NASICON materials is an important limitation that needs to be overcome. Inter-grain conduction of Li + ions in Li1·3Al0.3-xScxTi1.7(PO4)3 (LASTP) and Li1·3Al0.3-xYxTi1.7(PO4)3 (LAYTP) (where x = 0.01 and 0.07) samples is investigated. The samples, prepared by solid state reaction method, were characterised by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. Electrochemical Impedance Spectroscopy (EIS) was performed in the frequency range of 20 MHz to 1 Hz, and temperature range of 20 °C–100 °C. The grain boundary impedance and capacitance was found to vary with an external dc bias voltage. Higher grain boundary conductivity was found for sample containing higher yttrium concentration. Effect of space charge on grain boundary conductivity is evaluated in light of two competing models.

Analytical model for miniaturized patch antenna on metaferrite-like substrate

In this study, a 2-D mathematical model of a high-directive microwave antenna with a miniaturized volume profile is developed analytically. The antenna is a rectangular patch antenna on a metaferrite substrate. The substrate is a parallelepiped-shaped dielectric matrix with periodically embedded thin cylindrical ferromagnetic inclusions of a circular cross section. It is assumed that the inclusions are fully or partially magnetized by an external DC bias magnetic field. It has been shown that the use of such a metamaterial substrate, instead of a dielectric one with the same values of permittivity and permeability, leads to a miniaturization of the volume profile of the antenna and an increase in its efficiency and power gain. The commercial electromagnetic software is used in the study to validate the proposed antenna model.

Investigation of the Carrier Movement through the Tunneling Junction in the InGaP/GaAs Dual Junction Solar Cell Using the Electrically and Optically Biased Photoreflectance Spectroscopy

For examining the carrier movements through tunnel junction, electrically and optically-biased photoreflectance spectroscopy (EBPR and OBPR) were used to investigate the internal electric field in the InGaP/GaAs dual junction solar cell at room temperature. At InGaP and GaAs, the strength of p-n junction electric fields (Fpn) was perturbed by the external DC bias voltage and CW light intensity for EBPR and OBPR experiments, respectively. Moreover, the Fpn was evaluated using the Fast Fourier Transform (FFT) of the Franz—Keldysh oscillation from PR spectra. In the EBPR, the electric field decreased by increasing the DC bias voltage, which also decreased the potential barrier. In OBPR, when incident CW light is absorbed by the top cell, the decrement of the Fpn in the GaAs cell indicates that the photogenerated carriers are accumulated near the p-n junction. Photogenerated carriers in InGaP can pass through the tunnel junction, and the PR results show the contribution of the modification of the electric field by the photogenerated carriers in each cell. We suggest that PR spectroscopy with optical-bias and electrical-bias could be analyzed using the information of the photogenerated carrier passed through the tunnel junction.

Broadband Electronically Scanned Reflectarray Antenna With Liquid Crystals

In this letter, an electronically beam scanning reflectarray antenna is implemented using nematic liquid crystals (LCs). By loading a tunable phase shifter with a delay line structure in the resonance unit, the phase shift is achieved by tuning the dielectric constant of the LCs with a fixed structure through an external dc bias voltage for each unit. In doing so, dynamically controlling the reflection phase of each independent unit is realized. The experimental results show that the plane reflectarray unit can obtain a phase shift exceeding 360° with good linearity, and the maximum reflection loss is 7 dB. Moreover, a 10×10 LC-based planar reflectarray is fabricated and measured, and the bias voltage is loaded by a 100 outputs field-programmable gate array voltage module. In the frequency range of 22.1-26.1 GHz, its 3 dB relative bandwidth is 16.7%, the maximum gain of the main lobe is 20.2 dBi, and the maximum scanning angle is ±45°. The results verify the 2-D scanning functionality and the feasibility of improving the bandwidth of planar reflectarray antenna using LCs.

An Autonomous Frequency Reconfigurable Antenna Using Slotline Open-Loop Resonators

This paper presents a slotline open-loop resonators based frequency reconfigurable antenna with autonomous switching of frequency bands. The dual-port slot antenna is designed to operate at 2.1 GHz when excited at port-1, and when port-2 is excited, the antenna can be reconfigured to operate at 2.85 GHz and 5.52 GHz, respectively. Port-1 is used to receive the control signal, which is converted to a DC signal using a rectifier. The rectified control signal is used to switch the operating frequency bands of the port-2. The proposed antenna configuration gives the flexibility of remote/wireless control of the operating frequency. The antenna prototype is fabricated and measured for observing the frequency switching at port-2. The measured results show that the antenna has been effectively switched from lower band frequency (2.8 GHz) to upper band frequency (5.41 GHz) when the PIN diode is ON. The proposed antenna in its final configuration can be potentially suitable for transmitter reconfigurable antenna without the need for external DC bias voltage.

Enhanced tunability and temperature-dependent dielectric characteristics at microwaves of K0.5Na0.5NbO3 thin films epitaxially grown on (100)MgO substrates

K0.5Na0.5NbO3 thin films were deposited by pulsed laser deposition on (100)MgO substrates for microwave device applications. A fine epitaxial growth of pure perovskite phase was evidenced by X-ray diffraction. Dielectric characterizations were performed from 1 to 40 GHz using coplanar microwave devices printed on the 500 nm-thick K0.5Na0.5NbO3 thin films. Dielectric permittivity εr = 355 and loss tangent tanδ = 0.35 at 10 GHz were retrieved without biasing. A comparison of the results with those retrieved from the resonant cavity method (to characterize as-deposited films) showed no deleterious influence neither from the device patterning nor the thin film-device interface. A frequency tunability up to 22% was measured under a moderate external DC bias electric field Ebias = 94 kV/cm. Temperature measurements from 20° to 240°C exhibited a permittivity increase up to εr = 975 coupled to a loss decrease tanδ = 0.25 at 10 GHz. According to such measurements, an orthorhombic-tetragonal phase transition was evidenced close to 220 °C with an increase of the frequency tunability up to 34%. Comparison of the properties of such films with those grown on R-plane sapphire substrates demonstrated the benefit brought by the epitaxial growth of K0.5Na0.5NbO3 films on (100) MgO.

Versatile Airy-Beam Generation Using a 1-Bit Coding Programmable Reflective Metasurface

The Airy beam, known to present particular unique features, such as diffraction-free, self-healing, and self-bending, has attracted considerable interest in recent years. Here, an electronically controlled reflective coding metasurface is exploited to generate and dynamically manipulate the Airy beam over a wide frequency band in the microwave regime. By judiciously controlling the external dc bias voltage applied to the programmable metasurface, two distinct control states, ``0'' and ``1'', are engineered as digital codes for \ensuremath{-}\ensuremath{\pi}/2 and +\ensuremath{\pi}/2 phase responses, respectively. The programmable binary-phase-coding metasurface enables the generation and active reshaping of the Airy beam to be numerically simulated and experimentally validated. Moreover, the metasurface allows the bandwidth limitation of passive counterparts to be overcome and is able to modulate electromagnetic waves over a broad frequency range, spanning from 9 to 12 GHz, to realize diffraction-free Airy beams.

Characterisation of tunable graphene antenna

Graphene is a unique material that can display tuning characteristics. This characteristic originates from its surface complex conductivity, which is controlled by a chemical potential. Most characteristics of tunable graphene antenna have been studied on Terahertz frequency range, thus making it difficult to be realised practically. Besides that, the standard antenna that uses switching components may have trouble during installation, and consume size as can be seen in the reconfigurable antenna. With the integration of this material, a tunable antenna based on graphene operating at microwave frequency range is proposed. The antenna was designed and fabricated at 15 GHz with a gate electrode placed behind it. They are connected to external DC bias during the measurement. The biasing is applied from 0 V to 30 V. The result shows that resonance frequency tuned about 20 MHz and reflection coefficient magnitude improved 1.24 dB. Following this, an analytical calculation on chemical potential was also derived for enhancing the graphene tunability. The count shows that at least 2.85 kV of the gate voltage is needed to vary the chemical potential and less than 0.26 µm of dielectric spacer thickness is suitable for tuning with a given condition, respectively.

Suppression of high-power microwave window breakdown by the sweeping-out-electron effect with an external dc bias electric field

To suppress microwave window breakdown, an external parallel dc bias electric field is applied to sweep out the electrons from the discharge zone. The development of microwave window breakdown under an external dc electric field is investigated using particle-in-cell and Monte Carlo collision simulation. The results show that the number of multipactor electrons decreases with the strength of the external unidirectional dc electric field when the size of the microwave window is finite. In addition, the threshold of breakdown is strongly influenced by the direction of the external bidirectional dc electric field. When the electric field is directed from the center to the edge of the microwave window, breakdown occurs more readily than in the absence of the electric field. However, when the electric field is directed toward the center of the microwave window, the discharge process starts at the edge of the window and develops to the center of the window. This is because a smaller density of electrons at the window edge results in a smaller gas pressure and the low gas pressure above the dielectric surface thus makes formation of the plasma more difficult. As a result, the early stage of breakdown is suppressed and the maximum transmitting power is enhanced.

Electronically-engineered metasurface for directional beaming of electromagnetic waves through a subwavelength aperture.

Controlling diffracted waves has attracted extensive research interests these last years particularly for the potential application of beaming functionality. In this paper, we propose to realize on-axis beaming of diffracted electromagnetic waves by using a phase- gradient metasurface. The structure is optimally designed in order to transform surface waves to propagating waves and to enhance transmission through a subwavelength aperture. Both numerical simulations and near-field measurements are performed at microwave frequencies to validate the proposed concept. Furthermore, the metasurface is frequency-tunable and can be controlled by an external DC bias voltage. Consequently, by adjusting the electromagnetic response of each unit cell through the bias voltage, different phase gradients can be tailored, enabling broadband operation spanning from 9 GHz to 12 GHz.