Frequency Of AC Signal Research Articles

Design of Bi-Directional Transmission Gate Driver in Amorphous Silicon Technology for TFT-LCD Application

A novel bi-directional transmission gate driver circuit integrated by amorphous silicon thin film transistors (a-Si:H TFTs) has been proposed. In the proposed design, the noise suppression structure of the gate driver utilized the AC drive inverter to reduce the degradation of the pull down TFTs. The clock frequency of AC signal is 30 Hz, which could reduce dynamic power consumption of the circuit. In addition, the synchronous controlled method in this research could reduce the amount of device in gate driver.The simulated result shows the good output performance of the gate driver and match the circuit design. Figure 1

Design of Bi-Directional Transmission Gate Driver in Amorphous Silicon Technology for TFT-LCD Application

A novel bi-directional transmission gate driver circuit integrated by amorphous silicon thin film transistors (a-Si:H TFTs) has been proposed. In the proposed design, the noise suppression structure of the gate driver utilized the AC drive inverter to reduce the degradation of the pull down TFTs. The clock frequency of AC signal is 30 Hz, which could reduce dynamic power consumption of the circuit. In addition, the synchronous controlled method in this research could reduce the amount of device in gate driver.The simulated result shows the good output performance of the gate driver and match the circuit design.

Structural, morphological and electroluminescence studies of Zno:Co nanophosphor

The nanoparticles of zinc oxide (ZnO) doped with various concentrations of cobalt (Co) were synthesized by chemical precipitation method in the presence of capping agent polyvinylpyrrolidone (PVP). The effect of doping concentration on structural and morphological properties has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). Cell volume, bond length, texture coefficient, lattice constants and dislocation density are also studied. Here, we also compared the interplaner spacing and relative peak intensities from their standard values with different angles. Crystallite sizes have been calculated by Debye–Scherrer’s formula whose values are decreasing with increase in cobalt content up to 3 %. It has been seen that the growth orientation of the prepared ZnO nanorods was (101). The XRD analysis also ensures that ZnO has a hexagonal (wurtzite) crystal structure. The electroluminescence (EL) cells were prepared by placing pure and cobalt-doped ZnO nanoparticles between ITO-coated conducting glass plate and aluminium foil. Alternating voltage of various frequencies was applied, and EL brightness at different voltages was measured and corresponding current was also recorded. The voltage dependence of electroluminescence (EL) brightness of the ZnO:Co shows exponential increase. The linear voltage–current characteristic indicates ohmic nature. The EL brightness at a particular voltage is found to increase by increasing Co doping, but for higher percentage of Co the EL brightness is reduced. It is also seen that Co does not influence the threshold voltage. The brightness is also affected by increasing the frequency of AC signal.

Capacitance of the double electrical layer on the copper-group metals in molten alkali metal halides

The electrochemical impedance is measured to study the capacitance of the double electrical layer of metallic Au, Ag, and Cu as a function of potential and temperature in nine molten salts, namely, the chlorides, bromides, and iodides of sodium, potassium, and cesium. The C–E curve of a gold electrode has an additional minimum in the anodic branch. This minimum for silver is less pronounced and is only observed at low ac signal frequencies in cesium halides. The additional minimum is not detected for copper in any salt under study. This phenomenon is explained on the assumption that the adsorption of halide anions on a positively charged electrode surface has a predominantly chemical rather than an electrostatic character. The specific adsorption in this case is accompanied by charge transfer through the interface and the formation of an adsorbent–adsorbate covalent bond.

Frequency Dependence of Electrical Parameters of an Organic-Inorganic Hybrid Composite Based Humidity Sensor

The present study highlights the interdependence of ambient humidity levels on the electrical parameters of organic-inorganic hybrid composite based humidity sensor at varied AC frequencies of input signal. Starting from the bottom, the layer stack of the fabricated humidity sensor was 200-nm silver (Ag) thin film and 4 μm spun-coated PEPC+NiPC+Cu2O active layer. Silver thin films were deposited by thermal evaporator on well cleaned microscopic glass slides, which served as a substrate. Conventional optical lithography procedure was adapted to define pairs of silver-silver surface electrodes with two sorts of configurations, i.e., interdigitated and rectangular. Humidity-sensitive layers of organic-inorganic composite were then spun-cast upon the channel between the silver electrodes. The changes in relative humidity levels induced variation in capacitance and impedance of the sensors. These variations in electrical parameters of sensors were also found to be highly dependent upon frequency of input AC signal. Our findings reveal that the organic-inorganic composite shows higher humidity sensitivity at smaller orders of frequency. This finding is in accordance with the established fact that organic semiconductors-based devices are not applicable for high frequency applications due to their lower charge carrier mobility values. Two distinct geometries of semiconducting medium between the silver electrodes were investigated to optimize the sensing parameters of the humidity sensor. Furthermore, the effect of temperature change on the resistance of organic composite has also been studied.

Parameter Identification Method for Lithium-Ion Battery Model with Multi Frequency AC Signal Injection

Parameter Identification Method for Lithium-Ion Battery Model with Multi Frequency AC Signal Injection

Design and characterization of a passive, disposable wireless AC-electroosmotic lab-on-a-film for particle and fluid manipulation

A wirelessly powered and controlled biased-AC electroosmotic (biased-ACEO) lab-on-a-film (LOF) is presented here for particle and fluid manipulation. Amplitude modulation (AM) and inductive coupling are used for wireless transmission of low frequency signals required for excitation of biased-ACEO effects employed by the LOF for microfluidic functions. The LOF consists of a receiving coil (for receiving inductively transmitted high frequency signals), surface mounted devices (for recovering a low frequency AC signal) and an array of interdigitated electrodes (IDE, for excitation of biased-ACEO effects). Unlike existing wireless lab-on-a-chip devices that have cumbersome set-ups, require high voltages and perform only one microfluidic function, the presented LOF has a compact and flexible structure, works at very low voltage ranges, and can perform several microfluidic operations corresponding to a wirelessly-controlled voltage. When the level of the demodulated signal over the IDE is about 0.7V, the IDE performs particle enrichment over designated electrodes. The IDE functions as an active mixer at about 2V; and as a pump when the voltage reaches 3V. The LOF is prototyped rapidly on a flexible substrate at low cost using inexpensive benchtop equipment with an overall dimension of 10×20mm2. Though the electrode definition is limited to micro-scales, the LOF prototype has successfully demonstrated desired microfluidic functions. In addition to inductive transmission of low frequency signals, the printed circuit board-based LOF device offers a low cost and effective solution for using small, flexible microfluidic systems in nontraditional clinical diagnostic tools, disposable devices and heath care settings.

Calibration procedure for secular frequency scanning in ion trap mass spectrometers.

Mass spectra can be recorded using ion traps by scanning the frequency of an alternating current (ac) signal that corresponds to the secular frequency of a trapped ion. There is a considerable simplification in the instrumentation needed to perform such a scan compared with conventional scans of the radiofrequency (rf) amplitude. However, mass calibration is difficult. An algorithm that can be used to achieve mass calibration is investigated and the factors that affect ion mass assignments are discussed. Time domain data, recorded using a commercial benchtop linear ion trap mass spectrometer, are converted to the m/z domain using ion Mathieu parameter qu values which are derived from the dimensionless frequency parameter βu expressed as a continuing fraction in terms of qu . The relationship between the operating parameters of an ideal ion trap and the ion m/z ratio is derived from the Mathieu equations and expressed as an algorithm which through successive approximations yields the Mathieu qu value and hence m/z values and peak widths. The predictions of the algorithm are tested against experiment by sweeping the frequency of a small supplementary ac signal so as to cause mass-selective ejection of trapped ions. Calibration accuracy is always better than 0.1%, often much better. Peak widths correspond to a mass resolution of 250 to 500 in the m/z 100-1800 range in secular frequency scans. A simple, effective method of calibration of mass spectra recorded using secular frequency scans is achieved. The effects of rf amplitude, scan rate, and ac amplitude on calibration parameters are shown using LTQ linear ion trap data. Corrections for differences in ion mass must be made for accurate calibration, and this is easily incorporated into the calibration procedure. Copyright © 2016 John Wiley & Sons, Ltd.

Alternating electric field actuated oscillating behavior of liquid metal and its application

As a class of newly emerging functional material, Gallium based liquid metals have attracted increasing attentions in many fields, such as chip cooling, printed electronics and microfluidics, etc. Particularly, the motion control of liquid metal droplet has been recently tried for its importance in microelectromechanical system (MEMS), microfluidics and potential use in micro-machine or reconfigurable soft robot. This paper is dedicated to explore the motion behavior of liquid metal droplet under AC electric field. The quickly induced oscillation phenomena of liquid metal droplet and surrounding electrolyte solution were observed and the major factors to influence such behaviors are theoretically interpreted and experimentally investigated, including the size of the liquid metal droplet, electrode voltage, electrolyte solution concentration and AC signal frequency etc. Moreover, some typical features to distinguish AC filed actuation with DC field are observed, such as intensive fluid waving induced by the resonance stimulation, and the efficient inhibition of solution electrolysis. Finally, two important applications of adopting AC induced surface oscillation of liquid metal droplet to develop solution mixer as well as fluidic pump were demonstrated which successfully avoid gas generation inside electrolyte environment. The bulk oscillation effects of liquid metal as clarified here could be very useful in a variety of areas such as solution disturbance and mixing, and fluid oscillator or pump etc.

High Frequency Sensing with Enhanced Sensitivity in Graphene Nanogrid FET Immunosensor

:-FET based charge detection sensing mechanism with various nanostructures has many advantages like label free detection, femtomolar sensitivity and compatibility with electronic interface. However detecting charges in high ionic strength solution is a challenge due to the inherent problem of ionic screening beyond the Debye length.To overcome this effect, high frequency signal has been applied in single walled carbon nanotube structures which has enabled detection of biotin in presence of 100mM buffer solution [1]. But the limit of detection achieved is not satisfactory. In this work we superimpose a high frequency ac signal in the range of 100KHz to 10MHz across the drain and source terminal in a graphene nanogrid structure and applied it for detection of IgG-protein A binding in sub femtomolar regime. The graphene nanogrid structure has been developed on a nanoporous silicon oxide template as shown in Fig.1 and is an interconnected grid structure of bilayer reduced graphene oxide(RGO) which is composed of long and narrow strips alternating with series combination of short and narrow strips on planar regions and within pores.The long and short strips are interconnected during the deposition stage and hence the structure is expected to have fewer edges. Such a structure is expected to possess certain advantages in addition to the improved binding efficiency of the biomolecules due to large surface area to volume ratio. Firstly, in the nanopores, the biomolecules usually reside within a distance shorter than the original pore radius which statistically raises the charge transfer probability between the biomolecules and the surface even at high ionic strength of buffer. As a consequence, the heterogeneous charge transfer gets facilitated and the electrode potential reaches equilibrium faster for a given electrochemical system [2]. Secondly, such a graphene nanostructure has a size dependent effective energy gap which increases the transconductance of the device [3]. Due to the absence of edges, the conductance of the fabricated smooth nanogrid structure will be contributed by every section of the device and hence all the antigen molecules that get captured at any location contribute towards the change in conductance. Also there is a probable localization effect of the charge modulation after antigen capture within the corresponding quantum dots, which can result in an enhanced change of the overall carrier transport. Fabrication of the nanoporous silicon oxide template has been carried out by anodic etching of p-type silicon<100> wafers of 10–20 Ω-cm resistivity in a double pond electrochemical bath for 30 minute using a constant current density of 2.35 mA/cm2 with an electrolyte mixture of 48% hydrofluoric acid and dimethyl sulfoxide in the ratio of 1:9 by volume. The nanopores formed are of about 30nm thickness and 100 nm length. The silicon substrates have been oxidized for subsequent graphene deposition. Graphene has been deposited by electrophoretic method[4] and after that antibody has been immobilized through poly-l-lysine (PLL). Raman spectroscopic measurements have been performed for characterization of deposited graphene[Fig:2] and the spectra of the graphene shows three Raman bands at 1195,1590 and 2670 cm-1that assigned to the well-documented D,G, and 2D bands respectively in RGO. The bilayer thickness has been confirmed by the presence of a symmetric 2D band and 2D/G intensity ratio of around 1.4. The two lateral electrodes used for RGO deposition act as the drain and source electrodes. Graphene based FET has been realized with a platinum top gate electrode suspended in buffer. Protein A has been selected as the antigen and its different concentration has been listed using 100mM buffer in the range of 100KHz to 10MHz. An ac voltage of amplitude 20 mV has been fed between the drain-source terminal. The gate potential has been fixed at 0.2 V. It has been observed [Fig:3] that the drain current (Id ) decreases with frequency for 100mM which may be attributed to the slow decay of the surface potential resulting in effective increase of the Debye length and hence the capacitive impedance. We further plotted the sensitivity [Fig.:4], calculated as the fractional change in Id before and after Protein A attachment. A peak in sensitivity has been observed at a frequency of around 8MHz which corresponds to the optimum interaction of the antigen molecules with the graphene nanostructure. The intrinsic advantages of the graphene nanogrids(as discussed above) enable detection down to 0.1 fg/ml antigen in a high ionic strength buffer which has significant impact in point-of care applications. Figure 1

Features of Barrier Capacitance of Micropixel Avalanche Photodiodes at Different Frequencies

There has been investigated the capacitance of silicon micro pixel avalanche photodiodes (MAPD 3N) with deeply buried pixels under the effect of weak AC signal of different frequency (from 10 kHz to 1 MHz). A decreasing of the barrier capacitance with an increasing of AC signal frequency has been observed when small DC bias voltage (0-3 V) is applied to the structure. With the rise of voltage the observed dependence weakens and further saturates. It is established that capacity behavior like this within small voltage is referred to the peculiarity of MAPD structure under the investigation: presence of matrix of n + -regions between two epitaxial layers of p-type conductivity results in the appearance of some effective resistance between these layers connected in series with the measured capacity depending on AC signal frequency. The calculated values of ionized acceptor concentration from the slope of the dependence C -2 (Ubias) in epitaxial layer are: NA1 = (2.4 ±0.3)∙10 20 m -3 for Ubias up to 3 V, NA2 = (1.08±0.05)∙10 21 m -3 for Ubias from 3 to 10 V and NA3 = (2.13±0.27)∙ 10 21 m -3 for Ubias from 10 to 20 V respectively.

Characterization of interface defects in ALD Al2O3/p-GaSb MOS capacitors using admittance measurements in range from kHz to GHz

Atomic layer deposited (ALD) Al2O3/p-type GaSb Metal–Oxide–Semiconductor (MOS) capacitors are studied with capacitance–voltage (C–V) and conductance–voltage (G–V) measurements using AC signal frequencies covering the range from kHz to GHz. The potential and limitations of the measurements at GHz frequencies for oxide and interface defect characterization are described. The effect of bulk oxide traps in communication with the GaSb valence band via hole tunneling is highlighted. Modeling indicates that the C–V and G–V frequency dispersions observed in the accumulation, flat-band and depletion regions of the Al2O3/p-GaSb MOS capacitors are due to combined contributions of bulk-oxide traps and interface traps.

Study of structural, morphological, optical and electroluminescent properties of undoped ZnO nanorods grown by a simple chemical precipitation

AbstractIn this work, zinc oxide (ZnO) nanorods were obtained by a simple chemical precipitation method in the presence of capping agent: polyvinyl pyrrolidone (PVP) at room temperature. X-ray diffraction (XRD) result indicates that the synthesized undoped ZnO nanorods have hexagonal wurtzite structure without any impurities. It has been observed that the growth direction of the prepared ZnO nanorods is [1 0 1]. XRD analysis revealed that the nanorods have the crystallite size of 49 nm. Crystallite size is calculated by Debye-Scherrer formula and lattice strain is calculated by Williomson-Hall equation. Cell volume, Lorentz factor, Lorentz polarization factor, bond length, texture coefficient, lattice constants and dislocation density have also been studied. We also compared the interplanar spacings and relative peak intensities with their standard values at different angles. The scanning electron microscope (SEM) images confirmed the size and shape of these nanorods. It has been found that the diameter of the nanorods ranges from 1.52 μm to 1.61 μm and the length is about 4.89 μm. It has also been observed that at room temperature ultraviolet visible (UV-Vis) absorption band is around 355 nm (blue shifted as compared to the bulk). The average particle size has also been calculated by mathematical model of effective mass approximation equation, using UV-Vis absorption peak. Finally, the bandgap has been calculated using UV-absorption peak. Electroluminescence (EL) studies show that emission of light is possible at very small threshold voltage and it increases rapidly with increasing applied voltage. It is seen that smaller ZnO nanoparticles give higher electroluminescence brightness starting at lower threshold voltage. The brightness is also affected by increasing the frequency of AC signal.

Spurious Harmonic Response of Multipulse Quantum Sensing Sequences

Multipulse sequences based on Carr-Purcell decoupling are frequently used for narrow-band signal detection in single spin magnetometry. We have analyzed the behavior of multipulse sensing sequences under real-world conditions, including finite pulse durations and the presence of detunings. We find that these non-idealities introduce harmonics to the filter function, allowing additional frequencies to pass the filter. In particular, we find that the XY family of sequences can generate signals at the 2fac, 4fac and 8fac harmonics and their odd subharmonics, where fac is the ac signal frequency. Consideration of the harmonic response is especially important for diamond-based nuclear spin sensing where the NMR frequency is used to identify the nuclear spin species, as it leads to ambiguities when several isotopes are present.

Archaeal Tetraether Free Standing Lipid Membranes in a PDMS and PCB based Fluidic Platform

The polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius contains exclusively bipolar tetraether lipids, which are able to form extraordinarily stable vesicular membranes against a number of chemical, physical and mechanical stressors. In this study, we demonstrated that PLFE can also form free-standing “planar” membranes on micro-pores (∼100 micrometer) of polydimethylsiloxane (PDMS) thin films embedded in printed circuit board (PCB)-based fluidics. Using electrochemical impedance spectroscopy (EIS), we found that the dielectric properties of PLFE planar membranes suspended on the PDMS films are distinctly different from those obtained from diester lipid and triblock copolymer membranes. In addition to resistance (R) and capacitance (C) that were seen in all the membranes examined, PLFE planar membranes showed an inductance (L) component. Furthermore, PLFE planar membranes displayed a relatively large membrane resistance, suggesting that, among the membranes examined, PLFE planar membrane would be a better matrix for studying channel proteins and transmembrane events. PLFE planar membranes also exhibited a sharp decrease in phase angle with the frequency of the input AC signal at ∼1 MHz, which could be utilized to develop sensors for monitoring PLFE membrane integrity in fluidics. Since the stability of free-standing planar lipid membranes increases with increasing membrane packing tightness and PLFE lipid membranes are more tightly packed than those made of diester lipids, PLFE free-standing planar membranes are expected to be considerably stable. All these salient features make PLFE planar membranes particularly attractive for model studies of channel proteins and transmembrane events and for high-throughput drug screening.

P-I-N Amorphous Silicon Light-Addressable Potentiometric Sensors for High-photovoltage Chemical Image

For higher photo signal of chemical image sensor, a new device structure of P-I-N amorphous silicon (a-Si) on ITO/glass is first applied in light-addressable potentiometric sensor (LAPS). Niobium oxide (NbOx) is used as pH sensing membrane. All processes of device are lower than 300oC, which are suitable for glass substrate. Based on photovoltage versus gate bias characteristics, calculated pH sensitivity and linearity between pH 2 to 10 is 40mV/pH and 99.4%, respectively. Compare to conventional intrinsic amorphous silicon structure, improvement on photocurrent, and spatial resolution are 50% and 15%, respectively. In the meantime, higher frequency of ac signal of laser up to 20kHz could be used for high speed scanning by means of red laser and analog micromirror scanning system.

Design, fabrication, and characterization of archaeal tetraether free-standing planar membranes in a PDMS- and PCB-based fluidic platform.

The polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius contains exclusively bipolar tetraether lipids, which are able to form extraordinarily stable vesicular membranes against a number of chemical, physical, and mechanical stressors. PLFE liposomes have thus been considered appealing biomaterials holding great promise for biotechnology applications such as drug delivery and biosensing. Here we demonstrated that PLFE can also form free-standing "planar" membranes on micropores (∼100 μm) of polydimethylsiloxane (PDMS) thin films embedded in printed circuit board (PCB)-based fluidics. To build this device, two novel approaches were employed: (i) an S1813 sacrificial layer was used to facilitate the fabrication of the PDMS thin film, and (ii) oxygen plasma treatment was utilized to conveniently bond the PDMS thin film to the PCB board and the PDMS fluidic chamber. Using electrochemical impedance spectroscopy, we found that the dielectric properties of PLFE planar membranes suspended on the PDMS films are distinctly different from those obtained from diester lipid and triblock copolymer membranes. In addition to resistance (R) and capacitance (C) that were commonly seen in all the membranes examined, PLFE planar membranes showed an inductance (L) component. Furthermore, PLFE planar membranes displayed a relatively large membrane resistance, suggesting that, among the membranes examined, PLFE planar membrane would be a better matrix for studying channel proteins and transmembrane events. PLFE planar membranes also exhibited a sharp decrease in phase angle with the frequency of the input AC signal at ∼1 MHz, which could be utilized to develop sensors for monitoring PLFE membrane integrity in fluidics. Since the stability of free-standing planar lipid membranes increases with increasing membrane packing tightness and PLFE lipid membranes are more tightly packed than those made of diester lipids, PLFE free-standing planar membranes are expected to be considerably stable. All these salient features make PLFE planar membranes particularly attractive for model studies of channel proteins and transmembrane events and for high-throughput drug screening and artificial photosynthesis. This work can be extended to nanopores of PDMS thin films in microfluidics and eventually aid in membrane-based new lab-on-a-chip applications.

Optimization of spin-torque switching using AC and DC pulses

We explore spin-torque induced magnetic reversal in magnetic tunnel junctions using combined AC and DC spin-current pulses. We calculate the optimal pulse times and current strengths for both AC and DC pulses as well as the optimal AC signal frequency, needed to minimize the Joule heat lost during the switching process. The results of this optimization are compared against numeric simulations. Finally, we show how this optimization leads to different dynamic regimes, where switching is optimized by either a purely AC or DC spin-current, or a combination AC/DC spin-current, depending on the anisotropy energies and the spin-current polarization.

A Single Chip Integrated Sol-Gel Thin Film LC Sensor for Measuring Moisture in ppm Level

A simple single chip integrated moisture sensor capable of wireless operation through inductive coupling has been proposed. The structure consists of planar inductor and parallel plate capacitor fabricated by sol-gel thin film of γ-Al2O3 (5 μm thick). The sensor chip is capable of measuring ppm level moisture in gaseous environment. The resonance frequency shift of the sensor in the presence of moisture excited by a high frequency ac signal is measured by impedance analyzer (4294A Agilent). The frequency sensitivity of the structure for a moisture range from 100 to 5000 ppm is nearly 119 Hz/ppm. The response and recovery times are 7 and 24 s, respectively. The experimental results show that the output is linear (4.2%), reproducible and stable. Device can be applied for wireless moisture measurement in ppm level.

Selective deposition of graphene sheets on a flexible substrate by a nonuniform electric field

This study reports on the precise positioning of high-quality graphene sheets on a flexible polyethylene naphthalate substrate using a dielectrophoretic (DEP) force. Positive DEP assembly is carried out using a 100 kHz frequency AC signal with a peak-to-peak voltage of 10 V. The presence and quality of the graphene flakes aligned around the prepatterned electrodes are characterized by scanning electron microscopy, optical microscopy, and micro-Raman spectroscopy. Current–voltage measurements were also used to evaluate the electrical properties of these flexible devices under varying compressive (−) and tensile (+) strain conditions up to ±0.6%, where the currents decreased with increasing strains.