Square-wave Frequency Research Articles

Impact of inflection points on the performance of resonator integrated optic gyro

Resonator integrated optic gyro (RIOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. Instead of square-wave frequency modulation and sine-wave phase modulation, triangle-wave phase modulation eliminates the pulse error in the serrodyne wave phase modulation and reduces the backscattering noise, and is widely applied in RIOG. However, the attributed to the inflection points in triangle modulation waveforms induce output random noise, which would degrade the performance of the RIOG. In this work, the influence of such fluctuations on the performance of RIOG is theoretically analyzed and simulated. By analyzing the frequency response of averaging filter and lock-in amplifier, Pectinate filter is proposed to suppress the random noise. The experiment results from the established RIOG experimental setup demonstrated that the random noise caused by discontinuous frequency-modulation is effectively eliminated and the gyro bias stability is greatly improved from 1.96 to 0.11°/s.

Determination of lead and cadmium in seawater using a vibrating silver amalgam microwire electrode

Silver amalgamated electrodes are a good substrate to determine lead (Pb) and cadmium (Cd) in seawater because they have properties similar to mercury but without the free mercury (Hg). Here a silver amalgamated microwire (SAM) electrode is optimised for the determination of Pb and Cd in coastal waters and uncontaminated ocean waters. The SAM was vibrated during the deposition step to increase the sensitivity, and electroanalytical parameters were optimised. The Hg coating required plating from a relatively concentrated (millimolar) solution, much greater (500×) than used for instance to coat glassy carbon electrodes. However, the coating on the ex situ amalgamated electrode was found to be stable and could be used for up to a week to determine trace levels of Pb in seawater of natural pH. The limit of detection square-wave ASV (50Hz) using the pre-plated SAM electrode was 8pM Pb using a 1-min plating time at pH 4.5. The limit of detection in pH 2 seawater was 4pM using a 5-min plating time, and it was 12pM using a 10-min plating time at natural pH in the presence of air, using a square-wave frequency of 700Hz. The vibrating SAM electrode was tested on the determination of Pb in reference seawater samples from the open Atlantic (at the 20pM level), Pacific, and used for a study of Pb in samples collected over 24h in Liverpool Bay (Irish Sea).

Facile electrochemical approach for the effective detection of guanine

An electrochemical sensor for the sensitive determination of guanine has been developed, which is based on the electrodeposition of a nanostructured platinum thin film on a glassy carbon electrode. The effects of the electrodeposition time of the platinum thin film, pH, square-wave frequency and electroactive interferents on the voltammetric response of the sensor were evaluated. The optimized sensor exhibited excellent performance for the detection of guanine with a high sensitivity (157.8nAμM−1), a low detection limit (3.1×10−8M), a wide linear range (0.1–500μM), as well as good reproducibility, stability, and selectivity.

Theory of Square-Wave Voltammetry of Two-Electron Reduction with the Adsorption of Intermediate

Thermodynamically unstable intermediate of fast and reversible two-electron electrode reaction can be stabilized by the adsorption to the electrode surface. In square-wave voltammetry of this reaction mechanism, the split response may appear if the electrode surface is not completely covered by the adsorbed intermediate. The dependence of the difference between the net peak potentials of the prepeak and postpeak on the square-wave frequency is analyzed theoretically. This relationship can be used for the estimation of adsorption constant.

A Fault Diagnosis Method for Substation Grounding Grid Based on the Square-Wave Frequency Domain Model

A Fault Diagnosis Method for Substation Grounding Grid Based on the Square-Wave Frequency Domain ModelCurrent methods of fault diagnosis for the grounding grid using DC or AC are limited in accuracy and cannot be used to identify the locations of the faults. In this study, a new method of fault diagnosis for substation grounding grids is proposed using a square-wave. A frequency model of the grounding system is constructed by analyzing the frequency characteristics of the soil and the grounding conductors into which two different frequency square-wave sources are injected. By analyzing and comparing the corresponding information of the surface potentials of the output signals, the faults of the grounding grid can be diagnosed and located. Our method is verified by software simulation, scale model experiments and field experiments.

Characterisation of catechins in green and black teas using square-wave voltammetry and RP-HPLC-ECD

Eight green and three black teas have been analysed using square-wave voltammetry at a glassy-carbon electrode, at pH 2 and square-wave frequency 100 Hz. The SWV response of teas consisted of two partially resolved anodic peaks: peak 1 at around 0.372 V, and peak 2 around 0.491 V. First anodic peak was due to oxidation of pyrogallol catechins, i.e. epigallocatechin gallate (EGCG) and epigallocatechin (EGC), and peak 2 can be associated with oxidation of ortho-hydroquinone and galloyl groups in catechins, gallic acid, theaflavins, and other catechol-type phenolics present in tea. Peak 1 has been chosen for quantification purposes, and concentrations of catechins were calculated from the calibration plot constructed for EGC used as external standard. Amounts of catechins in green teas obtained by SWV were in good agreement with those obtained using reverse-phase high-performance liquid chromatography with electrochemical detection (RP-HPLC-ECD). For black tea samples the detector response of peak 1 was diminished due to interferences of coexisting polyphenols, and SWV obtained results were something lower than those obtained by HPLC-ECD.

Real Time Analysis of Neurotransmitters in the Brain Using a Micro-Electrode System

Neurotransmitters catechol and dopamine analogy levels are related to the systematic nerve activity. This assay was performed using cyclic voltammetry (CV) and square wave (SW) stripping voltammetry, while optimization was performed by the carbon fiber microelectrode (CFME) with wire-type reference and counter electrodes. In the electrolyte solutions, the analytical parameters of catechol were as follows: 8.5 pH, -0.4 V anodic, 0.3 V cathodic, 15s deposition time, 15 Hz SW frequency, 25 mV SW amplitude and incremental potential of 4 mV. Under optimal conditions, working ranges of 0-50 mgL(-1) CV, 0.01-50 mgL(-1) cathodic, 1-13 mgL(-1) anodic. The relative standard deviation of 0.02 %, n = 15 using 0.5 mgL(-1) standard. The detection limit was 4.0 ugL(-1). It can be used for in vivo direct analysis. Here, diagnostic applications were performed in the brain skeleton of living cells in real time. The developed techniques can be useful for nerve control and signal detections.

Exploiting Binding-Induced Changes in Probe Flexibility for the Optimization of Electrochemical Biosensors

Electrochemical sensors employing redox-tagged, electrode-bound oligonucleotides have emerged as a promising new platform for the reagentless detection of molecular analytes. Signal generation in these sensors is linked to specific, binding-induced changes in the efficiency with which an attached redox tag approaches and exchanges electrons with the interrogating electrode. We present here a straightforward means of optimizing the signal gain of these sensors that exploits this mechanism. Specifically, using square-wave voltammetry, which is exquisitely sensitive to electrode reaction rates, we can tune the frequency of the voltammetric measurements to preferentially enhance the signal associated with either the unbound or target-bound conformations of the probe. This allows us to control not only the magnitude of the signal gain associated with target binding but also the sign of the signal change, generating "signal-on" or "signal-off" sensors. This optimization parameter appears to be quite general: we show here that tuning the square-wave frequency can significantly enhance the gain of the sensors directed against specific oligonucleotide sequences, small molecules, proteins, and protein-small molecule interactions.

Partial Discharge Activity of Inter-turn Insulation under Different Parameters of Square Wave Voltage

Partial discharge (PD) activity of inter-turn insulation of electric motor winding is investigated under different parameters of square wave voltage, and the memory effect of deposited space charge in a cavity on PD activity is also studied. Under different frequency and rise time of square wave, discharge number, maximum discharge magnitude and phase resolved PD pattern is investigated. Increase in frequency and decrease in rise time both results in increase in maximum discharge magnitude and discharge number at square wave. Comparing the results of phase resolved PD patterns at different frequency of square wave, most of PD moves to zero point of square wave voltage with the increase in frequency. Meanwhile, with the reduction in rise time of square wave, a similar phenomenon can be observed. Through the analysis of a PD process at square wave voltage, the memory effect of deposited space charge after a discharge in cavity leads to superposition of electric field when the polarity of square wave voltage rapidly reverses. With the increase in frequency and reduction in rise time at square wave, superposition of electric field enhances. As a result, available discharge time prolongs during the rise time of square wave and overvoltage across the cavity increases. They result in the increase in discharge number and maximum discharge magnitude. Furthermore, for this reason, the position of PD shifts to zero point of square wave voltage.

Application of a Continuous Square-Wave Potential Program for Sub Nano Molar Determination of Ketotifen

An electroanalytical method has been developed for the determination of the ketotifen by continuous square wave adsorptive stripping voltammetry on a ultra-gold microelectrode (Au UME) in aqueous solution with phosphate buffer as supporting electrolyte. The best adsorption conditions were found to be pH 2.3, an accumulation potential of 300 mV (Au vs. Ag: AgCl-KCl 3 M) and an accumulation time of 400 ms. Variation of admittance in the detection process is created by inhibition of oxidation reaction of the electrode surface, by adsorption of ketotifen. Furthermore, signal-to-noise ratio was significantly increased by application of discrete fast Fourier transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some parameters such as square-wave frequency, eluent pH, and accumulation time were optimized. Effects of square-wave frequency, step potential and pulse amplitude were examined for the optimization of instrumental conditions. The calibration curve is linear in the range 2.0x10(-7)---5.0x10(-12) M with a detection limit of 2.0x10(-12) M (ca. 0.7 pg/ml). The method maybe applied direct determination of the drug in pharmaceutical and biological samples. For a concentration of 5.0x10(-8) M a recovery value of 99.89% is obtained.

Isopotential points in square-wave voltammetry of reversible electrode reactions

Isopotential points in square-wave voltammetry are described for the first time. Model calculations and real measurements (performed with UO22+ and Eu3+ in perchlorate and bromide solutions, respectively) indicate that such an intersection could be observed when backward components of the net response, resulting from an increase in frequency or reactant concentration, are presented together. The electrode reaction should be fully reversible because quasireversible or slower electron transfer processes give the isopoints only at increasing reactant concentrations but not at increasing square-wave frequencies. The effect could be used as an additional diagnostic criterion for recognition of reversible electrode reactions where products remain dissolved in the electrolyte solution.

Determinationation of kanamycin by square-wave cathodic adsorptive stripping voltammetry

A square-wave cathodic adsorptive stripping voltametric (SWCASV) method for the determination of kanamycin was developed on a thin-film mercury electrode (TFME). The optimal working conditions for the application of the method were found to be pH 8.0, provided by a Britton-Robinson (B.R.) buffer, and an adsorption potential of +0.30 V during 300 s. The equilibration time was applied during 10 s, and potential scans were performed at a scan rate of 40 mV/s, with a square-wave frequency of 100 Hz. The measuring-system response was linear over the kanamycin concentration range from 1.2 × 10−9 to 5.0 × 10−8 M and the detection limit achieved was 4.8 × 10−10 M. The relative error and relative standard deviation obtained were 1.20 and 4.67%, respectively. The voltammetric procedure was applied successfully to give a rapid and precise assay of kanamycin in kanamycin sulfate injection form.

Diagnosis of human hepatitis B virus in non-treated blood by the bovine IgG DNA-linked carbon nanotube biosensor

Objectives To identify an effective bioassay for human hepatitis B virus (HBV) using voltammetric sensor. Study design Electrode was prepared with bovine IgG immobilized onto a DNA-linked carbon nanotube electrode (BIDCE). Analytical BIDCE conditions were optimized through square wave (SW) stripping and cyclic voltammetry (CV). Results Optimum parameters of 75 Hz SW frequency, 0.1 V SW amplitude, −1.3 V SW accumulation potential, 100 s accumulation time, and 3.0 mV SW increment potential were obtained. Within working ranges of 0.035–0.242 mg/mL anti-bovine IgG, the relative standard deviation of 0.2 mL HBV was observed to be 0.04 ( n = 4). Conclusions Diagnostic application was performed through direct assay of HBV in non-treated human blood.

Indirect voltammetric determination of caffeine content in coffee using 1,4-benzoquinone modified carbon paste electrode

In this paper a simple and highly sensitive electroanalytical method for the determination of caffeine content using 1,4-benzoquinone modified carbon paste electrode is presented. The method is based on suppression of 1,4-benzoquinone peak current on addition of caffeine. Square-wave and cyclic voltammetric techniques were utilised for the investigation. The 1,4-benzoquinone modified electrode exhibited a well-defined peak with reproducible peak current values for repetitive measurements; and showed a decrease in peak current value with an increase in caffeine content. The result revealed two linear range regions between 0 mmol L −1 and 0.5 mmol L −1 and 0.5 mmol L −1 and 8.0 mmol L −1, with detection limits of 0.3 μmol L −1 and 5.1 μmol L −1, respectively. The method was then successfully applied to the determination of caffeine content in coffee samples. The effects of pH, electrode composition, step potential, pulse amplitude and square-wave frequency on the voltammetric responses were also investigated.

An experimental study of intermodulation effects in an atomic fountain frequency standard

The short-term stability of passive atomic frequency standards, especially in pulsed operation, is often limited by local oscillator noise via intermodulation effects. We present an experimental demonstration of the intermodulation effect on the frequency stability of a continuous atomic fountain clock where, under normal operating conditions, it is usually too small to observe. To achieve this, we deliberately degrade the phase stability of the microwave field interrogating the clock transition. We measure the frequency stability of the locked, commercial-grade local oscillator, for two modulation schemes of the microwave field: square-wave phase modulation and square-wave frequency modulation. We observe a degradation of the stability whose dependence with the modulation frequency reproduces the theoretical predictions for the intermodulation effect. In particular no observable degradation occurs when this frequency equals the Ramsey linewidth. Additionally we show that, without added phase noise, the frequency instability presently equal to 2×10-13 at 1 s, is limited by atomic shot-noise and therefore could be reduced were the atomic flux increased.

Development of anodic stripping voltammetry for determination of gallium in U–Ga alloy

Deposition potential, deposition time, square-wave frequency, rotation speed of the rotating disc electrode and gallium concentration have been studied in detail, for trace concentration level determination of gallium metal in U–Ga alloy by square-wave voltammetry anodic stripping analysis, in 1 M NaClO 4 + 0.5 M NaSCN at mercury film electrode (MFE). Optimum conditions have been found for Ga(III) determination by obtaining calibration graphs for the range 1–10 × 10 −7 M gallium. Error and standard deviation less than 1% were assessed of this method with all gallium standard solutions. The developed methodology was applied successfully as a subsidiary method for the determination of gallium content in synthetic U–Ga samples with very good precision and accuracy (under 1% error and std. dev.).

The Development of the Buck Type Electronic Dimming Ballast for 250W MHL

In this paper, we studied the development of the electronic ballast for 250W MH (Metal-Halide) lamps. We were able to improve the input power factor by using a PFC IC. To provide the lamp with the rated voltage required, we used the buck-type dc-dc converter. The stress of the switching devices in the inverter could be reduced by this method. To eliminate the acoustic resonance phenomena of MH lamps, the voltage of the lamp added the high frequency sine-wave to the low frequency square-wave by using the full bridge typed inverter. We have developed a simple igniter using the L and C elements. We could control the dimness of the lamp by varying the output voltage of the buck converter. The buck converter output voltage could be controlled by using a microprocessor.

Allowed Level of the Power Ripple in Low Frequency Square-Wave Ballasts of Metal-Halide Lamps

In order to avoid the acoustic instabilities in metal halide (MH) lamps a proper method is to supply the lamp with a low frequency square-wave current. Due to the topology of electronic ballasts for such an application, there is a high frequency ripple in the current or voltage waveform. It is known that such ripples with sufficient energy at the proper frequency are able to excite acoustic resonance in MH lamps. The threshold value for high frequency ripples in order to excite an acoustic mode and destabilize the lamp is under debate. This threshold is lamp dependent and should be measured experimentally for each lamp type. This paper addresses an automated experimental method to determine the threshold value of the power ripple in a frequency range of 10–400 kHz. The implementation of the proposed method which is based on the light flicker factor has been explained in a preceding paper. The experimental results show that less than 1 percent of power ripple at the resonance frequency is sufficient to excite a detectable (perceptible to the human eye) acoustic instability.

Improved Optical Heterodyne Methods for Measuring Frequency Responses of Photodetectors

An improved optical self-heterodyne method utilizing a distributed Bragg reflector (DBR) tunable laser and an optical fiber ring interferometer is presented in this paper. The interference efficiency can be increased by 7 dB compared with the scheme using the conventional Mach-Zehnder interferometer. The unsteady process that the beating frequency experiences in each tuning period is investigated. According to the measurement results, the wavelength and optical power of the tunable laser will be steady when the square-wave frequency is lower than 300 kHz. It has been shown that when a square-wave voltage is applied to the phase section of the tunable laser, the laser linewidths vary in a wide range, and are much larger than that under dc voltage tuning. The errors caused by the variations in the linewidth of the beat signal and optical power can be eliminated using the proposed calibration procedures, and the measurement accuracy can, therefore, be significantly improved. Experiments show that the frequency responses obtained using our method agree well with the data provided by the manufacturer, and the improved optical self-heterodyne method is as accurate as the intensity noise technique.

Anodic square-wave stripping voltammetric analysis of epinephrine using carbon fiber microelectrode

The behavior of epinephrine on a carbon fiber microelectrode (CFME) was studied with cyclic voltammetry and square-wave (SW) stripping voltammetry in order to find optimum conditions for its analysis using the CFME. An anodic stripping peak at about 0.20 V (vs. Ag/AgCl) was utilized. Under optimum conditions for anodic stripping (a pH value of 7.4, a deposition potential of − 0.5 V, a deposition time of 90 s, a final potential of 0.8 V, a SW frequency of 20 Hz, a step potential of 5 mV, and an amplitude of 45 mV), the calibration was linear in the concentration range of 0.0∼0.4 mg/L, and the detection limit was found to be 0.009 mg/L with a relative standard deviation 0.18% ( n = 12) at 0.2 mg/L. The analytical performance of the CMFE, which is unmodified, is comparable to or better than other voltammetric results with various modified electrodes.