Square-wave Frequency Research Articles

Inspection of an end quenched plain steel Jominy bar with photothermal radiometric techniques

The effect of the cooling rate on hardness and thermal conductivity in a metallurgical Jominy bar made of AISI 1018 steel, by means of a water end-quenched heat treatment process without diffusion-controlled case depth, is studied with photothermal radiometry (PTR). It is concluded that our two PTR techniques, common-mode rejection demodulation (CMRD) and conventional 50% duty-cycle square-wave frequency scan, are sensitive to low hardness values and gradients, unlike the high values all previous photothermal studies have dealt with to-date. Both PTR methods have yielded an anti-correlation between thermal conductivity and microhardness in this case as in previous cases with heat-treated and diffusion-controlled case depth profiles. It is shown that the cooling rate strongly affects both hardness and thermal conductivity in the Jominy-bar heat-treating process.

Inspection of an end quenched 0.15%–0.2% C, 0.6%–0.9% Mn steel jominy bar with photothermal radiometric techniques

The effect of the cooling rate on hardness and thermal conductivity in a metallurgical Jominy bar made of 0.15%–0.2% C, 0.6%–0.9% Mn (AISI 1018) steel, by means of a water end-quenched heat treatment process without diffusion-controlled case depth, is studied with photothermal radiometry (PTR). It is concluded that our two PTR techniques, common-mode rejection demodulation and conventional 50% duty-cycle square-wave frequency scan, are sensitive to low hardness values and gradients, unlike the high values all previous photothermal studies have dealt with to-date. Both PTR methods have yielded an anticorrelation between thermal conductivity and microhardness in this case as in previous cases with heat-treated and diffusion-controlled case depth profiles. It is shown that the cooling rate strongly affects both hardness and thermal conductivity in the Jominy-bar heat-treating process.

Square‐Wave Voltammetry of Quasi‐Reversible CE Reactions at Spherical Microelectrodes

AbstractA mathematical model for the CE mechanism in which the chemical together with the electrochemical reactions are quasi‐reversible at the surface of spherical macro and micro‐electrodes is presented for the case of square‐wave voltammetry. The analysis of voltammometric responses considers the influence of rate and equilibrium constants, together with the electrode radius, and their dependence on the square‐wave frequency (f). Both kinetics and the sphericity effect act synergistically on the electrochemical response. Also, the apparent electrode sphericity and the reversibility of the chemical as well as the electrochemical reactions are jointly affected by the variation of f. Disregarding the sphericity contribution in the calculation of kinetic parameters at a microelectrode may introduce errors even higher than one order of magnitude. The model allows the analysis of a more realistic and complex electrochemical system that requires not only the dependence of experimental responses on f, but also their fit with theoretical voltammograms, in order to provide some useful mechanistic information. Finally, concentration profiles are also studied to realize how the chemical contribution is buffering the absences of oxidized species at the electrode surface, and how those profiles are modified for the case of spherical macro and micro‐electrodes.

Trace Analysis of Lead at a Nafion-Modified Electrode Using Square-Wave Anodic Stripping Voltammetry

ASV using square-wave voltammetry was used with Nafion-coated glassy carbon electrodes for lead analysis and it was found that square-wave frequencies greater than 100 Hz could be employed satisfactorily for trace lead detection. Peak current increases with frequencies up to 1000 Hz at step potentials of up to 10 mV, though not linearly. However, the enhanced sensitivity allows the analysis of low levels of lead with concentrations down to 1 ppb detectable. This technique gave a value of 15.0±1.3 ppb lead in a diluted certified reference material with lead concentration of 14.7 ppb.

Evaluation of the accuracy of the optically pumped caesium beam primary frequency standard of BNM-LPTF

The primary frequency standard LPTF-JPO employs a caesium thermal beam, and optical pumping techniques. We present the main parts of the design. The short-term stability is reported, σy(τ) = 3.5 × 10−13 τ−1/2, where τ is the averaging time. The general expression for frequency shift for a square-wave frequency modulation is given. We discuss the determination of each frequency shift, and we present new methods to evaluate some of them. A relative combined standard uncertainty of 6.4 × 10−15 (1 σ) is obtained.

Microfabricated Array of Iridium Microdisks as a Substrate for Direct Determination of Cu2+or Hg2+Using Square-Wave Anodic Stripping Voltammetry

In this paper, we report for the first time the characterization and separate electrochemical determinations of Cu2+ and Hg2+ directly on a microlithographically fabricated array of iridium ultramicroelectrodes (Ir-UMEA). Square-wave anodic stripping voltammetry was used to optimize experimental parameters such as supporting electrolyte, square-wave frequency, and deposition time and potential. Reproducible stripping peaks were obtained for solutions containing low parts per billion (ppb) concentrations of either metal. Excellent linearity was obtained for Cu2+ in the 20−100 ppb range and for Hg2+ in the 1−10 ppb range when the bare iridium substrate was used. Detection limits were calculated to be 1 ppb (0.1 M KNO3 and 0.1 M HClO4, deposition time 180 s) and 5 ppb (0.1 M H2SO4, deposition time 120 s) for Cu2+ (S/N = 3) and 85 ppt for Hg2+ (deposition time 600 s). The experimental detection limits were determined to be 5 ppb for Cu2+ (deposition time 180 s) and 100 ppt for Hg2+ (deposition time 600 s). In...

Voltammetric determination of benzoylecgonine

Benzoylecgonine is a metabolyte of cocaine. Benzoylecgonine can be electrochemically detected by square-wave voltammetry at a mercury drop electrode in 0.5 mol/l KNO 3, at pH 9.2. The maximum response appears at −1.06 V vs. Ag|AgCl|3 M KCl and it depends on benzoylecgonine concentration, the square-wave frequency and amplitude, but it is independent of pH of solutions. The concentration of benzoylecgonine can be measured in the range between 1×10 −6 and 4×10 −5 mol/l.

New type of optical fibre analogue SSB data communication system using edge-emitting LED coupled to single-mode optical fibre

This paper describes a single-mode(SM) optical fibre SSB data communication system for use in place of power-line data transmission. In the optical transmitter, SSB data is fed through the squarewave frequency (SWFM) modulator to the edge-emitting LED (ELED) module. The light beam of the ELED module is fed to the SM optical fibre having a length of 12km. In the optical receiver, the light beam received through the SM optical fibre is detected by the PIN photodiode module, and fed to the SWFM detector to obtain the double-pulse frequency modulation (DPFM) signal voltage. The DPFM signal voltage at the output of the SWFM detector is fed to the low-pass filter (LPF) to obtain analogue SSB data. When the transmission was experimentally carried out, the spurious component was as low as −50–−70 dB and the SNR of SSB data as high as more than 65–70 dB. The optical transmitter and receiver were attached to the conventional analogue SSB data communication system to constitute a new optical fibre analogue SSB data communication system. During the field test utilizing the new system, the crosstalk and SNR were 60–70 dB and 60–70 dB on each channel, respectively. Copyright © 1999 John Wiley & Sons, Ltd.

New type of optical fibre analogue SSB data communication system using edge‐emitting LED coupled to single‐mode optical fibre

This paper describes a single-mode(SM) optical fibre SSB data communication system for use in place of power-line data transmission. In the optical transmitter, SSB data is fed through the squarewave frequency (SWFM) modulator to the edge-emitting LED (ELED) module. The light beam of the ELED module is fed to the SM optical fibre having a length of 12km. In the optical receiver, the light beam received through the SM optical fibre is detected by the PIN photodiode module, and fed to the SWFM detector to obtain the double-pulse frequency modulation (DPFM) signal voltage. The DPFM signal voltage at the output of the SWFM detector is fed to the low-pass filter (LPF) to obtain analogue SSB data. When the transmission was experimentally carried out, the spurious component was as low as −50–−70 dB and the SNR of SSB data as high as more than 65–70 dB. The optical transmitter and receiver were attached to the conventional analogue SSB data communication system to constitute a new optical fibre analogue SSB data communication system. During the field test utilizing the new system, the crosstalk and SNR were 60–70 dB and 60–70 dB on each channel, respectively. Copyright © 1999 John Wiley & Sons, Ltd.

Adsorptive stripping square-wave voltammetry of DNA

Abstract Faradaic currents produced by DNA at neutral pH are studied by square-wave voltammetry (SWV) in connection with an HMDE. Under these conditions single-stranded DNA produces a cathodic peak (due to the reduction of adenine and cytosine residues) which is better developed than the peak obtained by CV and DPV; the SWV peak can thus be measured at substantially lower DNA concentration (down to tens of nanograms per milliliter). The anodic peak G , which is due to oxidation of the guanine reduction product (formed at potentials around −1.85 V against an Ag|AgCl|3 M KCl electrode), is studied in greater detail. At potentials more negative than −1.85 V a deeper reduction of the guanine residue takes place which results in a decrease of peak G and in changes of the peak potential. The dependences of the peak G on the pulse amplitude and square-wave frequency are unusual. Using adsorptive stripping transfer voltammetry it is possible to determine DNA in the presence of an excess of guanosine. Methylation of the DNA guanine residues by dimethyl sulfate results in a decrease of the peak G . A DNA-modified electrode can be used as a sensor for the DNA damage by methylating agents.

Production of nanometric particles in radio frequency glow discharges in mixtures of silane and methane

The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by plasma-enhanced chemical vapor deposition (PECVD) are promising new materials for sintering ceramics, for making nanoscale filters, or for supporting catalytic surfaces. Common characteristics of these powders are their high purity and the easy control of their stoichiometry through the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon–carbon alloys exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor using mixtures of silane and methane at low pressure (<1 Torr) and low frequency square-wave modulated rf power (13.56 MHz). The a-Si1−xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH4]+[CH4]). The structure of the a-Si1−xCx:H powder was analyzed by several techniques. The particles appeared agglomerated, with a wide size distribution between 5 and 100 nm. The silane/methane gas mixture determined the vibrational features of these powders in the infrared. Silicon–hydrogen groups were present for every gas composition, whereas carbon–hydrogen and silicon–carbon bonds appeared in methane-rich mixtures (R<0.6). The thermal desorption of hydrogen revealed two main evolutions at about 375 and 660 °C that were ascribed to hydrogen bonded to silicon and carbon, respectively. The estimated hydrogen atom concentration in the sample was about 50%.

BIDIRECTIONAL TRANSMISSION OF ADDRESSED AUDIO SIGNAL THROUGH GI MULTIMODE OPTICAL FIBRES

This paper describes two types of bidirectional addressed audio signal transmission systems where the square-wave frequency modulation (SWFM) and intensity modulation (IM) are used to obtain the optical SWFM signals generated from LEDs at 850 nm. The first one is an addressed audio signal transmission network of tree structure. The sender and auxiliary receiver in the centre are connected to four terminals, each consisting of a receiver and an auxiliary sender, through pairs of optical fibres and an optical splitter used as an optical signal distributor. The second one is a new type of full-duplex one-to-one communication system. The sender and auxiliary receiver in one terminal are connected to the receiver and auxiliary sender in the other terminal through an optical fibre and a pair of directional couplers. Although LEDs in the second system deliver optical SWFM signals at the same wavelength of 850 nm at the same time, the communications are satisfactory because there is no interference from one LED to the other. In both the first and second experimental systems, the audio signal, address, and SWFM carrier occupy 10 Hz to 20 kHz, 65 kHz to 710 kHz, and 6 MHz, respectively. The SNR and distortion were 62 dB and 0.4 per cent, respectively.

Parallel transmission of vehicle mirror control signals by a single optical fiber

Describes a vehicle mirror control signal transmission system consisting of a transmitter, a single optical fiber, and a receiver terminal. The transmitter in the mirror controller to be operated by the driver controls the mirror functions, and the receiver terminal consists of a multifrequency receiver, a data processor, mirror control circuits to control an inner rearview mirror, and a pair of outside door mirrors. Multifrequency signals at 135, 235, 335, and 435 kHz are encoded to obtain 4-bit binary data that specifies the instructions to control these mirrors. The 4-bit multifrequency signal identified as 4-bit binary data is formed in accordance with the frequency division multiplexing (FDM) scheme, fed to the voltage-controlled oscillator (VCO) to obtain the square-wave frequency modulation (SWFM) signal in accordance with the SWFM scheme, and then transmitted from the transmitter to the receiver terminal through a single optical fiber. After the 4-bit binary data is reproduced from the 4-bit multifrequency signal, the mirrors are controlled by the data processor to accomplish their operating functions satisfactorily.

Squarewave frequency modulation techniques

Transmission of high-quality analogue sourced signals over copper or optical fibre links and networks demands a critical choice of modulation format to achieve both high performance and to avoid unnecessary bandwidth overhead penalties. Pulse time modulation (PTM) techniques are being increasingly employed to overcome many of the problems associated with traditional analogue and digital methods. Among the family of pulse time modulation techniques squarewave frequency modulation (SWFM) is particularly well suited to the transmission of high-quality wideband instrumentation and video signals, such as high definition TV, due to its attractive combination of performance and simplicity. This paper presents theoretical and practical aspects of SWFM and describes a number of experimental SWFM systems capable of transmitting signals from DC to 30 MHz. >

Optical and electronic properties of hydrogenated amorphous silicon films deposited by square-wave modulated RF discharges of silane-he mixtures

The optoelectronic properties of a-Si: H films deposited under very different plasma conditions have been studied as functions of the square-wave modulation frequency of a 13.56 MHz rf discharge. Results for two extreme deposition conditions are presented. At both high and low deposition rates, the modulation of the rf discharge results in a negligible effect or a deterioration of the film properties, particularly the photoconductivity which we have found to be the most sensitive parameter. At high deposition rates, modulation of the discharge at 10 Hz results in the incorporation of particles into the film which produce enhanced absorption in the film. Therefore, for our reactor configuration, the modulation of the discharge does not produce an improvement but rather a degradation of the film properties.

A tuning and testing frequency synthesizer

In this paper we describe the theory and application of a newly developed synthesizer that is especially suitable for cavities suffering instabilities and drift effects. The synthesizer presented here uses square-wave frequency modulation as its principle of operation. The synthesizer consists of two main phase-locked loops that are interconnected so that their outputs are alternately available. Spurious signals in the output spectrum have been measured to be more than 77 dB below the carrier at 405.782 kHz.

Properties of an optically pumped cesium-beam frequency standard with Φ=π between the two oscillatory fields

The properties of optically pumped cesium-beam resonators showing a phase difference, /spl Phi/, of /spl pi/ between the two oscillatory fields are analyzed. They are compared with those occurring with /spl Phi/=0, when the interrogation signal is slowly square-wave frequency modulated. The value of the operating parameters which optimizes the resonator properties is given for /spl Phi/=0 and /spl pi/,taking into account the effect of the noise sources which perturb the atom detection. It is shown that the design with /spl Phi/=/spl pi/ is superior. It provides a better frequency stability and smaller frequency offsets. The conclusion holds for short as well as long tubes. >

Determination of thyroxine in urine by cathodic stripping square-wave voltammetry.

A square-wave polarographic method for the determination of the amino acid thyroxine in urine, after isolation from the matrix on a C18 Sep-Pak cartridge and subsequent elution through a column packed with Amberlite IRA-400 anionic resin, was developed. The optimal working conditions for the application of the method were found to be pH 10, provided by a carbonate buffer, and a potential of -0.690 V during 10 min. The equilibration time was applied during 5 s, and potential scans were performed at a square-wave amplitude of 100 mV and a scan rate of 300 mV s-1, with a square-wave frequency of 100 Hz. The measuring-system response was linear over the thyroxine concentration range from 10 to 60 ng ml-1 and the detection limit achieved was 2.71 ng ml-1. The relative error and relative standard deviation obtained were 1.18 and 4.67%, respectively.

Determination of gallium by square-wave voltammetry anodic stripping, based on the electrocatalytic action of 2,2′-bipyridine in dimethylsulphoxide: comparison with an aqueous NaSCN/NaClO 4 electrolyte

Deposition potential, deposition time, square-wave frequency, 2,2′-bipyridine concentration, and gallium concentration have been studied in detail, for the determination of trace concentration levels of the metal by square-wave voltammetry anodic stripping analysis, in dimethylsulphoxide. Optimum conditions have been found for gallium(III) determination and results compared to those obtained in 0.5 M NaSCN + 4.2 M NaClO 4 aqueous electrolyte by obtaining calibration graphs for the range 1 × 10 −8 M−1 × 10 −5 M gallium. Accuracy (± 3%) and precision (4–6% SD) of this method were assessed with both 4 × 10 −8 M and 4 × 10 −7 M gallium solutions used as synthetic samples. The efficiency of solvent extraction of gallium with di-isopropyl ether was found to be 99.98% at a 4 × 10 −7 M gallium concentration. The proposed method was applied to the determination of the gallium content in rock mineral samples (using the above mentioned solvent extraction procedure), are compared to those obtained with the NaSCNNaClO 4 based electrolyte. No statistically significant difference was observed. Analytical procedures followed are given in detail.

Analytical utility of the iridium-based mercury ultramicroelectrode with square-wave anodic stripping voltammetry

The characterktics of the irldium-based hemkphwkai mercury uitramlcrodectrode (Ha-UME) in conjunction with squarewave anodic stripping voltammetry (SWASV) have been Investigated. Udng Hg-UMEs of 5-10-pn~ radii, samples were analyzed without any added electrolyte, deoxygenatlon, or forced convectlon. The peak stripping currents displayed a linear rdation8hip with d.porltion times varying from 1 to 1200 8. Peak potentlais and current remained substantlaily unchanged with electrolyte concentrations of 1-104 M. The reproduclblilty and useful lifetime of the Hg-UME was studied and found to be excellent over several days use. The application of SWASV theory for mercury film electrodes is shown to not entirely describe the rerpow at the Hg-UME, especially at low square-wave frequencies.