Analysis and design of frequency‐controlled oscillator for frequency‐locked stepping position control system

Abstract

A frequency‐locked stepping position servo system (FLSPS) is presented. The proposed microprocessor‐based sloped‐varied frequency‐controlled oscillator (SVFCO) is designed to achieve nearly the same acquisition times for different position commands. The slope‐varied technique is to quickly position for long distance servo during the wide‐range control. The motion profiles for position locking are adaptively built according to the periodically sampled frequency error. No motion profiles are required to be pre‐installed in the controller. The system model is built for stability investigation and simulation. A design example is realized to verify the theoretical predictions. System simulation and experimentation confirm that the system acquisition times for short, middle, and long distance servos are very close to each other. In comparison with the corresponding traditional stepping position system, the acquisition times of the FLSPS are improved by 53% and 73%.     

Resonator surface contamination-a cause of frequency fluctuations?

The mass loading effects of adsorbing and desorbing contaminant molecules on the magnitude and characteristics of frequency fluctuations in a thickness-shear resonator are studied. The study is motivated by the observation that the frequency of a thickness-shear resonator is determined predominantly by such mechanical parameters as the thickness of the resonator, elastic stiffnesses, mass loading of the electrodes, and energy trapping. An equation was derived relating the spectral density of frequency fluctuations to: (1) rates of adsorption and desorption of one species of contaminant molecules; (2) mass per unit area of a monolayer of molecules: (3) frequency constant; (4) thickness of resonator; and (5) number of molecular sites on one resonator surface. The induced phase noises were found to be significant in very-high-frequency resonators and are not simple functions of the percentage of area contaminated. The spectral density of frequency fluctuations was inversely proportional to the fourth power of the thickness if other parameters were held constant.     

Sinusoidal frequency estimation at low signal‐to‐noise ratio

Abstract

In this paper, an algorithm is developed to estimate the frequencies of the sinusoids corrupted by white noise. First, the input data is analyzed by a large order autoregressive (AR) spectral estimator, and then we root the prediction error filter (PEF) to get a set of zeros. Using a zero‐clustering algorithm, we partition the zeros into clusters. From these zero clusters, we construct filters to enhance the sinusoids. Then, using frequency estimators, we estimate the frequencies of the sinusoids from the filtered data. The results presented in this paper demonstrate that the proposed algorithm provides a better resolution ability and estimate accuracy than that of the conventional AR spectral estimator, especially for close sinusoids at low SNR.     

Low frequency Raman spectra of granular CoxAg1 − x films

A series of Co_xAg_1−x granular thin films were deposited on glass substrates using ion-beam co-sputtering technique at room temperature. The concentration of cobalt,x, was varied from 4 to 80 at.%. We report some results obtained using Raman scattering for these samples. The results show that there is a set of Stokes lines with almost same spacing in low frequency Raman spectra (LFRS), but it shows a sharp change in the spectra for x > 22 at.% samples. In nanostructured granular films, the metallic particle size is nearly equal to the phonon mean free path (PMFP) of bulkmetal, leading to phonon behavior showing quantized nature. The inelastic light scattering in our granular Co-Ag samples is not dominated by only a single mechanism. The change in the Raman spectra with different x and annealing treatment has also been presented.     

Self-seeded multi-wavelength Brillouin–erbium fibre laser with 20 GHz frequency gap

We demonstrate a self-seeded multi-wavelength Brillouin–erbium fibre laser with double Brillouin frequency gap. The twice channel gap is induced by the gain difference in different directions. Thirty-six stable output channels with 20?GHz frequency gap are obtained when the 980?nm pump power is 300?mW. The factor that induces the double frequency gap is investigated and proved.     

A frequency‐dependent droop scheme for parallel control of ups inverters

Abstract

This paper presents a frequency‐dependent droop scheme for paralleling UPS inverters with no control interconnection, so the inverters can be tightly connected with the load. At the fundamental frequency, the reference voltage of the inverter is generated as a reactor connected between the inverter and the load. The intention is to control the real and reactive power sharing of inverters with the Q‐V and P‐ω droop scheme employed in the power system without needing a true transfer reactor. At the harmonic frequency, the reference voltage is generated as a resistor connected between the inverter and the load. The intention is that the load harmonic current can be shared equally and the voltage waveform distortion will be low. Two 1KVA single‐phase inverters are designed and implemented, some simulation and experimental results are provided for demonstrating the effectiveness of the proposed approach.     

Investigation into β-cyclodextrin/acetotoluide interactions using low frequency dielectric spectroscopy

Low-frequency dielectric spectroscopy has been used to characterize samples of-cyclodextrin and ortho-, meta- and para-acetotoluide, both in aqueous solution and in the solid state. Similarly,-cyclodextrin/acetotoluide binary systems were studied as aqueous solutions and as freeze-dried solids. The para-acetotoluide binary systems exhibited the highest conductance in aqueous systems and showed anomalous behaviour in the solid state compared to the other two analogues. Previous studies by Jones and Parr have indicated that the para-acetotoluide gave the strongest evidence for complex formation with-cyclodextrin, hence the studies have demonstrated that the technique may be of use in studying drug interactions with cyclodextrin systems.     

Model crash frequency at highway–railroad grade crossings using negative binomial regression

Despite the fact that traffic collisions at highway–railroad grade crossings (HRGXs) are rare events, the impact of HRGX crashes is nevertheless more severe than highway crashes. Empirical studies show that traffic collisions at HRGXs are mainly attributed to railway-related and/or highway-related characteristics, particularly drivers’ abnormal behavior, driving around, or through an HRGX. These factors have different effects on crash likelihood (i.e., the number of traffic collisions or crash frequency) at an HRGX. To explore the causal relationship between crash frequency and the factors related to railroad and highway systems, we used a negative binomial regression model to identify the factors that are statistically significantly associated with traffic collisions at HRGXs, and conducted relevant sensitivity analyses to investigate the marginal effect of daily highway traffic on changes in crash frequency. The empirical study shows that the number of daily trains, the number of tracks, highway separation, annual averaged daily traffic (AADT), and crossing length had statistically significant effects on the mean number of traffic collisions (all p-values?≤?0.0487). Further, the marginal effect of the AADT on the change of crash frequency indicates that crash likelihood monotonically increases with the increase of AADT.     

Economically optimal sample size,frequency and capability indices using X¯ charts

In determining inspection plans for quality control, two important variables are the frequency of sampling and the sample size. Typical values are once per hour, with a sample of size 4 or 5. However, this may be far from the most appropriate or efficient scheme in a given setting. Also, the capability index necessary to produce zero defects under the historical maximum and average shift in the process is essential information in providing motivation for process improvement. This paper presents microcomputer-based software using readily available information for determining economically optimal sampling plans and zero-defects capability indices. Great economic benefits can result from more careful attention to sampling plans, and the attainment of zero defect process capability indices.     

Does the light shift drive frequency aging in the rubidium atomic clock?

Frequency aging in the rubidium (Rb) vapor-cell atomic clock plays a significant role in the device's timekeeping ability. Though many researchers have speculated on the physical mechanism(s) driving the linear, deterministic frequency change (i.e., deltaf(t)/fo = At), there is little unambiguous experimental data regarding the phenomenon. Here, long-term data were used from on-orbit global positioning system (GPS) Rb clocks to examine one postulated mechanism for frequency aging (i.e., the light-shift effect). Defining the light shift of the clock's fractional frequency as alphaI/Io, where alpha is the light-shift coefficient, we find that temporal variations of the relative light intensity, I/Io, cannot account for frequency aging. However, for the population of clocks considered here, we obtain the intriguing result that alpha/A = 1.7 +/- 1.5. Thus, it may be that frequency aging is driven by the light-shift effect through temporal variations of the light-shift coefficient.     

Low frequency dielectric relaxation from complex impedance and complex electric ‘modulus’

The low frequency dielectric characteristics of many materials are often difficult to obtain accurately because of the d.c. conductivity contribution, which is the major portion of the loss, and which has to be subtracted from the total dielectric loss. This is particularly true for small dielectric relaxation peaks which tend to be overwhelmed by the d.c. conduction loss. An equation was derived which enables one to calculate the dielectric characteristics at low frequency, for specimens with small dielectric relaxation peaks, without subtracting the d.c. conductivity, from the complex impedance plot and complex electric modulus plot.     

Experimental verification of a radar target discrimination technique using multiple‐frequency amplitude returns

Abstract

An experimental study of radar target discrimination using multiple‐frequency scattering amplitude without phase data is presented. Based on the concept of natural resonance frequencies, the technique is aspect‐angle independent so that a priori information of the aspect‐angle is not necessary. The radar cross sections of a spheroid and a thin wire are measured at different aspect ‐ and bistatic‐angles to distinguish different spheroids and wires in the resonance frequency range. The results show that the discrimination algorithm works well and can be applied to both monostatic and bistatic radars.     

A novel driver with adjustable frequency and phase for traveling‐wave type ultrasonic motor

Abstract

This paper describes the design of a traveling‐wave ultrasonic motor (TWUSM) drive circuit, intended to simultaneously employ both driving frequency and phase modulation control. The operating principles and a detailed analysis of the proposed driving circuit, consisting of voltage‐controlled oscillator (VCO), voltage‐controlled phase‐shifter circuit and non‐resonant power amplifier converter, are introduced. To drive the USM effectively, a two‐phase power amplifier converter using non‐resonant output was designed to provide a balanced two‐phase voltage source. Two‐phase output driving voltages could be maintained at the same peak voltage value as the driving frequency under varying phase‐modulation processes. Detailed experimental results are provided to demonstrate the effectiveness of the proposed driving circuit.     

Joint maximum-likelihood frequency offset and channel estimation for multiple-input multiple-output?orthogonal frequencydivision multiplexing systems

The problem of joint maximum-likelihood estimation of the carrier-frequency offset (CFO) and channel coefficients in multiple-input multiple-output orthogonal frequency-division multiplexing systems is investigated, assuming that a training sequence is available. The exact solution to this problem turns out to be too complex for practical purposes. To overcome this difficulty, the authors resort to the expectation?maximisation (EM) algorithm and propose an iterative scheme which iterates between estimating the channel parameters and the frequency offset. This results in an estimation algorithm of a reasonable complexity which is suitable for practical applications. Moreover, the Cramer?Rao bounds (CRB) for both CFO and channel estimators are developed to evaluate the performance of the proposed scheme. Simulation results show that the proposed algorithm achieves almost ideal performance compared with the CRBs in all ranges of signal-to-noise ratio for both channel and frequency offset estimates.     

How do gait frequency and serum-replacement interval affect polyethylene wear in knee-wear simulator tests?

Polyethylene wear (PE) is known to be a limiting factor in total joint replacements. However, a standardized wear test (e.g. ISO standard) can only replicate the complex in vivo loading condition in a simplified form. In this study, two different parameters were analyzed: (a) Bovine serum, as a substitute for synovial fluid, is typically replaced every 500,000 cycles. However, a continuous regeneration takes place in vivo. How does serum-replacement interval affect the wear rate of total knee replacements? (b) Patients with an artificial joint show reduced gait frequencies compared to standardized testing. What is the influence of a reduced frequency? Three knee wear tests were run: (a) reference test (ISO), (b) testing with a shortened lubricant replacement interval, (c) testing with reduced frequency. The wear behavior was determined based on gravimetric measurements and wear particle analysis. The results showed that the reduced test frequency only had a small effect on wear behavior. Testing with 1 Hz frequency is therefore a valid method for wear testing. However, testing with a shortened replacement interval nearly doubled the wear rate. Wear particle analysis revealed only small differences in wear particle size between the different tests. Wear particles were not linearly released within one replacement interval. The ISO standard should be revised to address the marked effects of lubricant replacement interval on wear rate.     

Preparation of an Mg–Gd–Zn alloy semisolid slurry by low frequency electro-magnetic stirring

The effects of low frequency electromagnetic stirring (LFEMS) including applied voltage, rotational frequency and cooling rate on the microstructure of semisolid slurry of the Mg–2.5Gd–1Zn (at.%) alloy have been investigated. The applied voltage, rotational frequency and cooling rate all have a remarkable influence on the microstructures of the slurries. The LFEMS treatment leads to the morphology of primary Mg particles evolved from dendritic to non-dendritic. The increase of applied voltage leads to refined primary Mg particles, while the increase in rotational frequency makes the α-Mg particles initially refined and then coarsened. The decrease of cooling rate also leads to refinement of primary Mg particles. The optimal processing parameters for the fabrication of semisolid slurry are found to be: applied voltage 300–350 V, rotational frequency 15–20 Hz and cooling rate below 1.4 K/min. Under the optimized parameters, fine and spherical primary Mg particles were obtained, and the average particle size is refined from ~ 680 to ~ 150 μm.     

Downtime variability: the impact of duration–frequency on the performance of serial production systems

It is intuitively appealing to measure downtime in terms of total time lost (i.e. frequency times duration). However, the same total downtime can be produced by an infinite number of frequency/duration combinations. This study reports the findings of a computer simulation study on the impact of varying combinations of downtime frequency/duration pairs on performance of serial production systems. The research reported here clearly shows that different downtime frequency/duration combinations affect serial production lines differently even when the total downtime remains equal. Analysis suggests that long duration, infrequently occurring variation has a much more negative impact on system performance than short duration, frequently occurring variation.     

Microstructure and properties of nc-TiC/a-C∶H films deposited by radio frequency reactive sputtering

Abstract

Amorphous carbon films containing titanium carbide (nc-TiC/a-C∶H) were deposited onto n-type silicon (100) by radio frequency reactive sputtering titanium target in an Ar–CH₄ mixed atmosphere. The composition and microstructure of the films were characterised by means of X-ray photoelectron spectroscopy, field emitted SEM, XRD and Raman spectra. The mechanical and tribological properties of the films were measured by a nanoindentation tester and a ball-on-disc UMT–2MT tribometer. By adjusting the CH₄ flowrate, Ti content in the films could be controlled, and a transition in structures of the films from loose polymer-like to glassy and dense nanostructure was observed. The density of coatings was improved by the introduction of TiC nanocrystalline particles. The mechanical and lubricious properties were different accordingly.     

Low-temperature sintered Mg2SiO4–CaTiO3 ceramics with near-zero temperature coefficient of resonant frequency

The microwave dielectric properties and the microstructures of (1 ? x)Mg₂SiO₄–xCaTiO₃ composite ceramics with Bi₂O₃–Li₂CO₃–H₃BO₃ (BLB) additions prepared by solid-state reaction method have been investigated. The crystalline phases were studied systematically by using the X-ray diffraction, microstructures by the scanning electron microscopy and composition analysis by the energy-dispersive spectroscopy. The results showed that the τ _f of (1 ? x)Mg₂SiO₄–xCaTiO₃ was related to the amount of CaTiO₃ phase constitutions. When x = 0.08 and 0.09, the τ _f of (1 ? x)Mg₂SiO₄–xCaTiO₃ were about ?3.0 ppm/°C and +6.8 ppm/°C. The microwave dielectric properties of 0.91Mg₂SiO₄–0.09CaTiO₃ ceramics samples with BLB additions sintered at 900–1,000 °C were characterized, and the permittivity and Q × f were associated with the amount of BLB and the sintering temperature. The sintering temperature of ceramics was reduced to 950 °C from about 1,250 °C and the temperature coefficient of resonant frequency (τ _f ) was modified to ?5.0 ppm/ °C with good Q × f. The addition of 12.0 wt% Bi₂O₃–Li₂CO₃–H₃BO₃ in 0.91Mg₂SiO₄–0.09CaTiO₃ ceramics sintered at 950 °C showed excellent dielectric properties of ε _r  = 7.7, Q × f = 11,300 GHz (f = 6.1 GHz) and τ _f  = ?5.0 ppm/ °C. This represented a very promising candidate material for LTCC applications.     

Combinatorial growth and analysis of Ti-In-Zn-O films deposited by radio‐frequency and direct-current magnetron co-sputtering system

The compositional dependence of co-sputtered Ti-In-Zn-O film properties was investigated by means of a combinatorial technique. The X-ray diffraction result showed that the amorphous Ti-In-Zn-O films were fabricated regardless of the Ti contents [Ti / (Ti + In + Zn), at.%] of 4.5-34.4 at.%. The surface of amorphous Ti-In-Zn-O film is quite smooth. The obtained surface roughness (R_RMS) values ranged from 0.5 nm to 1.7 nm. The superior resistivity of 3.8 × 10^− 4 Ω cm and the transmittance of 92% (at 550 nm) was obtained for the Ti-In-Zn-O film with the elemental composition ratio of 18.6/68.5/12.9 at.% [Ti/In/Zn, at.%]. The indium quantity actually could be reduced to as high as ~ 15 at.% compared to that of commercial indium tin oxide or indium zinc oxide having similar resistivity value of ~ 10^− 4 Ω cm. Overall, the amorphous Ti-In-Zn-O films may serve as a viable, low-cost alternative for flexible transparent conducting electrode applications.