Minimum Phase Difference Research Articles

Thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer

A thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer for measuring optical absorption and thermal diffusivity coefficients in pure solvents is described in this work. The approach combines the sensitivity of both thermal lensing methods and interferometry techniques. The photothermal effect is induced by a pump laser beam generating localized changes in the refractive index of the sample, which are observed as a shift in phase of the interference pattern. Each interference pattern is recorded by means of a digital camera and stored as digital images as a function of time. The images are then numerically processed to calculate the phase shifting map for a specific time. From each phase shifting map, the experimental phase difference as a function of time is calculated giving a phase-time transient, which is fitted to a mathematical model to estimate the optical absorption and thermal diffusivity of the sample. The experimental results show that the sensitivity is approximately λ/4800 for the minimum phase difference measured.

Modeling and validation of eccentricity effects in fine angle signals of high precision angular sensors

High precision optical angular sensors are extensively used for detection and control of position and velocity in payload rotating mechanisms and spacecraft actuators. The accuracy and thus the performance of the encoder are significantly affected due to installation eccentricity. In this paper, a comprehensive study of the causes of installation eccentricity is done. The apportionment of the resultant eccentricity is attributed to variations in diametrical clearances, doweling error, gluing error of the glass disc and bearing wobble. The effect of eccentricity changes during rotation. A new 3-center variable eccentricity model is introduced which improves upon the existing 2-centered one in previous literature. This new 3-centered model is able to better predict the deviations in the fine angle signals in a practical system due to variable eccentricity effect. The efficacy of the mathematical model was validated through two independent experiments- 1) by analyzing the electrical signals from opposite read-heads and 2) by performing mechanical measurements- both done on an actual sensor assembly. The eccentricity value calculated from the maximum and minimum phase difference of the fine angle signals is able to exactly match with the total phase difference variation over one complete rotation. It is observed that the variation in the phase difference between the fine angle sinusoidal signals given by two opposite read-heads varies as a shifted sine over one complete rotation and not as a symmetric sine as shown in previous literature. The eccentricity value obtained from mechanical measurement and that computed using the 3-centered model was matching within 0.1 µm. Both the experimental results support the effectiveness of the 3-centered model.

Sensitive detection of radio-frequency field phase with interacting dark states in Rydberg atoms.

An efficient scheme of phase measurement of a radio-frequency (RF) field is proposed by interacting dark states. Under the condition of electromagnetically induced transparency (EIT), the four-level Rydberg atom exhibits two windows. Compared with the transmission spectrum on resonance, the linewidths of absorption peaks off resonance are very narrow due to the interaction of double dark states. It is interesting to find that the distance of absorption peaks shifts approximately linearly with the phase of an RF field, which can be used to measure the RF field phase. Simulation results show that the linewidth of an absorption peak can be narrowed by more than one order of magnitude, and a narrow linewidth improves the detectable minimum phase difference by more than six times. It helps to reduce analyzation complexity and increase sensing resilience. The dependence of phase measurement on the control field and RF field is also investigated.

A New Method to Detect and Track the Resonance Frequency of Piezoelectric Transducers in Ultrasonic Power Supplies

In this paper, a new method is developed to detect and track the resonance frequency of ultrasonic transducers. In order to have an acceptable performance of transducers, power supplies should be able to detect and track the resonance frequency. Different methods have been used for this purpose. In this research, the voltage of the transducer and the phase difference between the voltage and current are used to find the resonant frequency. The maximum voltage of a transducer is founded in a predefined frequency interval. Afterward, the minimum phase difference between the voltage and current is obtained in a smaller interval around it. The simultaneous use of the voltage and phase shift increases the accuracy and speed of the algorithm. Since the transducer's voltage variations are relatively large near the resonant frequency, it is a versatile parameter compared to the current used in other methods to indicate the resonance frequency. The algorithm is implemented within a microcontroller. An FPGA is used to generate accurate frequency using the Direct Digital Synthesis (DDS) method. The algorithm can detect the resonant frequency under free conditions. Applying force to transducers or emerging the transducer's head to the water changes the resonant frequency. The experimental tests showed that the algorithm could find and track the resonant frequency automatically under loading conditions.

Hybrid beamforming in Multiuser mmWave Massive MIMO System

Conventional MIMO systems typically use full digital processing for optimal performance while it requires an independent radio frequency (RF) chain for each antenna, which is not feasible for large-scale antenna arrays due to the high cost, high-power consumption and high complexity of RF chain components in high frequencies. Fortunately, in recent years, the Hybrid beamforming has been proposed as an efficient and auspicious technique for the practical implementation of millimeter-Wave (mmWave) multiple-input multiple-output (MIMO) wireless systems. In this paper we propose a novel HBF (Hybrid beamforming) algorithm and simulate the sum rate of the proposed approach, then compare it with other algorithms in the sum rates. Specifically, the HBF algorithm as well as the maximizing minimum phase difference algorithm are based on the MMSE (Minimum Mean Square Error). For the full-digital beamforming and the beam steering, the ZF (zero forcing) criterion is employed. Simulations demonstrate that the performance of the proposed algorithm is similar to the full digital algorithm, and its robustness is confirmed by comparisons with other existing algorithms under the same channel model.

A real-time sampling and receiving algorithm based on time extension

In this paper, a real-time sampling and receiving algorithm based on time expansion is proposed. The algorithm has been verified by FPGA (field programmable gate array). Two sets of square wave signals, the phases of which can be controlled, are generated by using DTC (digital to time converter) to control the emission of the signal and receiving ADC (analog to digital converter) sampling. The phase difference between the two signals is an arithmetic sequence by adjusting the frequency multiplication ratio of the PLL (phase locked loop) and the reference frequency of the input signal, the minimum phase difference is 62 ps. The high-frequency signal is sampled by low-frequency ADC, which greatly reduces the design difficulty of the systems power and hardware system, and increases the maintainability of the system. The equivalent sampling frequency can reach 16 GS/s. The algorithm is implemented on FPGA with Verilog HDL, and the verification is completed.

Inertial effects of the semi-passive flapping foil on its energy extraction efficiency

The inertia plays a significant role in the response of a system undergoing flow-induced vibrations, which has been extensively investigated by previous researchers. However, the inertial effects of an energy harvester employing the mechanism of flow-induced vibrations have attracted little attention. This paper concentrates on a semi-passive energy extraction system considering its inertial effects. The incompressible Navier-Stokes equations are solved using a finite-volume based numerical solver with a moving grid technique. A partitioned method is used to couple the fluid and structure motions with the sub-iteration technique and an Aitken relaxation, which guarantees a strong fluid-structure coupling. In addition, a fictitious mass is added to resolve the numerical instability aroused by low density ratios. First, at a fixed mass ratio of r = 1, we identify an optimal set of parameters, at which a maximum efficiency of η = 34% is achieved. Further studies with r ranging from 0.125 to 100 are performed around the optimal parameters. The results show that for the semi-passive flapping energy harvester, the energy harvesting efficiency decreases monotonically with increasing mass ratio. We also notice that the total power extraction stays at a high level with little variation for r < 10; therefore, if we concern more about the amount of power extraction rather than its efficiency, the inertial effects can be neglectable for r < 10. Moreover, since one degree of freedom is released for the semi-passive system, it is possible for the system to automatically determine its optimal operational parameters. We note that the optimal phase difference ϕ = 82° has been well determined, which leads to a good timing of vortex-foil interactions. We note two different trends on phase difference for the effects of reduced frequency and mass ratio, respectively. By varying the reduced frequency f∗, an optimal f∗ is identified, at which the minimum phase difference is achieved. While the relationship between phase difference and mass ratio is monotonic, a maximum phase difference is achieved at the nearly zero mass ratio. Nevertheless, both trends point to the same optimal phase difference, i.e., ϕ = 82° at θ0 = 75°. Furthermore, the relationship between the leading edge vortex and the phase difference is systematically investigated, accounting for the physical reason of existence of the optimal phase difference.

A novel LTCC power combiner

AbstractA novel LTCC power combiner, which is adopted from conventional balun design, is presented. In contrast to the conventional balun network, our design provides one pair of nondifferential signals with minimum phase difference between the outputs. Experimental results are given in the paper to verify our theoretical analysis and design. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 255–257, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20269

The derivation of direction selectivity in the striate cortex.

In the central visual pathway of binocular animals, the property of directional selectivity (DS) is first exhibited in striate cortex. In this study, we sought to determine the neural circuitry underlying the transformation from non-DS neurons to DS cortical cells. In a well established model, DS receptive fields (RFs) are derived from the sum of two non-DS inputs with 90 degrees (quadrature) spatiotemporal phase differences. We explored possible input sources for this model, which include non-DS simple cells and lateral geniculate nucleus (LGN) neurons, by examination of spatiotemporal RFs of single cells and of pairs of cells. We find that distributions of non-DS simple RFs do not match the temporal predictions of the quadrature model because of a lack of long-latency responses. The long-latency inputs could potentially arise from lagged LGN afferents. However, analysis of cell pairs indicates that DS cells receive cortical input from non-DS simple cells for both short- and long-latency components, with temporal phase differences typically <90 degrees. Furthermore, the distribution of minimum phase differences needed to generate DS cells overlaps that exhibited by non-DS simple cells. Considered together, these results are consistent with a linear model whereby DS simple cells are formed from simple-cell inputs, with temporal phase differences often less than quadrature.

Quantitative Electron Holography - From The Basis of Dynamical Interaction to Holographic Materials Analysis

Quantitative analysis of a structure means to determine which atoms are where. The where is restricted by the lateral resolution, and the which is related to the sensitivity against differences of the atomic species. Electron holography is on the move to tackle both questions.• where - Lateral Resolution Electron holography has surmounted conventional electron microscopy in that it has reached atomic resolution both in the amplitude and phase images: with our CM30FEG/UT Special Tuebingen electron microscope, the information limit of 0.09nm and the pixel number of the 2048_ - CCD camera allow to take holograms with image details smaller than 0.095nm; the quality of correction of the aberrations allows an interpretable resolution approaching 0. lnm both in amplitude and phase [1].• which - Phase Detection Limit (PDL) The phase detection limit describes the minimum phase difference detectable well above a given noise level.

Amplitude and phase characteristics of the steady-state visual evoked potential

The amplitude and phase characteristics of the steady-state visual evoked potential (VEP) and grating perception were studied for an unbiased group of fifteen healthy female subjects. The variability of VEP data, as obtained by using a digital sweep technique, was high between subjects but relatively low within them. Earlier claims that psychophysical detection thresholds can be predicted from VEP amplitude values were confirmed, whereas no correlation could be established between amplitude values and the perception of suprathreshold contrast. By using a principle of minimum phase difference the importance of VEP phase as an indicator of data reliability and of perceptual encoding processes could also be established.

Properties of the Symmetrical Circuit and its Broad-Band Five-Port Design

The properties of the mismatched symmetrical five-port circuit are discussed, i.e., the equations for the maximum and minimum couplings of a mismatched symmetrical five-port circuit are derived by appropriate approximations. The approximate equations for the maximum and minimum phase differences due to mismatches of a symmetrical five-port circuit are also derived. Furthermore, a broad-band design theory of a symmetrical five-port circuit with microstrip line is propsed by applying a matching technique which adds a generalized compensating network and matching sections to the fundamental symmetrical five-port circuit. Thus, the bandwidth of the proposed broad-band symmetrical five-port circuit extends to about an octave. The experimental verification has been achieved, and, hence, the validity of the design method is confirmed.

On False-Lock Phenomena in Carrier Tracking Loops

The false-lock phenomena in carrier tracking loops for the suppressed carrier modulation signal, such as phase-shift keyed (PSK) signals, present serious problems to the design of digital communication systems. There are two kinds of false-lock phenomena: one is related to the loop delay time and the other is to the modulation frequency. This paper describes an analysis of the latter type obsered in the phase-lock loops (PLL's) comprising the remodulation or decision feedback. The mechanism of the false-lock phenomena is best described by using the minimum phase difference between the input modulated carrier and the voltage controlled oscillator (VC-O) output as a parameter. It is shown that the loop can be locked at the offset frequencies of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm(m/n)f_{c}</tex> in both the sampled and nonsampled control systems, where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m/n</tex> is a simple fraction and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> denotes the modulation frequency. The lock and capture ranges for these false-lock frequencies are derived.

Metachronal Co-ordination of the Comb Plates of the Ctenophore Pleurobrachia

ABSTRACT The activity of comb plates of Pleurobrachia was analysed from cine films. The interval between successive beats of a comb plate varied from several seconds to about 50 msec, in normal sea water; this variation in frequency was accompanied by a variation wave velocity. There was an almost linear relationship between wave velocity and frequency, ranging from a minimal wave velocity of about 20 mm./sec. at low frequencies to a maximal wave velocity of about 80 mm./sec. at the highest frequencies. The wave velocity was accelerated at low frequencies by increased Mg2+ concentrations, by ouabain and by curare, and the same substances decreased the wave velocity at high frequencies. The frequency of beat was accelerated by certain concentrations of adrenaline, serotonin, Mg2+, ouabain and curare. Decreases of frequency were found in acetylcholine (and eserine) and strychnine. These substances act on the excitability of the pacemaker. It is concluded that metachronal transmission is by a flow of electric current from one comb plate to the next. Depolarization, either by a recent excitation of the comb plate or by agents like ouabain causes increased excitability and a more rapid transmission. The minimum phase difference between adjacent comb plates was about 5 msec. The comb plates are almost entirely dependent on a conducted impulse for their excitation; occasionally a spontaneous excitation occurs. The membranelles of Stentor depend more on excitation within the ciliary base and less on the conducted impulse. The two systems are believed to share common features, but differ in the relative importance of these features. Reverse waves involving the beating of comb plates in the normal direction were observed. The wave velocity of these waves increased only slightly over a wide frequency range. Reverse waves of this type are believed to be transmitted by mechanical contact between the comb plates.