Half-power Points Research Articles

Analysis of Tapered Fibre Optic Surface Plasmon Resonance Bio-Sensor Chip With Highly Perturbed Taper Profiles.

A numerical model based on the Transfer matrix method (TMM) is proposed for the first time to study the gold coated tapered fibre optic surface plasmon resonance (SPR) with eight different types of taper profiles namely linear, exponential-linear, Gaussian, quadratic, sinusoidal, error function type and highly perturbed taper profile so-called chirp type of profile. The performance in terms of sensitivity, full width at half maximum (FWHM), detection accuracy (D.A.), amplitude dip, and half power points are estimated with respect to tapering ratio and choices of taper profile. It is found that sensitivity increased almost linearly with the taper ratio of each taper choice for the account of the reduction of detection accuracy. It has been found that sensitivity is highest for the case of chirp taper profile and lowest for the case of quadratic taper profile at low taper ratio. In this study, the aqueous solution is considered for sensor development which is adulterated by biomolecules species like DNA, blood samples, etc.

CMOS Linear Laser Driver for Intermediate Frequency over Fiber (IFoF) Links

The main objective of the proposed linear laser driver (LLD) is to reduce signal distortion in an analog direct modulation laser configuration used for intermediate frequency over fiber links. This work draws on an open-loop configuration featuring two differential pair blocks in a cascade arrangement to achieve a bandwidth measurement of 415 MHz at the half-power point, a total harmonic distortion of 4.57% for a fundamental frequency of 100 MHz, and an amplitude of 100 mVpp. The LLD provides a gain of 12.3 dB for a differential output and an output impedance of 46 Ω. The design, layout, and integration correspond to the process design kit for TSMC 65-nm CMOS technology. Experimental results show the advantage over other previously reported laser drivers.

Finding damping loss factor using circle-fit method on Nyquist diagrams.

Viscoelastic materials are commonly applied into vehicles sheet metal structures including the roof and doors in order to increase the amount of structural damping. The added damping from viscoelastic materials dissipates a greater amount of vibrational energy, subsequently reducing vibration displacement, structure borne noise, and energy flow to adjacent structures. Because damping treatments have the disadvantage of adding weight to the treated structure, adequate tools to characterize and evaluate their efficiency are necessary. In this paper, natural frequencies and modal damping are determined by applying circle-fit interpolation to measured data. Comparison to traditional peak picking and half-power point methods shows that this geometric approach allows modal frequencies to be identified more clearly, even for measurement systems with reduced frequency resolution and the process can be easily automated.

MeerKAT Primary-beam Measurements in the L Band

Abstract Full-polarization primary-beam patterns of MeerKAT antennas have been measured in the L band (856–1711MHz) by means of radio holography using celestial targets. This paper presents the observed frequency-dependent properties of these beams and guides users of this 64 antenna radio telescope that are concerned by its direction-dependent polarization effects. In this work, the effects on the primary beams due to modeling simplifications, bandwidth averaging, gravitational loading, and ambient temperature are quantified within the half-power region of the beam. A perspective is provided on the level of significance of typical use case effects. It is shown that antenna pointing is a leading cause of inaccuracy for telescope users in the presumed beam shape, introducing errors exceeding 1% in power near the half-power point of beams, owing to a telescope pointing accuracy of σ ≈ 0.′6. Disregarding these pointing errors, variability in the Stokes I beam shape relative to the array average is most commonly around 0.3% in power; however, the impact above 1500 MHz is on average triple that of the lower half of the band. This happens because the proportion of higher-order waveguide modes that are activated and propagate is sensitive to small manufacturing differences in the orthomode transducer for each receiver. Primary-beam correction verification test results for an off-axis spectral-index measurement experiment are included.

Asymptotic behavior of the added damping effect of a fuzzy substructure and the importance of modal overlap

The theory of fuzzy structures was introduced by Christian Soize in 1986 as a means of predicting the average vibroacoustic behavior of complex structures with imprecisely known internals. The damping and mass loading effects of a fuzzy internal substructure, modeled by random 1-dof oscillators, are analyzed through a boundary impedance. The Pierce-Sparrow-Russell and Strasberg-Feit models of fuzzy structures simplify the mathematics involved and concentrate on the physical concepts behind the added damping and mass loading effects of the internal substructure. Both models contain a problematic step in which a discontinuous impedance sum is replaced with a smooth integral. This paper explores the asymptotic behavior of the impedance sum in the limits of a large number N of attachments and small attachment damping ζ in order to determine the viability of this step. Modal overlap plays a crucial role, since half power points of individual attachment resonances overlap for small ζ when the density of attachments is high enough or for fewer attachments when the damping of individual attachments is high enough. It is found that the impedance sum sufficiently approaches the integral limit when Nζ ≧2. [Work originally sponsored by ONR.]

Development of the Dynamic Signal Analyzer Based on Labview+Arduino to Identify Structure Dynamic Characteristics

In this work, the dynamic signal analyzer (DSA) based on Labview+Arduino has been developed. The DSA is validated to acquire and analyze vibration of two degrees of freedom (2-DOF) structure as the test rig. Vibration signal generated by bump test method to the test rig. Vibrations of the test rig are measured by using micro-electro-mechanical system (MEMS)-based accelerometers. The measured vibrations are acquired and analyzed by using the DSA. In the DSA is used fast Fourier transform (FFT) method to obtain natural frequencies of the structure and half power point (HPP) method to estimate damping ratio of structure. From the testing was conducted can be concluded that the DSA capable to determine natural frequency and damping ratio of the 2-DOF structure. If the obtained results are compared to theoretically results, there are different results about less than 10%.

Constrained layer damping treatment of a model support sting

In transonic wind tunnel tests, the pulsating airflow is prone to induce the first order resonance of the sting support system. The resonance limits the wind tunnel test envelope, makes the test data inaccurate, and brings potential security risks. In this paper, a model support sting with constrained layer damping (CLD) treatment is proposed to reduce the first order resonance response. The CLD treatment mainly consists of material selection and geometric optimization processes. The damping performance of the optimized CLD sting is compared with an AISI 1045 steel sting with the identical diameter in laboratory. The frequency response curves of the CLD sting support system and the AISI 1045 steel sting support system are obtained by sine sweep tests. The test results show that the first order resonance response of the CLD sting support system is 37.3% of that of the AISI 1045 steel sting support system. The first order damping ratios are calculated from the frequency response curves by half power point method. It is found that the first order damping ratio of the CLD sting support system is approximately 2.6 times that of the AISI 1045 steel sting support system.

Effect of Electrical Damping Ratio on Maximum Average Power of an Electromagnetic Vibration Harvester at Resonance and off-Resonance Conditions

Energy harvesting has opened up new ways to power low energy electronics without any need for batteries. The most advanced types of harvesters are piezoelectric, electrostatic and electromagnetic which use kinetic energy in form of vibrations. Electromagnetic harvesters (EHs) are efficient, less costly and offer huge design flexibility. As such, in this paper some analytical and experimental studies on maximum average harvestable power (Pave) from typical design of EH using the popular coupling architecture (a cylindrical magnet oscillating in a copper coil) have been carried out. The effect of frequency of excitation and electrical (ζe ) and mechanical damping ratios (ζm) on Pave obtained from an EH has been investigated. For this purpose, an EH using NdFeB (neodymium magnet) magnet oscillating in a copper coil has been designed and developed. An experimental test set up has developed which comprises of (i) a cam-follower type drive mechanism to simulate a vibration source with variable amplitude and frequency of base excitation, (ii) a spring-mass system with an EH system in parallel with the spring to provide the relative motion between the magnet and the copper coil, (iii) the attendant instrumentation comprising of ultrasonic sensor to sense the displacements of base and mass, motor drive speed measurement and an open source platform (ARDUINO) with programmable circuit board and software and data acquisition system. Using the developed experimental set up, (i)frequency response curve for vibrating system with EH has been obtained from which equivalent electrical damping ζe has been determined using half power point method, and (ii)the values of relative displacements of magnet and coil, at various excitation frequencies have been recorded. Using the analytical expression for the Pave of SDOF EH has been determined both at resonance and off resonance conditions, for three different values of ζe namely ζe = ζm, ζe = 5ζm, and ζe = 10ζm. It is observed that the maximum Pave is obtained for condition ζe = ζm. As the value of ζe increases, the Pave increases, at resonant frequency and considerable power is made available at off-resonance frequencies. It is concluded that ζe should be increased to enhance the maximum average harvestable power from EH and vibrating system should be so designed to have ζm, as small as possible.

Time Discriminator for Satellite Radar Altimeter Tracker System

The article deals with the study of quasi-optimal TOA discriminator of an onboard echo-signal tracker of the altimeter carried by a space vehicle. In modern space-based altimeters, final data processing is imposed on the ground-based center receiving information from the spacecraft through a telemetry line, while the main task of an onboard delaylocked loop is to reliably retain the received echo-signal within the tracking window. The optimum discriminator of an onboard loop providing the potential accuracy of time measurement can appear difficult to implement. In the discriminator considered an error signal is proportional to the time mismatch between the half power point of the received power pattern and the tracking window. The equation for the equivalent time fluctuation variance is derived. It is also found that the discriminator proposed is as good at tracking precision as the maximum-power-point discriminator and maximums teepness discriminator, being at the same time much more attractive in terms of hardware complexity. The theoretical results are well consistent with the computer simulation. This simulation is performed both directly and using different methods of censoring the error signal at the discriminator output to effectively neutralize possible abnormal errors that are not taken into account by theoretical analysis.

Oberst and aging tests of damped CFRP materials: New fitting procedure and experimental results

Abstract Materials play a fundamental role in defining the vibrational and acoustic characteristics of structures and their importance is even increasing because of the continuing demand for lightweight products. Carbon Fibre Reinforced Plastics (CRFP) components are becoming more and more popular because of their excellent mechanical properties but are unfortunately almost unable to dissipate energy. This is one of the reasons why their usage is limited to structural components and does not directly affect acoustic and vibrational response, which are among the factors responsible for harshness and comfort. In vehicles, for example, large panels of CFRP are as noisy as metallic panels so that this kind of lightweight structures is only used when a limited mass is of paramount importance, e.g. in racing cars. The chance of incorporating a damping material in the stacking sequence of CF layers that define a composite seems to be a viable solution to ameliorate the vibrational behaviour of composite materials. This configuration permits to cure the damping layers together with the resins, in order to obtain both free and constrained layer solutions. In this paper, the Oberst beam method has been chosen to determine the elastic modulus and loss factor of such materials, as a function of both frequency and temperature. Three nominally identical samples for each configuration have been tested in a temperature controlled environment, according to the Oberst beam test method. The effects of aging have been simulated by an accelerated standard procedure, with cyclically varying temperature and humidity for a total of 792 h (3 cycles x 264 h). The analysis of experimental data has been performed in the frequency domain by a least square fitting procedure, aimed at outperforming the simple half-power point method. An open source version of the fitting technique has also been implemented and can be obtained from the authors under the CC-by license.

Novel method to measure unloaded quality factor of resonant cavities at room temperature

We demonstrated a novel method to measure the unloaded quality factor (Q factor) of high-Q resonant cavities. This method was used to obtain data with low errors and calculate the unloaded Q factor. This procedure was more reliable than traditional methods. The data required for the method were near the resonant frequency, not at the half-power points of the reflection coefficient curve or Smith chart. We applied the new method to measure a resonant cavity with an unloaded Q factor of ~ 100,000, obtaining good agreement between the measured and theoretical results.

Meterwavelength Single-pulse Polarimetric Emission Survey. IV. The Period Dependence of Component Widths of Pulsars

Abstract The core component width in normal pulsars, with periods (P) > 0.1 s, measured at the half-power point at 1 GHz, has a lower boundary line (LBL) that closely follows the P −0.5 scaling relation. This result is of fundamental importance for understanding the emission process and requires extended studies over a wider frequency range. In this paper we have carried out a detailed study of the profile component widths of 123 normal pulsars observed in the Meterwavelength Single-pulse Polarimetric Emission Survey at 333 and 618 MHz. The components in the pulse profile were separated into core and conal classes. We found that at both frequencies, the core, as well as the conal component widths versus period, had a LBL that followed the P −0.5 relation with a similar lower boundary. The radio emission in normal pulsars has been observationally shown to arise from a narrow range of heights around a few hundred kilometers above the stellar surface. In the past the P −0.5 relation has been considered as evidence for emission arising from last open dipolar magnetic field lines. We show that the P −0.5 dependence only holds if the trailing and leading half-power points of the component are associated with the last open field line. In such a scenario we do not find any physical motivation that can explain the P −0.5 dependence for both core and conal components as evidence for dipolar geometry in normal pulsars. We believe the period dependence is a result of a currently unexplained physical phenomenon.

High precision pointing error detection method for large radio telescope

In the paper, the main factors influencing pointing precision of large radio telescopes are discussed. Then the TianMa radio telescope (TM65 m) is selected for demonstration. The methods of detecting and separating the pointing errors which produce in all the segments from the subreflector to the track rail of the telescope are introduced. They includes: (1) half power point tracking to evaluate the overall antenna pointing error; (2) detecting the pointing error due to position changing of the subreflector support; (3) detecting the deviation of the antenna mount due to temperature changing; (4) detecting the asynchronization of the mechanical axis and the encode axis; (5) high precision pointing modeling based on the uneveness of track rail. A few measurement methods and their respective results are discussed.

Effect of beamwidth on detection of near-bottom targets with multibeam echosounders

In multibeam echosounding, beamwidth and sidelobe levels constrain detection of echoes from near-bottom targets that are often masked by echoes from the bottom received in the mainlobe of individual beams or through their sidelobes. Acoustic backscatter data collected with multibeam echosounders from various manufacturers indicate that the customary half power point (−3 dB) metric for the angular width of individual beams underestimates the masking effects of bottom echoes. A better fit of the detected bottom echo trace is obtained with beamwidths estimated 10 dB below the maximum response of each beam. The corresponding beamwidths are roughly 66% larger at −10 dB than at −3 dB for a canonical sinc squared beam pattern. Therefore, using the manufacturers’ nominal −3 dB beamwidth specifications yields underestimates by the same percentage of the area ensonified by the pulse within a beam, and corresponding overestimates of the detected acoustic backscatter level used to infer target strength or bottom back...

PV panel modeling with improved parameter extraction technique

An accurate model of the PV panel is useful to predict its behavior at all operating points for various applications. However, most of the manufacturers provide datasheet values at only open circuit point, short circuit point and maximum power point. Single mechanism five parameters (1M5P) model which contains a series and parallel resistance is presented. The model has five unknown parameters which need to be extracted. In this paper, the parameter extraction technique is improved for accuracy, simplicity and practicability. It requires minimum amount of data from the datasheet and does not require any complex iteration. The accuracy of the model with improved parameter extraction technique (IPET) is firstly validated with datasheet in the controlled irradiation environment. Secondly it is also compared under real-time uncontrolled irradiation environment in order to check the practicability of the model. Finally, the experiment for uncontrolled irradiation environment is carried out on three operating point’s i.e. maximum power point and two half power points to verify the accuracy of the model over the wider operating range.. The results of the model with IPET are in good agreement with both datasheet and experimental results with difference of less than 5%. It also shows significant improvement in accuracy when compared to the existing models.

Experimental study of vibration characteristics of FRP cables based on Long-Gauge strain

Steel cables as the most important components are widely used in the certain types of structures such as cablesupported bridges, but the long-span structures may result in an increase in fatigue under high stress and corrosion of steel cables. The traditional steel cable is becoming a more evident hindrance. Fiber Reinforced Polymer (FRP) cables with lightweight, high-strength are widely used in civil engineering, but there is little research in vibrational characteristics of FRP cables, especially on the damping characteristic. This article studied the two methods to evaluate dynamical damping characteristic of basalt FRP(BFRP) and glass FRP(GFRP) cables. First, the vibration tests of the B/G FRP cables with different diameter and different cable force were executed. Second, the cables forces were calculated using dynamic strain, static strain and dynamic acceleration respectively, which were further compared with the measured force. Third, experimental modal damping of each cables was calculated by the half power point method, and was compared with the calculation by Rayleigh damping theory and energy dissipation damping theory. The results indicate that (1) The experimental damping of FRP cables decreases with the increase of cable force, and the trend of experimental damping changes is roughly similar with the theoretical damping. (2) The distribution of modal damping calculated by Rayleigh damping theory is closer to the experimental results, and the damping performance of GFRP cables is better than BFRP cables.

Comparative study on the speckle filters for the very high-resolution polarimetric synthetic aperture radar imagery

With the emergence of very high-resolution airborne synthetic aperture radar systems, it is necessary to reinvestigate these proposed methods with respect to their despeckling performances. As for the very high resolution polarimetric synthetic aperture radar (PolSAR) data, the presumption that the resolution cell is much larger than the radar wavelength becomes ineffective. Therefore, some classic and new filters are thoroughly reviewed. For the evaluation of speckle filters, both indicators for polarimetric information and spatial information are listed. The absolute relative bias is introduced, with the purpose of measuring the filtering performance concerning the indicators for polarimetric information. Moreover, the ratio of half power point width is employed to quantitatively assess the degree of point target preservation. A series of experiments are carried out based on the real PolSAR imagery which is obtained from an uninhabited aerial vehicle synthetic aperture radar system. It can be concluded that existing filters can only attain good performance with reference to part of the indicators. As regards very high-resolution PolSAR imagery, it is necessary to conceive more apposite new filters or make improved versions of the existing filters.

Beam width estimation of microwave antennas using lock-in infrared thermography

The beam width of microwave antennas can be easily determined using infrared thermography. A thin absorption screen made up of some carbon loaded polymer is placed in front of a microwave antenna. The electromagnetic waves impinging the screen are partially absorbed by it, resulting in temperature rise of this screen. This temperature rise is monitored by an infrared camera. These infra red images of the temperature distribution are identical to the power distribution of the incident electromagnetic field at the screen location. The distance between half power points on the main lobe of the radiation pattern at the screen location in two orthogonal directions (E- and H-planes) can be easily found. From these distances the half power beam widths in both E- and H-planes can be calculated. Further from these beam widths, directivity is also calculated.The experiments were carried with a patch antenna radiating at 2.45GHz. In order to show the repeatability of the results, experiments were carried for different distances between patch antenna and absorption screen. A great agreement is seen between simulation, measurement and experimental (thermographic) results.The microwave source is modulated at a low frequency so as to avoid the lateral spread of heat on the absorption screen and to permit lock-in detection of temperature distribution.

Electromagnetic Field Propagation Characteristics of a Contactless Setting of Fuze

The electromagnetic field propagation characteristics of a contactless setting of fuze are proposed. Its typical scheme that includes two coils, an insulated resin cylinder and a metal hemisphere shell, is set up. Firstly, the near field is non-uniform spherical waves. Secondly, the electric field intensity vector E is parallel to xOy plane, while the magnetic field intensity vector H exists in arbitrary direction; the vector E only has a transverse component, which is perpendicular to its propagation direction, while the vector H has both transverse and radial ones. Thirdly, the amplitude of vector E is inversely proportional to the square of distance, while the amplitude of vector H inversely proportional to the cube of distance; both vectors E and H are directional. Fourthly, when latitude angle θ is equal to 90°, the amplitude of E is maximal, and it is zero as θ is equal to 0°; when latitude angle θ is equal to 0°, the amplitude of H is maximal, and it is minimal as 0 is equal to 90°. For E-plane, the beam width 2θ° between zero power points is 180°, while the beam width 2θ0 5 between half power points is 90°; for H-plane, the beam width 2θ° does not exist; the beam width 2θ0.5 is 2arcsin[(2/3)0.5]. Fifthly, there are reflection waves on the surface of both the insulated resin cylinder and the metal hemisphere shell that produce a full reflection phenomenon; it is possible to produce full transmission phenomenon on the surface of the cylinder. An experimental example is presented for verifying these theoretical predictions.

Pulsar timing noise from superfluid turbulence

Shear-driven turbulence in the superfluid interior of a neutron star exerts a fluctuating torque on the rigid crust, causing the rotational phase to walk randomly. The phase fluctuation spectrum is calculated analytically for incompressible Kolmogorov turbulence and is found to be red; the half-power point is set by the observed spin-down rate, the crust-superfluid lag, and the dynamical response time of the superfluid. Preliminary limits are placed on the latter quantities using selected time- and frequency-domain data. It is found that measurements of the normalization and slope of the power spectrum are reproduced for reasonable choices of the turbulence parameters. The results point preferentially to the neutron star interior containing a turbulent superfluid rather than a turbulent Navier-Stokes fluid. The implications for gravitational wave detection by pulsar timing arrays are discussed briefly.