Terms Of Frequency Bandwidth Research Articles

Towards an optimal frequency and time response of singe-tube pressure measurement systems under continuum-flow conditions

The pressure transmission tube, as part of a pressure measurement system, generally has a considerable influence on its dynamic characteristics. The paper deals with the mathematical modelling of the dynamic behaviour of pressure transmission tubes with the aim of providing guidelines for the optimal design of such systems in the frequency and time domains. The mathematical models used are based on linear wave theory and continuum flow mechanics with no-slip and isothermal boundary conditions. The frequency responses were evaluated in terms of frequency bandwidth and the transient step responses in terms of settling and rise times. Following a systematic analysis of these characteristic parameters, we derived an analytically formulated optimisation objective function defining the transition between the low-wavenumber and high-wavenumber pressure waves in the pressure transmission tubes. The demanded dynamic behaviour in the frequency and time domains can be achieved through an appropriate ratio between the actual tube radius and the so-called transition tube radius, which was derived as a function of the tube length, end volume and fluid properties.

Design, Implementation, and Characterization of a Compact Lock-in Add-on for Low-Frequency Impedance Measurements

Impedance measurements are crucial in a variety of applications, from the characterization of lithium batteries, microbial fuel cells, and biosensors to the study of polymers and material degradation, where strict requirements have to be met in terms of frequency bandwidth and current level. Here, we present a cost-effective compact solution for ultra-low-frequency impedance measurements, operating in a wide range, from 1 mHz to 250 kHz. Coupled to a lock-in amplifier, the designed circuit is based on a Howland current pump cascaded by a precision current divider in order to set the conversion factor at 100 nA/V, 1 μA/V, or 100 μA/V. Therefore, it is possible to generate very low-current signals to measure resistive impedances up to 100 MΩ. In addition, a feedback network is inserted to null the voltage drift induced by leakage currents and offset voltages, thus allowing the measurement of low-capacitance loads, experimentally tested down to 10 nF. Remarkably, the feedback network allows to perform measurements also in the presence of high voltage bias of the load and experimental results performed up to 60 V demonstrate the excellent stability of the designed system, thus a high voltage compliance. The proposed circuit is particularly interesting for the conditioning of both resistive and capacitive sensors and it is likely to be an effective solution for the implementation of a portable instrument for measuring signals from biosensors.

Effect of geometric non-linearity and tip mass on the frequency bandwidth of a cantilever piezoelectric energy harvester under tip excitation

The research community is investigating a variety of approaches to convert mechanical energies to useful electrical energy in order to fulfil the ever-increasing demand for energy and fulfil the requirements of the various sectors. In this regard, numerous contributions toward increasing the capacity and efficiency of the various energy harvesting techniques have been proposed in recent times; one such promising technology is piezoelectric-based vibration energy harvesting. In the present work, the effect of geometric nonlinearity and tip mass is investigated on the operational frequency range of a cantilever nonlinear piezoelectric energy harvester. The proposed mathematical model is based on an energy-based variational approach. The methodology is formulated for the piezoelectric patched cantilever beam and, eventually solved using an efficient numerical technique . An amplitude incremental iterative algorithm is used to solve the non-linear governing equations of motion for the proposed non-linear broadband harvester along with the experimental validation. Firstly, a parametric study is performed to determine the optimum piezoelectric patch dimensions. Subsequently, the attempt is made to increase the frequency bandwidth for optimum energy harvesting by taking advantage of geometrically non-linear behaviour. Additionally, a tip mass, appropriate for the excitation level, can be added to the harvester design to make it effective for lower excitation frequency. Increased frequency bandwidth for improved energy harvesting capacity with the hardening type nonlinearity and tip mass is meaningfully shown with the help of frequency-amplitude response. Furthermore, to interpret the efficacy of nonlinear harvesters in terms of frequency band-width, power spectral density plots with improved harvesting capability are presented and compared with the conventional linear vibration energy harvester.

Water-Cooled Fast-Response Wall-Static Pressure Probes for Harsh Combustor Environment Applications

The present paper discusses the design methodology for a water-cooled fast-response wall-static pressure probe intended for measurements in the combustion chamber of gas turbines, as well as the results from a series of tests performed with the prototype of the probe mounted in the primary zone of the combustion chamber of a turboshaft engine test rig. The first part of the present paper reviews the design methodology of a water-cooled fast-response wall static pressure probe intended for measurements of combustion noise and instabilities in gas turbine combustors, describing the optimization of measurement performance in terms of frequency bandwidth ([0 – 40kHz]) as well as the design of the cooling layout ensuring the sensor’s integrity within a harsh environment. The second part of the paper focuses on the analysis of the results obtained from trial tests performed using the probe prototype mounted in the primary zone of the combustion chamber of a helicopter engine test rig. The strengths and strong potential for further growth of the current probe design are highlighted, while its shortcomings and (short-term) solutions to these shortcomings are also discussed.

An Optimal Procedure for the Design of Discrete Constrained Lens Antennas with Minimized Optical Aberrations. Part II: Three-Dimensional Multifocal Architectures

Novel three-dimensional discrete lens antennas characterized by a number of focal points ranging from one to five and defined explicitly via analytical equations are presented in the paper. A procedure to derive rotationally symmetric afocal lenses starting from multifocal lenses that are not rotationally symmetric is proposed as well. In addition, an innovative method to identify the focal surface minimizing the optical aberrations is derived. The lenses are compared in terms of optical aberrations and accommodation constraints. The most suitable lens architectures depend mainly on the required angular field of view and magnification factor. It is shown that a reduction by a factor close to 3 in the optical aberrations can be obtained when selecting the most appropriate lens architecture and keeping comparable accommodation constraints. The results, derived exploiting a geometrical optics (GO) formulation, provide useful indications for the preliminary design of constrained lens antennas before adopting full wave rigorous techniques. Three-dimensional discrete lens antennas can offer significant advantages as compared to conventional analog beamforming networks (as those based on Butler matrixes) in terms of frequency bandwidth, number of beams and number of radiating elements.

Deblending and merging of 3D multi‐sweep seismic blended data

ABSTRACTSeismic blended source acquisition, also referred to as simultaneous source acquisition, is a cost‐effective technology that achieves a significant reduction in acquisition cycle time and increases seismic crew field productivity. The dispersed source array is a blended acquisition field technique that simultaneously employs sources emitting different types of sweeps (i.e. multi‐sweep), in terms of frequency bandwidth and length, which ultimately will result in a full broadband seismic data. In this paper, deblending of 3D multi‐sweep seismic blended data and the subsequent merging of the data volumes having different frequency bandwidths will be discussed. In specific data domains where the signal component is coherent, interference shots (i.e. blending noise) are randomly distributed in the data space according to its own shot firing time. Therefore, the deblending process, which separates interference shots from a signal component, becomes a noise attenuation problem. A sparse inversion methodology is applied in the frequency–wavenumber–wavenumber (f–kx–ky) domain to attenuate blending noise. By applying this deblending methodology to both dispersed source array's low‐ and mid‐high‐frequency bandwidths, we obtained high‐quality deblending results. For both frequency bandwidths of the deblended dispersed source array data, additional effort was made to combine the two datasets to a single broadband data volume. Consequently, deblending and merging of the dispersed source array blended data generated a broadband, deblended and well‐balanced seismic volume suitable for further processing and reservoir characterization applications.

Wave power extraction from a hybrid oscillating water column-oscillating buoy wave energy converter

Oscillating water column (OWC) devices and oscillating buoys (OBs) are two of the main types of wave energy converters (WECs). In this paper a hybrid oscillating water column-oscillating buoy wave energy converter is proposed, which we have named OWCOB. The oscillating buoy is hinged at the outer wall of the oscillating water column. As waves propagate through the OWCOB, the water column within the OWC chamber moves up and down, producing air flow to propel a turbine. Meanwhile, the oscillation of the OB drives a separate hydraulic system. To solve the wave diffraction and radiation problems of the OWCOB and investigate its energy capture performance, an analytical model is developed based on linear potential flow theory and the eigenfunction matching method. Assuming that the PTOs of the OWC and OB are both linear, the wave power extraction of the OWCOB is evaluated in the frequency domain. Of the two configurations considered, the OWCOB with the OWC opening waveward and the OB hinged leeward is found to have a broader primary frequency band of wave power capture compared to the OWCOB with the OWC opening and the OB on the same side. Further, a thorough sensitivity analysis of power capture is carried out considering the main design parameters (size and submergence of the OWC opening, distance between the OWC and the OB, OB hinge elevation, OB radius), which can form the basis of an optimization study for a particular wave climate. Importantly, we find that the OWCOB performs generally better than stand-alone OWCs and OBs, not least in terms of frequency bandwidth.

Dynamics of Transition Regime in Bistable Vibration Energy Harvesters

Vibration energy harvesting can be an effective method for scavenging wasted mechanical energy for use by wireless sensors that have limited battery life. Two major goals in designing energy harvesters are enhancing the power scavenged at low frequency and improving efficiency by increasing the frequency bandwidth. To achieve these goals, we derived a magnetoelastic beam operated at the transition between mono- and bi-stable regions. By improving the mathematical model of the interaction of magnetic force and beam dynamics, we obtained a precise prediction of natural frequencies as the distance of magnets varies. Using the shooting technique for the improved model, we present a fundamental understanding of interesting combined softening and hardening responses that happen at the transition between the two regimes. The transition regime is proposed as the optimal region for energy conversion in terms of frequency bandwidth and output voltage. Using this technique, low-frequency vibration energy harvesting at around 17 Hz was possible. The theoretical results were in good agreement with the experimental results. The target application is to power wildlife biologging devices from bird flights that have consistent high power density around 16 Hz (Shafer et al., 2015, “The Case for Energy Harvesting on Wildlife in Flight,” Smart Mater. Struct., 24(2), p. 025031).

A comparative study on switchable frequency‐selective surfaces

ABSTRACTA comparative study guide for several variant switchable frequency‐selective surfaces (SFSS) with different geometries is introduced. The unit cells are designed for the first realized frequency band to study the transmission coefficient bandwidth. Maximum transmission coefficient bandwidth obtained in the transparent state is around 9.62 GHz while the maximum bandwidth obtained in the reflective state is around 5.46 GHz for the solid interior triangle and square frequency‐selective surface, respectively. The maximum joint bandwidth for both transparent and reflective states is 5.46 GHz in the square‐solid‐interior unit cell. Practical results are compatible with simulated results and the obtained results are summarized in a table to provide a clear comparison between the proposed SFSS unit cells in terms of frequency bandwidth. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:839–844, 2016

A compact circularly polarized high gain S-band nanosatellite antenna using ramped convergence particle swarm optimization

In this article, a compact single layer coaxial probe fed circularly polarized high gain patch antenna for HORYU-IV nanosatellite S-band communication is presented. The proposed antenna consists of four asymmetric V-shaped slits, one at each corner of a rectangular patch, and a parasitic rectangular strip. Using ramped convergence particle swarm optimization algorithm to optimize some primary parameters of the antenna. Prototypes of the proposed design antenna was fabricated and studied experimentally. Measurement and simulation results are indicating that the proposed antenna realizes the required HORYU-IV nanosatellite specifications for low earth orbit satellite application in terms of frequency bandwidth, axial ratio (AR), right hand circular polarization (RHCP), gain, and 3-dB AR beamwidth. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1503–1508, 2015

Bistable electromagnetic generator based on buckled beams for vibration energy harvesting

Bistable piezoelectric generators have been demonstrated to outperform linear spring–mass–damper systems in terms of frequency bandwidth and harvested power from wideband vibrations. In this work, a nonlinear vibration energy harvester consisting of clamped–clamped buckled beams combined with a four-pole magnet across coil generator is investigated. By buckling the support beams, an elastic Duffing potential is provided so that the seismic mass can pass from being dynamically monostable to bistable. A theoretical model of the system is presented, and experimental tests are performed on a prototype. In the unbuckled state, the device exhibits higher maximum power at resonance than in the buckled, but, in general, no significant difference is noted in terms of average harvested power between monostable and bistable regimes under harmonic and band-limited stochastic vibrations. However, for an optimal acceleration level, the bistable configuration shows a factor of 2.5 times wider bandwidth and higher power outside from the natural resonance as compared with the monostable regime. It is also observed that the benefits of bistable dynamics mostly depend on the ratio between the characteristic cutoff frequency of the electrical circuit and the mechanical resonance.

Cancellation of Beam Squint with Frequency in Serial Beamforming Network-Fed Linear Array Antennas

This communication investigates the capability of serial beamforming networks to cancel beam squint with frequency in linear array applications. Such a property could be of interest for broadband applications with multiple narrow beams. The theoretical aspects are described, as well as the impact on the beamforming network design. It is found that the main limitation to achieving beam-squint cancellation in serial beamforming networks comes from the insertion phase of the different directional couplers needed. A specific design at S band with a single-beam four-element linear array is detailed. Experimental validation in microstrip technology is presented, confirming the cancellation of beam squint with frequency over a 9% bandwidth. The design of the elementary directional couplers is the main limitation in terms of frequency bandwidth. The applicability of such a design procedure to serial multiple beamforming networks, namely Blass and Nolen matrices, is discussed.

Acoustic positioning using a tetrahedral ultrashort baseline array of an acoustic modem source transmitting frequency-hopped sequences

Acoustic communications and positioning are vital aspects of unmanned underwater vehicle operations. The usage of separate units on each vehicle has become an issue in terms of frequency bandwidth, space, power, and cost. Most vehicles rely on acoustic modems transmitting frequency-hopped multiple frequency-shift keyed sequences for command-and-control operations, which can be used to locate the vehicle with a good level of accuracy without requiring extra signal transmission. In this paper, an ultrashort baseline acoustic positioning technique has been designed, simulated, and tested to locate an acoustic modem source in three dimensions using a tetrahedral, half-wavelength acoustic antenna. The position estimation is performed using the detection sequence contained in each message, which is a series of frequency-hopped pulses. Maximum likelihood estimation of azimuth and elevation estimation is performed using a varying number of pulse and various signal-to-noise ratios. Simulated and measured position estimation error match closely, and indicate that the accuracy of this system improves dramatically as the number of pulses processed increases, given a fixed signal-to-noise ratio.

Dual-band circularly polarized microstrip antenna for satellite applications

This letter presents a dual-band circularly polarized patch antenna dedicated to satellite communications. The dual-band behavior is obtained by inserting a small X-band microstrip patch antenna into a large L-band one. Both patches are printed on the same substrate and fed by electromagnetic coupling through two perpendicular slots etched in their ground planes. These slots are fed by two different 90/spl deg/ microstrip branch-line couplers printed on a stacked lower substrate. A prototype of the antenna was realized with a 1.5-mm-thick upper layer substrate and a 0.758-mm-thick feed layer substrate, both of the same dielectric material with a relative permittivity of /spl epsiv//sub r/=2.22. Simulation and measurement results are presented, showing this compact dual-band antenna achieves the required Meteosat specifications in terms of frequency bandwidth, circular polarization bandwidth, and isolation between the two communication bands.

The technique of correlation, selection of correlation parameters and applications to noise and vibration analysis

Following an analysis of the limitations imposed on the mathematical technique of correlation by its practical implementation, the applicability of correlation with acoustic noise and mechanical vibration signals is analysed in terms of frequency bandwidth and length of record. It is concluded that correlation is not as significant and useful a tool in the analysis of noise and vibration as might at first appear.

Stimulus complexity, state and infants' auditory behavioural responses.

SummaryFor some time it has been known that “complex” sound stimuli are more effective than pure tones in eliciting behavioural and other responses from infants aged 0–6 months. We have recently studied this issue in some detail, and confirm that stimulus complexity defined in terms of frequency bandwidth is of major importance in eliciting behavioural responses from infants aged 1 week, 6 weeks and 6 months. We have also found that the human voice is effective for 6 month old infants but apparently not for babies aged 1 and 6 weeks. These findings are modified by the baby's state of wakefulness, the effects of which are also considered. Comments are made on the implications of our data for clinical audiological assessments.

Effects of modulated very high frequency fields on specific brain rhythms in cats

The effects of exposures to low intensity (1 mW/sq.cm or less), very high frequency (VHF) (147 MHz) electrical fields, amplitude-modulated at biological frequencies (1–25 Hz), were studied on untrained and conditioned chronically implanted cats. The fields were applied between two aluminum plates (identical voltages, 180° phase shift) firmly anchored to the floor of an isolation booth, especially designed for use of VHF fields. The animals were restrained in a hammock, the longitudinal axis of the body kept parallel to the field plates. EEG and EOG were recorded through a system of low pass filters on a Model 6 Grass electroencephalograph and an Ampex FR 1100 tape recorder; behavior was continuously observed through a closed circuit TV. A series of animals was operantly trained to produce specific transient brain rhythms following periodic (every 30 sec) presentations of a light flash stimulus. The levels of performance were established (visual and spectral analysis) during conditioning and extinction schedules for a series of cats submitted to VHF fields amplitude-modulated at the dominant frequencies of the selected transient patterns and for a control group, in the absence of fields. The irradiated animals differed markedly from the control group in the rate of performance, accuracy (in terms of frequency bandwidth) of the reinforced patterns and resistance to extinction (minimum of 50 days versus 10 days). The specificity of the frequency of the modulation was tested on another group of untrained animals where spontaneous transient patterns were used to trigger for short epochs (20 sec following every burst) the VHF fields amplitude-modulated at various frequencies. The experimental results indicated clearly that the fields were acting as reinforces (increasing the rate of occurence of the spontaneous rhythms) only when modulated at frequencies close to the biologically dominant frequency of the selected intrinsic EEG rhythmic episodes. Various possible routes of interaction between the external fields and the CNS are discussed, and the hypothesis is offered that the amplitude-modulated VHF fields could influence the excitability of neuronal membranes.