Narrow Frequency Range Research Articles

Method for controlling vibration by exploiting piecewise-linear nonlinearity in energy harvesters.

Vibration energy is becoming a significant alternative solution for energy generation. Recently, a great deal of research has been conducted on how to harvest energy from vibration sources ranging from ocean waves to human motion to microsystems. In this paper, a theoretical model of a piecewise-linear (PWL) nonlinear vibration harvester that has potential applications in variety of fields is proposed and numerically investigated. This new technique enables automatic frequency tunability in the energy harvester by controlling the gap size in the PWL oscillator so that it is able to adapt to changes in excitations. To optimize the performance of the proposed system, a control method combining the response prediction, signal measurement and gap adjustment mechanism is proposed in this paper. This new energy harvester not only overcomes the limitation of traditional linear energy harvesters that can only provide the maximum power generation efficiency over a narrow frequency range but also improves the performance of current nonlinear energy harvesters that are not as efficient as linear energy harvesters at resonance. The proposed system is demonstrated in several case studies to illustrate its effectiveness for a number of different excitations.

Ultrawideband combined vibrator-slot Clavin type radiator

Background. Ultrawideband communication is a promising way of transmitting information that uses short electromagnetic pulses. It has great potential due to higher bandwidth than other methods of information transfer. This allows you to create ultra-fast wireless communication networks. But the implementation of ultra-wideband communication requires the use of compact and efficient pulsed emitters. Object. Create a compact pulsed combined antenna of electric and magnetic type, ultra-wideband analogue of the Clavin radiator, in which the necessary characteristics are provided by a strong interaction of its components. It is also necessary to analyze the directional, frequency and time characteristics of such a radiator. Methods: The numerical method of finite differences in time domain (FDTD) is used for the final calculation and optimization of the radiator. The initial design is calculated in a narrow frequency range by the method of electric and magnetomotive forces. Results. The multiparameter optimization of the antenna is carried out in order to find the optimal interaction between the electric and magnetic emitter while providing the required directional and frequency characteristics. The radiation patterns in the H and E planes for a number of frequencies are obtained, and the time dependences of the radiated field in these planes are constructed. Conclusions.The analog of the Clavin radiator can concentrate the energy of the radiation in a given direction and provide a wide range of operating frequencies, which in this implementation of antenna reaches 1 GHz. It should be noted the compactness of this structure and the presence of a number of geometric parameters, the change of which can improve the time parameters of the radiated field. The ultra-wideband combined vibrator-slot structure has several directions for further optimization of time, frequency and directional characteristics in accordance with the requirements of specific applications.

Reconfigurable Frequency Selective Rasorber Covering Extremely Wide Transmission Frequency Range

Rasorbers with reconfigurable transmission frequency are of great interest over the past few years. However, existing devices exhibit a limited number of operation modes and cover a narrow transmission frequency range, making them unacceptable for wideband applications. In this work, a high-performance reconfigurable rasorber with mechanically-controlled frequency selective surface (FSS) and an electronically-tuned resistive layer is proposed. Theoretical analysis based on transmission line theory and numerical simulations is performed to investigate the performance of the proposed device. The rasorber were fabricated and free-space measurements were also carried out to validate the simulation results. The device can operate between single-, dual- and triple-passband modes by mechanically tuning the FSS under a fixed external bias voltage. Under single-passband mode, the transmission frequency can also be tuned continuously through simultaneously controlling the mechanically-tunable FSS and electronically-tunable resistive layer. A minimum insertion loss as low as 0.16 dB at 4.03 GHz is achieved from the measurement results. The maximum measured fractional absorption bandwidth is 87.9%, comparable to the state-of-art maximum absorption bandwidth of existing reconfigurable rasorber. The measured overall fractional transmission frequency range under normal incidence wave is 63.9%, far beyond that of any other existing reconfigurable counterparts.

The frequency of cortical microstimulation shapes artificial touch

Intracortical microstimulation (ICMS) of the somatosensory cortex evokes vivid tactile sensations and can be used to convey sensory feedback from brain-controlled bionic hands. Changes in ICMS frequency lead to changes in the resulting sensation, but the discriminability of frequency has only been investigated over a narrow range of low frequencies. Furthermore, the sensory correlates of changes in ICMS frequency remain poorly understood. Specifically, it remains to be elucidated whether changes in frequency only modulate sensation magnitude-as do changes in amplitude-or whether they also modulate the quality of the sensation. To fill these gaps, we trained monkeys to discriminate the frequency of ICMS pulse trains over a wide range of frequencies (from 10 to 400 Hz). ICMS amplitude also varied across stimuli to dissociate sensation magnitude from ICMS frequency and ensure that animals could not make frequency judgments based on magnitude. We found that animals could consistently discriminate ICMS frequency up to ∼200 Hz but that the sensory correlates of frequency were highly electrode dependent: On some electrodes, changes in frequency were perceptually distinguishable from changes in amplitude-seemingly giving rise to a change in sensory quality; on others, they were not. We discuss the implications of our findings for neural coding and for brain-controlled bionic hands.

Design of Discretely Tunable Resonant Actuators Using Additive Inertial Units

Abstract Resonance is known to reduce the input energy requirements of various actuator systems. The favorable effects of resonance, however, are limited to a narrow frequency range. To overcome this limitation, we describe a general framework for using discrete units of inertia that can be activated in a binary sense to move a resonant frequency across a desired frequency range. We also enumerate the generalized physical cases in which actuators can energetically benefit from resonance. We develop closed-form optimal results for the idealized case of two binary additive inertial units and extend this to a general optimization scheme for higher numbers of units that introduce parasitic friction and added stiffness. We illustrate the concept of binary tuning with a representative linear translational system powered by a voice coil motor (VCM). The experimental results show good agreement with the intended theoretical design and show the general utility of the binary additive inertia approach.

Identification of the Viscoelastic Properties of Soft Thermal Interface Layers Through Forward and Inverse Measurement Techniques

The design for the reliability of automotive electronics involving viscoelastic materials requires accurate knowledge of material properties under critical frequency and temperature conditions. Both forward and inverse approaches for the dynamic characterization of a soft silicone-based thermal interface material used in electronic control units are presented and discussed. The classic forward characterization implying dynamic mechanical analysis and the principle of time–temperature superposition is applied in a first step. The identified material model under critical temperature conditions is restrained to a narrow frequency range and a validation for higher frequencies is needed. The proposed inverse method presented in the second part minimizes the residue between the measured and numerical transfer functions of single-lap joint specimens at chosen control frequency ranges located at the resonances of the structure. The specimens are excited by an electrodynamic shaker situated in an environmental chamber allowing measurements under different temperature conditions. The main outcome of the inverse approach is a validation of the results of forward characterization for a broad frequency range and under critical temperature conditions adopting a simple experimental arrangement and a barely complex numerical procedure.

Composite Right/Left-Handed Leaky-Wave Antennas for Wide-Angle Beam Scanning With Flexibly Chosen Frequency Range

A composite right/left-handed (CRLH) leaky-wave antenna (LWA) can effectively scan the radiation beam from backward-to-forward direction. However, in most cases, a large range of frequency sweep is required to achieve a wide-angle beam scan, which could limit their applications. An in-depth study is conducted on an equivalent circuit model for a CRLH LWA unit cell to find the controlling parameters on the frequency sweeping range. A systematic design guideline is given for a CRLH LWA for a wide-angle beam scan in a flexibly chosen frequency range. It is shown that beam scanning by sweeping frequency in a target range can be achieved by systematically designing the unit cell parameters. To verify our approach, a novel CRLH unit cell is developed and used to design an LWA for a wide-angle beam scan in a narrow frequency range. Finally, the concept is validated through realization of the antenna and its measurement. The measured results show that the antenna prototype can scan its beam from −56° to +51° when frequency sweeps from 5.1 to 6.11 GHz (i.e., 18.02% of fractional bandwidth).

Modeling of digital converter for GSM signals with MATLAB

In this study will simulate steady state of Digital Down Convertor (DDC) for GSM signal with a narrow frequency range. The MATLAB model that is described in this article simulates the work of the TIGC4016 Quad Digital Down Converter. This converter is used for digital mixing (down conversion) of signals, narrow band low-pass filtering and decimation. To implementation of the model, we use high sample-rate (69,333 MSPS) bandpass signal. The result contains low sample-rate (270.83 KSPS) baseband signal, thus facilitating the demodulation process.

Method of Measuring Effective Dielectric Permittivity of Partially Filled Waveguides Using a Mismatched T-Bridge

Introduction. Waveguides, partially filled with dielectric material (partially filled waveguides) are widely used in the super high frequency equipment. They have certain advantages over hollow waveguides, including the possibility of reducing sizes of a cross-section, increasing the power of radiation and suppressing undesired types of waves. Following the production of diverse new dielectric materials intended for use in super high frequency range devices, there is a need to continuously develop methods of calculation and measuring characteristics of partially filled waveguides.Statement of the problem. The theory of completely filled waveguides and waveguides with dielectric filling along narrow walls is developed quite thoroughly. However, its application to various waveguide devices requires the solution of transcendental equations, which is possible only using numerical methods. This makes it difficult to obtain information about any characteristics of a device. There is also an effect of a large number of factors influencing the characteristics of partially filled waveguides (degree of filling, position of a waveguide plate, magnitude of the dielectric permittivity, etc.). For the study of partially filled waveguides with different sample height, among others, this paper presents an approach, which is based on the representation of the relative permittivity of the medium in the form of two real functions, each of which depends on the cross-section from one coordinate. This is an approximate method for determining the proper scalar and vector functions of partially filled waveguides. The solution of the electrodynamic problem for partially filled waveguides is reduced to determining the propagation constant in a waveguide using exact or approximate methods. This paper presents the method which allows calculating the propagation constant at any frequency, by measuring the value of effective dielectric permittivity.Results and discussion. According to the results of the analysis, it is shown that known methods of measuring effective dielectric permittivity (using a measuring line, a panoramic indicator, and a bridge meter) have certain shortcomings in relation to the modification of partially filled waveguides, bandlimitedness, and a significant relative error of measurement with increasing effective dielectric permittivity. In particular, the lack of bridge meters is a very narrow frequency range in which the bridge remains matched. It is almost necessary to match the bridge at each frequency, reaching the absence of a signal in the arm E for identical loads that are connected to the side arm. For this, bridges have tuning elements in the form of pins, diaphragms, etc. The method for measuring effective dielectric permittivity of partially filled waveguides using an unmatched T-bridge, which does not have these deficiencies, is introduced.Conclusions. The scientific novelty of the proposed method for measuring effective permittivity of partially filled waveguides using an unmatched T-bridge is the possibility of providing broadbandness, increasing the accuracy of measurements, and the universality through the use of a panoramic indicator of the standing wave ratio using the voltage and electron-computer. One more point is the ability to measure effective dielectric permittivity when other measurement methods are not suitable. The results obtained should be used when designing new antenna systems, which include partly filled waveguides, as well as part of teaching and learning activities for creating new workplaces or improving existing ones aimed at laboratory and practical training using the above method of measurement.

Gene expression vs. sequence divergence: comparative transcriptome sequencing among natural Rhinolophus ferrumequinum populations with different acoustic phenotypes

BackgroundAlthough the sensory drive hypothesis can explain the geographic variation in echolocation frequencies of some bat species, the molecular mechanisms underlying this phenomenon are still unclear. The three lineages of greater horseshoe bat (Rhinolophus ferrumequinum) in China (northeast, central-east, and southwest) have significant geographic variation in resting frequencies (RF) of echolocation calls. Because their cochleae have an acoustic fovea that is highly sensitive to a narrow range of frequencies, we reported the transcriptomes of cochleae collected from three genetic lineages of R. ferrumequinum, which is an ideal organism for studying geographic variation in echolocation signals, and tried to understand the mechanisms behind this bat phenomenon by analyzing gene expression and sequence variation.ResultsA total of 8190 differentially expressed genes (DEGs) were identified. We identified five modules from all DEGs that were significantly related to RF or forearm length (FL). DEGs in the RF-related modules were significantly enriched in the gene categories involved in neural activity, learning, and response to sound. DEGs in the FL-related modules were significantly enriched in the pathways related to muscle and actin functions. Using 21,945 single nucleotide polymorphisms, we identified 18 candidate unigenes associated with hearing, five of which were differentially expressed among the three populations. Additionally, the gene ERBB4, which regulates diverse cellular processes in the inner ear such as cell proliferation and differentiation, was in the largest module. We also found 49 unigenes that were under positive selection from 4105 one-to-one orthologous gene pairs between the three R. ferrumequinum lineages and three other Chiroptera species.ConclusionsThe variability of gene expression and sequence divergence at the molecular level might provide evidence that can help elucidate the genetic basis of geographic variation in echolocation signals of greater horseshoe bats.

Mechanical oscillation accelerating nucleation and nuclei growth in hard-sphere colloidal glass

Crystallization from amorphous solids is generally caused by activating phonons in a wide frequency range during heat treatment. In contrast, the activation of phonons in a narrow frequency range using ultrasonic treatment also causes crystallization below the glass transition temperature. These behaviors indicate that crystallization is related to the atomic motion in the glass state, and it is suggested that the activation of specific atomic motion can cause crystallization without increasing temperature. In this study, we observe nucleation and nuclei growth caused by mechanical oscillation in a hard-sphere colloidal glass and evaluate the effect of mechanical oscillation on the structural evolution in the early stage of the crystallization. Oscillation between 5 and 100 Hz is applied to the colloidal glass, and it is observed that the nucleation rate increases under the 70 Hz oscillation, resulting in formation of stable nuclei in a short amount of time. The nuclei growth is also accelerated by the 70 Hz oscillation, whereas increases in the nucleation rate and nuclei growth were not observed at other frequencies. Finally, activation of the diffusion-based rattling of particles by caging is considered as a possible mechanism of the observations.

Concurrent wind and base vibration energy harvesting with a broadband bistable aeroelastic energy harvester

This paper presents a novel energy harvesting device driven by concurrent aeroelastic vibration and base vibratory excitation. The harvester undergoes flow-induced limit-cycle oscillation under galloping instability, and at the same time, inertia force induced vibration is present due to the base vibratory excitation. A limitation with a traditional linear aeroelastic energy harvester is that effective energy harvesting from combined sources is only achievable within a narrow frequency range. To overcome this issue, bistability is introduced by exploiting nonlinear restoring force. A lumped aero-electro-mechanical model is established to incorporate the mutual coupling between the wind flow, piezoelectric element, nonlinear structure and circuit. Dynamic responses are investigated for different bistable configurations. Results show that the proposed harvester achieves a significantly widened bandwidth over which the two excitation frequencies are forced to lock into each other, and both vibratory and aeroelastic energy are effectively harnessed.

Breakup of Closed Curve - Quasiperiodic Route to Chaos in Vibroimpact System

At present chaotic vibrations are the one of the most interesting and explored subjects in nonlinear dynamics. Particularly the routes to chaos in non-smooth dynamical systems are of the special scientists’ interest. Quasiperiodic route to chaos in nonlinear non-smooth discontinuous 2-DOF vibroimpact system is studied in this paper. In narrowfrequency range different oscillatory regimes have succeeded each other many times under very small control parameter varying. There were periodic subharmonic regimes - chatters, quasiperiodic, and chaotic regimes. There were the zones of transition from one regime to another, the zones of prechaotic and postchaotic motion. The hysteresis effects (jump phenomena) occurred for increasing and decreasing frequencies. The chaoticity of obtained regime has been confirmed by typical views of Poincare map and Fourier spectrum, by the positive value of the largest Lyapunov exponent, and by the fractal structure of Poincare map.

A novel inertial sensor exploiting magnetic fluid

Narrow available frequency range and low linearity of traditional magnetic fluid inertial sensors make them unpractical. A novel inertial sensor exploiting magnetic fluid is designed to solve these shortcomings. Through simulation and experiments, characteristics of magnetic fluid such as damping effect and levitation effect are studied. It shows that magnetic fluid has excellent damping effect which can be controlled by magnetic field. In order to improve the frequency response, both levitation and damping effect are used in sensors. Cylindrical permanent magnet is employed as the inertial mass, which can transform acceleration to the change of magnetic field. Linear hall sensor with high sensitivity is the transducer installed on the position where magnetic field gradient of cylindrical permanent magnet is maximal and has best linearity. Verification experiments of the designed sensor are conducted on vibration platform. Experimental results give that application of magnetic fluid for inertial sensor optimizes its performance greatly. Available frequency range of the designed sensor is increased by 256% after using magnetic fluid as damping material. This paper provides a reference for research on magnetic fluid and its application in inertial sensors.

Design and optimization of a broadband piezoelectric energy harvester

The conventional linear cantilever piezoelectric energy harvester has a relatively narrow working frequency range (1-2 Hz) and low energy harvesting performance. Therefore, a new effective host structure needs to be developed. This paper proposes a broadband piezoelectric energy harvesting structure to solve this problem. The proposed structure is composed of three beams. Based on the finite element analysis via ANSYS software, the theoretical model of this structure is established. The response characteristics of the energy harvester are analyzed, and the optimization design strategy is presented. The finite element simulation results show that the working frequency range of the presented harvester can be changed by adjusting the length ratio of each beam. Therefore, the result indicated that the proposed energy harvesting structure can widen the effective bandwidth and improve the energy harvesting performance.

Design of multiple-band filtering resonance devices at narrow frequency range using terahertz metamaterial resonator

Metamaterial resonant device consisted of U-shaped resonator embedded with metallic split-ring having two gaps is demonstrated, which can achieve multiple-band filtering at terahertz frequency. Four filtering dips are realized in a very narrow range of less than 1 THz, which is obviously superior to previous designs that multiple-band filtering dips appear in a fairly wide range. Near-field distributions of each resonance are given to reveal the mechanism of multiple-band filtering. Moreover, more filtering bands can be obtained in the same frequency range through appropriate structure optimization. The multiple-band filtering devices can find large application prospects in filtering, imaging, sensing etc.

Excitation of Surface Waves during by an Inhomogeneous Electromagnetic Wave Incident on the Plasma Boundary

We have studied the excitation of surface plasma waves during the propagation of a cylindrical electromagnetic wave in a layered plasma–dielectric medium. The dielectric—vacuum—plasma and vacuum–plasma–plasma layers have been considered. It is shown that no surface waves are excited by the cylindrical electromagnetic wave at the plasma–dielectric boundary (like in the case of a plane wave). A surface wave in a layered medium is excited in a quite narrow range of frequencies and angles of propagation. We have calculated the structures of the electromagnetic field and the electromagnetic energy flux and determined the integral reflection and transmission coefficients using both numerical an analytic asymptotic methods. It is shown that the contribution of the field from the lateral wave is negligibly small in all cases.

Effects of conductive polymer composite layering on EMI shielding during additive manufacturing

Abstract:Spin coating and drop casting are viable methods for rapid and low-cost additive manufacturing of components for flexible devices and sensors. We investigated the cumulative effects of layering a conductive polymer composite 2 wt% MWCNT filler in PEDOT:PSS on a Mylar substrate for application to electromagnetic interference (EMI) shielding. The optical transmittace of spin coated composite layers is 90%, 45%, and 20% with a thickness of 0.05 µm, 0.15 µm, and 0.45 µm respectively. Drop cast composite layers have 0% transmittance due to their much greater starting thickness of 4.4 µm. The addition of isopropyl alcohol (IPA) to the solution mixture and substrate heating to 40 °C improves the conductivity, and drying time of the cured composite layers to 10 min. This study shows that the cumulative effects of composite layering are additive, but the electrical properties do not scale the same way. A significant increase in the EMI SE is mainly attributed to the enhanced electrical conductivity of the composite. The insertion of a 50 µm gap in between two 15 µm composite layers accentuates the EMI shielding effectiveness (SE) significantly to a peak of 21 dB within a narrow frequency range in the Ku-band tested.

A load-based approach for optimizing a packed-bed thermal store

Abstract This paper presents a load-based optimization approach for improving the efficiency of a packed bed. The optimization is based on splitting the work-cycle of the thermal store into two frequency components: low and high. A packed bed is designed for each one of the two profiles. A packed bed can be customised much better for a duty-cycle that contains a narrow range of frequencies. The case study presented considers a 24 h working-cycle (12 h charge / 12 h discharge) with a 10 MW peak power and an exergy storage requirement of 33.3 MW h (76.3 MW h of heat). A packed bed was optimized for this duty-cycle using a one dimensional model that varies the aspect ratio and the rock size. This packed bed is the ‘reference case’ for the study. The aim of the load-based optimization is to create a two-bed system that achieves lower exergy losses than the reference case while keeping the overall storage capacity constant. A sign-preserving filter is used as the signal-splitting tool. Numerous different work-cycle “splits” are explored. Results show that the exergy losses of the packed bed can be considerably reduced. The optimum work-cycle split considers a low-frequency packed bed that supplies 85% of the storage capacity and a high-frequency packed bed that provides the remaining 15%. The combined losses of the two packed beds are 644 kW h, which represents a reduction of 25.5% in comparison to the exergy losses of the reference case. The study demonstrates that the “load-based optimization” allows replacing a packed bed with an equivalent but more efficient two-bed system at almost no additional cost.

Continuously tuning the resonant characteristics of microcantilevers by a laser induced photothermal effect

Microcantilever sensors are ultrasensitive devices with miniaturized size and fast responding capability. However, they are generally designed to operate in a very narrow frequency range, which has limited their applications. We present here an all-optical technique that enables efficient actuation and rapid tuning of the vibration behaviors of microcantilevers. In particular, the resonant frequency of a microcantilever beam can be continuously tuned remotely by a laser induced photothermal effect to cover a large range with boosted vibration amplitude, beneficial for improving the detection threshold for force and mass. The underlying principles for photothermal actuation and elastic nonlinearity are discussed in detail. A verification experiment proves its potentials in detecting acoustic waves with frequencies far from the initial resonant frequency of the microcantilever.