Target Frequency Range Research Articles

Tunable acoustic energy dissipation by fluid-structure interaction in elastomeric, resonant metamaterials

Helmholtz resonators are a classic means to absorb low frequency acoustic waves with great effectiveness and straightforward implementation. Yet, traditional Helmholtz resonators are tuned to absorb a specific frequency of wave energy and are unable to adaptively tailor damping capability. On the other hand, recent research on elastomeric metamaterials offers concepts for large and tunable damping properties using internal constituents that buckle to trap large elastic energy when subjected to geometric or load constraints. The research reported here draws from the principles of Helmholtz resonance and constrained metamaterials to device a resonant metamaterial with tunable acoustic energy dissipation. Using the fluid-structure interaction of an internal beam-like member with the resonator chamber, the metamaterial absorbs acoustic waves at a target frequency and tailors energy dissipation by changing external constraints that relatively magnify or suppress the interaction between acoustic pressure and damped beam member. An analytical model is developed to qualitatively characterize the behavior of the metamaterial observed in the laboratory. From the combined experimental and analytical studies, it is found that the metamaterial may significantly reduce the sound pressure level at the targeted frequency range while modulating the broadness of the absorption effect by way of external load control.

A Multiband Directional Coupler Using SOI CMOS for RF Front-End Applications

This letter introduces a novel multiband directional coupler for RF front-end applications. Conventional narrowband directional couplers are widely used for mobile applications because of their compact size. However, excessive power loss due to strong coupling in the higher frequency range severely limits their bandwidth. To resolve this issue, we propose a dual directional coupler employing a coupling switching stage, where the asymmetric coupled lines can be electrically coupled or floated to mitigate severe coupling loss. The proposed coupler has been implemented to an integrated circuit using the silicon-on-insulator process. The measured results showed a considerably enhanced bandwidth from 0.69 to 4 GHz covering the entire frequency band of long-term evolution with a low power loss of less than −0.21 dB in the target frequency range.

Design of Hydraulic Bushing and Vehicle Testing for Reducing the Judder Vibration

Generally, judder vibration is a low-frequency vibration phenomenon caused by a braking force imbalance that occurs when a vehicle is lightly decelerated within a range of 0.1 to 0.2g at a speed of 120 to 60 km/h. This comes from the change in the brake disk thickness (DTV), which is mainly caused by the side run-out (SRO) and thermal deformation. The adoption of hydro-bushing in the low arm G bushings of the vehicle front suspension has been done in order to provide great damping in a particular frequency range (<20Hz) in order to prevent this judder vibration from being transmitted to the body. The hydro bushing was formulated using a lumped parameter model. The fluid passage between the two chambers was modelled as a nonlinear element such as an orifice, and its important parameters (resistance, compliance) were measured using a simplified experimental setup. The main design parameters are the ratio of the cross-sectional area of the chamber to the fluid passage, the length of the fluid passage, etc., and their optimal design is such that the loss angle is greater than 45 ° in the target frequency range of 10 to 20 Hz. The hydro bushing designed for reducing the judder vibration was prepared for the actual vehicle application test and applied to the actual vehicle test. In this study, the proposed hydro bushing was applied to the G bushing of the low arm of the front suspension system of the vehicle. The loss angle of the manufactured hydro bushing was measured using acceleration signals before and after passing through the bushing. The actual vehicle test was performed on the noise dynamometer for the performance analysis of the judder vibration reduction.

Active vibration isolation using a six-axis orthogonal vibration isolation platform with piezoelectric actuators

Piezoelectric actuators (PEA) act an important role in active vibration control area due to the advantages of fast response, high output force, small size and light weight. A 6-axis orthogonal vibration isolation platform based on PEAs is designed, which satisfies the demands of heavy payload, small installation space and multi degree of freedom vibration isolation. The dynamic model of the six-axis orthogonal vibration isolation platform with PEAs is established using Newton-Euler method. With the layout of six PEAs around the axis of symmetry, the dynamic equations could be decoupled into two single-input-single-output (SISO) subsystems and two multi-input-multi-output (MIMO) subsystems. Based on the modal superposition method, the two MIMO subsystems are further decoupled. The control strategy for each SISO system is developed with LQR control method. To evaluate the effectiveness of the control method, the simulation and verification experiment are conducted. The simulation result and experimental data indicate that the decoupling control of the proposed six-axis orthogonal vibration isolation platform with piezoelectric actuators effectively reduces the vibration response of payload within the target frequency range of 20 Hz to 200 Hz.

Thin broadband microwave absorber with conductive and magnetic materials coated on a glass fabric

This paper presents a thin broadband microwave absorber that is manufactured by electrical modification of a glass fabric using two different types of coating techniques in the C band to the Ku band (4–18 GHz). Unlike the production method of conventional absorbers, the proposed microwave absorbers were manufactured using a triple-layered structure. The latter consists of glass/epoxy, Ni-coated glass fabric, and Ni-Co-coated glass fabric without dispersed carbonaceous nano-conductive particles in the polymer matrix. The glass fabric was coated with a Ni and a Ni-Co magnetic nanomaterial via electroless plating and RF magnetron sputtering techniques. The element components, phase identification, and magnetic properties of the conductive and magnetic material-coated glass fabrics were examined by energy-dispersive X-ray spectroscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. The results showed that high dielectric and magnetic properties can be obtained in the target frequency range owing to the conductive and the magnetic material. The proposed two types of broadband microwave absorbers have a low thickness value of 0.858 and 3.305 mm; the design of the broadband absorbers resulted in two strong resonance peaks near 8.5 and 16.3 GHz and satisfied the −10 dB absorption performance from 6.32 to 18 GHz.

Surface wave group velocity in the Osaka sedimentary basin, Japan, estimated using ambient noise cross-correlation functions

Inter-station cross-correlation functions estimated using continuous ambient noise or microtremor records were used to extract the seismic wave propagation characteristics of the Osaka sedimentary basin, Japan. Temporary continuous observations were conducted at 15 sites in the Osaka basin between 2011 and 2013. The data were analyzed using seismic interferometry. The target period range was 2–8 s. Cross-correlations between all of the possible station pairs were calculated and stacked to produce a year-long data set, and Rayleigh wave signals in the vertical and radial components and Love wave signals in the transverse component were identified from the results. Simulation of inter-station Green’s functions using the finite difference method was conducted to check the performance of the current three-dimensional velocity structure model. The measured time lag between the observed and theoretical Green’s functions was less than 2 s for most station pairs, which is less than the wave period of interest in the target frequency range. Group velocity tomography was applied to group delay times estimated by means of multiple filter analysis. The estimated group velocities for longer periods of 5–8 s exhibited spatial variation within the basin, which is consistent with the bedrock depth distribution; however, the group velocities for shorter periods of 2–3 s were almost constant over the studied area. The waveform and group velocity information obtained by seismic interferometry analysis can be useful for future reconstruction of a three-dimensional velocity structure model in the Osaka basin.Graphical .

Enhanced low- to mid-frequency sound absorption using parallel-arranged perforated plates with extended tubes and porous material

Porous sound absorptive material (PSAM) and micro-perforated plate (MPP) limited by space are weak in absorbing low- to mid- frequency noise. In order to improve sound absorption in 100–1600Hz, a compound sound absorber comprised of perforated plates with extended tubes (PPET) and a PSAM is proposed in this paper. A theoretical model is described to predict the sound absorption coefficients of two combinations: one has three parallel-arranged PPETs and a PSAM layer; the other one has two parallel-arranged PPETs, an MPP and a PSAM layer. The calculated results are then validated by the results measured in an impedance tube. The proposed combinations demonstrate superior sound absorption performance over more than three octaves in the targeted frequency range.

Topology optimization of periodic microstructures for enhanced loss factor using acoustic–structure interaction

In this work we present a topology optimization method for the design of 2D composite materials with a distribution of a solid constituent and a lossy acoustic medium for obtaining high loss factors. The method is based on a mixed displacement-pressure finite element (FE) formulation combined with the Bloch-wave condition. We solve the resulting FE eigenvalue problem on a repetitive unit cell with periodic boundary conditions and use a complex k(ω) eigenvalue formulation to compute the loss factor. We consider the optimization problem of maximizing the loss factor in a target frequency range with an additional constraint on the stiffness. In the provided example we demonstrate the effect of combined local resonators and acoustic resonances of similar frequency for creating an enhanced overall loss factor of the material.

Cross-guide Moreno directional coupler in empty substrate integrated waveguide

Substrate integrated waveguides (SIWs) combine the advantages of rectangular waveguides (low losses) and planar circuits (low cost and low profile). Empty substrate integrated waveguide (ESIW) has been proposed as a novel configuration in SIWs recently. This technology significantly reduces the losses of conventional SIW by removing its inner dielectric. The cross-guide directional coupler is a well-known low-profile design for having a broadband waveguide coupler. In this paper a cross-guide coupler with ESIW technique is proposed. In such a manner, the device can be integrated with microwave circuits and other printed circuit board components. It is the first time that a cross-guide coupler is implemented in ESIW technology. The designed, fabricated, and measured device presents good results as a matter of insertion loss of 1 dB (including transitions), reflection under 20 dB, coupling between 19.5 and 21.5 dB, and directivity higher than 15 dB over targeted frequency range from 12.4 GHz to 18 GHz. The coupler implemented in ESIW improves the directivity when compared to similar solutions in other empty substrate integrated waveguide solutions.

Continuous gradient and discretized layered designs for control of stress wave scattering

The scattering of stress waves in graded media is discussed in this paper using a conversion of the heterogeneous wave equation to a potential form. In this form, the scattering and inverse scattering methods of mathematical physics can be used with proper enforcement of the boundary conditions on the mechanical quantities, i.e. displacements and tractions. Two approaches for design of non-reflective media are analyzed, one for all frequencies with infinite thickness, and one with finite thickness for a target frequency range. In the latter approach, the transformed potential is set to zero, and the wave speed can have almost any desired profile, from which the profile of impedance is derived. The dispersive behavior of the finite thickness design is studied. Finally, an example is discussed in which a continuous non-reflective profile is discretized to a piece-wise constant profile and the effect of such unavoidable practical constraints on the scattering of the designed layer is shown to be minimal.

Feedforward control of sound transmission using an active acoustic metamaterial

Metamaterials have received significant interest in recent years due to their potential ability to exhibit behaviour not found in naturally occurring materials. This includes the generation of band gaps, which are frequency regions with high levels of wave attenuation. In the context of acoustics, these band gaps can be tuned to occur at low frequencies where the acoustic wavelength is large compared to the material, and where the performance of traditional passive noise control treatments is limited. Therefore, such acoustic metamaterials have been shown to offer a significant performance advantage compared to traditional passive control treatments, however, due to their resonant behaviour, the band gaps tend to occur over a relatively narrow frequency range. A similar long wavelength performance advantage can be achieved using active noise control, but the systems in this case do not rely on resonant behaviour. This paper demonstrates how the performance of an acoustic metamaterial, consisting of an array of Helmholtz resonators, can be significantly enhanced by the integration of an active control mechanism that is facilitated by embedding loudspeakers into the resonators. Crucially, it is then also shown how the active acoustic metamaterial significantly outperforms an equivalent traditional active noise control system. In both cases a broadband feedforward control strategy is employed to minimise the transmitted pressure in a one-dimensional acoustic control problem and a new method of weighting the control effort over a targeted frequency range is described.

Polypropylene Carbon Nanotubes Nanocomposites: Combined Influence of Block Copolymer Compatibilizer and Melt Annealing on Electrical Properties

We study the influence of melt annealing and the presence of a block copolymer compatibilizer on the electrical properties of polypropylene carbon nanotubes (CNT) nanocomposites from the DC limit to microwave frequencies and link it to the morphological details. We show that the compatibilizer concentration controls three types of morphologies: separate CNT agglomerates, a network of well dispersed but interconnected CNT, and individualized but separate nanotubes. This explains why conductivity reaches an optimum over the whole frequency range at a low compatibilizer concentration. We model the corresponding structures by a semiquantitative schematic equivalent electrical circuit. A key outcome of the work is the understanding and control of dispersion mechanisms in order to optimize the electrical performances for efficient EMI shielding depending on the targeted frequency range.

Effects of Geometry Design Parameters on the Static Strength and Dynamics for Spiral Bevel Gear

Considering the geometry design parameters, a quasi-static mesh model of spiral bevel gears was established and the mesh characteristics were computed. Considering the time-varying effects of mesh points, mesh force, line-of-action vector, mesh stiffness, transmission error, friction force direction, and friction coefficient, a nonlinear lumped parameter dynamic model was developed for the spiral bevel gear pair. Based on the mesh model and the nonlinear dynamic model, the effects of main geometry parameters on the contact and bending strength were analyzed. Also, the effects on the dynamic mesh force and dynamic transmission error were investigated. Results show that higher value for the pressure angle, root fillet radius, and the ratio of tooth thickness tend to improve the contact and bending strength and to reduce the risk of tooth fracture. Improved gears have a better vibration performance in the targeted frequency range. Finally, bench tests for both types of spiral bevel gears were performed. Results show that the main failure mode is the tooth fracture and the life was increased a lot for the spiral bevel gears with improved geometry parameters compared to the original design.

Spectrum Analyses and Extracting Components of Ultrasonic Echo Signals

On the basis of an analysis on ultrasonic signals collected by detecting type 6061 aluminum block and 60kg/m rail, a signal processing method is applied to separate echo signals from ultrasonic signal. Ultrasonic signals are extracted and analyzed based on the parameters such as sampling frequency, sampling time, band-pass width and so on, in the experiments. Then, on the time domain, the frequency analysis is carried out in the target frequency range from ultrasonic signal and the characteristic frequencies are obtained. Finally, the digital filter is designed to reduce noise in order to contrast and analysis. The experimental results indicate that noise signals are effectively suppressed in the ultrasonic signals and echo signals are obtained clearly.

Thin and lightweight radar-absorbing structure containing glass fabric coated with silver by sputtering

In this paper, a new radar-absorbing structure produced by electrical modification of glass fabric via the silver-sputtering coating technique is proposed. Although conventional radar absorbers are fabricated using a conductive carbon nanomaterial, such fabricated absorbers have many limitations in their electrical and mechanical performance. A thin and lightweight silver-coated glass-fabric microwave-absorbing structure (with a thickness of 1.82, 1.84 and 1.95mm, respectively) having good microwave-absorbing performance in the X-band (8.2–12.4GHz) was designed and fabricated without dispersing conductive carbon nanomaterials in the resin matrix. The morphology, element composition and phase identification of silver-coated glass fabrics were examined by SEM, EDS and XRD, respectively. In addition, interlaminar shear strength (ILSS) tests were conducted according to ASTM D 2344 to evaluate the mechanical performance of the proposed absorbers. Additionally, to design a thin broadband absorber using the silver-coated glass fabric, the absorbing performance of the proposed absorbers were analyzed from the C-band to the Ku-band (4–18GHz), and the proposed broadband absorber showed excellent performance in the target frequency range.

Investigation of the effects of the microstructure on the sound absorption performance of polymer foams using a computational homogenization approach

In this paper, a computational homogenization approach is exploited to study the effects of the microstructure of polymer foams on their acoustic properties. A Kelvin cell with partially-open thin membranes is adopted to represent the microstructure of the foam. By applying the homogenization approach, the effective material parameters are obtained based on a microscopic representative volume element (RVE) subjected to different loading conditions. Geometrical properties, including the opening and the thickness of the thin membranes and the cell size, are investigated. It is shown that when the opening of the membranes or the cell size are smaller, the sound absorption performance at low frequencies can be improved, at the expense of the mid-high frequency performance. Moreover, the optimal opening and optimal cell size for best sound absorption performance depend on the target frequency range. The effect of solid properties, including the stiffness and the loss factor, are also discussed. For low-stiffness materials, local resonance of the solid frame greatly affects the effective fluid density and the frame-borne wave, whereas global resonances can be utilized to improve the absorption performance in a specific frequency band.

Standardised acoustic characterisation of sonic crystals noise barriers: Sound insulation and reflection properties

This work presents sound insulation and sound reflection measurements conducted over sonic crystal noise barriers according to the European standards EN 1793-2, EN 1793-5 and EN 1793-6. In most of the reference literature, sound insulation and reflection properties of sonic crystals are measured or a diffuse sound field or in a direct sound field including the top and side edge diffraction effects together with the transmitted (or reflected) components. The aim of this work is to perform free-field measurements over a real-sized sample in order to window out all diffraction components and to verify the points of strength and weakness of the application of standardised measurements to sonic crystals. Diffuse field measurements in laboratory are also done for comparison purposes. Since the target frequency range for traffic noise spectrum is centred at around 1000Hz, a finite element based parametric investigation is performed to design unit cells capable of generating band gaps in the one-third octave bands ranging from 800Hz to 1250Hz. Then, 3×3m sonic crystal noise barriers are installed in the Laboratory of the University of Bologna and sound insulation and sound reflection measurements are performed according to the mentioned active standards for normal incidence. Sound insulation is measured for diffuse incidence too. The two methods give different results. The method more directly comparable to calculations is the free-field one. However, if on the one hand the application of a time window allows to compute the transmitted or reflected component only, on the other hand the time window itself limits the maximum width of the sample for which all reflections of the n-th order having a significant spectral content are included, and thus results critical in the analysis of this kind of noise barriers. Nevertheless, the standardised measurements allow a direct comparison between the performance of sonic crystals and common noise barriers.

Boundary Element Modelling of a Novel Simple Enhanced Bandwidth Schroeder Diffuser Offering Comparable Performance to a Fractal Design

It is well established that Schroeder diffusers may be used as surface treatment to promote diffuse sound fields in auditoria over a target frequency range. Quadratic Residue Diffusers are very effective within a design frequency bandwidth, and this frequency bandwidth may be significantly extended by a nested or fractal design. Publicly available data typically publish diffusion coefficients separately for the parent diffuser and the child diffuser, with some ambiguity surrounding the effect the two levels have on each other, and the performance at ‘crossover’ frequencies. This paper uses an optimised 2D boundary element method to investigate the differences in results when the parent and child diffusers are modelled separately, and as an integrated design. It is found that the scattering properties of the child diffuser are significantly modified by the well of the parent diffuser in which it is placed. More interestingly, the excellent scattering properties of the fractal design may be achieved with only a minor loss of bandwidth using a far simpler and more robust geometry in which the child diffuser is replaced by a concave surface at the base of the well in the parent diffuser. The paper outlines the optimisation of the boundary element code for this task, and compares results for a variety of well bottom shapes with the fractal design.

A Lasso-LS Optimization with a Frequency Variable Dictionary in a Multizone Sound System

This paper presents an approach for multizone wideband sound field generation using an efficient harmonic nested (EHN) dictionary for sparse loudspeakers’ placement and weight. Effectively, the nested arrays provide a priori knowledge of prospective loudspeaker locations based on the frequency bands of interest. The nested arrays are then further optimized in the Lasso stage to form an efficient loudspeakers’ location dictionary. The final loudspeaker locations and weightings are estimated by a two-stage Lasso-LS pressure matching optimization. In the first stage Lasso algorithm, the center band frequencies of octave bands from 1 kHz to 8 kHz were used to select active loudspeakers. A second stage then optimizes reproduction using all selected loudspeakers on the basis of a regularized LS algorithm. The results demonstrate that the proposed approach provides a solution for the multizone sound system with the mean squared error (MSE) under $-30 \text{dB}$ across the targeted frequency range (500 Hz-16 kHz) using a linear array e.g. 13 loudspeakers. While, the single-stage LS approach generates the MSE peaks of $-10 \text{dB}$ and $-9 \text{dB}$ at 9 kHz within the active and silent zones respectively using an identical number of loudspeakers and array length.

Root Cause Diagnosis of Plant-Wide Oscillations Based on Information Transfer in the Frequency Domain

Plant-wide oscillations generated in a single unit can negatively affect the overall control performance of the process; thus, it is necessary to detect them and diagnose their root cause. However, the interference of noise and the need for oscillation propagation routes pose more challenges for process engineers. In this paper, the concept spectral transfer entropy is proposed and its connection to the spectral Granger causality is derived. Moreover, an information transfer method incorporating spectral envelope algorithm and spectral transfer entropy is applied to provide new diagnostic guidance, whose feasibility and effectiveness have been demonstrated by both simulated and industrial case studies. Compared with current methods, the new procedure enjoys the following advantages: (a) performing oscillation detection and diagnosis within a targeted frequency range and mitigating the effects of measurement noise outside the bandwidth; (b) provides an nominal causal map reflecting the oscillation propagat...