Waveguide Absorbers Research Articles

Lightweight waveguide absorbers based on spiral acoustic black holes for reducing structural vibrations in mechanical systems

We present an ABH-based solution to address challenging industrial problems related to structural vibration and vibration-induced noise. To tackle those problems, we utilize lightweight waveguide absorbers (WGAs) based on spiral acoustic black holes (ABHs). The WGA is designed by combining a spiral acoustic black hole with a rod to absorb flexural waves and dampen the vibrations in dynamic systems. The WGAs are customized to industrial needs, pursuing both high-damping performance and lightness. Specifically, we design non-identical configurations of WGAs by taking multiple or broadband target frequency ranges into account. We then determine optimal attachment positions and directions of the designed WGAs while considering constraints on installation space and total weight of WGAs. Numerical and experimental results verify the feasibility to meet the requirements of industries through the use of WGAs, thereby opening up the possibility of practical applications to real-world problems.

Graphene-Based Dynamically Tunable Broadband Substrate-Integrated Waveguide Absorber in Microwave Frequency Band

Graphene-Based Dynamically Tunable Broadband Substrate-Integrated Waveguide Absorber in Microwave Frequency Band

Damping vibration of platform structure using modified acoustic black holes

We propose waveguide absorbers (WGAs) to dampen structural vibrations of platforms supporting vibrating systems. The waveguide absorber is designed by modifing a spiral acoustic black hole (ABH) to improve its damping performance while saving installation space and weight. The proposed WGA absorbs the flexural wave propagating in a platform to its end, resulting in vibration damping in the platform. To maximize the damping capability of WGA, we analyze the structural intensity field of the platform and attach the WGA based on the intensity field. Numerical and experimental results show that large reductions of peaks in mobility are achieved using the WGAs, showing the possibility to utilize the WGA in practice.

Modeling the frequency characteristics of the waveguide structure of a heterodyne receiver with sideband division for the range 211...275 GHz

The microwave properties of the components of the waveguide structure of a heterodyne receiver in the 211...275 GHz range with sideband separation based on a pair of superconductor–insulator–superconductor (SIS) tunnel junctions are described. The following elements of the waveguide were studied structures: hybrid four-port splitter, directional coupler, T-shaped splitter body and waveguide absorber. S parameters were calculated for all elements. For hybrid divider additionally shows a phase balance with deviations of less than 0.4 degrees, and an amplitude balance within 1 dB. The expected level of quality of band separation in a band separation receiver using the studied waveguide elements is analyzed; its value is more than –25 dB. The waveguide elements are designed taking into account the fact that the block will be manufactured using precision milling; the minimum dimensions of the waveguide structure are limited by the diameter of the cutter used; in our case, 100 μm was chosen. All numerical calculations were performed using the finite interval method in the HFSS package.

A Circular Eccentric Vibration Absorber With Circumferentially Graded Acoustic Black Hole Features

Abstract A previously proposed planar axisymmetric dynamic vibration absorber (DVA), with embedded acoustic black hole (ABH) features, has been shown to suffer from the very selective coupling with the host structure, thus compromising its vibration reduction performance. To tackle the problem, an eccentric ABH-based circular DVA whose thickness profile is tailored according to a circumferential gradient variation is proposed. This new configuration preserves the ABH profile in the radial direction and breaks the axisymmetric of the original DVA design at the same time. While the former permits the ABH features to fully play out in a continuous manner, the later entails a more effective coupling with the host structure. These salient properties have been demonstrated and confirmed both numerically and experimentally by examining a benchmark plate structure. For analyses, a coupling model embracing the host structure and the add-on DVAs is established which allows the calculation of the coupling coefficient, a vital quantity to guide the DVA design. Studies demonstrate the advantages of the proposed DVA over existing designs for the same given mass. The enriched structural coupling and the enhanced modal damping, arising from the eccentric and circumferentially graded ABH design, are shown to be the origin of such improvement. All in all, the physical process underpinning the dynamic absorber principle and waveguide absorber from the host structures is simultaneously consolidated, thus leading to superior broadband structural vibration suppression.

Vibration damping of plates using waveguide absorbers based on spiral acoustic black holes

We propose a waveguide absorber (WGA) based on an acoustic black hole (ABH) to damp vibrations in plate structures. The proposed WGA is composed of a spiral ABH and a rod connecting it to the surface of the plate. The geometrical dimensions of the WGA are determined, such that it has a lower cut-on frequency than a given target range of frequencies, by using a recently developed impedance method for curved ABHs. We then optimize the location of attachment and direction of the WGA on a simply supported uniform plate to minimize the peak levels of its surface-averaged mobility. The strategy used to find its optimum location and direction is based on an analysis of structural intensity that provides the distribution and direction of elastic wave energy propagating in the plate. The results of simulations and experiments show that large reductions of resonance peaks could be achieved below 500 Hz by attaching a couple of lightweight WGAs to a uniform plate. With practical applications in mind, we also applied the ABH-based WGAs to plates that form a box structure, where this is a simplified and scaled version of a box-type mechanical system.

A thin and low-cost scalable waveguide load absorber

In this paper, a set of simple S-band waveguide absorbers are designed and implemented on a low-cost FR4 substrate. This is to provide an alternative for conventional waveguide absorbers, which are generally bulky and costly. The proposed structure is composed of only two open-ended resonator strips on a low-cost, 3.2-mm thick FR4 board. These absorbers operate with the same fundamentals as absorbers based on the frequency selective surfaces. The proposed innovative waveguide absorber load is mode-independent and designed without any connection between the strips and the waveguide. Simulations and measurements indicated an approximately 2.2% of bandwidth, with a 99% absorption rate at the center frequency. A complete parameter study is also performed to show the robustness of the design, besides enabling tuning for use in other microwave waveguides. A good agreement between simulated and measured results confirms the functionality of the absorber.

Vibration suppressions using a dynamic absorber embedded with acoustic black hole features

By capitalizing on the acoustic black hole (ABH) phenomena, an ABH-featured vibration absorber is proposed for the broadband vibration suppressions of a primary structure. As an add-on device to be attached to the primary structure, the proposed absorber embraces the principles of both dynamic vibration absorbers and waveguide absorbers. Its design and implementation avoids the tedious parameter tuning, thus showing robustness to accommodate structural variations in the primary structure. Using a beam as a benchmark example, both numerical simulations and experiments show that multiple resonances of the primary structure can be significantly reduced, and the same absorber can be used for different primary systems. Analyses reveal the existence of three types of vibration reduction mechanisms, manifested differently and dominated by different physical process, i.e.,structural interaction, damping enhancement, and their combination. Comparisons with a conventional uniform beam absorber shows that the superiority of the proposed absorber is attributed to its ABH-specific features exemplified by the enriched system dynamics and the enhanced broadband damping.

A resonant beam damper tailored with Acoustic Black Hole features for broadband vibration reduction

By capitalizing on the Acoustic Black Hole (ABH) phenomenon, a so-called ABH-featured Resonant Beam Damper (ABH-RBD) is proposed for the broadband vibration suppressions of a primary structure. As an add-on device to be attached to the primary structure, the proposed ABH-RBD embraces the principles of both dynamic vibration absorbers and waveguide absorbers. Its design and implementation do not need a tedious parameter tuning, thus showing robustness to accommodate structural variations in the primary structure. Using a beam as a benchmark, both numerical simulations and experiments show that multiple resonances of the primary structure can be significantly reduced by the proposed ABH-RBD, and the same ABH-RBD is effective on different primary systems. Typical control effects and the underlying mechanisms are investigated. Analyses reveal the existence of three types of vibration reduction mechanisms, manifested differently and dominated by different physical process, i.e. structural interaction, damping enhancement and their combination. Comparisons with a conventional uniform beam absorber show that the superiority of the proposed ABH-RBD is attributed to its ABH-specific features exemplified by the enriched system dynamics and the enhanced broadband damping.

Controlling bridge vibrations using a viscoelastic waveguide absorber

The study aims to mitigate the impact of structure-borne noise from existing elevated railway bridges on residents living along the line. In the study, a viscoelastic waveguide absorber mounted on a track slab was proposed based on waveguide vibration absorption techniques by proceeding from the vibration transmitting path and using the track slab as the carrier. First, a dynamic model for the slab-mounted viscoelastic waveguide absorber was constructed, in which a vibration equation was derived and an energy consumption mechanism was obtained. Then, a Chinese railway track style II (CRTS II) ballastless track slab most widely used in Chinese elevated railways was modelled as the primary vibration system, on which an experimental modal analysis was performed. Additionally, a parameterized analysis was performed on the dynamic performance of the slab-mounted viscoelastic waveguide absorber based on the vibration absorption and energy consumption mechanism of the absorber to determine the optimum parameter configuration for the dissipater. Furthermore, the most suitable installation positions for the energy waveguide links were defined using a response surface method. Finally, a bridge vibration response control effectiveness under train loads was also investigated, and it indicated that the waveguide absorbers had a favourable effect in reducing the vibration and structure-borne noise from the elevated railway bridge.

Broadband near total light absorption in non-PT-symmetric waveguide-cavity systems.

We introduce broadband waveguide absorbers with near unity absorption. More specifically, we propose a compact non-parity-time-symmetric perfect absorber unit cell, consisting of two metal-dielectric-metal (MDM) stub resonators with unbalanced gain and loss side-coupled to a MDM waveguide, based on unidirectional reflectionlessness at exceptional points. With proper design, light can transport through the perfect absorber unit cell with reflection close to zero in a broad wavelength range. By cascading multiple unit cell structures, the overall absorption spectra are essentially the superposition of the absorption spectra of the individual perfect absorber unit cells, and absorption of ~ 100% is supported in a wide range of frequencies.

Pump dependence of the dynamics of quantum dot based waveguide absorbers

The nonlinear two stage recovery of quantum dot based reverse-biased waveguide absorbers is investigated experimentally and analytically as a function of the initial ground state occupation probability of the dot. The latter is controlled experimentally by the pump pulse power. The slow stage of the recovery is exponential and its basic timescale is independent of pump power. The fast stage of the recovery is a logistic function which we analyze in detail. The relative strength of slow to fast components is highlighted and the importance of higher order absorption processes at the highest pump level is demonstrated.

Refractive index dynamics of quantum dot based waveguide electroabsorbers

The refractive index dynamics of InAs/GaAs quantum dot based waveguide absorbers is studied using heterodyne pump-probe measurements. Absorption reduction due to the pump can be accompanied by either positive or negative refractive index changes depending on the wavelength used. This change in sign of the phase amplitude coupling can be understood by considering the atomlike nature of the quantum dot transitions involved.

High-Power Pulse Generation in GHz Range With 1064-nm DBR Tapered Laser

For high-power pulse generation at 1060-nm, distributed Bragg reflector tapered lasers were investigated. The lasers consist of a tapered section, a ridge waveguide (RW) absorber section and a passive grating section with a sixth-order surface grating. For the generation of short optical pulses, the tapered section was biased with a dc-current and the RW absorber section was modulated with a 1-GHz sinusoidal current. At a repetition rate of 1 GHz-6.3 W optical pulses with 74-ps full-width at half-maximum and a small spectral widths of 50 pm were generated.

Recovery time scales in a reversed-biased quantum dot absorber

The nonlinear recovery of quantum dot based reverse-biased waveguide absorbers is investigated both experimentally and analytically. We show that the recovery dynamics consists of a fast initial layer followed by a relatively slow decay. The fast recovery stage is completely determined by the intradot properties, while the slow stage depends on the escape from the dot to the wetting layer.

Intradot dynamics of InAs quantum dot based electroabsorbers

The carrier relaxation and escape dynamics of InAs/GaAs quantum dot waveguide absorbers is studied using heterodyne pump-probe measurements. Under reverse bias conditions, we reveal differences in intradot relaxation dynamics, related to the initial population of the dots’ ground or excited states. These differences can be attributed to phonon-assisted or Auger processes being dominant for initially populated ground or excited states, respectively.

Predicting folded beam waveguide absorber behavior using full translational and rotational degree of freedom coupling

Folded beam waveguide absorbers (WGAs) have been shown to be effective low-frequency damping devices. Early WGA studies were unable to accurately predict this damping behavior. These studies used only translational degrees of freedom (DOFs), which resulted in the underestimation of the WGA damping performance. A recent study [Munro and Hambric, ‘‘Modeling folded beam waveguide absorber behavior using translational and rotational degree of freedom frequency response function coupling,’’ Proc. NOISE-CON 2003] used translational and rotational DOF frequency response functions to predict folded beam WGA behavior when attached to a thick rectangular plate, where the plate and WGA rotational DOFs were estimated using the finite-differencing method. Each plate and WGA DOF was coupled independently using frequency domain substructure synthesis (FDSS) [Jetmundsen et al., ‘‘Generalized frequency domain synthesis,’’ J. Am. Helicopter Soc. 55–64, Jan (1988)], and the damping contributions due to each DOF were summed to give the total WGA damping prediction. This method gives a much improved damping estimate from previous methods but is inefficient for complex problems. In this study, all the DOFs for the plate and WGA are combined simultaneously using FDSS to predict the WGA damping behavior and plate response with folded beam WGAs attached.

Characterization of folded beam waveguide absorbers for damping of flexural vibrations in a thick plate

Characterization of folded beam waveguide absorbers for damping of flexural vibrations in a thick plate

FDTD characterization of waveguide-probe structures

The finite-difference time-domain (FDTD) technique is applied in the calculation of the S-parameters of diode mounting and waveguide-probe structures. The influence of the critical geometrical design parameters on the coupling of the coplanar feedline probe to the waveguide is investigated. A waveguide absorber based on analytic Green's functions is used to minimize the reflections over a wide band of frequencies.

Waveguide absorbers for structural damping

For a series of experimental measurements, Manfred Heckl attached strips of damping tape extending outward from the plate edges to increase the plate’s damping. He understood that vibrations induced in the tapes would extract vibrational energy from the plates, but did not explore their effects in detail. The present paper presents an analysis of the damping effects that attached wave-bearing systems can produce and illustrates realizations of waveguide absorbers in the shapes of tapered rods and beams. It also presents related experimental data and describes the general potential of waveguide absorbers.