Slow Wave Phenomena Research Articles

Experimental verifications of perforation-modulated slow-wave phenomenon

Slow wave phenomenon has been theoretically and numerically predicted inside a in a retarding based on the so-called sonic black hole (SBH). A perforation-modulated SBH (PMSBH) retarding structure is then proposed, in which the two physical processes (sound velocity reduction and absorption) can be balanced to enhance the black hole effects by modulating the perforation parameters. This work presents an experimental effort to confirm the theoretically predicted slow wave phenomenon as well as the ABH-induced sound absorption inside a PMSBH. Alongside some theoretical development, this study brings forward the concept of tunable design to improve the performance of SBH structures, which can benefit the design of sound wave manipulation and noise control devices.

A sonic black hole structure with perforated boundary for slow wave generation

Sonic black hole (SBH) allows for effective and broadband sound absorption in a retarding duct structure, in which two indispensable physical processes take place: wave retarding and energy dissipation. In this study, an SBH structure with perforated boundary (SBH-PB) is investigated, in which perforated acoustic boundaries are incorporated into the SBH to enhance the black hole effects through a simplified structural design. To predict acoustic performance and understand the physical mechanisms, this paper employs the transfer matrix method (TMM) to model and analyze the physics characteristics of an SBH-PB. Compared to the original form of SBH, the proposed SBH-PB is shown to entail better sound absorption owing to the increased energy dissipation by the small holes, while requiring a smaller number of inner rings. The validity of the TMM prediction is verified by experiments. Finally, the slow wave phenomenon in the retarding structure is also further studied and visualized by numerical simulation and experiment. The proposed structure holds promise for sound wave manipulation and the development of acoustic noise control devices.

A sonic black hole structure with perforated boundary for slow wave generation

A Sonic Black Hole (SBH) in a retarding duct structure incorporates two indispensable physical processes, i.e., wave energy focalization and dissipation, to entail slow-sound effect and broadband sound absorption. Original SBH design, however, involves a large number of inner rings inside the duct to produce the required impedance changes. In this study, a SBH configuration with perforated boundary (SBH-PB) is examined, in which perforated acoustic boundaries are used to achieve enhanced SBH effects. Upon a dedicated treatment of the perforated boundary (PB) with the backing cavity, the transfer matrix method (TMM) is adopted to analyze the acoustic characteristics of the SBH-PB and to explore the underlying physical mechanisms. The adoption of the PB is shown to bring about threefold benefits: increased accuracy of the TMM modeling owing to the weakened coupling among the backing cavities in the SBH-PB, enhanced sound absorption through micro-perforations, and the realization of SBH effects with a reduced number of inner rings. To visualize the slow-sound effect, the change of sound speed is examined through transient simulations using finite element method by capturing the wavefront propagation inside the duct. Finally, for the first time, an acoustic duct system replicating the transient simulations is developed to experimentally demonstrate the slow-wave phenomenon in the time domain. The proposed structure holds promises for sound wave manipulation and the development of acoustic noise control devices.

A graded metamaterial for broadband and high-capability piezoelectric energy harvesting

This work proposes a graded metamaterial-based energy harvester integrating the piezoelectric energy harvesting function targeting low-frequency ambient vibrations (<100 Hz). The harvester combines a graded metamaterial with beam-like resonators, piezoelectric patches, and a self-powered interface circuit for broadband and high-capability energy harvesting. Firstly, an integrated lumped parameter model is derived from both the mechanical and the electrical sides to determine the power performance of the proposed design. Secondly, thorough numerical simulations are carried out to optimize both the grading profile and wave field amplification, as well as to highlight the effects of spatial-frequency separation and the slow-wave phenomenon on energy harvesting performance and efficiency. Finally, experiments with realistic vibration sources validate the theoretical and numerical results from the mechanical and electrical sides. Particularly, the harvested power of the proposed design yields a five-fold increase with respect to conventional harvesting solutions based on single cantilever harvesters. Our results reveal that by bridging the advantages of graded metamaterials with the design targets of piezoelectric energy harvesting, the proposed design shows significant potential for realizing self-powered Internet of Things devices.

Direct constraint control for EM-based miniaturization of microwave passives

Handling constraints imposed on physical dimensions of microwave circuits has become an important design consideration over the recent years. It is primarily fostered by the needs of emerging application areas such as 5G mobile communications, internet of things, or wearable/implantable devices. The size of conventional passive components is determined by the guided wavelength, and its reduction requires topological modifications, e.g., transmission line folding, or utilization of compact cells capitalizing on the slow-wave phenomenon. The resulting miniaturized structures are geometrically complex and typically exhibit strong cross coupling effects, which cannot be adequately accounted for by analytical or equivalent network models. Consequently, electromagnetic (EM)-driven parameter tuning is necessary, which is computationally expensive. When the primary objective is size reduction, the optimization task becomes far more challenging due to the presence of constraints related to electrical performance figures (bandwidth, power split ratio, etc.), which are all costly to evaluate. A popular solution approach is to utilize penalty functions. Therein, possible violations of constraints degrade the primary objective, thereby enforcing their satisfaction. Yet, the appropriate setup of penalty coefficients is a non-trivial problem by itself, and is often associated to extra computational expenses. In this work, we propose an explicit approach to constraint handling, which is combined with the trust-region gradient-search procedure. In our technique, the decision about the adjustment of the search radius is determined based on the reliability of rendering the feasible region boundary by linear approximation models of the constraints. Comprehensive numerical experiments conducted using three miniaturized coupler structures demonstrate superiority of the presented method over the penalty function paradigm. Apart from the efficacy, its appealing features include algorithmic simplicity, and no need for tailoring the procedure for a particular circuit to be optimized.

Design, fabrication and sound absorption test of composite porous metamaterial with embedding I-plates into porous polyurethane sponge

Nowadays the use of porous polyurethane sponge (PPS) is very common for sound absorption, thanks to its light-weight feature and easy fabrication. However, in many circumstances the traditional PPS has very limited absorption capabilities, due to the slow wave phenomenon and/or to insufficient sub-wavelength sound absorption. In this paper, we propose a composite porous metamaterial (CPM) consisting in a porous polyurethane sponge with embedded multi-layer I-plates to mitigate this problem. To characterize the sound absorption coefficient of the proposed CPM, we resort to the Johnson-Champoux-Allard (JCA) model, where five acoustic parameters, namely porosity, flow resistivity, tortuosity, viscous, and thermal characteristic lengths, are determined by acoustic test methods. Numerical and experimental results show that the sound absorption performance of PPS in the CPM is remarkably improved, compared to a contrast structure and a pure porous material, taking advantage of a twofold mechanism of local acoustic energy dissipation of the I-plates and the slow wave phenomenon cancellation inside the structure. Finally, the effects of the geometrical parameters on average sound absorption coefficient are presented and discussed in detail. The scheme of this paper possesses potential application value for the design of broadband and efficient sound absorbers, providing a reference for researches of new acoustic functional devices with high absorption performances.

Tunable Substrate Integrated Waveguide Phase Shifter Using High Dielectric Constant Slab

This letter presents a low-cost, low-profile, and high-performance $Ka$ -band continuously tunable substrate integrated waveguide (SIW) phase shifter. The proposed phase shifter consists of a slot cut on the SIW’s broad wall and a high dielectric constant slab over the slot. The phase-shifting mechanism is based on perturbing the electric field of the SIW’s fundamental mode, TE10-like, by putting a high dielectric constant slab over the slot of SIW structure to create slow wave phenomena. A prototype is designed, fabricated, and measured. The fabricated phase shifter exhibits linear phase–frequency response behavior with an average insertion loss less than 1.5 dB with an insertion loss variation less than 0.5 dB over a phase shift range of 275° in the operating frequency band (29–31 GHz). The phase shifter consumes a maximum of 25-mW power.

ДИНАМИКА ПОРОВЯЗКОУПРУГОЙ КОНСОЛИ ПРИ РАЗЛИЧНОЙ ПРОНИЦАЕМОСТИ МАТЕРИАЛА

In present paper wave propagation poroviscoelastic solids is studied. Study of wave propagation in saturated porous media is an important issue of engineering sciences. The poroelasticity theory was developed and nowadays is an important to engineering applications. Also research is dedicated to modeling of a slow compressional wave in poroviscoelastic media by means of boundary-element method. Poroviscoelastic formulation is based on Biot's model of fully saturated poroelastic media with a correspondence principal usage. Standard linear solid model is employed in order to describe viscoelastic behavior of the skeleton in porous medium. The boundary-value problem of the three-dimensional dynamic poroviscoelasticity is written in terms of Laplace transforms. Direct approach of the boundary integral equation method is employed. The boundary-element approach is based on the mixed boundary-element discretization of surface with generalized quadrangular elements. Subsequent application of collocation method leads to the system of linear equations, and then to the solution in Laplace domain. Numerical inversion of Laplace transform is used to obtain time-domain solution. The problem of the load acting on a poroelastic prismatic solid is solved by means of developed software based on boundary element approach. An influence of permeability of porous material on dynamic responses is studied. Slow wave phenomena appearance is demonstrated. Viscosity parameter influence on dynamic responses of displacements and pore pressure is studied.

Slow wave microstrip line and its application in miniaturization

This article presents a technique for miniaturization. The miniaturization is brought about by reducing the velocity of the wave, a phenomenon called slow wave propagation. The technique is demonstrated in this work using a microstrip line. Electromagnetic simulations show that the slow wave microstrip line has a cut-off frequency of 18.76 GHz and hence behaves like a low pass filter. The low pass nature is also confirmed from the lumped equivalence. The fabrication complexity is reduced by replacing a substrate filled with plated vias with a substrate bearing three rows of plated vias beneath the microstrip line, both of which show similar performances. The slow wave concept is confirmed from the value of group delay and is found to be enhanced in the slow wave line by 21.21%. Implementation of slow wave also results in a 36.3% increase in the effective permittivity. Parametric studies are conducted to analyze the slow wave phenomenon. For proof of concept, the technique is compared to the standard Chebyshev filter. The proposed structure reduces area by 40%. The proposed structure is then fabricated and performance is measured. The measured and simulated results are in good agreement.

Research on the characteristics of the dynamic functional connectivity network related to aging

Brain aging can affect the strength of functional connectivity between brain regions. In recent years, studies have shown that functional connectivity is fluctuant over time, and can reflect more physiological and pathological information. Therefore, in the study resting state functional magnetic resonance imaging (fMRI) data of 32 elderly subjects and 36 younger subjects were selected, and the sliding window technique was used to estimate dynamic functional connectivity network. Then, the dependency of fluctuating energy difference on frequency band was studied using wavelet packet analysis, conducting the linear regression with age at the same time. Results showed that the fluctuating energy in older group was significantly higher than that in the young group in low frequency, and it was significantly lower than that in the young people in high frequency. These results suggested that the dynamic functional connectivity between networks in the elderly exist slow wave phenomenon, which may be related to the decreased reaction rate of the elderly. This article provides new ideas and methods for the research about brain aging, and promotes a theoretical basis for further understanding of the physiological significance of brain dynamic functional connectivity.

Distinct stick-slip modes in adhesive polymer interfaces

Stick-slip, manifest as intermittent tangential motion between two solids, is a well-known friction instability that occurs in a number of natural and engineering systems. In the context of adhesive polymer interfaces, this phenomenon has often been solely associated with Schallamach waves, which are termed slow waves due to their slow propagation speeds. We study the dynamics of a model polymer interface using coupled force measurements and high speed in situ imaging, to explore the occurrence of stick-slip linked to other slow wave phenomena. Two new waves—slip pulse and separation pulse—both distinct from Schallamach waves, are described. The slip pulse is a sharp stress front that propagates in the same direction as the Schallamach wave, while the separation pulse involves local interface detachment and travels in the opposite direction. Transitions between these stick-slip modes are easily effected by changing the sliding velocity or normal load. The properties of these three waves, and their relation to stick-slip is elucidated. We also demonstrate the important role of adhesion in effecting wave propagation.

In vivo radius bone evaluation of women in their late teens by two wave apparatus

Making use of the fast and slow wave phenomenon in cancellous bone, an ultrasonic bone measurement system, LD-100 (OYO electric),1 has been developed and is now commercially available in Japan. From the measurements of fast, slow, and echo waves, the system gives us cancellous bone density (mg/cm3), cancellous bone elasticity (GPa), and the cortical thickness (mm). The measurement area is the distal 5.5 % site of the radius of the non-dominant hand. In this study, the system was modified for the small radius of teenagers using annular array elements. Under the permission of the ethics committee at Doshisha university, radius bones of 111 high school students were measured (15-17 years old, female). The mean values of cortical thickness of the students were 93.7—97.7% of the young adult mean (YAM). The cancellous bone densities were 82.6—94.0% of YAM. The standard deviations of these values were higher than the deviations of YAM. These data possibly indicate that the growth of radius bone depends on the site and the outer cortical shell grows fast. For further discussions, more data should be necessary. 1. H. Sai, et al., Osteoporos Int. (2010) 21, 1781-1790

Miniaturized curved slotted patch antenna over a fractalized EBG ground plane

In this paper, a miniaturized coaxial feed curved-slotted microstrip patch antenna over a fractalized uniplanar compact electromagnetic bandgap (F-UC-EBG) ground plane is proposed and investigated. Compact size is achieved by cutting the curved slots along the orthogonal directions of the patch radiator. The curved-slotted microstrip patch antenna is 38.30% miniaturized as compared with the conventional microstrip patch antenna resonating at 2.38 GHz. Furthermore, the ordinary ground plane of the curved slotted patch antenna is replaced by the F-UC-EBG ground plane. Due to the slow wave phenomenon created in the F-UC-EBG structure and the better impedance matching at the lower frequency further miniaturization and improved performance are obtained. The proposed antenna shows 74.76% miniaturization as compared with the conventional microstrip patch antenna resonating at 1.57 GHz and has 2.61% 10-dB fractional bandwidth, 1.49 dB gain, and 81.59% radiation efficiency. The proposed antenna is fabricated on a low-cost FR4 substrate having an overall volume of 0.184λ0 × 0.184λ0 × 0.0236λ0 at 1.57 GHz GPS band. The measured and simulated results are in good agreement and predicting appropriateness of the antenna in portable and handheld communication systems for GPS applications.

Influence of the circumferential wave on the fast and slow wave propagation in small distal radius bone

An ultrasonic system is good for the evaluation of children because its noninvasiveness. The ultrasonic bone measurement system LD-100 has been developed on the basis of the principle of the fast and slow wave phenomenon in the wrist bone. In the measurement of small bones such as those of children, there are some problems due to the influences of circumferential waves on the fast and slow waves. When the diameters of the focused transducers were small, the appearance of the circumferential wave around the cortical bone became late, and it could avoid one of the influences of the circumferential waves.

Performance enhancement of a circularly polarized patch antenna for radio frequency identification readers using an electromagnetic band-gap ground plane

A miniaturized circularly polarized (CP) patch antenna with wide impedance matching and axial ratio bandwidths and a good efficiency using an electromagnetic band gap (EBG) ground plane is presented. CP is obtained with the truncated corners technique applied on a square patch and size reduction of this radiating element is based on the slow wave phenomenon created in the EBG structure. This antenna is fabricated on a 117 × 117 × 4 mm3 FR-4 substrate (eT = 4.4 and tan δ = 0.22) and dedicated to the European UHF radio frequency identification band (865–868 MHz). The measured bandwidth, realized gain, and total efficiency are 14.4%, 3.7 dBi, and 79%, respectively. Experimental and theorical results are presented and discussed. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1599–1602, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27642

Slow wave phenomena in photonic crystals

AbstractSlow light in photonic crystals and other periodic structures is associated with stationary points of the photonic dispersion relation, where the group velocity of light vanishes. It is shown that in certain cases, the vanishing group velocity is accompanied by the so‐called frozen mode regime, when the incident light can be completely converted into the slow mode with huge diverging amplitude. The frozen mode regime is a qualitatively new wave phenomenon – it does not reduce to any known electromagnetic resonance. Formally, the frozen mode regime is not a resonance, in a sense that it is not particularly sensitive to the size and shape of the photonic crystal. The frozen mode regime is more robust and powerful, compared to any known slow‐wave resonance. It has much higher tolerance to absorption and structural imperfections.

Low-cost surface-reduction technique for RFID reader antennas

A low-cost technique for surface reduction of patch antennas is presented. It is based on the slow wave phenomenon. To create slow wave, a frequency selective surface has been burned on the ground plane of a patch antenna. With this technique, a patch antenna has been designed. An antenna for RFID reader at 915 MHz has been designed and simulated. It uses a 1.6-mm-thick FR4 epoxy substrate (εr = 4.5 h = 1.6 mm tan (δ) = 0.02) measures 61 mm × 65 mm. His maximum gain is 2 dB. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1469–1471, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25241

Slow light phenomenon and extraordinary magnetooptical effects in periodic nanostructured media

Physical nature of the magnetooptical effects enhancement in periodic nanostructured media is investigated. The correlation between group velocity and the Faraday rotation peaks is found. The Faraday rotation gets its maximum values at vanishing group velocity. It is shown that in the vicinity of the photonic band gap the Faraday angle is inversely proportional to the group velocity and directly proportional to the magnetooptical parameter Q averaged along the period of the structure. At this the efficiency of light–magnetic-matter interaction increases significantly. Thus, the increase of the magnetooptical effects in magnetic periodic systems is related to the slow wave phenomenon.

A 3-dB multilayer coupler with UC-PBG structure

A novel broadside coupled stripline coupler with a uniplanar compact photonic bandgap (UC-PBG) structure is presented. Construction of the coupler is based on a stripline with two-dimensional periodically etched ground plane. The slow-wave phenomenon has been predicted and observed. Numerical and experimental investigations show an enhanced backward coupling effect. The usefulness of both phenomena in the coupler construction has been verified experimentally.

Slow-wave phenomena in modified coplanar waveguides

To accomplish a reduction in size as well as to obtain a good performance compared with the conventional half-wavelength coplanar waveguide (CPW) resonator, novel CPW structures are presented and investigated. The presented CPWs provide a /spl sim/70% reduction in the resonance frequency as well as a 20% increase in the Q factor over conventional CPW resonators. Moreover, good agreement between theoretical and experimental resonance frequencies has been confirmed.