scholarly journals Tunable Mechanical Filter for Longitudinal Vibrations

2007 ◽  
Vol 14 (5) ◽  
pp. 377-391 ◽  
Author(s):  
S. Asiri
Keyword(s):  
Wave Propagation ◽  
Spectral Width ◽  
Design Parameters ◽  
Vibration Source ◽  
Vibration Isolator ◽  
Force Transmission ◽  
Longitudinal Vibrations ◽  
Frequency Bands ◽  
Mechanical Filter ◽  
Vibration And Sound Radiation

This paper presents both theoretically and experimentally a new kind of vibration isolator called tunable mechanical filter which consists of four parallel hybrid periodic rods connected between two plates. The rods consist of an assembly of periodic cells, each cell being composed of a short rod and piezoelectric inserts. By actively controlling the piezoelectric elements, it is shown that the periodic rods can efficiently attenuate the propagation of vibration from the upper plate to the lower one within critical frequency bands and consequently minimize the effects of transmission of undesirable vibration and sound radiation. In such a filter, longitudinal waves can propagate from the vibration source in the upper plate to the lower one along the rods only within specific frequency bands called the “Pass Bands” and wave propagation is efficiently attenuated within other frequency bands called the “Stop Bands”. The spectral width of these bands can be tuned according to the nature of the external excitation. The theory governing the operation of this class of vibration isolator is presented and their tunable filtering characteristics are demonstrated experimentally as functions of their design parameters. The concept of this mechanical filter as presented can be employed in many applications to control the wave propagation and the force transmission of longitudinal vibrations both in the spectral and spatial domains in an attempt to stop/attenuate the propagation of undesirable disturbances.

scholarly journals Broadband Vibration Attenuation Using Hybrid Periodic Rods

2008 ◽  
Vol 5 (1) ◽  
pp. 7 ◽  
Author(s):  
S. Asiri
Keyword(s):  
Wave Propagation ◽  
Spectral Width ◽  
Design Parameters ◽  
Vibration Source ◽  
Vibration Isolator ◽  
Force Transmission ◽  
Frequency Bands ◽  
Spatial Domains ◽  
Specific Frequency ◽  
Vibration And Sound Radiation

This paper presents both theoretically and experimentally a new kind of a broadband vibration isolator. It is a table-like system formed by four parallel hybrid periodic rods connected between two plates. The rods consist of an assembly of periodic cells, each cell being composed of a short rod and piezoelectric inserts. By actively controlling the piezoelectric elements, it is shown that the periodic rods can efficiently attenuate the propagation of vibration from the upper plate to the lower one within critical frequency bands and consequently minimize the effects of transmission of undesirable vibration and sound radiation. In such a system, longitudinal waves can propagate from the vibration source in the upper plate to the lower one along the rods only within specific frequency bands called the "Pass Bands" and wave propagation is efficiently attenuated within other frequency bands called the "Stop Bands". The spectral width of these bands can be tuned according to the nature of the external excitation. The theory governing the operation of this class of vibration isolator is presented and their tunable filtering characteristics are demonstrated experimentally as functions of their design parameters. This concept can be employed in many applications to control the wave propagation and the force transmission of longitudinal vibrations both in the spectral and spatial domains in an attempt to stop/attenuate the propagation of undesirable disturbances. 

Periodic Struts for Gearbox Support System

2005 ◽  
Vol 11 (6) ◽  
pp. 709-721 ◽  
Author(s):  
S. Asiri ◽  
A. Baz ◽  
D. Pines
Keyword(s):  
Wave Propagation ◽  
Critical Frequency ◽  
Periodic Structures ◽  
Design Parameters ◽  
Force Transmission ◽  
Frequency Bands ◽  
New Class ◽  
Spatial Domains ◽  
Specific Frequency ◽  
Vibration And Sound Radiation

Passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called “pass bands” and wave propagation is completely blocked within other frequency bands called “stop bands”. In this paper, the emphasis is placed on developing a new class of these periodic structures called passive periodic struts, which can be used to support gearbox systems on the airframes of helicopters. When designed properly, the passive periodic strut can stop the propagation of vibration from the gearbox to the airframe within critical frequency bands, consequently minimizing the effects of transmission of undesirable vibration and sound radiation to the helicopter cabin. The theory governing the operation of this class of passive periodic struts is introduced and their filtering characteristics are demonstrated experimentally as a function of their design parameters. The presented concept of the passive periodic strut can be easily used in many applications to control the wave propagation and the force transmission in both the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.

Passive Periodic Engine Mount

2008 ◽  
Author(s):  
Ling Zheng ◽  
Woojin Jung ◽  
Zheng Gu ◽  
A. Baz
Keyword(s):  
Spectral Width ◽  
Shear Mode ◽  
Effective Width ◽  
Frequency Bands ◽  
Automotive Engine ◽  
New Class ◽  
Mechanical Filter ◽  
Transfer Matrix Approach ◽  
Specific Frequency ◽  
Engine Mount

The transmission of automotive engine vibrations to the chassis is isolated using a new class of mounts which rely in their operation on optimally designed and periodically distributed viscoelastic inserts. The proposed mount acts as mechanical filter for impeding the propagation of vibration within specific frequency bands called the ‘Stop Bands’. The spectral width of these bands is enhanced by making the viscoelastic inserts operate in a shear mode rather than compression mode. The theory governing the operation of this class of periodic mounts is presented using the theory of finite elements combined with the transfer matrix approach. The predictions of the performance of the mount are validated against the predictions of the commercial finite element code ANSYS and against experimental results obtained from prototypes of plain and periodic mounts. The obtained results demonstrate the feasibility of the shear mode periodic mount as an effectiveness means for blocking the transmission of vibration over a broad frequency band. Extending the effective width of the operating frequency bands of this class of mount through active control means is the ultimate goal of this study.

Localization and Control of Wave Propagation in Active Periodic Fluid-Loaded Shells

2001 ◽  
Author(s):  
M. Ruzzene ◽  
A. Baz
Keyword(s):  
Wave Propagation ◽  
Periodic Structures ◽  
Effective Means ◽  
Sound Radiation ◽  
Excitation Source ◽  
Proportional Control ◽  
Frequency Bands ◽  
Control Gain ◽  
Vibration And Sound Radiation ◽  
Attenuation Characteristics

Abstract Periodically placed actuators are used to control the wave propagation and to localize the vibration and sound radiation of fluid-loaded shells. The filtering capabilities of the resulting periodic structure can be actively tuned by modifying the feedback control gain of the actuators thus allowing for controlling the spectral width and location of the stop and pass bands as well as introducing controlled aperiodicity in the structure. A finite element model is developed to study the fundamental phenomena governing the coupling between the shell, actuators and the fluid domain surrounding the shell. The geometry of the shell and the fluid domain allows for the formulation of a harmonic-based model with uncoupled circumferential modes. The model is used to predict the pass and stop frequency bands for different proportional control gains and to evaluate the shell harmonic response and the sound radiation into the surrounding fluid. The obtained results indicate that the location and width of the stop bands as well as the attenuation characteristics of the shell can be modified by proper choice of the proportional control gain. Numerical simulations also demonstrate that the location of the stop bands can be identified from the frequency response function of the shell and from the sound intensity. The tunable characteristics of the proposed active shells allow for the introduction of controlled aperiodicty through proper adjustments of the actuators’ feedback gains. Disorder in periodic structures typically extends the stopbands into adjacent propagation zones and, more importantly, localizes the vibration energy near the excitation source. Both structural response and sound radiation are evaluated for increasing levels of aperiodicity. The results presented demonstrate the effectiveness of the proposed concept as an effective means for controlling the attenuation characteristics of fluid-loaded shells and for confining both vibration and sound radiation near the excitation source. Also, the presented analysis provides an invaluable means for designing fluid-loaded shells, which are quiet over desired frequency bands and where the energy can be spatially confined in well-defined restricted areas.

Active Control of Periodic Structures

2000 ◽  
Author(s):  
A. Baz
Keyword(s):  
Wave Propagation ◽  
Active Control ◽  
Periodic Structures ◽  
Spectral Width ◽  
Structural Vibration ◽  
Frequency Bands ◽  
Spatial Domains ◽  
Specific Frequency ◽  
The Individual ◽  
Unique Potential

Abstract Conventional passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the “Pass Bands” and wave propagation is completely blocked within other frequency bands called the “Stop Bands”. In this paper, the emphasis is placed on providing the passive structures with active control capabilities in order to tune the spectral width and location of the pass and stop bands in response to the structural vibration. Apart from their unique filtering characteristics, the ability of periodic structures to transmit waves, from one location to another, within the pass bands can be greatly reduced when the ideal periodicity is disrupted resulting in the well-known phenomenon of “Localization”. In the case of passive structures, the aperiodicity (or the disorder) can result from unintentional material, geometric and manufacturing variability. However, in the case of active periodic structures the aperiodicity is intentionally introduced by proper tuning of the controllers of the individual substructure or cell. The theory governing the operation of this class of Active Periodic structures is introduced and numerical examples are presented to illustrate their tunable filtering and localization characteristics. The examples considered include periodic/aperiodic spring-mass systems controlled by piezoelectric actuators. The presented results emphasize the unique potential of the active periodic structures in controlling the wave propagation both in the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.

Active Control of Periodic Structures

2001 ◽  
Vol 123 (4) ◽  
pp. 472-479 ◽  
Author(s):  
A. Baz
Keyword(s):  
Wave Propagation ◽  
Active Control ◽  
Periodic Structures ◽  
Spectral Width ◽  
Structural Vibration ◽  
Frequency Bands ◽  
Spatial Domains ◽  
Specific Frequency ◽  
The Individual ◽  
Unique Potential

Conventional passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the “Pass Bands” and wave propagation is completely blocked within other frequency bands called the “Stop Bands.” In this paper, the emphasis is placed on providing the passive structures with active control capabilities in order to tune the spectral width and location of the pass and stop bands in response to the structural vibration. Apart from their unique filtering characteristics, the ability of periodic structures to transmit waves, from one location to another, within the pass bands can be greatly reduced when the ideal periodicity is disrupted resulting in the well-known phenomenon of “Localization.” In the case of passive structures, the aperiodicity (or the disorder) can result from unintentional material, geometric and manufacturing variability. However, in the case of active periodic structures the aperiodicity is intentionally introduced by proper tuning of the controllers of the individual substructure or cell. The theory governing the operation of this class of Active Periodic structures is introduced and numerical examples are presented to illustrate their tunable filtering and localization characteristics. The examples considered include periodic/aperiodic spring-mass systems controlled by piezoelectric actuators. The presented results emphasize the unique potential of the active periodic structures in controlling the wave propagation both in the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.

scholarly journals Bandwidth Enhancement of Tri-band Rectangular Dielectric Resonator Antenna using Novel Offset Feed for WLAN/WIMAX Applications

2020 ◽  
Vol 9 (5) ◽  
pp. 2305-2308
Keyword(s):  
Dielectric Resonator ◽  
Microstrip Line ◽  
Return Loss ◽  
Radiation Efficiency ◽  
Antenna Design ◽  
Design Parameters ◽  
Dielectric Resonator Antenna ◽  
Bandwidth Enhancement ◽  
Frequency Bands ◽  
Rectangular Dielectric Resonator Antenna

In this article, a novel offset microstrip line feed Rectangular Dielectric Resonator Antenna is used for bandwidth enhancement. The parameters such as Bandwidth, Return Loss and Radiation efficiency are improved in the proposed antenna. A comparison is also shown for the proposed feed structure with and without conformal strips. The improvement in the bandwidth is observed from 25% to 65% by optimizing the antenna design parameters. It works in three frequency bands, that is, 2.03-3.69 GHz, 3.86-7.26 GHz, and 7.32-9.26 GHz. The proposed antenna is appropriate for WIMAX/WLAN applications.

Wave Propagation and Parametric Instability in Materials Reinforced by Fibers With Periodically Varying Directions

1975 ◽  
Vol 42 (4) ◽  
pp. 825-831 ◽  
Author(s):  
M. Schoenberg ◽  
Y. Weitsman
Keyword(s):  
Composite Material ◽  
Wave Propagation ◽  
Elastic Medium ◽  
Parametric Instability ◽  
Transversely Isotropic ◽  
Harmonic Waves ◽  
Fiber Reinforced ◽  
Frequency Bands ◽  
Structural Periodicity ◽  
Dominant Direction

This paper concerns the propagation of plane harmonic waves in an infinite fiber-reinforced elastic medium. The composite material is represented by an equivalent homogeneous transversely isotropic matter whose preferred directions coincide with the orientations of the fibers. The fibers are assumed to wobble periodically about a dominant direction, all fibers being parallel to each other. This wobbliness endows the material with a structural periodicity which generates dispersion at all frequencies and instability for various frequency bands. The zones of instability are analyzed in some detail.

Research on the Vibration Attenuation Rules and Wave Propagation Law under Impacting Drill on the Deep Soil Layer

2011 ◽  
Vol 250-253 ◽  
pp. 1971-1977
Author(s):  
Bo Zhang ◽  
Lian Jin Tao ◽  
Wen Pei Wang ◽  
Ji Dong Li
Keyword(s):  
Wave Propagation ◽  
Soil Layer ◽  
Ground Surface ◽  
Ground Vibration ◽  
Vibration Source ◽  
Vertical Acceleration ◽  
Deep Soil ◽  
Deep Soil Layer ◽  
Propagation Law ◽  
Vibration Attenuation

A field test is carried out to study the effect of vibration while treating foundation using vibroflotation method in the deep soil layer in Zhengzhou, China. The vibration attenuation rules and wave propagation rules in different formations caused by different numbers of drills are analyzed. Evaluate the influence on the adjacent buildings. The result shows that the vibration will be generated in foundation obviously in the process of construction using the method. Vibration force, impact frequency and site soil are important influence factors on ground vibration attenuation. The analysis reveals that the maximum vertical acceleration attenuation velocity was much greater in near area than that in the relative far area. The waves caused by vibration propagate in two ways: (1) surface wave is generated on the wall of drill hole and propagated to the ground surface, and attenuated in a certain distance (<8m); (2) shear wave was generated and propagated in the impacting formation and attenuated from the deep formation to the ground surface. Vibration amplitude is mainly distributed in the low frequency range in the areas which far away from vibration source and in the silt layer near the ground surface.

Predicting the Sound Transmission Loss of Honeycomb Panels using the Wave Propagation Approach

2011 ◽  
Vol 97 (5) ◽  
pp. 869-876 ◽  
Author(s):  
Sathish Kumar ◽  
Leping Feng ◽  
Ulf Orrenius
Keyword(s):  
Wave Propagation ◽  
Transmission Loss ◽  
Plate Theory ◽  
Sandwich Panels ◽  
Sound Transmission ◽  
Structural Vibration ◽  
Sound Transmission Loss ◽  
Resonance Frequencies ◽  
Fluid Coupling ◽  
Vibration And Sound Radiation

The sound transmission properties of sandwich panels can be predicted with sufficient degree of accuracy by calculating the wave propagation properties of the structure. This method works well for sandwich panels with isotropic cores but applications to panels with anisotropic cores are hard to find. Honeycomb is an example of anisotropic material which when used as a core, results in a sandwich panel with anisotropic properties. In this paper, honeycomb panels are treated as being orthotropic and the wavenumbers are calculated for the two principle directions. These calculated wavenumbers are validated with the measured wavenumbers estimated from the resonance frequencies of freely hanging honeycomb beams. A combination of wave propagation and standard orthotropic plate theory is used to predict the sound transmission loss of honeycomb panels. These predictions are validated through sound transmission measurements. Passive damping treatment is a common way to reduce structural vibration and sound radiation, but they often have little effect on sound transmission. Visco-elastic damping with a constraining layer is applied to two honeycomb panels with standard and enhanced fluid coupling properties. This enhanced fluid coupling in one of the test panels is due to an extended coincidence range observed from the dispersion curves. The influence of damping treatments on the sound transmission loss of these panels is investigated. Results show that, after the damping treatment, the sound transmission loss of an acoustically bad panel and a normal panel are very similar.

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