Vibration Transmittance Research Articles

Band folding induced broadband vibration suppression of star-shaped metamaterials: Theory and experiment

Metamaterials with bandgap features can block wave propagation in specific frequency ranges and thus have wide applications for vibration mitigation and noise reduction. In this study, we renovated the design of star-shaped metamaterial (SSM) to make it capable of producing lower and wider vibration bandgaps. Unlike traditional periodic truss structures in the literature, the designed SSM structure breaks the spatial symmetry, opening the degenerate points formed by the band folding effect, thereby producing extra bandgaps for vibration suppression. First of all, a finite element (FE) model of the SSM is established, and its band structures and vibration transmittance are calculated. The preliminary result validated our hypothesis, demonstrating that the proposed SSM structure created additional bandgaps for suppressing low-frequency and broadband vibrations. Subsequently, the frequency response analyses are conducted using the spectral element method (SEM) and experimental test. The effects of the structural parameters on the bandgaps of the proposed SSM are studied. In addition, we further extended and generalized the band folding design concept. We showed that one can produce more bandgaps by designing high-order SSMs. In general, this study presents an approach for designing truss structures with broadband vibration suppression performance.

Investigations on the Complex Band Diagram of Flexural Wave through the Fluid-Loaded Phononic Plate

This paper investigates the complex band diagram of flexural waves in the phononic plate with semi-infinite heavy fluid loading. The system under examination is a square plate lattice with two-dimensional periodicity immersed in a fluid domain with infinite height. The numerical models based on the wave field transformation and the Galerkin method combined with the finite element discretization technique are developed to investigate the real and imaginary parts of the dispersion relation of flexural waves propagating through the phononic plate incorporating the fluid-loading effects. A perfect agreement is found between the location and width of stop bands from the real band diagram and the attenuation diagram, which supports the validity of the numerical models. Moreover, the complex band diagram is verified by the transverse vibration transmittance of the finite phononic plate. The results demonstrate that the external fluid loading is able to adjust the location, bandwidth, and decaying level as well as affect the degree of attenuation anisotropy of the complete and directional band gaps.

Investigation on a lightweight type broad band-gap metamaterial beam for low-frequency vibration control

Phononic crystals (PCs) and acoustics/elastic metamaterials (AMs/EMs) have aroused increasing attentions for potential applications in low-frequency vibration control due to their outstanding mechanical and physical performances. So far, most reported metamaterials aim to obtain low-frequency broad band-gaps as required to satisfy the practical application. In this paper, we propose a new lightweight low-frequency broadband metamaterial beam. The low-frequency broadband from 390 to 920 Hz of the proposed metamaterial beam is confirmed through vibration transmittance frequency response functions (FRFs) obtained numerically and experimentally. Finally, the steady-state vibration deformations are acquired to illustrate the attenuating effect of the metamaterial beam band-gaps. The research in this paper offers a novel and advantageous method for designing of structures that both broadband damping and lightweight required, such as space-arm and framework of antenna in the field of aerospace.

Wave propagation in two-dimensional elastic metastructures with triangular configuration

A triangular configuration spring–mass model is proposed in this paper to investigate the dependence on structural parameters of elastic wave propagation in two-dimensional (2D) elastic metamaterials/metastructures (EMs). Based on the lattice dynamics, the dispersion relations of the multiple degrees of freedom (DOF) unit cell and the vibration propagation of elastic waves are derived. Moreover, the effects of the configuration angle, spring stiffness, and mass distribution on the frequency and width of bandgaps are explored. The bandgap can be widened by 31.5% or as low as 32 Hz by reasonably adjusting the stiffness and mass distribution. Finally, the asymmetric structure (Model II-1) with the most pronounced full-bandgap difference produced by scanning along two irreducible Brillouin zones (IBZs) of Γ-X-M-Γ and Γ-Y-M-Γ was selected to explore the directional bandgap properties of EM. The dispersion curves obtained by the eigenmode division method are more consistent with the attenuation ranges of the vibration transmittance and can be used to easily and comprehensively identify the bandgap properties. This research provides important clues and theoretical guidance for the design of vibration isolators, beams, plates and other renewed devices.

Propagation of elastic waves in metamaterial plates with various lattices for low-frequency vibration attenuation

Elastic wave propagation characteristics of elastic metamaterial plates embedded scatterer with various lattices are explored numerically and experimentally in this study, for the attenuation of in-plane longitudinal and out-of-plane flexural waves in the subwavelength frequency region. Firstly, the mathematical models of the elastic metamaterial plates are established, and the dispersion relations are derived by the plane wave expansion (PWE) method based on Bloch's theorem. Furthermore, the applicability of the irreducible Brillouin zone (IBZ) for different lattices is also investigated through iso-frequency contours. The analysis of the bandgap formation mechanism indicates that the proposed metamaterial plates can enlarge the bandgaps (BGs) in the low-frequency range by coupling Bragg and local resonance BGs. Moreover, the influences of the scatterer shapes, geometric and material parameters on the BGs are investigated, and which combination of parameters has positive significance for opening low-frequency broadband is also discussed. The results show that the vibration transmittance obtained by experiment and numerical calculation is in good agreement with the predicted results of band structures. Therefore, the elastic metamaterial plates should be promising in the application of low-frequency wave mitigation.

Early faults diagnosis and severity assessment of rolling element bearings on wireless signal transfer

Machine condition monitoring in remote locations and harsh environment where network infrastructure is not feasible, or hardwired network connectivity is not possible, wireless communications provides an alternative which also offer installation cost savings, improve reliability and quicker deployment. This paper describes the implementation of wireless sensor network (WSN) for early fault diagnosis of rolling element bearings based on signal autocorrelation technique. A low-power 2.4 GHz wireless HART transceiver, a low-cost wireless vibration transmitter, 26.76 mv/g accelerometers and a 1420 wireless gateway with AMS software was implemented. The research describes the methodology of acquiring peak values data in high frequency region. The noise was averaged out by applying four-time averaging and natural frequencies or fault frequencies of bearing elements was captured. The experimental results show that the signal autocorrelation algorithm can successfully diagnose the roller bearing faults at early stage on wireless signal transfer. As the raw data was processed before wireless transmission on analyzing unit and spectrum was transferred in JPG format on display unit, minimum power consumption has been noted. The technique provided a better alternative of wired system for real time condition monitoring of roller bearings in rotating equipment installed in remote area.

Bandgap coupling effects between hybrid nonlinear synchronized switch damping and linear two-order resonant bandgaps in piezoelectric meta-structures

To study the bandgap coupling mechanism between nonlinear synchronized switch damping and multi-order linear resonant bandgaps, this research investigates the bandgap coupling effects between nonlinear synchronized switch damping and two-order linear resonant bandgaps in a piezoelectric meta-structure. Specifically, a piezoelectric meta-structure with hybrid nonlinear synchronized switch damping and linear two-order linear resonant electrical networks is proposed. Based on the theoretical modeling of the proposed structure, band structure and vibration transmittance performance are investigated in detail. Results showed that bandgap coupling can produce a trade-off with the advantages of both nonlinear and two-order linear resonant bandgaps. The new bandgap can not only realize broadband wave attenuation performance but also greatly enhance the attenuation in selected frequency bands, which provides a new method to manipulate elastic waves in a diversified way.

Bolt loose judging device for offshore wind turbine

For the problem of bolt loose in the long-term operation of offshore wind turbine, we proposed a bolt loose judging device for offshore wind turbine. The bolt loose judging device for offshore wind turbine included vibration sensor, signal receiving and transmitter, CCD sensor, data analyzer, power supply, the communication line and the power supply line. The combination of data analyzer and CCD sensor was used to analyze whether the prefabricated symbols on the bolts change, so as to judge whether the bolts are loose. The whole system (except vibration sensor) has been in standby and dormant state at ordinary times, which is more simple and reliable under the harsh conditions at sea.

A device for measuring sternal bone connectivity using vibration analysis techniques.

Stability of bone splitting sternotomy is essential for normal healing after open cardiac surgery. Mechanical vibration transmittance may offer a means for early detection of separation of bone (diastasis) in the sternotomy and prevent further complications. This article describes the technical implementation and validation of vibration analysis-based prototype device built for measuring sternal bone connectivity after sternotomy. An in-house built measurement system, sternal vibration device, consisting of actuator, sensor, and main controller and signal acquisition unit was designed and manufactured. The system was validated, and three different test settings were studied in mockups (polylactide rods in ballistic gel) and in two human sternums: intact, stable wire fixation, and unstable wire fixation with a gap mimicking bone diastasis. The transmittance of vibration stimulus across the median sternotomy was measured. The validation showed that the force produced by the actuator was stable, and the sensor could be calibrated to precisely measure the acceleration values. The vibration transmittance response to material cut and sternotomy was evident and detectable in the 20 Hz to 2 kHz band. The transmittance decreased when the connectivity between the sternal halves became unstable. The trend was visible in all the settings. Technical solutions and description of validation process were given. The device was calibrated, and the vibration transmittance analysis differentiated intact and cut polylactide rod. In the sternum, intact bone, wire fixation with exact apposition, and with a gap were identified separately. Although further studies are needed to assess the accuracy of the method to detect different levels of diastases, the method appears to be feasible.

Vibration transmittance measures sternotomy stability \u2013 a preliminary study in human cadavers

BackgroundStability is essential for the normal healing of a sternotomy. Mechanical vibration transmittance may provide a new means of early detection of diastasis in the sternotomy and thus enable the prevention of further complications. We sought to confirm that vibration transmittance detects sternal diastasis in human tissue.MethodsTen adult human cadavers (8 males and 2 females) were used for sternal assessments with a device constructed in-house to measure the transmittance of a vibration stimulus across the median sternotomy at the second, third, and fourth costal cartilage. Intact bone was compared to two fixed bone junctions, namely a stable wire fixation and an unstable wire fixation with a 10 mm wide diastasis mimicking a widely rupturing sternotomy. A generalized Linear Mixed Model with the lme function was used to determine the ability of the vibration transmittance device to differentiate mechanical settings in the sternotomy.ResultsThe transmitted vibration power was statistically significantly different between the intact chest and stable sternotomy closure, stable and unstable closure, as well as intact and unstable closure (t-values and p-values respectively: t = 6.87, p < 0.001; t = 7.41, p < 0.001; t = 14.3, p < 0.001). The decrease of vibration transmittance from intact to stable at all tested costal levels was 78%, from stable to unstable 58%, and from intact to unstable 91%. The vibration transmittance power was not statistically significantly different between the three tested costal levels (level 3 vs. level 2; level 4 vs. level 2; level 4 vs. level 3; t-values and p-values respectively t = − 0.36, p = 0.723; t = 0.35, p = 0.728; t = 0.71, p = 0.484).ConclusionsVibration transmittance analysis differentiates the intact sternum, wire fixation with exact apposition, and wire fixation with a gap. The gap detection capability is not dependent on the tested costal level. The method may prove useful in the early detection of sternal instability and warrants further exploration.

Approaches to decrease the level of parasitic noise over vibroacoustic channel in terms of configuring information security tools

The article deals with influence of various ways to place vibration transmitters on efficiency of rooms safety for negotiations. Standing for remote vibration listening of window glass, electro-optical channel, the most typical technical channel of information leakage, was investigated. The modern system “Sonata-AB” of 4B model is used as an active protection tool. Factors influencing on security tools configuration efficiency have been determined. The results allow utilizer to reduce masking interference level as well as parasitic noise with keeping properties of room safety.

TECHNIQUE OF VIBRATION MONITORING

Vibration monitoring of machines is an integral part of their technical health estimation while in service and prevention of collapse resulting from resonance conditions operation or material fatigue. Aviation gas-turbine engines and land based gas turbine – typical representatives of the of machines which are subject obligatory vibro-monitoring. In most cases it should be carried out continuously, but, in some cases (for example, power-plants of light helicopters), vibro-monitoring is performed within periods reckoned in dozens of hours. Now one-axial vibration transmitters of various types are thus used. Anyway, the data received as a result of vibro-monitoring are processed, first of all, with the use of range verification and a number of smoothing modes and the estimation of a tendency of vibration change modes while in service, examples of which shown on the engines are displayed in a paper. In some cases, there is a necessity of the simplified estimation of a vibrational condition of the machine for additional points or holding operative primary vibro-monitoring without engaging of a rented control equipment. The possible solution is the use of the modern mobile devices equipped with acceleration transmitters and the specialized software for archiving and vibro-monitoring data presentation in real-time mode. In the training process these devices appear full-scale substitution of vibration pickups and an oscillograph sheaf at estimating critical frequencies of rotors rotation with the possibility of archiving of the monitored data for the further processing. The vibrational monitoring technique with the use of microelectromechanical systems of modern mobile devices, has a number of advantages over the other ways. Particularly, the simultaneous three-axial estimation of vibration acceleration and a vibration vector with the graphic and character data presentation in real-time mode and more archiving and operative data processing opportunities, is executed.

Vibration band gaps for elastic metamaterial rods using wave finite element method

Band gaps in elastic metamaterial rods with spatial periodic distribution and periodically attached local resonators are investigated. New techniques to analyze metamaterial systems are using a combination of analytical or numerical method with wave propagation. One of them, called here wave spectral element method (WSEM), consists of combining the spectral element method (SEM) with Floquet–Bloch׳s theorem. A modern methodology called wave finite element method (WFEM), developed to calculate dynamic behavior in periodic acoustic and structural systems, utilizes a similar approach where SEM is substituted by the conventional finite element method (FEM). In this paper, it is proposed to use WFEM to calculate band gaps in elastic metamaterial rods with spatial periodic distribution and periodically attached local resonators of multi-degree-of-freedom (M-DOF). Simulated examples with band gaps generated by Bragg scattering and local resonators are calculated by WFEM and verified with WSEM, which is used as a reference method. Results are presented in the form of attenuation constant, vibration transmittance and frequency response function (FRF). For all cases, WFEM and WSEM results are in agreement, provided that the number of elements used in WFEM is sufficient to convergence. An experimental test was conducted with a real elastic metamaterial rod, manufactured with plastic in a 3D printer, without local resonance-type effect. The experimental results for the metamaterial rod with band gaps generated by Bragg scattering are compared with the simulated ones. Both numerical methods (WSEM and WFEM) can localize the band gap position and width very close to the experimental results. A hybrid approach combining WFEM with the commercial finite element software ANSYS is proposed to model complex metamaterial systems. Two examples illustrating its efficiency and accuracy to model an elastic metamaterial rod unit-cell using 1D simple rod element and 3D solid element are demonstrated and the results present good approximation to the experimental data.

Flexural wave band gaps in metamaterial beams with membrane-type resonators: theory and experiment

This paper deals with flexural wave band gaps in metamaterial beams with membrane-type resonators. The proposed membrane-type resonator consists of a tensioned elastic membrane and a mass block attached to the center of the membrane. Numerical models based on finite element method are presented to predict the dispersion relation, band gaps and eigen-modes. It has shown that the metamaterial beams exhibit unique wave physics. A broad Bragg band gap (BBG) and two low-frequency locally resonant band gaps (LRBGs) can be observed due to the structural periodicity and locally resonant behavior respectively. The first LRBG can be ascribed to the combined resonance of the membranes and the masses, while the second LRBG is caused by the resonance of the membranes. The study of the effective property shows that negative mass density occurs in the LRBGs. The effects of membrane tension and mass magnitude (the weight of mass block) on the LRBGs are further analyzed. It is shown that both the two LRBGs move to high-frequency with the increase of the membrane tension. However, as the mass magnitude increases, the first LRBG moves to low-frequency and the second LRBG almost remains unchanged. It is further demonstrated that, when a larger unit cell with multiple kinds of masses (a larger unit cell incorporating multiple basic unit cells but with different weights of mass blocks within each basic unit cell) are used, the first LRBG can be broadened, which can be employed to achieve broadband vibration attenuation. Moreover, experimental measurements of vibration transmittance are conducted to validate the theoretical predictions. Good agreements between the experimental results and the theoretical predictions are observed.

Flexural wave band-gaps in phononic metamaterial beam with hybrid shunting circuits**Project supported by the National Natural Science Foundation of China (Grant Nos. 51275519 and 51175501).

Periodic arrays of hybrid-shunted piezoelectric patches are used to control the band-gaps of phononic metamaterial beams. Passive resistive-inductive (RL) shunting circuits can produce a narrow resonant band-gap (RG), and active negative capacitive (NC) shunting circuits can broaden the Bragg band-gaps (BGs). In this article, active NC shunting circuits and passive resonant RL shunting circuits are connected to the same piezoelectric patches in parallel, which are usually called hybrid shunting circuits, to control the location and the extent of the band-gaps. A super-wide coupled band-gap is generated when the coupling between RG and the BG occurs. The attenuation constant of the infinite periodic structure is predicted by the transfer matrix method, which is compared with the vibration transmittance of a finite periodic structure calculated by the finite element method. Numerical results show that the hybrid-shunting circuits can make the band-gaps wider by appropriately selecting the inductances, negative capacitances, and resistances.

Theoretical and Experimental Study of Locally Resonant and Bragg Band Gaps in Flexural Beams Carrying Periodic Arrays of Beam-Like Resonators

In this paper, we present a design of locally resonant (LR) beams using periodic arrays of beam-like resonators (or beam-like vibration absorbers) attached to a thin homogeneous beam. The main purpose of this work is twofold: (i) providing a theoretical characterization of the proposed LR beams, including the band gap behavior of infinite systems and the vibration transmittance of finite structures, and (ii) providing experimental evidence of the associated band gap properties, especially the coexistence of LR and Bragg band gaps, and their evolution with tuned local resonance. For the first purpose, an analytical method based on the spectral element formulations is presented, and then an in-depth numerical study is performed to examine the band gap effects. In particular, explicit formulas are provided to enable an exact calculation of band gaps and an approximate prediction of band gap edges. For the second purpose, we fabricate several LR beam specimens by mounting 16 equally spaced resonators onto a free-free host beam. These specimens use the same host beam, but the resonance frequencies of the resonators on each beam are different. We further measure the vibration transmittances of these specimens, which give evidence of three interesting band gap phenomena: (i) transition between LR and Bragg band gaps; (ii) near-coupling effect of the local resonance and Bragg scattering; and (iii) resonance frequency of local resonators outside of the LR band gap.

J022035 micro-MRIによる2層アガロースゲルのMRE画像

Magnetic resonance elastography (MRE) is a newly developed imaging technique that makes full use of the magnetic resonance imaging (MRI) visualization to measure the stiffness of tissue in the body organs using mechanical excitation. In this study, an excitation device for MRE by micro-MRI (0.3T) was constructed from a high power vibration generator and a bar type vibration transmitter made from GFRP. The stiffness was expressed by storage shear modulus G' and loss shear modulus G" of the modified stokes model for a viscoelastic medium. Using a micro-MRI system, the optimal excitation condition of frequency and amplitude of wave was examined using some gel specimens. Viscoelastic modulus distribution of two layered agarose gel specimens were measured in the excitation condition of amplitude (0.5, 1.0, and 1.5 mm) and frequency (62.5, 125, and 250 Hz). The distribution of G' was influenced by both the frequency and amplitude of excitation. The two layered specimen combined with two different concentration gel samples shows the same tendency of G' in the same concentration layer approaching similar values under the higher excitation amplitude and frequency conditions as the uniform agarose gel specimen. Clear differences of the wave propagation patterns were observed in the MR image and the difference of G' between each phase area could be measured quantitatively in this MRE system.

Transducer assembly for megasonic processing of an article and apparatus utilizing the same

A transducer assembly for the megasonic processing of an article and apparatus incorporating the same. The transducer assembly comprises a vibration transmitter having a portion configured to be positioned adjacent to and spaced from the surface of an article so that when fluid is applied to the surface of the article, a meniscus of the fluid forms between the surface of the article and the portion of the vibration transmitter. The transducer assembly also comprises a transducer coupled to the vibration transmitter, where the transducer can oscillate to propagate megasonic energy through the vibration transmitter and through the meniscus of the fluid. In one embodiment, the transducer is located within an enclosed space and at least one passageway is provided for flowing a gas in and/or out of the enclosed space. In an another embodiment, the portion of the vibration transmitter includes an elongated edge that is positioned close to and generally parallel to a surface of the article. In an apparatus incorporating the transducer assembly, a rotatable support is provided to support the article to be processed.

Design of Industrial Vibration Transmitter Using MEMS Accelerometer

This paper presents the overall design of an industrial vibration transmitter using Micro Electro Mechanical System (MEMS) capacitive accelerometer. It describes the accelerometer sensor interfacing circuit, rms-to-dc converter and voltage to current loop converter circuit design, calibration procedure and mounting methods. The industrial vibration transmitter output can be customized to obtain either acceleration or velocity with root mean square (rms) or peak (pk) value signal. The electronic circuit was designed to measure vibration in motion. The output of the transmitter is a current signal (4-20mA) which is proportional to input acceleration (0-10g rms). The AC coupling circuit for accelerometer sensor interfacing, RMS detector and industrial current loop converter circuit are implemented in a single printed circuit board. The prototype consists of 2 pin top connector for power input (24VDC), current output signal and stainless steel mechanical housing assembly with bottom thread connection for mounting. The loop powered acceleration vibration transmitter is employed for vibration monitoring and control applications. Keywords: Vibration transmitter, MEMS, capacitive accelerometer, AC coupling, RMS detector, current loop converter, condition monitoring.

Supporting device for ultrasonic vibration assembly

A device for supporting an ultrasonic vibration assembly comprises an ultrasonic vibrator, a vibration transmitter coupled to the end of the vibrator coaxially thereto, two flanges provided at a prescribed distance from each other on the outside circumferential surface of the transmitter so as to act as pistons, a cylinder in which the flanges are fitted so as to be movable in the axial direction of the cylinder, and mechanisms for feeding a pressurized fluid to two openings defined between the flanges and both the ends of the cylinder. The cross-sectional area of one portion of the interior of the cylinder is made different from that of the portion of the opening, and one of the flanges is made different in outside diameter from the other thereof and fitted in the end portion.