Mechanical Vibration Isolation Research Articles

Dynamic Mechanical Characterization of Polyurethane/Multiwalled Carbon Nanotube Composite Thermoplastic Elastomers

ABSTRACTAn effective analytical–experimental test method is used in the current work to characterize the vibration isolation behavior of thermoplastic polyurethane multiwalled carbon nanotube nanocomposites with five different concentrations. To determine the static compression stiffness and hysteresis of the specimens, compression and cyclic tests were conducted. The vibration isolation properties were determined through the analysis of transmissibility of a suitably designed test system. Thermoplastic polyurethane’s mechanical properties and vibration isolation properties were improved with the addition of multiwalled carbon nanotubes. Considering the obtained results, the dynamic stiffness of thermoplastic polyurethane and its capacity to isolate vibration can be adjusted by controlling the proportion of multiwalled carbon nanotubes.

Stochastic resonance in a nonlinear mechanical vibration isolation system

This paper concerns the effect that a stochastic resonance can have on a vibration isolation system. Rather than reducing the transmitted force, it is shown that it is possible to significantly mask the component of the force transmitted though the isolator, when the system is excited harmonically. This can be achieved by adding a very low intensity of random noise to the harmonic excitation force. The nonlinear mechanical vibration isolation system used in the study consists of a vertical linear spring in parallel with two horizontal springs, which are configured so that the potential energy of the system has a double-well. Prior to the analytical and numerical study, an experiment to demonstrate stochastic resonance in a mechanical system is described.

Nested trampoline resonators for optomechanics

Two major challenges in the development of optomechanical devices are achieving a low mechanical and optical loss rate and vibration isolation from the environment. We address both issues by fabricating trampoline resonators made from low pressure chemical vapor deposition Si3N4 with a distributed Bragg reflector mirror. We design a nested double resonator structure with 80 dB of mechanical isolation from the mounting surface at the inner resonator frequency, and we demonstrate up to 45 dB of isolation at lower frequencies in agreement with the design. We reliably fabricate devices with mechanical quality factors of around 400 000 at room temperature. In addition, these devices were used to form optical cavities with finesse up to 181 000 ± 1000. These promising parameters will enable experiments in the quantum regime with macroscopic mechanical resonators.

Study of the Mechanical Properties and Vibration Isolation Performance of a Molecular Spring Isolator

Molecular Spring Isolator(MSI) is a novel passive vibration isolation technique, providingHigh-Static-Low-Dynamic(HSLD) stiffness based on the use ofmolecular springmaterial. Themolecular springmaterial is a solid-liquid mixture consisting of water and hydrophobic nanoporous materials. Under a certain level of external pressure, water molecules can intrude into the hydrophobic pores of nanoporous materials, developing an additional solid-liquid interface. Such interfaces are able to store, release, and transform mechanical energy, providing properties like mechanical spring. Having been only recently developed, the basic mechanic properties of a MSI have not been studied in depth. This paper focuses on the stiffness influence factors, the dynamic frequency response, and the vibration isolation performance of a MSI; these properties help engineers to design MSIs for different engineering applications. First, the working mechanism of a MSI is introduced from a three-dimensional general view of the water infiltration massive hydrophobic nanoporous pores. Next, a wide range of influence factors on the stiffness properties of MSI are studied. In addition, thefrequency response functions(FRFs) of the MSI vibration isolation system are studied utilizing the matching method based on equivalent piecewise linear (EPL) system. Finally, the vibration isolation properties of MSI are evaluated by force transmissibility.

Influence of tire cord layers and arrangement direction on mechanical properties and vibration isolation of chloroprene rubber composite materials reinforced with polyester tire cord

Abstract Polyester tire cord is often used as reinforcement in the production of chloroprene rubber (CR) composite materials. This study investigated the influences of polyester tire cord layers and arrangement directions on the mechanical properties and vibration isolation of CR composite materials. The experimental results indicate that the optimal molding condition for bonding tire cord with CR composites is 170°C for 30 min, which enables tire cord-reinforced CR composites to exhibit maximum pull-out strength. The compression set, tensile strength, and tear strength of CR composites increased with the increasing number of tire cord layers, and the stretching direction parallel to the arrangement direction of the tire cord produced optimal reinforcement effect. Moreover, the storage modulus of CR composites is better than that of pure CR at low temperature, although it reduced the tan delta at glass transition temperature. Regarding the vibration isolation properties, the transmissibility ratio decreased at resonance frequency, while the damping ratio increased when the CR is reinforced with increasing number of tire cord layers.

Early Fire Detection Technology in Manned Spacecraft

During the manned space missions, the crucial concerns of the spacecraft and the crew's safety require long-term reliable, real-time, and accurate smoke monitoring of the cabin atmosphere to provide onset warning of fire. However, the absence of the thermal buoyancy effects in the microgravity environment makes the smoke particle movement more random and thereby brings more difficulties to the smoke detection. The prior spacecraft smoke detectors include the UV-sensing fire detectors, the Brunswick Defense particle-ionization smoke detector, and the Allied Signal light-scattering smoke detector. The need of more reliable and accurate fire detection technology is strengthened by a number of reported incidents of false alarms and no alarms in space missions. In order to increase the reliability of detection and reduce the response time, a novel early fire detection system for space missions, integrating the laser scattering smoke detection technology with the near-infrared laser photoacoustic (PA) trace gas measurement technology, is presented in this article. Since PA sensor measures the acoustic pressure wave that is directly related to the absorbed energy by gas molecules and detected by second harmonic technology, it is immune to the background signal and easily achieves ppm level of detection limits. The concentration of carbon monoxide is very low at normal atmosphere, but dramatically increases in nearly all types of fire events, so it was selected as the target gas for the fire signature. The PA part consists of two distribute feedback lasers: the gas cell with particle filters, and the ultrasensitive acoustic measurement unit with mechanical vibration isolation frame. The smoke detector part consists of the laser diode as light source, the photodiode to sense forward scattered light (30 °), and the labyrinth obscuration cell. The sample gas of both parts is sucked from the cabin air through a micropump, which can keep the system response time less than 2 s, even in the microgravity environment. The experimental results of the prototype device show that the detection limit of carbon monoxide is 0.3 ppm and attenuation sensitivity of the smoke is 0.05%/m with satisfying the detection requirements for space missions. The device is designed to reliably operate 5 years on orbit. With a lightweight (1.5 kg) and low power consumption (2 W), the proposed system, combining the PA gas detection technology with the laser scattering smoke detection technique, is suitable for reliable early fire detection in spacecraft.

Detection and Mitigation of Electrostatic Pull-in Instability in MEMS Parallel Plate Actuators

Electrostatic MEMS actuators are used in a wide variety of applications including micro-machined gyroscopes, high speed mechanical switches, variable capacitors, and vibration isolation devices. MEMS parallel plate actuators (PPAs) are simple to realize, yet complex nonlinear variable capacitors. If a DC voltage is applied in attempt to move the proof mass greater than 1/3 of the electrode rest gap distance, the device becomes unstable and the electrodes snap into contact. Most research into this pull-in phenomena is devoted to extending the operational range of motion past the 1/3 instability point. This usually involves the addition of complex external electronics. Many applications, however, only require that the actuator remain out of the pull-in region, and do not require an extended stable range of motion. If detection of the pull-in event is all that is required, then simpler solutions can be realized, minimizing the requirements on the driving signal. Once pull-in is reached, the velocity of the movable plate increases rapidly until the plates make contact. The decreasing distance causes a proportional increase in capacitance. To maintain a constant voltage across the plates, an inrush of current must flow into the actuator in response to the increased capacitance. This paper presents a method for detecting the inrush current using a transimpedance amplifier circuit to convert the current to a measurable voltage. Once pull-in is detected, the PPA is electrically shutdown to prevent damage to the actuator or the voltage source, thus mitigating pull-in. A simulation of the expected results was performed using a Simulink model for the actuator structure predicting the expected range of inrush current. This result was then verified using a silicon micro-machined PPA connected to the detection/mitigation circuit on a PCB. The experimental results follow closely with the simulation allowing precise control in mitigating the pull-in event.

Electromechanical Analogy Design Theory of Spiral Flywheel Motion Transformation System

A mechanical vibration system with spiral flywheel motion transformation system has merits of lower total mass and better vibration performance. In order to promote its application and reduce integrated design complexity, the dynamical activity of the spiral flywheel is encapsulated with the dynamical analysis. According to traditional force-current electromechanical analogy theory, a novel capacitor component without parallel or grounding constraint is proposed to analogize the spiral flywheel. The component can not only solve the analogy problem for the spiral flywheel, but also perfect the traditional electromechanical analogy theory. The circuit network method is employed so that design steps for the mechanical vibration system based on the spiral flywheel analogy can be presented. In the light of the proposed design theory, the spiral flywheel is applied in a single DOF vibration isolation example for desired performance. Thereby a novel mechanical network and vibration isolation effect that cannot be realized by traditional vibration components are realized. The result shows the effectiveness of the method, which lays a theoretical foundation for integrated design of the spiral flywheel motion transformation system in the mechanical vibration system.

Analysis and Development of a Passive Mechanical Vibration Abatement Device for Traffic Monitoring Cameras

Departments of Transportation throughout the United States and elsewhere employ close-circuit television (CCTV) cameras for roadway monitoring as part of increasingly sophisticated traffic management systems. Cameras used for this purpose are attached to various highway structures and poles as high as 65 ft, all susceptible to wind- and ground-induced vibrations which adversely affect image quality. This paper describes the engineering analysis, development, and testing of a low-cost, biaxial mechanical vibration isolator specifically aimed at horizontal high-frequency motion abatement in pole-mounted camera applications and similarly conditioned supports. The device works on the principle of force and displacement transmissibility reduction via the use of a lightly damped sprung interface with a tuned natural frequency. The isolator is inserted between the top of the structure (pole) and the seat of the camera, and operates by rejecting undesirable high-frequency modal vibrations experienced by the main support; this has the effect of diminishing high-acceleration ground inputs which are principally responsible for image distortion. While favorable to high-frequency performance, the physics of this configuration prescribe the presence of a low-frequency displacement or pan of the sprung mass (albeit found to be free of blur in experiment). This characteristic is complementary to that of electronic image stabilization technology, whose performance suffers when significant motion is present in the incoming video feed. For this reason, the proposed mechanical solution is presented as an ancillary technique to image processing in installations where high frequency or displacement conditions prevail at the camera support.

Mechanical equipment and ambulances. Strange bedfellows of cardiovascular services.

A case study will be presented regarding vibration and noise control design for an existing heart hospital. Facility expansion within a crowded site necessitates sandwiching a suite of new cardiac catheterization laboratories between mechanical equipment rooms above and the hospital’s main ambulance driveway below. The facility expansion also includes cardiac computed tomography, magnetic resonance imaging, and nuclear imaging, plus cardiovascular care, treatment, and administrative support spaces. Procedure and support spaces can be disturbed by mechanical equipment noise and vibration and noise from ambulance siren. Cardiac procedure instruments and imaging can be disturbed by low frequency noise and vibration from building mechanical systems, ambulance traffic, and building occupants. Design criteria for permissible building vibration and continuous background noise will be presented along with relevant sources and bases. Measurement evaluation results for design will be contrasted with criteria. Measures incorporated in design to mitigate vibration and noise on catheterization laboratories will be discussed. Measures considered in design include structural floor “detuning” concepts, stiffened supports for catheterization laboratory C‐arms, mechanical equipment vibration isolation mounts, and floating concrete floor systems for mechanical rooms. If available, postconstruction spectral analysis measurements of building noise and vibration will be presented.

Anti‐vibration and vibration isolator performance of poly(styrene‐butadiene‐ styrene)/ester‐type polyurethane thermoplastic elastomers

AbstractThis investigation presents novel thermoplastic elastomers (TPEs) based on poly(styrene‐butadiene‐styrene) (SBS) and ester‐type polyurethane (TPU‐EX) materials were prepared with varying compositions. A series of investigations were conducted on the relationships between mechanical properties, dynamic mechanical properties, anti‐vibration and vibration isolator properties given, and the different compositions. The experimental results show incompatibilities between SBS and TPU‐EX. SBS mechanical properties, dynamic mechanical properties, anti‐vibration and vibration isolator properties are improved with an increase in the amount of TPU‐EX, suggesting that the blending of SBS with TPU‐EX was consistent with the compound rule. Based on the obtained results, the viscoelasticity of SBS materials, their capacity to isolate vibration, and their anti‐vibration performance can be adjusted by controlling the proportion of TPU‐EX. Copyright © 2009 John Wiley & Sons, Ltd.

Nanotechnology research facility‐ A vibration and noise control design case study

Vibration and noise control would be critical to the success of a proposed nanotechnology and molecular research facility. Roadway traffic, a nearby power generation plant and buildings in the vicinity were potential sources of ground borne vibration disturbances. Mechanical equipment, occupant installed support apparata and occupant activities were potential sources of internally generated vibration disturbances. On‐site ground borne vibration was measured for comparison with generic floor vibration criteria for sensitive installations. Results were analyzed relative to criteria for potential disturbance of sensitive equipment, perception by occupants, audible radiated structure borne noise in acoustically sensitive spaces and resolution‐degrading motion for scanning and for transmission electron microscopes and other nanotechnology clean room equipment. Design guidelines and structural vibration control concepts were recommended to the structural engineers, including de‐tuning, damping and isolation methods. Recommendations were provided for mechanical noise control and vibration isolation. Architectural noise control, sound isolation and room acoustics guidelines were provided for research, office and meeting spaces. This case study will discuss the desired vibration and noise control objectives and the design solutions that were implemented. Building photographs will be presented. Post‐construction measurement results will be graphically compared with pre‐construction conditions to demonstrate apparent degree of success in mitigating vibration.

Periodic behavior of a nonlinear third order vibrating system

A theorem is proved to show that the third order differential equation x ‴+ f( t, x, x ′, x ″)=0 has nontrivial solutions characterized by x ′(0)= x ′( τ)=0 when x, x ′, x ″ and f( t, x, x ′, x ″) are bounded. A second condition is introduced to prove the existence of periodic solution for this equation. It is shown that the equation has a τ-periodic solution if f( t, x, x ′, x ″) is an even function with respect to x ′. The existence and periodicity conditions would be applied to third order systems such as viscoelastic mechanical vibration isolator system. The concepts of Green’s function and the Schauder’s fixed-point theorem have been used for proving the third-order-existence theorem.

Analysis and minimization of power flow in a mechanical vibration isolation system using a hybrid (active/passive) approach

Implementation of active control techniques in mechanical vibration isolation systems has been a challenging problem for a number of years where numerous physical control laws have been explored. An energy-based approach to the problem involving the energy transfer or power flow through the mount into the base structure is a first-principles approach to developing control laws and evaluating the system performance. A lumped-parameter model of a passive–active hybrid isolation mount has been developed and validated with experimental data. The mount device has a conventional passive compliant spring, embedded force and velocity sensors, and a piezoceramic actuation layer. This study investigates a complete set of possible layer configurations, that is, the optimal placement of sensors and actuator relative to the passive compliant isolator element. A number of different local physical control laws are examined and the level of power flow through the mount is used to evaluate the performance for the matrix of possible implementations. These results will be discussed with particular emphasis placed on the optimal control configuration and laws, and the related physics. a)Also with SFA, Inc., Largo, MD 20774.

Low-phase noise temperature-compensated cryogenic whispering gallery mode resonator operated at 63 K in a closed-cycle cooler

We report further progress on whispering gallery (WG) modes in a miniature temperature compensated composite dielectric sapphire and rutile resonator operating in a closed cycle cooler which can exhibit loaded Q/sub L/ values above 10/sup 7/ at /spl sim/10 GHz. The geometrical size of the dielectric pucks has been increased so that a compact loop-oscillator system is realized at a frequency close to the Cs atomic clock hyperfine frequency and an operating temperature of 63.5 K. Excellent long term temperature control (stability is better than 100 /spl mu/K) has been achieved. The high Q of the dielectric resonators can be used to produce low phase noise oscillators limited only by the performance of amplifiers and mixers. Effective mechanical vibration isolation is also demonstrated in a Giffard-McMahon cooler.

Taber vibration isolator for vacuum and cryogenic applications

We present a procedure for the design and construction of a passive, multipole, mechanical high-stop vibration isolator. The isolator, consisting of a stack of metal disks connected by thin wires, attenuates frequencies in the kilohertz range, and is suited to both vacuum and cryogenic environments. We derive an approximate analytical model and compare its predictions for the frequencies of the normal modes to those of a finite element analysis. The analytical model is exact for the modes involving only motion along and rotation about the longitudinal axis, and it gives a good approximate description of the transverse modes. These results show that the high-frequency behavior of a multistage isolator is well characterized by the natural frequencies of a single stage. From the single-stage frequency formulas, we derive relationships among the various geometrical parameters of the isolator to guarantee equal attenuation in all degrees of freedom. We then derive expressions for the attenuation attainable with a given isolator length, and find that the most important limiting factor is the elastic limit of the spring wire material. For our application, which requires attenuations of 250 dB at 1 kHz, our model specifies a six-stage design using brass disks of approximately 2 cm in both radius and thickness, connected by 3 cm steel wires of diameters ranging from 25 to 75 μm. We describe the construction of this isolator in detail, and compare measurements of the natural frequencies of a single stage with calculations from the analytical model and the finite element package. For translations along and rotations about the longitudinal axes, all three results are in agreement to within 10% accuracy.

Antivibration and vibration isolation of ENR/CR blends

The dynamic mechanical properties, hysteresis behavior, antivibration, and vibration isolation of blends of epoxidized natural rubber (ENR) and Neoprene (CR) with various blending ratios, were investigated. The experimental results of ENR/CR blends show that the vibration isolation of ENR is better than that of CR, and the vibration isolation of ENR/CR blends increases with increasing ENR content. Based on the data of vibration transmissibility ratio, ENR has better vibration isolation and the CR has better antivibration. Thus, antivibration and vibration isolation are complemented for the ENR/CR blends. © 1998 John Wiley & Sons, Inc. Adv Polym Techn 17: 329–338, 1998

Application of Nonlinear Localization to the Optimization of a Vibration Isolation System

We consider a passive nonlinear mechanical vibration isolator consisting of discrete mass, stiffness, and damping elements. We show that, by suitably designing the stiffness nonlinearities, we can induce localized nonlinear normal modes (NNMs) in this system. These are unforced oscillations analogous to the normal modes of classical linear vibration theory, with energies that are spatially confined. When the isolator with localized NNMS is subjected to harmonic excitations in certain frequency ranges, the resulting resonances become similarly localized and the level of the transmitted undesirable vibrations is greatly reduced. Hence, nonlinear localization can provide a valuable tool for developing improved vibration and shock isolation designs, otherwise unattainable using linear theory. In addition, we develop a technique that systematically optimizes the localized NNMs of the unforced isolator, by localizing the vibrational energy in a way that is compatible to the vibration isolation objectives. This ensures minimal transfer of unwanted disturbances when a harmonic excitation is applied to the system.

Insertion loss studies of a mechanical vibration isolation system

Machinery noise control along the path can be classified into three approaches, namely, by enclosure, absorption, and vibration isolation. The transmissibility of a vibration isolation mounting is given by the ratio of transmitted force to foundation and the excitation force, whereas the insertion loss is obtained by the ratio of forces at the foundation without and with isolation mounting. The performance of a vibration isolation system is usually described using transmissibility which depends on the isolation system parameters with the machine considered as a rigid mass. However, the insertion loss of a vibration isolation system depends on the system parameters and source impedance, which accounts for the nonrigid characteristics of the machine. The nonrigidity of the machine can also be characterized through a base plate supporting the machine. This study deals with analysis of a system consisting of machine, isolation mounting, and rigid foundation in terms of insertion loss and transmissibility using a single degree of freedom model. Such studies would be useful in isolation mounting design for reducing machinery vibration and noise.

Multi‐layered polymer hydrophone array

A piezoelectric polymer (PVDF) hydrophone array consists of multiple layers disposed symmetrically about a stiffener layer. The stiffener layer prevents flexural modes in the operating frequency band and provides a mounting structure for acceleration noise cancellation. The piezoelectric polymer layers are attached to the stiffener layer either directly or through intervening layers which provide mechanical vibration isolation of the polymer and stiffener layers.