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International audience; Vibrations of a mechanical structure can be reduced through a piezoelectric coupling to a passive electrical network exhibiting similar modal properties. For the control of a plate, the design of a two-dimensional analogous electrical network is considered. Depending on the mechanical boundary conditions, a finite difference formulation of the Kirchhoff-Love equation of motion shows that we need to ensure specific electrical connections along the edges of the analogous network. A numerical model involving an assembly of element matrices validates the electrical topology. Then, the passive electrical circuit is implemented with capacitors, inductors and transformers, whose practical design is closely described. Focusing on the analogue of a clamped plate, experiments prove the ability of the proposed electrical network to approximate the behavior of the mechanical structure.

The small size of wearable devices limits the efficiency and scope of possible user interactions, as inputs are typically constrained to two dimensions: the touchscreen surface. We present SoundTrak, an active acoustic sensing technique that enables a user to interact with wearable devices in the surrounding 3D space by continuously tracking the finger position with high resolution. The user wears a ring with an embedded miniature speaker sending an acoustic signal at a specific frequency (e.g., 11 kHz), which is captured by an array of miniature, inexpensive microphones on the target wearable device. A novel algorithm is designed to localize the finger’s position in 3D space by extracting phase information from the received acoustic signals. We evaluated SoundTrak in a volume of space (20cm × 16cm × 11cm) around a smartwatch, and show an average accuracy of 1.3 cm. We report on results from a Fitts’ Law experiment with 10 participants as the evaluation of the real-time prototype. We also present a set of applications which are supported by this 3D input technique, and show the practical challenges that need to be addressed before widespread use.

FingerPing is a novel sensing technique that can recognize various fine-grained hand poses by analyzing acoustic resonance features. A surface-transducer mounted on a thumb ring injects acoustic chirps (20Hz to 6,000Hz) to the body. Four receivers distributed on the wrist and thumb collect the chirps. Different hand poses of the hand create distinct paths for the acoustic chirps to travel, creating unique frequency responses at the four receivers. We demonstrate how FingerPing can differentiate up to 22 hand poses, including the thumb touching each of the 12 phalanges on the hand as well as 10 American sign language poses. A user study with 16 participants showed that our system can recognize these two sets of poses with an accuracy of 93.77% and 95.64%, respectively. We discuss the opportunities and remaining challenges for the widespread use of this input technique.

The current technology push to connect everyday objects via the “internet of things” has fueled significant advances in low-power processing and communication devices. One aspect of these connected products that still needs attention is the means by which they are powered. An attractive and feasible option is the use of energy harvesting from acoustic fields. Previous work developing a piezoelectric energy harvesting device has generated 2.6 mW of power from a hydraulic test rig. This paper presents an implementation of an energy harvesting device connected to a communications system that allows it to store energy and communicate sensor readings via Bluetooth Low Energy.

Distributions of piezoelectric patches bonded to structures provide a means to alter or control, through active or passive means, the dynamic response of the host structure. Numerous active control schemes for such composite structures have been explored. Alternatively, for certain structures, a passive electrical network may be implemented which presents an electrical analog of the modal response of the structure, effectively providing a multi-modal, distributed passive tuned mass modal damper capability. Numerous tuned-mass damper design concepts (“tunings”) may be applied to such a passive network. Further, the distributed network analog, when coupled with active control concepts, permits a hybrid distributed passive-active modal control capability. This paper explores this hybrid distributed network control concept applied to a clamped rectangular plate. A unit-cell discrete representation of the plate leads to an electrical analog comprised of passive inductors, transformers and resistors. Addition of synthetic (or controlled) impedances at a limited set of points within the network permits dynamic adjustment of the frequency response of the system.

Energy harvesting from an acoustic field is challenging given the low energy density available in most acoustic phenomena. A notable exception is in the domain of pumped, pressurized fluids, where acoustic pressure amplitudes may be on the order of 5~10% of the mean static pressure, in some applications reaching mega-pascal amplitudes, corresponding to acoustic intensities advantageous for energy harvesting. However, the static pressures that are common within pressurized systems require mechanically robustness for pressure containment, which prevents the use of common energy harvester configurations. Nonetheless, energy densities may be high enough such that non-resonant configurations are feasible; and, the fact that the acoustic pressure within pumped systems typically has a relatively narrow band spectrum means that power conditioning circuits may be optimized for power conversion. With power available from the pumped fluid itself, through what is termed a Hydraulic Pressure Energy Harvester, it then becomes possible to implement self-powered wireless sensing nodes. This paper describes a proof-of-concept HPEH implementation and demonstration of a multi-functional self-powered wireless sensor for use in a hydraulic application.

This study addresses the effects of frequency and load resistance on energy harvesting using a mechanically excited ferroelectric rhombohedral to ferroelectric orthorhombic phase transformation in [011] cut Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN-PMN-PT) single crystals. The crystals were mechanically driven through the phase transformation, and voltage across a resistive load was measured. The effects of frequency and resistive load on the electrical energy generated were measured. Over the range of frequencies and load impedances tested, the crystals behaved as a charge source. The current increased linearly with frequency, and the voltage increased linearly with load impedance. Impedance matching to maximize the energy harvested is discussed. The energy harvested using the phase transformation was on average 27 times, with a peak of 108 times, the energy harvested using the same crystals operating in the linear piezoelectric regime under the same stress excitation amplitude.

Water hammer, a common problem in plumbing, is characterized by an impulsive increase in pressure. The pressure rise and associated momentum transfer may cause plumbing noise and vibration, and, potentially, catastrophic plumbing component failures. Water hammer arresters are required in building codes to be proximate to fast-acting valves, such as present in washing machines and other appliances. Commercially available water hammer arresters introduce compliance with a free-piston air spring as the means to limit the peak pressure during water hammer. Syntactic foam, comprising microspheres within a host polymer matrix, may be suitable for application in a water hammer arrester device. Foam-based arresters also enable flow-through designs, which may reduce other fluid-borne noise in addition to controlling water hammer. A prototype flow-through, in-line syntactic water hammer arrester device has been designed and tested. The flow-through design demonstrates adequate performance for service as a water hammer arrester, as well as significant insertion loss against fluid-borne noise.Water hammer, a common problem in plumbing, is characterized by an impulsive increase in pressure. The pressure rise and associated momentum transfer may cause plumbing noise and vibration, and, potentially, catastrophic plumbing component failures. Water hammer arresters are required in building codes to be proximate to fast-acting valves, such as present in washing machines and other appliances. Commercially available water hammer arresters introduce compliance with a free-piston air spring as the means to limit the peak pressure during water hammer. Syntactic foam, comprising microspheres within a host polymer matrix, may be suitable for application in a water hammer arrester device. Foam-based arresters also enable flow-through designs, which may reduce other fluid-borne noise in addition to controlling water hammer. A prototype flow-through, in-line syntactic water hammer arrester device has been designed and tested. The flow-through design demonstrates adequate performance for service as a water ham...

The control of vibrating structures using piezoelectric elements attached to simple control circuits, known as shunts, is a widely studied field. Many different shunt circuits have been researched that have been shown to obtain effective performance in both narrow and broadband frequency ranges. Yet, the choice for the exact parameters of the circuit elements for these vibration-suppressing shunts can be found by various methods. In this study, a new method of selecting the circuit parameters of a negative capacitance shunt is presented. The method predicts the magnitude of the strain-induced voltage caused by the vibrating substrate computed from a single voltage measurement. Therefore, minimizing the strain-induced voltage will mean that the deflection of the structure is also minimized. The tuning theory is confirmed experimentally, which validates that it is possible to experimentally obtain the shunt parameters that produce maximum control through measurement of the shunt response. The suppression ability of the shunt is also compared to the maximum power dissipated. It is found that at high frequency, the parameters that cause maximum power dissipated obtain maximum suppression, but there is no correlation between maximum power dissipated and maximum suppression at low frequency.

Hydraulic systems that operate over a broad range of load pressures pose challenges for suppression of fluid-borne noise. A common type of noise control device, a bladder-style suppressor, performs well only over a relatively narrow range of load or system pressures. This paper considers the problem of finding the optimal charge pressure(s) in either a single suppressor or two suppressors in series for maximum fluid-borne noise suppression in a weighted sense. The transmission loss, a measure of pressure ripple (dynamic pressure fluctuation) reduction, for the suppressors is predicted by an equivalent fluid model. The optimum configuration is sought through maximization of an objective function. The objective function is a summation of weighted transmission losses, where the weighting captures the duty cycle of the load pressure through a time weighting factor, and frequency weighting factor captures the spectral content of the pressure ripple. The duty-cycle weighting biases the objective functio...

Pressurized bladder style in-line hydraulic noise suppressors are commonly used in industry for broadband pressure ripple reduction, but predictive models for these suppressors are not available in the literature. To address this shortcoming, a linear acoustic model is developed for a commercially available suppressor, in which the acoustic field is analyzed through expansion into multiple radial modes. Bladder mass, perforate layer impedance, and inlet/outlet extensions are included in the model, and transmission loss predictions are validated against experimental data. The presented theoretical model has been shown to correspond well to experimental data at frequencies below about 1300 to 2300 Hz, depending on system and precharge pressures. In addition, simulations show that small variations in bladder precharge temperature or rubber bladder mass do not significantly affect transmission loss. While inclusion of the perforate layer significantly affects modeling results, it is observed that bett...

International audience; Multimodal passive damping of a mechanical structure can be implemented by a coupling to a secondary structure exhibiting similar modal properties. When considering a piezoelectric coupling, the secondary structure is an electrical network. A suitable topology for such a network can be obtained by a finite difference formulation of the mechanical equations, followed by a direct electromechanical analogy. This procedure is applied to the Kirchhoff-Love theory in order to find the electrical analogue of a clamped plate. The passive electrical network is implemented with inductors, transformers and the inherent capacitance of the piezoelectric patches. The electrical resonances are tuned to approach those of several mechanical modes simultaneously. This yields a broadband reduction of the plate vibrations through the array of interconnected piezoelectric patches. The robustness of the control strategy is evaluated by introducing perturbations in the mechanical or electrical designs. A non-optimal tuning is considered by way of a uniform variation of the network inductance. Then, the effect of local or boundary modifications of the electromechanical system is observed experimentally. In the end, the use of an analogous electrical network appears as an efficient and robust solution for the multimodal control of a plate.

International audience; A two-dimensional array of piezoelectric transducer (PZT) shunted on negative capacitance circuit is designed and applied to achieve broadband vibration reduction of a flexible plate over tunable frequency bands. Each surface-bonded patch is connected to a single independent negative capacitance synthetic circuit. A finite element-based design methodology is used to predict and optimize the attenuation properties of the smart structure. The predictions are then experimentally validated by measuring the harmonic response of the plate and evaluating some derived quantity such as the loss factor and the kinetic energy ratio. The validated model is finally used to explore different configurations with the aim of defining some useful design criteria. The results obtained clearly show how the proposed strategy represents a robust and effective solution for the control of vibrations in complex structures.

Noise is an ongoing concern in the fluid power industry. A great deal of research has been invested in reducing flow pulsations in hydraulic systems, from design modifications to adding noise control components. The physical principles of noise reduction are the same as for air, however, the much higher sound speed of hydraulic fluid makes creating compact noise control devices difficult. This paper introduces a Helmholtz resonator design that uses a compliant, voided urethane lining to increase the apparent volume of the device. The addition of the lining permits much smaller physical sizes for the same resonance frequency. Specifically, the design presented here has a total volume of 0.31 L and generates 20 dB of transmission loss at a resonance frequency of 37 Hz when the hydraulic system is pressurized at 2.07 MPa. At this pressure, it has a total volume that is two orders of magnitude smaller than a similar, unlined device of the same resonance frequency. Experimental data is presented that d...

This article proposes a new, simple, and efficient strategy, allowing one to optimize the diffusion operator between a passive beam coupled to a like beam equipped with a periodically distributed network of shunted piezoelectric patch actuators. A multimodal wave dispersion model is used to compute the diffusion operator and analyze the stability properties of the combined system. Based on this mathematical tool, specific optimization procedures are introduced to allow maximization or minimization of the wave transmissibility between the passive and the active distributed beam. A specific example is used to demonstrate the capability of the shunted piezoelectric system to induce total reflection through the total absorption of incoming propagating flexural waves while guaranteeing the stability, robustness, and realizability of such a system.

This article proposes a new, simple and efficient approach, allowing one to reduce and construct piezoelectric super elements guaranteeing an accurate representation of the electrical impedance without the need for static correction. This allows the electronic coupling to be fully addressed in the optimization of passive shunted piezoelectric transducers, energy harvesting piezoelectric systems or dense distributed transducers. The model obtained through this approach is also versatile, of small size, and is therefore quite tractable for use in intensive computation algorithms. Two example systems are used to demonstrate the numerical accuracy and convergence properties of the proposed approach.

A state-switched absorber (SSA) is a derivative of a classical tuned vibration absorber (TVA). An SSA is a mass-spring-damper system that is capable of instantaneously changing its stiffness, thus is capable of instantaneously changing its resonance frequency. Between instantaneous switch events, the absorber is a passive device, acting similarly to a classical TVA. When a switch event occurs, the SSA instantly changes its stiffness, effectively `retuning' its resonance frequency. At this point, the SSA remains tuned to this new frequency until the next switch event, where it changes frequencies again. Previous research has shown that applying a maximum work extraction switching rule to a two-stiffness-state absorber results in improved performance of the SSA over classical vibration absorbers. The article at hand investigates the two-state, maximum work extraction switching rule in more detail. Specifically, the explanation of how the switching rule reduces the vibration of the base to which it is attached is considered. The article also details the stability of such a switching rule.

High-frequency dither forces are often used to reduce unwanted vibration in frictional systems. This paper examines how the effectiveness of these dither-cancellation techniques is influenced by the type of periodic signal employed. The paper uses the method of averaging as well as numerical integration to study a single-degree-of-freedom (SDOF) system consisting of a mass in frictional contact with a translating surface. Recently, it was found that sinusoidal dither forces had the ability to stabilize or destabilize such a system, depending on the system and frictional characteristics as well as the amplitude and frequency of the dither signal [1]. This paper extends this analysis to general, periodic dither forces. In particular, the system response for sinusoidal dither waveforms is compared to that of triangular dither waveforms and square dither waveforms. It is found that, for a given amplitude and frequency of the dither signal, square waveforms are much more effective in canceling friction-induced oscillations than sinusoidal dither; likewise, sinusoidal waveforms are more effective than triangular waveforms for a given amplitude and frequency. A criterion is developed that relates the effectiveness of the waveform to the properties of the integral of the dither signal.Copyright © 2005 by ASME

An alternate approach to exciting a one-dimensional structure with discontinuities using a piezoelectric actuator is presented and examined. Instead of being bonded to the uniform side of a beam, the piezoelectric actuator is attached such that it spans two adjacent rib discontinuities. In this configuration, the actuator generates an eccentric actuation force on the structure and induces both axial and transverse motions. The goal of this work is to first model the axial and transverse response caused by the piezoelectric actuator. Then, the change in that response is examined for the case where an external disturbance force is present. The system is modeled by coupling the piezoelectric strain and structural dynamic response. The characteristics of the voltage-generated piezoelectric forces are discussed through numerical examples. The structural response found using the dynamic force–voltage model for the actuator is then compared to the response when the actuator model is approximated by its static or zero-frequency value. Furthermore, the ability of the actuator to potentially provide better control authority by using this alternate configuration is examined. The numerical study shows that when the actuator spans two discontinuities, there is potential for greater control authority than when that same actuator is placed on the uniform side of the structure.

The purpose of this work is to use magnetorheological elastomers (MREs) as field-dependent springs within three vibration absorber configurations, and to determine their vibration absorption characteristics. Magnetorheological elastomers are fabricated from silicone gel and iron microparticles, and implemented as tunable springs in three vibration absorber configurations, which excited the MREs in shear, squeeze mode, and compression. Each vibration absorber configuration exploits different magneto-mechanical properties, achieving very different results. The MRE iron concentration is varied to find the largest natural frequency shift for the squeeze-mode absorber due to an applied magnetic field. Absorbers with MREs containing 35% iron by volume exhibits the largest natural frequency shift, 507%. MREs containing 35% iron are placed into shear and longitudinal mode vibration absorber devices, which exhibit 470% and 180% frequency increases, respectively.

A state-switched absorber (SSA) is a device that is capable of switching between discrete stiffnesses; thus, it is able to instantaneously switch between resonance frequencies. The state-switched absorber is essentially a passive vibration absorber between switch events; however, at each switch event the SSA instantly “retunes” its natural frequency and maintains that frequency until the next switch event. This paper considers the optimization of the state-switched absorber applied to a continuous vibrating system and details the experimental validation of these simulation results. A simulated annealing optimization algorithm was utilized to optimize the state-switched absorber. For the most part, the SSA performed only marginally better than a classical tuned vibration absorber (TVA). However, for a select few cases considered, the SSA was able to reduce the kinetic energy of the plate to which it is attached by 12.9dB over that of a classical tuned vibration absorber. The optimal SSA location on a clamped square plate was near the center of the plate for the vast majority of the forcing cases considered. To experimentally validate the simulation, a SSA was fabricated by employing magnetorheological elastomers to achieve a stiffness change. For several two-force component excitations, several tuning configurations of the SSA were applied and the kinetic energy of the system was found and optimized. As with the majority of the optimization cases, the experiments showed the SSA outperforming the TVA by only 2dB. When comparing the observed results to those found via simulation, the simulations accurately predicted the performance of the SSA in the experiments.

This work examines how friction-induced oscillations in a traditional mass-on-a-moving-belt system are affected by high-frequency excitations, commonly referred to as dither signals. Two different friction laws are considered: a Stribeck friction law governed by a relationship that is cubic in the slip velocity, and an exponentially-based friction law that steadily decreases with slip velocity. Although in both cases the friction force has an initial negative slope versus relative velocity, their stability characteristics are quite different. In particular, it is shown that tangential dither can either stabilize or destabilize an initially stable system, depending on the nature of the friction law, and on other system and dither parameters. The behavior of the systems is studied through use of an averaging technique and through direct numerical simulation. The numerical study validates the stability predictions from the averaging method, and quantifies the partial-cancellation performance of tangential dither.

Syntactic foam, specifically a host urethane embedded with hollow microspheres, has been shown to be an effective method to treat pressure pulsations, also known as noise, within a hydraulic system; however, the current generation of foam becomes less effective with increasing system pressure, particularly ineffective above 7 MPa. Material modeling predicts that increasing the initial internal pressure of a microsphere will allow voids within the foam to retain their size at pressures up to 35 MPa and the foam will remain compliant at those pressures. Noise is attenuated by an expansion chamber lined with syntactic foam when the system pressure causes embedded microspheres to collapse, which leaves a gaseous void within the host urethane, greatly reducing the effective bulk modulus of the foam. Predicted material properties are then used in conjunction with a previously developed linear acoustic model to predict the effectiveness of developmental syntactic foams. Changing the mechanical properties of the current host urethane does not have a drastic impact on the overall performance unless the properties have been reduced to the approximate order as the properties of the void. The factors with the most consequence on noise control effectiveness are the internal pressure of the microspheres and system pressure.Copyright © 2015 by ASME

Hydraulic pressure energy harvesters (HPEH) are devices that convert the dynamic pressure within hydraulic systems into usable electrical power through axially loaded piezoelectric stacks excited off-resonance by the fluid. Within hydraulic systems, the dominant frequency is typically a harmonic of the pump operating frequency. The pressure fluctuations coupled with the piezoelectric stack can be amplified by creating a housing design that includes a Helmholtz resonator tuned to the dominant frequency of the fluid excitation. A Helmholtz resonator is an acoustic device that consists of a cavity coupled to a fluid medium via a neck, or in this case a port connection to the fluid flow, that acts as an amplifier when within the bandwidth of its resonance. The implementation of a piezoelectric stack within the HPEH allows for a Helmholtz resonator to be included within the fluidic environment despite the significantly higher than air static pressures typical of fluid hydraulic systems (on the order of one to tens of MPa). The resistive losses within the system, such as from energy harvesting and viscous losses, can also be used to increase the bandwidth of the resonance; thus increasing the utility of the device. This paper investigates the design, modeling, and performance of hydraulic pressure energy harvesters utilizing a Helmholtz resonator design.

The qualification of anechoic and hemianechoic chambers requires selection of signal type and acquisition bandwidth to be used. This work demonstrates that, while a broadband random source may be used, the signal at points removed from the source are not composed of random combinations of direct and reflected waves, except in the limit of infinite bandwidth. It is shown that chamber qualification may be represented as finding the ratio of two transfer functions, where one includes the reflected waves, and the other is the free-field transfer function between the source and receiver. Consideration of this approach leads to a generic representation for the deviation from free-field performance where bandwidth is demonstrated to suppress the dominant modulation contributions of reflections. It is demonstrated that pure-tone qualifications will always exhibit a higher deviation from free-field performance than a broadband qualification. Finally, it is shown that the use of an incoherent source model in method-of-images simulations for the broadband performance of anechoic chambers is fundamentally flawed.

Dither control is a method of introducing high-frequency control efforts into a system to suppress a lower-frequency disturbance. One application of dither control is the suppression of automotive brake squeal. Brake squeal is a problem that has plagued the automotive industry for years. Placing a piezoceramic stack actuator in the piston of a floating caliper brake creates an experimental normal dither system. Many theoretical models indicate a reduction in the braking torque due to the normal dither signal. Using a Hertzian contact stiffness model, the loss in friction is due to lowering the average normal force. There are also theories that the dither signal eliminates the “stick-slip” oscillation causing an effective decrease in the friction force. Yet another theory indicates that the effective contact area is reduced, lowering the mean coefficient of friction. A particular approach considering a single-degree-of-freedom friction oscillator predicts a maximum friction reduction of 10%, occurring at the primary resonance of the system. This paper will concentrate on validating this claim by experimentally determining braking torque reduction for a variety of dither control signals. Several dither control frequencies were chosen at system resonances, while others were chosen at frequencies most likely to provide control of the system. These frequencies were chosen based on previous squeal suppression research. The results indicate that dither control frequencies at system resonances have a greater impact on the braking system’s performance. In general, dither control reduces braking torque by no more than 2%.

Hydraulic Pressure Energy Harvesters (HPEHs) use the direct piezoelectric effect to extract electrical power from the dynamic pressure ripple present in hydraulic systems. As with other energy harvesters, an HPEH is intended to be an enabling technology for powering sensor nodes. To date, HPEH devices have been developed for high-pressure, high-dynamic pressure ripple systems. High-pressure applications are common in industrial hydraulics, where static pressures may be up to 35 MPa. Other fluid systems, such as cross-country pipelines as well as water distribution networks operate at much lower pressures, e.g., from around 1 to 4 MPa, with proportionally lower dynamic pressures. Single-crystal piezoelectric materials are incorporated into the HPEH design, along with means to increase the load transfer into the piezoelectric material as well as increased output harvester circuits, so as to increase the power output of these devices. The load transfer from the pressurized fluid into the piezoelectric material is through an interface, where the interface area may be designed such that the area exposed to the fluid is greater than the cross-sectional area of the piezoelectric, yielding higher stress in the material than the pressure in the fluid. Furthermore, given the relatively large capacitance of the piezoelectric elements used in HPEH devices, inductive-tuned resonant harvester circuits implemented with passive elements are feasible. HPEH devices integrating these features are shown to produce viable power outputs from low dynamic pressure systems.Copyright © 2014 by ASME

Significant interest has been generated by the possibilities of active vibration control through the implementation of state switching, with a specific implementation embodied through piezoceramic shunting. A state-switched absorber (SSA) is a vibration absorber that has the unique ability to change its resonant state amongst multiple distinct resonant states while in motion, thereby increasing the effective bandwidth over that of a single frequency device and thereby allowing control of multi-frequency, transient, and time-varying disturbances. In contrast, a switch-shunted damper (SSD) is a variant of an SSA that is used to increase the damping of the structure to which the damper is applied. Active vibration control applications discussed in the literature indicate the potential advantages of SSDs which employ piezoelectric ceramics as switchable springs with control algorithms that require switching states at points of non-zero strain. However, consideration of the constitutive equations for piezoelectric materials indicates a discontinuity in the electrical and mechanical conditions imposed by switching the stiffness at non-zero strains. A prototype SSD has been built and tested to experimentally investigate switching control logic and electrical and mechanical discontinuities at switching points; experimental measurements with this prototype SSD indicate that quarter-cycle switching algorithms which include switching states at a condition of maximum strain yield enhanced damping effectiveness but also leads to the generation of potentially undesirable mechanical transients.

A state-switched device is conceptually capable of instantaneously changing its mass, stiffness, or damping. Such a device will exhibit different dynamical response properties (modes and resonance frequencies) depending on its current state. A state-switched vibration absorber exploits the state-switching concept for the purposes of enhanced vibration suppression. Between each state switch, it is fundamentally a passive vibration absorber, but one which exhibits a different tuning frequency for each possible state. A state-switched vibration absorber therefore has a greater effective bandwidth than a classical passive absorber. This paper considers the role of damping in the state-switching concept for a simple one-degree of freedom system and for a two-degree of freedom system. Certain values of damping in the system improve performance, while other values hinder the performance of the state-switched absorber, as compared to classical absorbers. The predicted performance of the system also depends upon the particular damping model used, such as viscous absorber or system modal damping. Damping values also affect the frequency of switch events that occur during the response of the system. In general, the highest relative performance of the state-switched absorber as compared to a classical vibration absorber occurs at low values of damping.

An optimization program based on M. J. Box's Complex Method was implemented in a computational design tool for constrained optimization of acoustic environments produced by vibrating structures. The tool can treat interior and exterior environments, and can consider acoustic and structural excitations. The tool integrates finite element and boundary element methods to perform the requisite structural acoustic analyses. The new optimization component described in this paper contains unique additions to Box's original algorithm. The optimizer executes stand-alone, or can be used as a starting point generator for another optimizer, thus creating a hybrid algorithm. This paper describes the new optimizer's algorithm and the results of an example optimization to reduce the interior noise levels within an unstiffened cylindrical shell. Design variables were selected as the shell thicknesses, subject to upper and lower bounds. All analyses were performed at a single excitation frequency. The results demonstrate effective performance of the optimizer, and the potential to obtain significant noise level reductions though the use of other-than-uniform thickness distributions.

Qualification of anechoic chambers is intended to demonstrate that the chamber supports the intended free-field environment within some permissible tolerance bounds. Key qualification issues include the method used to obtain traverse data, the analysis method for the data, and the use of pure tone or broadband noise as the chamber excitation signal. This paper evaluates the relative merits of continuous versus discrete traverses, of fixed versus optimal reference analysis of the traverse data, and of the use of pure tone versus broadband signals. The current practice of using widely space discrete sampling along a traverse is shown to inadequately sample the complexity of the sound field extant with pure tone traverses, but is suitable for broadband traverses. Continuous traverses, with spatial resolution on the order of 15% of the wavelength at the frequency of interest, are shown to be necessary to fully resolve the spatial complexity of pure tone qualifications. The use of an optimal reference method for computing the deviations from inverse square law is shown to significantly improve the apparent performance of the chamber for pure tone qualifications. Finally, the use of broadband noise as the test signal, as compared to pure tone traverses over the same span, is demonstrated to be a marginal indicator of chamber performance.

This paper presents a screening technique to assess the impact on model fidelity introduced by variations in the properties or positions of features in harmonically forced fluid-loaded structural acoustic models. The perspective taken is one of knowledge of a reference state, with a desire to determine the impact on the total radiated acoustic power due to perturbations in the reference state. Such perturbations change the predicted resonance frequencies of a structure under consideration, and hence, change the predicted response amplitudes. The method uses a single degree of freedom response model in the local region of each fluid-loaded resonance, coupled with eigenvalue sensitivities or variations, to estimate the perturbation impact. The perturbation is scaled by the degree to which each given mode participates in the response quantity of interest. The SDOF model yields results that indicate that proportional bandwidth analysis will be less sensitive to perturbation than constant bandwidth analysis. This is demonstrated through comparison of a constant bandwidth analysis and a 1/3 octave analysis applied to the same system. Elements of the analysis method are not necessarily restricted to model perturbations nor acoustic power, rather they may be used to assess the perturbation of any quadratic response quantity of interest due to changes in resonance frequency.

A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. State-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously ‘retuning’ the state-switched absorber to a new frequency. In between state switches, the operation of such a device is passive, being fundamentally a passive vibration absorber. This concept has improved performance over classical passive vibration absorbers or dampers, particularly for disturbances with multiple spectral components. This paper considers the application of such a device for the purpose of vibration control on beams subjected to harmonic point-force excitation.

This paper presents an experimental investigation into the application of “dither” control for the active control and suppression of automobile disc brake squeal. Dither control is characterized by the application of a control effort at a frequency higher than the disturbance to be controlled. In the particular system considered here, a vibro-acoustic analysis of a disc brake system during squeal determined the acoustic squeal signature to be emanating from the brake rotor. This squeal was eliminated, and could even be prevented from occurring, through the application of a harmonic force with a frequency higher than the squeal frequency. The harmonic force was generated by a stack of piezoelectric elements placed within the brake's caliper piston. The harmonic force represented a small variation about the mean clamping force exerted by the brake upon the rotor. The high-frequency vibration in the brake system due to the action of the control system was not heard if an ultrasonic control frequency was used. More importantly, the active control system is shown to be able to prevent squeal from even occurring. This gives rise to a possible active control system integrated into the brake system of automobiles to prevent squeal.

Having been lured away from Exxon to pursue a Ph.D. by Gary Koopmann, I had no idea during a 1989 visit to the TU in Berlin, with the Berlin Wall still a looming presence, that he was laying the ground work with Herr Dr. Prof. Manfred Heckl of the Institute of Technical Acoustics to host me should I receive the Hunt. When I arrived in July 1990, the wall had fallen, and great changes were underway. The year passed all too quickly, with Pink Floyd at “The Wall,” technical visits to Dresden, Gottingen, and ISVR, and more. The work I did in that year remains some of my highest cited work. Having already accepted a faculty position at Georgia Tech made the year much less stressful. The connections and colleagues I made at the TU remained throughout my career. At GT I explored a number of areas triggered by my Hunt year, including structural acoustic optimization, acoustic mode representation for exterior fields, and active structural acoustic control which led to a sabbatical year, with results akin to my Hun...

Fluid power hydraulic systems, common on a wide variety of industrial and construction equipment, frequently exhibit undesirable noise characteristics. The noise is primarily due to the pump-induced pressure pulsation in the fluid. One means to control this fluid-borne noise is through the use of a suppressor integrating compliance, as may be introduced using a pressurized bladder, or an elastic compliant liner exposed to the fluid. This compliance causes an impedance change at the inlet to the suppressor. Within the suppressor, the compliance leads to a reduced sound speed, which may then lead to fluid particle velocities high enough for damping to become effective. Classical dissipative noise control means, as is common in air or gas mufflers, is otherwise ineffective in fluid systems because of the low particle velocity. An engineered solid material, a syntactic foam, is under development for use in hydraulic systems. The syntactic foam of interest is comprised of microspheres dispersed in a polymer. P...

Negative capacitance shunt damping is an effective broadband method for attenuating flexural vibration. However, proper selection of the location of the piezoelectric patches on a structure to maximize reduction has been an ongoing question in the field. Acoustic black holes are a recently developed concept to reduce vibrations on thin vibrating structures. By engineering the geometric or material properties of these thin structures, it is possible to minimize the reflected wave by gradually reducing the wave speed. However, the flexural wave speed cannot be reduced to zero on a realized structure. Therefore, when acoustic black holes are implemented, some of the incident wave energy is reflected because the wave speed must be truncated. Similarly due to the reduction in wave speed, the transverse velocity significantly increases within the acoustic black hole. It is therefore possible to add piezoelectric transducers to acoustic black hole regions on a structure to utilize negative capacitance shunt damping to address both of these issues. Consequently, the transducers are placed in the locations where the greatest control can be made and the reflected waves can be attenuated. The combination of negative capacitance shunt damping with acoustic black holes shows increased suppression of vibration over shunt damping alone.

The use of personal protective clothing that covers the head is a common practice in many industries. Such personal protective clothing will impact the sound pressure level and the frequency content of sounds to which the wearer will be exposed. The use of such clothing, then, may impact speech and alarm audibility. A measure of the impact of such clothing is its insertion loss. Insertion loss measurements were performed on four types of personal protective clothing which utilize cloth and plastic hood configurations to protect the head. All clothing configurations tested at least partially cover the ears. The measurements revealed that insertion loss of the items tested was notable at frequencies above 1000 Hz only and was a function of material stiffness and acoustic flanking paths to the ear. Further, an estimate of the clothing's noise reduction rating reveals poor performance in that regard, even though the insertion loss of the test articles was significant at frequencies at and above 1000 Hz.

This paper presents the development and application of the Surface Variational Principle (SVP) for the evaluation of axisymmetric interior acoustic domains. The interior form of the SVP is first developed in the same manner as the existing exterior form. Then, the surface pressure and normal velocity are represented with a Ritz expansion using basis functions that span the entire wetted surface of the object of interest. The resultant formulation is used to analyze the interior acoustic response of a harmonically forced, right circular elastic cylinder. This validation model was chosen as both the structural and acoustic responses can be solved analytically. Results are presented for two models: one with a length to radius ratio of 2.4, and another with a ratio of 12.3. The SVP is shown to well reproduce the analytical solution for this geometry, and displays the asymptotic convergence expected of its variational formulation. The SVP formulation developed here is not restricted to right-circular cylindrical geometries, and may, indeed, be readily applied to any axisymmetric body.

Changes in the vibro-acoustic response of a fluid-loaded plate due to variations in some of the modeling details associated with an attached substructure are examined. The attached substructure consists of a smaller plate supported by springs along each edge. To examine the important modeling issues, three studies are performed. In the first study, discrete changes in the system response due to discrete changes in the size of the region over which the spring elasticity is distributed are examined. In the second study, substructure modeling issues are examined by varying the number of degrees-of-freedom included in the substructure model. Finally, sensitivity relationships that express changes in the system response to changes in the scale of the spring elements are developed. These relationships are used to examine changes in the system response due to small variations in the scale of the distributed elasticity. Both the combined system response and acoustic radiation are computed using the Acoustic Surface Variational Principle and Hamilton's Principle. For the example cases considered, it is shown that details associated with the scale of the spring are only important for frequencies near or below the resonances of the isolated subsystem. Furthermore, only the dynamics of the substructure including rigid-body type motions are important.

The use of a modal representation for the exterior acoustic field of a structure has received increasing attention in recent years. This modal approach generally seeks a set of orthogonal functions, representing independent surface velocity distributions, termed acoustic radiation modes, which diagonalize a radiation operator in the exterior domain of the structure. These orthogonal acoustic radiation modes may be found, among other methods, through an eigenvalue analysis of a radiation operator and possess a corresponding set of eigenvalues that are proportional to the radiation efficiencies of the acoustic radiation modes. In free space, the acoustic radiation modes of a sphere display a grouping characteristic in their radiation efficiencies, where each acoustic radiation mode’s radiation efficiency within a group has the same frequency dependency. This is a consequence of the fact that the acoustic radiation modes of a sphere are the spherical harmonics. Further, the acoustic radiation modes of an arbitrary three-dimensional structure exhibit the same frequency grouping as those for the sphere. The basis for the arbitrary structure’s grouping follows from the sphere’s grouping. The observation that the acoustic radiation modes of an arbitrary body are dominated by spherical harmonics provides insight on the behavior of such modes. These results have significance for various applications of acoustic radiation modes, including active noise control design, radiation modeling, etc.

A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. For example, state-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously “retuning” the state-switched absorber to a new frequency. This paper briefly develops the fundamental analysis tools for a Single-Degree-of-Freedom state-switchable device, and then considers the application of such a device for the purpose of vibration control in a 2-DOF system. Simulation results indicate that state-switched vibration absorbers may be advantageous over classical passive tuned vibration absorbers under certain conditions.

Results of a research program to develop computational methods to minimize noise transmission into aircraft fuselage interiors are discussed. A design tool to perform a constrained optimization of the acoustic environment within a vibrating structure is developed utilizing e nite element methods and boundary element methods (FEM/BEM), and its application to aircraft cabin noise problems is studied. The results of a study to optimize the cross section shapes of frames and stringers of an idealized aircraftlike stiffened cylinder are reviewed. The structure is optimized for minimum noise at specie ed points in the interior, as a result of a single frequency (tonal) exterior acoustic disturbance. For the cylinder and excitation frequency studied, it has been found that spatially varying the stiffener sizes over the cylinder is more important than optimizing the shape of the cross sections. Because FEM/BEM methods are only reliable for lower frequencies, the problems studied are applicable to low-frequency tonal noise such as seen in turboprop aircraft.

This paper presents a technique to assess the impact on model fidelity introduced through discretization of attachments on harmonically forced fluid-loaded structural acoustic models. While fluid loading is included, it is not a requirement or restriction to the methods presented. The perspective taken is one of knowledge of a reference state, with a desire to determine the impact on the total radiated acoustic power due to perturbations in the reference state. Such perturbations change the predicted resonance frequencies of a structure under consideration and, hence, change the predicted response amplitudes. The method uses a single degree of freedom response model in the local region of each fluid-loaded resonance, coupled with eigenvalue sensitivities, to estimate the perturbation impact. The sensitivity of the eigenvalues to changes in model detail is derived based on variations in the spatial representation of attached features (e.g., point versus distributed attachments). Elements of the analysis me...