Dominik Niederberger

Adaptive multi-mode resonant piezoelectric shunt damping

Multiple-modes of structural vibration can be suppressed through the connection of an electrical impedance to the terminals of a bonded piezoelectric transducer. The so-called resonant shunts, one commonly used class of shunt impedances, provide good nominal damping performance but they are highly sensitive to variations in transducer capacitance and structural resonance frequencies. This paper introduces a new technique for the online adaptation of multi-mode resonant shunts. By minimizing the relative phase difference between a vibration reference signal and the shunt current, circuit component values can be optimally tuned online. Experiments on a cantilever beam validate the proposed technique and demonstrate the simplicity of implementation. The adaptive law converges quickly and maintains optimal performance in the presence of environmental uncertainties.

An autonomous shunt circuit for vibration damping

This paper describes the implementation of an autonomous switching resistor–inductor (R–L) shunt circuit for the control of structure vibration. The resulting switch shunt circuit, compared to present shunt circuit techniques, does not require a power for its operation and is almost as effective. Moreover, experiments show that the damping performance is robust against temperature variations due to environmental conditions, whereas present shunt circuits lose their damping performance. The proposed autonomous switching R–L shunt circuit requires a small number of electronic components, therefore making it a viable and effective solution for the control of structural vibration.

Control of Resonant Acoustic Sound Fields by Electrical Shunting of a Loudspeaker

Low-frequency reverberant sound fields are usually suppressed by means of either adaptive feedforward control or Helmholtz resonator. Feedforward systems utilize a noise reference signal, error microphone, and loudspeaker to cancel sound propagating in one direction. Due to the requirement for multiple transducers and a powerful digital signal processor, feedforward systems are the most complex and expensive option for acoustic noise reduction. Helmholtz resonators, comprising auxiliary coupled acoustic chambers, are a popular passive technique for the control of dominant acoustic modes. Although lightly damped acoustic modes can be heavily attenuated, the resonators are difficult to tune and require unpractically large cavity volumes at frequencies below 200 Hz. This paper introduces a new technique for the control of low-frequency reverberant sound fields. By connecting an electrical impedance to the terminals of an acoustic loudspeaker, the mechanical dynamics, and hence, acoustic response can be made to emulate a sealed acoustic resonator. No microphone or velocity measurement is required. In some cases, the required electrical circuit is simply the parallel connection of a capacitor and resistor. With the addition of a single pressure microphone, a technique for online circuit adaptation is proposed. Experimental application to a closed acoustic duct results in 14-dB pressure attenuation of a single acoustic mode. Active impedances can be designed by viewing the system model from a feedback control perspective. The resulting electrical impedances, although not passive, are experimentally shown to attenuate four acoustic modes by up to 10 dB.

Structural Vibration Control via R-L Shunted Active Fiber Composites

This article presents a successful extension of passive R-L shunt damping to piezoelectric ceramic elements working in direct 3-3 mode and a performance comparison to elements working in indirect 3-1 mode. A new circuit topology is implemented to synthesize the very large inductances required by the low inherent piezoelectric device capacitance at relatively low frequencies. This allows for efficient tuning of the R-L circuit to the structure resonance frequency to be damped. The vibration suppression performance of monolithic piezoelectric ceramic actuators and active fiber composites is compared in this study. For this purpose, different actuators are bonded on aluminum cantilever plates. An integrated FE model is implemented for the prediction of structure resonance frequencies, optimum values for electric components, and the resulting vibration suppression performance. The passive structure, bonded active patch, and shunted electrical network are analyzed within the same FE model. Active fiber composite patches working in the direct 3-3 mode show equivalent specific damping performance compared to conventional monolithic 3-1 actuated patches. Issues related to the sensitivity of R-L shunts to variations in environmental and operational conditions are discussed in this study. In short, monolithic actuators operating on the 3-1 piezoelectric effect seem to be the best for use in R-L shunting.

Adaptive electromagnetic shunt damping

This paper presents a new type of passive vibration control: adaptive electromagnetic shunt damping. We propose a single-mode resonant shunt controller that adapts to environmental conditions using two different adaptation strategies. The first technique is based on minimizing the root mean square (RMS) vibration, while the second minimizes the phase difference between two measurable signals. An experimental comparison shows that relative phase adaptation performs better than the RMS technique.

Adaptive resonant shunted piezoelectric devices for vibration suppression

This paper presents a new adaptation technique for R-L shunted piezoelectric patches (PZT) bonded on mechanical structures for single mode vibration suppression. For the implementation of the adaptive R-L shunt circuit, a new variable inductor circuit controlled by transistors is developed. Additionally, a new modeling method for shunted PZTs based on equivalent transformer and gyrator circuits is presented. This leads to a comprehensive model that simplifies the search for optimal shunt circuits. Furthermore, it allows simulating the system consisting of the structure, the PZT patch and a complex transistor or other non-linear shunts on standard electronic simulators like PSpice or Saber. Damping performance of R-L shunted piezoelectric devices is very sensitive to environmental factors changing the circuit’s resonance frequency corresponding to the damped vibration mode. This requires fast adaptive tuning of the R-L shunted circuit, which is implemented using a new adaptation technique. The tuning direction of this adaptation law is obtained by detecting the phase shift between the velocity of the mechanical structure and the current in the shunt circuit. As the exact value of the phase for this technique is not required, one can reduce the adaptation problem to multiplication and integration of current and velocity. The performance of the presented new adaptive R-L shunt is compared with the common adaptation law based on minimizing the RMS value of the strain and then experimentally verified. The adaptive R-L shunt, which minimizes the phase-shift, can tune to the optimal parameters within seconds, but it needs an additional velocity sensor. In contrast, the R-L shunt minimizing the RMS value works without extra sensors, but needs some minutes to tune optimally. The new adaptive R-L shunt circuit can be implemented in small analog electronic chips that allows integrating it in smart materials.

Design of optimal autonomous switching circuits to suppress mechanical vibration

This paper demonstrates the use of a hybrid system approach to design optimal controllers for smart damping materials. Recently, controllers have been used to switch piezoelectric materials for mechanical vibration suppression. These controllers allow a small implementation and require little or no power. However, the control laws to switch these circuits are derived heuristically and it remains unclear, if better control laws exist. We present a new control approach based on a hybrid system framework. This allows to derive optimal switching laws by solving a receding horizon optimal control problem with multi-parametric programming. Additionally, we show how to implement the optimal switching laws with analog electronic circuitry such that the resulting damping circuits do not require power for operation. Simulations show the improvement of the damping compared with heuristically derived circuits and experiments demonstrate that the autonomous damping circuits can suppress vibration without requiring additional power.

A new control approach for switching shunt damping

This paper presents a new control approach for piezoelectric switching shunt damping. Recently, semi-active controllers have been used to switch piezoelectric materials in order to damp vibration. These switching shunt circuits allow a small implementation and require only little power supply. However, the control laws to switch these shunts are derived heuristically and therefore it remains unclear, if a better control law for a given shunt topology exists. We present a new control approach based on the Hybrid System Framework. This allows the modelling of the switched composite system as a hybrid system. Once the hybrid system description is obtained, a receding horizon optimal control problem can be solved in order to get the optimal switching sequence. As the computation time to solve this optimisation problem is too long for real-time applications, we will show that the problem can be solved off-line and the solution stored in a look-up table. This allows a real-time implementation of the switch controller. Moreover, control rules can be derived from this look-up table, and we will demonstrate that in some situations the controllers proposed in previous papers generate near optimal switching. In this paper, we will investigate several shunt topologies with switches and compare the performance between the heuristically derived control laws and the optimal new control laws. Simulations and experiments show the improvement with the new controllers. This is very promising, since this new control approach can be applied for more complex shunt circuits with many switches, where the derivation of a switching law would be very difficult.

Vibration control via shunted embedded piezoelectric fibers

The scientific community has put significant efforts into the manufacturing of sensors and actuators made of piezoceramic fibers with interdigitated electrodes. These allow for increased conformability, integrability in laminate structures and offer high coupling factors. They are of particular interest for damping applications. This paper presents a comparison between piezoceramic monolithic actuators and Active Fiber Composites (AFCs) for shunt damping. For this purpose, the different actuators were bonded on aluminum cantilever plates, respectively embedded in a glass fiber composite cantilever plate. The vibration suppression was attained by converting the electric charge by means of the converse piezoelectric effect and dissipated through robust resonant shunt circuits. A new circuit topology was used, which enables efficient damping even with low piezoelectric capacitance. An integrated FE model was implemented for prediction of the natural frequencies, the optimum values for the electric components and the resulting damping performance. Patches working in the direct 3-3 mode show much better specific damping performance than the 3-1 actuated patch. The comparison between monolithic and AFC actuators shows that AFCs fulfill integrability and performance requirements for the planned damping applications.

Online-Tuned Multi-Mode Resonant Piezoelectric Shunt for Broadband Vibration Suppression

Abstract Broadband structural vibration can be suppressed through the connection of an electrical impedance to the terminals of a bonded piezoelectric transducer. This is referred to as piezoelectric shunt damping. Good nominal damping performance has been obtained with resonant shunts, but these shunts are highly sensitive to variations in structural resonance frequencies. In this paper, we present an online tuned multi-mode resonant shunt controller. For optimal tuning, the parameters of this shunt are adjusted online by minimizing the relative phase difference between a vibration reference signal and the shunt current. Experiments validate the proposed technique and demonstrate the simplicity of implementation. The tuning law converges quickly and maintains optimal performance in the presence of environmental uncertainties.