Smart double panel with decentralised active dampers for control of sound transmission

This report presents the results of a theoretical study of active sound transmission control through a double panel. The double panel material and geometrical properties have been chosen so as to emulate section of an aircraft fuselage, or bodywork of a vehicle. It consists of two plates: an aluminium plate simply supported along all the edges and a honeycomb plate with all the edges free. The two plates, having the same length and width, are connected using elastic mounts, so that a double panel with a thin rectangular cavity between the plates is formed. Since the two plates are linked by the mounting system, and since the air is confined in the cavity between them, they form a structurally and acoustically coupled system. The sound transmission properties of the system are studied in such a way that the aluminium plate (“source panel”) is excited using a plane acoustic wave, while the honeycomb plate (“radiating panel”) radiates sound into free field.The aim of the active control is to reduce the sound transmitted in a broad frequency band, but with a particular focus on the reduction of the sound transmission at lower frequencies of the band. Decentralised velocity feedback control systems (applying active damping) are implemented, with purpose of reducing sound transmission at resonance frequencies. Control sensors and actuators are embedded into the double plate system as a regular array, so that a smart double panel is created. The theoretical study includes analysis of the passive sound transmission in terms of a parametric study, implementation of the active control using skyhook velocity sensors and skyhook force actuators, and the performance/stability analysis in case when reactive actuators and skyhook velocity sensors are used. In the latter case the actuating force is obtained using actuators located in the air cavity which can react off the two plate

Comparison of smart panels for tonal and broadband vibration and sound transmission active control

This paper presents a comprehensive overview of the principal features of smart panels equipped with feed-forward and feedback systems for the control of the flexural response and sound transmission due respectively to tonal and to stochastic broadband disturbances. The smart panels are equipped with two types of actuators: first, distributed piezoelectric actuators formed either by small piezoelectric patches or large piezoelectric films bonded on the panels and second, point actuators formed by proof-mass electromagnetic transducers. Also, the panels encompass three types of sensors: first, small capacitive microphone sensors placed in front of the panels; second, distributed piezoelectric sensors formed by large piezoelectric films bonded on the panels and third point sensors formed by miniaturized accelerometers. The proposed systems implement both single-channel and multi-channel feed-forward and feedback control architectures. The study shows that, the vibration and sound radiation control performance of both feed-forward and feedback systems critically depends on the sensor-actuator configurations

Sweeping piezoelectric patch vibration absorbers

This paper presents a simulation study concerning the low-mid frequencies control of flexural vibration in a lightly damped thin plate, equipped with five time-varying shunted vibration absorbers. The panel is excited by a rain-on-the-roof broad frequency band stationary disturbance. The absorbers are composed of piezoelectric patches connected to time-varying RL shunt circuits. Continuous, sweeping, variations over time of the shunts are implemented in such a way as to swing the resonance frequency and damping factor of the absorbers within certain ranges and in this way to reduce the resonant response of multiple flexural modes of the hosting plate. A single patch absorber implementing the sweeping shunt is first presented and its performance is compared to that of a classical patch absorber with time-invariant RL shunt. The same analysis is conducted for a multiple patch system using five shunted absorbers. The control performance is assessed considering the spectrum of the total flexural kinetic energy of the system in the 20 Hz to 1000 Hz frequency band. The study shows that the configuration with five time-varying shunted piezoelectric patches reduces the resonance peaks of the kinetic energy spectrum by 5 to 15 dB

Flywheel proof mass actuator for active vibration control

This paper presents the experimental results of a new proof mass actuator for the implementation of velocity feedback control loops to reduce the flexural vibration of a thin plate structure. Classical proof mass actuators are formed by coil–magnet linear motors. These actuators can generate constant force at frequencies above the fundamental resonance frequency of the spring–magnet system, which can be used to efficiently implement point velocity feedback control loops. However, the dynamics of the spring–magnet system limit the stability and control performance of the loops when the actuators are exposed to shocks. The proof mass actuator investigated in this paper includes an additional flywheel element that improves the stability of the velocity feedback loop both by increasing the feedback gain margin and by reducing the fundamental resonance frequency of the actuator. This paper is focused on the stability and control performance of decentralized velocity feedback control loops

Self-Assembled Nanometer-Scale Magnetic Networks on Surfaces: Fundamental Interactions and Functional Properties

Nanomagnets of controlled size, organized into regular patterns open new perspectives in the fields of nanoelectronics, spintronics, and quantum computation. Self-assembling processes on various types of substrates allow designing fine-structured architectures and tuning of their magnetic properties. Here, starting from a description of fundamental magnetic interactions at the nanoscale, we review recent experimental approaches to fabricate zero-, one-, and two-dimensional magnetic particle arrays with dimensions reduced to the atomic limit and unprecedented areal density. We describe systems composed of individual magnetic atoms, metal-organic networks, metal wires, and bimetallic particles, as well as strategies to control their magnetic moment, anisotropy, and temperature-dependent magnetic behavior. The investigation of self-assembled subnanometer magnetic particles leads to significant progress in the design of fundamental and functional aspects, mutual interactions among the magnetic units, and their coupling with the environment

Optimisation of a velocity feedback controller to minimise kinetic energy and maximise power dissipation

In this study the active vibration control of a structure modelled as a single degree of freedom system and excited by a white noise force is considered. The control system consists of an inertial actuator driven with a signal proportional to the velocity of the structure under control measured by an ideal collocated sensor. The optimisation of the physical and control parameters of the control system such as the internal damping of the actuator, its natural frequency and the feedback gain of the controller are considered such that either the kinetic energy of the host structure is minimised or the power dissipated by the control system is maximised. This type of control system is only conditionally stable therefore a stability condition has to be satisfied by the optimisation process. The paper shows that the two optimisation criteria are equivalent.<br/

Sensor-actuator transducers for smart panels

During the past fifteen years there has been a lot of research work on active control of sound radiation by smart structures with both embedded structural actuators and sensors. The main principles of this new approach have been investigated and are now well established. Both feed–forward and feedback control schemes have been studied. Feed–forward control is particularly suited to the control of tonal disturbances for which a reference signal is available. In this case the structural actuators are driven in such a way as to rearrange the vibration of the panel so that the total sound radiation detected via the structural actuators is minimised. Normally single channel systems are used with distributed sensor–actuator pairs designed to control the most efficient radiating mode of the structure. This approach is known as Active Acoustic Structural Control (ASAC). Feedback control is instead advantageous for the control of steady state broad band disturbances. Its implementation relies heavily on the collocation and duality of the sensor–actuator transducers in which case the feedback control system is bound to be unconditionally stable. In principle, the most advantageous approach is to implement single channel feedback ASAC systems, although some fundamental problems related to stability have been highlighted when distributed sensor–actuator pairs are used. However recent work has shown that excellent control results can also be obtained with arrays of decentralised feedback control systems using point actuators and sensors. In this case the control system is driven to implement Active Vibration Control (AVC) only which however can be set to minimise both the vibration and sound radiation by the structure. Although the main principles of both ASAC and AVC approaches for the control of sound radiation by smart structures have been pinned down, there is still a lot of research work in progress on the sensor–actuator transducers. In this paper the main features of both strain and inertial sensor and actuator transducers are discussed with reference to both ASAC and AVC control systems. Particular emphasis is given to the physics of control and to the stability issues involved in both adaptive feed–forward and feedback control systems. Finally some new directions for research are proposed where the control transducers are also made adaptive in order to provide better collocation and duality propertie

Sistemi di controllo vibro-acustico per veicoli trasporto passeggeri

La nuova generazione di veicoli per il trasporto passeggeri, in particolare auto e aerei, richiede soluzioni innovative per la riduzione del rumore interno che possano soddisfare i nuovi criteri di progettazione. In particolare, dato il crescente costo del carburante causato dalla riduzione delle scorte di petrolio e vista la sempre pi\uf9 pressante richiesta per la riduzione delle emissioni di gas inquinanti nell\u2019aria, vi \ue8 un grande interesse a realizzare veicoli leggeri a basso consumo. Le tecnologie del controllo attivo del rumore e delle vibrazioni offrono soluzioni interessanti che possono essere efficacemente combinate a trattamenti passivi leggeri per il controllo del rumore a basse e medie frequenze audio. La parte introduttiva dell\u2019articolo offre una panoramica dei principi del controllo attivo del rumore con sistemi in \u201cfeed-forward\u201d e \u201cfeedback\u201d per il controllo di disturbi tonali e stocastici rispettivamente. Le tre sezioni seguenti presentano i concetti base del controllo attivo del rumore all\u2019interno di un veicolo, l\u2019isolamento attivo della trasmissioni delle vibrazioni generate da specifiche componenti meccaniche ed infine il controllo della trasmissione del rumore attraverso le pareti sottili del veicolo