Recent work conducted on developing a fiber tip based Fabry-Perot (FTFP) sensor system for acoustic measurements is presented in this article. It has been determined that this system can be used to detect acoustic fields in the frequency range of 20 Hz-6 kHz with an optical phase sensitivity of 0.095 rad/Pa. A series of experiments is performed to investigate the possibility and potential use of this sensor system, which is designed to be implemented in a multiplexed architecture for providing response measurements to a structural acoustic control system.

/pdf/acoustic-measurements-using-a-fiber-optic-sensor-system-9znk3yupsl.pdf

Acoustic Measurements Using a Fiber Optic Sensor System

The twenty-first century could be called the 'Multifunctional Materials Age' The inspiration for multifunctional materials comes from nature, and therefore these are often referred to as bio-inspired materials Bio-inspired materials encompass smart materials and structures, multifunctional materials and nano-structured materials This is a dawn of revolutionary materials that may provide a 'quantum jump' in performance and multi-capability This book focuses on smart materials, structures and systems, which are also referred to as intelligent, adaptive, active, sensory and metamorphic The purpose of these materials from the perspective of smart systems is their ability to minimize life-cycle cost and/or expand the performance envelope The ultimate goal is to develop biologically inspired multifunctional materials with the capability to adapt their structural characteristics (such as stiffness, damping and viscosity) as required, monitor their health condition, perform self-diagnosis and self-repair, morph their shape and undergo significant controlled motion over a wide range of operating conditions

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Smart Structures Theory

Sound radiation from a plate into an acoustic cavity is controlled using patches of active piezoelectric-damping composites (APDC) The APDC under consideration consists of piezoelectric fibers embedded across the thickness of a visco-elastic matrix in order to control the compressional damping characteristics of the composite The effectiveness of the APDC treatments in attenuating the sound radiation from thin plates into cavities is demonstrated theoretically and experimentally A finite element model (FEM) is developed in order to describe the dynamic interaction between the plate, the APDC patches and the acoustic cavity The FEM is used to predict the dynamics of the plate/acoustic cavity and the sound pressure distribution for different control strategies The predictions of the FEM are validated experimentally using a square aluminum plate whose sides are 298 cm long and have a thickness of 004 cm The plate is mounted on a cavity The test plate is treated with a single APDC patch placed at the plate center The patch is and is made of 15-25% lead zirconate titanate (PZT) fibers embedded in soft and hard polymeric resin matrices and provided with silver-epoxy electrodes Vibration and sound pressure level attenuations of about 70% are obtained, at the plate/cavity first mode of vibration, with a maximum control voltage of 330 V using a derivative feedback controller Such attenuations are attributed to the effectiveness of the APDC treatment in increasing the modal damping ratios by about a factor of four over those of conventional passive constrained layer damping (PCLD) treatments Comparisons between the theoretical predictions of the FEM and the experimental results indicate close agreement between theory and experiments The obtained results suggest the potential of the APDC treatments in controlling the sound radiation from plates into acoustic cavities Such potential can be exploited in many critical applications such as cabins of aircrafts and automobiles to ensure a quiet environment for the occupants

https://iopscience.iop.org/article/10.1088/0964-1726/7/1/002/pdf

Control of sound radiation from a plate into an acoustic cavity using active piezoelectric-damping composites

Sound transmission through a flexible panel into an enclosure: structural–acoustics model

This paper presents a model reduction method and uncertainty modeling for the design of a low-order H∞ robust controller for suppression of smart panel vibration. A smart panel with collocated piezoceramic actuators and sensors is modeled using solid, transition, and shell finite elements, and then the size of the model is reduced in the state space domain. A robust controller is designed not only to minimize the panel vibration excited by applied uniform acoustic pressure, but also to be reliable in real world applications. This paper introduces the idea of Modal Hankel Singular values (MHSV) to reduce the finite element model to a low-order state space model with minimum model reduction error. MHSV measures balanced controllability and observability of each resonance mode to deselect insignificant resonance modes. State space modeling of realistic control conditions are formulated in terms of uncertainty variables. These uncertainty variables include uncertainty in actuators and sensors performances, uncertainty in the knowledge of resonance frequencies of the structure, damping ratio, static stiffness, unmodeled high resonance vibration modes, etc. The simplified model and the uncertainty model are combined as an integrated state space model, and then implemented in the H∞ control theory for controller parameterization. The low-order robust controller is easy to implement in an analog circuit to provide a low cost solution in a variety of applications where cost may be a limiting factor.

Design of Robust Vibration Controller for a Smart Panel Using Finite Element Model

Analytical and experimental studies undertaken for controlling noise in the interior of a three-dimensional enclosure with a flexible wall are presented. The rigid walls are constructed from acrylic material, and the flexible wall, which is clamped along all four edges, is constructed from aluminium material. Noise generated by an external speaker is transmitted into the enclosure through the flexible boundary and active control is realized by using lead zirconate titanate (PZT) piezoelectric actuators bonded to the flexible boundary. Condenser microphones are used for noise measurements. For harmonic external disturbances, optimization analyses are carried out in the frequency domain to determine the optimal voltage inputs to the piezoelectric actuators for global and local noise control. In the associated experiments, analog feedforward control is implemented by using acoustic error signals for different panel and cavity controlled modes.

https://iopscience.iop.org/article/10.1088/0964-1726/5/1/010/pdf

Active control of interior noise in a three-dimensional enclosure

Analytical investigations into performance functions for interior noise control are presented. Three different performance functions for global control and one performance function for local control are developed and investigated. These performance functions are based on the squared pressure, the panel kinetic energy, and the air particle kinetic energy. As an illustration, noise control in the interior of a three-dimensional enclosure with a flexible boundary clamped along the edges is considered. Active control is realized by using lead zirconate titanate (PZT) patches as distributed actuators and interior microphones as error sensors. For tonal external disturbances, optimization analyses are carried out in the frequency domain to determine the optimal voltage inputs to the piezoelectric actuators and the optimal values of performance functions. Issues such as the number of actuators and their locations are investigated when the disturbance frequency is close to one of the following frequencies: a) resonance frequency of a symmetric or an asymmetric panel mode; b) off-resonance frequency, and c) resonance frequency of a cavity mode. The controlled responses obtained for the different performance functions are analysed by using pressure contours, zones of quiet, and modal amplitude and modal rearrangement control mechanisms. Based on the results of the numerical studies, it is determined that use of the energy-based performance function results in better pressure contours and zones of quiet inside the enclosure. The location of the actuators is found to have a significant influence on the magnitude of noise reduction. The results of the studies are relevant to interior noise control in enclosures such as rotorcraft cabins.

https://iopscience.iop.org/article/10.1088/0964-1726/6/3/009/pdf

A Sampath

Papers

Active control of interior noise in a three-dimensional enclosure

Studies on performance functions for interior noise control