The Use of Optimally Shaped Piezo-electric Film Sensors in the Active Control of Free Field Structural Radiation, Part 2: Feedback Control

Abstract

Feedback control of free field structural radiation is considered. State equations are formulated with a transformation which decouples the acoustic power error criterion. Using the resultant equations, expressed in terms of ' 'transformed mode'' states, the order of the state equations can be significantly reduced at low frequencies. Two experimental implementations of feedback control strategies using shaped piezoelectric polymer film sensors to measure the transformed system states are described. The first of these is a simple analog implementation. The second implementation is in discrete time, where an adaptive algorithm for optimizing the weights of IIR filters for practical use is described. It is shown that by using the outlined control approach significant levels of low frequency acoustic power attenuation can be obtained with no control spillover and subsequent increase in higher frequency acoustic power output.

Piezoelectric Array Sensing of Volume Displacement: A Hardware Demonstration

“…The distribution looks very similar to the theoretical predictions based on the analytical model of a simply supported plate and shown in Figure 6(b). Figure 7 compares the volume displacement FRF <( ) reconstructed according to equation (7) with the coe$cients G of Figure 6(a) (dotted line) with the FRF <( ) calculated according to equation (6) from FRF D I ( ) measured by the scanner vibrometer (full line). The comparison is shown for the three locations of the disturbance source; Figure 7(a)}7(c) correspond, respectively, to the loudspeaker in positions 1}3 in Figure 5.…”

“…The agreement is good for all source locations. 6. CONCLUSIONS A piezoelectric array sensor connected to a linear combiner has been developed to reconstruct the volume displacement in real time.…”

“…However, acceleration sensors, especially small ones, are less sensitive at low frequency, where the volume velocity is the most relevant. For a plate without rigid-body modes, various sensors have been proposed based on a shaped piezopolymer "lm bonded to the plate, for sensing the volume displacement or velocity [3,4], for reconstructing the sound pressure at a given point in the far "eld [5], or for evaluating the radiated sound power [6]; these sensors can have complex shapes which may make them costly, di$cult to manufacture, and sensitive to minor changes in their geometry, bonding conditions or material properties. Alternative strategies for evaluating the total radiated acoustic power from a set of discrete strain information at a regular mesh were developed in reference [7], but these approaches were computationally intensive and were not suited to real-time applications with the existing microprocessor technology.…”

An Acoustic-Based Modal Filtering Approach to Sensing System Design for Active Control of Structural Acoustic Radiation: Theoretical Development

“…To implement a feedforward control system that aims to attenuate this performance measure, the pressure measurements are decomposed (modal filtering) using C + , and the relatively small number of resulting signals (multipole amplitudes) are passed through filters which have frequency characteristics defined by A a , weighting the importance of the signals [13,15]. For feedback control, the decomposed multipole signals provide the controller inputs, and the weighting terms can be included in the controller design process through a variety of means.…”

Practical implementation of an acoustic-based modal filtering sensing technique for active noise control

“…In practice, some noise sources are structural, others are not. The structural approach to modal filtering has seen the use of shaped sensors [11,[13][14][15], accelrometors [7,9,12,[16][17][18][19][20][21] or pizeo patches [18,[22][23][24][25] implemented on rectangular panels with simply supported boundary conditions.…”