THE USE OF OPTIMALLY SHAPED PIEZOELECTRIC FILM SENSORS IN THE ACTIVE CONTROL OF FREE-FIELD STRUCTURAL RADIATION .1. FEEDFORWARD CONTROL

Feedforward active control of free field structural radiation rising v ibration control sources and piezo-electric polymer film error sensors is considered. The problem of what should be measured by the sensors is first examined, where it is shown that orthonormal decomposition of the equation governing the acoustic power output of the structure wil l define the optimal quantities, which are described using the in vacu o structural modes as a basis function. Computer simulations show that by using only a few of these quantities as error signals, practically the maximum levels of acoustic power attenuation cart be obtained at low frequencies. Tonal and broadband experimental results are presente d using the shaped piezo-electric polymer film sensors which demonstra te the effectiveness of the described approach.