ABSTRACT
The acoustic radiation from a vibrating structure can be reduced by an active control system provided the system has a suitable sensing capability. The radiation of sound from a structure is in general a spatially distributed phenomenon and it is often necessary to extract information about the behaviour of the structure over its entire surface. The major source of acoustic radiation from a structure at low frequencies is the integrated normal velocity or volume velocity of the structure. For the purposes of active control it is therefore important that this quantity be measured. This can be achieved by using a number of point sensors, but the complexity of the system required to deal with these sensors can become prohibitive. Alternatively, a single distributed PVDF sensor can be used to measure the volume velocity of a structure due to bending, but unfortunately such a sensor is incapable of detecting the whole body motion of the structure. An alternative distributed sensor which uses PVDF as a distributed accelerometer (in the d„ mode), can in principle, directly measure the volume velocity of the structure due to any arbitrary motion. Unfortunately, PVDF is very sensitive to strain on the structure’s surface and this masks any signal output due to acceleration. Methods of desensitising the PVDF sensor to surface strain are discussed.
