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The University of Southampton

Research project: Active Structural Acoustic Control - Dormant

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The poor sound transmission loss at low frequencies of double wall constructions can be improved with ASTC systems. For example the sound transmission/radiation by the walls facing the interior of a room could be reduced with "Active Structural Acoustic Control" (ASAC) systems. This control approach improves the transmission loss of the enclosure walls by driving structural actuators mounted on the panels or frame structure of the double wall (Shakers, PZT patches, PVDF foils) in such a way as to minimise the vibration components of the panels that mainly contribute to the radiation of sound to the interior. These vibration components, also called radiation modes (Elliott and Johnson 1993), could be efficiently excited and measured by means of shaped piezoelectric foils that are embedded in the panels themselves (Johnson and Elliott 1995).

At present ISVR is investigating a particular configuration of an ASAC control system where two shaped PVDF foils are glued on either sides of an aluminium panel. 

ASAC control system


The quadratic shaping of the two foils allows the measurement of the net volume velocity component of the plate vibration and allows the application of a uniform force on the panel. It has been shown that in the low frequency range, where the panel is relatively small compared to an acoustic wavelength, the largest contribution to the sound radiation from the panel is due to the net volume velocity of the panel itself. Therefore, by driving the uniform force distributed actuator to minimise the volume velocity of the panel measured with the shaped PVDF foil the sound radiation from the panel at low frequency can be reduced.

The novelty introduced by this project is the matched and collocated sensing actuation system. Two benefits are expected by the use of a collocated volume velocity sensor and a uniform force actuator: first, spillover phenomena could be avoided and second, it should be possible to implement a feedback control architecture which allows the use of this control system in applications where a reference signal of the incident noise on the panel is not available as well.

With this technology the walls of an enclosure would be formed by a number of these panels which work as modular systems. In this way a simple, light and inexpensive control system can be built. In fact each panel would be equipped with two light PVDF foils to form a matched and collocated sensor/actuator pair and small and simple Single-Input-Single-Output (SISO) analogue controller would be sufficient to drive the uniform force actuator to minimise the measured volume velocity.

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