Active control of sound transmission through windows with carbon nanotube-based transparent actuators

This paper explores the development of active sound transmission control systems for windows that can achieve a significant reduction in window noise transmission. Two major challenges need to be addressed in order to make the development of such noise blocking windows feasible. These are the need for a distributed actuation system that is optically transparent and the unavailability of a real-time reference signal that can be used by the active control system to provide advance information on the noise affecting the window. To address the first challenge, a transparent thin-film actuator (speaker) is first developed for the control system, which consists of a piezoelectric poly (vinylidene fluoride) (PVDF) thin film coated with compliant carbon nanotube-based transparent conductors on both sides. The developed thin-film speaker shows excellent acoustic response over a broadband frequency range, and has the advantages of being flexible, transparent, thin, and lightweight. To address the second challenge of providing a time-advanced reference signal from a moving noise source, a small microphone array distributed on the outside wall of the home is used. New noise source identification algorithms are employed, by which an appropriate microphone from the array can be chosen to provide a reference signal. Experimental results show that over 12 dB reduction in sound transmission is achieved globally in the case of broadband sound, which demonstrates the effectiveness of the control system in blocking sound transmission.