Noise is an environmental pollutant with recognized impacts on the psychological and physiological health of humans. Many porous materials are often limited by low sound absorption over a broad frequency range, delicacy, excessive weight and thickness, poor moisture insulation, high temperature instability, and lack of readiness for high volume commercialization. Herein, an efficient and robust lamella-structure is reported as an acoustic absorber based on self-assembled interconnected graphene oxide (GO) sheets supported by a grill-shaped melamine skeleton. The fabricated lamella structure exhibits ≈60.3% enhancement over a broad absorption band between 128 and 4000 Hz (≈100% at lower frequencies) compared to the melamine foam. The enhanced acoustic absorption is identified to be structure dependent regardless of the density. The sound dissipation in the open-celled structure is due to the viscous and thermal losses, whereas it is predominantly tortuosity in wave propagation and enhanced surface area for the GO-based lamella. In addition to the enhanced acoustic absorption and mechanical robustness, the lamella provides superior structural functionality over many conventional sound absorbers including, moisture/mist insulation and fire retardancy. The fabrication of this new sound absorber is inexpensive, scalable and can be adapted for extensive applications in commercial, residential, and industrial building structures.

No abstract

Traditional local active noise control systems minimise the measured acoustic pressure to generate a zone of quiet at the physical error sensor location. The resulting zone of quiet is generally limited in size and this requires the physical error sensor be placed at the desired location of attenuation, which is often inconvenient. To overcome this, a number of virtual sensing algorithms have been developed for active noise control. Using the physical error signal, the control signal and knowledge of the system, these virtual sensing algorithms estimate the error signal at a location that is remote from the physical error sensor, referred to as the virtual location. Instead of minimising the physical error signal, the estimated error signal is minimised with the active noise control system to generate a zone of quiet at the virtual location. This paper will review a number of virtual sensing algorithms developed for active noise control. Additionally, the performance of these virtual sensing algorithms in numerical simulations and in experiments is discussed and compared

No abstract

No abstract

An experiment was performed to investigate the implementation of shaped PVDF modal sensors on a simply supported rectangular plate to control specific modes of the vibration. The plate was excited by a steady-state harmonic point force while the control was achieved by two independent piezoelectric actuators bonded to the surface of the plate. A two-channel adaptive controller based on the multi-input multi-output filtered X LMS algorithm was used to provide feed-forward control. Two PVDF modal sensors were shaped such that the (3,1) mode was the dominant structural mode observed by the sensors. With this configuration, the amplitude of the (3,1) mode can be minimized regardless of excitation frequency. A comparative test was performed by using two accelerometers as error sensors. Results indicate that for both on and off-resonance excitations, the shaped PVDF modal sensors are superior to point-error sensors, such as accelerometers for controlling specific structural modes.

No abstract

No abstract