Absorption of sound in cellular foams

To further enhance the sound absorption of metal foams via combining the high sound absorption and good heat conductivity of the cellular foam metals, the use and acoustic modeling of these materials are reviewed. The predictions made by three viscous models developed by the authors for the propagation of sound through open-cell metal foams are compared with an experiment both for the metal foams and for the polymer substrates used to manufacture the foam. All models are valid in the limit of low Reynold's number which is valid for the typical cell dimensions found in metal foams provided the amplitude of the waves is below 160 dB. The first model considers the drag experienced by acoustic waves as they propagate passing rigid cylinders parallel to their axes, the second considers the propagation normal to their axes, and the third considers the propagation passing the spherical joints. All three are combined together to give a general model of the acoustic behavior of the foams. In particular, the sound absorption is found to be significant and well predicted by the combined model. In addition, a post-processing technique is described for the experiment used to extract the fundamental wave propagation characteristics of the material.

Biomimicking of natural cellular materials

The role that microstructure plays in the mechanical efficiency of natural cellular materials is examined here. The focus of this study is on elastic behaviour. Two natural materials with microstructures resistant to local bucking: plant stems and animal quills have also been examined.

Optimisation of a piezoelectric system for energy harvesting from traffic vibrations

Piezoelectric systems are viewed as a promising approach to energy harvesting from environmental vibrations. The energy harvested from real vibration sources is usually difficult to estimate analytically. Therefore, it is hard to optimise the associated energy harvesting system. This work investigates the optimisation of a piezoelectric cantilever system using a genetic algorithm based approach with numerical simulations. The genetic algorithm globally considers the effects of each parameter to produce an optimal frequency response to scavenge more energy from the real vibrations while the conventional sinusoidal based method can only optimise the resistive load for a given resonant frequency. Experimental acceleration data from the vibrations of a vehicle-excited manhole cover demonstrates that the optimised harvester automatically selects the right frequency and also synchronously optimises the damper and the resistive load. This method shows great potential for optimizing the energy harvesting systems with real vibration data. ©2009 IEEE.