Haydar Aygün

Sound absorption by clamped poroelastic plates

Measurements and predictions have been made of the absorption coefficient and the surface acoustic impedance of poroelastic plates clamped in a large impedance tube and separated from the rigid termination by an air gap. The measured and predicted absorption coefficient and surface impedance spectra exhibit low frequency peaks. The peak frequencies observed in the absorption coefficient are close to those predicted and measured in the deflection spectra of the clamped poroelastic plates. The influences of the rigidity of the clamping conditions and the width of the air gap have been investigated. Both influences are found to be important. Increasing the rigidity of clamping reduces the low frequency absorption peaks compared with those measured for simply supported plates or plates in an intermediate clamping condition. Results for a closed cell foam plate and for two open cell foam plates made from recycled materials are presented. For identical clamping conditions and width of air gap, the results for the different materials differ as a consequence mainly of their different elasticity, thickness, and cell structure.

Behaviour of ultrasonic waves in porous rigid materials: an anisotropic Biot-Attenborough model

© Published under licence by IOP Publishing Ltd. The anisotropic pore structure and elasticity of cancellous bone cause wave speeds and attenuation in cancellous bone to vary with angle. Anisotropy has been introduced into Biot theory by using an empirical expression for the angle-and porosity-dependence of tortuosity. Predictions of a modified anisotropic Biot-Attenborough theory are compared with measurements of pulses centred on 100 kHz and 1 MHz transmitted through water-saturated porous samples. The samples are 13 times larger than the original bone samples. Despite the expected effects of scattering, which is neglected in the theory, at 100 kHz the predicted and measured transmitted waveforms are similar.

Empirical angle‐dependent tortuosity functions and sound transmission through cancellous bone.

Recent literature concerning the angle dependence of sound transmission through cancellous bone has suggested that it might be due either to elastic anisotropy or to microgeometrical anisotropy in the pore structure; e.g., an angle‐dependent tortuosity. The elastic anisotropy approach has been found able to explain the observed variation in fast wave speed with angle better than the angle‐dependent tortuosity at the cost of underpredicting slow wave speeds. In reality, it is likely that both influences are present in cancellous bone. Nevertheless the angle‐dependent tortuosity approach has been revisited on the basis of orthotropic data for sound transmission through air‐filled stereo‐lithographical bone replicas [Attenborough et al., JASA 118, 2779 (2005)]. [Work supported by Leverhulme Grant F/00181/N.]