Modeling Of The Dispersion, Excitation Intensity, And Attenuation Of Ultrasonic Guided Waves In Long Cortical Bone

This paper models long cortical bone using the columnar cylindrical shell, mainly studies on the dispersion and attenuation characteristics, excitation intensity of guided waves in the long cortical bone. It is mainly divided into three parts, the first part of the cortical bone is assumed to a transversely isotropic elastic column, first set up an elastic bone shell in vacuum (V/B/V) model, namely the inner and outer boundary of the bone shell is free. First, we analysis of the dispersion characteristics of the guided waves in long cortical bone, including the phase velocity and group velocity, and investigate the influence of anisotropic parameter and bone thickness on the dispersion characteristics of the test. However, bones are filled by fatlike bone marrow and are embedded under soft tissues of the human body. To this end, we use the compressible viscous fluid to simulate bone marrow, using water instead of soft tissue by ignoring vicious attenuation of the soft tissue, so we establish an elastic long bone model filled marrow outer covering a water (M/B/W) model. At the same time, compared with the V/B/V model, we study the dispersion characteristics of the guided wave propagation in M/B/W model. Then, the circinal acoustic source was located in outer water layer of long cortical bone. We investigate the excitation intensity and the attenuation of the guided wave. In the M/B/W model, if axisymmetric models were the separately excited in the low frequency region, the anisotropy feature and the change of thickness of the long bone were all reflected (using the second order axisymmetric mode and the lowest order axisymmetric mode).Bone is a heterogeneous, porous, and anisotropic material with a complex structure. In order to emphasize the effect of porosity and permeability on the propagation characteristics of guided waves. First of all, we can ignore the anisotropic properties of long bones, bone is assumed to be isotropic porous medium. Firstly, the first model which a porous bone shell is in vacuum (V/B/V) was set up. We built a relationship about the skeleton modulus and the matrix modulus of the long bone. The effects of porosity and permeability mainly on the dispersion and attenuation characteristics of guided waves were investigated. The porosity increase, the phase velocities and the group velocities of the guided wave decrease, and the dispersion curves of the guide wave are all moved to the low frequency. Next, in order to combine with the clinical examination, we also established a long cortical model inside filling with water and outside surrounded by a water layer (W/B/W). As the porosity increase, the excitation intensity of the lowest order axisymmetric mode increases slightly, while the excitation intensity of the second axisymmetric mode is obviously decreased in the high frequency.Basing on the theory of Biot, the long bone shell was modeled as transversely isotropic fluid saturated porous media. The transversely isotropic porous medium is assumed that matrix material is transversely isotropic, and the arrangement of porosity is isotropic. Basing on the above hypothesis, we set up two kinds of physical model, the first is long bone in the vacuum (V/B/V), the research mainly focus on the impact of the anisotropic characteristic on the dispersion, the excitation intensity, and attenuation. The second model that a long cortical inside filling with water and outside surrounded by a water layer (W/B/W) was established, mainly studied the effect of anisotropy on the dispersion and excitation.