Temperature-dependent dielectric properties of human bone constituents at THz frequencies : contrast mechanisms and bound water dynamics

THz time domain spectroscopy (THz-TDS) was used to investigate the dielectric properties of constituents of human bone. We report experimental values for refractive index and absorption coefficient for four major anhydrous constituents of bone: Collagen, Hydroxyapatite, Calcite and Amorphous calcium phosphate. We varied the sample temperature in order to explore the physical mechanisms underpinning the THz dielectric function of these constituents. Experimental data were well described using the Debye model for collagen, or the Lorentz model for mineral compounds, respectively. A fitting procedure based on Particle Swarm Optimization was implemented in order to extract the fitting parameters such as relaxation times and oscillator strengths