Figure 1. Dielectric constant and loss of collagen aqueous solution and pure water.

Dielectric constant and loss of 4 wt% collagen aqueous solution (open symbols) and pure water (filled symbols) in the frequency range of (a) TDR and THz-TDS and (b) TDR measurements. In Fig. 1(a), experimental results reported in the literature³²,³³ are also shown for comparison. Our result for water agree with the reference data and other reports³⁴,³⁵, thus suggesting that our experimental setup works well in the measured frequency range. A surprising fact is that there is essentially no difference between the experimental values for the complex permittivity of pure water and that of the aqueous solution of collagen, although the viscosity values are very different. Similar results were obtained for all of the collagen aqueous solutions with different concentrations. This result can be examined in detail in Fig. 1(b) for the TDR frequency range. The values of the dielectric constant and loss for the pure water and the aqueous collagen solution behave in the same manner in the entire frequency range of the TDR measurements. Moreover, these are well described using the dielectric parameters of water at the same temperature reported in the literature³⁴. Adding collagen to pure water does not greatly affect the dielectric dispersion of the water in the measured frequency range. Note that dielectric loss for the collagen aqueous solution at lower frequencies, approximately 1 GHz, is slightly greater than that for the pure water. It seems that this deviation is due to the large contribution of the dc conductivity of the solution caused by ionic contamination.