2.2. Detection of Blood Permeating the Textile

We purchased a human whole blood sample, in which EDTA-2K was added as an anticoagulant, from Tennessee Blood Service via Bizcom Japan, and phosphate-buffered saline (PBS) was used as a substitute for sweat. Before and after dropping blood or PBS onto the textile-based sensor, the impedance Z and phase θ between the electrodes were measured using a 3532-50 LCR HiTESTER manufactured by Hioki E. E. From the obtained data, the reactance X was calculated as

In this study, we will discuss the frequency dependence of the values of

where ω is angular frequency and f is frequency. X can thus be represented as

where L and C are the nominal inductive and capacitive lumped components, respectively, in a simple (series connected) RLC model. Thus, the value indicated in Equation (2) is equivalent to C; namely,

if the sensor contains no inductive component. The value of C is often discussed when dealing with dielectric dispersion assuming that L = 0. However, the value estimated in the experiment is X, and we cannot determine accurate values for L and C. Therefore, in this study, we discuss the value indicated in Equation (2).