**2.2 Design consideration for a measurement system**

The value of the measured bioimpedance Z is varying, but the base value of it, Z0, is huge compared to the information carrying modulation ΔZ(t) (see Eq. (1)

**Figure 2.** *Block diagram of the measurement device.*

**Figure 3.** *The prototyped version of a wearable impedance measurement device.*

**Figure 4.** *Image of the 32-bit impedance acquisition system prototype.*

**Figure 5.** *Measured bioimpedance values on top of the radial artery on the Nyquist diagram [23].*

in Chapter 3.1). Several observations can be drawn from the generalized measurement results in **Figure 5**. The first observation is that the greyish, slightly smeared information carrying signal, ΔZ(t), is tiny compared to the base value Z0 of the acquired bioimpedance. Next, the imaginary part Im Z of the impedance vector Z is nearly 10 times smaller than the real part Re Z. Third, the modulation is roughly in the direction of the vector of the impedance base value Z0. The conclusion is that the role of Im Z is low, and less attention can be paid into the accuracy of the vector measurements when designing the device, especially the synchronous detector of it. A root problem in designing a suitable electronics is whether to use analog or digital realisation of the synchronous detector.
