1. Bioimpedance Measurement
Dept. of Biomedical Engineering
YOUNHO HONG

2. Impedance measure + Z - constant current source i=0 measured known
resistance
reactance

3. Impedance measure (Example) You are given with i(t) = I sin(2πft)1
1+j Re Im i V t 1
You are given with i(t) = I sin(2πft)
You measure v(t) = V sin(2πft+θ)

4. Impedance measure
(Example) Z

5. Impedance measure

6. Impedance measure Z X ? phase-sensitive Demodulation sin(2πft)
cos(2πft)
phase-sensitive Demodulation

7. Impedance measure
In-phase Component

8. Impedance measure
Quadrature Component

9. Impedance measure V=VI+jVQ Vsin θ V θ Vcosθ (Quadrature Component)
(In-phase Component)
(Quadrature
Component)
V=VI+jVQ

10. Two-electrode Method Inject current and then measure voltage V I skin
equivalent circuit V
Inject current
and then measure voltage
ZC1
ZC2 Zb

11. Two-electrode Method Im Re Zbcosθb Zc1cosθ1 Zc2cosθ2 Zc1sinθ1 Zc2sinθ2
Zbsinθb

12. Four-electrode MethodV I
skin E1 E3 E4 E2
ZC1
ZC3
Zb1
Zb2
ZC4
ZC2 Zb

13. Three-electrode MethodV I
skin E1 E3 E2
ZC1
ZC3
ZC2
Zb1 Zb
We can measure skin impedance
using Three and Four electrode Method

14. Noise Effect

15. Spectrum Analizer “ DFT “ f1 f2 f3 fN … X V(t) … A1 A3 A2 AN
sinw1t / cosw1t
V(t) …
sinw2t / cosw2t
sinwNt / coswNt
“ DFT “

16. Bio Impedance SpectroscophyZ + -
Repeat measurement for many frequencies θ f Zb f

17. Thank you.