Bioimpedance Measurement

Dept. of Biomedical Engineering 2003200449 YOUNHO HONG Bioimpedance Measurement

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

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

Impedance measure (Example) Z

Impedance measure

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

Impedance measure In-phase Component

Impedance measure Quadrature Component

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

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

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

Four-electrode Method I V E1 E3 E4 E2 skin ZC1 ZC3 ZC4 ZC2 Zb1 Zb Zb2

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

Noise Effect

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

Bio Impedance Spectroscophy θ Zb f Repeat measurement for many frequencies + Z f -

Thank you.