Bioimpedance Measurement

Presentation on theme: "Bioimpedance Measurement"— Presentation transcript:

Bioimpedance Measurement
Dept. of Biomedical Engineering YOUNHO HONG

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

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)

Impedance measure (Example) Z

Impedance measure

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

Impedance measure In-phase Component

Impedance measure Quadrature Component

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

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

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

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

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

Noise Effect

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

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

Thank you.