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**Bioimpedance Measurement**

Dept. of Biomedical Engineering YOUNHO HONG

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

resistance reactance

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**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)

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Impedance measure (Example) Z

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Impedance measure

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

cos(2πft) phase-sensitive Demodulation

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Impedance measure In-phase Component

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Impedance measure Quadrature Component

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**Impedance measure V=VI+jVQ Vsin θ V θ Vcosθ (Quadrature Component)**

(In-phase Component) (Quadrature Component) V=VI+jVQ

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**Two-electrode Method Inject current and then measure voltage V I skin**

equivalent circuit V Inject current and then measure voltage ZC1 ZC2 Zb

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

Zbsinθb

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**Four-electrode Method**

V I skin E1 E3 E4 E2 ZC1 ZC3 Zb1 Zb2 ZC4 ZC2 Zb

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**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

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Noise Effect

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**Spectrum Analizer “ DFT “ f1 f2 f3 fN … X V(t) … A1 A3 A2 AN**

sinw1t / cosw1t V(t) … sinw2t / cosw2t sinwNt / coswNt “ DFT “

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**Bio Impedance Spectroscophy**

Z + - Repeat measurement for many frequencies θ f Zb f

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Thank you.

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