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Published byRey Lombard Modified about 1 year ago

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Bioimpedance Measurement Dept. of Biomedical Engineering YOUNHO HONG

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

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

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Impedance measure (Example) Z

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Impedance measure

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Z X X ? ? 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 Vsin θ Vcos θ Re Im V θ (In-phase Component) (Quadrature Component) V=V I +jV Q

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Two-electrode Method V I skin electrode equivalent circuit V Z C1 Z C2 ZbZb Inject current and then measure voltage

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Two-electrode Method Re Im Z b cos θ b Z c1 cos θ 1 Z c2 cos θ 2 Z c1 sin θ 1 Z c2 sin θ 2 Z b sin θ b

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Four-electrode Method V I skin E1E3E4E2 Z C1 Z C3 Z b1 Z b2 Z C4 Z C2 ZbZb

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Three-electrode Method V I skin E1E3E2 Z C1 Z C3 Z C2 Z b1 ZbZb We can measure skin impedance using Three and Four electrode Method

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Noise Effect

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Spectrum Analizer A1A1 A3A3 A2A2 f1f1 ANAN f2f2 f3f3 fNfN … … X X sinw 1 t / cosw 1 t V(t) X … … sinw 2 t / cosw 2 t sinw N t / cosw N t “ DFT “

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

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