# Electrical Impedance of Biological Tissues

Electrical Impedance of Biological Tissues

Electrical impedance (or simply impedance or total resistance) measures opposition to a sinusoidal alternating current (AC). Electrical impedance extends the concept of resistance to AC circuits. Impedance is the complex generalization of resistance. In most cases, impedance is a function of the frequency (ω in radians/sec or in hertz), resistance (in ohms), inductance (in henries), and capacitance (in farads):

Z

f

R

L

C

Z=+

2

R

2

(-)

X

L

X

C

The reactance - is the imaginary part of the impedance, =ωL; =1/(ωC). We consider the impedance to be a function of frequency only; and are constant parameters. The impedance over a range of excitation frequencies is plotted. In the case of biological tissues, the impedance is .

X

L

X

C

X

L

X

C

L

C

Z=+

2

R

2

X

C

The plots show the impedance (total resistance) in red, the biological tissue impedance in gray, and the capacitance resistance in green.

Z

C