4.1 Measurement of Electrical Biosignals

|

93

Fig. 4.1: Simulation result for potential distribution on the body surface during ECG; the coloring

indicates the potential in volts: The simulation was performed using CST Studio Suite software. The

cardiac vector was simulated by two point charges inside the heart with a static potential difference

of 100 mV. The numerical body model contains all real tissue components with a spatial resolution

of approximately 1 mm³.

RH

CH

Sebaceous gland

Muscle

Pain receptors

Epidermis

Upper skin

Dermis

Subcutaneous

Sweat pore

Sweat gland

Hair root

Blood vessels

Fat cells

Fig. 4.2: Structure of the skin (left, after [4]): The DC component of the current flows along the hair

ducts and sweat glands, which are located within the lower skin layers and penetrate the uppermost

skin layer. Electrical equivalent circuit of the skin (right). For simulation purposes, CH = 200 nF and

a resistance value RH = 2 kΩcan be assumed. In fact, the values depend on several factors and can

therefore vary considerably.

4.1.1 Electrodes

The next link in the electrical measuring chain between the biosignal source and the

measuring amplifier are the electrodes. They represent the coupling element between