**6. Signal amplification**

Computational Intelligence in Electromyography Analysis – 398 A Perspective on Current Applications and Future Challenges

**Figure 3.** Diagram of a biological signal acquisition system [3].

enters at an amplitude of μV and must be amplified and filtered [3].

5). The human body is actually a good antenna for electromagnetic energy [3].

In signal acquisition, analyzable information is obtained by studying the physical quantities involved in the activation process. These physical quantities can be measured by sensors that convert them into electrical signals and then record them using a data acquisition system (Figure 3). Computers make data acquisition more efficient and reliable and have the

Sensors and transducers are devices that convert physical quantities into electrical signals or current. Signal conditioners are electronic devices that modify the input signal in some way, whether by amplification, attenuation, filtering or isolation. The EMG signal, for example,

There are basically two techniques capturing an EMG signal: either monopolar or bipolar electrodes. In the monopolar configuration, only one electrode is placed on the skin over the muscle in question (Figure 4). This electrode detects the electrical potential relative to a reference electrode, which is placed in a location unaffected by the electrical activity generated by the analyzed muscle. In the bipolar configuration, two electrodes are used on the muscle as well as a reference (or ground) electrode placed in a neutral location (Figure

**Figure 4.** A) Schematic representation of a unipolar amplifier. B) Schematic representation of a bipolar

advantage of combining data storage with analysis and processing capability [21].

**5. Biological amplifiers** 

amplifier [3].

Gain is defined as the ratio between the voltage that enters and exits the amplifier. Gain should be selected to suit the characteristics of the experiment, the studied muscle, the electrode type and the use planned for the amplified signal. Considering that a sEMG signal has a maximum voluntary contraction amplitude not exceeding 5 mV peak-to-peak (Figure 6), the gain can be adjusted between 10 and 1000x. It is important to choose a gain that does not exceed at any stage the voltage expected from the system, or there will be a risk of either losing part of information or damaging the system itself [1].

**Figure 5.** Appropriate gain range [3].
