**3.4. General concerns**

Computational Intelligence in Electromyography Analysis – 434 A Perspective on Current Applications and Future Challenges

**Figure 8.** Skin Preparation prior to application of EMG electrodes

EMG electrode placement will be discussed in detail under this section.

fibers, and as a result, an improved superimposed signal is observed.

**3.3. EMG electrode placement** 

the muscle fibers.

Application of surface EMG electrodes requires proper skin preparation beforehand. In order to obtain a good quality EMG signal, the skin's impedance must be considerably reduced. For this purpose, the dead cells on the skin e.g. hair must be completely removed from the location where the EMG electrodes are to be placed. It is advisable to use an abrasive gel to reduce the dry layer of the skin [9]. There should be no moisture on the skin. The skin should be cleaned with alcohol in order to eliminate any wetness or sweat on the

The application of EMG electrodes requires adequate know how of the skeletal muscles. The

In most cases, two detecting surfaces (or EMG electrodes) are placed on the skin in bipolar configuration [14, 15]. In order to acquire the best possible signal, the EMG electrode should be placed at a proper location and its orientation across the muscle is important. The surface EMG electrodes should be placed between the motor unit and the tendinous insertion of the muscle, along the longitudinal midline of the muscle [15]. The distance between the center of the electrodes or detecting surfaces should only be 1-2 cm. The longitudinal axis of the electrodes (which passes through both detecting surfaces) should be parallel to the length of

As mentioned previously, the EMG detecting surfaces should be placed in between the motor unit and the tendon insertion of the muscle. Detecting surfaces placed on the belly of the muscle has proved to be a more than acceptable location. Here, the target muscle fiber density is the highest [15]. Figure 9 shows the proper EMG electrode placement. When the electrodes are arranged in this way, the detecting surfaces intersect most of the same muscle

The electrodes should not be placed elsewhere. In the past, a misconception prevailed that the EMG detecting surfaces should be placed on the motor unit. But, as a matter of fact, the electrode location on the motor point serves as the worst location for signal detection [15].

**3.2. Skin preparation** 

skin.

Before we move on to the signal acquisition phase, it is very important to get acquainted with the EMG signal and the various concerns and factors affecting the qualitative properties of the signal.

The EMG signal's amplitude lies in between 1-10 mV, making it a considerably weak signal. The signal lies in the frequency range from 0-500 Hz and most dominant in between 50-150 Hz [15].

The EMG signal is highly influenced by noise [16], as shown in Figure 10. The characteristics of electrical noise can be caused from various sources. Ambient noise can be caused by electromagnetic radiation sources e.g. radio transmission devices, fluorescent lights and power line interference from electrical wires. These interferences are almost impossible to avoid from external means. This particular noise exists in the frequency range of 50-60 Hz. Noise can also be generated from motion artifact. The two main sources of this noise are instability of electrode skin interface and movement of the electrode cable and lies mostly in the range of 0- 20 Hz. It can be eliminated by proper set of EMG equipment and circuitry. The maximum fidelity of the signal is determined by the acquired EMG signal-to-noise ratio [5, 14].

#### **3.5. Reference electrode placement**

The signal from the EMG detecting surfaces is gathered with respect to a reference. An EMG reference electrode acts as a ground for this signal. It should be placed far from the EMG detecting surfaces, on an electrically neutral tissue [15].

Signal Acquisition Using Surface EMG and Circuit Design Considerations for Robotic Prosthesis 437

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through three different configurations: monopolar, bipolar and multipolar.

**Figure 11.** A Three Amplifier Instrumentation Amplifier

*3.6.1. Monopolar configuration* 

vicinity of the detecting surface [5, 14].

**Figure 12.** Monopolar signal acquisition technique

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A small gain of 5 or 6 is recommended for signal acquisition. Extensive amplification will be carried out in further steps. The placement of the EMG detecting surfaces can be done

The monopolar configuration is implemented using only a single electrode on the skin with respect to a reference electrode as shown in Figure 12. This method is used because of its simplicity, but is strictly not recommended as it detects all the electrical signals in the

**Figure 10.** EMG Spectrum and noise influence on this spectrum [16]
