**3.2. Skin preparation**

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 skin.

Signal Acquisition Using Surface EMG and Circuit Design Considerations for Robotic Prosthesis 435

Similarly, the electrodes should neither be placed at or near the tendon nor at the edge of the muscle. The muscle fibers become thinner and smaller in number when they approach the tendon of the muscle resulting in a weak EMG signal, proving the fact that electrode placement near the tendon is not feasible. If the electrode is placed at the edge of the muscle, the chances of crosstalk from other muscles will considerably increase, and the resultant

**Figure 9.** The ideal position of the electrode (two detecting surfaces) is between the innervation zone

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

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

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

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

fidelity of the signal is determined by the acquired EMG signal-to-noise ratio [5, 14].

signal will be disturbed by those of other muscles [15].

(or motor unit) and the tendinous insertion (or belly of the muscle) [15]

**3.4. General concerns** 

properties of the signal.

**3.5. Reference electrode placement** 

detecting surfaces, on an electrically neutral tissue [15].

Hz [15].

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