Week 3

Next task, I need to find a variety of EMG circuit design so that we can compare and make reference for this project. 

[1]

                                                       Figure 1 : The Schematics Designed Circuit

From this schematic designed circuit,Danny Ng do mentioned disposable surface electrode are used to pick up the signal. He did an amplifier and signal conditioning circuit. Above, I attached the schematic designed of Danny Ng. 

The amplitude of the signal pick up is low, so amplification is needed to measure the detected signal. A differential amplifier is needed because of the high common mode rejection ratio (CMRR). Two electrodes are connected in between the region of interest and the ground electrode is connected to a reference point. A driven feedback is implemented in the design to improve the signal quality. Second order active low pass and active high pass filter are used to further amplify the signal  and filter off the unwanted part of the signal.A low-pass filter is an electronic filter that passes low-frequency signals and attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. For  high-pass filter, is an electronic filter that passes high-frequency signals but attenuates (reduces the amplitude of) signals with frequencies lower than the cutoff frequency.


As the design uses single supply, a 5v to -5v converter is used to power the active amplifier. Isolation amplifier and supply isolation is added as some basic safety implementation in the circuit. 

Isolation amplifiers provide electrical isolation and an electrical safety barrier. They protect data acquisition components from common mode voltages, which are potential differences between instrument ground and signal ground. Instruments that are applied in the presence of a common mode voltage without an isolation barrier allow ground currents to circulate, leading in the best case to a noisy representation of the signal under investigation. In the worst case, assuming that the magnitude of common mode voltage or current is sufficient, instrument destruction is likely. Isolation amplifiers are used in medical instruments to ensure isolation of a patient from power supply leakage current.

                               Figure 2 : The Signal detected from the electrode when the muscle are moved




[2]

                                                                               Figure 3 : EMG Analysis Circuit

The following circuit was designed and built to test the overall surface EMG system (electrodes & amplifier).

[3]

                                                                Figure 4 : EMG Schematic Circuit
 

[4]

                                                                            Figure 5 : EMG Signal Conditioning Circuit

Week 2

Research about the EMG electrodes. The EMG signal is measured either non-invasively with surface electrodes or invasively with wire or needle electrodes. Since typical EMG signal levels are in the region of 400 μV to 3 mV (depending on many factors), the measured EMG signal is almost always pre-amplified, amplified.

EMG can be recorded from the skin surface or by placing an electrode directly within the subject’s muscle. This is usually referred to as a fine-wire recording. Surface EMG is generally recorded with either passive or active electrodes placed on the intact skin surface over the belly of the subjects muscle, while fine-wire recordings use a wire electrode that is inserted into the muscle by a trained (and, in most cases, licensed) professional. Each electrode type has specific advantages and disadvantages.


Examples of EMG electrodes : 

Figure 1 : Connection Method of Disposable EMG Monopolar Needle Electrodes

Figure 2 : Surface EMG Electrodes