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This paper is a review of multi-channel surface electromyography (sEMG) electrode used in the research for investigating the properties of muscles. Over 300 papers from five recognized journals were examined from the year 2000 to 2013 with only 64 stating the use of multi-channel electrodes in their research. The review determined that multi-channel electrodes can be classified as linear array or 2D array electrodes. The 2D array is the basis for developing the high-spatial-resolution sEMG (HSR-sEMG) or high density sEMG (HD-sEMG). The important factors considered in this review of the electrodes are: 1) the material used; 2) the inter-electrode distance; and 3) the configuration for the collection of the electromyography signals. The basic configurations of the sEMG electrodes are monopolar, bipolar, and double differential. It was found that the majority of the linear array electrodes were used to collect either bipolar or double differential signals. The 2D array electrodes were used to collect monopolar signals. The HSR-sEMG electrodes used a normal double differentiating filter, referred to as Laplacian configuration. The HD-sEMG has versatility being able to collect all types of signals, such as monopolar, bipolar, double differential, or signals filtered by Laplacian configuration.

This paper presents findings from a study of five healthy subjects performing 50% maximum voluntary contraction until complete fatigue of the muscle. An overlapping window technique was used to find the values for mean frequency (MNF), median frequency (MDF) of the power spectrum, root mean square (RMS) and muscle fibre conduction velocity (MFCV). The surface electromyography signal (sEMG) was collected from the vastus lateralis muscle using a three channel Laplacian electrode. The results show the MNF and MDF values showed a consistent trend with each other where they remained at steady values between 20-30% and 75-80% of the signal after which they fell 15-30% of this value. The RMS showed a linear increase in value. The MFCV showed a similar trend to that found in the MNF and MDF values. 

This paper covers the design aspects of a new multi-channel electrode for the acquisition of surface electromyography signals from a selected muscle. The new multi-channel electrode has 11 pins where the monopolar signals produced will be configured in a software either as Linear array or Laplacian configuration. The design specification of the pre-amplifier ideally was to have a voltage gain of 500 with bandpass filtering of 5 Hz-1 kHz. The final design of the pre-amplifier circuit using an INA 118 instrumentation amplifier was built and tested to give values for voltage gain of 484 with bandpass filtering of 6.8 Hz-1.02 kHz. The software configuration that gives clearer and more defined signals in terms of motor unit action potentials for future signal processing is the Laplacian rather than Linear array.

To date various signal processing techniques have been applied to surface electromyography (SEMG) for feature extraction and signal classification. Compared with traditional analysis methods which have been used in previous application, continuous wavelet transform (CWT) enhances the SEMG features more effectively. This paper presents methods of analysing SEMG signals using CWT and LabVIEW for extracting accurate patterns of the SEMG signals. We used the scalogram and frequency-time based spectrum to plot the power of the wavelet transform and enhance the diagnosis features of the signal. As a result, clinical interpretation of SEMG can be improved by extracting time-based information as well as scales, which can be converted to frequencies. Using the extracted features of the dominant frequencies of the wavelet transform and the related scales, we were able to train and validate an artificial neural network (ANN) for SEMG classification.