EMG signals are measured with a High density array of gold plated pins used as dry electrodes pressed on the skin. No electrode gel is used because this would short the space between the closely spaced electrodes (5mm) Because the electrodes are simply pressed on the skin, very high electrode impedances (up to 1MOhm) can be found. However, thanks to BioSemi's high quality battery powered front-end, excellent signal quality is still assured (noise is smaller than 10uVpp) even with these difficult electrodes. The array is developed as an alternative to invasive methods like needle electrodes. The array setup provides a lot of extra information about the EMG topography.
The EMG Flex Print consists of 126 silver chloride dot electrodes. It is shaped in a matrix of 9x14 dots. The dots cover an area of 32x52 mm. The application of the Flex Print is done as following:
First, a double sided adhesive sticker with 128 holes is sticked on the Flex Print, and then a small amount of gel is applied to the sticker. Then the protective cover is removed from the sticker and the Flex Print is sticked to the skin. The Flex Print is semi-disposable and has to be replaced after about 50 measurements.
BioSemi Flex Prints are double layer flexprints, with vias so that the wires are on the back side, to minimize crosstalk.Also, BioSemi Flex Prints have very durable silver contact pads.
This means that the silver dots on BioSemi Flex Prints have a deposit of a relatively thick silver layer, this is necessary because the Flex Prints are cleaned after every use. Moreover, the silver dots on BioSemi Flex Prints protrude more from the Flexprint than the Flexprints from competing companies, who have relatively thin electrode bodies.