CAPITEL: Design and Implementation of a wireless 6 channel EMG measurement system for permanent in vivo use: in vitro results

Abstract

Introduction Surface Electromyography of partial limb amputees is used to control prostheses. Implantable EMG systems offer a higher Signal to Noise Ratio (SNR) as well as improved muscle specificity, and a more convenient daily use. Material and methods We present a design for an implantable device (“implant”) with 6 channels, each suitable for an electrode array with 3 electrodes. The implant uses an ADS1298 analog front end with ADG2188 multiplexers for versatile electrode array configuration. The analog input is filtered with a balanced analog bandpass filter with corner frequencies of 30 and 800 Hz. The ADC sample rate is 2 KHz per channel, with 9 bits resolution. The dimensions of the PCB implant are 17.2 x 14.1x2.15 mm. To measure the SNR a sinusoidal signal with a peak to peak amplitude of 7 mV and a frequency of 200 Hz was applied to each input. To simulate muscle impedance, an equivalent muscle impedance model (Figure 1) was placed between the generator and each channel of the implant [1]. We have implemented two data transmission methods: wired duplex communication and wireless inductive link. The wired link is used to transfer raw data, while only the 6 EMG envelopes, with an update rate of 20 Hz, are sent via the wireless link. Results Each analog input channel performed with a SNR better than 52 dB, both for wired and wireless operation. Wired data was received successfully at 115200 bps and wireless data at 1080 bps. Discussion Our design achieves a high SNR and data rate. These early results are promising and we are packaging the PCBs for in-vivo testing. Conclusion We have demonstrated a very compact design suitable for the monitoring of 6 EMG channels, with options for raw data or EMG envelope transmission. [1] Kalvoy, H, 2009, doi: 10.1088/0967-3334/30/2/002