Miniature active concentric ring sensor for localized body surface EMG measurement

EMG detection is critical in gait analysis. Localized EMG detection usually calls for invasive method using needle electrode. Body surface EMG provides global information about the muscle activity of a general area. This global information is not as useful compared with the localized EMG signal. Concentric ring electrode with built-in amplifier provides superior localized EMG signal from body surface. A light weight (2 gm) miniature (15 mm in diameter 3.5 mm in thickness) active concentric ring sensor (Harbinger Technology HT-EMG, Chung-Ho City, Taipei County, Taiwan) with high input impedance (10 GΩ) is used to obtain localized EMG activity form body surface without skin preparation. The amplifier is mounted directly above the concentric ring electrode with low system noise (0.7 mV rms at gain of 1000) with a high pass filter of 15 Hz and a low pass filter at 10 kHz. The reference connection is at the back, on top of the active sensor. The high common mode rejection ratio (118 dB typical) with high input impedance and lightweight makes concentric ring EMG active sensor user-friendly and easily adaptable to most EMG acquisition system.